WO2018117087A1 - Negative electrode for lithium-ion battery, and lithium-ion battery - Google Patents

Abstract

[Problem] To provide a negative electrode for a lithium-ion battery with excellent energy density and cycle characteristics. [Solution] This negative electrode for a lithium-ion battery has a negative electrode active substance layer, and is characterized in that the negative electrode active substance layer comprises the non-bonded body of a mixture of a pressure relieving material, a carbon-based negative electrode active substance, and silicon and/or a silicon compound, and the pressure relieving material is an aggregate of a conductive carbon filler.

Description

Negative electrode for lithium ion battery and lithium ion battery

The present invention relates to a negative electrode for a lithium ion battery and a lithium ion battery.

In recent years, reduction of carbon dioxide emissions has been strongly desired for environmental protection. In the automobile industry, there are high expectations for reducing carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and we are eager to develop secondary batteries for motor drives that hold the key to their practical application. Has been done. As a secondary battery, attention is focused on a lithium ion battery that can achieve a high energy density and a high output density.

In order to increase the energy density of a lithium ion battery, a silicon-based material having a larger theoretical capacity than a carbon material conventionally used as a negative electrode active material has attracted attention. However, when a silicon-based material is used as the negative electrode active material, the volume change of the material accompanying charge / discharge is large. For this reason, the silicon-based material is self-destructed by volume change or is easily peeled off from the current collector surface, so that it is difficult to improve cycle characteristics.

For example, Japanese Unexamined Patent Application Publication No. 2016-103337 discloses a lithium ion in which expansion of a negative electrode is suppressed by adjusting a mixing ratio of at least one of silicon and a silicon compound and carbon and a particle diameter thereof to a predetermined range. A battery is disclosed.

However, since the negative electrode described in Japanese Patent Application Laid-Open No. 2016-103337 uses a binder, if the electrode thickness is too thick, the negative electrode active material is peeled off from the surface of the negative electrode current collector. was there. In addition, the binder may restrict the expansion and contraction of silicon and the silicon compound, and may easily break. Furthermore, the effect of suppressing the expansion of the negative electrode is not sufficient, and there is room for further improvement.

The present invention has been made in view of the above problems, and an object thereof is to provide a negative electrode for a lithium ion battery excellent in energy density and cycle characteristics.

The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve the above problems.

That is, the present invention is a negative electrode for a lithium ion battery having a negative electrode active material layer, wherein the negative electrode active material layer is a non-binding mixture of silicon and / or a silicon compound, a carbon-based negative electrode active material, and a pressure relaxation material. A negative electrode for a lithium ion battery, wherein the pressure relaxation material is an aggregate of conductive carbon filler; and a lithium ion battery including the negative electrode.

1 (a) and 1 (b) are cross-sectional views schematically showing the state of the negative electrode active material layer constituting the negative electrode for a lithium ion battery of the present invention before and after charging.

Hereinafter, the present invention will be described in detail.

The negative electrode for a lithium ion battery of the present invention is a negative electrode for a lithium ion battery having a negative electrode active material layer, and the negative electrode active material layer comprises silicon and / or a silicon compound, a carbon-based negative electrode active material, and a pressure relaxation material. It consists of the non-binding body of a mixture, The said pressure relaxation material is an aggregate of an electroconductive carbon filler, It is characterized by the above-mentioned. The negative electrode for a lithium ion battery of the present invention having such a configuration is excellent in energy density and cycle characteristics.

The negative electrode active material layer constituting the negative electrode for a lithium ion battery of the present invention contains an aggregate of conductive carbon filler as a pressure relaxation material. Since the aggregate of the conductive carbon filler has innumerable spaces between the conductive carbon fillers, it can be deformed and contracted according to the pressure from the outside. Therefore, when the silicon and / or silicon compound in the negative electrode active material layer expands due to charging, the volume change of the negative electrode as a whole can be suppressed by contracting the pressure relaxation material. On the other hand, when silicon and / or silicon compound contracts due to discharge, the volume of the negative electrode as a whole can be suppressed by expanding the pressure relaxation material. Therefore, peeling of the negative electrode active material layer can be suppressed by suppressing expansion / contraction of the negative electrode accompanying charge / discharge, and cycle characteristics can be improved.

Furthermore, in the negative electrode for a lithium ion battery of the present invention, the negative electrode active material layer is a non-binding body of a mixture comprising silicon and / or a silicon compound, a carbon-based negative electrode active material, and a pressure relaxation material. The non-binding body means that silicon and / or silicon compound, carbon-based negative electrode active material and pressure relaxation material constituting the negative electrode active material layer are not fixed to each other by a binder (also called a binder). means.

A negative electrode active material layer in a conventional lithium ion battery is manufactured by applying a slurry in which a negative electrode active material and a binder are dispersed in a solvent to the surface of a negative electrode current collector, etc., and heating and drying. The negative electrode active material layer is in a state of being hardened with a binder. At this time, the negative electrode active materials are fixed to each other by the binder, and the positions of the negative electrode active materials are fixed. When the negative electrode active material layer is hardened with a binder, excessive stress is applied to silicon and / or silicon compounds due to expansion / contraction during charge / discharge, and the self-destruction is likely to occur.

Further, since the negative electrode active material layer is fixed to the surface of the negative electrode current collector by the binder, the negative electrode active material layer solidified by the binder by expansion and contraction during charging and discharging of silicon and / or silicon compound May be cracked, or the negative electrode active material layer may be peeled off from the surface of the negative electrode current collector.

On the other hand, in the negative electrode active material layer constituting the negative electrode for a lithium ion battery of the present invention, the components (silicon and / or silicon compound, carbon-based negative electrode active material and pressure relaxation material) in the negative electrode active material are bound to each other. The position is not fixed. Therefore, self-destruction caused by expansion / contraction during charging / discharging of silicon and / or silicon compound can be suppressed. Furthermore, since the negative electrode active material layer constituting the negative electrode for a lithium ion battery of the present invention is not fixed to the negative electrode current collector surface by a binder, expansion during charging and discharging of silicon and / or silicon compounds -The negative electrode active material layer does not crack or peel off due to shrinkage. Therefore, deterioration of cycle characteristics can be suppressed.

Therefore, the negative electrode for a lithium ion battery of the present invention is excellent in energy density and cycle characteristics.

Hereinafter, the configuration of the negative electrode for a lithium ion battery of the present invention will be described.

The negative electrode active material layer constituting the negative electrode for a lithium ion battery of the present invention is a non-binding body of a mixture comprising silicon and / or a silicon compound, a carbon-based negative electrode active material, and a pressure relaxation material.

Since the negative electrode active material layer contains silicon and / or silicon compound, the energy density is excellent. Furthermore, since the pressure relaxation material is included, expansion of the negative electrode active material layer due to expansion / contraction during charging / discharging of silicon and / or silicon compound can be suppressed. In addition, since the negative electrode active material layer is a non-binding body that does not contain a binder, silicon and / or silicon compounds are less likely to self-destruct due to expansion / contraction during charge / discharge, and the negative electrode active material layer is collected. It is possible to suppress an increase in internal resistance due to peeling from the surface of the electric body or generation of cracks.

The reason why the negative electrode for a lithium ion battery of the present invention can suppress the expansion of the negative electrode will be described with reference to FIGS. 1 (a) and 1 (b).

1 (a) and 1 (b) are cross-sectional views schematically showing the state of the negative electrode active material layer constituting the negative electrode for a lithium ion battery of the present invention before and after charging. FIG. 1A schematically shows a state before charging, and FIG. 1B schematically shows a state after charging.

As shown in FIG. 1 (a) and FIG. 1 (b), the negative electrode active material layer 1 constituting the negative electrode for a lithium ion battery of the present invention comprises silicon and / or silicon compound 11, carbon-based negative electrode active material 13 and pressure. It consists of the relaxation material 15, and the volume of silicon and / or the silicon compound 11 expands by charging. However, innumerable pressure relaxation materials 15 exist around the silicon and / or the silicon compound 11. Since the pressure relaxation material 15 is an aggregate of conductive carbon filler, it can be deformed (shrink) flexibly with respect to stress, and the volume expansion of silicon and / or silicon compound 11 causes the pressure relaxation material 15 to shrink. Is offset by Therefore, volume expansion as the whole negative electrode active material layer can be suppressed.

The pressure relaxation material is composed of an aggregate of conductive carbon filler. The bulk density of the conductive carbon filler constituting the aggregate is not particularly limited, but is 0.01 to 0.7 g / cm ³ from the viewpoint of absorbing the volume expansion during charging of silicon and / or silicon compound. Is preferred. The bulk density of the conductive carbon filler is measured according to JIS K5101-12-1 Pigment test method-Part 12: Apparent density or apparent specific volume-Section 1: Standing method.

The electrical resistivity of the conductive carbon filler is not particularly limited, but from the viewpoint of conductivity, it is preferably 60 μΩm or less, more preferably 50 μΩm or less, further preferably 40 μΩm or less, and more preferably 30 μΩm or less. It is particularly preferred.

Examples of the conductive carbon filler include carbon [graphite and carbon black (acetylene black, ketjen black (registered trademark), furnace black, channel black, thermal lamp black, etc.]), PAN-based carbon fiber, and pitch-based carbon fiber. Carbon fibers, carbon nanofibers and carbon nanotubes.

Among these, at least one selected from the group consisting of carbon fiber, carbon nanofiber, and carbon nanotube is more preferable from the viewpoint of absorbing volume expansion during charging of silicon and / or silicon compound and from the viewpoint of conductivity. preferable.

The aspect ratio of the conductive carbon filler is not particularly limited as long as it is 1 or more, but is preferably 20 to 10,000 from the viewpoint of absorbing volume expansion during charging of silicon and / or silicon compounds. The aspect ratio of the conductive carbon filler can be measured by observing the conductive carbon filler with a scanning electron microscope (hereinafter also referred to as SEM).

The aggregate of conductive carbon filler (hereinafter also referred to as aggregate) is a collection of conductive carbon fillers in a lump shape having a diameter of 1 μm or more. The size of the aggregate of the conductive carbon filler is more preferably 1.5 to 50 μm in diameter, and further preferably 5 to 50 μm in diameter. When the size of the aggregate is within the above range, the pressure relaxation performance is further improved, which is preferable.

