JP2013235685A - Negative electrode material for lithium ion secondary batteries, negative electrode for lithium ion secondary batteries arranged by use thereof, and lithium ion secondary battery arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for lithium ion secondary batteries which achieves a high capacity and good cycle characteristic.SOLUTION: The negative electrode material for lithium ion secondary batteries comprises: active material particle containing at least one element A selected from a group consisting of Si, Sn, Al, Pb, Sb, Bi, Ge, In, and Zn. The active material particle is covered with a binding agent layer. When the volume of the active material particle before charging is denoted by V, and the volume after the charging is denoted by V, and the reversible shrinkage degree of the binding agent is denoted by ε[%], the following relational expression holds: ε≥((V/V)-1)×100.

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery, and more particularly to a negative electrode material for a high capacity and long life lithium ion secondary battery.

  Conventionally, lithium ion secondary batteries using graphite as a negative electrode active material have been put into practical use. Also, a negative electrode is formed by kneading a negative electrode active material, a conductive aid such as carbon black, and a resin binder to prepare a slurry, and applying and drying on a copper foil. Yes.

  On the other hand, with the aim of increasing the capacity, negative electrodes for lithium ion secondary batteries using metals such as silicon (Si) and tin (Sn), which have large theoretical capacities as lithium compounds, and alloys thereof as negative electrode active materials have been developed. However, such a negative electrode active material expands in volume by occlusion of lithium ions during charging. For example, when silicon is used as the negative electrode active material, the volume of silicon that has occluded lithium ions expands to about four times that of the silicon before occlusion, so a negative electrode that uses a silicon-based alloy as a negative electrode active material is Repeat expansion and contraction during the discharge cycle. For this reason, the negative electrode active material is peeled off and dropped off, and there is a problem that the life is extremely short as compared with the conventional graphite electrode.

  Therefore, for the purpose of constraining volume changes due to insertion and extraction of lithium ions, including, for example, Si phase grains and at least a part of the Si-containing solid solution or intermetallic compound that at least partially surrounds the Si phase grains. A negative electrode material for non-aqueous electrolyte secondary batteries made of alloy particles is disclosed (Patent Document 1).

  However, even in the invention described in Patent Document 1, it is insufficient to suppress the volume expansion of silicon, and deterioration of cycle characteristics cannot be sufficiently prevented.

  In addition, as a binder having high strength and excellent cycle characteristics used together with a negative electrode active material such as silicon, a binder such as polyimide is used, and is slurried with an organic solvent together with the negative electrode active material, applied onto a copper foil, dried, and then the negative electrode is formed. Although a negative electrode is manufactured by forming, a sufficient cycle characteristic is not obtained even in this method.

  Such a negative electrode material 7 has a large capacity drop in the initial tens of cycles. As a result of examining this cause, a so-called solute type binder 9 that forms a slurry applied to a current collector together with an active material in a state of being dissolved in a solvent such as polyimide is coated with a slurry applied to the current collector. By drying, the active material particles 3 are solidified in a state of being coated (FIG. 9A). However, when the active material particles 3 are largely expanded during charging, the coated binder layer follows and expands. The binder layer remains broken even when the active material particles 3 contract by volume due to the discharge (FIG. 9B). It was inferred that the active material particles 3 were easily pulverized at the time of filling, and that the active material particles 3 were peeled off and dropped off, which was the cause of capacity reduction.

Japanese Patent No. 3562398

  The present invention has been made in view of the above-described problems, and an object of the present invention is to obtain a negative electrode material for a lithium ion secondary battery that realizes high capacity and good cycle characteristics.

  As a result of intensive studies to achieve the above object, the present inventors have used lithium-occluded lithium in the negative electrode by using a resin having a specific reversible expansion / contraction rate as a binder for the negative electrode of the lithium ion secondary battery. Thus, the present inventors have found that the binder can expand and follow the volume change of the negative electrode active material particles accompanying the release, and realize high capacity and good cycle characteristics, leading to the present invention.

That is, the present invention
(1) having active material particles containing at least one element A selected from the group consisting of Si, Sn, Al, Pb, Sb, Bi, Ge, In, and Zn, at least on the surface of the active material particles A portion is covered with a binder layer, the volume of the active material particles before charging is V ₀ , the volume of the active material particles after charging is V, and the reversible stretching rate of the binder is A negative electrode material for a lithium ion secondary battery, wherein ε [%] satisfies the relational expression ε ≧ ((V / V ₀ ) ^1/3 −1) × 100.
(2) The binder layer is polyimide, polyamideimide, polybenzimidazole, polyamide, polyacryl, polyurethane, polyester, polyesterimide, epoxy, phenol resin, and precursors, modified bodies, neutralized bodies, salts, The negative electrode material for a lithium ion secondary battery according to (1), comprising any one or more of a mixture.
(3) The negative electrode material for a lithium ion secondary battery according to (1) or (2), wherein the binder layer covers 50% or more of the surface of the active material particles.
(4) The negative electrode material for a lithium ion secondary battery according to any one of (1) to (3), wherein the binder layer has a thickness of 2 nm to 1500 nm.
(5) The active material particles are particles including the element A and the element M, and the element M includes Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, and Y. , Zr, Nb, Mo, Tc, Ru, Rh, Ba, a lanthanoid element (excluding Pm), Hf, Ta, W, Re, Os, and at least one element selected from the group consisting of Ir, The particle has at least a first phase that is a single element or a solid solution of the element A and a second phase that is a single element or a compound of the element M, and the particle includes the first phase and the first phase. Both the second phase and the second phase are exposed to the outer surface and bonded via an interface, and the outer surface other than the interface is substantially spherical or polygonal in the first phase. The negative electrode material for a lithium ion secondary battery according to any one of (1) to (4) .
(6) The particles are Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ba, lanthanoid elements (Pm The element M ′ that is at least one element selected from the group consisting of Hf, Ta, W, Re, Os, and Ir, and the element M ′ constitutes the second phase. The lithium ion secondary battery according to (5), wherein the element M is an element of a different type and further has another second phase that is a simple substance or a compound of the element M ′. Negative electrode material.
(7) The particles further include an element A ′ that is at least one element selected from the group consisting of Si, Sn, Al, Pb, Sb, Bi, Ge, In, and Zn, and the element A ′ The lithium ion according to (5) or (6), which is a different element from the element A and further has a third phase that is a single element or a solid solution of the element A ′. Negative electrode material for secondary batteries.
(8) The lithium ion secondary battery according to (7), wherein the third phase is bonded to at least one of the first phase and the second phase via an interface. Negative electrode material.
(9) The negative electrode material for a lithium ion secondary battery according to any one of (1) to (8), wherein the active material particles have an average particle diameter of 2 nm to 15 μm.
(10) A negative electrode for a lithium ion secondary battery using the negative electrode material according to any one of (1) to (9).
(11) a positive electrode capable of occluding and releasing lithium ions; a negative electrode for a lithium ion secondary battery according to (10); and a separator disposed between the positive electrode and the negative electrode; A lithium ion secondary battery in which the positive electrode, the negative electrode, and the separator are provided in an electrolyte having a property.
It is.

