WO2014109366A1

WO2014109366A1 - Nonaqueous electrolyte secondary battery

Info

Publication number: WO2014109366A1
Application number: PCT/JP2014/050241
Authority: WO
Inventors: 植苗圭一郎; 巨勢丈裕
Original assignee: 日立マクセル株式会社; 旭硝子株式会社
Priority date: 2013-01-11
Filing date: 2014-01-09
Publication date: 2014-07-17
Also published as: JP2016076292A

Abstract

This nonaqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, a nonaqueous electrolyte solution and a separator, and is characterized in that: the positive electrode is provided with a positive electrode mixture layer that contains a lithium-containing transition metal composite oxide; the negative electrode is provided with a negative electrode mixture layer that contains a graphite carbon material, a material containing an element that forms an alloy with lithium, and a binder; the binder contains a water-soluble adhesive resin and a fluorine-containing elastic copolymer that has a constituent unit based on two or more monomers including at least one monomer that is selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride; and if M₁ is the mass of the water-soluble adhesive resin contained in the negative electrode mixture layer and M₂ is the mass of the fluorine-containing elastic copolymer contained in the negative electrode mixture layer, the mass ratio M₂/M₁ is from 0.1 to 2 (inclusive).

Description

Non-aqueous electrolyte secondary battery

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

Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are widely used as power sources for portable devices such as personal computers and mobile phones. There are great expectations. As a negative electrode material (negative electrode active material) of such a non-aqueous electrolyte secondary battery, in addition to lithium (Li) and Li alloy, graphite such as natural graphite and artificial graphite that can insert and desorb Li ions Carbon materials are used.

However, recently, there has been a demand for higher capacity for batteries used in miniaturized and multifunctional portable devices, and in response to this, the graphite carbon material widely used as a negative electrode active material is replaced. New negative electrode materials are being studied. As a new negative electrode material, tin (Sn) alloy, silicon (Si) alloy, Si oxide, Li nitride, Li metal, etc. are attracting attention, but at present, any of these new negative electrode materials is charge / discharge. It is inferior to the graphitic carbon material in terms of cycle characteristics. This is because the graphitic carbon material has a layered structure, and the expansion / contraction of the material when Li is doped or undoped between the layers during charge / discharge is about 10% in terms of the interlayer distance. On the other hand, in the above-described new negative electrode material, the Li content during charging / discharging is large, so that the material expands and contracts very much. This is presumably because the charge / discharge cycle characteristics, that is, the capacity retention rate with respect to the initial capacity, is worse than that of the graphitic carbon material.

For example, Patent Document 1 describes that high capacity can be achieved by using a mixture of graphitic carbon material and Si oxide as a negative electrode active material. However, when the mixing ratio of the graphitic carbon material is lowered, as described above, it is considered that the mechanical strength and the electronic conductivity of the electrode are lowered and the charge / discharge cycle characteristics are lowered.

As a method of solving such a problem, for example, there is a method of suppressing charge reduction and improving charge / discharge cycle characteristics by adding a conductive auxiliary such as acetylene black, carbon black, ketjen black and the like. Proposed. Recently, new conductive assistants such as vapor-grown carbon fibers disclosed in Patent Document 2 and carbon nanofibers disclosed in Patent Document 3 have also been proposed.

Further, for example, in Patent Document 4, it is generally used as a negative electrode binder in a non-aqueous electrolyte secondary battery including a negative electrode including a graphite material and a material containing Si as a constituent element as a negative electrode active material. There has been proposed a method for improving the mechanical strength of the electrode and improving the charge / discharge cycle characteristics by using polyacrylic acid instead of polyvinylidene fluoride (PVDF) and styrene butadiene rubber (SBR). Furthermore, Patent Document 5 proposes a method for improving charge / discharge cycle characteristics by using a copolymer of tetrafluoroethylene and propylene as a binder and needle coke as a negative electrode active material.

Japanese Patent Laid-Open No. 9-289011 JP 2004-103435 A JP 2004-186067 A JP 2007-95670 A International Publication No. 2011/055760

When the above-mentioned new negative electrode material is used as the negative electrode active material, the capacity can be increased as compared with the graphitic carbon material. On the other hand, the expansion / contraction of the negative electrode active material increases with charge / discharge, and sufficient charge / discharge cycle characteristics are obtained. I can't get it. Patent Document 4 proposes that polyacrylic acid is used as a negative electrode binder in a nonaqueous electrolyte secondary battery including a negative electrode including a graphitic carbon material and a material containing Si as a constituent element as a negative electrode active material. However, although the technique described in Patent Document 4 can improve the charge / discharge cycle characteristics as compared with a case where a material containing Si as a constituent element is used alone as a negative electrode active material, a graphitic carbon material as a negative electrode active material Compared with the case where is used alone, the charge / discharge cycle characteristics and load characteristics are not satisfactory. Also in Patent Document 5, there is still room for examination in terms of characteristics regarding application to a material having a high capacity, such as the above-described new negative electrode material, but having large expansion / contraction due to charge / discharge.

The present invention has been made in view of the above circumstances, and provides a non-aqueous electrolyte secondary battery having high capacity and excellent load characteristics and charge / discharge cycle characteristics.

The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the positive electrode is a positive electrode composite including a lithium-containing transition metal composite oxide. The negative electrode includes a negative electrode mixture layer including a graphitic carbon material, a material including an element alloying with lithium, and a binder. The binder includes tetrafluoroethylene, hexafluoropropylene, and fluorine. A negative electrode mixture comprising a fluorinated elastic copolymer having a constitutional unit based on two or more monomers including at least one monomer selected from the group consisting of vinylidene fluoride, and a water-soluble adhesive resin. When the mass of the water-soluble adhesive resin contained in the layer is M ₁ and the mass of the fluorinated elastic copolymer contained in the negative electrode mixture layer is M ₂ , the mass ratio M ₂ / M ₁ is 0.1 or more. 2 or less It is a sign.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having a high capacity and excellent load characteristics and charge / discharge cycle characteristics.