Whether the aggregate of the conductive carbon filler is present in the negative electrode active material layer can be confirmed by observing the cross section of the negative electrode active material layer with an SEM. The diameter of the aggregate is the diameter of the circumscribed circle of the aggregate. Moreover, let the average diameter of an aggregate be the average of the diameter of the circumscribed circle of 50 aggregates extracted at random from the enlarged observation image of the cross section of a negative electrode active material layer.

The weight of the aggregate of conductive carbon filler (preferably an aggregate composed of conductive carbon filler having an aspect ratio of 1 or more, preferably 20 to 10,000) relative to the weight of the negative electrode active material layer. The ratio is preferably 3 to 30% by mass, more preferably 3 to 25% by mass, still more preferably 3 to 20% by mass, and particularly preferably 3 to 15% by mass. The content is preferably 3 to 10% by mass.

It is preferable that the above ratio is in this range in that the expansion and contraction of silicon and / or silicon compounds during charging / discharging can be sufficiently absorbed, and the amount of pressure relaxation material does not increase, so that the energy density can be further increased. Furthermore, it is preferable in that the cycle durability can be increased.

The mass mixing ratio of the total of silicon and silicon compounds contained in the mixture constituting the negative electrode active material layer and the carbon-based negative electrode active material is preferably 5:95 to 95: 5 from the viewpoint of capacity retention ratio and the like. The ratio is more preferably 5:95 to 50:50, and further preferably 5:95 to 35:65.

When the mass mixing ratio is in the above range, the effect of improving the energy density by silicon and / or silicon compound is sufficient. Moreover, the volume expansion at the time of charge of a negative electrode active material layer does not become large too much.

In addition, when the carbon-based negative electrode active material is a carbon-based coated negative electrode active material described later, the mass of the negative electrode coating layer constituting the carbon-based coated negative electrode active material is not taken into account when calculating the mass mixing ratio.

The thickness of the negative electrode active material layer is not particularly limited, but is preferably 100 to 2500 μm, more preferably 150 to 2000 μm, and more preferably 200 to 1000 μm from the viewpoint of achieving both energy density and input / output characteristics. More preferably it is.

Note that the thickness of the negative electrode active material layer is determined before the negative electrode active material layer is charged or when the negative electrode active material layer is discharged to the value of the electrode potential +0.05 V (vs. Li ^/ Li ⁺ ) or less. Of thickness.

Silicon may be crystalline silicon, amorphous silicon, or a mixture thereof.

Examples of the silicon compound include silicon oxide (SiO _x ), carbon-coated silicon oxide (see “Preparation of carbon-coated silicon oxide particles” in Example 4), Si—C composite, Si—Al alloy, It is preferably at least one selected from the group consisting of Si—Li alloy, Si—Ni alloy, Si—Fe alloy, Si—Ti alloy, Si—Mn alloy, Si—Cu alloy and Si—Sn alloy.

Examples of the Si—C composite include silicon carbide, a carbon particle whose surface is covered with silicon and / or silicon carbide, and a silicon particle whose surface is covered with carbon and / or silicon carbide. In the case where the surface of the carbon particle is coated with silicon and / or silicon carbide or the surface of the silicon particle is coated with carbon and / or silicon carbide, the polymer compound may be used in combination. For example, the silicon particles whose surface is coated with carbon include silicon compound particles formed by forming a coating layer containing a polymer compound and carbon (conductive material; conductive agent) on the surface of the silicon particles. The polymer compound and the coating layer are the same as those described in the following “Carbon-based coated negative electrode active material” section.

Even if silicon and / or silicon compound particles are single particles (also referred to as primary particles), composite particles obtained by agglomeration of primary particles (that is, primary particles composed of silicon and / or silicon compounds) May form secondary particles) obtained by agglomeration. The composite particles may be agglomerated when primary particles of silicon and / or silicon compound particles are agglomerated by the adsorption force, or may be agglomerated by binding of primary particles via another material. As a method of forming composite particles by binding secondary particles through other materials, for example, primary particles of silicon and / or silicon compound particles and a polymer compound (coating resin) described later are mixed. A method is mentioned. Specifically, composite particles (secondary particles) in which silicon compound particles (primary particles) in which a coating layer containing a polymer compound (coating resin) and carbon (conductive material; conductive agent) is formed on the surface of silicon particles are aggregated (See “Production of Silicon Composite Particles” in Example 9).

The volume average particle diameter of silicon and silicon compound is not particularly limited, but is preferably 0.1 to 30 μm from the viewpoint of durability. In particular, when composite particles are formed, the primary particle diameter is preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm, and more preferably 0.1 to 2 μm. Further preferred. When composite particles are formed, the secondary particle diameter is preferably 10 to 30 μm. The volume average particle diameter of the silicon and / or silicon compound particles is measured by the following method. When the composite particles are formed, the secondary particle diameter of the composite particles is obtained as the volume average particle diameter.

Examples of the carbon-based negative electrode active material include carbon-based materials [for example, graphite, non-graphitizable carbon, amorphous carbon, resin fired bodies (for example, those obtained by firing and carbonizing phenol resin, furan resin, etc.), cokes (for example, pitch) Coke, needle coke, petroleum coke, etc.)], or conductive polymers (such as polyacetylene and polypyrrole), metal oxides (titanium oxide and lithium / titanium oxide), and metal alloys (lithium-tin alloys, lithium- A mixture of an aluminum alloy, an aluminum-manganese alloy, etc.) with a carbon-based material. Among the above carbon-based negative electrode active materials, those that do not contain lithium or lithium ions may be subjected to a pre-doping treatment in which some or all of the inside contains lithium or lithium ions.

The volume average particle size of the carbon-based negative electrode active material is preferably 0.01 to 50 μm, more preferably 0.1 to 25 μm, more preferably 15 to 20 μm, from the viewpoint of the electrical characteristics of the negative electrode for a lithium ion battery. More preferably.

In this specification, the volume average particle size of silicon, silicon compound and carbon-based negative electrode active material is the particle size (Dv50) at an integrated value of 50% in the particle size distribution determined by the microtrack method (laser diffraction / scattering method). means. The microtrack method is a method for obtaining a particle size distribution using scattered light obtained by irradiating particles with laser light. In addition, the Nikkiso Co., Ltd. microtrack etc. can be used for the measurement of a volume average particle diameter.

Further, when silicon and a silicon compound form composite particles, the primary particle diameter is within several to several tens of fields using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the particle diameters of the observed particles is adopted.

When the negative electrode active material layer contains silicon and / or a silicon compound and a carbon-based negative electrode active material, particles composed of silicon and / or a silicon compound and particles composed of a carbon-based negative electrode active material may be mixed and used. Granulated particles containing both silicon and / or a silicon compound and a carbon-based negative electrode active material may be used. When using granulated particles containing both silicon and / or a silicon compound and a carbon-based negative electrode active material, the silicon and / or silicon compound is fixed to the surface of the carbon-based negative electrode active material via a negative electrode coating layer described later. Granulated particles may be used.

The carbon-based negative electrode active material may be the carbon-based negative electrode active material itself, and a carbon-based coating in which a part or all of the surface of the carbon-based negative electrode active material is coated with a negative electrode coating layer containing a polymer compound. Although it may be a negative electrode active material, it is preferably a carbon-based coated negative electrode active material.

The negative electrode coating layer includes a polymer compound, and may further include a conductive material as necessary.

The carbon-based negative electrode active material is a part of or the entire surface of the carbon-based negative electrode active material covered with a negative electrode coating layer containing a polymer compound. In the negative electrode active material layer, Even if the carbon-based coated negative electrode active materials are in contact with each other, the negative electrode coating layers are not irreversibly bonded on the contact surface, and the bonding is temporary and can be easily loosened by hand. Therefore, the carbon-based coated negative electrode active materials are not fixed by the negative electrode coating layer. Therefore, the negative electrode active material layer containing the carbon-based coated negative electrode active material does not have the carbon-based negative electrode active materials bound to each other.

Note that whether or not the negative electrode active material layer contains a binder can be confirmed by observing whether or not the negative electrode active material layer collapses when the negative electrode active material layer is completely impregnated in the electrolytic solution. When the negative electrode active material layer is a binder containing a binder, the shape can be maintained for one minute or longer, but when the negative electrode active material layer is a non-binder containing no binder The shape collapses in less than a minute.

The binder contained in the negative electrode active material layer in the conventional lithium ion battery also includes high molecular compounds such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, and styrene-butadiene rubber. The binder is used by being dissolved or dispersed in water or an organic solvent, and is dried and solidified by volatilizing the solvent component (or dispersion medium component) to form the negative electrode active material particles and the negative electrode active material particles and the current collector. Are firmly fixed to form a negative electrode active material layer. On the other hand, the negative electrode coating layer covers part or all of the surface of the carbon-based negative electrode active material. Even if the carbon-based coated negative electrode active materials are in contact with each other in the negative electrode active material layer, the negative electrode coating layer is coated on the contact surface. The layers are not firmly bonded and fixed, and the negative electrode coating layer and the binder are different members.

Examples of the polymer compound constituting the negative electrode coating layer include thermoplastic resins and thermosetting resins. For example, fluororesins, acrylic resins, urethane resins, polyester resins, polyether resins, polyamide resins, epoxy resins, polyimides Examples thereof include resins, silicone resins, phenol resins, melamine resins, urea resins, aniline resins, ionomer resins, polycarbonates, polysaccharides (such as sodium alginate), and mixtures thereof. Among these, acrylic resins, urethane resins, polyester resins or polyamide resins are preferable, and acrylic resins are more preferable.

Among these, a polymer compound having a liquid absorption rate of 10% or more when immersed in an electrolytic solution and a tensile elongation at break in a saturated liquid absorption state of 10% or more is more preferable.

The liquid absorption rate when immersed in the electrolytic solution is obtained by the following formula by measuring the weight of the polymer compound before the immersion in the electrolytic solution and after the immersion.

As an electrolytic solution for obtaining the liquid absorption rate, preferably EC ethylene carbonate (EC), propylene carbonate (PC) at a volume ratio: PC = 1: a solvent mixture at 1, the LiPF ₆ as an electrolyte 1mol / An electrolytic solution dissolved to a concentration of L is used.

Immersing in the electrolyte when determining the liquid absorption rate is performed at 50 ° C. for 3 days. By immersing at 50 ° C. for 3 days, the polymer compound becomes saturated. The saturated liquid absorption state refers to a state in which the weight of the polymer compound does not increase even when immersed in the electrolytic solution.

