WO2018084319A1

WO2018084319A1 - Negative electrode for lithium-ion battery, and lithium-ion battery

Info

Publication number: WO2018084319A1
Application number: PCT/JP2017/040163
Authority: WO
Inventors: 南　和也; 勇輔中嶋; 大澤　康彦; 雄樹草地; 佐藤　一; 赤間　弘; 堀江　英明
Original assignee: 日産自動車株式会社
Priority date: 2016-11-07
Filing date: 2017-11-07
Publication date: 2018-05-11
Also published as: CN109923699A; CN109923699B

Abstract

[Problem] To provide a negative electrode for a lithium-ion battery having high energy density and excellent quick charge characteristics. [Solution] A negative electrode for a lithium-ion battery, the negative electrode comprising: a negative electrode collector; a negative electrode active material layer formed on the surface of the negative electrode collector; and a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte including lithium ions. The negative electrode for a lithium-ion battery is characterized in that the negative electrode active material layer contains a negative electrode active material and voids, the voids are filled with the nonaqueous electrolyte solution, and the ratio of the battery capacity based on the total amount of lithium ions in the nonaqueous electrolyte solution present in the negative electrode active material layer to the battery capacity based on the total amount of the negative electrode active material is 3-17%.

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 secondary battery that can achieve a high energy density and a high output density.

As for lithium ion secondary batteries, various studies have been conducted in order to further improve battery characteristics such as output. For example, as lithium ion secondary batteries capable of increasing capacity, nano-sized oxidation is performed on conductive carbon powder. A battery using a negative electrode active material on which tin particles are supported is known (see JP 2011-253620 A).

On the other hand, it is also required to be able to handle rapid charging. In general, in order to enable rapid charging without lowering the energy density of the battery, a thin film is also formed on components other than the electrode active material layer (positive electrode active material layer or negative electrode active material layer), such as separators and current collectors. It is necessary to make it. However, if the separator is made too thin, there is a problem that an internal short circuit is likely to occur due to precipitated lithium, and if the current collector is made too thin, there is a problem that the internal resistance of the battery increases. That is, if the charging rate is increased by reducing the thickness of the electrode, there is a problem that the volume occupied by the separator and the current collector in the entire battery increases, and the energy density of the entire battery decreases. In addition, when the amount of the negative electrode active material per unit volume is increased in order to improve the energy density in the thinned electrode (increasing the packing density of the negative electrode active material), the nonaqueous electrolyte present around the negative electrode active material Therefore, even if the conventional battery capable of increasing the capacity described in Japanese Patent Application Laid-Open No. 2011-253620 is used, it is difficult to cope with rapid charging. There was a problem that it was difficult to achieve both capacity enhancement (energy density improvement).

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a negative electrode for a lithium ion battery having high energy density and excellent quick charge 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 lithium battery comprising a negative electrode current collector, a negative electrode active material layer formed on the surface of the negative electrode current collector, a nonaqueous electrolyte solution containing an electrolyte containing lithium ions and a nonaqueous solvent. The negative electrode for an ion battery, wherein the negative electrode active material layer includes a negative electrode active material and a void, and the void is filled with the non-aqueous electrolyte, and the battery capacity based on the total amount of the negative electrode active material A negative electrode for a lithium ion battery, wherein the ratio of the battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer is 3 to 17%; and The present invention relates to a lithium ion battery.

Hereinafter, the present invention will be described in detail. Note that in this specification, a lithium ion battery includes a lithium ion secondary battery.

The present invention relates to a lithium ion battery comprising a negative electrode current collector, a negative electrode active material layer formed on the surface of the negative electrode current collector, a nonaqueous electrolyte solution containing an electrolyte containing lithium ions and a nonaqueous solvent. The negative electrode active material layer includes a negative electrode active material and a void, and the void is filled with the non-aqueous electrolyte, and the battery capacity based on the total amount of the negative electrode active material is A negative electrode for a lithium ion battery, wherein a ratio of a battery capacity based on a total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer is 3 to 17%. When the negative electrode for a lithium ion battery of the present invention is used, a lithium ion battery having high energy density and excellent quick charge characteristics can be obtained. In this specification, “X to Y” indicating a range includes X and Y, and means “X or more and Y or less”.

As a result of diligent research on the problems of lithium ion batteries whose electrodes have been thinned by conventional methods, the number of lithium ions present around the negative electrode active material has decreased with the thinning of the electrodes. It was speculated that this was the cause.

In the prior art, when the distance between the positive electrode and the negative electrode is shortened by thinning the separator, the diffusion distance of lithium ions is shortened, and it is considered that rapid charging can be supported. On the other hand, when the packing density of the negative electrode active material is increased in order to increase the energy density, the amount of the non-aqueous electrolyte present around the negative electrode active material is relatively reduced, and the It is thought that charging will not be possible. In addition, if the amount of the negative electrode active material is increased without increasing the packing density of the negative electrode active material, the distance between the positive electrode and the negative electrode becomes long. Conceivable.

The problem with rapid charging is the movement rate of lithium ions from the positive electrode to the negative electrode inside the lithium ion battery (also called the diffusion rate), but there is a sufficient amount of lithium ions around the negative electrode active material. In this case, when the charging reaction is started, first, lithium ions present around the negative electrode active material are taken into the negative electrode active material. In the case where charging does not end even when lithium ions around the negative electrode active material are taken into the negative electrode active material, it is considered that lithium ions desorbed from the positive electrode are taken into the negative electrode active material and the charging reaction proceeds.

Here, it is considered that the lithium ions existing around the negative electrode active material before the start of charging can respond to rapid charging because the distance between the lithium ions and the negative electrode active material is very close. On the other hand, in order for lithium ions present in the positive electrode to be taken into the negative electrode, it is necessary to move between the positive electrode and the negative electrode, so that the diffusion rate of lithium ions is rate-limiting and cannot be used for rapid charging.

