JP5489353B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having good charge / discharge cycle characteristics.

  Non-aqueous electrolyte secondary batteries, including lithium ion secondary batteries, are used as power sources for portable devices such as personal computers and mobile phones, so that they have the characteristics required according to these applied devices. It is configured. In particular, mobile phones, whose market is expected to grow further, are expected to have higher performance, so that higher capacities are required in response to such demands.

Non-aqueous electrolyte secondary batteries currently on the market use LiCoO _{2 as} the positive electrode active material and graphite as the negative electrode active material, except for a part. The battery is designed at a utilization rate very close to 372 mAh / g, and a new negative electrode material in place of graphite is required for higher capacity.

As such negative electrode materials, Sn (tin) alloy, Si (silicon) alloy, Si oxide, Li (lithium) nitride, Li metal, and the like have been studied. For example, ultrafine particles of Si are dispersed in SiO ₂ . SiO _x having a structure has attracted attention (for example, Patent Documents 1 to 4). When this material is used as a negative electrode active material, since Si that reacts with Li is an ultrafine particle, charging and discharging are performed smoothly. On the other hand, the SiO _x particle itself having the above structure has a small surface area, and thus the negative electrode mixture layer The coating property when forming a coating material for forming the electrode and the adhesion of the negative electrode mixture layer to the current collector are also good.

JP 2004-47404 A Japanese Patent Laid-Open No. 2005-259697 JP 2007-242590 A JP 2009-266705 A

However, SiO _x has a very large volume change accompanying charging / discharging of the battery as compared with, for example, graphite. For this reason, in a battery using SiO _x as the negative electrode active material, the strength and electronic conductivity of the negative electrode are usually lowered while repeatedly expanding and contracting due to charge and discharge, and charge / discharge cycle characteristics, that is, capacity retention ratio relative to initial capacity. However, it becomes worse than a battery using graphite as a negative electrode active material.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having good charge / discharge cycle characteristics while including a negative electrode containing a material containing Si and O as constituent elements. Is to provide.

The non-aqueous electrolyte secondary battery of the present invention that has achieved the above object has a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator containing a lithium metal composite oxide as a positive electrode active material, and the negative electrode Is a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5. Hereinafter, the material is referred to as “SiO _x ”), and Graphite conductive assistant containing graphite as a negative electrode active material and having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more, and a graphite conductive agent having a fiber shape with an aspect ratio of 3 or more and an average length of 1 μm or less It has a negative electrode mixture layer containing an auxiliary agent on one side or both sides of a current collector.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery with favorable charging / discharging cycling characteristics can be provided, providing the negative electrode containing the material which contains Si and O in a structural element.

It is a schematic diagram which shows an example of the nonaqueous electrolyte secondary battery of this invention, (a) Top view, (b) Cross-sectional view. FIG. 2 is a perspective view of FIG. 1.

The negative electrode according to the non-aqueous electrolyte secondary battery of the present invention contains SiO _x and graphite as a negative electrode active material, and has a fiber shape having an aspect ratio of 3 or more and a graphite conductive assistant having an average length of 10 μm or more, It has a negative electrode mixture layer containing a fibrous conductive auxiliary agent having an aspect ratio of 3 or more and an average length of 1 μm or less.

For example, SiO _x has poor conductivity as compared with graphite or the like that is widely used as a negative electrode active material for non-aqueous electrolyte secondary batteries. Therefore, in the negative electrode using SiO _x as the negative electrode active material, it is necessary to use a conductive additive in order to increase the conductivity in the negative electrode mixture layer.

However, SiO _x has a larger volume change with charge / discharge of the battery than, for example, graphite. Therefore, for example, at the time of charging, conductivity is impaired in the thickness direction of the negative electrode mixture layer that expands due to the influence of SiO _x , and this contributes to a decrease in charge / discharge cycle characteristics of the battery. In non-aqueous electrolyte secondary batteries, generally, acetylene black, carbon black, ketjen black, etc. are used as conductive assistants for electrodes. When the mixture layer expands in the thickness direction, it is considered that SiO _x and the conductive auxiliary agent are separated from each other, and the conductive auxiliary agent cannot sufficiently contribute to the electron conduction between the SiO _x particles.