In addition, the electrolyte solution used when manufacturing a lithium ion battery using the negative electrode for lithium ion batteries of this invention is not limited to the said electrolyte solution, You may use another electrolyte solution.

When the liquid absorption is 10% or more, lithium ions can easily permeate the polymer compound, so that the ionic resistance in the negative electrode active material layer can be kept low. *

The liquid absorption rate is more preferably 20% or more, and further preferably 30% or more.

Further, a preferable upper limit value of the liquid absorption is 400%, and a more preferable upper limit value is 300%.

The tensile elongation at break in the saturated liquid absorption state was determined by punching the polymer compound into a dumbbell shape and immersing it in an electrolytic solution at 50 ° C. for 3 days in the same manner as the measurement of the liquid absorption rate. The state can be measured according to ASTM D683 (test piece shape Type II). The tensile elongation at break is a value obtained by calculating the elongation until the test piece breaks in the tensile test according to the following formula.

When the tensile elongation at break in the saturated liquid absorption state of the polymer compound is 10% or more, the polymer compound has appropriate flexibility, so that the negative electrode coating layer is peeled off due to the volume change of the negative electrode active material during charge / discharge It becomes easy to suppress.

The tensile elongation at break is more preferably 20% or more, and further preferably 30% or more.

The preferable upper limit value of the tensile elongation at break is 400%, and the more preferable upper limit value is 300%.

The acrylic resin is preferably a resin comprising a polymer (A1) having an acrylic monomer (a) as an essential constituent monomer.

The polymer (A1) is a monomer composition comprising a monomer (a1) having a carboxyl group or an acid anhydride group as the acrylic monomer (a) and a monomer (a2) represented by the following general formula (1). A polymer is preferred.

[In the formula (1), R ¹ represents a hydrogen atom or a methyl group, and R ² represents a straight chain having 4 to 12 carbon atoms or a branched alkyl group having 3 to 36 carbon atoms. ].

Monomers (a1) having a carboxyl group or an acid anhydride group include (meth) acrylic acid (a11), monocarboxylic acids having 3 to 15 carbon atoms such as crotonic acid and cinnamic acid; (anhydrous) maleic acid and fumaric acid Dicarboxylic acids having 4 to 24 carbon atoms such as itaconic acid, citraconic acid and mesaconic acid; polycarboxylic acids having a valence of 6 to 24 carbon atoms such as aconitic acid and the like. Can be mentioned. Among these, (meth) acrylic acid (a11) is preferable, and methacrylic acid is more preferable.

In the monomer (a2) represented by the general formula (1), R ¹ represents a hydrogen atom or a methyl group. R ¹ is preferably a methyl group.

R ² is preferably a linear or branched alkyl group having 4 to 12 carbon atoms or a branched alkyl group having 13 to 36 carbon atoms.

(A21) An ester compound in which R ² is a linear or branched alkyl group having 4 to 12 carbon atoms. Examples of the linear alkyl group having 4 to 12 carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, Nonyl group, decyl group, undecyl group, dodecyl group can be mentioned. Examples of the branched alkyl group having 4 to 12 carbon atoms include 1-methylpropyl group (sec-butyl group), 2-methylpropyl group, 1,1-dimethylethyl group (tert-butyl group), 1-methylbutyl group, 1 , 1-dimethylpropyl group, 1,2-dimethylpropyl group, 2,2-dimethylpropyl group (neopentyl group), 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group 1-methylhexyl group, 2-methylhexyl group, 2-methylhexyl group, 4-methylhexyl group, 5-methylhexyl group, 1-ethylpentyl group, 2 Ethylpentyl group, 3-ethylpentyl group, 1,1-dimethylpentyl group, 1,2-dimethylpentyl group, 1,3-dimethylpentyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2-ethylpentyl group, 1-methylheptyl group, 2-methylheptyl group, 3-methylheptyl group, 4-methylheptyl group, 5-methylheptyl group, 6-methylheptyl group, 1,1-dimethylhexyl group, 1,2-dimethylhexyl group, 1,3-dimethylhexyl group, 1,4-dimethylhexyl group, 1,5-dimethylhexyl group, 1-ethylhexyl group, 2-ethylhexyl group, 1-methyloctyl group, 2- Methyl octyl group, 3-methyl octyl group, 4-methyl octyl group, 5-methyl octyl group, 6-methyl octyl group, 7-methyl octyl group Group, 1,1-dimethylheptyl group, 1,2-dimethylheptyl group, 1,3-dimethylheptyl group, 1,4-dimethylheptyl group, 1,5-dimethylheptyl group, 1,6-dimethylheptyl group 1-ethylheptyl group, 2-ethylheptyl group, 1-methylnonyl group, 2-methylnonyl group, 3-methylnonyl group, 4-methylnonyl group, 5-methylnonyl group, 6-methylnonyl group, 7-methylnonyl group, 8- Methylnonyl group, 1,1-dimethyloctyl group, 1,2-dimethyloctyl group, 1,3-dimethyloctyl group, 1,4-dimethyloctyl group, 1,5-dimethyloctyl group, 1,6-dimethyloctyl group 1,7-dimethyloctyl group, 1-ethyloctyl group, 2-ethyloctyl group, 1-methyldecyl group, 2-methyldecyl group, 3-methyl Rudecyl group, 4-methyldecyl group, 5-methyldecyl group, 6-methyldecyl group, 7-methyldecyl group, 8-methyldecyl group, 9-methyldecyl group, 1,1-dimethylnonyl group, 1,2-dimethylnonyl group, 1 , 3-dimethylnonyl group, 1,4-dimethylnonyl group, 1,5-dimethylnonyl group, 1,6-dimethylnonyl group, 1,7-dimethylnonyl group, 1,8-dimethylnonyl group, 1-ethylnonyl Group, 2-ethylnonyl group, 1-methylundecyl group, 2-methylundecyl group, 3-methylundecyl group, 4-methylundecyl group, 5-methylundecyl group, 6-methylundecyl group, 7 -Methylundecyl group, 8-methylundecyl group, 9-methylundecyl group, 10-methylundecyl group, 1,1-dimethyldecyl group, 1,2-dimethyldecyl group Group, 1,3-dimethyldecyl group, 1,4-dimethyldecyl group, 1,5-dimethyldecyl group, 1,6-dimethyldecyl group, 1,7-dimethyldecyl group, 1,8-dimethyldecyl group 1,9-dimethyldecyl group, 1-ethyldecyl group, 2-ethyldecyl group and the like. Of these, 2-ethylhexyl group is particularly preferable.

(A22) An ester compound in which R ² is a branched alkyl group having 13 to 36 carbon atoms Examples of the branched alkyl group having 13 to 36 carbon atoms include a 1-alkylalkyl group [1-methyldodecyl group, 1-butyleicosyl group, 1-hexyloctadecyl group, 1-octylhexadecyl group, 1-decyltetradecyl group, 1-undecyltridecyl group, etc.], 2-alkylalkyl group [2-methyldodecyl group, 2-hexyloctadecyl group, 2- Octylhexadecyl group, 2-decyltetradecyl group, 2-undecyltridecyl group, 2-dodecylhexadecyl group, 2-tridecylpentadecyl group, 2-decyloctadecyl group, 2-tetradecyloctadecyl group, 2- Hexadecyloctadecyl group, 2-tetradecyleicosyl group, 2-hexadecyleicosyl group, etc.], 3 34-alkylalkyl groups (3-alkylalkyl groups, 4-alkylalkyl groups, 5-alkylalkyl groups, 32-alkylalkyl groups, 33-alkylalkyl groups, 34-alkylalkyl groups, etc.), and propylene oligomers (7 To 11-mer), ethylene / propylene (molar ratio 16/1 to 1/11) oligomer, isobutylene oligomer (7 to 8-mer), and α-olefin (5 to 20 carbon atoms) oligomer (4 to 8-mer) And a mixed alkyl group containing one or more branched alkyl groups such as a residue obtained by removing a hydroxyl group from an oxo alcohol obtained from the above.

The polymer (A1) preferably further contains an ester compound (a3) of a monovalent aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid.

Examples of the monovalent aliphatic alcohol having 1 to 3 carbon atoms constituting the ester compound (a3) include methanol, ethanol, 1-propanol and 2-propanol.

The content of the ester compound (a3) is preferably 10 to 60% by mass, and preferably 15 to 55% by mass based on the total weight of the polymer (A1) from the viewpoint of suppressing volume change of the negative electrode active material. More preferably, it is more preferably 20 to 50% by mass.

The polymer (A1) may further contain an anionic monomer salt (a4) having a polymerizable unsaturated double bond and an anionic group.

Examples of the structure having a polymerizable unsaturated double bond include a vinyl group, an allyl group, a styryl group, and a (meth) acryloyl group.

Examples of the anionic group include a sulfonic acid group and a carboxyl group.

An anionic monomer having a polymerizable unsaturated double bond and an anionic group is a compound obtained by a combination thereof, such as vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid and (meth) acrylic acid. It is done.

In addition, the (meth) acryloyl group means an acryloyl group and / or a methacryloyl group.

Examples of the cation constituting the salt (a4) of the anionic monomer include lithium ion, sodium ion, potassium ion and ammonium ion.

When the anionic monomer salt (a4) is contained, the content thereof is preferably 0.1 to 15% by mass based on the total weight of the polymer compound from the viewpoint of internal resistance and the like. It is more preferably ˜15% by mass, and further preferably 2-10% by mass.

The polymer (A1) preferably contains (meth) acrylic acid (a11) and an ester compound (a21), and more preferably contains an ester compound (a3).

Particularly preferably, methacrylic acid is used as (meth) acrylic acid (a11), 2-ethylhexyl methacrylate is used as ester compound (a21), and methyl methacrylate is used as ester compound (a3). Methacrylic acid, 2-ethylhexyl Most preferred is a copolymer of methacrylate and methyl methacrylate.

The polymer compound includes (meth) acrylic acid (a11), the monomer (a2), an ester compound (a3) of a monovalent aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid, and a polymerization used as necessary. A monomer composition comprising a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group, and the monomer (a2) and the (meth) acrylic acid The weight ratio of (a11) [the monomer (a2) / (meth) acrylic acid (a11)] is preferably 10/90 to 90/10.

When the weight ratio of the monomer (a2) and the (meth) acrylic acid (a11) is 10/90 to 90/10, the polymer obtained by polymerizing the monomer has good adhesion to the negative electrode active material and peels off. It becomes difficult.

The weight ratio is preferably 30/70 to 85/15, and more preferably 40/60 to 70/30.

