JP2018190563A - Negative electrode active material for electric device, and electric device arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric device superior in cycle durability.SOLUTION: An objective is achieved by a negative electrode active material for an electric device comprising a Si-containing alloy, which is to be used as a negative electrode active material for an electric device. In the negative electrode active material, the Si-containing alloy has a fine structure which has first phases including a silicified transition metal (silicide) as a primary component, second phases including Al in a part thereof, and amorphous or low-crystallinity Si as a primary component, and third phases including Sn as a primary component. Further, a part of the fine structure includes a plurality of independent first phases, and another part makes an eutectic crystal structure of first and second phases; third phases are more finely distributed in the eutectic crystal structure than first and second phases.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a negative electrode active material for electric devices and an electric device using the same. The negative electrode active material for an electric device and the electric device using the same according to the present invention include, for example, a driving power source and an auxiliary power source for a motor of a vehicle such as an electric vehicle, a fuel cell vehicle, and a hybrid electric vehicle as a secondary battery or a capacitor. Used for.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Electric devices such as secondary batteries for motor drive that hold the key to their practical application. Is being actively developed.

  As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used in a mobile phone, a notebook personal computer or the like. Therefore, lithium ion secondary batteries having the highest theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

  Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

Conventionally, carbon / graphite-based materials that are advantageous in terms of charge / discharge cycle life and cost have been used for negative electrodes of lithium ion secondary batteries. However, since carbon / graphite-based negative electrode materials are charged / discharged by occlusion / release of lithium ions into / from graphite crystals, the charge / discharge capacity of the theoretical capacity 372 mAh / g or more obtained from LiC ₆ which is the maximum lithium-introduced compound. There is a disadvantage that cannot be obtained. For this reason, it is difficult to obtain a capacity and energy density that satisfy the practical use level of the vehicle application with the carbon / graphite negative electrode material.

On the other hand, a battery using a material that is alloyed with Li for the negative electrode is expected as a negative electrode material for vehicle use because the energy density is improved as compared with a conventional carbon / graphite negative electrode material. For example, the Si material occludes and releases _3.75 mol of lithium ions per mol as shown in the following reaction formula (A) in charge / discharge, and the theoretical capacity is 3600 mAh / liter in Li ₁₅ Si ₄ (= Li _3.75 Si). g.

  However, a lithium ion secondary battery using a material that is alloyed with Li for the negative electrode has a large expansion and contraction in the negative electrode during charge and discharge. For example, when Li ions are occluded, the volume expansion is about 1.2 times in graphite materials, whereas in Si materials, when Si and Li are alloyed, transition from the amorphous state to the crystalline state causes a large volume change. (Approximately 4 times), there was a problem of reducing the cycle life of the electrode. In the case of the Si negative electrode active material, the capacity and the cycle durability are in a trade-off relationship, and there is a problem that it is difficult to improve the cycle durability while exhibiting a high capacity.

Here, Patent Document 1 discloses an invention that aims to provide a non-aqueous electrolyte secondary battery having a negative electrode pellet having a high capacity and an excellent cycle life. Specifically, it is a Si-containing alloy obtained by mixing Si powder and titanium powder by a mechanical alloying method and wet-pulverizing the first phase mainly composed of Si and a silicide of titanium (such as TiSi ₂ ). ) Containing a second phase containing) is disclosed as a negative electrode active material. At this time, it is also disclosed that at least one of these two phases is amorphous or low crystalline.

International Publication No. 2006/129415 Pamphlet

  According to the study by the present inventors, although it is said that the electric device such as a lithium ion secondary battery using the negative electrode pellet described in Patent Document 1 can exhibit good cycle durability. Therefore, it has been found that the cycle durability may not be sufficient.

  Then, an object of this invention is to provide the means which can improve the cycling durability of electric devices, such as a lithium ion secondary battery.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, a first phase mainly containing transition metal silicide, a second phase containing Al and containing amorphous or low crystalline Si as a main component, and a first phase mainly containing Sn. Three phases, part of which is a plurality of independent first phases, and part of which is a eutectic structure of the first phase and the second phase, It has been found that the above problem can be solved by using, as a negative electrode active material for an electric device, a Si-containing alloy having a microstructure in which the phase is more finely dispersed than the first phase and the second phase. It came to complete.

  In the Si-containing alloy constituting the negative electrode active material according to the present invention, the second phase (Si phase) in the eutectic structure is hard and conductive due to the addition of Sn and Al to the Si-Ti alloy in the microstructure. It is included in the first phase (silicide phase) in the eutectic structure having higher properties. As a result, when charging / discharging, the second phase (Si phase) in the eutectic structure is enveloped by the silicide phase (the first phase in the eutectic structure and a plurality of independent first phases outside it). Therefore, expansion and contraction are suppressed, and Si of the first phase reacts uniformly by imparting electrical conductivity, so that durability is hardly deteriorated. Furthermore, since the third phase (Sn phase) is finely dispersed in the eutectic structure, particularly around the second phase (Si phase), the second phase (Si phase) is likely to become amorphous. As a result, cycle durability can be improved while showing the high capacity | capacitance of the electric device in which the said negative electrode active material is used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view schematically showing an outline of a laminated flat non-bipolar lithium ion secondary battery which is a typical embodiment of an electric device according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing the appearance of a stacked flat lithium ion secondary battery that is a representative embodiment of an electric device according to the present invention. FIG. 3A is a drawing schematically showing the microstructure of the SiSnTiAl quaternary alloy, which is the Si-containing alloy of the present embodiment, based on HAADF-STEM and EDX, and FIG. It is drawing which expanded and represented typically a part of eutectic structure part of 3 (a). FIG. 4A is a diagram schematically showing an enlarged part of the microstructure of the SiSnTi ternary alloy containing no Al based on HAADF-STEM and EDX, and FIG. 1 is an enlarged view schematically showing a part of a eutectic structure portion of a microstructure of a SiSnTiAl quaternary alloy that is a Si-containing alloy based on HAADF-STEM and EDX. 5A is a phase diagram of Si—Al, FIG. 5B is a phase diagram of Si—Sn, and FIG. 5C is a phase diagram of Al—Sn. FIG. 6A shows a BF (Bright-) of Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (low magnification) of a sample prepared by FIB method for the Si-containing alloy (particle) of the present embodiment. field) -STEM Image (bright field-scanning transmission electron microscope image). FIG. 6B is a drawing showing a HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image) of the active material particles in the same field of view as FIG. FIG. 7A shows a Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (medium magnification) obtained by enlarging a portion surrounded by a square frame in FIG. 6B (a portion of a eutectic structure). It is drawing which shows BF (Bright-field) -STEM Image (bright field-scanning transmission electron microscope image). FIG.7 (b) is drawing which represents the HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image) of the active material particle in the same visual field as FIG.7 (a). FIG. 8 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure of the alloy of Example 1. FIG. 8A shows a Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging a portion surrounded by a square frame in FIG. It is drawing which represents HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 8B is a diagram showing mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8C is a diagram showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8D shows the mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8E is a drawing (upper right) in which mapping data of Sn, Si, Ti measured in the same field of view as HAADF-STEM (upper left FIG. 8A) is superimposed. 9 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure of the alloy of Example 1. FIG. FIG. 9A shows a Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging a portion surrounded by a square frame in FIG. 7B (a portion of a eutectic structure). It is drawing which represents HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 9B is a diagram showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9C is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9D is a diagram showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9E is a drawing (upper right) in which mapping data of Al, Si, Ti measured in the same field of view as HAADF-STEM (upper left FIG. 9A) is superimposed. FIG. 10A is an enlarged photograph of a lattice image obtained by HAADF-STEM of the Si-containing alloy (specifically, SiSnTiAl alloy) of the present embodiment. FIG. 10 (B) is a photograph showing a diffraction pattern obtained by performing a fast Fourier transform (FFT) process on the lattice image (HAADF-STEM image) of the silicon-containing alloy of Example 1 shown in FIG. 10 (A). It is. FIG. 10C shows an inverse Fourier transform image obtained by performing inverse fast Fourier transform processing on the extracted figure from which the data of the diffraction ring portion corresponding to the Si (220) plane of FIG. 10B is extracted. It is a photograph which shows. FIG. 10C ′ is a diagram obtained in the same manner as FIGS. 10A to 10C below for the second phase (a-Si phase) in the eutectic structure of the alloy of Example 1. It is drawing equivalent to 10 (C). It is drawing which represented typically the "major axis diameter of a periodic arrangement area | region (MRO)." 4 is a TTT diagram for precipitation of Si having a liquid phase composition (Si _70.9 Sn _7.4 Ti _19.9 -Al _1.8 ) at the start of eutectic in the alloy composition (alloy type) of Example 1. FIG. 13 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure (eutectic structure portion) of the alloy of Example 2. FIG. FIG. 13A shows HAADF-STEM in Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging the eutectic portion of the microstructure of the alloy of Example 2. It is drawing showing Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 13B is a diagram showing mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13C is a diagram showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13D is a diagram showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13E is a drawing (upper right) in which mapping data of Sn, Si, Ti measured in the same field of view as HAADF-STEM (upper left FIG. 13A) is superimposed. 14 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure (eutectic structure portion) of the alloy of Example 2. FIG. FIG. 14A shows HAADF-STEM in Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging the eutectic portion of the microstructure of the alloy of Example 2. It is drawing showing Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 14B is a diagram showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14C is a diagram showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14D is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14E is a drawing (upper right) in which mapping data of Al, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 14A) is superimposed. Drawing corresponding to FIG. 10C obtained in the same manner as in the following FIGS. 10A to 10C for the second phase (a-Si phase) in the eutectic structure of the alloy of Example 2. It is. It is a TTT diagram with respect to precipitation of Si of the liquid phase composition (Si _64.6 Sn _14.2 Ti _18.0 Al _3.2 ) at the start of eutectic in the alloy composition (alloy type) of Example 2. FIG. 17 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure (eutectic structure portion) of the alloy of Comparative Example 1. FIG. 17 (a) shows HAADF-STEM Image (high angle scattering dark field−) of Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging the microstructure of the alloy of Example 2. It is drawing which shows a scanning transmission electron microscope image. FIG. 17B is a diagram showing mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 17A). FIG. 17C is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 17A). FIG. 17D is a diagram showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 17A). FIG. 17E is a drawing (upper right) in which mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 17A). 18 shows the second phase (a-Si phase) in the eutectic structure of the alloy of Comparative Example 1 obtained in the same manner as in the following FIGS. 10 (A) to 10 (C). It is drawing equivalent to. It is a graph (drawing) which shows the relationship between the number of charging / discharging cycles and a discharge capacity maintenance factor about each lithium ion secondary battery (coin cell) produced in Examples 1-2 and the comparative example 1. FIG. It is a schematic diagram of a TTT diagram.

  Hereinafter, embodiments of a negative electrode active material for an electric device of the present invention, a negative electrode for an electric device using the same, and an electric device will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following modes. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  Hereinafter, a basic configuration of an electric device to which the negative electrode active material for an electric device of the present invention can be applied will be described with reference to the drawings. In the present embodiment, a lithium ion secondary battery will be described as an example of an electric device.

  First, in a negative electrode for a lithium ion secondary battery, which is a typical embodiment of a negative electrode including a negative electrode active material for an electric device according to the present invention, and a lithium ion secondary battery using the same, a cell (single cell layer) ) Voltage is large, and high energy density and high power density can be achieved. Therefore, the lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of the present embodiment is excellent as a vehicle driving power source or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for a vehicle driving power source or the like. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable devices such as mobile phones.

  That is, the lithium ion secondary battery that is the subject of the present embodiment may be any one that uses the negative electrode active material for the lithium ion secondary battery of the present embodiment described below. It should not be restricted in particular.

  For example, when the lithium ion secondary battery is distinguished by form / structure, it can be applied to any conventionally known form / structure such as a stacked (flat) battery or a wound (cylindrical) battery. Is. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. Is.

  When distinguished by the type of electrolyte layer in the lithium ion secondary battery, a solution electrolyte type battery using a solution electrolyte such as a nonaqueous electrolyte solution for the electrolyte layer, a polymer battery using a polymer electrolyte for the electrolyte layer, etc. It can be applied to any conventionally known electrolyte layer type. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as polymer electrolyte). It is done.

  Therefore, in the following description, the non-bipolar (internal parallel connection type) lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of this embodiment will be described very simply with reference to the drawings. However, the technical scope of the lithium ion secondary battery of the present embodiment should not be limited to these.

<Overall battery structure>
FIG. 1 schematically shows the overall structure of a flat (stacked) lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”), which is a typical embodiment of the electrical device of the present invention. FIG.

  As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior body. . Here, in the power generation element 21, the positive electrode in which the positive electrode active material layer 15 is disposed on both surfaces of the positive electrode current collector 12, the electrolyte layer 17, and the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. It has a configuration in which a negative electrode is laminated. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. The positive electrode current collector 15 located on both outermost layers of the power generation element 21 has the positive electrode active material layer 15 disposed only on one side, but the active material layers may be provided on both sides. . That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost negative electrode current collector is positioned on both outermost layers of the power generation element 21, and one side of the outermost negative electrode current collector or A negative electrode active material layer may be disposed on both sides.

  The positive electrode current collector 12 and the negative electrode current collector 11 are attached to the positive electrode current collector plate 27 and the negative electrode current collector plate 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between the end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via a positive electrode lead and a negative electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

  The lithium ion secondary battery described above is characterized by a negative electrode. Hereinafter, main components of the battery including the negative electrode will be described.

<Active material layer>
The active material layer 13 or 15 contains an active material, and further contains other additives as necessary.

[Positive electrode active material layer]
The positive electrode active material layer 15 includes a positive electrode active material.

(Positive electrode active material)
Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-such as those obtained by replacing some of these transition metals with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, a composite oxide containing lithium and nickel is used, and more preferably Li (Ni-Mn-Co) O ₂ and a part of these transition metals substituted with other elements (hereinafter, Simply referred to as “NMC composite oxide”). The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

  As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _2, etc. that have been proven in general consumer batteries. Compared to the above, the capacity per unit weight is large, and the energy density can be improved, so that a battery having a compact and high capacity can be produced, which is preferable from the viewpoint of cruising distance. In addition, LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in terms of a larger capacity, but there are difficulties in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has life characteristics as excellent as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

  In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. Of course, positive electrode active materials other than those described above may be used.

  The average particle diameter of the positive electrode active material contained in the positive electrode active material layer 15 is not particularly limited, but is preferably 1 to 30 μm, more preferably 5 to 20 μm from the viewpoint of increasing the output. In the present specification, the “particle diameter” refers to the outline of the active material particles (observation surface) observed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among any two points. In this specification, the value of “average particle diameter” is the value of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the particle diameter shall be adopted. The particle diameters and average particle diameters of other components can be defined in the same manner.

  The positive electrode active material layer 15 can include a binder.

(Binder)
The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector. Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethylcellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene Copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene Fluororesin such as copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine Rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-teto Fluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE fluororubber), vinylidene fluoride-chlorotrifluoroethylene Vinylidene fluoride-based fluororubbers such as epoxy-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamideimide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the active material layer. These binders may be used alone or in combination of two.

  The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1-10 mass%.

  The positive electrode (positive electrode active material layer) can be applied by any one of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method in addition to a method of applying (coating) a normal slurry. Can be formed.

[Negative electrode active material layer]
The negative electrode active material layer 13 includes a negative electrode active material.

(Negative electrode active material)
In this embodiment, the negative electrode active material has a quaternary alloy composition represented by Si-Sn-M (M is one or more transition metal elements) -Al, and the microstructure is A first phase (also referred to as a silicide phase) containing transition metal silicide (silicide) as a main component and a second phase (Si phase) containing Al and containing amorphous or low-crystalline Si as a main component Or a-Si phase (also referred to as amorphous Si phase)) and a third phase (also referred to as Sn phase) containing Sn as a main component, and a part of the plurality of independent first phases, And a part is a eutectic structure of the first phase and the second phase, and in the eutectic structure, the third phase is finer than the first phase and the second phase. It is made of a dispersed Si-containing alloy.