On the other hand, in the negative electrode for lithium ion batteries of the present invention, the non-aqueous electrolyte is filled in the voids present around the negative electrode active material, and the negative electrode active material layer with respect to the battery capacity based on the total amount of the negative electrode active material Since the battery capacity ratio (battery capacity ratio) based on the total amount of lithium ions in the non-aqueous electrolyte present in the battery is 3 to 17%, lithium that can be rapidly charged around the negative electrode active material It can be said that there are enough ions. When the ratio of the battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer is less than 3%, there are not enough lithium ions that can be used for rapid charging around the negative electrode active material. If it exceeds 17%, the rapid charge characteristics deteriorate due to an increase in solution resistance due to the increase in the concentration of the electrolyte and precipitation of lithium salts. The battery capacity ratio is preferably 5 to 17%, more preferably 10 to 17%.

Furthermore, since a sufficient amount of lithium ions is present around the negative electrode active material in the negative electrode for a lithium ion battery of the present invention, it is not necessary to consider the diffusion rate of lithium ions between the positive electrode and the negative electrode in rapid charging. That is, in the negative electrode for a lithium ion battery of the present invention, even if the energy density is increased by increasing the amount of the negative electrode active material, the diffusion rate of lithium ions between the positive electrode and the negative electrode does not affect the charging rate. Therefore, the quick charge characteristic is not deteriorated.

Therefore, the lithium ion battery using the negative electrode for the lithium ion battery of the present invention can achieve both rapid charging and improved energy density.

In addition, the battery capacity based on the total amount of the negative electrode active material is a theoretical battery capacity based on the weight of the negative electrode active material constituting the negative electrode active material layer. However, the theoretical value of the battery capacity refers to that which can withstand repeated charge and discharge, and excludes the initial charge capacity when repeated charge and discharge is difficult due to irreversible reaction. Also, the battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer means that all the lithium ions in the non-aqueous electrolyte contained in the negative electrode active material layer are converted into the negative electrode active material. It is the battery capacity when inserted.

The battery capacity based on the total amount of the negative electrode active material is calculated according to the following formula.
Battery capacity [mAh / cm ² ] = negative electrode active material capacity [mAh / g] × negative electrode active material basis weight [mg / cm ² ] / 10 ³
Note that the negative electrode active material capacity [mAh / g] represents the negative electrode active material (in the case where the negative electrode active material is a coated negative electrode active material coated with a coating layer containing a polymer compound), ethylene carbonate A mixture of non-aqueous electrolyte prepared by dissolving LiN (FSO ₂ ) ₂ at a ratio of 3 mol / L in a mixed solvent of (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) to form an aramid After applying to one side of a separator [manufactured by Japan Vilene Co., Ltd.], press for 10 seconds at a pressure of 10 MPa to prepare an electrode, and it is incorporated into the battery pack in a state facing the counter electrode (metal lithium) through the separator, Discharge capacity when discharged from 0.0 V to 1.5 V (discharge rate: 1/20 C) at room temperature, charge / discharge measuring device “Battery Analyzer 1470 type” [Stock Board Toyo obtained by measuring at Technica Ltd.] and the like.

The battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer can be uniquely derived from the thickness of the negative electrode active material layer, the porosity, and the electrolyte concentration of the non-aqueous electrolyte. It can be adjusted by combining them in a timely manner. The calculation formula is as follows.
Battery capacity [mAh / cm ² ] based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer = electrode void volume [cm ³ ] × the electrolyte concentration of the non-aqueous electrolyte [mol / L] / 10 ³ × capacity conversion constant [mAh / mol] / electrode area [cm ² ]
Capacity conversion constant [mAh / mol]: 26806
The capacity conversion constant represents the battery capacity per lithium ion.
Electrode void volume [cm ³ ] = Porosity [volume%] × Electrode film thickness [μm] / 10 ⁴ × electrode area [cm ² ]
The battery capacity ratio (battery capacity ratio) based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer with respect to the battery capacity based on the total amount of negative electrode active material is the type of negative electrode active material, negative electrode active It can be controlled by the weight of the negative electrode active material in the material layer, the porosity of the negative electrode active material layer, the electrolyte concentration of the non-aqueous electrolyte, and the like.

For example, when the basis weight of the negative electrode active material layer is increased or the porosity is decreased, the battery capacity based on the total amount of the negative electrode active material is increased and the battery capacity ratio is decreased. On the other hand, increasing the electrolyte concentration of the non-aqueous electrolyte or increasing the porosity of the negative electrode active material layer increases the battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer. As a result, the battery capacity ratio increases.

As the negative electrode active material constituting the negative electrode for a lithium ion battery of the present invention, those conventionally used as an active material for a negative electrode of a lithium ion battery can be suitably used.

Examples of the 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 and petroleum coke etc.), silicon carbide and carbon fiber etc.], conductive polymers (eg polyacetylene and polypyrrole etc.), metals (tin, silicon, aluminum, zirconium and titanium etc.), metal oxides (titanium oxide, Lithium-titanium oxide, silicon oxide, etc.) and metal alloys (for example, lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy and lithium-aluminum-manganese alloy). Two or more negative electrode active materials may be used in combination.

Among the negative electrode active materials described above, those that do not contain lithium or lithium ions may be subjected to a pre-doping treatment in which lithium or lithium ions are included in part or all of the active material in advance. Among these, from the viewpoint of capacity and output characteristics, a carbon-based material or a metal oxide is preferably used as the negative electrode active material.

The volume average particle diameter of the negative electrode active material is preferably from 0.01 to 100 μm, more preferably from 0.1 to 20 μm, and even more preferably from 2 to 20 μm, from the viewpoint of the electric characteristics of the battery.

In the present specification, the volume average particle diameter of the negative electrode active material means a particle diameter (Dv50) at an integrated value of 50% in a particle size distribution obtained by a microtrack method (laser diffraction / scattering method). 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.

In the negative electrode for a lithium ion battery of the present invention, the negative electrode active material layer includes a negative electrode active material and voids. A sufficient amount of lithium ions can be disposed around the negative electrode active material by filling the voids with the non-aqueous electrolyte containing lithium ions in the negative electrode active material layer.

The void volume in the negative electrode active material layer is such that the battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer is 3 to 17% of the battery capacity based on the total amount of negative electrode active material. The total volume of the voids is preferably 35 to 60% by volume, more preferably 35 to 50% by volume, based on the total volume of the negative electrode active material layer. When voids of 35 to 60% by volume of the total volume are formed in the negative electrode active material layer, a sufficient amount of lithium ions is arranged around the negative electrode active material by filling the voids with a non-aqueous electrolyte. can do.