  According to the present invention, a negative electrode material for a lithium ion secondary battery realizing high capacity and good cycle characteristics, a negative electrode for a lithium ion secondary battery using the negative electrode material, and a negative electrode for the lithium ion secondary battery are used. A lithium ion secondary battery can be obtained.

(A)-(c) The conceptual diagram which shows the negative electrode material 1 for lithium ion secondary batteries which concerns on 1st Embodiment. (A)-(c) The schematic sectional drawing of the particle | grains 11 used as an active material particle. (A)-(b) The schematic sectional drawing of the particle | grains 11 used as an active material particle. (A)-(b) The schematic sectional drawing of the particle | grains 17 used as an active material particle. (A)-(c) Schematic explanatory drawing of the particle | grains 21 used as an active material particle. (A)-(b) Schematic explanatory drawing of the particle | grains 21 used as an active material particle. Explanatory drawing which shows the manufacturing apparatus of particle | grains. FIG. 3 is a cross-sectional view showing a configuration of a lithium ion secondary battery 61. (A)-(c) The conceptual diagram which shows the negative electrode material 7 for the conventional lithium ion secondary battery.

Hereinafter, a negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention will be described in detail based on the drawings.
(1. Configuration of negative electrode material 1)
(1-1. First Embodiment)
FIG. 1 is an explanatory diagram showing a negative electrode material 1 according to the first embodiment. FIG. 1A is an explanatory view showing the negative electrode material 1 before charging according to the present invention. The active material particles 3 are primary particles or secondary aggregates in which a plurality of primary particles are aggregated, and the surface thereof is a binder 5. Covered with. The secondary aggregate may be a composite formed by physical adsorption, mechanical alloying or sintering, or may be granulated with a binder. FIG.1 (b) is a figure which shows the negative electrode material 1 at the time of charge, and FIG.1 (c) is a figure which shows the negative electrode material 1 at the time of discharge. Note that the binder 5 does not necessarily cover 100% of the surface of the active material particles 3, and may cover 50% or more of the surface area of the active material particles 3. Note that it is preferable that the binder 5 covers 80% or more of the surface of the active material particles 3. Further, it is more preferable that the binder 5 covers 100% of the surface of the active material particles 3. If the binder 5 covers 50% or more of the surface of the active material particles 3 or most of the surface, the effect of suppressing the pulverization of the active material particles 3 and the active material particles 3 are peeled off from the current collector. The effect which prevents doing is acquired.

  In the negative electrode material 1, the surface of the active material particles 3 is covered with the binder 5, and a binder layer is formed (FIG. 1A). The volume of the active material particles 3 expands due to occlusion of lithium at the time of charging, and at this time, the binder layer is in an extended state following the expansion of the active material particles 3 (FIG. 1B). Thereafter, by discharging, the volume of the active material particles 3 once expanded by contraction contracts, and the binder layer 5 also returns to the original state while being in close contact with the active material particles 3 (FIG. 1C). The binder layer is suitable and exhibits an effect as long as it covers 50% or more of the surface of the active material particles, but more preferably 80% or more, and further 100%, that is, covers the entire surface. Particularly preferred.

  The thickness of the binder layer 5 is preferably 2 nm to 1500 nm in an unstretched state. If the thickness is less than 2 nm, partial coating may occur or the binding force may be insufficient. If the thickness is greater than 1500 nm, the conductivity of the electrode may be reduced.

  The active material particle 3 is made of an active material that can be occluded by alloying lithium, and such an active material is made of Si, Sn, Al, Pb, Sb, Bi, Ge, In, and Zn. It contains at least one element A selected from the above. Particularly preferably, Si is the main component.

  The average particle diameter of the active material particles 3 is not particularly limited, but is preferably 2 nm to 15 μm. The active material particles 3 may be primary particles or secondary aggregates in which a plurality of primary particles are aggregated.

  In the negative electrode production (details of the production method will be described later), the binder 5 is prepared by preparing a mixed slurry together with the active material particles 3 in a state dissolved in a solvent, and applying and drying to a current collector. The agent 5 is solidified in a state of covering the surface of the active material particles 3 to form a binder layer. If the active material particles are nano-sized, the binder 5 has a larger amount of adsorption than the micron-sized (1000 nm or more) particles, so that the blending ratio is preferably increased. The blending ratio of the binder 5 is also affected by the type and amount of the conductive additive, but is 2 to 25% by weight when the active material particles are nano-sized, and 0.1 to 5% by weight when the active material particles are micron-sized. Is preferred.

The binder 5 can be used by being dissolved in water or an organic solvent, and is made of a resin having a characteristic that the reversible stretching ratio ε [%] satisfies the condition of the following formula (1). In the following formula (1), V ₀ represents the volume of the active material particles 3 before charging, and V represents the volume of the active material particles 3 after charging.
ε ≧ ((V / V ₀ ) ^1/3 −1) × 100 (1)
The reversible expansion / contraction ratio ε can be obtained at a thickness of 25 μm and 25 ° C. according to JIS K7163.
The volumes V and V ₀ of the active material particles 3 can be obtained by image analysis such as an electron microscope.
If the active material particles 3 to be used are tested by the following method, the volume before charging and the volume after charging are measured, and the reversible expansion / contraction ratio ε is calculated by the equation (1), the active material particles to be used 3 can be selected.

<Test method>
The volume of the active material particles before charging can be calculated from the average particle diameter. The volume of the active material expanded by the full charge can be obtained by image analysis such as an electron microscope after disassembling and cleaning the electrode while maintaining an inert atmosphere.

  For example, if the active material particles 3 are made of silicon (Si) and the volume after charging is four times the volume before charging, the binder 5 is about 60% or more reversible from the above formula (1). The negative electrode material 1 of the present invention can be obtained by using a resin having a general expansion / contraction ratio.

The above equation (1) can be considered as follows. Assuming that the active material particle 3 is a sphere, when the volume of the active material particle expands from V ₀ to V, the radius of the sphere becomes (V / V ₀ ) ^1/3 times. That is, the active material particle 3 has a radius that is larger by ((V / V ₀ ) ^1/3 −1) × 100)% of the radius before the expansion due to volume expansion. The same can be said about the length of). Therefore, the binder satisfying the relational expression (1) and having a reversible expansion / contraction ratio ε [%] equal to or greater than the elongation (expansion) of the active material particles 3 sufficiently follows the expansion of the active material particles. It can be stretched and does not cause a decrease in capacity due to breakage of the binder layer.