  In this embodiment, since the first phase (silicide phase) is mainly composed of a transition metal silicide (silicide), M is a transition metal that forms silicide with Si (referred to as a silicide-forming element). It has 1 or more types. That is, when M is one transition metal element, it is a silicide forming element constituting the first phase (silicide phase). Further, when M is two or more transition metal elements, at least one kind is a silicide forming element constituting the first phase (silicide phase). The remaining transition metal element may be a transition metal element contained in the second phase (a-Si phase) or the third phase (Sn phase), or the silicide constituting the first phase (silicide phase). It may be a forming element. Or the transition metal element which comprises the phase (transition metal phase) which transition metals other than the 1st phase, the 2nd phase, and the 3rd phase crystallized may be sufficient.

  As described above, the Si-containing alloy constituting the negative electrode active material in the present embodiment is first a quaternary system represented by Si—Sn—M (M is one or more transition metal elements) —Al. The alloy composition is as follows. More specifically, the Si-containing alloy constituting the negative electrode active material in the present embodiment is a Si—Sn—M (M is one or two or more transition metal elements) —Al alloy having the following chemical formula ( It has a composition represented by 2).

  In the chemical formula (1), A is an inevitable impurity, M is one or more transition metal elements, and x, y, z, w, and a represent mass% values, 0 <x <100, 0 <y <100, 0 <z <100, 0 <w <100, a is the remainder, and x + y + z + w + a = 100.

  Preferably, the Si-containing alloy is a Si—Sn—Ti—Al alloy and has a composition represented by the following chemical formula (1).

  In the above chemical formula (1), A is an inevitable impurity, and x, y, z, w and a represent mass% values, where x, y, z and w are 58 ≦ x ≦, respectively. 68, 2 ≦ y ≦ 10, 25 ≦ z ≦ 35, 0.3 ≦ w ≦ 3, a is the remainder, and x + y + z + w + a = 100.

As apparent from the chemical formula (2), the Si-containing alloy (having _a composition of Si _x Sn _y M _z Al _w A _a ) according to the present embodiment is composed of Si, Sn, M (transition metal), and Al. It is a quaternary system. By having such a composition, high cycle durability can be realized.

  Further, in the present specification, the “inevitable impurities” means an Si-containing alloy that exists in a raw material or is inevitably mixed in a manufacturing process. The inevitable impurities are originally unnecessary impurities, but are a very small amount and do not affect the characteristics of the Si alloy.

  In the present embodiment, it is particularly preferable to select Ti, which is one of silicide forming elements, as an additive element (M: transition metal) to the negative electrode active material (Si-containing alloy). -The cycle life can be improved by suppressing the phase transition of the crystal. This also increases the capacity of conventional negative electrode active materials (for example, carbon-based negative electrode active materials). Therefore, according to a preferred embodiment of the present invention, in the composition represented by the chemical formula (2), M is preferably titanium (Ti). In particular, when Ti is selected as the additive element to the negative electrode active material (Si-containing alloy), Sn is added as the second additive element, and Al is added as the third additive element, it becomes even more amorphous during Li alloying. -The cycle life can be improved by suppressing the phase transition of the crystal. This also increases the capacity of conventional negative electrode active materials (for example, carbon-based negative electrode active materials). Therefore, according to a preferred embodiment of the present invention, in the composition represented by the chemical formula (2), M is preferably titanium (Ti).

  Here, in the Si-based negative electrode active material, when Si and Li are alloyed during charging, the Si phase transitions from the amorphous state to the crystalline state, causing a large volume change (about 4 times). As a result, there is a problem that the active material particles themselves are broken and the function as the active material is lost. For this reason, the negative electrode active material has the composition represented by the chemical formula (2), preferably the chemical formula (1) and the fine structure, thereby suppressing the phase transition of the Si-phase amorphous-crystal during charging. The collapse of the particles themselves can be suppressed, the function (high capacity) as an active material is maintained, and the cycle life can be improved.

As described above, the Si-containing alloy (having the composition of Si _x Sn _y M _z Al _w A _a ) according to the present embodiment is a quaternary of Si, Sn, M (transition metal, preferably Ti) and Al. It is a system. Here, the sum of the constituent ratios of each constituent element (mass ratio x, y, z, w, a) is 100% by mass, but there is no particular limitation on each value of x, y, z, w. Preferably, it is as follows.

  In the composition represented by the above chemical formula (2), preferably the chemical formula (1), x (Si composition ratio; mass%) is preferably 68 or less, more preferably 67 or less, and even more preferably 66. It is as follows. Further, x is preferably 58 or more, more preferably 58.5 or more, and more preferably 59 or more. Within such a range, it is excellent in terms of maintaining durability against charge / discharge (insertion / desorption of Li ions) and balance of initial capacity, and can sufficiently improve durability and obtain a high capacity. The effect of can be expressed more efficiently.

  In the composition represented by the above chemical formula (2), preferably the chemical formula (1), y (Sn composition ratio; mass%) is preferably 10 or less, more preferably 9 or less, and still more preferably 8 .5 or less. Moreover, y is preferably 2 or more, more preferably 3 or more. Within such a range, reversible insertion and desorption of Li ions during charge / discharge is achieved by increasing the distance between Si tetrahedrons in the Si phase by solid solution in the second phase (Si phase). It is excellent in that it is possible. Thereby, durability can fully be improved and the effect of the present invention can be expressed more efficiently.

  In the composition represented by the chemical formula (2), preferably the chemical formula (1), z (composition ratio of transition metal element M, preferably Ti; mass%) is preferably 35 or less, more preferably 34 or less. Yes, more preferably 33 or less, still more preferably 32 or less, and particularly preferably 31 or less. Z is preferably 25 or more, more preferably 28 or more, and still more preferably 29 or more. Within such a range, it is excellent in terms of maintaining durability against charge / discharge (insertion / desorption of Li ions) and balance of initial capacity, and can sufficiently improve durability and obtain a high capacity. The effect of can be expressed more efficiently.

  In the composition represented by the above chemical formula (2), preferably the chemical formula (1), w (Al composition ratio; mass%) is preferably 3 or less, more preferably 2.5 or less. More preferably, it is 2.0 or less. Further, w is preferably 0.3 or more, more preferably 0.35 or more, and more preferably 0.4 or more. Within such a range, the primary crystal silicide precipitate (first phase) can be refined, the eutectic ratio of the silicide can be kept large, and the critical cooling rate for amorphization is achieved. Is excellent in that it can be reduced, the durability can be sufficiently improved, and the effects of the present invention can be expressed more efficiently.

  In the composition represented by the chemical formula (2), preferably the chemical formula (1), x + y + z + w is a maximum of 100 (not exceeding 100).

  As described above, Si is a main component, transition metal element M, in particular, Ti is relatively included, Sn is also included to some extent, and a small amount of Al is included. This is preferable because the microstructure of the alloy can be easily obtained. Further, the transition metal element M (especially Ti) is selected as the additive element to the main component Si of the Si-containing alloy, Sn is added as the second additive element within the above range, and Al as the third additive element is within the above range. By adding a small amount, Al (further Sn) can be sufficiently dispersed (solid solution) in a part of the Si phase. Further, when Al enters, the Sn phase (third phase) becomes the eutectic silicide phase (first phase) in the eutectic structure of the silicide phase (first phase) and the Si phase (second phase). ) And the eutectic Si phase (second phase). That is, the Sn phase is dispersed (solid solution) in the Si phase, and is not segregated as crystalline Sn in the Si phase, but in the microstructure, the boundary portion between the silicide phase of the eutectic structure and the Si phase, Is finely dispersed in the boundary portion between the independent silicide phase and the eutectic structure. Further, since the Sn phase functions as an Sn active material, sufficient cycle durability can be obtained while maintaining a high capacity. Moreover, Al can be dispersed relatively uniformly over the entire eutectic Si phase. Therefore, by adding Al to the Si—Sn—Ti alloy, the amorphous forming ability of the amorphous Si alloy can be increased, and the degree of amorphousness can be increased. Therefore, the chemical structure of the a-Si phase (second phase) is less likely to change even when Li is inserted and desorbed due to charge and discharge, and higher cycle durability is obtained. Al that is not dispersed or dissolved in the Si phase does not segregate as crystalline Al in the Si phase, and does not segregate in the microstructure, but the boundary between the silicide phase of the eutectic structure and the Si phase, and an independent silicide. Disperses (crystallizes) at the boundary between the phase and the eutectic structure. However, the preferred numerical ranges of the composition ratios of the constituent elements described above are merely for explaining the preferred embodiments, and are within the technical scope of the present invention as long as they are included in the claims. It is.

  In the composition represented by the chemical formula (2), preferably the chemical formula (1), as described above, A is an impurity (inevitable impurity) other than the four components derived from the raw materials and the manufacturing method. In the composition represented by the chemical formula (2), preferably the chemical formula (1), a (mass%) is preferably less than 0.5, and more preferably less than 0.1.

  Whether or not the negative electrode active material (Si-containing alloy) has the composition represented by the chemical formula (2), preferably the chemical formula (1), is determined by qualitative analysis by fluorescent X-ray analysis (XRF) and inductively coupled plasma (ICP). ) It can be confirmed by quantitative analysis by emission spectroscopy.

(Microstructure of Si-containing alloy)
FIG. 3A is a drawing schematically showing the microstructure of the SiSnTiAl quaternary alloy, which is the Si-containing alloy of the present embodiment, based on HAADF-STEM and EDX, and FIG. It is drawing which expanded and represented typically a part of eutectic structure part of 3 (a). FIG. 4A is a diagram schematically showing an enlarged part of the microstructure of the SiSnTi ternary alloy containing no Al based on HAADF-STEM and EDX, and FIG. 1 is an enlarged view schematically showing a part of a eutectic structure portion of a microstructure of a SiSnTiAl quaternary alloy that is a Si-containing alloy based on HAADF-STEM and EDX. 5A is a phase diagram of Si—Al, FIG. 5B is a phase diagram of Si—Sn, and FIG. 5C is a phase diagram of Al—Sn.

As shown in FIGS. 3A and 3B and FIG. 4B, the Si-containing alloy constituting the negative electrode active material in this embodiment has a microstructure 31 of (1) a transition metal silicide (silicide). ) As a main component (silicide phase). Also, (2) a part of Al (further Sn) (specifically, Al (further Sn) is dispersed (solid solution) inside the Si crystal structure), amorphous or low crystalline It has the 2nd phase (a-Si phase) which has Si as a main component. Furthermore, (3) it has a third phase (Sn phase) containing Sn as a main component. Further, (4) a part of the plurality of independent first phases 32 and (5) a part of the first phase 34 and the second phase 35 form a eutectic structure 33. Furthermore, (6) the third phase 36 is more finely dispersed in the eutectic structure 33 than the first phase 34 and the second phase 35. The Si-containing alloy of the present embodiment has a configuration in which the second phase 35 is eutectic with the first phase 34 and further enters a plurality of independent first phase 32 gaps (FIG. 3A). reference). In addition, the first phases (silicide phases) 32 and 34 are superior to the second phase (a-Si phase) 35 in terms of hardness and electron conductivity. Therefore, it can be said that the effects of the present invention can be achieved by the following mechanism of action (see the microstructure drawing of Example 1). That is, since the microstructure 31 of the alloy has the above-described configuration, the expansion of the second phase 35 in the eutectic structure 33, particularly the main component Si active material in the charge / discharge process, is a first phase that is eutecticized. 34 can be suppressed by wrapping, and the plurality of independent first phases 32 can be suppressed by wrapping the second phase 35 in the eutectic structure. This suppresses the amorphous-crystal phase transition (crystallization to Li ₁₅ Si ₄ ) when Si and Li are alloyed during charging. As a result, the expansion and contraction of the Si-containing alloy in the charge / discharge process is reduced, and the first phase (silicide phase) 34 composed of the silicide having conductivity is combined with the second phase (a-Si phase) 35. By eutecticization, the second phase (a-Si phase) 35, in particular, the main component Si active material can be reacted uniformly. As a result, cycle durability can be improved while showing the high capacity | capacitance of the electric device in which the said negative electrode active material is used. In particular, by adding Al to the SiSnTi alloy, if the third phase 36 is finely dispersed around the second phase (a-Si phase) 35, the second phase (a-Si phase) 35 is likely to become amorphous. Excellent durability. More specifically, the second phase (a-Si phase) 35 is easily amorphized not only because the third phase 36 is dispersed, but also in the second phase (a-Si phase) 35. This is because the particles are dispersed almost uniformly (see FIG. 5 and the calculation result of the amorphous forming ability (critical cooling rate)). That is, Al is adjacent to Al—Si in the liquid phase state is more stable, Al—Al and Si—Si adjacent to Al—Si are more stable than Al—Si in the solid phase state, and when cooled rapidly with Al contained in Si, overcooling occurs. Even if it enlarges, it becomes difficult to produce Si crystal | crystallization, and an amorphous formation ability improves. As a result of Al being almost uniformly dispersed in the second phase (a-Si phase) 35, the third phase (Sn phase) 36 is finely dispersed (Sn is bonded to Ti, so Si (first phase)). A second phase) 35 and a TiSi ₂ phase (first phase) 34 (formed at the boundary). The fine dispersion of the third phase (Sn phase) 36 is necessary for improving the durability. This is because the main component of the third phase (Sn phase) 36 has a large volume expansion during charge and discharge. It is. Therefore, if Sn (third phase) is dispersed more finely than the first phase and the second phase in the eutectic structure 33 due to Al entering the alloy, the durability is further improved. On the other hand, in the SiSnTi ternary alloy used in Comparative Example 1, as shown in FIG. 4A, in the microstructure 31 ′, the silicide phase 32 ′ wraps the Si phase 35 ′ and the Sn phase 36 ′ (fine It can be said that the effect of suppressing the expansion of the Si active material by wrapping (in a two-stage structure) cannot be sufficiently exhibited because the structure does not become a structure.

  Whether or not the Si-containing alloy has such a microstructure is determined by, for example, observing the Si-containing alloy using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). The same field of view as the image can be confirmed by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy).

  Hereinafter, in the present embodiment, the Si-containing alloy (negative electrode active material) having the above microstructure will be described.

(1) First phase (silicide phase) mainly composed of transition metal silicide (silicide)
In the Si-containing alloy having a microstructure, the first phase (silicide phase) is mainly composed of a transition metal silicide (silicide). This first phase (silicide phase) is superior in terms of hardness and electronic conductivity compared to the second phase (a-Si phase). For this reason, the silicide phase (first phase) plays a role of maintaining the shape of the Si active material in the a-Si phase (second phase) against the stress at the time of expansion, and the a-Si phase. The low electronic conductivity of (especially Si active material) can be improved. Further, the silicide phase (first phase) includes a transition metal silicide (eg, TiSi ₂ ), and thus has excellent affinity with the a-Si phase (second phase), and particularly has a volume during charging. Cracking at the (crystal) interface during expansion can be suppressed.

As described above, in the composition represented by the chemical formula (2), preferably the chemical formula (1), M is preferably titanium (Ti). In particular, by selecting Ti as the additive element to the Si-containing alloy, adding Sn as the second additive element, and adding a small amount of Al as the third additive element, in the eutectic structure of the Si-containing alloy, The phase and the second phase can be made finer (compared to the independent silicide phase). As a result, the cycle life (durability) can be improved by further suppressing the amorphous-crystal phase transition during Li alloying (further charge / discharge). This also makes the negative electrode active material (Si-containing alloy) of the present invention have a higher capacity than conventional negative electrode active materials (for example, carbon-based negative electrode active materials). Therefore, it is preferable that the silicide phase (first phase) mainly composed of a transition metal silicide (silicide) in the microstructure is titanium silicide (TiSi ₂ ).

  In the above-described silicide phase (first phase), “having silicide as a main component” means 50 mass% or more, preferably 80 mass% or more, more preferably 90 mass% or more, particularly preferably 95 mass% of the silicide phase. % Or more, and most preferably 98% by mass or more is silicide. Ideally, the silicide is 100% by mass. However, the alloy may contain inevitable impurities that are present in the raw material or are inevitably mixed in the manufacturing process. Therefore, it is practically difficult to obtain 100% by mass of the first phase.

(2) Second phase (Si phase or a-Si phase) containing Al in part and mainly containing amorphous or low crystalline Si
In the Si-containing alloy having a microstructure, the second phase (Si phase) partially contains Al (preferably Sn) and mainly contains amorphous or low-crystalline Si. This second phase (Si phase) is a phase containing amorphous or low crystalline Si as a main component. Further, Al (preferably further Sn) is included in a part of the second phase, specifically, Al (preferably further Sn) is dispersed in Si and dissolved (dispersed in a solid solution state). It is sufficient if it is dispersed or (finely) dispersed in the form of being included in Si.