In the present specification, the void refers to a void included in the negative electrode active material layer in a state where the negative electrode is not impregnated with the non-aqueous electrolyte. The porosity can also be obtained by image analysis of the cross section of the negative electrode active material layer by X-ray computed tomography (CT) or the like.

However, when the negative electrode active material layer contains an electrolytic solution and other components and an X-ray CT image of the negative electrode active material layer including voids cannot be obtained, the measurement is performed by the following method.
The porosity is the total volume value of each component obtained by dividing the weight of each solid component (excluding the electrolyte) constituting the negative electrode active material layer having a constant volume by the true density of each component. The value obtained by subtracting from the volume of can be calculated by further dividing by the volume of the negative electrode active material layer.

The weight and true density of each solid component can be determined by solid-liquid separation of a cleaning solution obtained by cleaning the negative electrode with a non-aqueous solvent, and removing the non-aqueous solvent.

The solid component is not separated into a component that dissolves in a non-aqueous solvent and a component that does not dissolve, and as a mixture of solid components, the weight is divided by the true density to obtain the volume of the entire solid component, You may replace with the method of measuring a weight and a true density for every component.

The thickness of the negative electrode active material layer (hereinafter also simply referred to as “film thickness”) is not particularly limited, but is preferably 100 μm or more and 1500 μm or less, and preferably 150 μm or more and 1200 μm from the viewpoint of achieving both energy density and input / output characteristics. Or less, more preferably 200 μm or more and 800 μm or less.

The amount of the non-aqueous electrolyte that the negative electrode active material layer can hold per unit area is not particularly limited, but is preferably 6 to 120 μL / cm ² .

The reference surface per unit area is a surface parallel to the surface of the negative electrode current collector. When the amount of the non-aqueous electrolyte that the negative electrode active material layer can hold per unit area is 6 μL / cm ² or more, the total amount of lithium ions present around the negative electrode active material is sufficiently obtained, and the rate characteristics are excellent. The amount of the non-aqueous electrolyte solution that can be held per unit area can be determined by calculating from the porosity and film thickness of the negative electrode active material layer.

The negative electrode current collector is not particularly limited, but copper, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer (polymer having an electron conductive skeleton) or non-conductive polymer material as a resin Examples thereof include a material to which a conductive material is added if necessary, and a foil containing a conductive material such as conductive glass. Among these, from the viewpoint of safety, it is preferable to use a resin current collector containing a conductive material and a resin as the negative electrode current collector.

The conductive material contained in the resin current collector is selected from conductive materials. Specifically, metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.), etc. , And mixtures thereof, but are not limited thereto. These conductive materials may be used alone or in combination of two or more. Alternatively, an alloy or metal oxide of the above metal may be used. From the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium and a mixture thereof are preferable, silver, aluminum, stainless steel and carbon are more preferable, and carbon is more preferable. In addition, as these conductive materials, a particulate ceramic material or a resin material may be coated with a conductive material (a metal material among the above-described conductive materials) by plating or the like.

The average particle diameter of the conductive material is not particularly limited, but is preferably from 0.01 to 10 μm, more preferably from 0.02 to 5 μm, from the viewpoint of the electric characteristics of the battery. More preferably, the thickness is 03 to 1 μm. The “particle diameter of the conductive material” means the maximum distance among any two points on the contour line of the conductive material. 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, and in a form that is put into practical use as a so-called filler-based conductive resin composition such as carbon nanofiller and carbon nanotube. There may be.

The conductive material may be a conductive fiber having a fibrous shape. Examples of conductive fibers include carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers obtained by uniformly dispersing highly conductive metal and graphite in synthetic fibers, and metals such as stainless steel. Examples thereof include fiberized metal fibers, conductive fibers in which the surface of organic fiber is coated with metal, and conductive fibers in which the surface of organic fiber is coated with a resin containing a conductive substance. Among these conductive fibers, carbon fibers are preferable. A polypropylene resin in which graphene is kneaded is also preferable. When the conductive material is a conductive fiber, the average fiber diameter is preferably 0.1 to 20 μm.

The resins contained in the resin current collector include 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).

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 , A sulfonylimide-based electrolyte having fluorine atoms such as LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) _{2, and} a fluorine atom such as LiC (CF ₃ SO ₂ ) ₃ are used. Examples thereof include a sulfonylmethide-based electrolyte. Among these, a sulfonylimide-based electrolyte having a fluorine atom is preferable from the viewpoint of ion conductivity at a high concentration and a thermal decomposition temperature, and LiN (FSO ₂ ) ₂ is more preferable. LiN (FSO ₂ ) ₂ may be used in combination with other electrolytes, but is more preferably used alone.

The electrolyte concentration of the non-aqueous electrolyte is not particularly limited, but is preferably 1 to 5 mol / L, and preferably 1.5 to 4 mol / L from the viewpoints of the handleability of the non-aqueous electrolyte and battery capacity. More 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 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, and preferably do not contain a nitrile compound. More preferred are lactone compounds, cyclic carbonates and chain carbonates, and particularly preferred is a mixture of cyclic carbonate and chain carbonate. Most preferred is a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) or a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC).

The negative electrode active material layer may further contain a conductive material. Examples of the conductive material include conductive fibers.

When the negative electrode active material layer further includes a conductive fiber, the conductive fiber can function to assist electronic conduction in the negative electrode active material layer, and the conductive fiber described above with respect to the resin current collector is used as the conductive fiber. The same thing as a property fiber can be used. When the negative electrode active material layer further contains conductive fibers, it is preferable to use a coated negative electrode active material described later as the negative electrode active material.

When the negative electrode active material layer further contains conductive fibers, the content of the conductive fibers contained in the negative electrode active material layer is preferably 25% by weight or less with respect to the total weight of the negative electrode active material layer.

However, it goes without saying that a conductive agent having no fibrous form may be used. For example, a conductive agent having a particulate (for example, spherical) form can be used. When the conductive agent is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, plate, column, indefinite shape, flake shape, and spindle shape. As the conductive agent having a particulate (for example, spherical) form, the same conductive material as that described for the resin current collector can be used.