The monomer constituting the polymer (A1) includes a monomer (a1) having a carboxyl group or an acid anhydride group, a monomer (a2) represented by the above general formula (1), a carbon number of 1 to 3 In addition to the ester compound (a3) of a monovalent aliphatic alcohol of (meth) acrylic acid and an anionic monomer salt (a4) having a polymerizable unsaturated double bond and an anionic group, As long as the physical properties of the coalescence (A1) are not impaired, the monomer (a1), the monomer (a2) represented by the general formula (1), a monovalent aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic It can be copolymerized with an ester compound (a3) with an acid and may contain a radically polymerizable monomer (a5).

The radical polymerizable monomer (a5) is preferably a monomer not containing active hydrogen, and the following monomers (a51) to (a58) can be used.

(A51) Hydrocarbons formed from (meth) acrylic acid and straight chain aliphatic monools having 13 to 20 carbon atoms, alicyclic monools having 5 to 20 carbon atoms, or araliphatic monools having 7 to 20 carbon atoms Carbyl (meth) acrylate As the monool, (i) linear aliphatic monool (tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecyl alcohol, arachidyl alcohol Etc.), (ii) alicyclic monools (cyclopentyl alcohol, cyclohexyl alcohol, cycloheptyl alcohol, cyclooctyl alcohol etc.), (iii) araliphatic monools (benzyl alcohol etc.) and mixtures of two or more thereof Can be mentioned.

(A52) Poly (n = 2 to 30) oxyalkylene (carbon number 2 to 4) alkyl (carbon number 1 to 18) ether (meth) acrylate [methanol ethylene oxide (hereinafter abbreviated as EO) 10 mol adduct (meta ) Acrylate, propylene oxide of methanol (hereinafter abbreviated as PO), 10 mol adduct (meth) acrylate, etc.].

(A53) Nitrogen-containing vinyl compound (a53-1) Amide group-containing vinyl compound (i) (Meth) acrylamide compound having 3 to 30 carbon atoms, such as N, N-dialkyl (1 to 6 carbon atoms) or diaralkyl (carbon number) 7 to 15) (meth) acrylamide (N, N-dimethylacrylamide, N, N-dibenzylacrylamide, etc.), diacetone acrylamide,
(Ii) An amide group-containing vinyl compound having 4 to 20 carbon atoms excluding the (meth) acrylamide compound, such as N-methyl-N-vinylacetamide, cyclic amide [pyrrolidone compound (6 to 13 carbon atoms, such as N- Vinylpyrrolidone etc.)].

(A53-2) (Meth) acrylate compound (i) Dialkyl (1 to 4 carbon atoms) aminoalkyl (1 to 4 carbon atoms) (meth) acrylate [N, N-dimethylaminoethyl (meth) acrylate, N, N -Diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, morpholinoethyl (meth) acrylate, etc.]
(Ii) Quaternary ammonium group-containing (meth) acrylate {quaternary amino group-containing (meth) acrylate [N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, etc.]] (Quaternized with a quaternizing agent such as methyl chloride, dimethyl sulfate, benzyl chloride, dimethyl carbonate, etc.)}.

(A53-3) Heterocycle-containing vinyl compound Pyridine compound (carbon number 7 to 14, for example, 2- or 4-vinylpyridine), imidazole compound (carbon number 5 to 12, for example, N-vinylimidazole), pyrrole compound (carbon number) 6 to 13, for example, N-vinylpyrrole), pyrrolidone compounds (having 6 to 13 carbon atoms, for example, N-vinyl-2-pyrrolidone).

(A53-4) Nitrile group-containing vinyl compound A nitrile group-containing vinyl compound having 3 to 15 carbon atoms such as (meth) acrylonitrile, cyanostyrene, cyanoalkyl (1 to 4 carbon atoms) acrylate.

(A53-5) Other nitrogen-containing vinyl compounds Nitro group-containing vinyl compounds (carbon number 8 to 16, for example, nitrostyrene) and the like.

(A54) Vinyl hydrocarbon (a54-1) Aliphatic vinyl hydrocarbon An olefin having 2 to 18 or more carbon atoms (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), Dienes having 4 to 10 or more carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.) and the like.

(A54-2) Alicyclic vinyl hydrocarbon Cyclic unsaturated compound having 4 to 18 or more carbon atoms, such as cycloalkene (for example, cyclohexene), (di) cycloalkadiene [for example, (di) cyclopentadiene], terpene ( For example, pinene and limonene) and inden.

(A54-3) Aromatic vinyl hydrocarbon Aromatic unsaturated compounds having 8 to 20 or more carbon atoms, such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butyl Styrene, phenyl styrene, cyclohexyl styrene, benzyl styrene.

(A55) Vinyl ester Aliphatic vinyl ester [C4-15, for example, alkenyl ester of aliphatic carboxylic acid (mono- or dicarboxylic acid) (for example, vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, Vinyl methoxyacetate)],
Aromatic vinyl esters [containing 9 to 20 carbon atoms, eg alkenyl esters of aromatic carboxylic acids (mono- or dicarboxylic acids) (eg vinyl benzoate, diallyl phthalate, methyl-4-vinyl benzoate), aromatic ring containing aliphatic carboxylic acid Esters (eg acetoxystyrene)].

(A56) Vinyl ether Aliphatic vinyl ether [C3-15, such as vinyl alkyl (C1-10) ether (vinyl methyl ether, vinyl butyl ether, vinyl 2-ethylhexyl ether, etc.), vinyl alkoxy (C1-6) Alkyl (1 to 4 carbon atoms) ether (vinyl-2-methoxyethyl ether, methoxybutadiene, 3,4-dihydro-1,2-pyran, 2-butoxy-2'-vinyloxydiethyl ether, vinyl-2-ethyl Mercaptoethyl ether, etc.), poly (2-4) (meth) allyloxyalkanes (2-6 carbon atoms) (diallyloxyethane, triaryloxyethane, tetraallyloxybutane, tetrametaallyloxyethane, etc.)]
Aromatic vinyl ether (8-20 carbon atoms such as vinyl phenyl ether, phenoxystyrene).

(A57) Vinyl ketone Aliphatic vinyl ketone (having 4 to 25 carbon atoms, such as vinyl methyl ketone, vinyl ethyl ketone) and aromatic vinyl ketone (having 9 to 21 carbon atoms, such as vinyl phenyl ketone).

(A58) Unsaturated dicarboxylic acid diester Unsaturated dicarboxylic acid diester having 4 to 34 carbon atoms such as dialkyl fumarate (two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms) ), Dialkyl maleate (two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms).

Of those exemplified as (a5) above, (a51), (a52) and (a53) are preferable from the viewpoint of withstand voltage.

In the polymer (A1), a monomer (a1) having a carboxyl group or an acid anhydride group, a monomer (a2) represented by the general formula (1), a monovalent aliphatic alcohol having 1 to 3 carbon atoms and ( The content of the ester compound (a3) with meth) acrylic acid, the salt (a4) of the anionic monomer having a polymerizable unsaturated double bond and an anionic group, and the radical polymerizable monomer (a5) Based on the weight of the combined (A1), (a1) is 0.1 to 80% by mass, (a2) is 0.1 to 99.9% by mass, (a3) is 0 to 60% by mass, and (a4) is The content is preferably 0 to 15% by mass and (a5) is preferably 0 to 99.8% by mass.

When the monomer content is within the above range, the liquid absorbability to the non-aqueous electrolyte is good.

The preferable lower limit of the number average molecular weight of the polymer (A1) is 3,000, more preferably 50,000, still more preferably 100,000, particularly preferably 200,000, and the preferable upper limit is 2,000,000. It is preferably 1,500,000, more preferably 1,000,000, and particularly preferably 800,000.

The number average molecular weight of the polymer (A1) can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.

・ Device: Alliance GPC V2000 (manufactured by Waters)
・ Solvent: Orthodichlorobenzene ・ Standard material: Polystyrene ・ Detector: RI
Sample concentration: 3 mg / ml
Column stationary phase: PLgel 10 μm, MIXED-B 2 in series (manufactured by Polymer Laboratories)
Column temperature: 135 ° C.

The polymer (A1) is a known polymerization initiator {azo initiator [2,2′-azobis (2-methylpropionitrile), 2,2′-azobis (2,4-dimethylvaleronitrile, etc.)] , Peroxide initiators (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.)} by a known polymerization method (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.) Can be manufactured.

The amount of the polymerization initiator used is preferably 0.01 to 5% by mass, more preferably 0.05 to 2% by mass, based on the total weight of the monomers, from the viewpoint of adjusting the number average molecular weight within a preferable range. More preferably, the content is 0.1 to 1.5% by mass. The polymerization temperature and polymerization time are adjusted according to the type of polymerization initiator, etc., but the polymerization temperature is preferably −5 to 150 ° C. (more preferably 30 to 120 ° C.), and the reaction time is preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

Examples of the solvent used in the solution polymerization include esters (having 2 to 8 carbon atoms such as ethyl acetate and butyl acetate), alcohols (having 1 to 8 carbon atoms such as methanol, ethanol and octanol), hydrocarbons (having carbon atoms). Examples thereof include 4 to 8, such as n-butane, cyclohexane and toluene, ketones (having 3 to 9 carbon atoms such as methyl ethyl ketone) and amide compounds (such as N, N-dimethylformamide (DMF)). From the viewpoint of adjusting the number average molecular weight within a preferable range, the amount of the solvent used is preferably 5 to 900% by mass, more preferably 10 to 400% by mass, and still more preferably 30 to 300% based on the total weight of the monomers. % By mass. The monomer concentration is preferably 10 to 95% by mass, more preferably 20 to 90% by mass, and still more preferably 30 to 80% by mass.

Examples of the dispersion medium in emulsion polymerization and suspension polymerization include water, alcohol (for example, ethanol), ester (for example, ethyl propionate), light naphtha, and the like. Examples of emulsifiers include higher fatty acid (10 to 24 carbon atoms) metal salts (for example, sodium oleate and sodium stearate), higher alcohol (10 to 24 carbon atoms) sulfate metal salt (for example, sodium lauryl sulfate), ethoxylated tetramethyl Examples include decynediol, sodium sulfoethyl methacrylate, and dimethylaminomethyl methacrylate. Furthermore, you may add polyvinyl alcohol, polyvinylpyrrolidone, etc. as a stabilizer.