FIG. 1 is a plan view schematically showing an example of the nonaqueous electrolyte secondary battery of the present invention. 2 is a cross-sectional view taken along line II of the nonaqueous electrolyte secondary battery of FIG.

Generally, organic solvent-based polyvinylidene fluoride (PVDF) or water-dispersed styrene-butadiene rubber (SBR) is used as the binder for the negative electrode of the non-aqueous electrolyte secondary battery. Organic solvent-based PVDF is a negative electrode using both a graphitic carbon material and a material containing an element that forms an alloy with lithium, because the adhesiveness with a metal foil as a current collector varies greatly depending on the type of the graphitic carbon material. Then, the range of use is limited. In particular, when natural graphite having a scale shape is used as the graphitic carbon material, the adhesiveness is extremely poor. On the other hand, water-dispersed SBR requires the use of a water-soluble adhesive resin such as carboxymethylcellulose (CMC) as a thickener, but has a problem that sufficient characteristics cannot be realized in load characteristics.

In contrast, as a result of intensive studies by the present inventors, a non-aqueous electrolyte secondary battery including a negative electrode having a negative electrode mixture layer containing a graphite carbon material and a material containing an element alloying with lithium as a negative electrode active material In which the binder of the negative electrode mixture layer has a structural unit based on two or more monomers including at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride An elastic copolymer (also referred to as fluorine-containing rubber) and a water-soluble adhesive resin are used, and the mass of the water-soluble adhesive resin contained in the negative electrode mixture layer is M ₁ and contained in the negative electrode mixture layer. When the mass of the fluorinated elastic copolymer is M ₂ , when the mass ratio M ₂ / M ₁ is 0.1 or more and 2 or less, it is found that load characteristics and charge / discharge cycle characteristics can be improved. The present invention has been completed.

Hereinafter, each component of the non-aqueous electrolyte secondary battery of the present invention will be described.

<Negative electrode>
The negative electrode according to the non-aqueous electrolyte secondary battery of the present invention has a negative electrode mixture layer containing a negative electrode active material and a binder, for example, on one side or both sides of a current collector.

The negative electrode according to the present invention can be obtained by, for example, adding a suitable solvent [N-methyl-2-pyrrolidone (NMP), etc.] to a mixture (negative electrode mixture) containing a negative electrode active material, a binder and the like and kneading the mixture sufficiently. The paste-like or slurry-like negative electrode mixture-containing composition is applied to one or both sides of the negative electrode current collector, and the solvent is removed by drying or the like to form a negative electrode mixture layer having a predetermined thickness and density. Can be manufactured. However, the manufacturing method of the negative electrode according to the present invention is not limited to the above manufacturing method.

The binder for the negative electrode mixture layer is selected from the group consisting of tetrafluoroethylene (hereinafter also referred to as TFE), hexafluoropropylene (hereinafter also referred to as HFP), and vinylidene fluoride (hereinafter also referred to as VdF). A fluorinated elastic copolymer having a structural unit based on two or more monomers including at least one monomer is used. The fluorinated elastic copolymer has a greater adhesive force than, for example, PVDF, and can improve the adhesion between the negative electrode mixture layer and the current collector, so the load characteristics of the non-aqueous electrolyte secondary battery and Charge / discharge cycle characteristics can be improved.

The structural unit based on two or more monomers in the fluorinated elastic copolymer is, for example, a structural unit based on two or three monomers selected from the group consisting of TFE, HFP and VdF. A constitutional unit based on one or more monomers selected from the group consisting of TFE, HFP and VdF, and a constitution based on one or more other monomers copolymerizable with the monomer It may be a structural unit including a unit.

The fluorine content of the fluorinated elastic copolymer is preferably 50% by mass or more, more preferably 53% by mass or more, and preferably 74% by mass or less, and 70% by mass or less. It is more preferable that When the fluorine content of the fluorinated elastic copolymer is too low, the electrolytic solution resistance and the voltage resistance tend to be insufficient.

The fluorine content of the fluorine-containing elastic copolymer is obtained by fluorine content analysis, and indicates the ratio of the mass of fluorine atoms to the total mass of all atoms constituting the fluorine-containing elastic copolymer.

When the fluorinated elastic copolymer has a structural unit based on another monomer in addition to a structural unit based on TFE, a structural unit based on HFP, or a structural unit based on VdF, Is preferably propylene (hereinafter also referred to as P), ethylene (hereinafter also referred to as E), or perfluoro (alkyl vinyl ether) (hereinafter also referred to as PAVE), and more preferably propylene.

Examples of PAVE include perfluoro (methyl vinyl ether) (hereinafter also referred to as PMVE), perfluoro (propyl vinyl ether) (hereinafter also referred to as PPVE), and these may be used alone or in combination of two or more kinds. Can be used in combination.

Specific examples of the fluorinated elastic copolymer include a TFE / P copolymer (meaning a copolymer comprising a structural unit based on TFE and a structural unit based on P. The same applies hereinafter), TFE / P / VdF copolymer, VdF / HFP copolymer, VdF / TFE copolymer, TFE / VdF / HFP copolymer, TFE / PAVE copolymer, E / HFP copolymer, TFE / P / E copolymer , TFE / P / PAVE copolymer, TFE / P / VdF / PAVE copolymer, VdF / PAVE copolymer, VdF / TFE / PAVE copolymer, VdF / TFE / HFP / PAVE copolymer, etc. It is done.

Among these, TFE / P copolymer, TFE / P / VdF copolymer, VdF / HFP copolymer, VdF / TFE copolymer, TFE / VdF / HFP copolymer, TFE / PAVE copolymer, A TFE / P / PAVE copolymer or TFE / P / VdF / PAVE copolymer is preferred, and a TFE / P copolymer or TFE / P / VdF copolymer is particularly preferred.