The negative electrode active material is preferably partially or entirely covered with a coating layer containing a polymer compound. A negative electrode active material in which part or all of the surface is coated with a coating layer is also referred to as a coated negative electrode active material. When the surface of the negative electrode active material is coated with the coating layer, the volume change of the negative electrode is relieved and the negative electrode can be prevented from expanding. Furthermore, the wettability of the negative electrode active material with respect to the non-aqueous solvent can be improved.

Examples of the polymer compound constituting the coating layer include a polymer compound having a liquid absorption rate of 10% or more when immersed in a non-aqueous electrolyte and a tensile elongation at break in a saturated liquid absorption state of 10% or more. preferable.

The liquid absorption rate when immersed in the non-aqueous electrolyte is obtained by the following equation by measuring the weight of the polymer compound before and after being immersed in the non-aqueous electrolyte.
Absorption rate (%) = [(weight of polymer compound after immersion in non-aqueous electrolyte−weight of polymer compound before immersion in non-aqueous electrolyte) / weight of polymer compound before immersion in non-aqueous electrolyte] × 100
As a non-aqueous electrolyte for obtaining the liquid absorption rate, LiPF ₆ as an electrolyte was added at a concentration of 1 mol / liter in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC: DEC = 3: 7. A nonaqueous electrolytic solution dissolved to a concentration of L is used.

Immersing in non-aqueous electrolyte when calculating 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 non-aqueous electrolyte.

In addition, the non-aqueous electrolyte used when manufacturing a lithium ion battery is not limited to the said non-aqueous electrolyte, You may use another non-aqueous electrolyte.

When the liquid absorption rate is 10% or more, the polymer compound sufficiently absorbs the non-aqueous electrolyte, and lithium ions can easily permeate the polymer compound. The movement of lithium ions between electrolytes is not hindered. If the liquid absorption rate is less than 10%, the non-aqueous electrolyte does not easily penetrate into the polymer compound, so that the lithium ion conductivity is lowered and the performance as a lithium ion battery may not be sufficiently exhibited. The liquid absorption is more preferably 20% or more, and further preferably 30% or more. Moreover, as a preferable upper limit of a liquid absorption rate, it is 400%, and as a more preferable upper limit, it is 300%.

The tensile elongation at break in the saturated liquid absorption state is obtained by punching the polymer compound into a dumbbell shape and immersing in a non-aqueous electrolyte at 50 ° C. for 3 days in the same manner as the measurement of the liquid absorption rate described above to saturate the polymer compound. As a liquid absorption state, it can measure based on 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.
Tensile elongation at break (%) = [(length of specimen at break−length of specimen before test) / length of specimen before test] × 100
When the tensile elongation at break in the saturated liquid absorption state of the polymer compound is 10% or more, the polymer compound has an appropriate flexibility, so that the coating layer peels off due to the volume change of the negative electrode active material during charge / discharge. It becomes easy to suppress this. The tensile elongation at break is more preferably 20% or more, and further preferably 30% or more. Further, the preferable upper limit value of the tensile elongation at break is 400%, and the more preferable upper limit value is 300%.

Subsequently, the polymer compound constituting the coating layer will be specifically described. Examples of the polymer compound constituting the coating layer include thermoplastic resins and thermosetting resins, such as vinyl resins, urethane resins, polyester resins, polyamide resins, epoxy resins, polyimide resins, silicone resins, phenol resins, Examples include melamine resins, urea resins, aniline resins, ionomer resins, polycarbonates, polysaccharides (such as sodium alginate), and mixtures thereof. Of these, vinyl resins are preferred.

The vinyl resin is a resin comprising a polymer (A1) having the vinyl monomer (a) as an essential constituent monomer.
In particular, the polymer (A1) is a monomer containing a vinyl monomer (a1) having a carboxyl group or an acid anhydride group as the vinyl monomer (a) and a vinyl monomer (a2) represented by the following general formula (1). A polymer of the composition is preferred.
CH ₂ = C (R ¹ ) COOR ² (1)
[In Formula (1), R ¹ is a hydrogen atom or a methyl group, and R ² is a straight chain or branched alkyl group having 4 to 36 carbon atoms. ]
Among the vinyl resins, those having a liquid absorption rate of 10% or more when immersed in a non-aqueous electrolyte and a tensile elongation at break in a saturated liquid absorption state of 10% or more are more preferable.

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

In the vinyl 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) 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, -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 -Methyloctyl group, 3-methyloctyl group, 4-methyloctyl group, 5-methyloctyl group, 6-methyloctyl group, 7-methyloctyl group Tyl 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-methyloctyl group, Tildecyl 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-dimethyl Sil 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. Among these, a 2-ethylhexyl group is 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- Hexadecyl octadecyl group, 2-tetradecyleicosyl group, 2-hexadecyleicosyl group, etc.], 3 to 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 weight, and preferably 15 to 55% by weight based on the total weight of the polymer (A1) from the viewpoint of suppressing volume change of the negative electrode active material. More preferred is 20 to 50% by weight.

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, its content is preferably 0.1 to 15% by weight based on the total weight of the polymer compound from the viewpoint of internal resistance and the like. It is more preferably ˜15% by weight, and further preferably 2-10% by weight.

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 above vinyl monomer (a2), an ester compound (a3) of a monovalent aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid, and if necessary. A monomer composition comprising a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group to be used is polymerized, and the vinyl monomer (a2) and the (meta ) Acrylic acid (a11) weight ratio [the ester compound (a21) / (meth) acrylic acid (a11)] is preferably 10/90 to 90/10. When the weight ratio of vinyl monomer (a2) to (meth) acrylic acid (a11) is 10/90 to 90/10, the polymer obtained by polymerizing this has good adhesion to the negative electrode active material and is peeled off. It becomes difficult to do. The weight ratio is, for example, 20/80 to 85/15, preferably 30/70 to 85/15, and more preferably 40/60 to 70/30.