Therefore, in the present invention, first, graphite that can enhance the conductivity in the negative electrode mixture layer containing SiO _x having poor conductivity by acting as an active material and also as a conductive auxiliary agent together with SiO _x is used as the negative electrode. Used as an active material, the volume change in the thickness direction of the negative electrode mixture layer accompanying charging / discharging of the battery is suppressed as much as possible. Furthermore, as a conductive auxiliary for the negative electrode, the average is a fiber shape having an aspect ratio of 3 or more. A graphitic conductive assistant having a length of 10 μm or more was used so that the electron conduction between the SiO _x particles was good even when the negative electrode mixture layer expanded due to charging of the battery.

However, in a battery using SiO _x and graphite as the negative electrode active material, since the volume change amount of SiO _x and graphite is different, in the vicinity of SiO _x particles having a large expansion amount due to charging, a negative electrode mixture layer is formed during charging. Distortion occurs and remains unresolved during discharge. Therefore, when the battery is discharged after charging, the SiO _x particles are isolated from the graphite particles and the like in the negative electrode mixture layer, and locally lack of conductivity, which may cause deterioration in charge / discharge cycle characteristics of the battery. It was also found out. This problem cannot be solved only by using a graphite conductive aid having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more.

Therefore, in the present invention, a graphite conductive assistant having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more and a graphite conductive assistant having an aspect ratio of 3 or more and an average length of 1 μm or less are used as the negative electrode. It was decided to be included in the mixture layer. The graphite conductive additive having an aspect ratio of 3 or more and an average length of 1 μm or less has a property of easily adhering to, for example, SiO _x particles in the negative electrode mixture layer and is discharged after charging the battery. Even in this case, the contact between SiO _x and the graphite conductive additive can be kept good. Therefore, it is possible to prevent SiO _{x from} being isolated in the negative electrode mixture layer in a discharged state, and to smoothly charge and discharge SiO _x .

Thus, in the nonaqueous electrolyte secondary battery of the present invention, in addition to using graphite as an active material together with SiO _{x as} a negative electrode active material, the non-aqueous electrolyte secondary battery has a fiber shape with an aspect ratio of 3 or more and an average length of By providing a negative electrode using a different graphite conductive additive, the capacity reduction due to charge / discharge is suppressed to enhance the charge / discharge cycle characteristics, and the load characteristics are also good due to this configuration.

  The aspect ratio of the graphite conductive assistant having an aspect ratio of 3 or more and an average length of 10 μm or more, and the graphite conductive assistant having an aspect ratio of 3 or more and an average length of 1 μm or less. The average length is obtained by actually measuring 100 or more particles by observation with a scanning electron microscope and averaging the values. In addition, about the graphite conductive support agent whose average length is 10 micrometers or more, circularity is measured about 100 or more particles by the particle | grain image analyzer "FPIA-3000" (detection range: about 0.7 micrometer-160 micrometers) made by Hosokawa Micron. Alternatively, the particle size distribution may be measured, and an average value may be calculated from the result.

  Examples of the graphitic conductive aid having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more used for the negative electrode include vapor-grown carbon fiber, graphite carbon fiber, and the like. Can be selected from commercially available products.

  Further, examples of the graphite conductive assistant having a fiber shape with an aspect ratio of 3 or more and an average length of 1 μm or less used for the negative electrode include carbon nanotubes, vapor-grown carbon fibers, and the like. Can be selected from commercially available products.

Then, the negative active material according to the negative electrode, to complex with SiO _x and the carbon material, and graphite used.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is sufficient that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5 in combination with Si. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

Incidentally, SiO _x may be complexed complexed with carbon material, as such complexes, for example, it is preferable that the surface of the SiO _x is coated with a carbon material. As described above, SiO _x has poor conductivity. In the negative electrode according to the present invention, graphite that can also function as a conductive auxiliary is used in combination with SiO _x as a negative electrode active material, so that it is possible to ensure a certain degree of conductivity in the negative electrode, and the above fiber shape in, but also to use the average length of different kinds of graphite conductive agent, as long as complexes complexed with carbon material SiO _x, for example, simply SiO _x and the carbon material (graphite or the graphite conduction A conductive network in the negative electrode is formed better than when a material obtained by mixing a conductive material such as an auxiliary agent is used.

The complex of the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, such as granules of SiO _x and the carbon material can be cited.