A more preferred composition of the fluorinated elastic copolymer is described below. When the composition is in the following range, excellent adhesion to the current collector, excellent electrolytic solution resistance and voltage resistance can be obtained, and the charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery can be further improved. Can do.

(TFE / P copolymer)
The ratio of the structural unit based on TFE / the structural unit based on P is preferably 30 to 80/70 to 20 (mol%, provided that the total is 100 mol%; the same applies hereinafter), and 40 to 70/60. It is more preferably from 30 to 30 (mol%), most preferably from 60 to 50/40 to 50 (mol%).

(TFE / P / VdF copolymer)
The ratio of the structural unit based on TFE / the structural unit based on P / the structural unit based on VdF is preferably in the range of 30 to 85/15 to 70 / 0.01 to 50 (mol%), more preferably 30 70/20 to 60/1 to 40 (mol%).

The Mooney viscosity of the fluorinated elastic copolymer in the present invention is preferably 10 or more, more preferably 50 or more, further preferably 80 or more, and preferably 200 or less, More preferably, it is 180 or less, and further preferably 150 or less.

Mooney viscosity is based on Japanese Industrial Standard (JIS) K6300, using an L-shaped rotor with a diameter of 38.1 mm and a thickness of 5.54 mm, preheating time of 1 minute, and rotor rotation time of 10 minutes at 100 ° C. It is a measure of the molecular weight of polymer materials such as rubber. Moreover, it shows that it is a high molecular weight indirectly, so that the value is large. When the Mooney viscosity is in the above range, the mechanical strength of the negative electrode mixture layer can be increased to further improve the charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery.

The method for producing the fluorinated elastic copolymer is not particularly limited, and for example, it can be produced by using the production method described in Patent Document 5 (International Publication No. 2011/055760). Especially, it is preferable that a fluorine-containing elastic copolymer is manufactured by emulsion polymerization.

In the present invention, a water-soluble adhesive resin is used in combination with the fluorinated elastic copolymer as a binder for the negative electrode mixture layer. Thereby, the ionic conductivity of the negative electrode can be increased to further improve the load characteristics of the non-aqueous electrolyte secondary battery, and the mechanical strength of the negative electrode mixture layer can be increased to increase the charge / discharge cycle of the non-aqueous electrolyte secondary battery. The characteristics can be further improved.

Specific examples of the water-soluble adhesive resin include, for example, at least one selected from the group consisting of celluloses, acrylic acid polymers, and alginic acid polymers. More specifically, carboxymethyl cellulose (CMC) and its salts, hydroxypropyl cellulose (HPC) and its salts, alginic acid and its salts, polyacrylic acid and its salts, and the like can be mentioned.

If the mass ratio M ₂ / M ₁ of the mass M ₂ of the fluorinated elastic copolymer to the mass M ₁ of the water-soluble adhesive resin in the negative electrode mixture layer is too small, non-aqueous electrolysis by using both of the above binders in combination. Since the effect of improving the load characteristics of the liquid secondary battery tends to be small, it needs to be 0.1 or more, preferably 0.2 or more, and more preferably 0.3 or more.

On the other hand, if the mass ratio M ₂ / M ₁ is too large, the effect of improving the charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery by using both the binders tends to be less than 2 or less. And is preferably 1.5 or less, more preferably 1 or less.

The negative electrode active material used for the negative electrode mixture layer of the negative electrode according to the present invention is a material containing a graphitic carbon material and an element alloying with lithium.

Examples of the graphitic carbon material include natural graphite such as flaky graphite; artificial graphite obtained by graphitizing graphitized carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB) and carbon fibers at 2800 ° C. or higher; Etc.

Examples of the element relating to a material containing an element that forms an alloy with lithium include Si, Sn, Ga, Ge, In, and Al. As a material containing the element to be a negative electrode active material, in addition to the element alone or an alloy of the elements, an alloy of the element and Co, Ni, Fe, Mn, Ti, Zr, etc., an oxide of the element, Compounds such as nitrides and carbides can be exemplified. Among these, Si or Sn is preferable as an element to be alloyed with lithium, and simple elements of these elements, alloys containing these elements, and oxides of these elements are preferably used as the active material.

Among the materials containing an element that forms an alloy with lithium as exemplified above, in particular, in order to increase the capacity of the non-aqueous electrolyte secondary battery, the general formula SiO _x (however, the atomic ratio x of O to Si is 0. It is preferable to use a material represented by 5 ≦ x ≦ 1.5 (hereinafter, the material is simply referred to as “SiO _x ”).

SiO _x is not limited to the Si oxide, and may contain a Si microcrystalline or amorphous phase. In this case, the atomic ratio of Si and O is determined by the Si microcrystalline or amorphous phase. The ratio includes Si. That is, the SiO _x to SiO ₂ matrix of amorphous Si (e.g., microcrystalline Si) is include the dispersed structure, the SiO ₂ of the amorphous, dispersed therein 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. 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.

As the particle size of SiO _x , in order to enhance the effect of compounding with the carbon material described later, and to prevent miniaturization during charging and discharging, a laser diffraction scattering type particle size distribution measuring device, for example, “MICRO The number average particle diameter measured by “Track HRA” or the like is preferably about 0.5 to 10 μm.

The particle form of SiO _x may be primary particles or composite particles in which a plurality of primary particles are combined.

SiO _x is preferably a composite that is combined with a carbon material. For example, it is desirable that the surface of SiO _x be coated with the carbon material. Since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive aid) is used, and SiO _x and the conductive material in the negative electrode are used. Therefore, it is necessary to form a good conductive network by mixing and dispersing with each other. If it is a composite in which SiO _x is combined with a carbon material, for example, a conductive network in the negative electrode is better than when using a material obtained by simply mixing SiO _x and a conductive material such as a carbon material. Formed.

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 used in combination with a conductive material (such as a carbon material), a better conductive network can be formed in the negative electrode. A lithium secondary battery with higher capacity and better battery characteristics (for example, charge / discharge cycle characteristics) can be realized. 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 granule. 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.