The monomer constituting the polymer (A1) includes a vinyl monomer (a1) having a carboxyl group or an acid anhydride group, a vinyl monomer (a2) represented by the above general formula (1), and a carbon number of 1 In addition to the ester compound (a3) of a monovalent aliphatic alcohol of 1 to 3 and (meth) acrylic acid and a salt of an anionic monomer having a polymerizable unsaturated double bond and an anionic group (a4) As long as the physical properties of the polymer (A1) are not impaired, the vinyl monomer (a1), the vinyl monomer (a2) represented by the general formula (1), and a monovalent aliphatic alcohol having 1 to 3 carbon atoms, It can be copolymerized with an ester compound (a3) with (meth) acrylic acid and may contain a radical 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 ) Propylene oxide of acrylate, 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) amide group having 4 to 20 carbon atoms, excluding the above (meth) acrylamide compounds Vinyl compounds such as N-methyl-N-vinylacetamide, cyclic amides [pyrrolidone compounds (having 6 to 13 carbon atoms, such as N-vinylpyrrolidone)]
(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 7-14, such as 2- or 4-vinylpyridine), imidazole compound (carbon number 5-12, such as N-vinylimidazole), pyrrole compound (carbon number) 6 to 13, for example, N-vinylpyrrole), pyrrolidone compound (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 compounds Vinyl compound Nitro group-containing vinyl compound (carbon number 8 to 16, for example, nitrostyrene) etc. (a54) Vinyl hydrocarbon (a54-1) Aliphatic vinyl hydrocarbon Olefin having 2 to 18 or more carbon atoms (ethylene, propylene, Butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), diene having 4 to 10 or more carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7- Octadiene etc.) (a54-2) Alicyclic vinyl hydrocarbon charcoal Cyclic unsaturated compounds having 4 to 18 or more primes, such as cycloalkene (eg cyclohexene), (di) cycloalkadiene [eg (di) cyclopentadiene], terpene (eg pinene and limonene), indene (a54-3) Aromatic vinyl hydrocarbons C8-20 aromatic unsaturated compounds such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, 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 azide) Page , 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 Ester (eg acetoxystyrene)]
(A56) Vinyl ether aliphatic vinyl ether [C3-15, such as vinylalkyl (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 (carbon number 8-20, eg vinyl phenyl ether , Phenoxystyrene)
(A57) Vinyl ketone aliphatic vinyl ketone (having 4 to 25 carbon atoms, such as vinyl methyl ketone, vinyl ethyl ketone), 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 straight, 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 vinyl monomer (a1) having a carboxyl group or an acid anhydride group, a vinyl monomer (a2) represented by the above general formula (1), a monovalent aliphatic alcohol having 1 to 3 carbon atoms And (meth) acrylic acid ester compound (a3), a salt of an anionic monomer having a polymerizable unsaturated double bond and an anionic group (a4), and a radically polymerizable monomer containing no active hydrogen (a5) ) Based on the weight of the polymer (A1), (a1) is 0.1 to 80% by weight, (a2) is 0.1 to 99.9% by weight, and (a3) is 0 to 60% by weight. It is preferable that (a4) is 0 to 15% by weight, and (a5) is 0 to 99.8% by weight. When the content of the monomer is within the above range, the liquid absorptivity 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.
Apparatus: Alliance GPC V2000 (manufactured by Waters)
Solvent: Orthodichlorobenzene Reference 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-methylbutyronitrile), 2, 2′-azobis (2,4-dimethylvaleronitrile, etc.)], peroxide-based initiators (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.), etc.} (Bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.).

The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the monomers, from the viewpoint of adjusting the number average molecular weight within a preferable range. More preferably, it is 0.1 to 1.5% by weight, and the polymerization temperature and polymerization time are adjusted according to the type of the 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). 4 to 8, for example, n-butane, cyclohexane and toluene) and ketone (having 3 to 9, for example, methyl ethyl ketone), amide (for example, dimethylformamide (hereinafter abbreviated as DMF), dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter, In view of adjusting the number average molecular weight to a preferred range, the amount used is preferably 5 to 900% by weight, more preferably 10 to 400% by weight, based on the total weight of the monomers. More preferably, it is 30 to 300% by weight, and the monomer concentration is 10 to 9 Preferably wt%, more preferably 20 to 90 wt%, more preferably 30 to 80 wt%.

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, and examples of the emulsifier include higher fatty acid (carbon number 10 to 24) metal salt. (For example, sodium oleate and sodium stearate), higher alcohol (10 to 24 carbon atoms) sulfate metal salt (for example, sodium lauryl sulfate), ethoxylated tetramethyldecynediol, sodium sulfoethyl methacrylate, dimethylaminomethyl methacrylate, etc. Is mentioned. Furthermore, you may add polyvinyl alcohol, polyvinylpyrrolidone, etc. as a stabilizer.

The monomer concentration of the solution or dispersion is preferably 10 to 95% by weight, more preferably 20 to 90% by weight, more preferably 30 to 80% by weight. The amount of the polymerization initiator used in the solution or dispersion is The content is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the above.

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 vinyl 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 negative electrode active material with the polymer (A1). Specifically, a negative electrode active material and a resin solution containing the polymer (A1) are mixed and removed to produce a coated negative electrode active material in which the negative electrode active material is coated with the polymer (A1), and then crosslinked. The solution containing the agent (A ′) is mixed with the coated negative electrode active material and heated to cause solvent removal and a crosslinking reaction, and the polymer (A1) is crosslinked by the crosslinking agent (A ′). A method of causing a reaction to be a molecular compound on the surface of the negative electrode active material is exemplified.

Although heating temperature is adjusted according to the kind of crosslinking agent, when using a polyepoxy compound (a'1) as a crosslinking agent, 70 degreeC or more is preferable, and when using a polyol compound (a'2), it is 120 degreeC. The above is preferable.

The coating layer may further contain a conductive agent, and as the conductive agent that can be contained in the coating layer, the same conductive material as that contained in the resin current collector can be suitably used. The same applies to preferred forms, average particle diameters, and the like.

The ratio of the total weight of the polymer compound and the conductive agent contained in the coating layer is not particularly limited, but is preferably 0 to 25% by weight with respect to 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 11% by weight. The ratio of the weight of the conductive agent to the weight of the negative electrode active material is not particularly limited, but is preferably 0 to 14% by weight.

Hereinafter, a method for producing the above-described coated negative electrode active material will be described. The coated negative electrode active material can be produced, for example, by mixing a polymer compound and a negative electrode active material. When the coating layer contains a conductive agent, it may be produced, for example, by mixing a polymer compound, a conductive agent, and a negative electrode active material. A coating material was prepared by mixing a polymer compound and a conductive agent. Then, you may manufacture by mixing this coating | covering material and a negative electrode active material. By the above method, at least a part of the surface of the negative electrode active material is coated with the coating layer containing the polymer compound.