In addition, since the composite in which the surface of SiO _x is coated with a carbon material is further combined with a conductive material (carbon material or the like), a better conductive network can be formed in the negative electrode. Thus, it is possible to realize a non-aqueous electrolyte secondary battery with higher capacity and better battery characteristics (for example, charge / discharge cycle characteristics). The complex of the SiO _x and the carbon material coated with a carbon material, for example, like granules the mixture was further granulated with SiO _x and the carbon material coated with a carbon material.

Further, as SiO _x whose surface is coated with a carbon material, the surface of a composite (for example, a granulated body) of SiO _x and a carbon material having a smaller specific resistance value is further coated with a carbon material. Those can also be preferably used. In a non-aqueous electrolyte secondary battery having a negative electrode containing SiO _x as a negative electrode active material, a better conductive network can be formed when SiO _x and a carbon material are dispersed inside the granulated body. In addition, battery characteristics such as heavy load discharge characteristics can be further improved.

Preferred examples of the carbon material that can be used to form a composite with SiO _x include carbon materials such as low crystalline carbon, carbon nanotubes, and vapor grown carbon fibers.

The details of the carbon material include at least one selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. A seed material is preferred. Fibrous or coil-like carbon materials are preferable in that they easily form a conductive network and have a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention, and even if SiO _x particles expand and contract. This is preferable in that it has a property of easily maintaining contact with the particles.

Graphite used in combination with SiO _x as the negative electrode active material can also be used as a carbon material related to a composite of SiO _x and a carbon material. Graphite, like carbon black, has high electrical conductivity and high liquid retention, and also has the property of easily maintaining contact with the SiO _x particles even when they expand and contract. Therefore, it can be preferably used for forming a complex with SiO _x .

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable for use when the composite with SiO _x is a granulated body. Fibrous carbon material can follow the expansion and contraction of SiO _x with the charging and discharging of the battery due to the high shape is thin threadlike flexibility, also because bulk density is large, many and SiO _x particles It is because it can have a junction. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used. In addition, the above-mentioned graphite conductive auxiliary having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more, or a graphite conductive additive having an aspect ratio of 3 or more and an average length of 1 μm or less _It may be used as a carbon material to be combined with _x, and it is particularly preferable to use a graphite conductive assistant having an average length of 1 μm or less for the carbon material to be combined with SiO _x .

The fibrous carbon material can also be formed on the surface of the SiO _x particles by, for example, a vapor phase method.

The specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, while the specific resistance value of the carbon material exemplified above is usually 10 ^{−5 to} 10 kΩcm.

The composite of SiO _x and the carbon material may further have a material layer (a material layer containing non-graphitizable carbon) that covers the carbon material coating layer on the particle surface.

When a composite of SiO _x and a carbon material is used for the negative electrode, the ratio of SiO _x and the carbon material is based on SiO _x : 100 parts by mass from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. The carbon material is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. Further, in the composite, if the ratio of the carbon material to be combined with SiO _x is too large, it may lead to a decrease in the amount of SiO _x in the negative electrode mixture layer, and the effect of increasing the capacity may be reduced. SiO _x: relative to 100 parts by weight, the carbon material, and more preferably preferably not more than 50 parts by weight, more than 40 parts by weight.

The composite of the SiO _x and the carbon material can be obtained, for example, by the following method.

First, a manufacturing method in the case of combining SiO _x will be described. A dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, and sprayed and dried to produce composite particles including a plurality of particles. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. In addition to the above method, similar composite particles can be produced also by a granulation method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

Incidentally, the SiO _x, in the case of manufacturing a granulated body with small carbon material resistivity value than SiO _x is adding the carbon material in the dispersion liquid of SiO _x are dispersed in a dispersion medium, the dispersion by using a liquid, by a similar method to the case of composite of SiO _x may be a composite particle (granule). Further, by granulation process according to the similar mechanical method, it is possible to produce a granular material of the SiO _x and the carbon material.

Next, when the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon-based material The gas is heated in the gas phase, and carbon generated by pyrolysis of the hydrocarbon-based gas is deposited on the surface of the particles. As described above, according to the vapor deposition (CVD) method, the hydrocarbon-based gas spreads to every corner of the composite particle, and the surface of the particle and the pores in the surface are thin and contain a conductive carbon material. Since a uniform film (carbon material coating layer) can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon material.

In the production of SiO _x coated with a carbon material, the processing temperature (atmosphere temperature) of the vapor deposition (CVD) method varies depending on the type of hydrocarbon gas, but usually 600 to 1200 ° C. is appropriate. Among these, the temperature is preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the treatment temperature, the less the remaining impurities, and the formation of a coating layer containing carbon having high conductivity.