  This second phase (Si phase) is a phase involved in occlusion / release of lithium ions during operation of the lithium ion secondary battery which is the electrical device of this embodiment, and is a phase capable of electrochemically reacting with Li. It is. Since the second phase is mainly composed of Si, a large amount of Li can be occluded and released per weight and per volume. However, since Si has poor electron conductivity, the second phase may contain a trace amount of additive elements such as phosphorus and boron, transition metals, and the like. Note that the second phase is preferably more amorphous than the first phase (silicide phase). By setting it as such a structure, a negative electrode active material (Si containing alloy) can be made into a higher capacity | capacitance. Whether or not the second phase is more amorphous than the first phase is determined by electron diffraction analysis (first phase and second phase using high angle annular dark field scanning transmission electron microscope (HAADF-STEM)). Each observation image of the phase can be confirmed by a diffraction pattern obtained by fast Fourier transform (FFT). Specifically, according to electron beam diffraction analysis, a net pattern (lattice spot) of a two-dimensional dot array is obtained for a single crystal phase, and a Debye-Scherrer ring (diffraction ring) is obtained for a polycrystalline phase, A halo pattern is obtained for the amorphous phase. By using this, the above confirmation becomes possible.

  As described above, in the composition represented by the chemical formula (2), preferably the chemical formula (1), M is preferably titanium (Ti). In particular, when Ti is formed by selecting Ti as an additive element to the negative electrode active material (Si-containing alloy), adding Sn as the second additive element, and further adding a small amount of Al as the third additive element. Further, the cycle life can be improved by further suppressing the amorphous-crystal phase transition. This also makes the negative electrode active material (Si-containing alloy) of the present invention have a higher capacity than conventional negative electrode active materials (for example, carbon-based negative electrode active materials). Accordingly, the Si phase (second phase) mainly composed of amorphous or low crystallinity in the microstructure is mainly made of amorphous Si from the viewpoint of realizing higher cycle durability. It is preferable to use it as a component.

  From the above, the transition metal silicide of the first phase in the microstructure is titanium silicide (TiSi2), and the second phase is an Si phase containing Al and Sn. Is preferred. With such a configuration, cycle durability can be improved while exhibiting a high capacity of the electric device. Furthermore, the first phase transition metal silicide in the microstructure is titanium silicide, and the second phase is made of amorphous Si containing Al and Sn. The main component is preferable. With such a configuration, cycle durability can be further improved while showing a high capacity of the electric device.

  In the a-Si phase (second phase), “mainly composed of amorphous or low crystalline Si” means 50% by mass or more, preferably 80% by mass or more of the Si phase, more preferably The Si is 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 98% by mass or more. However, the alloy may contain inevitable impurities that are present in the raw material or are inevitably mixed in the manufacturing process. Therefore, it is practically difficult to obtain 100% by mass of the second phase.

In the second phase (Si phase), “partially contains Al” means that, for example, when comparing FIG. 9B and FIG. This is because it is a portion not included (Si portion functions as an active material), but a portion containing Al in the Si phase is observed. In particular, Al is relatively uniformly dispersed throughout the eutectic part. In the eutectic part, a portion where Al is overlapped with Si is concentrated. This is probably because Al is eutectic with Si in this portion (see FIG. 9B). In the portion containing Al in the Si phase, Al is dispersed and dissolved in Si, or is dispersed in the form of being included in Si. In addition, the remaining part of Al in the eutectic structure is not the Si phase, but crystallized in a finely finely dispersed form such as the inside of the silicide phase in the eutectic structure and the boundary part of the silicide phase or Si phase. An Al phase containing Ti as a main component or a TiAl _x Si _y (x + y = 2) compound phase is formed. This also applies to the entire microstructure. In addition to the inside of the silicide phase in the eutectic structure, the boundary between the silicide phase and the Si phase, the inside of the independent silicide phase and the boundary with the independent silicide phase, etc. In addition, it is crystallized in a finely dispersed form as a whole to form an Al phase or a TiAl _x Si _y (x + y = 2) compound phase. In addition to the Al phase containing Al as a main component, a compound TiAl _x Si _y (x + y = 2) compound phase in which a part of TiSi ₂ is replaced with Al is added to EDX of Si—Al—Ti. In the mapping composite image (FIG. 9 (e)), there is a part where three elements overlap, and the homepage of NIMS (National Institute for Materials Science) (inorganic material database, TiAl _0.3 Si _1.7 compound (C49-TiSi by "main component" that is because it has been shown that the same crystalline structure and ₂₎ are present .al, 50 wt% or more of Al phase, preferably 80 wt% or more, more preferably 90 mass % Or more, particularly preferably 95% by mass or more, and most preferably 98% by mass or more is Sn, however, it is present in the raw material or inevitably mixed in the manufacturing process. It may include inevitable impurities. Therefore, Al of get of 100 wt% in practice, it is difficult.

  This is because the second phase (Si phase) must contain Al, but does not necessarily contain Sn. Al is almost uniformly dispersed in the second phase, so that Sn is pushed out to the periphery of the second phase. As a result, the third phase containing Sn as the main component is the periphery of the second phase (the first phase). It is considered that the first phase and the second phase are dispersed more finely than the second phase.

  In the second phase (Si phase), “a part of Sn can be included” is, for example, when comparing FIG. 8B and FIG. 8E, in many cases, Sn is contained in the Si phase. This is because it is a portion that hardly contains (Si portion functions as an active material), but a portion containing Sn in the Si phase can be seen. Moreover, in the part containing Sn in the Si phase, Sn is dispersed and dissolved in Si, or is dispersed in a form of being included in Si (Sn—Si solid solution or Sn included therein functions as an active material). To do). By distributing Sn in the Si phase, the degree of amorphousness of the second phase (Si phase) can be increased, and the durability is excellent. Moreover, when Sn (Sn which is dispersed and dissolved in the Si crystal structure) is contained in the second phase (Si phase), the Sn also has a weight compared to the carbon negative electrode material (carbon negative electrode material). A large amount of Li can be occluded and released per area and per volume.

(3) Third phase mainly composed of Sn In the Si-containing alloy having a microstructure, the third phase is mainly composed of tin (Sn). This third phase (Sn phase) is a negative electrode active material having a capacity higher than that of a carbon-based negative electrode active material, and is excellent in that it has Sn as a main component, which is smaller in expansion and contraction during charge / discharge than Si. Yes. “Sn as a main component” means 50 mass% or more of the third phase (Sn phase), preferably 80 mass% or more, more preferably 90 mass% or more, particularly preferably 95 mass% or more, most preferably 98 mass% or more is Sn. However, the alloy may contain inevitable impurities that are present in the raw material or are inevitably mixed in the manufacturing process. Therefore, it is practically difficult to obtain Sn having a mass of 100% by mass.

(4) About the structure in which a part is a plurality of independent first phases The Si-containing alloy is characterized in that a part thereof is a plurality of independent first phases in the microstructure. One. Since a part of the microstructure is a plurality of independent silicide phases (first phases), a plurality of expansions of the second phase (a-Si phase) in the eutectic structure in the charge / discharge process are performed. The independent first phase can be suppressed and suppressed. Moreover, the low electronic conductivity of a-Si phase (especially Si active material) can be improved.

(5) Regarding a configuration in which a part of the first phase and the second phase have a eutectic structure, the Si-containing alloy includes a part of the first phase and the second phase in the microstructure. One of the features is that it has a eutectic structure. In the microstructure, a part of the first phase and the second phase have a eutectic structure, so that the expansion of the second phase (a-Si phase) in the eutectic structure in the charge / discharge process is caused. , The eutectic first phase can be suppressed and suppressed. Moreover, the low electronic conductivity of a-Si phase (especially Si active material) can be improved. Furthermore, by adding Al, the first phase (silicide phase, eg, TiSi ₂ phase) in the eutectic structure is rounded (see FIGS. 3B, 8B, 8E, etc.). Since the first phase (silicide phase) in the eutectic structure is rounded, stress concentration generated at the corners is eliminated, and it is considered that the durability is further improved.

(6) About the structure in which the third phase is finely dispersed in the eutectic structure than in the first phase and the second phase The Si-containing alloy is in the fine structure in the eutectic structure. One of the characteristics is that the third phase (Sn phase) is more finely dispersed than the first phase (silicide phase) and the second phase (Si phase). This is because the third phase (Sn phase) is finely dispersed in the eutectic part due to the small amount of Al contained in the Si-containing alloy (FIGS. 7B and 8B-8). (See (e)). Sn in the eutectic structure may be partly contained in the second phase (Si phase), but most of the Sn is not in the second phase (Si phase) but in the first phase in the eutectic structure. Crystallized at the boundary between the phase and the second phase, etc., an Sn phase mainly composed of Sn (third phase; functioning as an active material) is formed (see FIG. 8E). This also applies to the entire microstructure. In addition to the boundary between the first and second phases in the eutectic structure, crystallization occurs at the boundary with the independent first phase. Thus, an Sn phase (third phase; functioning as an active material) is formed. The third phase (Sn phase) can also store and release a large amount of Li per weight and volume as compared with the carbon negative electrode material (carbon negative electrode material).

  The Si-containing alloy is obtained by melting a predetermined alloy raw material by a liquid quenching roll solidification method, quenching at a predetermined cooling rate, and alloying, so that a plurality of independent first phases become primary crystals in the liquid phase. Crystallization occurs, and the eutectic structure of the first phase and the second phase crystallizes in the liquid phase of the gap between the independent first phases, and further, the third phase becomes the first phase in the eutectic structure. It is obtained by finer dispersion than the phase and the second phase.

A plurality of phases may exist in each of the above-described plurality of independent first phases (silicide phases) and first phases (silicide phases) in the eutectic structure, for example, transition metal elements Two or more phases (for example, MSi ₂ and MSi) having different composition ratios of M and Si may exist. Moreover, two or more phases may exist by including a silicide with different transition metal elements. Here, the type of transition metal contained in the first phase (silicide phase) is not particularly limited, but is preferably at least one selected from the group consisting of Ti, Zr, Ni, Cu, and Fe, and more Ti or Zr is preferable, and Ti is particularly preferable. These elements exhibit higher electronic conductivity and higher strength than silicides of other elements when silicides are formed. In particular, TiSi ₂ which is silicide when the transition metal element is Ti is preferable because it exhibits very excellent electron conductivity.

In particular, when the transition metal element M is Ti and there are two or more phases having different composition ratios in the silicide phase (for example, TiSi ₂ and TiSi), the silicide phase is 50 mass% or more, preferably 80 mass% or more, More preferably, 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass is the TiSi ₂ phase.

  The fine structure of the Si-containing alloy has the configurations (structures) described in (1) to (6) above, for example, high-resolution STEM (scanning transmission electron microscope) observation, EDX (energy dispersive X-ray spectroscopy). The structure of the microstructure of the Si-containing alloy (particle) that is the negative electrode active material particle can be clarified by elemental analysis, electron diffraction measurement, and EELS (electron energy loss spectroscopy) measurement. Examples of the analysis apparatus (analysis method) include XPS (X-ray photoelectron spectroscopy), TEM-EDX (transmission electron microscope-energy dispersive X-ray spectroscopy), and STEM-EDX / EELS (scanning transmission electron microscope). Energy dispersive X-ray spectroscopy / electron energy loss spectrometer), Cs-STEM (spherical aberration corrected scanning transmission electron microscope image), HAADF-STEM (high angle scattering dark field-scanning transmission electron microscope image), BF- STEM (bright field-scanning transmission electron microscope image) or the like can be used. However, in this embodiment, it is not limited to these, and various observation apparatuses (apparatus conditions, measurement conditions) used for the microstructure of existing alloys may be used.

(Analysis of microstructure of Si-containing alloys)
Hereinafter, the microstructure of the negative electrode active material having the above-described microstructure will be described with reference to an example using the Si-containing alloy (particles) that are the negative electrode active material particles produced in Example 1 as a sample. However, the structure of the microstructure of the alloy (particle) can be clarified in the same manner for the Si-containing alloy (particle) that is the negative electrode active material obtained in the other embodiment. Further, Example 2 and Comparative Example 1 can also be analyzed by using the same method.

1: Analysis method 1-1: Sample preparation FIB (focused ion beam) method; Microsampling system (manufactured by Hitachi, Ltd., FB-2000A)
An Al grid is used.

  1-2: STEMimage, EDX, EELS (Electron Energy Loss Spectroscopy) measuring apparatus and conditions are as follows.

1) Apparatus; atomic resolution analytical electron microscope JEOL JEM-ARM200F
EDX (Energy dispersive X-ray Spectroscopy)
; JED-2300 made by JEOL
(100mm ² silicon drift (SDD) type)
; System; Analysis Station
EELS (Electron Energy Loss Spectroscopy)
GATAN GIF Quantum
Image acquisition; Digital Micrograph
2) Measurement conditions; acceleration voltage: 200 kV
Beam diameter: about 0.2nmφ (diameter)
Energy resolution: about 0.5eV FWHM
1-3: Electron diffraction measurement apparatus and conditions are as follows.

1) Apparatus; Field Emission Electron Microscope JEOL JEM2100F
Image acquisition; Digital Micrograph
2) Measurement conditions; acceleration voltage: 200 kV
Beam diameter: about 1.0 nmφ (diameter) 2: (Quantitative mapping) analysis by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) FIG. 6A shows the Si-containing alloy of the present embodiment. Among Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (low magnification) of a sample prepared by FIB method (particles), BF (Bright-field) -STEM Image (bright field-scanning transmission electron microscope image) It is drawing which represents. FIG. 6B is a drawing showing a HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image) of the active material particles in the same field of view as FIG. The measurement object is 2% by mass on the surface of the Si-containing alloy (particles) in which the negative electrode active material particle size obtained by pulverizing the quenched ribbon alloy having the alloy composition of the present embodiment has an average particle diameter D50 = 7 μm (D90 = 18 μm). The cross-section of the negative electrode active material particles produced by coating the alumina was used as an observation target. As the quenched ribbon alloy, one represented by the alloy composition of Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 of Example 1 was used.

  FIG. 7A shows a Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (medium magnification) obtained by enlarging a portion surrounded by a square frame in FIG. 6B (a portion of a eutectic structure). It is drawing which shows BF (Bright-field) -STEM Image (bright field-scanning transmission electron microscope image). FIG.7 (b) is drawing which represents the HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image) of the active material particle in the same visual field as FIG.7 (a).

FIG. 8 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 8A shows a Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging a portion surrounded by a square frame in FIG. It is drawing which represents HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 8B is a diagram showing mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8C is a diagram showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8D shows the mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8E is a drawing (upper right) in which mapping data of Sn, Si, Ti measured in the same field of view as HAADF-STEM (upper left FIG. 8A) is superimposed. Since the mapping of FIGS. 8B to 8E can actually be colored (colored), for example, if Sn is green, Si is blue, and Ti is red, silicide (TiSi ₂ ) is Since the blue of Si and the red of Ti are mixed, it can be distinguished at a glance. However, in the application drawing, it is necessary to submit a black and white image. These are included in FIG. 6B and FIG. 7B. Those skilled in the art can easily obtain the same analysis information from quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) as in FIG. It is because it can be obtained. Incidentally, in FIGS. 8B to 8D, a portion where Sn, Si and Ti are not present is represented in black, and a portion where these elements are present is represented in gray shading or white. Thereby, the presence and distribution state of Si, Sn, and Ti among the elements constituting the active material alloy Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 (negative electrode active material of Example 1) can be confirmed. .

FIG. 9 is a diagram showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 9A shows a Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging a portion surrounded by a square frame in FIG. 7B (a portion of a eutectic structure). It is drawing which represents HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 9B is a diagram showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9C is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9D is a diagram showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9E is a drawing (upper right) in which mapping data of Al, Si, Ti measured in the same field of view as HAADF-STEM (upper left FIG. 9A) is superimposed. 9B to 8E can actually be colored (colored). For example, if Al is green, Si is blue, and Ti is red, silicide (TiSi ₂ ) is Since the blue of Si and the red of Ti are mixed, it can be distinguished at a glance. However, in the application drawing, it is necessary to submit a black and white image. These are included in FIG. 6B and FIG. 7B. Those skilled in the art can easily obtain the same analysis information from the quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) as in FIG. It is because it can be obtained. Incidentally, in FIGS. 9B to 9D, a portion where Al, Si, and Ti are not present is expressed in black, and a portion where these elements are present is expressed in gray shading or white. Thereby, the presence and distribution state of Al, Sn, and Ti among the elements constituting the active material alloy Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 (negative electrode active material of Example 1) can be confirmed. .