  The material of the binder 5 is soluble in water or an organic solvent, and a mixed slurry of the active material particles 3 and the binder 5 is applied to a current collector and dried to bind to the surface of the active material particles 3. What forms the coating layer by the agent 5 can be used. Polyimide, polyamideimide, polybenzimidazole, polyamide, polyacryl, polyurethane, polyester, polyesterimide, epoxy, phenol resin, and modified products and neutralized products thereof Resins that can be used in a varnish shape, such as salts and mixtures, can be used. In particular, polyimide, polyamideimide, polybenzimidazole, and polyamide can be suitably used. Moreover, it replaces with a polyimide and the said mixed slurry may be prepared using polyimide precursors, such as a polyamic acid, and you may make it polyimide in a negative electrode manufacturing process. The binder 5 may be used alone or in combination of two or more.

(1-2. Effects in the first embodiment)
As described above, the negative electrode material 1 according to the present invention uses the active material particles 3 having a capacity per unit volume higher than that of carbon, and is capable of following the expansion of the active material particles 3 due to charging. Since the binder layer made of the binder having the active material particles covers the active material particles, the binder layer does not break due to the expansion of the active material particles, and the active material particles are not pulverized. Therefore, the capacity is higher than that of the conventional lithium ion secondary battery and the battery has good cycle characteristics.

(1-3. Second Embodiment)
Next, a second embodiment of the active material according to the present invention will be described. In the second embodiment, the active material particles 3 in the first embodiment described above are composed of particles containing an element A and an element M described later.

  FIG. 2 is a schematic sectional view showing the particles 11 constituting the active material particles of the present invention. The particle 11 includes an element A and an element M.

  As in the first embodiment, the element A is one element selected from the group consisting of Si, Sn, Al, Pb, Sb, Bi, Ge, In, and Zn. The element A is an element that easily stores lithium.

  The element M is Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ba, and a lanthanoid element (excluding Pm). ), At least one element selected from the group consisting of Hf, Ta, W, Re, Os, and Ir, wherein the active material particles are a single phase or a solid solution of the element A; A second phase that is a simple substance or a compound of the element M is formed.

The particle 11 has at least a first phase 13 and a second phase 15.
The first phase 13 may be a single element A or a solid solution containing the element A as a main component. Further, the first phase 13 may be crystalline or amorphous. The element that forms a solid solution with the element A can be selected from elements other than those listed in the group of the element A. The first phase 13 can occlude lithium. The first phase 13 becomes amorphous when occluded by lithium and alloyed and then desorbed and dealloyed.

Further, the second phase 15 may be a single element M or a compound containing the element M as a main component. The second phase 15 has a small capacity and a small volume change even when lithium is occluded. For example, Co has a discharge capacity of 58 mAh / g as CoSi ₂ , Fe has a discharge capacity of 60 mAh / g as FeSi ₂ , Ni has a discharge capacity of 198 mAh / g as NiSi ₂ , etc., but has a discharge capacity as compared with element A such as Si and Sn. The volume change is negligible because it is small. The fact that the silicon compound reacts with lithium means that lithium can pass through the silicon compound, and contributes to an improvement in the utilization rate of the silicon phase.

If possible combinations form an element A and element M compound, the second phase 15 may be formed from MA _Y like a compound of element A and element M. On the other hand, if the element A and the element M are a combination that does not form a compound, the second phase 15 may be a single element or a solid solution of the element M.

For example, when the element A is Si and the element M is Cu, the second phase 15 can be formed of copper silicide that is a compound of the element M and the element A.
For example, when the element A is Si and the element M is Ag or Au, the second phase 15 can be formed of a single element of the element M or a solid solution containing the element M as a main component.
Further, when the element A is Si and the element A ′ is Sn or Al, the second phase 15 can be formed of a single element or a solid solution of the element A ′.

When element A is Si, Si and element M can form a compound represented by MA _Y (0.1 <Y ≦ 3). Specific examples of such compounds include FeSi ₂ , CoSi ₂ , NiSi ₂ (Y = 2), Rh ₃ Si ₄ (Y = 1.33), and Ru ₂ Si ₃ (Y = 1.5). ), Sr ₃ Si ₅ (Y = 1.67), Mn ₄ Si ₇ , Tc ₄ Si ₇ (Y = 1.75), IrSi ₃ (Y = 3), Cu ₃ Si (Y = 0.33), etc. Can be illustrated. Here, the atomic ratio of the element M in the total of Si and the element M is preferably 0.01 to 27%. When the atomic ratio is 0.01 to 25%, both cycle characteristics and high capacity can be achieved when the particles 11 are used as the negative electrode active material. On the other hand, if it is less than 0.01%, the volume change of the particles 11 during occlusion of lithium cannot be suppressed, and if it exceeds 27%, the merit of high capacity is particularly lost.

  For example, as shown in FIG. 2, both the first phase 13 and the second phase 15 of the particle 11 are exposed on the outer surface of the particle 11 and are bonded to each other through the interface. The interface between the first phase 13 and the second phase 15 is a flat surface or a curved surface. Further, the interface may be stepped. The first phase 13 has a substantially spherical outer surface. The interface shape of the joint portion between the first phase 13 and the second phase 15 is circular or elliptical. By the presence of the second phase 15 that does not easily store lithium on the first phase 13 that expands due to lithium storage, expansion of the first phase 13 due to lithium storage can be suppressed.

  Note that the outer surface of the first phase 13 has a substantially spherical shape means that the surface of the first phase 13 other than the interface where the first phase 13 and the second phase 15 are in contact is generally a smooth curved surface. In other words, it means that the first phase 13 has a spherical shape or an elliptical spherical shape except for the point where the first phase 13 and the second phase 15 are in contact with each other. The expression “sphere” or “elliptical sphere” does not mean a geometrically exact sphere or ellipsoid. The shape is different from the shape having a corner on the surface, as represented by the shape of particles formed by the crushing method.

  In addition, the second phase 15 that is a single element or a compound of the element M may be dispersed in the first phase 13 as in the particle 11 illustrated in FIG. The second phase 15 is covered with the first phase 13. Like the second phase 15 exposed on the outer surface, the second phase 15 hardly absorbs lithium. Further, as shown in FIG. 2C, a part of the second phase 15 covered with the first phase 13 may be exposed on the surface. That is, the entire periphery of the second phase 15 is not necessarily covered with the first phase 13, and only a part of the periphery of the second phase 15 may be covered with the first phase 13.

  In FIG. 2B, the plurality of second phases 15 are dispersed in the first phase 13, but a single second phase 15 may be included.

  As in the second phase 15 ′ shown in FIG. 3A, it may have a polyhedral shape due to the influence of the stability of the element M simple substance or compound crystal.

  Further, a plurality of second phases 15 may be provided on the first phase 13 like the particles 11 shown in FIG. For example, in the particle manufacturing process, the ratio of the element M is small, the collision frequency between the elements M in the gas state or the liquid state is low, the relationship between the melting points of the first phase 13 and the second phase 15 and wetting. It is conceivable that the second phase 15 is dispersed and joined to the surface of the first phase 13 due to the property, the influence of the cooling rate and the like.