  As the liquid source of the hydrocarbon-based gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

In addition, after the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is covered with a carbon material by a vapor deposition (CVD) method, a petroleum-based pitch or a coal-based pitch is used. At least one organic compound selected from the group consisting of a thermosetting resin and a condensate of naphthalene sulfonate and aldehydes is attached to a coating layer containing a carbon material, and then the organic compound is attached. The obtained particles may be fired.

Specifically, a dispersion liquid in which a SiO _x particle (SiO _x composite particle or a granulated body of SiO _x and a carbon material) coated with a carbon material and the organic compound are dispersed in a dispersion medium is prepared, The dispersion is sprayed and dried to form particles coated with the organic compound, and the particles coated with the organic compound are fired.

  An isotropic pitch can be used as the pitch, and a phenol resin, a furan resin, a furfural resin, or the like can be used as the thermosetting resin. As the condensate of naphthalene sulfonate and aldehydes, naphthalene sulfonic acid formaldehyde condensate can be used.

As a dispersion medium for dispersing the SiO _x particles coated with the carbon material and the organic compound, for example, water or alcohols (ethanol or the like) can be used. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. The firing temperature is usually 600 to 1200 ° C., preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the processing temperature, the less the remaining impurities, and the formation of a coating layer containing a high-quality carbon material with high conductivity. However, the processing temperature needs to be lower than the melting point of SiO _x .

Examples of graphite used as a negative electrode active material together with SiO _x include natural graphite such as scaly graphite; artificial graphite obtained by graphitizing graphitized carbon such as pyrolytic carbons, MCMB, and carbon fiber at 2800 ° C. or higher; Etc.

In the negative electrode according to the present invention, from the viewpoint of satisfactorily ensuring the effect of the high capacity by using a SiO _x, the content of SiO _x in the anode active material, is 0.01% by mass or more It is preferably 1% by mass or more, more preferably 3% by mass or more. Further, from the viewpoint of better avoiding the problem due to the volume change of SiO _x due to charge / discharge, the content of SiO _x in the negative electrode active material is preferably 20% by mass or less, and 15% by mass or less. It is more preferable.

The negative electrode is a paste obtained by sufficiently kneading an appropriate solvent (dispersion medium) into a mixture (negative electrode mixture) containing SiO _x , graphite, the above-mentioned fiber-shaped graphite conductive additive, and a binder. Or a slurry-like negative electrode mixture-containing composition is applied to one or both sides of the current collector, the solvent (dispersion medium) is removed by drying or the like, and a calendar treatment is performed as necessary to obtain a predetermined thickness. And it can manufacture through the process of forming the negative mix layer which has a density. However, the manufacturing method of the negative electrode is not limited to the above method, and may be manufactured by other manufacturing methods.

  Examples of the binder used in the negative electrode mixture layer include starch, polyvinyl alcohol, polyacrylic acid, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, and other polysaccharides and modified products thereof; polyvinylchloride, Thermoplastic resins such as polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene Rubber (SBR), butadiene rubber, polybutadiene, fluororubber, polyethylene oxide and other polymers having rubbery elasticity, and modified products thereof. May be used alone or two or more al.

  To the negative electrode mixture layer, a conductive material other than the above-described fiber-shaped graphite conductive auxiliary may be added as a conductive auxiliary. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the nonaqueous electrolyte secondary battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, Use one or more materials such as acetylene black, etc., genus powder (copper, nickel, aluminum, silver, etc.), metal fibers, polyphenylene derivatives (described in JP-A-59-20971). Can do. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

In the negative electrode mixture layer, the total amount of the negative electrode active material (SiO _x and graphite) is preferably 90 to 95% by mass, and the amount of the binder is preferably 1 to 4% by mass.

  In addition, the content of the graphite conductive additive having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more in the negative electrode mixture layer is the effect of its use (especially the conductivity in the negative electrode mixture layer in the charged state). From the viewpoint of ensuring a good (enhancing effect) property, the content is preferably 0.1% by mass or more, and more preferably 0.3% by mass or more. However, if the amount of graphite conductive assistant having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more in the negative electrode mixture layer is too large, the amount of other components is reduced, resulting in inconvenience. There is a fear. Therefore, the content of the graphite conductive additive having an aspect ratio of 3 or more and an average length of 10 μm or more in the negative electrode mixture layer is preferably 2% by mass or less, and preferably 1% by mass or less. Is more preferable.