Details of the carbon material include at least 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. One 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 the SiO _x particles expand and contract. However, it is preferable in that it has a property of easily maintaining contact with the particles.

Moreover, the graphitic carbon material used as a negative electrode active material can also be used as a carbon material related to a composite of SiO _x and a carbon material. Graphite carbon materials, like carbon black, have high electrical conductivity and high liquid retention, and even when SiO _x particles expand and contract, they can easily maintain contact with the particles. Since it has properties, 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 as a material used when the composite with SiO _x is a granulated body. Fibrous carbon material is due to the high shape is thin threadlike flexibility can follow the expansion and contraction of SiO _x with the charging and discharging of the battery, and in order bulk density is large, SiO _x particles and many It is because it can have the following junction point. 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. The fibrous carbon material can also be formed on the surface of the SiO _x particles by, for example, a gas 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.

When a composite of SiO _x and carbon material is used for the negative electrode, the ratio of SiO _x and 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, which may reduce the effect of increasing the capacity. SiO _x : The carbon material is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and most preferably 40 parts by mass or less with respect to 100 parts by mass of SiO _x .

The primary particles of SiO _x can be obtained by, for example, a method in which a mixture of Si and SiO ₂ is heated and the generated silicon oxide gas is cooled and precipitated. Furthermore, a fine Si phase can be formed inside the particles by heat-treating the obtained SiO _x under an inert gas atmosphere. By adjusting the heat treatment temperature and time at this time, the half width of the (111) diffraction peak of the formed Si phase can be controlled. Usually, the heat treatment temperature is set in a range of about 900 to 1400 ° C., and the heat treatment time is set in a range of about 0.1 to 10 hours.

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

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 liquid 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.

In the case of producing a granulated body of SiO _x and a carbon material having a specific resistance value smaller than that of SiO _x , the carbon material is added to a dispersion in which SiO _x is dispersed in a dispersion medium. The composite particles (granulated material) may be obtained by the same method as that used when combining SiO _x . 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 system 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 phase growth (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 covering the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) with a carbon material by a vapor deposition (CVD) method, petroleum pitch, coal pitch, 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 the carbon material coating layer of SiO _x particles, and then the organic compound is attached. The obtained particles may be fired.

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

Isotropic pitch can be used as the pitch, and phenol resin, furan resin, 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 liquid 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 .

A material containing an element that forms an alloy with lithium, such as SiO _x , has a higher capacity than a carbon material that is widely used as a negative electrode active material of a non-aqueous electrolyte secondary battery, but it accompanies charging / discharging of the battery. Since the volume change is large, in a non-aqueous electrolyte secondary battery using a negative electrode having a negative electrode mixture layer with a high content of a material containing an element alloyed with lithium, the negative electrode (negative electrode mixture) is obtained by repeated charge and discharge. There is a risk that the layer) will deteriorate due to a large volume change and the capacity will decrease. That is, the charge / discharge cycle characteristics may be deteriorated. Graphite carbon materials are widely used as negative electrode active materials for non-aqueous electrolyte secondary batteries, and have a relatively large capacity, but are associated with charging and discharging of batteries as compared with materials containing elements that alloy with lithium. Volume change is small. Therefore, the combined use of a graphite carbon material and a material containing an element alloying with lithium in the negative electrode active material has an effect of improving the capacity of the battery as the amount of the material containing the element alloying with lithium is reduced. While suppressing the reduction as much as possible, the deterioration of the charge / discharge cycle characteristics of the battery can be satisfactorily suppressed.

The content of the material containing an element that forms an alloy with lithium (for example, SiO _x ) in the entire negative electrode active material is 0.01 mass from the viewpoint of favorably securing the effect of increasing the capacity by using the material. % Or more, 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 the material containing the element alloying with lithium due to charge / discharge, in the entire negative electrode active material of the material containing the element alloying with lithium (for example, SiO _x ) The content in is preferably 20% by mass or less, and more preferably 15% by mass or less.

In the negative electrode mixture layer of the negative electrode according to the present invention, a conductive material may be further 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, acetylene black, ketjen black, channel black, furnace black, lamp black, Carbon black such as thermal black; conductive fiber such as carbon fiber and metal fiber; metal powder such as aluminum powder, nickel powder, copper powder and silver powder; conductive whisker composed of carbon fluoride; zinc oxide; potassium titanate; Examples thereof include conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives (described in JP-A-59-20971), and these may be used alone. More than one species may be used in combination. Among these, carbon black excellent in liquid absorbency is preferable, and ketjen black and acetylene black are more preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

The particle size of the carbon material used as the conductive additive related to the negative electrode mixture layer is, for example, a number average particle size measured using the laser diffraction / scattering particle size distribution analyzer, and is 0.01 μm or more. Is preferably 0.02 μm or more, more preferably 10 μm or less, and even more preferably 5 μm or less.

The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per side of the negative electrode current collector. The density of the negative electrode mixture layer (calculated from the mass and thickness of the negative electrode mixture layer per unit area laminated on the negative electrode current collector) is 1.0 g / cm ³ or more and 1.9 g / cm ³ or less. Preferably there is.

As the composition of the negative electrode mixture layer, for example, the amount of the negative electrode active material (the total amount of the graphitic carbon material and the material containing an element alloying with lithium) is preferably 80 to 99% by mass. The amount is preferably 1 to 20% by mass. In addition, when the conductive additive is contained in the negative electrode mixture layer, it is preferable to use the conductive assistant within a range in which the amount of the negative electrode active material and the amount of the binder satisfy the above-described preferable values.

As the current collector for the negative electrode, copper or nickel foil, punching metal, mesh, expanded metal, or the like can be used, but copper foil is usually used. In the negative electrode current collector, when the thickness of the whole 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 of the thickness is 5 μm in order to ensure mechanical strength. It is desirable to be.