  When the plurality of second phases 15 are provided on the first phase 13, the area of the interface between the first phase 13 and the second phase 15 is widened to further suppress the expansion and contraction of the first phase 13. Can do. Further, since the second phase 15 has higher conductivity than the first phase 13, the movement of electrons is promoted by the second phase 15, and the particle 11 has a plurality of current collecting spots in each particle 11. It will be. Therefore, the particles 11 having a plurality of the second phases 15 become a negative electrode material having a high powder conductivity, the conductive auxiliary agent can be reduced, and a high capacity negative electrode can be formed. Furthermore, a negative electrode having excellent high rate characteristics can be obtained.

When two or more elements selected from the group that can select the element M are included as the element M, the second phase 15 that is a compound of one element M and the element A includes another element. M may be contained as a solid solution or a compound. That is, even when two or more elements selected from the group from which the element M can be selected are included in the particles, there may be cases where the other second phase 19 is not formed like the element M ′ described later. is there. For example, when the element A is Si, one element M is Ni, and the other element M is Fe, Fe may exist in NiSi ₂ as a solid solution. In addition, when observed by EDS, the distribution of Ni and the distribution of Fe may be approximately the same or different, and another element M may be uniformly contained in the second phase 15. For example, it may be partially contained.

  The particles may contain an element M ′ in addition to the element M. Element M ′ is Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ba, lanthanoid elements (except Pm) , Hf, Ta, W, Re, Os, Ir, and at least one element selected from the group consisting of elements different from the element M constituting the second phase.

  The particle 17 shown in FIG. 4A includes the element M and the element M ′, and has another second phase 19 in addition to the second phase 15 which is a simple substance or a compound of the element M. For example, there is a second phase 15 at one end of the first phase 13, another second phase 19 at the other end, and the particle 17 has a shape in which two small spheres are joined to the surface of a large sphere. Can have. The other second phase 19 is a simple substance or a compound of the element M ′ and, like the second phase 15, hardly absorbs lithium. Further, the particle 17 may include a solid solution (not shown) composed of the element M and the element M ′. For example, the second phase 15 is a compound of Si and Fe, the other second phase 19 is a compound of Si and Co, and the solid solution composed of the elements M and M ′ is a solid solution of Fe and Co. Etc.

  Further, as shown in FIG. 4B, the second phase 15 that is a simple substance or a compound of the element M and the other second phase 19 that is a simple substance or a compound of the element M ′ are included in the first phase 13. It may be dispersed in the inside. FIGS. 4A and 4B show an example in which two types of elements are selected from the group of elements from which the element M and the element M ′ can be selected, but even if three or more types of elements are selected. Good.

  Even when two or more kinds of elements are selected from the group of the element M and the element M ′ as described above, the group of the element M and the element M ′ with respect to the total of the elements of the group of the element A, the element M, and the element M ′. The total atomic ratio of these elements is preferably 0.01 to 30%.

  In the present invention, it is preferable that the first phase 13 is mainly crystalline silicon and the second phase 15 is crystalline silicide. The first phase 13 is more preferably Si to which phosphorus or boron is added. The conductivity of silicon can be increased by adding phosphorus or boron. Indium and gallium can be used instead of phosphorus, and arsenic can be used instead of boron. By increasing the conductivity of the silicon of the first phase 13, the negative electrode using such particles has a low internal resistance, allows a large current to flow, and has a good high rate characteristic.

  Further, in the present invention, the average particle diameter of the particles 11 and 17 and 21 described later is preferably 2 nm to 15 μm, more preferably 30 to 1500 nm, and further preferably 50 to 500 nm. Since the yield stress increases when the particle size is small according to the Hall Petch's law, if the average particle size of the primary particles is 2 to 1500 nm, the particle size is sufficiently small, the yield stress is sufficiently large, and it becomes difficult to pulverize by charge / discharge. If the average particle size is smaller than 2 nm, it is difficult to handle the particles after synthesis. If the average particle size is larger than 1500 nm, the particle size becomes large and the yield stress is not sufficient. The active material particles 3 are composed of primary particles or secondary aggregates of the particles 11, the particles 17, and the particles 21. The primary particles are preferably 30-1500 nm, more preferably 50-500 nm.

  Since the fine particles are usually present in an aggregated state, the average particle size of the particles herein refers to the average particle size of the primary particles. For particle measurement, image information of an electron microscope (SEM) and a volume-based median diameter of a dynamic light scattering photometer (DLS) are used in combination. For the average particle size, confirm the particle shape in advance using an SEM image, obtain the particle size by image analysis (for example, “A Image-kun” (registered trademark) manufactured by Asahi Kasei Engineering), or disperse the particles in a solvent to obtain DLS (for example, , OLSKA Electronics DLS-8000). If the fine particles are sufficiently dispersed and not agglomerated, almost the same measurement results can be obtained with SEM and DLS. In addition, even when the shape of the particle is a highly developed structure such as acetylene black, the average particle size is defined by the primary particle size here, and the average particle size can be obtained by image analysis of the SEM photograph. it can.

  Note that oxygen may be bonded to the outermost surface of the particle 11 or 17. This is because when particles are taken out into the air, oxygen in the air reacts with elements on the surface of the particles. That is, the outermost surface of the particle 11 or 17 may have an amorphous layer having a thickness of about 0.5 to 15 nm, and in particular, when the first phase is mainly crystalline silicon, it has an oxide film layer. You may do it.

(1-4. Effects in the Second Embodiment)
When the first phase 13 occludes lithium, the volume expands. However, since the second phase 15 hardly occludes lithium, the expansion of the first phase 13 in contact with the second phase 15 is suppressed. That is, even if the first phase 13 occludes lithium and attempts to expand the volume, the second phase 15 hardly expands. Therefore, the second phase 15 exhibits an effect like a wedge or a pin, and the particle 11 Or the expansion of the whole 17 is suppressed. Therefore, compared with particles that do not have the second phase 15, the particles 11 or 17 that have the second phase 15 are less likely to expand when occludes lithium, and a restoring force works during the release of lithium, and the original shape. It becomes easy to return to. Therefore, according to the present invention, even if the particles 11 or 17 occlude lithium, strain associated with volume expansion is relieved, and a binder having a low reversible expansion / contraction rate can be used. It becomes easy to follow the binder layer, and a decrease in discharge capacity during cycle characteristics is suppressed.

  Furthermore, since the particles 11 or 17 are difficult to expand, even if the particles are put out into the atmosphere, they hardly react with oxygen in the atmosphere. On the other hand, if the particles having only one phase are left in the atmosphere without surface protection, the particles react with oxygen from the surface, and oxidation proceeds from the surface to the inside of the particles, so that the whole particles are oxidized. However, when the particles 11 or 17 are left in the atmosphere, the outermost surface of the particles reacts with oxygen, but the particles are difficult to expand as a whole, so that the oxygen does not easily enter the interior, and oxidation reaches the center of the particles. Hateful. Therefore, normal metal nanoparticles have a large specific surface area and are likely to oxidize and generate heat and volume expansion. However, the particles 11 or 17 do not need to be specially coated with an organic substance or metal oxide, and are not used in the atmosphere. Can be handled as powder.