As the negative electrode active material and the polymer compound, those described for the coated negative electrode active material can be preferably used.

The coated negative electrode active material is prepared by, for example, dropping and mixing a polymer solution containing a polymer compound over a period of 1 to 90 minutes in a state where the negative electrode active material is put in a universal mixer and stirred at 300 to 1000 rpm. Stir further. Further, if necessary, a conductive agent is mixed, and then, if necessary, stirring is continued for 10 minutes to 1 hour. After reducing the pressure to 0.007 to 0.04 MPa while stirring, the stirring and the degree of vacuum are maintained. It can be obtained by raising the temperature to 50 to 200 ° C. and holding for 10 minutes to 10 hours, preferably 1 to 10 hours. Thereafter, the coated negative electrode active material obtained as a powder may be classified.

The mixing ratio of the negative electrode active material and the polymer compound is not particularly limited, but it is preferable that the negative electrode active material: polymer compound = 1: 0.001 to 0.1 by weight ratio.

Subsequently, a method for producing the negative electrode for a lithium ion battery of the present invention will be described. Examples of the method for producing a negative electrode for a lithium ion battery according to the present invention include, for example, a negative electrode active material and a conductive agent to be used as needed, based on the weight of a non-aqueous electrolyte or a non-aqueous solvent of the non-aqueous electrolyte. After applying the dispersion liquid in the form of a slurry at a concentration of% by weight to the negative electrode current collector with a coating device such as a bar coater, the dispersion liquid is dried as necessary to obtain a nonaqueous electrolyte or a nonaqueous electrolyte solution. Examples include a method in which a negative electrode active material layer obtained by removing a solvent and the like is pressed with a press if necessary, and the obtained negative electrode active material layer is impregnated with a predetermined amount of a non-aqueous electrolyte. Note that the negative electrode active material layer obtained from the dispersion does not need to be directly formed on the negative electrode current collector, for example, a negative electrode active material layer obtained by applying the dispersion on the surface of an aramid separator or the like, You may arrange | position so that a negative electrode electrical power collector may be contacted.

In addition, the drying performed as necessary after applying the dispersion liquid can be performed using a known dryer such as a forward air dryer, and the drying temperature is determined by the dispersion medium (non-aqueous electrolyte or It can be adjusted according to the type of nonaqueous solvent of the nonaqueous electrolytic solution.

If necessary, a binder such as polyvinylidene fluoride (PVdF) contained in a known negative electrode for a lithium ion battery may be added to the dispersion, but the negative electrode active material is the above-described coated negative electrode active material. It is preferable not to add a binder. Specifically, the binder content is preferably 1% by weight or less, more preferably 0.5% by weight or less, with respect to 100% by weight of the total solid content contained in the negative electrode active material layer. The amount is preferably 0.2% by weight or less, particularly preferably 0.1% by weight or less, and most preferably 0% by weight.

Here, the binder is a polymer material added to bind the negative electrode active material particles and other members and maintain the structure of the negative electrode active material layer, and is a polymer compound for the coating layer contained in the coating layer. Not included. The binder is an insulating material that does not cause a side reaction (oxidation-reduction reaction) during charge and discharge, and generally satisfies the following three points: (1) A slurry used for the production of an active material layer is stable. Maintaining the state (having a dispersing action and a thickening action); (2) Electrode active particles, conductive assistants, etc. are adhered to each other, the mechanical strength as an electrode is maintained, and the particles are electrically Keeping contact; (3) Has adhesion (binding force) to the current collector.

In a conventional negative electrode for a lithium ion battery, it is necessary to maintain a conductive path by fixing a negative electrode active material in the negative electrode with a binder. However, when the coated negative electrode active material is used, it is not necessary to add a binder because the conductive path can be maintained without fixing the negative electrode active material in the negative electrode by the action of the coating layer. By not adding a binder, since the negative electrode active material is not immobilized in the negative electrode, the ability to relax the volume change of the negative electrode active material is further improved.

When a binder is added to the dispersion in which the negative electrode active material is slurried, the amount of addition is determined from the point that the active material layer can be molded while a sufficient amount of voids are formed in the negative electrode active material layer. It is preferably 0.1 to 20% by weight based on the minute weight.

Examples of the binder include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, and polypropylene.

The pressure at which the dried slurry is pressed is not particularly limited. However, if the pressure is too high, a sufficient amount of voids cannot be formed in the negative electrode active material layer. Since it is not observed, it is preferable to press at 1 to 200 MPa.

The preferred form of the negative electrode current collector is as described above.

In the negative electrode for a lithium ion battery of the present invention, the dispersion medium is a non-aqueous electrolyte or a non-aqueous solvent of the non-aqueous electrolyte, and when the applied dispersion is dried, the negative electrode active material layer obtained after drying The weight of the non-aqueous electrolyte obtained by impregnating the non-aqueous electrolyte into the negative electrode active material layer depends on the amount of voids in the negative electrode active material layer and the electrolyte concentration of the non-aqueous electrolyte. Can be adjusted.

The impregnation of the non-aqueous electrolyte with respect to the negative electrode active material layer is performed by a method in which the non-aqueous electrolyte is dropped and impregnated on the surface of the negative electrode active material layer formed by the above method using a dropper or the like. Can do.

The lithium ion battery of the present invention is a battery using the above-described negative electrode for lithium ion battery, and is combined with an electrode serving as a counter electrode of the above negative electrode for lithium ion battery, and stored in a cell container together with a separator, It can be manufactured by a method of injecting and sealing the cell container.

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 containing 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.

Examples of the separator include a microporous film made of polyethylene or polypropylene, a laminated film of a porous polyethylene film and porous polypropylene, a nonwoven fabric containing synthetic fibers (such as polyester fibers and aramid fibers) or glass fibers, and silica on the surface 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, those described in the negative electrode for lithium ion batteries of the present invention can be suitably used.

The positive electrode used for a known lithium ion battery can be used as the electrode (positive electrode) that is the counter electrode of the negative electrode for the lithium ion battery.