<Positive electrode>
The positive electrode according to the nonaqueous electrolyte secondary battery of the present invention has a positive electrode mixture layer containing a positive electrode active material or the like, for example, on one side or both sides of a current collector.

The positive electrode according to the present invention is, for example, a paste or slurry obtained by adding a solvent (NMP or the like) to a mixture (positive electrode mixture) containing a positive electrode active material, a binder, a conductive additive, etc., and sufficiently kneading. The positive electrode mixture-containing composition is applied to one or both sides of the positive electrode current collector, and a positive electrode mixture layer having a predetermined thickness and density can be formed. However, the manufacturing method of the positive electrode according to the present invention is not limited to the above manufacturing method.

As the positive electrode active material, a lithium-containing transition metal composite oxide capable of inserting and extracting lithium ions is used. Examples of the lithium-containing transition metal composite oxide include those conventionally used in non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, specifically Li _y CoO ₂ (however, 0 ≦ y ≦ 1.1.), Li _z NiO ₂ (where 0 ≦ z ≦ 1.1), Li _e MnO ₂ (where 0 ≦ e ≦ 1.1), Li _a Co _b M ¹ _1-b O ₂ (where M ¹ is at least one metal element selected from the group consisting of Mg, Mn, Fe, Ni, Cu, Zn, Al, Ti, Ge and Cr) Yes, 0 ≦ a ≦ 1.1, 0 <b <1.0), Li _c Ni _1-d M ² _d O ₂ (where M ² is Mg, Mn, Fe, Co, Cu, At least one metal element selected from the group consisting of Zn, Al, Ti, Ge and Cr, and 0 ≦ c ≦ 1.1, 0 d <a _{_{1.0.), Li f Mn g}} Ni h Co 1-gh O 2 ( where is 0 ≦ f ≦ 1.1,0 <g < 1.0,0 <h <1.0 And lithium-containing transition metal composite oxides having a layered structure, etc., and only one of these may be used, or two or more may be used in combination.

Examples of the binder for the positive electrode material mixture layer include polysaccharides such as starch, polyvinyl alcohol, polyacrylic acid, CMC, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, and modified products thereof; polyvinyl chloride, polyvinyl pyrrolidone, polytetra Thermoplastic resins such as fluoroethylene (PTFE), PVDF, polyethylene, polypropylene, polyamideimide, polyamide and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, SBR, butadiene rubber, polybutadiene , Fluororubber, polyethylene oxide and other polymers having rubbery elasticity and their modified products, etc., and only one of them may be used or two or more may be used in combination. There.

As the conductive auxiliary agent related to the positive electrode mixture layer, the conductive auxiliary agents exemplified above as the conductive auxiliary agent related to the negative electrode mixture layer can be used.

As the positive electrode current collector, the same as those used for the positive electrode of the conventionally known non-aqueous electrolyte secondary battery can be used, and the material of the positive electrode current collector is the non-aqueous electrolysis that is configured. If it is a chemically stable electronic conductor in a liquid secondary battery, it will not be specifically limited. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among these, aluminum or an aluminum alloy is particularly preferable. This is because they are lightweight and have high electron conductivity. For the positive electrode current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above materials is used. Further, the surface of the positive electrode current collector can be roughened by surface treatment. The thickness of the positive electrode current collector is not particularly limited, but is usually 1 to 500 μm.

The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per side of the positive electrode current collector. The density of the positive electrode mixture layer is calculated from the mass and thickness of the positive electrode mixture layer per unit area laminated on the positive electrode current collector, and is preferably 3.0 to 4.5 g / cm ³ .

As the composition of the positive electrode mixture layer, for example, the amount of the positive electrode active material is preferably 60 to 98% by mass, the amount of the binder is preferably 1 to 15% by mass, and the amount of the conductive auxiliary agent is 1 It is preferably from 25% by mass.

<Non-aqueous electrolyte>
In the nonaqueous electrolyte solution according to the nonaqueous electrolyte secondary battery of the present invention, an electrolyte solution prepared by dissolving a lithium salt (inorganic lithium salt or organic lithium salt or both) in an organic solvent may be used. it can.

Examples of the organic solvent related to the non-aqueous electrolyte include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl. Ethyl carbonate (MEC), γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, acetic acid Methyl, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative Body, diethyl ether, include aprotic organic solvents such as 1,3-propane sultone, may be used those either alone, or in combination of two or more. 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.

Examples of the inorganic lithium salt for constituting the non-aqueous _{_{electrolyte, LiClO 4, LiBF 4, LiPF}} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, lower aliphatic carboxylic acid Examples thereof include Li, LiAlCl ₄ , LiCl, LiBr, LiI, chloroborane Li, and lithium tetraphenylborate, and one or more of these can be used.

Examples of the organic lithium salt for constituting the non-aqueous electrolyte include LiCF ₃ 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 (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [wherein Rf represents a fluoroalkyl group. Etc., and one or more of these can be used.

Among these non-aqueous electrolytes, a solvent containing at least one chain carbonate selected from dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, and at least one cyclic carbonate selected from ethylene carbonate and propylene carbonate, An electrolytic solution in which LiPF ₆ is dissolved is preferable.

The concentration of the lithium salt in the non-aqueous electrolyte is, for example, suitably 0.2 to 3.0 mol / L, preferably 0.8 to 2.0 mol / L, preferably 0.9 to More preferably, it is 1.6 mol / L.

In addition, for the purpose of improving charge / discharge cycle characteristics, safety such as high-temperature storage and overcharge prevention, the non-aqueous electrolyte includes, for example, acid anhydride, sulfonate ester, dinitrile, 1,3-propane. Sultone, diphenyl disulfide, cyclohexylbenzene, vinylene carbonate (VC), biphenyl, fluorobenzene, t-butylbenzene, cyclic fluorinated carbonate [trifluoropropyl carbonate (TFPC), fluoroethylene carbonate (FEC), etc.], or chain Fluorinated carbonate (such as trifluorodimethyl carbonate (TFDMC), trifluorodiethyl carbonate (TFDEC), trifluoroethylmethyl carbonate (TFEMC)), etc. (including derivatives of the above-mentioned compounds) as appropriate. Rukoto can also. The cyclic fluorinated carbonate and the chain fluorinated carbonate can also be used as a solvent, such as ethylene carbonate.