In the above analysis, for the STEM image observation, a bright-field (BF) STEM image formed using an electron beam transmitted through the sample and a dark field formed using an electron beam scattered from the sample. There are two types of observation methods for (Dark-field: DF) STEM images. In the BF-STEM images shown in FIGS. 6A and 7A, similarly to the normal TEM image, the transmission images showing the internal structure of the sample, FIGS. 6B, 7B, and 8 are used. In the (HA) DF-STEM image shown in (a) and FIG. 9 (a), a composition image that provides a contrast reflecting the composition of the sample can be observed. In particular, HAADF (high angle scattering annular dark field) is an imaging method referred to as a Z-contrast image because elastic scattering electron contrast due to atomic number (Z) is dominant. A substance with a large atomic number appears bright (see FIGS. 6B, 7B, 8A, and 9A). In HAADF-STEM (High Angle Scattering Circular Dark Field Scanning Transmission Microscopy), an image is applied by operating a thinly focused electron beam while operating a sample, and the scattered electrons are detected at a high angle by a ring detector. can get. Since a material having a large Z ² ρ is scattered at a higher angle, heavier elements are darker in the STEM image and brighter in the HAADF-STEM image. Since a contrast proportional to the atomic weight (Z) is obtained, it is also called a Z contrast image. In STEM-EDX quantitative mapping, the characteristic X-rays generated from each point are taken into an EDS (Energy-Dispersive-Spectroscope) detector while narrowing down the electron beam and scanning the sample, thereby obtaining information on the composition distribution of the sample. Can be obtained. In transmission electron microscope (TEM) measurement, since there is almost no diffusion of an electron beam as seen in scanning electron microscope (SEM) measurement, measurement can be performed with a spatial resolution of nanometers.

As shown in FIG. 6B, among the portions surrounded by a square frame (eutectic structure), there are a plurality of (relatively large) light gray portions corresponding to silicide (TiSi ₂ ) indicated by three arrows. It can be confirmed that they exist independently (a plurality of independent first phases). That this is silicide, there are a plurality of the same light gray portions as in FIG. 6B in FIG. 7B in which the portion surrounded by the square frame (eutectic structure) in FIG. Further, there are a plurality of portions in FIG. 8A and FIG. 9A in which the portion (eutectic structure) surrounded by the square frame in FIG. 7B is enlarged. In FIG. 8 (a) or FIG. 9 (a), when the same light gray portion as FIG. 6 (b) is colored in FIG. 8 (e) or FIG. 9 (e), the blue of Si and the red of Ti This is because the mixed pink (that is, silicide phase) has been confirmed. This is because, even when viewing FIGS. 8 and 9 as black and white images, the gray portion indicating the presence of Ti in the microstructure of the sample based on the Ti mapping data in FIGS. 8 (d) and 9 (d). It can be confirmed that there are multiple. Further, from the Si mapping data of FIG. 8C and FIG. 9C, Si overlaps with the gray portion indicating the presence of Ti in FIG. 8D and FIG. 9D in the microstructure of the sample. A gray portion indicating the presence of can be confirmed. This can be determined by comparing FIGS. 8 (a) (c) (d) (e) and FIGS. 9 (a) (c) (d) (e). Further, it can be confirmed that Sn (white portion) hardly exists in a light gray portion (relatively large) corresponding to the silicide (TiSi ₂ ) in FIG. From the Sn mapping data in FIG. 8 (b), there is almost a gray portion indicating the presence of Sn overlapping the gray portion indicating the presence of Ti in FIG. 8 (d) in the microstructure of the sample. It can be confirmed that they are not. For these reasons, the microstructure of the Si-containing alloy (particles) of the present embodiment has the first phase (silicide phase) containing the transition metal silicide (silicide) of (1) as a main component. And it can confirm that a part of said (4) has a some independent 1st phase (silicide phase).

  Next, the microstructure of the sample is obtained from the mapping data in which Sn, Si, Ti are superimposed in FIG. 8E on the upper right and the mapping data in which the Ti, Si, Ti are superimposed in FIG. 9E on the upper right. Among them, the first phase (silicide phase) and the second phase containing Al and Sn (a-Si phase) have a eutectic structure (crystalline (solid solution) having different composition ratios, amorphous or low It can be confirmed that the structure is a crystalline structure in which the first phase and the second phase are mixed.

  Specifically, in FIG. 8 (e) and FIG. 9 (e), the sample corresponds to a second phase (a-Si phase) partially containing Al and Sn in the microstructure of the sample (relatively first. It can be confirmed that the dark gray portion (Si + Sn portion) smaller than the first phase and the gray portion corresponding to the first phase (silicide phase) (relatively larger than the second phase) are mixed. . From this, it can be seen that the fine second phase (a-Si phase) and the first phase (silicide phase) are eutectic (having a eutectic structure). The eutectic structure can be confirmed by the following when coloring FIGS. 8 (e) and 9 (e). That is, in FIG. 8 (e) and FIG. 9 (e), the dark gray portion (second phase) (which is relatively smaller than the first phase) is mainly Si blue (including a small amount of Al and Sn). Si blue and Sn green are mixed in blue-green, and one gray portion (first phase) is pink in which Si blue and Ti red are mixed. Then, it corresponds to the Si phase (second phase) containing Al and Sn (relatively smaller than the first phase) and the blue and blue-green portions and the silicide phase (first phase) ( Since pink portions (relatively larger than the second phase) are mixed, it can be confirmed that these are eutectic structures.

  Further, even when viewed in a black and white image, the presence of Ti is shown (relatively small) in the microstructure (eutectic structure) of the sample from the Ti mapping data of FIGS. 8D and 9D. It can be confirmed that a large number of gray portions are present (dotted). Further, from the mapping data of Si in FIGS. 8C and 9C, a gray portion indicating the presence of Si is present in almost the entire microstructure of the sample in FIGS. 8D and 9D. Can be confirmed. Further, from the comparison of the Sn mapping data in FIG. 8B and the Ti mapping data in FIG. 8D, in the portion where Ti is scattered in the microstructure (eutectic structure) in FIG. It can be confirmed that the gray portion indicating the presence of Sn in FIG. That is, both Si and Ti are present (relatively larger than the second phase) in the microstructure (eutectic structure) of FIGS. 8B, 8C, 8D to 8D. It can be confirmed that a large number of gray portions are scattered. From the comparison between the Al mapping data in FIG. 9B and the Ti mapping data in FIG. 9D, a graph showing a portion where Ti is scattered in the microstructure (eutectic structure) in FIG. It can be confirmed that there is not much gray portion indicating the presence of Al in 9 (b). That is, both Si and Ti are present (relatively larger than the second phase) in the microstructures (eutectic structures) of FIGS. 9B, 9C, 9D, and 9D. It can be confirmed that a large number of gray portions are scattered. Further, a portion in which the gray portion (silicide) is not scattered (a portion in which many relatively small black portions are scattered) in the microstructures (eutectic structures) in FIGS. 8D and 9D. 8 (b) (c) and FIG. 9 (b) (c) are mainly dotted with a lot of Si (including a small amount of Al and Sn), Sn + Si and Al + Si. It can be confirmed. Also from these facts, from the microstructures (eutectic structures) shown in FIGS. 8E and 9E, a silicide phase (first phase) and a Si phase (second phase) partially containing Al and Sn. ) And a eutectic structure.

  From these facts, the microstructure of the Si-containing alloy (particles) of the present embodiment contains Al and Sn in part of the above (2) (specifically, inside the crystal structure of Si) And a second phase (a-Si phase) mainly composed of amorphous or low crystalline Si (in which Al and Sn are dispersed and solid-dissolved). It can be confirmed that the first phase and the second phase have a eutectic structure.

  7 (b), FIG. 8 (a), and FIG. 9 (a), the white portion in the eutectic structure is the third phase (Sn phase, trace amount of Si). , Ti, and Al may be included). Further, from FIGS. 8A to 8E, the third phase (Sn phase) in the eutectic structure is more finely dispersed than the first phase and the second phase in the eutectic structure. I understand that. In particular, by adding Al to the SiSnTi alloy, it can be confirmed that the third phase is finely dispersed at the boundary (periphery) of the first phase and the second phase in the eutectic structure (FIG. 8A ) To (e)). In addition, as shown in FIG.6 (b), the Sn phase of a white part may crystallize in parts other than an independent 1st phase and a eutectic structure. These also function as Sn active materials, but they do not expand and contract during the charge / discharge process as much as Si, and the expansion and contraction of the third phase (Sn phase) in the eutectic structure is the expansion and contraction of the Si phase in the eutectic structure. This can be prevented in the same manner as the suppression mechanism. In addition, since the independent first phase and the Sn other than the eutectic structure have an independent first phase in the vicinity thereof, the expansion is similar to the expansion / contraction suppression mechanism by the independent first phase. Shrinkage can be prevented. Therefore, even if the white part (Sn phase) of the grade seen by FIG.6 (b) exists, deterioration of a negative electrode active material alloy can fully be suppressed.

  From these facts, it is confirmed that the microstructure of the Si-containing alloy (particles) of the present embodiment has a third phase (Sn phase) further comprising (3) Sn as a main component in (3) above. it can. Moreover, it can confirm that the 3rd phase (Sn phase) is disperse | distributing more finely than the 1st phase and 2nd phase in a eutectic structure in the eutectic structure of said (6).

3: Analysis by electron diffraction and (powder) X-ray diffraction (XRD) measurement A relatively large gray portion in the HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image) of FIG. Indicates an independent first phase (silicide phase) as described above. In addition, a portion surrounded by a square frame includes a relatively small dark gray portion (Si + Sn portion) corresponding to a second phase (a-Si phase) partially containing Al and Sn, and a first phase (silicide). A eutectic structure in which a relatively small gray portion corresponding to (phase) is mixed is shown. A diffraction pattern (not shown) is obtained by subjecting the independent silicide phase region, the silicide phase region and the a-Si phase region in the eutectic structure of FIG. obtain. From these diffraction patterns, a two-dimensional dot array net pattern (lattice spot) is obtained for the single crystal phase, a Debye-Scherrer ring (diffraction ring) is obtained for the polycrystalline phase, and a halo is obtained for the amorphous phase. A pattern is obtained. Furthermore, the crystal structure of the two-dimensional dot array net pattern (silicide phase) can be specified. That is, from these diffraction patterns, a net pattern of a two-dimensional point array is obtained, and it can be confirmed that it is a single crystal phase. Further, it can be confirmed from the diffraction pattern that the Si phase (second phase) in the eutectic structure is a Debye-Scherrer ring (diffraction ring) and is a polycrystalline phase. Furthermore, a diffractive ring with a halo pattern is obtained, and it can be confirmed that the Si phase (second phase) is an amorphous phase having amorphous or low crystalline Si (a-Si). That is, it is confirmed by electron beam diffraction analysis that the Si phase (second phase) in the eutectic structure has amorphous or low crystalline Si (a-Si) by amorphization. it can. Furthermore, it can be confirmed from the diffraction pattern that the a-Si phase (second phase) is more amorphous than the silicide phase (first phase). Similar results are obtained for the other examples.

(Size of each phase in the microstructure of Si-containing alloy)
1. Regarding the relationship between the size of the independent first phase and the size of the eutectic structure Next, in the Si-containing alloy (particle) of the present embodiment, the size of the independent first phase in the microstructure of the alloy is It is preferable that it is larger than the size of the eutectic structure of the first phase and the second phase (see FIGS. 3A and 6). This is because by having such a configuration, the effects of the present invention can be expressed more effectively. That is, a relatively small-sized eutectic structure (the second phase is eutectic with the first phase) enters a gap between a plurality of independent relatively large-sized first phases in the microstructure. It can be configured. As a result, the expansion of the second phase (a-Si phase) in the relatively small size eutectic structure during the charge / discharge process (suppressed by the eutectic first phase), a plurality of independent relative This is because the first phase having a large size is more easily suppressed.

(Independent first phase size)
Here, the domain size of the independent first phase (silicide phase) in the microstructure of the alloy is preferably in the range of 200 to 600 nm. If the domain size of the independent first phase is within the above range, a relatively small size (the second phase is the first phase) in the gap between the plurality of independent relatively large first phases in the microstructure. A structure in which a eutectic structure (eutectic with one phase) enters can be adopted. As a result, the expansion of the second phase (a-Si phase) in the relatively small size eutectic structure during the charge / discharge process (suppressed by the eutectic first phase), a plurality of independent relative This is because the first phase having a large size is more easily suppressed.

Regarding the value of the domain size (diameter) of the independent first phase in the microstructure of the alloy, of the low magnification (0.5 μm scale bar) in Cs-STEM of the microstructure portion other than the eutectic structure The gray part (TiSi ₂ part indicated by the arrow in FIG. 6B) is regarded as an independent first phase. That is, the low-magnification Si EDX element mapping with Cs-STEM and M (for example, Ti) EDX element mapping are compared, and among the regions where Si is present and M is present, the regions other than the eutectic structure are independent. In the EDX element mapping of M, the intensity is 1/10 of the maximum value as a threshold, and binarized image processing is performed for a region that is equal to or greater than this threshold. From the obtained binarized image, It can be obtained as an arithmetic average value of measured values obtained by measuring five or more phases by the method of reading the dimensions of each independent first phase.

2. Regarding the magnitude relationship between the first phase to the third phase in the eutectic structure The domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase. Is preferably smaller than the domain size of the second phase. This is because, when a small amount of Al enters the Si-containing alloy, the second phase becomes finer than the first phase in the eutectic structure, and the third phase consists of the first phase and the second phase in the eutectic structure. This is because it is finely dispersed by the grain boundary of the phase. That is, in the eutectic structure, the domain size of the second phase is smaller than the domain size of the first phase, and the second phase is included in the first phase that is harder and more conductive. Therefore, when charging / discharging, the second phase (Si phase) in the eutectic structure is surrounded by the first phase (silicide phase), so expansion and contraction are suppressed, and Si reacts uniformly by imparting conductivity. Therefore, it is difficult for durability to deteriorate. In addition, since the third phase (Sn phase) is more finely dispersed around the first phase and the second phase (Si phase) in the eutectic structure, the second phase (Si phase) becomes amorphous. It becomes easy and has excellent durability. From these, the domain size of the independent first phase is larger than the size of the eutectic structure of the first phase and the second phase, and the domain size of the second phase is The domain size of the third phase is preferably smaller than the domain size of the second phase. As a result, the expansion of the second phase in the eutectic structure in the charge / discharge process, in particular, the Si active material as the main component, is suppressed by enveloping the eutectic first phase, and a plurality of independent first phases The phase can be suppressed by enclosing the second phase in the eutectic structure. Then, amorphous at the time of alloying Si and Li during charging - crystal phase transition _{(crystallization} into _Li 15 Si ₄₎ is suppressed. As a result, expansion and contraction of the Si-containing alloy during the charge / discharge process is reduced, and the first phase (silicide phase) composed of the conductive silicide and the second phase (a-Si phase) are eutectic. Thus, the second phase (a-Si phase), in particular, the main component Si active material can be reacted uniformly. As a result, cycle durability can be improved while showing the high capacity | capacitance of the electric device in which the said negative electrode active material is used. In particular, by adding Al to the SiSnTi alloy, if the third phase is finely dispersed around the second phase, the second phase (a-Si phase) is likely to become amorphous and excellent in durability. More specifically, the reason why the second phase (a-Si phase) becomes amorphous easily is that Al is almost uniformly dispersed in the second phase (a-Si phase). Then, Al is almost uniformly (homogeneously) dispersed in the second phase (a-Si phase), so that Sn is pushed out to the periphery of the second phase, and as a result, the third containing Sn as a main component. Are dispersed more finely around the second phase (between the first phase and the second phase) than in the first phase and the second phase. Therefore, when the third phase is finely dispersed around the second phase (Al is almost uniformly dispersed in the second phase), the second phase (a-Si phase) is likely to become amorphous. It can be said. That is, Al is adjacent to Al—Si in the liquid phase state is more stable, Al—Al and Si—Si adjacent to Al—Si are more stable than Al—Si in the solid phase state, and when cooled rapidly with Al contained in Si, overcooling occurs. Even if it enlarges, it becomes difficult to produce Si crystal | crystallization, and an amorphous formation ability improves. As a result of Al being dispersed almost uniformly in the second phase (a-Si phase), the third phase (Sn phase) is finely dispersed (Sn is bonded to Ti, so Si (second phase)). Phase) and a TiSi ₂ phase (first phase). The fine dispersion of the third phase (Sn phase) is necessary for improving the durability, because the main component of the third phase (Sn phase) Sn has a large volume expansion during charge and discharge. . Therefore, if Sn (third phase) is dispersed more finely than the first phase and second phase in the eutectic structure due to Al entering the alloy, the durability is further improved.