The lithium ion battery of the present invention is characterized by using the negative electrode for a lithium ion battery of the present invention. Since the lithium ion battery of the present invention uses the negative electrode for a lithium ion battery of the present invention, it is possible to obtain a lithium ion battery that can be rapidly charged and has a high energy density.

Next, the present invention will be specifically described by way of examples. However, 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 weight”.

<Production Example 1: Preparation of polymer compound for coating layer and solution thereof>
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 mixture 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-dimethyl) (Valeronitrile) 1.7 parts and 2,2′-azobis (2-methylbutyronitrile) 4.7 parts dissolved in DMF 58.3 parts and a four-necked flask were blown with nitrogen, Under stirring, 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 concentration of 50%. To this, 789.8 parts of DMF was added to obtain a polymer compound solution for a coating layer having a resin solid content concentration of 30% by weight. The number average molecular weight by GPC measurement of the obtained polymer compound for coating layers was 7 ± 10,000.

<Production Example 2: Production of coated negative electrode active material particles>
It was obtained in Production Example 1 with 100 parts of non-graphitizable carbon powder 1 (volume average particle diameter 20 μm) being put into a universal mixer high speed mixer FS25 [manufactured by Earth Technica Co., Ltd.] and stirred at room temperature at 720 rpm. 6.1 parts of the polymer compound solution for coating layer was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.

Next, 11.3 parts of acetylene black [DENKA BLACK (registered trademark) manufactured by Denka Co., Ltd.], which is a conductive agent, was added in 2 minutes 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 212 μm to obtain coated negative electrode active material particles.

<Production Example 3: Production of coated negative electrode active material particles>
In the production example 2, the non-graphitizable carbon powder 1 (volume average particle diameter 20 μm) was changed to artificial graphite (volume average particle diameter 18 μm), and the same procedure as in Production Example 2 was repeated. Material particles were obtained.

<Production Example 4: Preparation of negative electrode active material particles>
Coated negative electrode active material particles obtained in Production Example 2 and silicon oxide (SiO) (volume average particle diameter 6 μm) were coated negative electrode active material particles obtained in Production Example 2: SiO = 95: 5 (weight ratio) The mixture obtained by mixing was used as negative electrode active material particles of Production Example 4.

<Example 1>
[Preparation of negative electrode active material slurry for lithium ion battery]
20 parts of non-aqueous electrolyte prepared by dissolving LiN (FSO ₂ ) ₂ at a rate of 3 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) and carbon fiber [ Osaka Gas Chemical Co., Ltd. Donakabo Milled S-243: average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS / cm 2 parts and planetary agitation type mixing kneader {Awatori Kentaro [Sinky Co., Ltd. ] Was added at 2000 rpm for 7 minutes, and then 50 parts of the non-aqueous electrolyte and 98 parts of the coated negative electrode active material particles produced in Production Example 2 were added. Mix for 5 minutes, add 25 parts of the non-aqueous electrolyte, and then stir with Awatori Netaro for 1 minute at 2000 rpm, and then add 50 parts of the non-aqueous electrolyte. Was further mixed for 1.5 minutes with agitation by Awatori Rentaro was added in 2000 rpm, to prepare a negative active material slurry.

[Preparation of negative electrode for lithium ion battery and lithium ion battery for negative electrode evaluation]
The obtained negative electrode active material slurry was applied to one side of an aramid separator [manufactured by Japan Vilene Co., Ltd.], pressed at a pressure of 10 MPa for about 10 seconds, and a negative electrode active material layer having a thickness of about 250 μm on the aramid separator (3 cm × 3 cm) was fixed. The basis weight (also referred to as basis weight) of the negative electrode active material layer was determined from the weight change of the aramid separator before and after forming the negative electrode active material layer, and found to be 20.7 mg / cm ² . Moreover, when the porosity was calculated | required with the following method from the X-ray CT image obtained by measuring the fixed negative electrode active material layer with the X-ray CT apparatus, it was 45 volume%.

First, an X-ray CT image is obtained as a cross-sectional image in two directions: a thickness direction of an aramid separator and a direction perpendicular thereto. Thereafter, for the 50 μm × 50 μm region extracted at 10 random locations in the cross-sectional images in each direction, the area occupied by the voids in the entire region was determined, and the average value thereof was taken as the porosity.
Subsequently, a copper foil (3 cm × 3 cm, thickness 50 μm) with a terminal (5 mm × 3 cm) and a separator [Celguard (registered trademark) 3501 PP made by Celgard) (5 cm × 5 cm) and a terminal (5 mm × 3 cm) Laminated copper foil (3cm x 3cm, thickness 50μm) is laminated in the same direction in the direction of two terminals, and sandwiched between two commercially available heat-sealing aluminum laminate films (8cm x 8cm) The one side where the terminal comes out was heat-sealed to produce a laminate cell for negative electrode evaluation. Next, an aramid separator (3 cm × 3 cm) having a negative electrode active material layer fixed between one copper foil and the separator is inserted so that the negative electrode active material layer and the copper foil are in contact with each other, and an electrode (3 cm × 3 cm negative electrode active material) The negative electrode for a lithium ion battery according to Example 1 was prepared by injecting 70 μL of the non-aqueous electrolyte into the layer) and causing the electrode to absorb the non-aqueous electrolyte. Next, 70 μL of nonaqueous electrolyte was injected onto the separator. Thereafter, a lithium foil was inserted between the separator and the other copper foil, and two sides orthogonal to the one side heat-sealed first were heat sealed. Thereafter, 70 μL of nonaqueous electrolyte was injected from the opening, and the laminate was sealed by heat-sealing the opening while evacuating the inside of the cell using a vacuum sealer to obtain a lithium ion battery 1 for negative electrode evaluation. .

From the porosity of the negative electrode active material layer and the concentration of the non-aqueous electrolyte, the battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer is compared with the battery capacity based on the total amount of the negative electrode active material. When the ratio (hereinafter also referred to as battery capacity ratio) was determined, it was 10.0%.

<Example 2>
A lithium ion battery negative electrode and a negative electrode evaluation lithium ion battery 2 according to Example 2 were prepared in the same procedure as in Example 1 except that the electrolyte concentration of the non-aqueous electrolyte was changed from 3 mol / L to 1 mol / L. .

The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 3.3%.