The monomer concentration of the solution or dispersion is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and still more preferably 15 to 85% by mass. The amount of the polymerization initiator used is preferably 0.01 to 5% by mass, more preferably 0.05 to 2% by mass, based on the total weight of the monomers.

In the polymerization, known chain transfer agents such as mercapto compounds (such as dodecyl mercaptan and n-butyl mercaptan) and / or halogenated hydrocarbons (such as carbon tetrachloride, carbon tetrabromide and benzyl chloride) can be used. .

The polymer (A1) contained in the acrylic resin is a crosslinking agent (A ′) having a reactive functional group that reacts the polymer (A1) with a carboxyl group {preferably a polyepoxy compound (a′1) [polyglycidyl ether]. (Bisphenol A diglycidyl ether, propylene glycol diglycidyl ether, glycerin triglycidyl ether, etc.) and polyglycidylamine (N, N-diglycidylaniline and 1,3-bis (N, N-diglycidylaminomethyl)), etc.] And / or a crosslinked polymer formed by crosslinking with a polyol compound (a′2) (ethylene glycol or the like)}.

Examples of the method of crosslinking the polymer (A1) using the crosslinking agent (A ′) include a method of crosslinking after coating the carbon-based negative electrode active material with the polymer (A1). Specifically, a coated negative electrode active material in which a carbon-based negative electrode active material is coated with a polymer (A1) is produced by mixing and removing a solvent containing a carbon-based negative electrode active material and a polymer (A1). After that, the solution containing the cross-linking agent (A ′) is mixed with the coated negative electrode active material and heated to cause solvent removal and a cross-linking reaction, so that the polymer (A1) is converted by the cross-linking agent (A ′). There is a method in which a reaction that is crosslinked to become a polymer compound is caused on the surface of the carbon-based negative electrode active material.

The heating temperature is adjusted according to the type of the crosslinking agent, but when the polyepoxy compound (a′1) is used as the crosslinking agent, it is preferably 70 ° C. or higher, and when the polyol compound (a′2) is used. Preferably it is 120 degreeC or more.

The conductive material is selected from conductive materials.

Specifically, in addition to the conductive carbon filler described above, metal [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.] can be used.

These conductive materials may be used alone or in combination of two or more. Further, these alloys or metal oxides may be used. From the viewpoint of electrical stability, preferably aluminum, stainless steel, conductive carbon filler, silver, copper, titanium and a mixture thereof, more preferably silver, aluminum, stainless steel and conductive carbon filler, still more preferably. It is a conductive carbon filler. Moreover, as these conductive support materials, the thing which coated the electroconductive material (metal thing among the above-mentioned electroconductive materials) by plating etc. around the particulate ceramic material or the resin material may be used. A polypropylene resin kneaded with graphene is also preferable as the conductive material.

In addition, carbon [graphite and carbon black (acetylene black, ketjen black (registered trademark), furnace black, channel black, thermal lamp black, etc.), etc.] is preferable as the conductive carbon filler used for the conductive material.

The aspect ratio of the conductive carbon filler used for the conductive material is preferably 1 or more and less than 20.

The average particle diameter of the conductive material is not particularly limited, but is preferably 0.01 to 10 μm and more preferably 0.02 to 5 μm from the viewpoint of the electrical characteristics of the negative electrode for a lithium ion battery. Preferably, it is 0.03 to 1 μm. In the present specification, “particle diameter” means the maximum distance L among the distances between any two points on the particle outline. The value of “average particle size” is the average value of the particle size of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

The shape (form) of the conductive material is not limited to the particle form, and may be a form other than the particle form, for example, a fibrous conductive material.

Fibrous conductive materials include conductive fibers made by uniformly dispersing highly conductive metal and graphite in synthetic fibers, metal fibers made from metal such as stainless steel, and the surface of organic fibers as metal. And conductive fibers in which the surface of an organic substance is coated with a resin containing a conductive substance.

The average fiber diameter of the fibrous conductive material is preferably 0.1 to 20 μm.

The ratio of the total weight of the polymer compound and the conductive material contained in the negative electrode coating layer is not particularly limited, but is preferably 25% by mass or less based on the weight of the negative electrode active material.

The ratio of the weight of the polymer compound to the weight of the negative electrode active material is not particularly limited, but is preferably 0.1 to 20% by mass.

The ratio of the weight of the conductive material to the weight of the negative electrode active material is not particularly limited, but is preferably 10% by mass or less.

Subsequently, the negative electrode current collector will be described.

Examples of the material constituting the negative electrode current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof. Of these, aluminum and copper are more preferable, and copper is particularly preferable from the viewpoints of weight reduction, corrosion resistance, and high conductivity. The negative electrode current collector may be a current collector made of baked carbon, conductive polymer, conductive glass, or the like, or may be a resin current collector made of a conductive material and a resin.

The shape of the negative electrode current collector is not particularly limited, and may be a sheet-like current collector made of the above material and a deposited layer made of fine particles made of the above material.

The thickness of the negative electrode current collector is not particularly limited, but is preferably 50 to 500 μm.

As the conductive material constituting the resin current collector, the same conductive material as the optional component of the negative electrode coating layer can be suitably used.

The resin constituting the resin current collector includes polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), polytetra Fluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin or a mixture thereof Is mentioned.

From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferable, and polyethylene (PE), polypropylene (PP) and polymethylpentene are more preferable. (PMP).

Hereinafter, a method for producing the negative electrode for a lithium ion battery of the present invention will be described.

As a method for forming the negative electrode active material layer, for example, a material in which a flocculant is added to a conductive carbon filler which is silicon and / or a silicon compound, a carbon-based negative electrode active material, and a pressure relaxation material as necessary is used as a solvent ( A dispersion mixed at a concentration of 30 to 60% by mass based on the weight of the non-aqueous electrolyte or the non-aqueous solvent constituting the non-aqueous electrolyte) is applied onto the negative electrode current collector with a coating device such as a bar coater. Thereafter, drying is performed as necessary to remove the solvent, and if necessary, pressing with a press machine (for example, at a pressure of 1 to 200 MPa) and impregnating with a predetermined amount of non-aqueous electrolyte as necessary can be mentioned. It is done.

In addition, silicon and / or a silicon compound and a carbon-based negative electrode active material dispersed in a solvent and a mixture of a pressure relaxation material and an aggregating agent were prepared separately, and after the pressure relaxation material formed an aggregate, And / or you may mix with the dispersion liquid in which the silicon compound and the carbon-type negative electrode active material were disperse | distributed.

In addition, the negative electrode active material layer obtained from the dispersion liquid used as the negative electrode active material layer can be obtained, for example, by applying the above dispersion liquid on the surface of an aramid separator or the like and drying it. As a method of drying the dispersion applied on the aramid separator, the solvent may be removed by suction from the back surface of the surface on which the dispersion is applied. At this time, it is only necessary to remove the solvent in the dispersion to such an extent that it can be separated from the aramid separator while maintaining the shape of the negative electrode active material layer, and it is not necessary to completely remove the solvent in the dispersion. Moreover, in the said formation method of a negative electrode active material layer, it replaces with an aramid separator, a release member (aramid nonwoven fabric) is used, a negative electrode active material layer is produced on this aramid nonwoven fabric, Then, a negative electrode active material layer is formed from an aramid nonwoven fabric. May be peeled off and placed (formed) on the negative electrode current collector (see Example 1). Similarly, the positive electrode active material layer may be disposed (formed) on the positive electrode current collector.

As a method of drying after applying the dispersion liquid to be the negative electrode active material layer, it can be performed using a known dryer such as a forward air dryer, and the drying temperature and drying time are determined by the dispersion medium contained in the dispersion liquid. It can adjust suitably according to the kind of (solvent).

When the carbon-based negative electrode active material is used as the carbon-based negative electrode active material, for example, a polymer solution containing a polymer compound is added in a state where the carbon-based negative electrode active material is put in a universal mixer and stirred at 30 to 50 rpm. Mix dropwise over 1-90 minutes, further mix conductive material as necessary, raise temperature to 50-200 ° C. with stirring, reduce pressure to 0.007-0.04 MPa and hold for 10-150 minutes Can be obtained.

The blending ratio of the carbon-based negative electrode active material and the polymer compound is not particularly limited, but the weight ratio of carbon-based negative electrode active material: polymer compound is preferably 1: 0.001 to 0.1. .

Examples of the solvent include 1-methyl-2-pyrrolidone, methyl ethyl ketone, N, N-dimethylformamide (DMF), dimethylacetamide, N, N-dimethylaminopropylamine and tetrahydrofuran.

When producing a lithium ion battery using the negative electrode for a lithium ion battery of the present invention, a counter electrode is combined, accommodated in a cell container together with a separator, a non-aqueous electrolyte is injected, and the cell container is sealed. It can be manufactured by a method or the like.

Further, in the negative electrode for a lithium ion battery of the present invention in which the negative electrode active material layer is formed only on one surface of the negative electrode current collector, a positive electrode active material layer made of the positive electrode active material is formed on the other surface of the negative electrode current collector. It is also possible to produce a bipolar electrode by laminating the bipolar electrode with a separator and storing it in a cell container, injecting a non-aqueous electrolyte, and sealing the cell container.

As the electrode (positive electrode) that is the counter electrode of the negative electrode for a lithium ion battery of the present invention, a positive electrode used for a known lithium ion battery can be used.

Examples of separators include polyethylene or polypropylene porous films, laminated films of porous polyethylene films and porous polypropylene, non-woven fabrics made of synthetic fibers (such as polyester fibers and aramid fibers) or glass fibers, and silica on the surfaces thereof. In addition, known separators for lithium ion batteries, such as those to which ceramic fine particles such as alumina and titania are attached, may be mentioned.

As the non-aqueous electrolyte, a non-aqueous electrolyte containing an electrolyte and a non-aqueous solvent used in the production of a lithium ion battery can be used.

As the electrolyte, those used in known electrolyte solutions can be used, and preferable examples include lithium salt electrolytes of inorganic acids such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ and LiClO ₄ , Fluorine such as Li (FSO ₂ ) ₂ N (abbreviated as LiFSI), Li (CF ₃ SO ₂ ) ₂ N (abbreviated as LiTFSI) and Li (C ₂ F ₅ SO ₂ ) ₂ N (abbreviated as LiBETI) Examples thereof include sulfonylimide electrolytes having atoms, and sulfonylmethide electrolytes having fluorine atoms such as LiC (CF ₃ SO ₂ ) ₃ (abbreviated as LiTFSM).