(Domain size of the first phase in the eutectic structure)
As described above, the domain size (diameter) of the first phase (silicide phase) in the eutectic structure should be larger than the domain size (diameter) of the fine third phase (Sn phase) in the eutectic structure. However, it is preferably larger than the domain size (diameter) of the second phase (a-Si phase) in the eutectic structure. As a result, the expansion of the second phase in the eutectic structure, particularly the Si active material as the main component, is suppressed by enveloping the eutectic relatively large-sized first phase (see FIG. 3B). ), Cycle durability can be improved. From this viewpoint, the domain size (diameter) of the first phase (silicide phase) in the eutectic structure is preferably in the range of 20 to 70 nm. The domain size of the first phase in the eutectic structure is more preferably 60 nm or less, still more preferably 55 nm or less, and particularly preferably 50 nm or less. The domain size of the first phase in the eutectic structure is more preferably 25 nm or more, and more preferably 30 nm or more.

  Regarding the domain size (diameter) value of the first phase (silicide phase) in the eutectic structure, high-magnification (25 nm scale bar) Si EDX element mapping in Cs-STEM for the eutectic structure part and Compare the EDX elemental mapping of M (eg, Ti). Then, a region where Si is present and M is also regarded as a silicide phase, the intensity of 1/10 of the maximum value is set as a threshold in the EDX element mapping of M, and binarized image processing is performed for a region that is equal to or greater than the threshold. From the obtained binarized image, it can be obtained as an arithmetic average value of measured values obtained by measuring five or more phases by a method of reading the dimensions of each first phase in the eutectic structure. .

(Size of the second phase in the eutectic structure)
The size of the second phase (a-Si phase) in the eutectic structure may be larger than the domain size (diameter) of the fine third phase (Sn phase) in the eutectic structure as described above. However, it is preferably smaller than the domain size (diameter) of the first phase (silicide Sn phase). As a result, the expansion of the second phase in the eutectic structure, particularly the Si active material as the main component, is suppressed by enveloping the eutectic relatively large-sized first phase (see FIG. 3B). ), Cycle durability can be improved. From this viewpoint, the size of the second phase is preferably as small as possible. Specifically, the size of the second phase in the eutectic structure is preferably 30 nm or less, more preferably 28 nm or less, and further preferably 25 nm or less. On the other hand, the lower limit of the size of the second phase is not particularly limited, but is preferably 5 nm or more, more preferably 8 nm or more, and further preferably 10 nm or more.

  In addition, about the value of the domain size (diameter) of a 2nd phase (a-Si phase), EDX element mapping of Si of high magnification (25 nm scale bar) and M (for example, Ti) EDX in HAADF-STEM The element mapping is compared, the region where Si is present and M is not present is regarded as the second phase (a-Si phase), and the intensity is 1/10 of the maximum value in the EDX element mapping of M, and below this threshold Obtained by measuring five or more phases by a technique of performing binarized image processing on the region to be obtained and reading the dimensions of each second phase (a-Si phase) from the obtained binarized image. It can be obtained as an arithmetic average value of the measured values.

(Size of the third phase in the eutectic structure)
As described above, the domain size (diameter) of the third phase (Sn phase) in the eutectic structure is smaller than the first phase and the second phase in the eutectic structure, and may be finely dispersed. That's fine. Specifically, Al is dispersed almost uniformly in the second phase (a-Si phase) in the eutectic structure, so that the third phase is finely dispersed around the second phase. If the third phase is finely dispersed around the second phase (Al is almost uniformly dispersed in the second phase), the second phase (a-Si phase) is likely to be amorphous. That is, Al is adjacent to Al—Si in the liquid phase state is more stable, Al—Al and Si—Si adjacent to Al—Si are more stable than Al—Si in the solid phase state, and when cooled rapidly with Al contained in Si, overcooling occurs. Even if it enlarges, it becomes difficult to produce Si crystal | crystallization, and an amorphous formation ability improves. As a result of Al being dispersed almost uniformly in the second phase (a-Si phase), the third phase (Sn phase) is finely dispersed (Sn is bonded to Ti, so Si (second phase)). Phase) and a TiSi ₂ phase (first phase). The fine dispersion of the third phase (Sn phase) is necessary for improving the durability, because the main component of the third phase (Sn phase) Sn has a large volume expansion during charge and discharge. . Therefore, if Sn (third phase) is finely dispersed (smaller) than the first phase and the second phase in the eutectic structure due to Al entering the alloy, the durability is further improved. From this point of view, it is preferable that the domain size of the third phase is smaller. Specifically, the size of the third phase in the eutectic structure is preferably 10 nm or less, more preferably 9 nm or less, and even more preferably 8 nm or less. The domain size of the third phase is preferably 3 nm or more, more preferably 4 nm or more, and further preferably 5 nm or more.

  As for the domain size (diameter) value of the third phase (Sn phase), high magnification (25 nm scale bar) Sn EDX element mapping, Si EDX element mapping and M (for example, in HAADF-STEM) Compare the EDX elemental mapping of Ti). A region where Si is present and M is present is regarded as a first phase (silicide phase), and a region where Si is present and M is not present is regarded as a second phase (a-Si phase). A region in which the Sn phase is finely dispersed around (boundary) the first phase (silicide phase) and the second phase (a-Si phase) is regarded as a third phase (Sn phase). In the EDX elemental mapping, the intensity is 1/10 of the maximum value as a threshold value, and binarized image processing is performed for a region where the intensity is less than or equal to this threshold value. It can be obtained as an arithmetic average value of measured values obtained by measuring five or more phases by a method of reading the dimension of (Sn phase).

  Next, the particle diameter of the Si-containing alloy constituting the negative electrode active material in the present embodiment is not particularly limited, but the average particle diameter is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm. .

  Moreover, in this embodiment, the preferable range of the size of the periodic arrangement area | region (MRO) about the 2nd phase (a-Si phase) in the eutectic structure of the above-mentioned alloy is prescribed | regulated. Here, the size of the periodic array region (MRO) for the second phase (a-Si phase) is measured by the following TEM-MRO analysis. The same measurement was performed for the examples.

(Measurement of size of periodic array region (MRO) of second phase (a-Si phase) by TEM-MRO analysis)
In this measurement, a Fourier transform process is performed from a lattice image obtained by a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) of a Si-containing alloy to obtain a diffraction pattern. In this diffraction pattern, when the distance between Si tetrahedrons was set to 1.0, an inverse Fourier transform process was performed on a diffraction ring portion existing in a width of 0.7 to 1.0. From the Fourier transform image, attention can be paid to the periodic array, and the size of the periodic array region (MRO) can be measured.

-Lattice image by HAADF-STEM observation Here, observation using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) can be usually performed using HAADF-STEM and a computer. For observation by HAADF-STEM, a method of observing (monitoring) with a computer by enlarging a lattice image (interference image) created by electrons transmitted through the sample to be observed by applying an electron beam to the sample to be observed can be used. According to a transmission electron microscope (TEM), it is possible to obtain a high-resolution observation image enlarged to the atomic level and having high contrast. For example, FIG. 10A is an enlarged photograph of a lattice image obtained by HAADF-STEM of the Si-containing alloy (specifically, SiSnTiAl alloy) of the present embodiment.

  Next, a Fourier transform process is performed from the lattice image obtained by HAADF-STEM to obtain a diffraction pattern. At this time, the Fourier transform process can be performed by, for example, software “Digital Micrograph” manufactured by Gatan. It should be noted that other versatile software that can be easily reproduced (implemented) by those skilled in the art may be used for the Fourier transform processing from the lattice image obtained by the HAADF-STEM. Here, the HAADF-STEM image shown in FIG. 10A has a bright part and a dark part. The bright part corresponds to the part where the atomic sequence exists, and the dark part corresponds to the part between the atomic sequence.

Diffraction pattern Next, Fourier transform (FT) processing is performed on a 40 nm square portion (portion surrounded by a broken line) of the lattice image (HAADF-STEM image) shown in FIG. Here, a diffraction pattern (diffraction data) including a plurality of diffraction spots corresponding to a plurality of atomic planes is acquired by performing a Fourier transform process on a range surrounded by a broken line of the acquired lattice image. This Fourier transform processing can be performed by, for example, software “Digital Micrograph” manufactured by Gatan. For the Fourier transform process, other general-purpose software that can be easily reproduced (implemented) by those skilled in the art may be used.

  FIG. 10 (B) is a photograph showing a diffraction pattern obtained by performing a fast Fourier transform (FFT) process on the lattice image (HAADF-STEM image) of the silicon-containing alloy of Example 1 shown in FIG. 10 (A). It is. In the diffraction pattern shown in FIG. 10B, a plurality of diffraction ring portions (diffraction spots) are observed in a ring shape (annular) around the brightest spot that can be seen in the center as the intensity indicating the absolute value. The

  In the diffraction pattern shown in FIG. 10 (B), a diffraction ring portion having a width of 0.7 to 1.0 when the distance between Si regular tetrahedrons is 1.0 is determined. Here, the Si tetrahedral distance is equivalent to the distance between the central Si atom of the Si tetrahedral structure and the central Si atom of the adjacent Si regular tetrahedral structure (simply abbreviated as Si-Si distance). To do. Incidentally, this distance corresponds to the surface interval of the Si (220) plane in the Si diamond structure. Therefore, in this step, among the plurality of diffraction ring portions (diffraction spots), the diffraction ring portion corresponding to the Si (220) plane is assigned, and the diffraction ring portion is assigned a distance between Si tetrahedrons of 1. A diffraction ring portion having a width of 0.7 to 1.0 when 0 is set. For the attribution of the diffraction ring portion (diffraction line), for example, a known document (gazette, academic book, etc.) or a document related to various silicon electron diffraction lines published on the Internet can be used. For example, “Technical Report”, Vol. 9, March 2007, I.I. Engineering Department Technical Workshop 8. Acquisition of technology related to electron diffraction pattern observation by transmission electron microscope, Noriyuki Saito, Shigeyasu Arai, Graduate School of Engineering, Engineering Department, Materials / Analysis Technology System (http: //eng.engg. /V9/047.pdf) etc., and can be carried out with reference to literature relating to electron diffraction lines of silicon.

Inverse Fourier transform image Next, the diffraction ring portion existing in a width of 0.7 to 1.0, that is, the Si (220) plane when the distance between the above-mentioned Si tetrahedrons of the diffraction pattern is 1.0. Inverse Fourier transform processing is performed for the corresponding diffraction ring portion. An inverse Fourier transform image is acquired by performing an inverse Fourier transform process on the diffraction ring portion corresponding to the Si (220) plane (extracted figure / extracted data from which data is extracted). The inverse Fourier transform process can be performed by, for example, software “Digital Micrograph” manufactured by Gatan. For the inverse Fourier transform process, other general-purpose software that can be easily reproduced (implemented) by those skilled in the art may be used.

  FIG. 10C shows an inverse Fourier transform image obtained by performing inverse fast Fourier transform processing on the extracted figure from which the data of the diffraction ring portion corresponding to the Si (220) plane of FIG. 10B is extracted. It is a photograph which shows. As shown in FIG. 10C, in the obtained inverse Fourier transform image, a light / dark pattern composed of a plurality of bright portions (bright portions) and a plurality of dark portions (dark portions) is observed. Most of the bright and dark portions are amorphous regions (Si amorphous regions) that are irregularly arranged without periodic arrangement. However, as shown in FIG. 10 (C), areas where the bright portions are periodically arranged (periodic arrangement portions existing in the ellipses surrounded by broken lines in FIG. 10 (C)) are scattered (scattered). ing. That is, in the inverse Fourier transform image shown in FIG. 10C, in the amorphous region other than the periodic array portion existing in the ellipse surrounded by the broken line, the bright portion and the dark portion are straight and bent in the middle. They are not stretched into a shape and are not regularly arranged. In addition, there is a portion where the brightness contrast is weak between the bright portion and the dark portion. The bright and dark pattern structure consisting of bright and dark portions in the amorphous region other than the periodic array portion present in the ellipse surrounded by the broken line is that the sample to be observed is amorphous or fine in the amorphous region. It shows that it has a crystalline (precursor of MRO) structure. Therefore, by acquiring an inverse Fourier transform image as shown in FIG. 10C, a region (a crystallization region or a region having a periodic arrangement existing in an ellipse surrounded by a broken line in an amorphous region (amorphous region). Whether or not it has a crystal structure region) can be easily analyzed. This “region having a periodic array” is also referred to as a “periodic array region (MRO)” in this specification.

  FIG. 10C ′ is a diagram obtained in the same manner as FIGS. 10A to 10C below for the second phase (a-Si phase) in the eutectic structure of the alloy of Example 1. It is drawing equivalent to 10 (C). Specifically, for the second phase (a-Si phase) in the eutectic structure of Example 1, data of the diffraction ring portion corresponding to the Si (220) plane of the drawing corresponding to FIG. 10B was extracted. It is a photograph which shows the inverse Fourier-transform image obtained by performing an inverse fast Fourier-transform process with respect to an extracted figure. FIG. 15 shows the second phase (a-Si phase) in the eutectic structure of the alloy of Example 2 obtained in the same manner as FIGS. 10 (A) to 10 (C) below. It is drawing equivalent to. Specifically, for the second phase (a-Si phase) in the eutectic structure of Example 2, data of the diffraction ring portion corresponding to the Si (220) plane of the drawing corresponding to FIG. 10B was extracted. It is a photograph which shows the inverse Fourier-transform image obtained by performing an inverse fast Fourier-transform process with respect to an extracted figure. 18 shows the second phase (a-Si phase) in the eutectic structure of the alloy of Comparative Example 1 obtained in the same manner as in the following FIGS. 10 (A) to 10 (C). It is drawing equivalent to. Specifically, for the second phase (a-Si phase) in the eutectic structure of Comparative Example 1, data of the diffraction ring portion corresponding to the Si (220) plane of the drawing corresponding to FIG. It is a photograph which shows the inverse Fourier-transform image obtained by performing an inverse fast Fourier-transform process with respect to an extracted figure.

  In this embodiment, the “periodic array region (MRO)” refers to a region in which at least three bright portions are continuously arranged in a substantially straight line and are regularly arranged in two or more rows. This periodic array region (MRO) indicates that the sample to be observed has a crystal structure. That is, the “periodic array region (MRO)” indicates a crystallization (crystal structure) region scattered (scattered) in the Si amorphous region occupying most of the Fourier image.

  FIG. 11 is a drawing schematically showing “major axis diameter of periodic array region (MRO)”. In FIG. 11, the dark portion A (the bright portion in FIG. 10C) of the periodic array region (MRO) is represented by a black circle ● for convenience, and the region (Si) arranged irregularly adjacent to the region having the periodic array. For the sake of convenience, the dark part B (the bright part in FIG. 10C) of the amorphous region is indicated by white circles. In FIG. 11, as the “periodic array region (MRO)”, the dark portions (bright portions in FIG. 10C) arranged in a straight line with three consecutive points are arranged in parallel adjacent to two rows. The description is made using regions. In this embodiment, the “major axis diameter of the periodic array region (MRO)” can be obtained as follows. First, as shown in FIG. 11, the midpoint of the shortest route connecting the dark portion A (●) of the “periodic array region (MRO)” and the dark portion B (◯) of the irregularly arranged region adjacent thereto. Take C. Four points D1 to D4 in the major axis direction and the minor axis direction are selected from a one-dot dashed frame drawn by connecting these intermediate points C (which may not match the elliptical equation), and at least the major axis is selected among them. An ellipse drawn by an elliptic equation using two points in the direction (preferably all four points) (the ellipse enclosed by a broken line in FIG. 10C; an ellipse drawing software that can be drawn on the image can be used) The major axis diameter (L) can be determined. For example, as shown in FIG. 11, the length of the dark part A1 (●) at both ends, which is the longest in the major axis direction of the “periodic array region (MRO)”, can be measured using image analysis software (for example, , Measured using the data of the major axis diameter by the ellipse drawing software). Next, the length of the dark portion B1 (◯) of the irregularly arranged region adjacent to the dark portion A1 (●) at both ends in the major axis direction of the “periodic array region (MRO)” is similarly measured. From these, the midpoint between both ends connecting the dark portion A1 (●) at both ends in the major axis direction of the “periodic array region (MRO)” and the dark portion B1 (◯) of the irregularly arranged region adjacent thereto. The length of C1 is obtained, and this length can be used as the major axis diameter (L). In FIG. 10C, an ellipse surrounded by a broken line has a periodic array with two major axis directions as the major axis diameter and two minor axis directions as the minor axis diameter as shown in FIG. An ellipse is drawn by an elliptic equation (using ellipse drawing software that can be drawn on an image) so that all regions are included.