  Further, according to the second embodiment, the second phase 15 includes the element M, and thus has high conductivity, and has the first phase 13 including the low conductivity element A as the main phase. The conductivity of the particles 11 or 17 as a whole increases dramatically. In other words, the particle 11 or 17 is equivalent to a structure having a current collecting spot for each particle, and becomes a negative electrode material having conductivity even with a small amount of conductive auxiliary agent, and forms a high-capacity electrode. In addition, a negative electrode active material having excellent high rate characteristics can be obtained. In particular, by using a highly conductive metal element such as Fe or Cu for the second phase 15, a negative electrode active material with better conductivity can be obtained as compared to the case of using only silicon nanoparticles.

  Further, the particle 11 including the second phase 15 in the first phase 13 and the particle 17 including the second phase 15 and the other second phase 19 in the first phase 13 are the first A larger part of the phase 13 comes into contact with a phase in which lithium is not occluded, and the expansion of the first phase 13 is more effectively suppressed. As a result, the particle 17 can exhibit the effect of suppressing volume expansion with a small amount of the element M, and can effectively increase the amount of the element A such as Si that can occlude lithium. Cycle characteristics are improved.

The particles 17 having both the second phase 15 exposed on the outer surface and the other second phase 19 have the same effect as described above, and the current collection spot for each particle is increased, and the current collection performance is effective. Improve. When two or more elements M and elements of the group of element M ′ are added, two or more kinds of compounds are formed, and these compounds are easily separated from each other.
Since it has the 2nd phase 15 containing the element M in addition to the 1st phase 13 which occludes lithium, the catalytic action of this 2nd phase 15 has an unsaturated bond in a molecule | numerator in electrolyte solution, and reduction polymerization In the case where an organic material that can be used is included, a stable organic film can be effectively formed on the surface of the negative electrode active material layer, decomposition of the electrolyte material can be prevented, and cycle characteristics can be improved.

(1-5. Third embodiment)
Next, a third embodiment of the active material according to the present invention will be described. In the following embodiment, the same number is attached | subjected to the element which fulfill | performs the same aspect as 2nd Embodiment, and the duplicate description is avoided.

  FIG. 5 is a schematic cross-sectional view of the particles 21 constituting the active material particles of the present invention. As shown in FIG. 5A, the particle 21 has a third phase 23 in addition to the first phase 13 and the second phase 15 which are the same as described above. The third phase 23 includes an element A ′ that is at least one element selected from the group consisting of Si, Sn, Al, Pb, Sb, Bi, Ge, In, and Zn, and is different from the element A Elements. These elements A ′ are elements that easily store lithium. The third phase 23 may be a single element of element A ′ or a solid solution containing element A ′ as a main component. The element that forms a solid solution with the element A ′ may be an element selected from the group capable of selecting the element A ′, or may be an element not listed in the group. The third phase 23 can occlude lithium.

The first phase 13, the second phase 15, and the third phase 23 are all exposed on the outer surface, and the outer surfaces of the first phase 13, the second phase 15, and the third phase 23 are substantially spherical. It may be a shape. The second phase 15 is bonded to the first phase 13, and the third phase 23 is bonded to at least one of the first phase 13 and the second phase 15 through an interface. For example, the first phase 13 has a second phase 15 at one end and a third phase 23 at the other end, and the particle 21 has a shape in which two small spheres are joined to the surface of a large sphere. be able to. The interface between the third phase 23 and the first phase 13 is a flat surface or a curved surface. On the other hand, as shown to Fig.6 (a), the 2nd phase 15 and the 3rd phase 23 may be joined via the interface.
For such particles 21, in consideration of lithium storage characteristics, conductivity, etc. as the negative electrode active material, for example, the first phase 13 is Si, the second phase 15 is a compound of Si and Fe, and the third For example, the phase 23 is Sn.

  Further, like the particle 21 shown in FIG. 5B, the second phase 15 that is a simple substance or a compound of the element M, or the third phase 23 that is a simple substance or a solid solution of the element A ′ is the first phase. 13 may be dispersed. Further, a phase (not shown) which is a compound of the element A ′ and the element M may be dispersed. Although these phases 15 and 23 are covered with the 1st phase 13, as shown in Drawing 5 (c), some phases 15 and 23 may be exposed to the surface. That is, it is not always necessary to cover all of the periphery of the phases 15 and 23 dispersed in the first phase 13 with the first phase 13, and only a part of the periphery is covered with the first phase 13. Also good. Note that a plurality of phases may be dispersed in the first phase 13, for example, any of the second phase 15, the third phase 23, and a phase that is a compound of the element A ′ and the element M. May be dispersed.

  Further, the shape of the surface other than the interface of the third phase 23 may be a spherical surface whose surface is generally smooth like the third phase 23 shown in FIG. 5A, or FIG. 6B. As shown in the third phase 23 ′ shown in FIG. The polyhedron shape is formed by peeling after the particles 11, 17, or 21 are bonded via the third phase 23.

Moreover, the 1st phase 13 and the 3rd phase 23 can suppress the site | part which reacts with lithium by containing oxygen. When oxygen is included, the capacity decreases, but volume expansion accompanying lithium occlusion can be suppressed. Amount of oxygen z is, for example _AO z, when a A'O _z, 0 <z <1 is preferably in the range. When z is 1 or more, the Li storage sites of the element A and the element A ′ are suppressed, and the capacity is greatly reduced.

  When the particles include the element A, the element A ′, the element M, and the element M ′, the atomic ratio of the element M and the element M ′ in the total is about 0.01 to 27% for the same reason as above. It is preferable to do. When the atomic ratio is 0.01 to 27%, when the particles 21 are used as the negative electrode active material, both cycle characteristics and high capacity can be achieved.

  In addition, various other aspects can be considered for the configuration of the particles 21 according to the present invention. For example, a plurality of third phases 23 can be provided on the surface of the first phase 13. For example, the particle 21 can further contain two or more kinds of elements A ′. For example, the second element A ′ is one element selected from the group of the elements A ′ and is a different kind of element from the first element A ′. For example, silicon can be used as the element A, and tin or aluminum can be used as the element A ′. The element A ′ may form another third phase as a simple substance or a solid solution, or may form a compound with the element M, the element M ′, and the like. The other third phase, like the third phase 23, has a spherical outer surface and can be exposed on the outer surface of the particles 21. Further, a phase that is a compound of the element A ′ and the element M may be dispersed in the first phase 13 or the third phase 23. Further, the particles 21 may contain an element M ′ in addition to the element M.

  Thus, the particles 21 include compounds and solid solution phases of various compositions from various combinations of elements A, A ′, elements M, and elements M ′. be able to. Such a phase may be exposed on the surface of the particle 21 or may be dispersed in the first phase 13 or in any other phase.