  Furthermore, the content of the graphite conductive additive having an aspect ratio of 3 or more and an average length of 1 μm or less in the negative electrode mixture layer is the effect of its use (particularly, the negative electrode mixture layer in a state of being discharged after charging). From the viewpoint of ensuring a good effect of increasing the conductivity within the range, it is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more. However, if the amount of the graphite conductive additive having an aspect ratio of 3 or more and an average length of 1 μm or less in the negative electrode mixture layer is too large, the amount of other components is reduced, resulting in inconvenience. There is a fear. Therefore, the content of the graphite conductive additive having an aspect ratio of 3 or more and an average length of 1 μm or less in the negative electrode mixture layer is preferably 2% by mass or less, and 1.5% by mass or less. More preferably.

  The thickness of the negative electrode mixture layer (thickness per one side of the current collector) is preferably 10 to 100 μm, for example.

  As the current collector for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is 5 μm in order to ensure mechanical strength. Is desirable.

  For the positive electrode according to the nonaqueous electrolyte secondary battery of the present invention, for example, one having a structure having a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive additive and the like on one side or both sides of a current collector is used. it can.

As the positive electrode active material, a conventionally used non-aqueous electrolyte secondary battery, that is, a lithium metal composite oxide capable of occluding and releasing lithium ions is used. Specific examples of the lithium metal composite oxide that can be used as the positive electrode active material include, for example, Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Lithium-containing transition metal oxide having a layered structure represented by Al, Mg, etc., LiMn ₂ O ₄ and lithium manganese oxide having a spinel structure in which a part of the element is substituted with another element, LiMPO ₄ (M: Co, An olivine type compound represented by Ni, Mn, Fe, etc.) can be used. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiMn _{3 / 5} Ni _1/5 Co _1/5 O ₂ etc.). For the positive electrode active material, for example, only one of these may be used, or two or more may be used in combination.

  As the binder for the positive electrode mixture layer, the same binders as those exemplified above as the binder for the negative electrode mixture layer can be used. In addition, as the conductive auxiliary agent related to the positive electrode mixture layer, for example, graphite (graphite carbon material) such as natural graphite (flaky graphite), artificial graphite; acetylene black, ketjen black, channel black, furnace black, Carbon materials such as carbon black such as lamp black and thermal black; carbon fiber;

  For the positive electrode, for example, a paste-like or slurry-like positive electrode mixture-containing composition in which a positive electrode active material, a binder, and a conductive additive are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) is prepared. The binder may be dissolved in a solvent), and this is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the manufacturing method of the positive electrode is not limited to the above method, and may be manufactured by other manufacturing methods.

The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per side of the current collector, and the density of the positive electrode mixture layer (the mass of the positive electrode mixture layer per unit area laminated on the current collector, (Calculated from the thickness) is preferably 3.0 to 4.5 g / cm ³ . Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 60-95 mass%, for example, it is preferable that the quantity of a binder is 1-15 mass%, and the quantity of a conductive support agent. Is preferably 3 to 20% by mass.

  The current collector can be the same as that used for the positive electrode of a conventionally known non-aqueous electrolyte secondary battery. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

  Moreover, you may form the lead body for electrically connecting with the other member in a non-aqueous-electrolyte secondary battery according to a conventional method as needed to the positive electrode and negative electrode which concern on this invention.

  The non-aqueous electrolyte secondary battery of the present invention is only required to have the above-described negative electrode and positive electrode, and there are no particular restrictions on other configurations and structures, and conventionally known non-aqueous electrolyte secondary batteries It is possible to apply the configuration and the structure adopted in FIG.

  The separator according to the nonaqueous electrolyte secondary battery of the present invention is a porous film composed of polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymer; polyester such as polyethylene terephthalate or copolymer polyester; Is preferred. In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator has a melting point, that is, a thermoplastic resin having a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 ° C. in accordance with JIS K 7121 as a component. Preferably, it is a single layer porous film mainly composed of polyethylene or a laminated porous film comprising a porous film such as a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. Is preferred. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is desirable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More desirable.