  Further, in this embodiment, the “size obtained from the average value of the major axis diameters of a maximum of five points” refers to the “periodic array region (MRO)” in the inverse Fourier transform image and a plurality of obtained For the “periodic array region (MRO)”, the major axis diameter is obtained from the ellipse drawn according to the definition of the “major axis diameter of the periodic array region (MRO)”. From the obtained major axis diameters, five points are calculated from the larger major axis diameter, the average value is calculated, and the average value is taken as the size of the periodic array region (MRO). The “maximum of 5 points” is the “major axis diameter of the periodic array region (MRO)” obtained from the inverse Fourier transform image (in the field of view of 40 × 40 nm; see FIG. 10C). This is because there are cases where it is less than 5 points (4 points or less). In this case, an average value of all major axis diameters of the “periodic array region (MRO)” obtained from the inverse Fourier transform image is calculated, and the size (size) of the average value is calculated as the periodic array region (MRO). The size of In the present embodiment, a plurality (two or more) of “periodic array regions (MRO)” in the inverse Fourier transform image (40 × 40 nm field of view) may exist, but preferably three or more, more preferably 4 or more, more preferably 5 or more. Further, the upper limit value of the number of “periodic array regions (MRO)” in the inverse Fourier transform image (40 × 40 nm field of view) may be in a range where the characteristics (effects) of Si amorphous are not impaired. Or less is preferred.

(Size of periodic array area (MRO))
In a preferred embodiment of the present invention, the size of the periodic array region (MRO) is preferably 6 nm or less, more preferably 5 nm or less, further preferably 4 nm or less, particularly preferably 3 nm or less, and particularly preferably 2.5 nm or less. It is. When the size of the periodic array region (MRO) satisfies the above range (requirement), Si is sufficiently amorphized, and the expansion of Si particles during charge / discharge can be mitigated, greatly improving durability. It is possible to provide a Si alloy active material that can be improved easily. That is, when Si is sufficiently amorphized, the diffraction ring portion of the Si (220) plane required for obtaining a Si alloy having high durability can be expressed (confirmed). In addition, from the inverse Fourier transform image of the diffraction ring portion of the Si (220) surface, MRO (Si crystallized region) having regularity in the amorphous is formed, and by making the size of this MRO smaller, it becomes amorphous. When it is used as an active material, it becomes difficult to form an irreversible Li—Si alloy crystal phase. Furthermore, since the degree of amorphization progresses, the expansion of the active material particles during charge / discharge can be relaxed, and the durability can be greatly improved. The lower limit of the size of the periodic array region (MRO) is not particularly limited, but may be 1 nm or more from a theoretical viewpoint.

  In another preferable embodiment of the present invention, a preferable range of the distance between Si tetrahedrons for the second phase (a-Si phase) in the eutectic structure of the alloy described above is also defined. Here, the value of the Si tetrahedral distance for the second phase (a-Si phase) in the eutectic structure is also measured by the TEM-MRO analysis described above for the measurement of the periodic array region (MRO). (The same measurement was performed for the examples described later). Specifically, first, in a region (amorphous region) that does not include a periodic array region (MRO) that exists in an ellipse surrounded by a broken line of the inverse Fourier transform image as shown in FIG. For example, an arbitrary 20 nm square (20 × 20 nm field of view) region is secured (selected), and the number of bright portions (corresponding to dots = Si regular tetrahedron units) in this field region is measured. Next, a value obtained by dividing 20 nm, which is the length of one side of the visual field, by the square root of the number of bright portions is defined as a distance between Si regular tetrahedra. For example, if the number of bright portions (corresponding to dots = Si regular tetrahedron unit) in an arbitrary 20 nm square field region is 100, 20 nm ÷ √ (100) = 20 nm / 10 = 2 nm is Si regular tetrahedron. It becomes a distance.

(Si tetrahedral distance)
In a preferred embodiment of the present invention, the Si tetrahedral distance in the amorphous region is preferably more than 0.36 nm, more preferably 0.40 nm or more, and still more preferably 0.44 nm or more. Particularly preferably, the thickness is 0.48 nm or more. When the distance between the Si tetrahedrons in the amorphous region satisfies the above range, the amorphous region can be made amorphous. As a result, Li ions can be easily inserted / extracted between the expanded Si—Si during charge / discharge. The durability of the negative electrode and the electric device using the negative electrode active material of this embodiment can be greatly improved. The upper limit value of the distance between the Si tetrahedrons in the amorphous region is not particularly limited, but can be said to be 0.55 nm or less from a theoretical point of view.

(Method for producing negative electrode active material)
There is no particular limitation on the method for producing the negative electrode active material for an electrical device according to the present embodiment, and conventionally known knowledge can be referred to as appropriate, but in this embodiment, the Si-containing alloy has the second phase in the microstructure. (Si phase) is eutectic with the first phase (silicide phase), and further enters a gap between a plurality of independent first phases. Further, the third phase (Sn phase) is more finely dispersed in the eutectic structure than the first phase and the second phase. In particular, due to the addition of Al, the third phase has a finely dispersed structure due to grain boundaries between the second phase and the first phase in the eutectic structure. Furthermore, a configuration in which the second phase in the eutectic structure is made finer than the first phase and the third phase (Sn phase) is made finer than the second phase is preferable. As a method for producing a negative electrode active material comprising such an Si-containing alloy, a method for producing a quenched ribbon alloy by a liquid quench roll solidification method (also simply referred to as a liquid rapid solidification method) is provided as follows. That is, according to another aspect of the present invention, there is provided a method for producing a negative electrode active material for an electric device comprising the Si-containing alloy having the fine composition, preferably having the structure of the chemical formula (1). Specifically, a method for producing a negative electrode active material for an electric device, comprising producing a quenched ribbon (ribbon) alloy of an Si-containing alloy by a liquid rapid solidification method using a mother alloy having the same composition as the Si-containing alloy Is also provided. Preferably, after preparing a quenched ribbon of an Si-containing alloy, the negative electrode active material for an electric device is obtained by performing a pulverization treatment to obtain the above-described average particle diameter to obtain the negative electrode active material for an electric device made of the Si-containing alloy. It is a manufacturing method. As described above, by performing the liquid rapid solidification method to manufacture the negative electrode active material (Si-containing alloy), it is possible to manufacture the alloy having the above-described microstructure. This provides a manufacturing method that can effectively contribute to the improvement of cycle durability while exhibiting a high capacity of the Si-containing alloy active material. Hereinafter, the manufacturing method according to the present embodiment will be described.

<Liquid quenching roll solidification method (preparation process of quenched ribbon ribbon)>
First, a liquid quench roll solidification method is performed using a mother alloy having the same composition as the desired Si-containing alloy. Thereby, a rapidly cooled ribbon is produced.

  Here, in order to obtain a master alloy, high-purity raw materials (single ingots) are used as raw materials for silicon (Si), tin (Sn), aluminum (Al), and transition metals (for example, titanium (Ti)). , Wire, plate, etc.). Subsequently, in consideration of the composition of the Si-containing alloy (negative electrode active material) to be finally produced, a master alloy in the form of an ingot or the like is produced by a known technique such as an arc melting method.

  Thereafter, a liquid quench roll solidification method is performed using the mother alloy obtained above. This step is a step of rapidly cooling and solidifying the melt obtained by melting the master alloy obtained above, and is performed by, for example, a high-frequency induction melting-liquid quench roll solidification method (a twin roll or a single roll quench method). be able to. Thereby, a rapidly cooled ribbon (ribbon) alloy is obtained. The liquid quench roll solidification method is often used as a method for producing an amorphous alloy, and there are many knowledges about the method itself. The liquid rapid roll coagulation method can be performed using a commercially available liquid rapid solidification apparatus (for example, a liquid rapid solidification apparatus NEV-A05 type manufactured by Nisshin Giken Co., Ltd.).

  Specifically, using a liquid rapid solidification apparatus NEV-A05 manufactured by Nissin Giken Co., Ltd., a melting apparatus with an injection nozzle (for example, a quartz nozzle) installed in a chamber adjusted by reducing the gauge pressure after Ar replacement. ), The above-mentioned master alloy is put in, melted to a predetermined temperature range by an appropriate melting means (for example, high frequency induction heating), and then made of metal or ceramics (especially heat) at a predetermined rotation speed at a predetermined injection pressure. By spraying onto a roll (made of Cu having excellent conductivity), it is possible to produce a ribbon-like alloy = quenched ribbon (ribbon) alloy that is continuously formed horizontally from above the roll.

At this time, the atmosphere in the chamber is preferably replaced with an inert gas (He gas, Ne gas, Ar gas, N ₂ gas, or the like). After the replacement with the inert gas, the gauge pressure in the chamber is desirably adjusted to a range of -0.03 to -0.07 MPa (0.03 to 0.07 MPa in absolute pressure).

  Moreover, the melting temperature of the mother alloy in the melting apparatus (for example, quartz nozzle) with an injection nozzle should just be more than melting | fusing point of an alloy. As the melting means, conventionally known melting means such as high frequency induction heating can be used.

  Moreover, it is desirable to adjust the injection pressure of the mother alloy from the nozzle of a melting apparatus (for example, a quartz nozzle) with an injection nozzle in the range of 0.03 to 0.09 MPa as a gauge pressure. The said injection pressure can be adjusted with a conventionally well-known method. Moreover, it is desirable to adjust the differential pressure between the chamber internal pressure and the injection pressure within the range of 0.06 to 0.16 MPa.

  Moreover, it is desirable to adjust the rotation speed and peripheral speed of the roll when jetting the mother alloy to the range of 4000 to 6000 rpm (40 to 65 m / sec as the peripheral speed).

  Further, the cooling rate of the ribbon-like alloy = quenched ribbon (ribbon) alloy is preferably 1.6 million ° C./second or more, more preferably 2 million ° C./second or more, further preferably 3 million ° C./second or more, particularly Preferably it is 5 million degrees C / sec or more. The method for obtaining the cooling rate is as described above. By adjusting the cooling rate within the above range, it is excellent in that the Si-containing alloy having the above-described microstructure of the present invention can be produced, and the effects of the alloy can be effectively expressed.

  In the present embodiment, the above-described Si-containing alloy = quenched ribbon (ribbon) alloy having the desired microstructure is adjusted by adjusting the cooling rate, jetting pressure, and the like in the liquid quench roll solidification method to the ranges specified above. It can be produced.

(Crushing process of rapidly cooled ribbon (ribbon) alloy)
Then, the pulverization process of the obtained ribbon-like alloy (quenched ribbon (ribbon) alloy) is performed. For example, using an appropriate pulverizing apparatus (for example, planetary ball mill apparatus P-6 manufactured by Frichtu, Germany), an appropriate pulverizing ball (for example, zirconia pulverizing ball) in an appropriate pulverizing pot (for example, zirconia pulverizing pot) Then, a rapidly cooled ribbon (ribbon) alloy is charged and pulverization is performed at a predetermined rotational speed for a predetermined time. The quenched ribbon (ribbon) alloy may be coarsely pulverized with an appropriate pulverizer so as to be easily put into the pulverizer.

  As the grinding treatment conditions at this time, the rotational speed of the grinding machine (mill apparatus) may be in a range that does not impair the alloy microstructure formed by the liquid quench roll solidification method, and is less than 500 rpm, preferably 100 to 480 rpm. More preferably, it is desirable to adjust to the range of 300 to 450 rpm. The pulverization time may be in a range that does not impair the alloy microstructure formed by the liquid quench roll solidification method, for example, less than 12 hours, preferably 0.5 to 10 hours, and more preferably 0.5 to 3 It is desirable to adjust to the time range.

  The pulverization process is usually performed in a dry atmosphere, but the particle size distribution after the pulverization process may be large or small. For this reason, you may perform once or more combining the grinding | pulverization process and classification process for adjusting a particle size.

(Mechanical alloying process)
Following the process of producing the quenched ribbon (ribbon) alloy, mechanical alloying treatment may be performed on the obtained ribbon-like alloy (quenched ribbon (ribbon) alloy) as necessary. At this time, if necessary, a crushing step of the quenched ribbon (ribbon) alloy may be performed, and a mechanical alloying process may be performed on the obtained pulverized product. By performing the mechanical alloying treatment after the liquid rapid solidification method, the distance between the Si regular tetrahedrons in the obtained alloy can be increased, and the size of the periodic array region (MRO) can also be reduced.

  The mechanical alloying process can be performed using a conventionally known method. For example, by using a ball mill device (for example, a planetary ball mill device), a pulverized ball and an alloy raw material powder are put into a pulverizing pot, and a high energy is applied by increasing the number of rotations, thereby achieving alloying. The rotation speed of the ball mill device is, for example, 500 rpm or more, preferably 600 rpm or more. Further, the mechanical alloying treatment time is, for example, 12 hours or more, preferably 24 hours or more, more preferably 30 hours or more, further preferably 36 hours or more, and particularly preferably 42 hours or more. Yes, most preferably 48 hours or more. In addition, although the upper limit of the time for alloying process is not set in particular, it may usually be 72 hours or less.

  The mechanical alloying process by the above-described method is usually performed in a dry atmosphere, but the particle size distribution after the mechanical alloying process may have a very large or small width. For this reason, it is preferable to perform the grinding | pulverization process and / or classification process for adjusting a particle size.

As described above, the predetermined alloy included in the negative electrode active material layer has been described, but the negative electrode active material layer may contain other negative electrode active materials. Examples of the negative electrode active material other than the predetermined alloy include natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, carbon such as hard carbon, pure metal such as Si and Sn, and the predetermined composition. Alloy-based active material out of ratio, or metal oxide such as TiO, Ti ₂ O ₃ , TiO ₂ , SiO ₂ , SiO, SnO ₂ , lithium such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN And transition metal composite oxides (composite nitrides), Li—Pb alloys, Li—Al alloys, Li, and the like. However, from the viewpoint of sufficiently exerting the effects exhibited by using the predetermined alloy as the negative electrode active material, the content of the predetermined alloy in the total amount of 100% by mass of the negative electrode active material is preferably It is 50-100 mass%, More preferably, it is 80-100 mass%, More preferably, it is 90-100 mass%, Especially preferably, it is 95-100 mass%, Most preferably, it is 100 mass%.

(Amorphous forming ability)
As described above, in the present embodiment, the microstructure of the Si-containing alloy preferably contains a first phase mainly composed of a transition metal silicide and a part of Al (and Sn), and is amorphous. It has a second phase mainly composed of high quality or low crystalline Si and a third phase mainly composed of Sn. Furthermore, a part is a plurality of independent first phases, and a part is a eutectic structure of the first phase and the second phase, and the third phase is the first phase in the eutectic structure. The structure has a finer dispersion than the phase and the second phase. In order to efficiently express the effects of the present invention, it is preferable that the Si phase (second phase) in the eutectic structure is sufficiently amorphized.

As a specific index of amorphous forming ability, critical cooling rate, liquidus temperature, T ₀ curve, glass transition temperature, crystallization temperature, and the like are used. Among them, the critical cooling rate can compare the amorphous forming ability even when the alloy systems are different.

  The critical cooling rate is the minimum cooling rate at which atoms or molecules become an amorphous phase. By setting the cooling rate in the production of the alloy to be equal to or higher than the critical cooling rate, an alloy having an amorphous phase can be produced. That is, an alloy composition having a low critical cooling rate is considered to have high amorphous forming ability because it can be made amorphous even when slowly cooled.