  Note that oxygen may be bonded to the outermost surface of the particle 21. This is because when the particles 21 are taken out into the air, oxygen in the air reacts with elements on the surface of the particles 21. That is, the outermost surface of the particle 21 may have an amorphous layer having a thickness of about 0.5 to 15 nm, and in particular, when the first phase is mainly crystalline silicon, it has an oxide film layer. May be.

(1-6. Effects in the third embodiment)
According to the third embodiment, the same effect as that obtained in the second embodiment can be obtained. However, according to the third embodiment, volume expansion occurs when the first phase 13 occludes lithium, and expansion also occurs when the third phase 23 occludes lithium. However, since the electrochemical potential for storing lithium differs between the first phase 13 and the third phase 23, when one phase preferentially occludes lithium and one phase expands in volume, The volume expansion of one phase is relatively reduced, and the other phase makes it difficult for one phase to be volume expanded. Therefore, compared with the particles without the third phase 23, the particles 21 having the first phase 13 and the third phase 23 are less likely to expand when occludes lithium. Therefore, according to the third embodiment, even if the particles 21 occlude lithium, the volume expansion is suppressed, and a decrease in discharge capacity during cycle characteristics is suppressed.

(1-7. Other aspects)
Moreover, what coat | covered at least one part of the surface of said particle | grains 11, 17, 21 with copper, tin, zinc, silver, nickel, or carbon can also be considered, for example. The thickness of the coating is exemplified as being in the range of 0.01 to 0.5 μm. For example, in such a configuration, in the particle 17 shown in FIG. 5, Cu is selected as the element M ′, and another second phase 19, which is a single element M ′, is formed on the surface of the first phase 13. It can also be understood that the first phase 13 and the second phase 15 are not bonded (not shown).

  Thus, by covering the surface of the particles with a material having good conductivity, the conductivity of the entire negative electrode is improved and the cycle characteristics are also improved without using a conductive aid or the like. Further, since the surface of the negative electrode active material is coated, oxidation of silicon or the like can be suppressed. By covering the surface, resistance to volume changes due to charge / discharge is improved.

  Furthermore, although the particles 11, 17, and 21 have been shown as examples having a curved surface, the active material particles 3 may be primary particles or secondary aggregates. Further, the active material particles 3 may be primary particles of polygonal particles such as pulverized particles, or secondary aggregates. The secondary aggregate may be an aggregate of a plurality of particles by adsorption, or may be an aggregate formed by sintering, mechanical alloying, a binder, spray drying, or the like.

(1-8. Method for producing particles)
Here, the manufacturing method of particle | grains is demonstrated.
Particles having a relatively small particle size can be synthesized by a gas phase synthesis method. In particular, particles can be produced by converting the raw material powder into plasma and heating it to a temperature equivalent to 10,000 K, followed by cooling.

  A specific example of a manufacturing apparatus used for manufacturing particles will be described with reference to FIG. In the particle manufacturing apparatus 37 shown in FIG. 7, a high frequency coil 46 for generating plasma is wound around the upper outer wall of the reaction chamber 39. An AC voltage of several MHz is applied to the high frequency coil 46 from a high frequency power source 47. A preferred frequency is 4 MHz. The upper outer wall around which the high-frequency coil 46 is wound is a cylindrical double tube made of quartz glass or the like, and cooling water is passed through the gap to prevent the quartz glass from melting by plasma.

  In addition, a sheath gas supply port 43 is provided in the upper part of the reaction chamber 39 together with the raw material powder supply port 41. The raw material powder 42 supplied from the raw material powder feeder is supplied into the plasma 49 through the raw material powder supply port 41 together with the carrier gas 45 (rare gas such as helium and argon). The sheath gas 44 is supplied to the reaction chamber 39 through the sheath gas supply port 43. Note that the raw material powder supply port 41 is not necessarily installed above the plasma 49 as shown in FIG. 7, and a nozzle can be installed in the lateral direction of the plasma 49. The raw material powder supply port 41 may be water-cooled with cooling water. In addition, the property of the raw material of the particle | grains supplied to plasma is not restricted only to powder, You may supply the raw material powder slurry and gaseous raw material.

  The reaction chamber 39 plays a role of maintaining the pressure in the plasma reaction part and suppressing the dispersion of the produced fine powder. The reaction chamber 39 is also water-cooled to prevent damage due to plasma. A suction tube is connected to the side of the reaction chamber 39, and a filter 51 for collecting the synthesized fine powder is installed in the middle of the suction tube. The suction pipe connecting the reaction chamber 39 and the filter 51 is also water-cooled with cooling water. The pressure in the reaction chamber 39 is adjusted by the suction capability of a vacuum pump (not shown) installed on the downstream side of the filter 51.

  The method for producing particles is a bottom-up method in which the particles are solidified via plasma and gas and liquid, and the particles are deposited. Therefore, the particles are formed into a spherical shape at the stage of droplets, and the first phase 13 and the second phase 15 are It becomes a spherical shape. On the other hand, in a top-down method for reducing large particles, such as the crushing method and the mechanochemical method, the shape of the particles is rugged and is significantly different from the spherical shape of the particles 11.

  In addition, when the mixed powder of each powder of the element A and the element M is used for raw material powder, the particle | grains 11 in 2nd Embodiment are obtained. On the other hand, when a mixed powder of each of the elements A, M, and M ′ is used as the raw material powder, the particles 17 in the second embodiment are obtained. Further, when a mixed powder of each of the elements A, M (or element M and element M ′) and the element A ′ is used as the raw material powder, the particles 21 in the third embodiment are obtained.

  Further, the method for particle surface coating is not particularly limited, and various known methods can be employed. Electroless plating or displacement plating is used for coating the metal, and the surface oxidation of particles such as silicon is small, and electroplating is possible if the particles are conductive. For coating the carbon, a method of heat treatment in an inert or reducing atmosphere after mixing an inorganic carbon source such as carbon black or an organic carbon source such as polyvinyl alcohol can be used. In addition, a thermal decomposition CVD method in which the surface of particles is coated with carbon by heating the hydrocarbon gas to 600 ° C. or higher to be thermally decomposed can also be used.

(2. Production of negative electrode for lithium ion secondary battery)
Next, the manufacturing method of the negative electrode for lithium ion batteries is demonstrated. The negative electrode of the present invention can be formed by applying a coating liquid containing at least a negative electrode active material, a conductive additive and a binder to a current collector and drying it. The coating liquid can be prepared, for example, by charging a slurry raw material into a mixer and kneading to form a slurry (coating liquid). The slurry raw materials are negative electrode active material particles, conductive assistants, binders, thickeners, solvents, and the like.