  As such a resin porous membrane, for example, a porous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known non-aqueous electrolyte secondary battery or the like, that is, a solvent extraction method Alternatively, an ion permeable porous membrane produced by a dry or wet stretching method can be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

Moreover, as a characteristic of the separator, a Gurley value represented by the number of seconds in which 100 ml of air permeates the membrane under a pressure of 0.879 g / mm ² is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  Even when the inside of the non-aqueous electrolyte secondary battery is 150 ° C. or higher, for example, the lithium metal composite oxide represented by the general composition formula (1) having excellent thermal stability is used as the positive electrode active material. If so, you can keep it safe.

  As the non-aqueous electrolyte, a solution in which an electrolyte salt is dissolved in an organic solvent can be used. Examples of the solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 1, 2 -Dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, Sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone, etc. Aprotic organic solvents, and the like, may be used these alone, or in combination of two or more of these. Also, amine imide organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can be used. Among these, a mixed solvent of EC, MEC, and DEC is preferable. In this case, it is more preferable to include DEC in an amount of 15% by volume to 80% by volume with respect to the total volume of the mixed solvent. This is because such a mixed solvent can enhance the stability of the solvent during high-voltage charging while maintaining the low temperature characteristics and charge / discharge cycle characteristics of the battery high.

As the electrolyte salt related to the non-aqueous electrolyte, a salt of a fluorine-containing compound such as lithium perchlorate, lithium organic boron, trifluoromethanesulfonate, imide salt, or the like is preferably used. Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OSO ₂ ) ₂ [where Rf Represents a fluoroalkyl group. These may be used alone or in combination of two or more thereof. Among these, LiPF ₆ and LiBF ₄ are more preferable because of good charge / discharge characteristics. This is because these fluorine-containing organic lithium salts have a large anionic property and are easily ion-separated, so that they are easily dissolved in the solvent. The concentration of the electrolyte salt in the solvent is not particularly limited, but is usually 0.5 to 1.7 mol / L.

  In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, and fluorobenzene are used for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of the non-aqueous electrolyte. An additive such as t-butylbenzene may be added as appropriate. The lithium metal composite oxide used for the positive electrode active material in the battery of the present invention contains Mn. Since the surface activity of such a lithium metal composite oxide can be stabilized, an additive containing sulfur element is added. Is particularly preferred.

  The nonaqueous electrolyte secondary battery of the present invention includes, for example, an electrode laminate in which the negative electrode and the positive electrode are laminated with the separator interposed therebetween, and an electrode wound body in which this is wound in a spiral shape. The electrode body and the non-aqueous electrolyte solution are sealed in an exterior body according to a conventional method. As the form of the battery, similarly to the conventionally known non-aqueous electrolyte secondary battery, a cylindrical battery using a cylindrical (cylindrical or rectangular) outer can, or a flat (in plan view) A flat battery using a circular or square flat can), a soft package battery using a metal-deposited laminated film as an outer package, and the like. The outer can can be made of steel or aluminum.

  The non-aqueous electrolyte secondary battery of the present invention has excellent charge / discharge cycle characteristics, good load characteristics, and can have a high capacity. Therefore, these characteristics are utilized to make a small and multifunctional portable device. It can be preferably used for various applications to which conventionally known non-aqueous electrolyte secondary batteries are applied.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

  In addition, the aspect ratio and average length of the vapor growth carbon fiber and the carbon nanotube used in Examples and Comparative Examples described later are values obtained by the above-described method by observation with a scanning electron microscope.

Example 1
<Preparation of positive electrode>
Contains a positive electrode mixture prepared by dispersing LiCoO _{2 as a} positive electrode active material, carbon black as a conductive auxiliary agent, and PVDF as a binder in a mass ratio of 93: 3: 4 in NMP. The paste is intermittently applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 10 μm while adjusting the thickness, dried, and then subjected to a calendar treatment, so that the thickness of the positive electrode mixture layer is equal to one side of the current collector. A positive electrode having a diameter of 70 μm was produced. The positive electrode was cut into a predetermined shape, and a tab was welded to the exposed portion of the aluminum foil to form a lead portion.