In a preferred embodiment of the production method of the present invention, from the viewpoint of sufficiently amorphizing the second phase in the eutectic structure, the critical cooling rate F of the liquid phase composition at the start of the eutectic in the master alloy composition. Is 4 × 10 ⁷ K / sec or less, preferably 3 × 10 ⁷ K / sec or less. More preferably, it is 2.8 × 10 ⁷ K / sec or less, further preferably 2.5 × 10 ⁷ K / sec or less, and particularly preferably 2.2 × 10 ⁷ K / sec or less. Further, the lower limit of the critical cooling rate F is not particularly limited, and is, for example, 1 × 10 ⁶ K / sec or more.

  Hereinafter, calculation of the critical cooling rate of the liquid phase composition at the start of eutectic in the alloy composition will be described using the alloy composition used in Example 1 as an example. For the alloy compositions of Example 2 and Comparative Example 1, the critical cooling rate of the liquid phase composition at the start of eutectic can be determined by the same method.

[Calculation of liquid phase composition at the start of eutectic by Thermo-Calc's Seil solidification simulator]
Swedish Thermo-Calc software AB (Japan agency: Itochu Techno Solutions Co., Ltd.) integrated thermodynamic calculation system: Thermo-Calc Ver2015a, solid solution general-purpose database: SSOL5 (SGTE * Solution Database, SGTE * Solution Database, Ver. 5.0), the sill solidification calculation is performed on the Si—Sn—Ti—Al quaternary alloy of Example 1 using the Sile model. For the Sile model and Sile solidification calculation, see metal vol. 77, no. 8 (p.898-p.904). In the Shyle model conditions, atomic diffusion in the solid phase is negligible, complete mixing in the liquid phase, the solid-liquid interface is smooth, local equilibrium is established at the solid-liquid interface, the solidification direction is one direction, Assume that solidification begins at the liquidus temperature and that the latent heat of solidification moves quickly.
* SGTE: Scientific Group Thermodata Europe
The liquid phase composition at the start of the eutectic in the alloy composition can be obtained by the sill solidification calculation.

The alloy composition of Example 1 has a structure composed of primary crystal silicide (TiSi ₂ ) and eutectic (TiSi ₂ + Si), and has few Si phases and Al single phases. That is, the precipitated phase becomes a silicide (TiSi ₂ ) phase and a Si phase. Here, since the composition of the solid phase is considered to be constant regardless of the temperature, it is considered that the actual state is well reproduced even if such a Sile model is used. In the alloy composition of Example 1, the liquid phase composition at the start of the eutectic is Si _70.9 Sn _7.4 Ti _19.9 Al _1.8 . In addition, the same result was obtained also in the alloy composition of Example 2 (the liquid phase composition at the start of the eutectic is described in FIG. 12 (Example 1) and FIG. 16 (Example 2)).

[Amorphous formation ability calculation]
The amorphous forming ability is evaluated by a critical cooling rate at which crystals crystallize from the liquid phase. A TTT diagram (constant temperature transformation curve) showing the time required for crystals to grow until the volume fraction becomes X when quenched from a liquid phase region to a temperature T below the liquidus temperature and kept isothermal. The critical cooling rate is calculated from this. Using a thermodynamic calculation software Thermo-Calc Ver 2015a and a thermodynamic database: SSOL5, a required thermodynamic quantity is obtained and a TTT curve is calculated.

  Hereinafter, a method for calculating the TTT curve will be described. For the calculation method of the critical cooling rate, see, for example, Metal Vol. 77 (2007) No. 10 (p. 1148 to p. 1153).

  The following formula (1) of Johnson-Mehl-Avrami's kinetic treatment based on the homogeneous nucleation growth theory (retention time: volume fraction of crystals produced at t: nucleation frequency: I, nucleation growth rate) : U) is derived by Davies and Uhlmann as shown in the following formula (2).

Here, G _m is a driving force for crystallizing a crystal from the liquid phase, G ^* is a free energy for generating a spherical crystal nucleus from the liquid phase, η is a viscosity coefficient, and Nv is the number of atoms per unit volume. Represents.

G ^* can be expressed by the following formula (3) as σ _m (solid-liquid interface energy). G _m can be approximated by the following equation (4). σ _m is empirically expressed as the following equation (5), and is shown to be about 0.41 by Saunders and Miodownik.

  f is the ratio of the sites to which atoms can move at the solid-liquid interface, and is expressed by the following formula (6) according to Uhlmann.

The viscosity coefficient η of the liquid alloy can be approximated by a Doottle equation (the following equation (7)). Here, A, B and C are constants. f _T is the relative free volume in the liquid, and E _H is the vacancy generation energy. According to Ramachandrarao, E _H can be estimated from T _g (glass transition temperature) as shown in the following formula (8). Here, assuming that T _g = 0.6 _Tm , f _T = 0.03, η = 10 ¹² Pa · S, and B = 1, the constants A and C of the following formula (7) were calculated.

For the alloy composition of Example 1 (mother alloy having the same composition as the Si-containing alloy), after obtaining the eutectic initiation composition in the above-described sill solidification simulation, the glass transition temperature, the liquidus temperature, and the melting enthalpy are obtained. A TTT curve (FIG. 20) was calculated from the above equation (2), and a critical cooling rate R _c was calculated from the following equation (9). A TTT diagram relating to the composition of the alloy of Example 1 (the master alloy having the same composition as the Si-containing alloy) is shown in FIG. 12 (Example 1). A TTT diagram relating to the alloy composition of Example 2 obtained in the same manner as Example 1 is shown in FIG. The TTT diagram relating to the alloy composition of Comparative Example 1 is omitted.

From the above, in the alloy composition of Example 1 (mother alloy having the same composition as the Si-containing alloy), the critical cooling rate is calculated to be 2.0 × 10 ⁷ K / sec. In the alloy of Example 2 (mother alloy having the same composition as the Si-containing alloy), the critical cooling rate was calculated to be 1.9 × 10 ⁷ K / sec, and the alloy of Comparative Example 1 (the Si-containing alloy and In the mother alloy having the same composition), the critical cooling rate is calculated to be 4.3 × 10 ⁷ K / sec.

  Subsequently, the negative electrode active material layer 13 includes a binder.

(Binder)
The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector. There is no restriction | limiting in particular also about the kind of binder used for a negative electrode active material layer, What was mentioned above as a binder used for a positive electrode active material layer can be used similarly. Therefore, detailed description is omitted here.

  Note that the amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to It is 20 mass%, More preferably, it is 1-15 mass%.

(Requirements common to the positive and negative electrode active material layers 15 and 13)
The requirements common to the positive and negative electrode active material layers 15 and 13 will be described below.

  The positive electrode active material layer 15 and the negative electrode active material layer 13 include a conductive additive, an electrolyte salt (lithium salt), an ion conductive polymer, and the like as necessary. In particular, the negative electrode active material layer 13 essentially includes a conductive additive.

(Conductive aid)
The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  The content of the conductive additive mixed into the active material layer is in the range of 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more with respect to the total amount of the active material layer. In addition, the content of the conductive additive mixed in the active material layer is 15% by mass or less, more preferably 10% by mass or less, and further preferably 7% by mass or less with respect to the total amount of the active material layer. is there. By defining the compounding ratio (content) of the conductive aid in the active material layer within the above range, the electronic conductivity of the active material itself is low and the electrode resistance can be reduced by the amount of the conductive aid. The That is, it is possible to sufficiently ensure the electronic conductivity without hindering the electrode reaction, to suppress the decrease in the energy density due to the decrease in the electrode density, and to improve the energy density due to the increase in the electrode density. .

  Moreover, the conductive binder having the functions of the conductive assistant and the binder may be used in place of the conductive assistant and the binder, or may be used in combination with one or both of the conductive assistant and the binder. . As the conductive binder, commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used.

(Electrolyte salt (lithium salt))
Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

(Ion conductive polymer)
Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about the nonaqueous electrolyte secondary battery.

  There is no particular limitation on the thickness of each active material layer (active material layer on one side of the current collector), and conventionally known knowledge about the battery can be referred to as appropriate. For example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm in consideration of the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity.

<Current collector>
The current collectors 11 and 12 are made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

  There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

  The shape of the current collector is not particularly limited. In the laminated battery 10 shown in FIG. 1, in addition to the current collector foil, a mesh shape (such as an expanded grid) can be used.

  In the case where the negative electrode active material is formed directly on the negative electrode current collector 12 by sputtering or the like, it is desirable to use a current collector foil.

  There is no particular limitation on the material constituting the current collector. For example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material can be employed.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material by sputtering to the current collector.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin.

  The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to contain an alloy or metal oxide containing. Moreover, there is no restriction | limiting in particular as electroconductive carbon. Preferably, it includes at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

  The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

<Electrolyte layer>
A liquid electrolyte or a polymer electrolyte can be used as the electrolyte constituting the electrolyte layer 17.

  The liquid electrolyte has a form in which a lithium salt (electrolyte salt) is dissolved in an organic solvent. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), Examples include carbonates such as methylpropyl carbonate (MPC).

As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 SO 3 , etc. A compound that can be added to the active material layer of the electrode can be employed.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the liquid electrolyte (electrolytic solution) is injected into a matrix polymer made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block ion conduction between the layers.

  Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  The ratio of the liquid electrolyte (electrolytic solution) in the gel electrolyte is not particularly limited, but is preferably about several mass% to 98 mass% from the viewpoint of ionic conductivity. In the present embodiment, the gel electrolyte having a large amount of electrolytic solution having a ratio of the electrolytic solution of 70% by mass or more is particularly effective.

  In the case where the electrolyte layer is composed of a liquid electrolyte, a gel electrolyte, or an intrinsic polymer electrolyte, a separator may be used for the electrolyte layer. Specific examples of the separator (including non-woven fabric) include a microporous film made of polyolefin such as polyethylene and polypropylene, a porous flat plate, and a non-woven fabric.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

<Current collector plate and lead>
A current collecting plate may be used for the purpose of taking out the current outside the battery. The current collector plate is electrically connected to the current collector and the lead, and is taken out of the laminate sheet that is a battery exterior material.

  The material which comprises a current collector plate is not specifically limited, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and aluminum is more preferable from the viewpoint of light weight, corrosion resistance, and high conductivity. Copper or the like is preferable. Note that the same material may be used for the positive electrode current collector plate and the negative electrode current collector plate, or different materials may be used.

  The positive terminal lead and the negative terminal lead are also used as necessary. As the material of the positive terminal lead and the negative terminal lead, a terminal lead used in a known lithium ion secondary battery can be used. It should be noted that the part taken out from the battery outer packaging material 29 has a heat insulating property so as not to affect the product (for example, automobile parts, particularly electronic devices) by contacting with peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

<Battery exterior material>
As the battery exterior material 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV.

  In addition, said lithium ion secondary battery can be manufactured with a conventionally well-known manufacturing method.

<Appearance structure of lithium ion secondary battery>
FIG. 2 is a perspective view showing the appearance of a stacked flat lithium ion secondary battery.

  As shown in FIG. 2, the stacked flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive current collector 59 for taking out power from both sides thereof, a negative current collector, and the like. The electric plate 58 is pulled out. The power generation element 57 is wrapped by the battery outer packaging material 52 of the lithium ion secondary battery 50 and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode current collector plate 59 and the negative electrode current collector plate 58 to the outside. Sealed. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery (stacked battery) 10 shown in FIG. The power generation element 57 is formed by laminating a plurality of single battery layers (single cells) 19 including a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

  The lithium ion secondary battery is not limited to a laminated flat shape (laminate cell). In a wound type lithium ion battery, a cylindrical shape (coin cell), a prismatic shape (square cell), or such a cylindrical shape deformed into a rectangular flat shape Further, it may be a cylindrical cell, and is not particularly limited. The cylindrical or prismatic shape is not particularly limited, for example, a laminate film or a conventional cylindrical can (metal can) may be used as the exterior material. Preferably, the power generation element is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  Further, the removal of the positive electrode current collector plate 59 and the negative electrode current collector plate 58 shown in FIG. 2 is not particularly limited. The positive electrode current collector plate 59 and the negative electrode current collector plate 58 may be drawn out from the same side, or the positive electrode current collector plate 59 and the negative electrode current collector plate 58 may be divided into a plurality of parts and taken out from each side. It is not limited to the one shown in FIG. Further, in a wound type lithium ion battery, instead of the current collector plate, for example, a terminal may be formed using a cylindrical can (metal can).

  As described above, the negative electrode and the lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of the present embodiment are an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, a fuel cell vehicle, and a hybrid. It can be suitably used as a large-capacity power source for fuel cell vehicles. That is, it can be suitably used for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density.

  In the above embodiment, the lithium ion battery is exemplified as the electric device. However, the present invention is not limited to this, and can be applied to other types of secondary batteries and further to primary batteries. Moreover, it can be applied not only to batteries but also to capacitors.

  The invention is explained in more detail using the following examples. However, the technical scope of the present invention is not limited only to the following examples.

(Example 1)
[Production of Si-containing alloy (alloy active material)]
The alloy type was Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 (Si ₆₅ % by mass—Sn _4.8 % by mass—Ti ₂₉ % by mass—Al _1.2 % by mass), which was prepared by a liquid rapid solidification method. This will be described in detail below. Specifically, a high purity metal Si ingot (5N), a high purity Sn plate (3N), a high purity Ti wire (3N), a high purity Al shot (3N) are used, and an Si alloy ( Ingot alloy of Si 65% by mass, Sn 4.8% by mass, Ti 29% by mass, Al 1.2% by mass) was produced. The ingot alloy was pulverized and roughly crushed to a diameter of about 2 mm so that it could be easily put into a quartz nozzle. This was used as a mother alloy of a liquid rapid solidification method (quenching roll solidification method).

Subsequently, using the coarsely pulverized ingot alloy powder as a mother alloy, a ribbon-like alloy = quenched ribbon (ribbon) alloy was produced as a Si-containing alloy by a liquid rapid solidification method. Specifically, using a liquid rapid solidification apparatus NEV-A05 type manufactured by Nisshin Giken Co., Ltd., Si ₆₅ Sn was placed in a quartz nozzle installed in a chamber reduced to a gauge pressure of −0.03 MPa after Ar substitution. A mother alloy of _4.8 Ti ₂₉ Al _1.2 was put and melted by high frequency induction heating. Thereafter, it was sprayed onto a Cu roll having a rotational speed of 4000 rpm (peripheral speed: 41.9 m / sec) at an injection pressure of 0.03 MPa to produce a ribbon-like alloy. The cooling rate of the alloy in the liquid rapid solidification method was 4.6 × 10 ⁶ ° C./second. The critical cooling rate of the mother alloy composition was 2.0 × 10 ⁷ K / sec. The thickness of the obtained ribbon-like alloy (quenched ribbon alloy) was 18 μm.

  Thereafter, the obtained ribbon-like alloy (quenched ribbon alloy) was pulverized. Specifically, the ribbon-like alloy (quenched ribbon alloy) was crushed and roughly crushed to a diameter of about 2 mm so that it could be easily put into a ball mill apparatus. Next, using a planetary ball mill device P-6 manufactured by Fricht, Germany, zirconia pulverized balls and coarsely pulverized ribbon-like alloy (quenched ribbon alloy) powder were charged into a zirconia pulverization pot and pulverized at 400 rpm for 1 hour. The process was implemented and the Si containing alloy (negative electrode active material) of the same alloy composition as an alloy seed | species was obtained. The average particle diameter D50 of the obtained Si-containing alloy (negative electrode active material) powder was 7.2 μm, and D90 was 18 μm.

[Production of negative electrode]
80 parts by mass of the Si-containing alloy (Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 ) produced above as a negative electrode active material, 5 parts by mass of acetylene black as a conductive additive, and 15 parts by mass of polyamideimide as a binder Were mixed and dispersed in N-methylpyrrolidone to obtain a negative electrode slurry. Next, the obtained negative electrode slurry was uniformly applied to both surfaces of a negative electrode current collector made of copper foil so that the thickness of the negative electrode active material layer was 30 μm, and dried in a vacuum for 24 hours. Obtained.