The electrolyte concentration of the non-aqueous electrolyte is not particularly limited, but is preferably 1 to 5 mol / L, more preferably 1.5 to 4 mol / L from the viewpoint of the handleability of the electrolyte and the battery capacity. Preferably, it is 2 to 3 mol / L.

As the non-aqueous solvent, those used in known non-aqueous electrolytes can be used, for example, lactone compounds, cyclic or chain carbonates, chain carboxylates, cyclic or chain ethers, phosphate esters. , Nitrile compounds, amide compounds, sulfones and the like and mixtures thereof.

Examples of the lactone compound include 5-membered rings (such as γ-butyrolactone and γ-valerolactone) and 6-membered lactone compounds (such as δ-valerolactone).

Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate and butylene carbonate.

Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate.

Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.

Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,4-dioxane and the like.

Examples of the chain ether include dimethoxymethane and 1,2-dimethoxyethane.

Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, tri (trichloromethyl) phosphate, Tri (trifluoroethyl) phosphate, tri (triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphosphoran-2-one, 2-trifluoroethoxy-1,3,2- Examples include dioxaphospholan-2-one and 2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one.

Examples of nitrile compounds include acetonitrile.

Examples of the amide compound include N, N-dimethylformamide (hereinafter also referred to as DMF).

Examples of the sulfone include chain sulfones such as dimethyl sulfone and diethyl sulfone, and cyclic sulfones such as sulfolane.

The non-aqueous solvent may be used alone or in combination of two or more.

Among the nonaqueous solvents, lactone compounds, cyclic carbonates, chain carbonates, and phosphates are preferable from the viewpoint of battery output and charge / discharge cycle characteristics. More preferred are a lactone compound, a cyclic carbonate and a chain carbonate, and particularly preferred is a cyclic carbonate or a mixture of a cyclic carbonate and a chain carbonate. Most preferred is a mixture of ethylene carbonate (EC) and propylene carbonate (PC), a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), or a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). It is.

Next, the present invention will be specifically described by way of examples. However, the technical scope of the present invention is not limited to the examples without departing from the gist of the present invention. Unless otherwise specified, “part” means “part by weight” and “%” means “% by mass”.

<Example 1>
[Production of resin current collector]
In a twin-screw extruder, 70 parts of polypropylene [trade name “Sun Allomer PL500A”, manufactured by Sun Allomer Co., Ltd.], 25 parts of carbon nanotube [trade name: “FloTube 9000”, manufactured by CNano] and dispersant [trade name “Yumex 1001” Sanyo Chemical Industries, Ltd.] 5 parts was melt kneaded at 200 ° C. and 200 rpm to obtain a resin mixture.

The obtained resin mixture was passed through a T-die extrusion film molding machine and stretched and rolled to obtain a conductive film for a resin current collector having a thickness of 100 μm. Subsequently, the obtained conductive film for a resin current collector was cut into 3 cm × 3 cm, and after nickel deposition was performed on one surface, a resin current collector to which a current extraction terminal (5 mm × 3 cm) was connected was obtained. .

[Preparation of polymer compound solution for coating layer]
A 4-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 407.9 parts of DMF and heated to 75 ° C. Next, a monomer compounded solution containing 242.8 parts of methacrylic acid, 97.1 parts of methyl methacrylate, 242.8 parts of 2-ethylhexyl methacrylate and 116.5 parts of DMF, and 2,2′-azobis (2,4-dimethylvalero) Nitrile) 1.7 parts and 2,2′-azobis (2-methylbutyronitrile) 4.7 parts dissolved in 58.3 parts DMF and an initiator solution were stirred while nitrogen was blown into a four-necked flask. Then, radical polymerization was carried out by continuously dropping with a dropping funnel over 2 hours. After completion of dropping, the reaction was continued at 75 ° C. for 3 hours. Subsequently, the temperature was raised to 80 ° C., and the reaction was continued for 3 hours to obtain a copolymer solution having a resin solid content concentration of 50% by mass. To this, 789.8 parts of DMF was added to obtain a polymer compound solution for a coating layer having a resin solid concentration of 30% by mass.

[Production of carbon-based coated negative electrode active material particles]
Non-graphitizable carbon powder [Carbotron (registered trademark) PS (F), manufactured by Kureha Battery Materials Japan Co., Ltd., volume average particle size 18 μm] 68.2 parts of universal mixer high speed mixer FS25 [Earth Co., Ltd. In a state of stirring at room temperature and 720 rpm, 33.3 parts of the polymer compound solution for coating layer was added dropwise over 2 minutes, followed by further stirring for 5 minutes. Then, the pressure is reduced to 0.01 MPa while maintaining the stirring, and then the temperature is raised to 140 ° C. while maintaining the stirring and the degree of vacuum, and the volatile matter is distilled off by maintaining the stirring, the pressure and the temperature for 8 hours. Thus, carbon-based coated negative electrode active material particles (N-1) were obtained. The obtained carbon-based coated negative electrode active material particles (N-1) had a volume average particle diameter of 18 μm.

[Preparation of conductive carbon filler A]
Conductive carbon filler A is, Eiichi Yasuda, Asao Oya, Shinya Komura, Shigeki Tomonoh, Takashi Nishizawa, Shinsuke Nagata, Takashi Akatsu, CARBON, 50,2012,1432-1434 and Eiichi Yasuda, Takashi Akatsu, Yasuhiro Tanabe, Kazumasa Nakamura, Yasuto Hoshikawa, Naoya Miyajima, TANSO, 255, 2012, pages 254 to 265 were used as a reference for production.

As a carbon precursor, 10 parts by weight of synthetic mesophase pitch AR · MPH [Mitsubishi Gas Chemical Co., Ltd.] and 90 parts by weight of polymethylpentene TPX RT18 [Mitsui Chemicals Co., Ltd.] are uniaxially extruded at a barrel temperature of 310 ° C. in a nitrogen atmosphere. A resin composition was prepared by melt-kneading using a machine. Subsequently, the resin composition was melt-extruded and spun at 390 ° C. The spun resin composition was placed in an electric furnace and held at 270 ° C. for 3 hours under a nitrogen atmosphere to stabilize the carbon precursor. Next, the electric furnace was heated to 500 ° C. over 1 hour and held at 500 ° C. for 1 hour to decompose and remove polymethylpentene. The electric furnace was heated up to 1000 ° C. over 2 hours and held at 1000 ° C. for 30 minutes. Of the remaining carbon fiber precursor, 90 parts by weight together with 500 parts by weight of water and 1000 parts by weight of φ0.1 mm zirconia balls Placed in a container and ground for 5 minutes. The zirconia balls were classified and then dried at 100 ° C. to obtain a conductive carbon filler A.

From the measurement result by SEM, the average fiber diameter of the conductive carbon filler A was 0.3 μm, and the average fiber length was 26 μm (the aspect ratio was 87). The electrical resistivity of the conductive carbon filler A was 50 μΩm, and the bulk density of the conductive carbon filler A measured according to JIS K5101-12-1 was 0.5 g / cm ³ .

[Preparation of negative electrode active material slurry]
95.05 parts of electrolyte solution X prepared by dissolving LiPF ₆ in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC) at a ratio of 1 M (mol / L) was coated with carbon. Negative electrode active material particles (N-1) 3.2 parts, silicon oxide particles [manufactured by Sigma-Aldrich Japan, volume average particle diameter 1.5 μm] (N-21) 1.5 parts, the above-mentioned conductivity as a pressure relaxation material After adding 0.25 part of carbon filler A, it mixed for 5 minutes at 1000 rpm using the planetary stirring type mixing kneading apparatus {Awatori Kentaro [made by Sinky Co., Ltd.]}, and the negative electrode active material slurry 1 was produced.

[Preparation of negative electrode active material layer]
The obtained negative electrode active material slurry 1 was dropped on a φ23 mm aramid nonwoven fabric (manufactured by Japan Vilene, 2415R) equipped with a φ15 mm mask so as to have a basis weight of 39.4 mg / cm ^2, and suction filtration (reduced pressure) The negative active material layer 1 according to Example 1 was manufactured by laminating on an aramid nonwoven fabric and pressing the pressure at 5 MPa for about 10 seconds. The thickness of the negative electrode active material layer 1 was 450 μm. The thickness of the negative electrode active material layer 1 was measured with a contact-type film thickness meter (the thicknesses of the negative electrode active material layers in the following examples and comparative examples were also measured in the same manner).

Further, when an observation cross section prepared by cutting the obtained negative electrode active material layer 1 under freezing was enlarged and observed with an SEM, an aggregate of the conductive carbon filler A was confirmed, and the average diameter was 10 μm. It was.

[Preparation of battery exterior material]
A direction in which two terminals come out in the same direction with a copper foil (3 cm × 3 cm, thickness 17 μm) with a terminal (5 mm × 3 cm) and a carbon coated aluminum foil (3 cm × 3 cm, thickness 21 μm) with a terminal (5 mm × 3 cm) Were laminated in order, and were sandwiched between two commercially available heat-bonding aluminum laminate films (10 cm × 8 cm), and one side where the terminals came out was heat-sealed to prepare a battery exterior material.

[Preparation of positive electrode active material slurry]
2 parts of the conductive carbon filler A and 98 parts of LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder as the positive electrode active material particles were mixed with the electrolyte X to prepare a positive electrode active material slurry 1.

[Preparation of positive electrode active material layer]
The obtained positive electrode active material slurry 1 was dropped on a φ23 mm stainless steel mesh [SUS316 twilled weave 2300 mesh manufactured by Sunnet Kogyo Co., Ltd.] with a mask of φ15 mm so as to have a basis weight of 78 mg / cm ^2. Then, the positive electrode active material layer 1 according to Example 1 was produced on a stainless steel mesh by suction filtration (reduced pressure).

[Production of lithium-ion batteries]
The resin current collector was placed on the copper foil of the battery exterior material, the negative electrode active material layer 1 from which the aramid nonwoven fabric was peeled was placed thereon, and 100 μL of the electrolyte X was added. A separator (5 cm × 5 cm, thickness 23 μm, Celgard 2500 made of polypropylene) was placed on the negative electrode active material layer 1, and 100 μL of electrolyte solution X was added. The stainless steel mesh was peeled off from the produced positive electrode active material layer 1 and laminated so as to face the negative electrode active material layer 1 through a separator, and 100 μL of electrolyte solution X was added. Further, a resin current collector was laminated on the positive electrode active material layer 1, and the battery exterior material was covered thereon so that the carbon-coated aluminum foil of the battery exterior material overlapped. Out of the outer periphery of the battery outer packaging material, heat sealing is performed on two sides orthogonal to one side that has been heat-sealed first, and the remaining opening is heat sealed while vacuuming the inside of the cell using a vacuum sealer. The lithium ion battery 1 according to Example 1 having the sealed negative electrode for a lithium ion battery of the present invention was obtained.