  When the active material contains Si or Sn, a high-capacity negative electrode can be formed. However, since the volume change of the active material is large, the binder can flexibly follow the volume change of the active material with a charge / discharge cycle. When the binder is used, the electrode can be prevented from collapsing and cycle characteristics are improved. Furthermore, since an increase in the interface between the active material and the electrolytic solution and a new surface of the active material can be suppressed, a continuous side reaction of the electrolytic solution can be suppressed and efficiency is improved. As a result, cycle characteristics are improved and consumption of the electrolyte can be suppressed.

  In the solid content in the slurry, for example, the blending of 25 to 90% by weight of the active material particles, 5 to 70% by weight of the conductive additive, 1 to 30% by weight of the binder, and 0 to 25% by weight of the thickener is a guide be able to.

  As the mixer, a general kneader used for preparing a slurry can be used, and a device called a kneader, a stirrer, a disperser, a mixer, or the like that can prepare a slurry may be used. Moreover, as a thickener, it is suitable to use polysaccharides, such as carboxymethylcellulose and methylcellulose, as a 1 type, or 2 or more types of mixture. Moreover, water or an organic solvent can be used as a solvent. When preparing an organic slurry, N-methyl-2-pyrrolidone (NMP) can be used as a solvent. The solvent is appropriately selected according to the type of binder used.

  The conductive assistant is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel, silver and the like. A single powder of carbon, copper, tin, zinc, nickel, or silver may be used, or a powder of each alloy may be used. For example, general carbon black such as furnace black and acetylene black can be used. In addition, carbon nanohorns can be added as conductive aids. In particular, when the element A of the particle is silicon having low conductivity, silicon is exposed on the surface of the particle, and the conductivity becomes low. Therefore, it is preferable to add carbon nanohorn as a conductive additive. Here, the carbon nanohorn (CNH) has a structure in which a graphene sheet is rounded into a conical shape, and the actual form is an aggregate in the form of a radial sea urchin with many CNHs facing the apex to the outside. Exists as. The outer diameter of the CNH sea urchin-like aggregate is about 50 nm to 250 nm. In particular, CNH having an average particle size of about 80 nm to 150 nm is preferable. Any one of these materials may be used, or two or more of these materials may be used in combination.

  The average particle size of the conductive assistant also refers to the average particle size of the primary particles. Even when the structure shape is highly developed such as acetylene black, the average particle diameter can be defined by the primary particle diameter here, and the average particle diameter can be obtained by image analysis of the SEM photograph.

  Moreover, you may use both a particulate-form conductive support agent and a wire-shaped conductive support agent. The wire-shaped conductive aid is a wire made of a conductive material, and the conductive materials listed in the particulate conductive aid can be used. As the wire-shaped conductive assistant, a linear body having an outer diameter of 300 nm or less, such as carbon fiber, carbon nanotube, copper nanowire, or nickel nanowire, can be used. By using a wire-shaped conductive aid, electrical connection with the negative electrode active material or current collector is easily maintained, and the current collection performance is improved. Cracks are less likely to occur. For example, it is conceivable to use copper powder as the particulate conductive auxiliary agent and to use vapor grown carbon fiber (VGCF) as the wire-shaped conductive auxiliary agent. In addition, you may use only a wire-shaped conductive support agent, without adding a particulate-form conductive support agent.

  The length of the wire-shaped conductive assistant is preferably 0.1 μm to 2 mm. The outer diameter of the conductive additive is preferably 2 nm to 500 nm, more preferably 10 nm to 200 nm. If the length of the conductive auxiliary agent is 0.1 μm or more, the length is sufficient to increase the productivity of the conductive auxiliary agent, and if the length is 2 mm or less, application of the slurry is easy. Further, when the outer diameter of the conductive auxiliary agent is larger than 2 nm, the synthesis is easy, and when the outer diameter is smaller than 500 nm, the slurry is easily kneaded. The measuring method of the outer diameter and length of the conductive material was performed by image analysis using SEM.

  Next, the slurry is applied to one surface of the current collector using, for example, a coater. As the coater, a general coating apparatus capable of applying the slurry to the current collector can be used. For example, a coater using a roll coater or a doctor blade, a comma coater, or a die coater.

  The current collector is a foil made of at least one metal selected from the group consisting of copper, nickel, and stainless steel. Each metal may be used independently and may be used as each alloy. The thickness is preferably 4 μm to 35 μm, and more preferably 8 μm to 18 μm.

  Then, in order to dry at about 50-150 degreeC and adjust thickness, the negative electrode for lithium ion secondary batteries can be obtained through a roll press. When polyimide or polyamideimide is used as the binder, it is further fired in the range of 150 ° C to 450 ° C. Firing conditions such as the firing temperature and firing time depend on the type and boiling point of the solvent in addition to the molecular weight and chemical structure of the polymer constituting the binder, and are therefore preferably selected appropriately depending on the type of binder. .

(3. Production of positive electrode for lithium ion secondary battery)
As the positive electrode, various positive electrodes capable of inserting and extracting lithium ions can be used. This positive electrode for a lithium ion battery is prepared by mixing a positive electrode active material, a conductive additive, a binder and a solvent to prepare a positive electrode active material composition, which is directly applied onto a metal current collector such as an aluminum foil. -It can be manufactured by drying.

Any positive electrode active material can be used as long as it is generally used. For example, LiCoO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , compounds such as LiFePO ₄ are exemplified.

  For example, carbon black is used as the conductive assistant, polyvinylidene fluoride (PVdF), a water-soluble acrylic binder is used as the binder, and N-methyl-2-pyrrolidone (NMP) is used as the solvent. Water, etc. can be used. At this time, the contents of the positive electrode active material, the conductive additive, the binder, and the solvent are at levels normally used in non-aqueous electrolyte secondary batteries and the like.

(4. Separator)
Any separator can be used as long as it has a function of insulating electronic conduction between the positive electrode and the negative electrode and is usually used in a non-aqueous electrolyte secondary battery. For example, a microporous polyolefin film, a porous aramid resin film, a porous ceramic, a nonwoven fabric, etc. can be used.

(5. Electrolyte / Electrolyte)
As the electrolytic solution and the electrolyte, a non-aqueous organic electrolytic solution having lithium ion conductivity used for a lithium ion secondary battery, a Li polymer battery, or the like can be used.

  Specific examples of the organic electrolyte solvent include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di Ethers such as butyl ether and diethylene glycol dimethyl ether; aprotic such as benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethylchlorobenzene, nitrobenzene Solvent, or two or more of these solvents Mixed solvent of thereof.

The electrolyte of the organic electrolyte includes LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAlO ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) A mixture of one or more electrolytes made of a lithium salt such as ₂ can be used.

  The electrolyte can contain an organic substance having an unsaturated bond in the molecule and capable of reductive polymerization. By adding such an organic substance to the electrolyte, an effective solid electrolyte interface film can be formed on the surface of the negative electrode active material, and decomposition of the electrolyte material can be suppressed. Examples of the substance having an unsaturated bond in the molecule and capable of undergoing reductive polymerization at the time of charging include, for example, carbonates such as fluoroethylene carbonate, vinylene carbonate (VC), vinyl ethylene carbonate, and derivatives thereof, and unsaturated carboxylic acid esters. , Phosphoric acid esters, boric acid esters, alcohols and the like can be used. Among them, it is shown as a preferable example that vinylene carbonate (VC) is used.