[Production of lithium ion secondary battery (coin cell)]
The negative electrode produced above and the counter electrode Li were opposed to each other, and a separator (polyolefin, film thickness 20 μm) was disposed therebetween. Next, a laminate of a negative electrode, a separator, and a counter electrode Li was disposed on the bottom side of a coin cell (CR2032, material: stainless steel (SUS316)). Furthermore, in order to maintain insulation between the positive electrode and the negative electrode, a gasket is attached, the following electrolyte is injected with a syringe, a spring and a spacer are stacked, the upper side of the coin cell is overlapped, and sealed by caulking. Thus, a lithium ion secondary battery (coin cell) was obtained.

In addition, as the electrolytic solution, six lithium carbonate (supporting salt) is added to an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC: DEC = 1: 2 (volume ratio). A solution obtained by dissolving lithium fluorophosphate (LiPF ₆ ) so as to have a concentration of 1 mol / L was used.

(Example 2)
The alloy type was changed to Si ₆₁ Sn _7.2 Ti ₃₀ Al _1.8 (Si ₆₁ % by mass—Sn _7.2 % by mass—Ti ₃₀ % by mass—Al _1.8 % by mass), and the injection pressure in the liquid rapid solidification method was changed to 0. A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 1 except that the pressure was 05 MPa. The cooling rate of the alloy in the liquid rapid solidification method was 4.0 × 10 ⁶ ° C./second. The critical cooling rate of the mother alloy composition was 1.9 × 10 ⁷ K / sec. The thickness of the obtained ribbon-like alloy (quenched ribbon alloy) was 20 μm. The obtained Si-containing alloy (negative electrode active material) powder had an average particle diameter D50 of 6.8 μm and D90 of 20 μm.

(Comparative Example 1)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 1 except that the alloy type was changed to Si ₆₀ Sn ₁₀ Ti ₃₀ . The cooling rate of the alloy in the liquid rapid solidification method was 4.6 × 10 ⁶ ° C./second. The critical cooling rate of the mother alloy composition was 4.3 × 10 ⁷ K / sec. The thickness of the obtained ribbon-like alloy (quenched ribbon alloy) was 18 μm. Moreover, it was the average particle diameter D50 = 6.5micrometer (D90 = 17micrometer) of the obtained Si containing alloy (negative electrode active material) powder.

[Analysis of the structure of the anode active material]
The structure (fine structure) of the negative electrode active material (Si-containing alloy) produced in Example 1 was analyzed. The details are as described above with reference to FIGS. 6 to 9. From the microstructure of the alloy of Example 1, the first phase mainly composed of a silicide of Ti element (silicide) as a transition metal is used. (Silicide phase), a second phase (a-Si phase) mainly containing amorphous Si or low crystalline Si, and a third phase mainly containing Sn (silicide phase) Sn phase). Furthermore, from the microstructure of the alloy of Example 1, some of the independent first phases and some of the first and second phases are eutectic structures. It was confirmed that the third phase was more finely dispersed in the crystal structure than the first phase and the second phase. The third phase (Sn phase) in this eutectic structure is finely dispersed in the grain boundary portion (co-external portion) between the first phase and the second phase, particularly around the second phase. It was confirmed that crystallization occurred. From the microstructure of the alloy of Example 1, the domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase is smaller than the domain size of the second phase. It was confirmed that it was small. Further, it was confirmed that the Si phase (second phase) in the eutectic structure was an amorphous phase having amorphous or low crystalline Si (a-Si). That is, it has been confirmed that the Si phase (second phase) in the eutectic structure has amorphous or low crystalline Si (a-Si) by making it amorphous.

  In Example 2, the same results as in FIGS. 6 to 9 were obtained. Moreover, about the comparative example 1, as shown to Fig.4 (a), the result different from FIG.4 (b) and FIGS. 6-9 is obtained. 13 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure (eutectic structure portion) of the alloy of Example 2. FIG. FIG. 13A shows HAADF-STEM in Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging the eutectic portion of the microstructure of the alloy of Example 2. It is drawing showing Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 13B is a diagram showing mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13C is a diagram showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13D is a diagram showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13E is a drawing (upper right) in which mapping data of Sn, Si, Ti measured in the same field of view as HAADF-STEM (upper left FIG. 13A) is superimposed. 14 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure (eutectic structure portion) of the alloy of Example 2. FIG. FIG. 14A shows HAADF-STEM in Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging the eutectic portion of the microstructure of the alloy of Example 2. It is drawing showing Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 14B is a diagram showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14C is a diagram showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14D is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14E is a drawing (upper right) in which mapping data of Al, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 14A) is superimposed. FIG. 17 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure (eutectic structure portion) of the alloy of Comparative Example 1. FIG. 17 (a) shows HAADF-STEM Image (high angle scattering dark field−) of Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (high magnification) obtained by enlarging the microstructure of the alloy of Example 2. It is drawing which shows a scanning transmission electron microscope image. FIG. 17B is a diagram showing mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 17A). FIG. 17C is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 17A). FIG. 17D is a diagram showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 17A). FIG. 17E is a drawing (upper right) in which mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 17A).

  That is, from the microstructure of the alloy of Example 2, a first phase (silicide phase) mainly composed of a silicide of Ti element (silicide) as a transition metal and a part of Al (and Sn) are included. And having a second phase (a-Si phase) mainly containing amorphous or low crystalline Si and a third phase (Sn phase) mainly containing Sn. (See FIGS. 13 and 14), Cs-STEM (spherical aberration corrected scanning transmission electron microscope image) (low magnification) and (medium magnification) are the same microstructure as in FIGS. 6 and 7 of Example 1. Because of this, the drawing was omitted). Furthermore, from the microstructure of the alloy of Example 2, some of the independent first phases and some of the first and second phases are eutectic structures. It was confirmed that the third phase was more finely dispersed in the crystal structure than the first phase and the second phase (see FIGS. 13 and 14). The third phase (Sn phase) in this eutectic structure is finely dispersed in the grain boundary portion (co-external portion) between the first phase and the second phase, particularly around the second phase. It was confirmed that crystallization occurred (see FIGS. 13 and 14). From the microstructure of the alloy of Example 2, the domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase is smaller than the domain size of the second phase. It was confirmed that it was small. Further, it was confirmed that the Si phase (second phase) in the eutectic structure was an amorphous phase having amorphous or low crystalline Si (a-Si). That is, it has been confirmed that the Si phase (second phase) in the eutectic structure has amorphous or low crystalline Si (a-Si) by making it amorphous (FIG. 13, (See FIG. 14). On the other hand, in the SiSnTi ternary alloy used in Comparative Example 1, as shown in FIG. 4A and FIG. 17, the microstructure 31 ′ has a silicide phase 32 ′ that is a Si phase 35 ′ and a Sn phase 36 ′. Since it does not have an enveloping (microstructure) structure, it can be said that the effect of suppressing the expansion of the Si active material by encapsulating (in a two-stage manner) cannot be sufficiently exhibited.

Furthermore, the domain size of the independent first phase (TiSi ₂ phase) and the first phase in the eutectic structure in the microstructure of the Si-containing alloy of the negative electrode active material produced in Examples 1-2 and Comparative Example 1 The domain sizes of the second phase and the third phase are as described above. Specifically, for the alloy compositions of Examples 1 and 2 and Comparative Example 1, the domain size of the independent first phase and the first phase in the eutectic structure (TiSi ₂ phase) determined by the measurement method described above. The results of the domain sizes of the second phase (Si phase) and the third phase (Sn phase) are shown in Table 1 below.

[Evaluation of amorphous forming ability (critical cooling rate)]
In the negative electrode active material (Si-containing alloy) produced in Example 1, the critical cooling rate in the liquid phase composition at the start of the eutectic of the mother alloy composition is as described above with reference to FIG. It was described in the sentence. In the negative electrode active material (Si-containing alloy) produced in Example 2, the critical cooling rate in the liquid phase composition at the start of eutectic of the mother alloy composition was calculated. The results are shown in FIG. 16 and described in the text of Example 2. In the negative electrode active material (Si-containing alloy) produced in Comparative Example 1, the critical cooling rate in the liquid phase composition at the start of eutectic of the mother alloy composition was calculated. This result is described in the sentence of Comparative Example 1.

[Evaluation of cycle durability]
Each lithium ion secondary battery (coin cell) produced in each of Examples 1 and 2 and Comparative Example 1 was subjected to cycle durability evaluation according to the following charge / discharge test conditions.

(Charge / discharge test conditions)
1) Charge / discharge tester: HJ0501SM8A (Hokuto Denko Co., Ltd.)
2) Charging / discharging conditions [charging process] 0.3C, 2V → 10mV (constant current / constant voltage mode)
[Discharge process] 0.3C, 10mV → 2V (constant current mode)
3) Thermostatic bath: PFU-3K (Espec Corp.)
4) Evaluation temperature: 300K (27 ° C.).

  The evaluation cell is in a constant current / constant voltage mode in the charging process (referring to the Li insertion process to the evaluation electrode) in a thermostat set to the above evaluation temperature using a charge / discharge tester. The battery was charged from 2 V to 10 mV at 0.3 C. Thereafter, in the discharge process (referring to the Li desorption process from the electrode for evaluation), a constant current mode was set and discharge was performed from 0.3 C, 10 mV to 2 V. The charge / discharge test was conducted from the initial cycle (1 cycle) to 50 cycles under the same charge / discharge conditions with the above charge / discharge cycle as one cycle. And the result of having calculated | required the ratio (discharge capacity maintenance factor [%]) of the 50th cycle discharge capacity with respect to the discharge capacity (initial discharge capacity) of the 1st cycle is shown in following Table 2 and FIG. Here, FIG. 19 is a drawing showing the relationship between the number of charge / discharge cycles and the discharge capacity retention rate [%] for each lithium ion secondary battery (coin cell) produced in Examples 1 and 2 and Comparative Example 1. is there.

  From the results shown in Table 1, the lithium ion batteries using the negative electrode active materials of Examples 1 and 2 are maintained at a high discharge capacity retention rate after 50 cycles, and are excellent in cycle durability. I understand that. Further, in Examples 1 and 2 using the Si alloy negative electrode, the capacity is higher than that of the negative electrode active material using the carbon material (this point is not limited to showing a comparative example using the carbon material. Since it is publicly known (see Background Art), the comparative example is omitted). Thus, high cycle durability was able to be realized while showing a high capacity because the Si-containing alloy constituting the negative electrode active material is a quaternary system represented by Si-Sn-M (transition metal element) -Al. By having an alloy composition. Further, the microstructure includes a first phase mainly composed of silicide, a second phase partially including Al and mainly composed of amorphous or low crystalline Si, and Sn as a main component. And a third phase. And in such a microstructure, a part is a plurality of independent first phases, and a part is a eutectic structure of the first phase and the second phase. This is because the third phase is more finely dispersed than the first phase and the second phase.

  On the other hand, it can be seen that the lithium ion battery using the negative electrode active material of Comparative Example 1 does not have sufficient cycle durability. This is because, in the negative electrode active material of Comparative Example 1, since there was no addition of Al as in the Examples, an independent first phase was formed as shown in Table 1, but the second phase in the eutectic structure And the first phase are about the same size. For this reason, the expansion of the second phase (Si phase) in the eutectic structure during the charge / discharge process cannot be sufficiently suppressed by the eutectic first phase, and so to suppress it by suppressing the two-stage structure. It seems that it is not possible. In addition, since there is no Al addition, the second phase in the eutectic structure is not made finer than the first phase, and the third phase is finely dispersed at the grain boundaries of the first and second phases. However, a relatively large phase is localized and formed without being dispersed. Therefore, since the second phase cannot be sufficiently clathrated with the first phase, when charged / discharged, the second phase cannot sufficiently suppress expansion and contraction due to the first phase, and conductivity is insufficient. The second phase (Si) cannot react uniformly and seems to have deteriorated durability. Further, since the relatively large phase of the third phase does not disperse and is localized around the second phase (Si), the second phase is difficult to become amorphous. It seems that the cycle durability was not sufficiently obtained due to the difference from the microstructure.

Moreover, when compared with Example 1 and 2, it is thought that it is based on the following reasons that Example 2 is more excellent in cycle durability. This is because the domain size of the independent first phase is larger in Example 2. As a result, the expansion of the second phase in the eutectic structure in the charge / discharge process, in particular, the Si active material as the main component, is suppressed by enveloping the eutectic first phase. This is probably because the effect of suppressing by suppressing the two-stage structure, in which one phase is suppressed by enveloping the eutectic structure (especially the second phase), is obtained more remarkably. This suppresses the amorphous-crystal phase transition (crystallization to Li ₁₅ Si ₄ ) when Si and Li are alloyed during charging. As a result, the expansion and contraction of the Si-containing alloy in the charge / discharge process is reduced (and the first phase (silicide phase) composed of the conductive silicide and the second phase (a-Si phase) are eutectic. The second phase (a-Si phase), in particular, the main component Si active material can be uniformly reacted. As a result, it is considered that the cycle durability is further improved while showing the high capacity of the electric device in which the negative electrode active material is used.

10, 50 Lithium ion secondary battery (stacked battery),
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 electrolyte layer,
19 cell layer,
21, 57 power generation element,
25, 58 negative electrode current collector plate,
27, 59 positive current collector,
29, 52 Battery exterior material (laminate film),
31 The microstructure of the SiSnTiAl quaternary alloy (Si-containing alloy) of the present embodiment,
Microstructure of 31 ′ SiSnTi ternary alloy (Si-containing alloy),
32 a plurality of independent first phases (silicide phases),
32 'silicide phase,
33 eutectic structure,
34 The first phase (silicide phase) in the eutectic structure,
35 the second phase (a-Si phase) in the eutectic structure,
35 'Si phase,
36 a third phase (Sn phase) finely dispersed in the eutectic structure than the first phase and the second phase;
36 'Sn phase.

Claims (12)

A negative electrode active material for an electrical device made of a Si-containing alloy,
The microstructure of the Si-containing alloy includes a first phase mainly composed of a transition metal silicide (silicide), a part containing Al, and a first phase mainly composed of amorphous or low crystalline Si. Having a second phase and a third phase based on Sn;
Furthermore, a part is a plurality of independent first phases, and part is a eutectic structure of the first phase and the second phase,
A negative electrode active material for an electrical device, wherein the third phase is finely dispersed in the eutectic structure as compared with the first phase and the second phase.   The domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase is smaller than the domain size of the second phase. The negative electrode active material for electrical devices as described. The silicide as a main component of the first phase in the microstructure is TiSi ₂ , and the second phase is a Si phase containing Sn. Negative electrode active material for electrical devices.   The domain size of the first phase in the eutectic structure in the microstructure is 20 to 70 nm, the domain size of the second phase in the eutectic structure is 5 to 30 nm, and the domain size of the third phase is The negative electrode active material for an electric device according to any one of claims 1 to 3, wherein the negative electrode active material is in a range of 3 to 10 nm. The Si-containing alloy is a Si-Sn-Ti-Al alloy,
The following chemical formula (1):
(In the above chemical formula (1),
A is an inevitable impurity,
x, y, z, w and a represent mass% values, where x, y, z and w are 58 ≦ x ≦ 68, 2 ≦ y ≦ 10, 25 ≦ z ≦ 35, 0, respectively. 3 ≦ w ≦ 3, a is the remainder, and x + y + z + w + a = 100. )
5. The negative electrode active material for an electric device according to claim 1, wherein the negative electrode active material has a composition represented by:   The x, y, z, and w are 59 ≦ x ≦ 66, 3 ≦ y ≦ 8.5, 28 ≦ z ≦ 31, and 0.4 ≦ w ≦ 2.5, respectively. 5. The negative electrode active material for electrical devices according to 5.   7. The negative electrode active material for an electric device according to claim 1, wherein the domain size of the independent first phase in the microstructure is in a range of 200 to 600 nm. It is a manufacturing method of the negative electrode active material for electric devices of any one of Claims 1-7,
A method for producing a negative electrode active material for an electrical device, comprising: producing a quenched ribbon of a Si-containing alloy by a liquid rapid solidification method using a mother alloy having the same composition as the Si-containing alloy.   The method for producing a negative electrode active material for an electric device according to claim 8, comprising subjecting the quenched ribbon to mechanical alloying. 10. The method for producing a negative electrode active material for an electric device according to claim 8, wherein a critical cooling rate in the liquid rapid solidification method is 2.2 × 10 ⁷ K / sec or less.   A negative electrode for electric devices, comprising the negative electrode active material for electric devices according to any one of claims 1 to 7.   An electric device comprising the negative electrode for an electric device according to claim 11.