<Production of negative electrode>
A mixture containing SiO and graphite in a mass ratio of 2: 8 (negative electrode active material), SBR and CMC as a binder (1: 2 in mass ratio), and an average aspect ratio of 8.6 as a conductive auxiliary agent. And a carbon nanotube having an average length of 13 μm and carbon nanotubes having an average aspect ratio of 20 and an average length of 0.2 μm (a mass ratio of 1: 1) at a mass ratio of 94: 3: 3 A negative electrode mixture-containing paste prepared by dispersing the mixture in water was intermittently applied to both sides of a 15 μm thick copper foil (negative electrode current collector) while adjusting the thickness, dried, and then subjected to a calendar treatment. A negative electrode having a negative electrode mixture layer thickness of 60 μm per side of the current collector was prepared. The negative electrode was cut into a predetermined shape, and a tab was welded to the exposed portion of the copper foil to form a lead portion.

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were stacked while interposing a polyethylene microporous membrane separator having a thickness of 20 μm, and wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body was crushed into a flat shape, put into an aluminum alloy 463450 rectangular outer can, and a non-aqueous electrolyte (ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate at a volume ratio of 1: 1: 1). LiPF ₆ was dissolved in the mixed solvent at a concentration of 1.1 mol / l, and a solution in which vinylene carbonate was added in an amount of 1% by mass was injected.

  After injecting the nonaqueous electrolyte, the outer can was sealed, and a nonaqueous electrolyte secondary battery having the structure shown in FIG. 1 and the appearance shown in FIG. 2 was produced.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 is spirally wound through the separator 3 as described above, and then pressed so as to be flattened and accommodated in a rectangular tube-shaped outer can 4 together with the electrolyte as a flat wound electrode body 6 Has been. However, in FIG. 1, in order to avoid complication, the metal foil, electrolyte solution, etc. as a collector used in producing the negative electrode 1 and the positive electrode 2 are not shown.

  The outer can 4 is made of an aluminum alloy and constitutes an outer casing of the battery. The outer can 4 also serves as a positive electrode terminal. An insulator 5 made of a polyethylene sheet is disposed at the bottom of the outer can 4, and is connected to one end of each of the negative electrode 1 and the positive electrode 2 from the flat wound electrode body 6 made of the negative electrode 1, the positive electrode 2 and the separator 3. The negative electrode lead body 7 and the positive electrode lead body 8 are drawn out. Further, a stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the outer can 4 through a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the armored can 4, and the opening part of the armored can 4 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. (See FIG. 1 and FIG. 2, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of Example 1, the outer can 4 and the lid plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 8 to the lid plate 9, and the negative electrode lead body 7 is welded to the lead plate 13. The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 7 and the terminal 11 through the lead plate 13, but depending on the material of the outer can 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members among the members constituting the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Example 2
The conductive assistant was changed to vapor-grown carbon fibers with an average aspect ratio of 5.2 and an average length of 40 μm, and carbon nanotubes with an average aspect ratio of 20 and an average length of 0.2 μm (mass ratio of 1: 1). A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Example 3
Other than changing the conductive assistant to vapor-grown carbon fibers having an average aspect ratio of 300 and an average length of 50 μm, and carbon nanotubes having an average aspect ratio of 20 and an average length of 0.2 μm (mass ratio of 1: 1) Produced a negative electrode in the same manner as in Example 1, and produced a nonaqueous electrolyte secondary battery in the same manner as in Example 1 except that this negative electrode was used.

Example 4
Other than changing the conductive assistant to vapor-grown carbon fibers having an average aspect ratio of 300 and an average length of 50 μm, and carbon nanotubes having an average aspect ratio of 20 and an average length of 0.8 μm (mass ratio of 1: 1) Produced a negative electrode in the same manner as in Example 1, and produced a nonaqueous electrolyte secondary battery in the same manner as in Example 1 except that this negative electrode was used.

Comparative Example 1
A negative electrode was produced in the same manner as in Example 1 except that the conductive auxiliary agent was changed to only vapor-grown carbon fibers having an average aspect ratio of 300 and an average length of 50 μm. Example 1 except that this negative electrode was used. In the same manner, a non-aqueous electrolyte secondary battery was produced.

Comparative Example 2
A negative electrode was produced in the same manner as in Example 1 except that the conductive auxiliary agent was changed to only vapor-grown carbon fibers having an average aspect ratio of 20 and an average length of 0.2 μm. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Comparative Example 3
Other than changing the conductive assistant to vapor-grown carbon fibers having an average aspect ratio of 30 and an average length of 5 μm, and carbon nanotubes having an average aspect ratio of 20 and an average length of 0.2 μm (1: 1 by mass ratio) Produced a negative electrode in the same manner as in Example 1, and produced a nonaqueous electrolyte secondary battery in the same manner as in Example 1 except that this negative electrode was used.