<Separator>
As the separator according to the nonaqueous electrolyte secondary battery of the present invention, it is preferable that the separator has sufficient strength and can hold a large amount of the nonaqueous electrolyte. For example, the separator has a thickness of 5 to 50 μm and an aperture ratio of 30 to 70%. A microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous membrane constituting the separator may be, for example, one using only PE or one using PP only, may contain an ethylene-propylene copolymer, and may be made of PE. A laminate of a membrane and a PP microporous membrane may be used.

Furthermore, the separator is composed of a porous layer mainly composed of a resin having a melting point of 140 ° C. or lower and a porous layer mainly including a resin having a melting point of 150 ° C. or higher or an inorganic filler having a heat resistant temperature of 150 ° C. or higher. A laminated separator can be used. Here, “melting point” means a melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of Japanese Industrial Standard (JIS) K7121, and “the heat resistant temperature is 150 ° C. or higher”. This means that deformation such as softening is not observed at least at 150 ° C.

The thickness of the separator (a separator made of a microporous membrane made of polyolefin or the laminated separator) is more preferably 10 to 30 μm.

<Battery configuration>
There is no restriction | limiting in particular as a form of the nonaqueous electrolyte secondary battery of this invention. For example, any of a coin shape, a button shape, a sheet shape, a laminated shape, a cylindrical shape, a flat shape, a square shape, a large size used for an electric vehicle, etc. may be used.

Further, when introducing the positive electrode, the negative electrode, and the separator into the non-aqueous electrolyte secondary battery, depending on the form of the battery, a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are stacked via the separator, It can be used as a wound electrode body obtained by laminating a negative electrode with a separator and winding it in a spiral shape.

Since the non-aqueous electrolyte secondary battery of the present invention has a high capacity and excellent battery characteristics, taking advantage of these characteristics, including power supplies for small and multifunctional portable devices, It can be preferably used for various applications to which conventionally known nonaqueous 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.

(Example 1)
<Preparation of positive electrode>
LiCoO _{2 as a} positive electrode active material: 93 parts by mass, carbon black as a conductive additive: 3 parts by mass, and PVDF as a binder: 4 parts by mass are mixed uniformly using NMP as a solvent. A positive electrode mixture-containing slurry was prepared. The positive electrode mixture-containing slurry is applied to one side of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried, and then subjected to pressure molding with a roller press, whereby the thickness of one side of the positive electrode current collector is increased. A 70 μm positive electrode mixture layer was formed. Then, this was cut | disconnected to 25 mm x 35 mm, and the strip-shaped positive electrode was obtained.

<Production of negative electrode>
As a negative electrode active material, the mass ratio of SiO (a material in which Si is dispersed in an amorphous SiO ₂ matrix and the molar ratio of SiO ₂ and Si is 1: 1) and graphite is 1: 4. A mixture containing was prepared. This negative electrode active material, carbon black as a conductive additive, and a fluorinated elastic copolymer of TFE / P = 56/44 (molar ratio) obtained by emulsion polymerization (fluorine content 57 mass%, Mooney viscosity 90 ) And an aqueous dispersion of CMC that is a water-soluble adhesive resin (CMC concentration is 2% by mass) to prepare a negative electrode mixture-containing slurry. In this negative electrode mixture-containing slurry, the ratio (mass ratio) of the negative electrode active material, carbon black, fluorinated elastic copolymer, and CMC is 94: 1.5: 1.5: 3. I made it. Here, the mass ratio M ₂ / M ₁ of the mass M ₂ of the fluorinated elastic copolymer to the mass M ₁ of the water-soluble adhesive resin (CMC) was 0.5.

The negative electrode mixture-containing slurry is applied to one side of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried, and then press-molded with a roller press to obtain a thickness on one side of the negative electrode current collector. Formed a negative electrode mixture layer having a thickness of 50 μm. Then, this was cut | disconnected to 30 mm x 35 mm, and the strip-shaped negative electrode was obtained.

<Battery assembly>
The positive electrode and the negative electrode were overlapped with a PE microporous membrane separator (thickness 25 μm, porosity 45%) to form a laminated electrode body. This laminated electrode body was inserted into an exterior body made of a 10 cm × 20 cm aluminum laminate film. Next, after dissolving LiPF ₆ at a concentration of 1 mol / L in a solution in which EC, DEC and MEC are mixed at a volume ratio of 1: 1: 1, VC is further dissolved in an amount of 1% by mass. The prepared nonaqueous electrolyte solution: 1 g was injected into the exterior body. Then, the opening part of the exterior body was sealed and the nonaqueous electrolyte secondary battery of the cross-sectional structure shown in FIG. 2 was produced with the external appearance shown in FIG.

Here, FIG. 1 and FIG. 2 will be described. FIG. 1 is a plan view schematically showing the nonaqueous electrolyte secondary battery of this example, and FIG. 2 is a cross-sectional view taken along the line II of FIG. It is. In FIG. 2, a nonaqueous electrolyte secondary battery 1 includes a laminated electrode body constituted by laminating a positive electrode 5 and a negative electrode 6 with a separator 7 in an exterior body 2 constituted by two laminated films, A non-aqueous electrolyte solution (not shown) is accommodated, and the outer package 2 is sealed at its outer peripheral portion by thermally fusing upper and lower laminate films. In FIG. 2, the thickness of the nonaqueous electrolyte secondary battery 1 is indicated as T. In FIG. 2, in order to avoid making the drawing complicated, the layers of the laminate film constituting the exterior body 2, and the electrode mixture layer and the current collector constituting the positive electrode 5 and the negative electrode 6 are distinguished. Not shown.