<Example 2>
[Production of carbon-coated silicon particles]
Silicon particles (volume average particle diameter 1.5 μm, manufactured by Sigma-Aldrich Japan) (N-23) were placed in a horizontal heating furnace, and 1100 ° C./1000 Pa, average residence time of about 2 while venting methane gas into the horizontal heating furnace. Chemical vapor deposition for a period of time was performed to obtain silicon-based negative electrode active material particles (volume average particle diameter 1.5 μm) (N-22) having a carbon content of 2% by mass and coated with carbon.

[Preparation of negative electrode active material slurry]
Change 1.5 parts of silicon oxide particles (N-21) to 1.5 parts of silicon-based negative electrode active material particles (N-22), and use 3 parts of carbon-based coated negative electrode active material particles (N-1). The same procedure as in Example 1, except that the amount of conductive carbon filler A used was changed to 0.5 part, the amount of electrolyte X used was changed to 95 parts, and the kneading conditions were changed to 2000 rpm for 10 minutes. A negative electrode active material slurry 2 was prepared.

[Preparation of negative electrode active material layer]
A negative electrode active material layer 2 according to Example 2 was prepared in the same procedure as in Example 1, except that the obtained negative electrode active material slurry 2 was changed so that the basis weight was 86.7 mg / cm ^2. did. The thickness of the negative electrode active material layer 2 was 1000 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 2 under freezing was enlarged and observed with an SEM, aggregates of the conductive carbon filler A were confirmed, and the average diameter was 15 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 2 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 171.6 mg / cm ^2. An active material layer 2 was produced.

Using the obtained positive electrode active material layer 2 and negative electrode active material layer 2, a lithium ion battery 2 according to Example 2 was manufactured in the same procedure as in Example 1.

<Example 3>
[Preparation of negative electrode active material slurry]
1.5 parts of silicon oxide particles (N-21) were changed to 1.2 parts of silicon particles (N-23), and the amount of carbon-based coated negative electrode active material particles (N-1) used was changed to 2.3 parts. The procedure was the same as in Example 1 except that the amount of conductive carbon filler A used was changed to 1.5 parts, the amount of electrolyte X used was changed to 95 parts, and the kneading conditions were changed to 2000 rpm for 5 minutes. A negative electrode active material slurry 3 was prepared.

[Preparation of negative electrode active material layer]
A negative electrode active material layer 3 according to Example 3 was produced in the same procedure as in Example 1 except that the obtained negative electrode active material slurry 3 was used and the basis weight was changed to 17.3 mg / cm ² . . The thickness of the negative electrode active material layer 3 was 200 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 3 under freezing was enlarged and observed with an SEM, aggregation of the carbon conductive filler A was confirmed, and the average diameter was 10 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 3 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 34.3 mg / cm ^2. An active material layer 3 was produced.

Using the obtained positive electrode active material layer 3 and negative electrode active material layer 3, a lithium ion battery 3 according to Example 3 was manufactured in the same procedure as in Example 1.

<Example 4>
[Production of carbon-coated silicon oxide particles]
Silicon oxide particles (N-21) are placed in a horizontal heating furnace, and a chemical vapor deposition operation is performed at 1100 ° C./1000 Pa and an average residence time of about 2 hours while venting methane gas into the horizontal heating furnace, and the carbon content is 2 mass. %, Silicon-based negative electrode active material particles (volume average particle diameter 1.5 μm) (N-24) whose surface was coated with carbon were obtained.

[Preparation of negative electrode active material slurry]
1.5 parts of silicon oxide particles (N-21) are changed to 0.25 parts of silicon-based negative electrode active material particles (N-24), and the amount of carbon-based coated negative electrode active material particles (N-1) used is 4. The same procedure as in Example 1 except that 3 parts, the amount of conductive carbon filler A used was changed to 0.5 parts, the amount of electrolyte used was changed to 95 parts, and the kneading conditions were changed to 2000 rpm for 5 minutes. Thus, negative electrode active material slurry 4 was prepared.

[Preparation of negative electrode active material layer]
Using the obtained negative electrode active material slurry 4, a negative electrode active material layer 4 according to Example 4 was produced in the same procedure as in Example 1. The thickness of the negative electrode active material layer 4 was 450 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 4 under freezing was enlarged and observed with an SEM, aggregates of the conductive carbon filler A were confirmed, and the average diameter was 10 μm.

[Preparation of positive electrode active material layer]
Using the positive electrode active material slurry 1 obtained in the same manner as in Example 1, a positive electrode active material layer 4 according to Example 4 was produced in the same procedure as in Example 1.

Using the obtained positive electrode active material layer 4 and negative electrode active material layer 4, a lithium ion battery 4 according to Example 4 was produced in the same procedure as in Example 1.

<Example 5>
[Preparation of negative electrode active material layer]
The negative electrode active material slurry 1 obtained in the same manner as in Example 1 was used, and the negative electrode active material according to Example 5 was obtained in the same procedure as in Example 1 except that the basis weight was changed to 25 mg / cm ^2. Material layer 5 was prepared. The thickness of the negative electrode active material layer 5 was 350 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 5 under freezing was enlarged and observed with an SEM, an aggregate of the conductive carbon filler A was confirmed, and the average diameter was 10 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 5 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 49.5 mg / cm ^2. An active material layer 5 was produced.

Using the obtained positive electrode active material layer 5 and negative electrode active material layer 5, a lithium ion battery 5 according to Example 5 was manufactured in the same procedure as in Example 1.

<Example 6>
[Preparation of negative electrode active material layer]
The negative electrode active material slurry 2 obtained in the same manner as in Example 2 was used and the negative electrode active material according to Example 6 was changed in the same procedure as in Example 2 except that the basis weight was changed to 45 mg / cm ^2. Material layer 6 was prepared. The thickness of the negative electrode active material layer 6 was 610 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 6 under freezing was enlarged and observed with an SEM, an aggregate of the conductive carbon filler A was confirmed, and the average diameter was 15 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 6 in the same procedure as in Example 1 except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 89.1 mg / cm ^2. An active material layer 6 was produced.

Using the obtained positive electrode active material layer 6 and negative electrode active material layer 6, a lithium ion battery 6 according to Example 6 was manufactured in the same procedure as in Example 1.

<Example 7>
[Preparation of negative electrode active material layer]
The negative electrode active material slurry 3 obtained in the same manner as in Example 3 was used, and the negative electrode active material according to Example 7 was changed in the same procedure as in Example 3, except that the basis weight was changed to 15 mg / cm ^2. Material layer 7 was prepared. The thickness of the negative electrode active material layer 7 was 210 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 7 under freezing was enlarged and observed with an SEM, an aggregate of the conductive carbon filler A was confirmed, and the average diameter was 10 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 7 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 29.7 mg / cm ^2. An active material layer 7 was produced.

Using the obtained positive electrode active material layer 7 and negative electrode active material layer 7, a lithium ion battery 7 according to Example 7 was manufactured in the same procedure as in Example 1.

<Example 8>
[Preparation of negative electrode active material layer]
The negative electrode active material slurry 4 obtained in the same manner as in Example 4 was used, and the negative electrode active material according to Example 8 was used in the same procedure as in Example 4 except that the basis weight was changed to 25 mg / cm ^2. The material layer 8 was produced. The thickness of the negative electrode active material layer 8 was 320 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 8 under freezing was enlarged and observed with an SEM, aggregates of the conductive carbon filler A were confirmed, and the average diameter was 10 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 8 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 49.5 mg / cm ^2. An active material layer 8 was produced.

Using the obtained positive electrode active material layer 8 and negative electrode active material layer 8, a lithium ion battery 8 according to Example 8 was manufactured in the same procedure as in Example 1.

<Example 9>
[Production of composite particles]
3 parts of silicon particles (N-23) are put into a universal mixer high speed mixer FS25 [Earth Technica Co., Ltd.] and stirred at room temperature at 720 rpm with a polyacrylic acid resin solution (solvent: ultrapure water, solid content) 10 parts) was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Next, 1 part of acetylene black [Denka Co., Ltd., Denka Black (registered trademark), powdered product with an average primary particle size of 35 nm] was added while stirring, and stirring was continued for 30 minutes. Thereafter, the pressure was reduced to 0.01 MPa while maintaining the stirring, and then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of vacuum, and the volatile matter was distilled off by maintaining the stirring, the degree of vacuum and the temperature for 8 hours. . The obtained powder was classified with a sieve having an opening of 20 μm to obtain composite particles (volume average particle diameter 30 μm) (N-25).

[Preparation of negative electrode active material slurry]
The silicon oxide particles (N-21) 1.5 parts were changed to composite particles (N-25) 3 parts, the amount of carbon-based coated negative electrode active material particles (N-1) was changed to 3 parts, and the conductivity 0.25 part of carbon filler A is changed to 0.2 part of conductive carbon filler C, and the electrolyte is Li (FSO ₂ ) in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1: 1). ₂ N ((Lithium bis (fluorosulfonyl) imide: LiFSI) was dissolved in a ratio of 2M (mol / L) and changed to 93.8 parts of electrolyte Y, and the kneading conditions were changed to 2000 rpm for 10 minutes. Otherwise, a negative electrode active material slurry 9 according to Example 9 was produced in the same procedure as in Example 1.

The conductive carbon filler C includes carbon nanofiber [manufactured by Showa Denko KK, VGCF (registered trademark), aspect ratio 60 (average fiber diameter: about 150 nm, average fiber length: about 9 μm), electrical resistivity 40 μΩm, bulk A density of 0.04 g / cm ³ ] was used.

[Preparation of negative electrode active material layer]
A negative electrode active material layer 9 according to Example 9 was produced in the same procedure as in Example 1 except that the obtained negative electrode active material slurry 9 was used and the weight per unit area was changed to 25 mg / cm ² . The thickness of the negative electrode active material layer 9 was 360 μm.