  In order to obtain a stable solid electrolyte interface film, such an organic substance is preferably added in an amount of about 0.1 wt% to 10 wt% of the electrolyte weight. Furthermore, it is more preferable to add about 1 to 5% by weight. When the addition amount is in the range of 0.1% by weight to 10% by weight, it can be reduced during charging to form a stable film on the surface of the negative electrode active material layer, and the decomposition of the electrolyte material can be prevented. . When the addition amount is less than 0.1% by weight, it is difficult to sufficiently form a stable film on the surface of the negative electrode active material, and when the addition amount exceeds 10% by weight, it is reduced. Since the amount increases, the formed solid electrolyte interface film becomes thick, and the impedance of the battery increases, which is not preferable.

(6. Assembly of lithium ion secondary battery)
In the lithium ion secondary battery of the present invention, a separator is disposed between the positive electrode and the negative electrode as described above to form a battery structure. After winding or stacking such battery structures into a cylindrical or rectangular battery case, an electrolyte is injected to complete a lithium ion secondary battery.

  Specifically, as shown in FIG. 8, in the lithium ion secondary battery 61 of the present invention, the positive electrode 63 and the negative electrode 65 are stacked and arranged in the order of separator-positive electrode-separator-negative electrode via the separator 67, The electrode plate group is formed by winding so that the positive electrode 63 is on the inner side, and this is inserted into the battery can 69. The positive electrode 63 is connected to the positive electrode terminal 73 via the positive electrode lead 71, and the negative electrode 65 is connected to the battery can 69 via the negative electrode lead 75, and chemical energy generated inside the lithium ion secondary battery 61 is externally output as electric energy. It can be taken out. Next, after filling the battery can 69 with the nonaqueous electrolyte solution 68 so as to cover the electrode plate group, the upper end (opening portion) of the battery can 69 is composed of a circular lid plate and the positive electrode terminal 73 on the upper portion thereof. The lithium ion secondary battery 61 of the present invention can be manufactured by attaching the sealing body 77 having a built-in safety valve mechanism thereto via an annular insulating gasket.

(7. Effect of lithium ion secondary battery according to the present invention)
The lithium ion secondary battery according to the present invention uses a negative electrode active material having a unit volume and a capacity per unit weight higher than that of carbon, and extends following the expansion of the active material due to charging, and follows the active material during discharge. In addition, since the shrinkable binder layer covers the active material particles, the negative electrode active material is not easily pulverized, has a larger capacity than a conventional lithium ion secondary battery using carbon as an active material, and has good cycle characteristics. Furthermore, since an increase in the interface between the active material and the electrolytic solution and a new surface of the active material can be suppressed, a continuous side reaction of the electrolytic solution can be suppressed and efficiency is improved. As a result, high capacity and cycle characteristics are improved, and consumption of the electrolyte can be suppressed.

DESCRIPTION OF SYMBOLS 1 ......... Negative electrode material 3 ......... Active material particle 5 ......... Binder 7 ......... Negative electrode material 9 ......... Binder 11 ......... Particle 13 ......... First phase 15 ......... Second phase 17 .... Particles 19 .... Other second phase 21 ... ... Particles 23 ... ... Third phase 37 ... ... Particle production equipment 39 ... ... Reaction chamber 41 ... ... Raw materials Powder supply port 42 ... Raw material powder 43 ... Sheath gas supply port 44 ... Sheath gas 45 ... Carrier gas 46 ... High frequency coil 47 ... High frequency power supply 49 ... Plasma 51 ... Filter 61 ......... Lithium ion secondary battery 63 ......... Positive electrode 65 ......... Negative electrode 67 ......... Separator 69 ......... Battery can 71 ......... Positive lead 73 ......... Positive terminal 75 ......... Negative lead 77 ... ... Sealing body

Claims (11)

Having active material particles containing at least one element A selected from the group consisting of Si, Sn, Al, Pb, Sb, Bi, Ge, In, Zn,
At least part of the surface of the active material particles is covered with a binder layer;
When the volume of the active material particles before charging is V ₀ , the volume of the active material particles after charging is V, and the reversible expansion / contraction rate of the binder is ε [%],
ε ≧ ((V / V ₀ ) ^1/3 −1) × 100
The negative electrode material for lithium ion secondary batteries characterized by satisfying the following relational expression:   The binder layer is composed of polyimide, polyamideimide, polybenzimidazole, polyamide, polyacryl, polyurethane, polyester, polyesterimide, epoxy, phenol resin, and precursors, modified bodies, neutralized bodies, salts, and mixtures thereof. The negative electrode material for a lithium ion secondary battery according to claim 1, comprising any one or more.   The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the binder layer covers 50% or more of the surface of the active material particles.   The thickness of the said binder layer is 2 nm or more and 1500 nm or less, The negative electrode material for lithium ion secondary batteries of any one of Claims 1-3 characterized by the above-mentioned. The active material particles are composed of particles containing the element A and the element M,
The element M is Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ba, a lanthanoid element (excluding Pm). At least one element selected from the group consisting of Hf, Ta, W, Re, Os, Ir,
The particles have at least a first phase that is a simple substance or a solid solution of the element A and a second phase that is a simple substance or a compound of the element M, and
The particles have both the first phase and the second phase exposed on the outer surface and bonded via an interface;
5. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein an outer surface other than the interface of the first phase is substantially spherical or polygonal. The particles include Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ba, lanthanoid elements (excluding Pm), An element M ′ that is at least one element selected from the group consisting of Hf, Ta, W, Re, Os, and Ir;
The element M ′ is an element different in kind from the element M constituting the second phase,
The negative electrode material for a lithium ion secondary battery according to claim 5, further comprising another second phase that is a single element or a compound of the element M ′. The particles further include an element A ′ that is at least one element selected from the group consisting of Si, Sn, Al, Pb, Sb, Bi, Ge, In, and Zn,
The element A ′ is a different element from the element A,
The negative electrode material for a lithium ion secondary battery according to claim 5, further comprising a third phase that is a single element or a solid solution of the element A ′.   The negative electrode material for a lithium ion secondary battery according to claim 7, wherein the third phase is bonded to at least one of the first phase and the second phase via an interface.   9. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the active material particles have an average particle diameter of 2 nm to 15 μm.   The negative electrode for lithium ion secondary batteries using the negative electrode material of any one of Claims 1-9. A positive electrode capable of inserting and extracting lithium ions;
A negative electrode for a lithium ion secondary battery according to claim 10,
Having a separator disposed between the positive electrode and the negative electrode;
A lithium ion secondary battery, wherein the positive electrode, the negative electrode, and the separator are provided in an electrolyte having lithium ion conductivity.

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