The positive electrode 5 is connected to the positive electrode external terminal 3 through a lead body in the non-aqueous electrolyte secondary battery 1, and the negative electrode 6 is also connected to the non-aqueous electrolyte secondary battery 1, although not shown. And connected to the negative external terminal 4 (FIG. 1) through the lead body. As shown in FIG. 1, the positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn out to the outside of the exterior body 2 so that they can be connected to an external device or the like.

(Example 2)
In a boiling bed reactor, SiO gas (average particle diameter 5 μm) heated to about 1000 ° C. is brought into contact with a mixed gas of 25 ° C. composed of methane and nitrogen gas, and low crystalline carbon is formed on the surface by vapor phase growth. SiOC particles (composite of SiO and carbon material) on which a coating layer was formed were prepared. The ratio of the carbon material in this composite was 20 parts by mass with respect to 100 parts by mass of SiO. The composite of SiO and carbon material and graphite were mixed at a mass ratio of 1: 4, and a negative electrode was produced in the same manner as in Example 1 except that this mixture was used as a negative electrode active material. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that.

(Example 3)
Instead of the fluorinated elastic copolymer of Example 1 (Mooney viscosity 90), the fluorinated elastic copolymer of TFE / P = 56/44 (molar ratio) obtained by emulsion polymerization (fluorine content 57 mass%). A negative electrode was prepared in the same manner as in Example 1 except that an aqueous dispersion containing a Mooney viscosity of 130) at a content of 32% by mass was used. An electrolyte secondary battery was produced.

Example 4
The ratio (mass ratio) of the negative electrode active material, carbon black, fluorinated elastic copolymer, and CMC was 93.5: 1.5: 2: 2.5, and the mass M _{1 of the} water-soluble adhesive resin. A negative electrode was prepared in the same manner as in Example 1 except that the mass ratio M ₂ / M ₁ of the mass M ₂ of the fluorine-containing elastic copolymer to 0.8 was changed to 0.8, and Example 1 except that this negative electrode was used. Similarly, a non-aqueous electrolyte secondary battery was produced.

(Example 5)
The ratio (mass ratio) of the negative electrode active material, carbon black, fluorinated elastic copolymer, and CMC was 94: 1.5: 2.5: 2, and the content of the water-soluble adhesive resin with respect to the mass M ₁ was included. A negative electrode was prepared in the same manner as in Example 1 except that the mass ratio M ₂ / M ₁ of the mass M ₂ of the fluoroelastic copolymer was changed to 1.25, and in the same manner as in Example 1 except that this negative electrode was used. Thus, a non-aqueous electrolyte secondary battery was produced.

(Example 6)
The ratio (mass ratio) of the negative electrode active material, carbon black, fluorinated elastic copolymer, and CMC was 93.5: 1.5: 1.05: 3.45, and the mass of the water-soluble adhesive resin except that the mass ratio M ₂ / M ₁ 0.3 mass M ₂ of the fluorinated elastic copolymer for the M ₁ in the same manner as in example 1 to prepare a negative electrode, the embodiment except for the use of this negative electrode In the same manner as in Example 1, a nonaqueous electrolyte secondary battery was produced.

(Example 7)
A negative electrode was produced in the same manner as in Example 1 except that polyacrylic acid (PAA) was used in place of CMC, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used. did.

(Comparative Example 1)
A negative electrode was produced in the same manner as in Example 1 except that SBR was used instead of the aqueous dispersion of the fluorinated elastic copolymer of Example 1, and the same procedure as in Example 1 was conducted except that this negative electrode was used. 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 an aqueous dispersion of PTFE (fluorine content: 76%) was used instead of the aqueous dispersion of the fluorinated elastic copolymer of Example 1. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that it was used.

(Comparative Example 3)
The ratio (mass ratio) of the negative electrode active material, carbon black, fluorinated elastic copolymer, and CMC was 93.5: 1.5: 0.33: 4.17, and the mass of the water-soluble adhesive resin except that the mass ratio M ₂ / M ₁ 0.08 mass M ₂ of the fluorinated elastic copolymer for the M ₁ in the same manner as in example 1 to prepare a negative electrode, the embodiment except for the use of this negative electrode In the same manner as in Example 1, a nonaqueous electrolyte secondary battery was produced.

(Comparative Example 4)
The ratio (mass ratio) of the negative electrode active material, carbon black, fluorinated elastic copolymer, and CMC was 93.5: 1.5: 3.5: 1.0, and the mass of the water-soluble adhesive resin except that the mass ratio M ₂ / M ₁ of the mass M ₂ of the fluorinated elastic copolymer 3.5 for M ₁ in the same manner as in example 1 to prepare a negative electrode, the embodiment except for the use of this negative electrode In the same manner as in Example 1, a nonaqueous electrolyte secondary battery was produced.

For the nonaqueous electrolyte secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4, the following charge / discharge cycle characteristic evaluation, load characteristic evaluation, and battery swelling evaluation during high-temperature storage were performed.

<Charge / discharge cycle characteristics evaluation>
About each battery of an Example and a comparative example, it charges to voltage 4.2V with the constant current of 10 mA of electric current, and is charged with the constant voltage of 4.2V subsequently, constant current-constant voltage charge (total time of charge: 5 hours) Then, a charge / discharge cycle in which a constant current was discharged to 2.5 V at a constant current of 10 mA was repeated 500 times at a temperature of 20 ° C. Then, the discharge capacity at the first cycle, the discharge capacity at the 100th cycle, and the discharge capacity at the 500th cycle are measured, and the capacity retention rate after 100 cycles and The capacity maintenance rate was obtained.