Comparative Example 4
Other than changing the conductive assistant to vapor-grown carbon fibers having an average aspect ratio of 300 and an average length of 50 μm, and carbon nanotubes having an average aspect ratio of 160 and an average length of 1.6 μm (mass ratio of 1: 1) Produced a negative electrode in the same manner as in Example 1, and produced a nonaqueous electrolyte secondary battery in the same manner as in Example 1 except that this negative electrode was used.

Comparative Example 5
A negative electrode was produced in the same manner as in Example 1 except that the conductive auxiliary agent was changed to Ketjen Black [“EC600JD (trade name)” manufactured by Lion Corporation], and the same as in Example 1 except that this negative electrode was used. Thus, a non-aqueous electrolyte secondary battery was produced.

  About the nonaqueous electrolyte secondary battery of each said Example and a comparative example, it charges with a constant current until it becomes 4.2V with the electric current of 900mA, and is followed by the constant current constant voltage charge which charges with the constant voltage of 4.2V (Total charge time 3 hours), a series of operations to perform a constant current discharge with a current of 900 mA and a final voltage of 2.5 V as one cycle, this is performed 500 cycles, and the initial discharge capacity (the discharge of the first cycle) Capacity) and the discharge capacity at the 500th cycle. Then, the ratio of the discharge capacity at the 500th cycle to the initial discharge capacity was expressed as a percentage to obtain the charge / discharge cycle capacity maintenance ratio.

  In addition, for the non-aqueous electrolyte secondary batteries of the respective Examples and Comparative Examples (batteries different from those for which the charge / discharge cycle capacity retention rate was determined), except for the first cycle, the third cycle, and every 100 cycles The charge / discharge cycle was carried out for 500 cycles under the same conditions as the charge / discharge cycle capacity retention rate measurement. For the first cycle, the third cycle, and every 100th cycle, the battery was charged under the same conditions as the charge / discharge cycle capacity maintenance rate measurement, and then the constant current charge with a current of 1800 mA and a final voltage of 2.5V was made. Went. The ratio of the discharge capacity at the third cycle, the 100th cycle, and the 500th cycle (discharge capacity at a current of 1800 mA) to the discharge capacity at the first cycle (discharge capacity at a current of 1800 mA) is expressed as a percentage. The load characteristics were evaluated.

  Table 1 shows the charge / discharge cycle capacity retention ratio and load characteristics obtained as described above.

As shown in Table 1, in addition to using graphite as a negative electrode active material together with SiO _x , a negative electrode using two types of graphite conductive assistants having an appropriate aspect ratio in a fiber shape and an appropriate average length is used. The non-aqueous electrolyte secondary batteries of Examples 1 to 4 have charge / discharge cycle capacities as compared with the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 5 in which the conductive auxiliary agent for the negative electrode is not configured as described above. High retention rate and excellent charge / discharge cycle characteristics. Moreover, the nonaqueous electrolyte secondary batteries of Examples 1 to 4 have good load characteristics even after 500 cycles of charge and discharge.

1 Negative electrode 2 Positive electrode 3 Separator

Claims (3)

A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator containing a lithium metal composite oxide as a positive electrode active material,
The negative electrode contains a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5), and graphite as a negative electrode active material, and A negative electrode mixture layer containing a graphite conductive assistant having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more, and a graphite conductive assistant having a fiber shape of an aspect ratio of 3 or more and an average length of 1 μm or less. On one or both sides of the current collector ,
The content of the graphite conductive additive having an aspect ratio of 3 or more and an average length of 10 μm or more in the negative electrode mixture layer is 0.1 to 2% by mass,
The aspect ratio is the average length in the three or more fibrous form of less graphitic conductive additive 1 [mu] m, the content in the negative electrode mixture layer, a non-aqueous electrolyte, wherein 0.1 to 2% by mass Rukoto Liquid secondary battery. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the graphite conductive additive having a fiber shape with an aspect ratio of 3 or more and an average length of 10 μm or more is a vapor-grown carbon fiber . The aspect ratio of an average length of 1μm or less of graphite Shitsushirube Densuke agent 3 or more fiber-shaped non-aqueous electrolyte secondary battery according to claim 1 or 2 is a carbon nanotube.

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