The observation cross section prepared by cutting the obtained negative electrode active material layer 9 under freezing was enlarged and observed with an SEM. As a result, an aggregate of the conductive carbon filler C was confirmed, and the average diameter was 20 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 9 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 49.5 mg / cm ^2. An active material layer 9 was produced.

The lithium ion battery 9 according to Example 9 was used in the same procedure as in Example 1 except that the obtained positive electrode active material layer 9 and negative electrode active material layer 9 were used and the electrolyte solution Y was used instead of the electrolyte solution X. Manufactured.

<Example 10>
[Preparation of negative electrode active material slurry]
The amount of the composite particles (N-25) used was changed to 0.25 parts, the amount of the carbon-based coated negative electrode active material particles (N-1) was changed to 4.3 parts, and the conductive carbon filler C 0. A negative electrode active material slurry 10 was prepared in the same procedure as in Example 9, except that 2 parts were changed to 0.15 parts of conductive carbon filler A and the amount of electrolyte Y used was changed to 95.3 parts.

[Preparation of negative electrode active material layer]
A negative electrode active material layer 10 according to Example 10 was produced in the same procedure as in Example 9, except that the obtained negative electrode active material slurry 10 was changed so that the basis weight was 40 mg / cm ² . The thickness of the negative electrode active material layer 10 was 500 μm.

When the observation cross section prepared by cutting the obtained negative electrode active material layer 10 under freezing was enlarged and observed with an SEM, an aggregate of the conductive carbon filler A was confirmed, and the average diameter was 10 μm.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 10 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 79.2 mg / cm ^2. An active material layer 10 was produced.

Using the obtained positive electrode active material layer 10 and negative electrode active material layer 10, a lithium ion battery 10 according to Example 10 was manufactured in the same procedure as in Example 9.

<Example 11>
[Preparation of negative electrode active material slurry]
Except for changing 0.2 part of the conductive carbon filler C to 0.3 part of the conductive carbon filler A and changing the amount of the electrolyte Y used to 93.7 parts, the negative electrode active Material slurry 11 was prepared.

[Preparation of negative electrode active material layer]
Using the obtained negative electrode active material slurry 11, a negative electrode active material layer 11 according to Example 11 was produced in the same procedure as in Example 9. The thickness of the negative electrode active material layer 11 was 350 μm.

Further, when an observation cross section prepared by cutting the obtained negative electrode active material layer 11 under freezing was enlarged and observed with an SEM, an aggregate of the conductive carbon filler A was confirmed, and the average diameter was 15 μm. It was.

[Preparation of positive electrode active material layer]
A positive electrode according to Example 11 in the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 49.5 mg / cm ^2. An active material layer 11 was produced.

Using the obtained positive electrode active material layer 11 and negative electrode active material layer 11, a lithium ion battery 11 according to Example 11 was manufactured in the same procedure as in Example 9.

<Example 12>
[Preparation of negative electrode active material slurry]
A negative electrode active material slurry 12 was prepared in the same procedure as in Example 11 except that 0.3 part of the conductive carbon filler A was changed to 0.2 part of the conductive carbon filler A and 0.1 part of the conductive carbon filler B. did.

The conductive carbon filler B includes acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.], aspect ratio 1 (powder product having an average primary particle size of 35 nm), electrical resistivity 60 μΩm, and bulk density 0.04 g / cm. ³ ] was used.

[Preparation of negative electrode active material layer]
Using the obtained negative electrode active material slurry 12, a negative electrode active material layer 12 according to Example 12 was produced in the same procedure as in Example 11. The thickness of the negative electrode active material layer 12 was 360 μm.

Moreover, when the observation cross section prepared by cutting the obtained negative electrode active material layer 12 under freezing was enlarged and observed with an SEM, an aggregate composed of the conductive carbon filler A and the conductive carbon filler B could be confirmed. The average diameter was 15 μm.

[Preparation of positive electrode active material layer]
According to the procedure of Example 12, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 49.5 mg / cm ^2. A positive electrode active material layer 12 was produced.

Using the obtained positive electrode active material layer 12 and negative electrode active material layer 12, a lithium ion battery 12 according to Example 12 was manufactured in the same procedure as in Example 9.

<Comparative Example 1>
[Preparation of negative electrode active material slurry]
The amount of electrolyte X used was changed to 90 parts, 1.5 parts of silicon oxide particles (N-21) were changed to 1.7 parts of silicon particles (N-23), and carbon-based coated negative electrode active material particles (N -1) was changed to 3.3 parts and the conductive carbon filler A was changed to 0 part. Was made.

[Preparation of negative electrode active material layer]
The obtained negative electrode active material slurry 13 was laminated on an aramid nonwoven fabric so that the basis weight was 15 mg / cm ^2, and then dried at 100 ° C. for 15 minutes. A negative electrode active material layer 13 according to Comparative Example 1 was produced. The thickness of the negative electrode active material layer 13 was 200 μm.

[Preparation of positive electrode active material layer]
According to the same procedure as in Example 1, except that the positive electrode active material slurry 1 obtained in the same manner as in Example 1 was used and the basis weight was changed to 29.7 mg / cm ^2. A positive electrode active material layer 13 was produced.

Using the obtained positive electrode active material layer 13 and negative electrode active material layer 13, a lithium ion battery 13 according to Comparative Example 1 was manufactured in the same procedure as in Example 1.

<Comparative example 2>
[Preparation of negative electrode active material slurry]
A negative electrode active material slurry 14 according to Comparative Example 2 was prepared in the same procedure as in Example 11 except that the electrolytic solution Y was changed to the electrolytic solution X and the amount of the conductive carbon filler A was changed to 0 part. did.

[Preparation of negative electrode active material layer]
A negative electrode active material layer 14 according to Comparative Example 2 was produced from the obtained negative electrode active material slurry 14 in the same procedure as in Example 11. The thickness of the negative electrode active material layer 14 was 340 μm.

[Preparation of positive electrode active material layer]
Using the positive electrode active material slurry 1 obtained in the same manner as in Example 1, a positive electrode active material layer 14 according to Comparative Example 2 was produced in the same procedure as in Example 11.

Using the obtained positive electrode active material layer 14 and negative electrode active material layer 14, a lithium ion battery 14 according to Comparative Example 2 was manufactured in the same procedure as in Example 1.

[Measurement of battery characteristics]
For the lithium ion batteries 1 to 14 according to Examples 1 to 12 and Comparative Examples 1 to 2, the battery characteristics (capacity maintenance ratio after 10 cycles, expansion coefficient of the negative electrode active material layer at the first charge) are measured by the following methods. did.

With respect to the produced lithium ion batteries 1 to 14 according to Examples 1 to 12 and Comparative Examples 1 to 2, a charge / discharge test was performed by the following method using a charge / discharge measurement apparatus “HJ0501SM” [made by Hokuto Denko Co., Ltd.] The expansion rate of the negative electrode active material layer after the first charge and the ratio of the discharge capacity at the 10th cycle to the discharge capacity at the 1st cycle (also referred to as the capacity retention rate after 10 cycles) were obtained. The results are shown in Table 1.

Charging / discharging in which the lithium ion battery for battery characteristic evaluation is charged to 4.2 V with a current of 0.1 C under a condition of 45 ° C., and discharged to 2.5 V with a current of 0.05 C after 10 minutes of rest. The process (charge / discharge cycle) was repeated 10 times (10 cycles) with a pause of 10 minutes.

In addition, the expansion coefficient of the negative electrode active material layer after the first charge was calculated by the following formula (2).

Moreover, the capacity maintenance rate was calculated by the following formula (3). It means that the larger the value of the capacity retention rate, the better the cycle characteristics with less decrease in capacity.

Note that the amount of increase in the thickness of the negative electrode active material layer after the first charge is obtained by subtracting the thickness of the negative electrode active material layer before the first charge from the thickness of the negative electrode active material layer after the first charge. The thickness of the negative electrode active material layer was measured using a contact-type film thickness meter [ABS Digimatic Indicator ID-CX manufactured by Mitutoyo Corporation].

From the results of Table 1, the negative electrodes for lithium ion batteries of Examples 1 to 12 and the lithium ion batteries using the same were compared with the negative electrodes for lithium ion batteries of Comparative Examples 1 and 2 and the lithium ion batteries using the same. It can be seen that expansion of the negative electrode active material layer is suppressed and the cycle characteristics are excellent.

The negative electrode for lithium ion batteries of the present invention is particularly useful as a negative electrode for bipolar secondary batteries and lithium ion batteries used for mobile phones, personal computers, hybrid vehicles, and electric vehicles.

This application is based on Japanese Patent Application No. 2016-2469994 filed on December 20, 2016 and Japanese Patent Application No. 2017-238950 filed on December 13, 2017, and its disclosure The contents are cited as a whole by reference.

1 negative electrode active material layer,
11 silicon and / or silicon compounds,
13 Carbon-based negative electrode active material,
15 Pressure relief material.

Claims (7)

A negative electrode for a lithium ion battery having a negative electrode active material layer,
The negative electrode active material layer comprises a non-binding body of a mixture comprising silicon and / or a silicon compound, a carbon-based negative electrode active material, and a pressure relaxation material,
The negative electrode for a lithium ion battery, wherein the pressure relaxation material is an aggregate of conductive carbon filler. 2. The negative electrode for a lithium ion battery according to claim 1, wherein a mass mixing ratio of a sum of the silicon and the silicon compound contained in the mixture and the carbon-based negative electrode active material is 5:95 to 95: 5. The negative electrode for a lithium ion battery according to claim 1 or 2, wherein a ratio of the weight of the pressure relaxation material to the weight of the negative electrode active material layer is 3 to 30% by mass. The silicon compound includes silicon oxide (SiO _x ), carbon-coated silicon oxide, Si—C composite, Si—Al alloy, Si—Li alloy, Si—Ni alloy, Si—Fe alloy, Si—Ti alloy, The negative electrode for a lithium ion battery according to any one of claims 1 to 3, wherein the negative electrode is at least one selected from the group consisting of a Si-Mn alloy, a Si-Cu alloy, and a Si-Sn alloy. The negative electrode for a lithium ion battery according to any one of claims 1 to 4, wherein the conductive carbon filler has an aspect ratio of 20 to 10,000. The negative electrode for a lithium ion battery according to any one of claims 1 to 5, wherein the conductive carbon filler is at least one selected from the group consisting of carbon nanofibers, carbon fibers, and carbon nanotubes. A lithium ion battery comprising the negative electrode for a lithium ion battery according to any one of claims 1 to 6.

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