Formula (1): Capacity retention rate after 100 cycles (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100
Formula (2): Capacity maintenance ratio (%) after 500 cycles = (discharge capacity at 500th cycle / discharge capacity at the first cycle) × 100

<Evaluation of load characteristics>
About each battery which measured the said capacity maintenance rate, a charging / discharging cycle is further repeated on the same conditions as the time of the said charging / discharging cycle characteristic evaluation, but discharge is a constant current of 20 mA about the 1st cycle and the 100th cycle. Then, the battery was discharged at a constant current up to 2.5 V, and the discharge capacity at the first cycle and the discharge capacity at the 100th cycle (discharge capacity at 20 mA discharge) were measured. And using this measurement result and the value of the discharge capacity (discharge capacity at the time of 10 mA discharge) of the 1st cycle and the 100th cycle measured in the above-mentioned charge / discharge cycle characteristic evaluation, the following formulas (3) and (4) ) To determine the initial load characteristics and the load characteristics after 100 cycles.

Formula (3): Initial load characteristic (%) = (discharge capacity at 20 mA discharge in the first cycle / discharge capacity at 10 mA discharge in the first cycle) × 100
Formula (4): Load characteristics after 100 cycles (%) = (discharge capacity at 20 mA discharge at 100th cycle / discharge capacity at 10 mA discharge at 100th cycle) × 100

<Battery expansion evaluation during high temperature storage>
For each battery in Examples and Comparative Examples (using a battery different from the battery evaluated above), the charge / discharge cycle is repeated under the same conditions as in the charge / discharge cycle characteristics evaluation. After completion of charging, the battery was stored in a high-temperature bath at 85 ° C. in an air atmosphere for 24 hours, the thickness T (FIG. 2) of the battery before and after storage was measured, and the difference Δt (mm) between the battery thickness T before and after storage was determined. . Normally, when the battery is stored at such a high temperature in a charged state, a reaction occurs between Li in the active material and the electrolytic solution in the negative electrode, and gas is generated and the battery swells. Δt represents an increase in battery thickness.

Table 1 shows the main configurations of the batteries of the examples and comparative examples. Table 2 shows the evaluation results.

As shown in Table 1 and Table 2, the binder according to the negative electrode mixture layer contains at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride. A fluorine-containing elastic copolymer having a structural unit based on a body and a water-soluble adhesive resin, and a mass ratio M ₂ of a mass M ₂ of the fluorine-containing elastic copolymer to a mass M ₁ of the water-soluble adhesive resin The non-aqueous electrolyte secondary batteries of Examples 1 to 7 with / M ₁ being an appropriate value have good load characteristics at the initial stage and after 100 cycles, and the capacity retention ratio after 100 cycles and after 500 cycles is good. The charge / discharge cycle characteristics were high and the battery thickness increase Δt after storage at 85 ° C. was all 0.1 mm or less.

In contrast, the batteries of Comparative Examples 1 and 2 using SBR or PTFE as the binder for the negative electrode mixture layer have good initial load characteristics as in the batteries of Examples 1 to 7, but after 100 cycles. The load characteristics are deteriorated and the charge / discharge cycle characteristics are also inferior. Further, in the battery of Comparative Example 3 in which the mass ratio M ₂ / M ₁ of the mass M ₂ of the fluorinated elastic copolymer to the mass M ₁ of the water-soluble adhesive resin was too small, the load characteristics were significantly reduced. On the other hand, in the battery of Comparative Example 4 in which the mass ratio M ₂ / M ₁ is too large, the initial load characteristics are as high as those of the batteries of Examples 1 to 7, but the capacity retention rate decreases after 100 cycles and the load characteristics are reduced. Also declined.

Further, the battery thickness increase Δt after storage at 85 ° C. was 0.2 mm or more in the batteries of Comparative Examples 1 and 3. When the scanning electron microscope (SEM) observation is performed on each negative electrode before battery assembly for each of the batteries in Examples and Comparative Examples, for example, in the negative electrode of Comparative Example 1, the SBR used was CMC that is a water-soluble adhesive resin. It was found that the TFE / P used in Examples 1 to 7 and the PTFE used in Comparative Example 2 were present separately from CMC, while they existed in a spherical shape inside. That is, in the batteries of Examples 1 to 7 and Comparative Example 2, TFE / P and PTFE surely covered the surface of the negative electrode active material without being obstructed by CMC, and as a result, Li in the active material and the electrolyte solution It is considered that the generation of gas is reduced by suppressing the reaction with and the increase amount Δt of the battery thickness is reduced.

The present invention can be implemented in forms other than those described above without departing from the spirit of the present invention. The embodiments disclosed in the present application are merely examples, and the present invention is not limited thereto. The scope of the present invention is construed in preference to the description of the appended claims rather than the description of the above specification, and all modifications within the scope equivalent to the claims are construed in the scope of the claims. It is included.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Exterior body 3 Positive electrode external terminal 4 Negative electrode external terminal 5 Positive electrode 6 Negative electrode 7 Separator

Claims

A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator,
The positive electrode includes a positive electrode mixture layer containing a lithium-containing transition metal composite oxide,
The negative electrode includes a negative electrode mixture layer including a graphitic carbon material, a material containing an element alloyed with lithium, and a binder.
The binder includes a fluorinated elastic copolymer having a structural unit based on two or more monomers including at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride; , Including water-soluble adhesive resin
When the mass of the water-soluble adhesive resin contained in the negative electrode mixture layer is M 1 and the mass of the fluorinated elastic copolymer contained in the negative electrode mixture layer is M 2 , the mass ratio M 2 / M 1 is A non-aqueous electrolyte secondary battery characterized by being 0.1 or more and 2 or less.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the water-soluble adhesive resin is a cellulose.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the fluorinated elastic copolymer contains a structural unit based on propylene.
The material containing an element that forms an alloy with lithium is a material represented by a general formula SiO x , and an atomic ratio x of O to Si in the general formula is 0.5 ≦ x ≦ 1.5. The nonaqueous electrolyte secondary battery as described.
The nonaqueous electrolyte secondary battery according to claim 4, wherein a surface of the material represented by the general formula SiO x is coated with a carbon material.