<Example 3>
A lithium ion battery negative electrode and a negative electrode evaluation lithium ion battery 3 according to Example 3 were prepared in the same procedure as in Example 1, except that the electrolyte concentration of the non-aqueous electrolyte was changed from 3 mol / L to 5 mol / L. . The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 16.7%.

<Example 4>
The same procedure as in Example 1 was followed to Example 4 except that the electrolyte concentration of the non-aqueous electrolyte was changed from 3 mol / L to 2 mol / L and the type of electrolyte was changed from LiN (FSO ₂ ) ₂ to LiPF _6. The negative electrode for lithium ion batteries and the lithium ion battery 4 for negative electrode evaluation were produced. The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 6.7%.

<Example 5>
The electrolyte concentration of the non-aqueous electrolyte was changed from 3 mol / L to 2 mol / L, and the electrolyte type was changed from LiN (FSO ₂ ) ₂ to LiPF ₆ : LiN (CF ₃ SO ₂ ) ₂ = 1: 1 (weight ratio). Example 5 was performed in the same manner as in Example 1 except that the mixture was changed to a mixture, and the basis weight of the negative electrode active material was changed from 20.7 mg / cm ² to 38.4 mg / cm ² to change the film thickness to 445 μm. The negative electrode for lithium ion batteries which concerns on this, and the lithium ion battery 5 for negative electrode evaluation were produced. The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 6.6%.

<Example 6>
For a lithium ion battery according to Example 6 in the same procedure as in Example 1 except that the basis weight of the negative electrode active material was changed from 20.7 mg / cm ² to 8.6 mg / cm ² and the film thickness was changed to 100 μm. A negative electrode and a lithium ion battery 6 for negative electrode evaluation were prepared. The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 9.7%.

<Example 7>
For a lithium ion battery according to Example 7 in the same procedure as in Example 1 except that the basis weight of the negative electrode active material was changed from 20.7 mg / cm ² to 103.2 mg / cm ² and the film thickness was changed to 1200 μm. A negative electrode and a lithium ion battery 7 for negative electrode evaluation were prepared. The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 9.7%.

<Example 8>
A negative electrode for a lithium ion battery according to Example 8 according to the same procedure as in Example 1 except that the basis weight of the negative electrode active material was changed from 20.7 mg / cm ² to 6 mg / cm ² and the film thickness was changed to 70 μm. A lithium ion battery 8 for negative electrode evaluation was produced. The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 9.6%.

<Example 9>
The electrolyte concentration of the non-aqueous electrolyte is changed from 3 mol / L to 1 mol / L, and the negative electrode active material slurry is placed on the aramid separator so that the film thickness of the negative electrode active material layer is 306 μm and the porosity is 55% by volume. A negative electrode for a lithium ion battery and a lithium ion battery 9 for negative electrode evaluation according to Example 9 were produced in the same procedure as in Example 1 except that the press condition after coating was changed to about 10 seconds at 4 MPa. The film thickness of the negative electrode active material layer was 306 μm, and the porosity was 55% by volume. The battery capacity ratio was 5.0%.

<Example 10>
Instead of the coated negative electrode active material particles produced in Production Example 2, the coated negative electrode active material particles produced in Production Example 3 were used, and the press conditions after applying the negative electrode active material slurry on the aramid separator were 15 MPa. A lithium ion battery negative electrode and a negative electrode evaluation lithium ion battery 10 according to Example 10 were produced in the same procedure as in Example 1 except that the time was changed to about 10 seconds. The basis weight of the negative electrode active material layer was 50 mg / cm ² , the film thickness of the negative electrode active material layer was 380 μm, and the porosity was 40% by volume. The battery capacity ratio was 8.1%.

<Example 11>
Instead of 98 parts of the coated negative electrode active material particles produced in Production Example 2 used in the production of the negative electrode active material slurry for a lithium ion battery, 98 parts of the negative electrode active material particles prepared in Production Example 4 were used, and a non-aqueous electrolyte solution was used. A lithium ion battery negative electrode and a negative electrode evaluation lithium ion battery 11 according to Example 11 were prepared in the same procedure as in Example 1 except that the electrolyte concentration was changed to 2 mol / L. The basis weight of the negative electrode active material layer was 33.2 mg / cm ² , the film thickness of the negative electrode active material layer was 323 μm, and the porosity was 45% by volume. The battery capacity ratio was 4.8%.

<Comparative Example 1>
A lithium ion battery negative electrode and a negative electrode comparative evaluation lithium ion battery 1 according to Comparative Example 1 in the same procedure as Example 1, except that the electrolyte concentration of the non-aqueous electrolyte was changed from 3 mol / L to 0.5 mol / L. Was made. The porosity of the negative electrode active material layer was the same as in Example 1. The battery capacity ratio was 1.7%.

<Comparative example 2>
In Example 1, the electrolyte concentration of the non-aqueous electrolyte was changed from 3 mol / L to 5.5 mol / L, but the electrolyte salt was precipitated in the electrolyte, and a non-aqueous electrolyte that could be used for a battery could not be produced. The battery was not manufactured. Note that the battery capacity ratio is 18.1% when it is assumed that a battery is manufactured in the same manner as in Example 1 using a non-aqueous electrolyte having an electrolyte concentration of 5.5 mol / L.

<Comparative Example 3>
A negative electrode for a lithium ion battery and a lithium ion battery 3 for comparative evaluation of negative electrode according to Comparative Example 3 in the same procedure as in Example 5 except that the electrolyte concentration of the nonaqueous electrolytic solution was changed from 2 mol / L to 0.5 mol / L. Was made. The film thickness and porosity of the negative electrode active material layer were the same as in Example 5. The battery capacity ratio was 1.6%.

<Comparative example 4>
Change the electrolyte concentration of the non-aqueous electrolyte from 3 mol / L to 1 mol / L, and apply the negative electrode active material slurry on the aramid separator so that the negative electrode active material has a porosity of 30% by volume and a film thickness of 214 μm. A negative electrode for a lithium ion battery and a lithium ion battery 4 for comparative evaluation of negative electrode according to Comparative Example 4 were prepared in the same procedure as in Example 1 except that the pressing conditions after the change were changed to about 10 seconds at 50 MPa. The film thickness of the negative electrode active material layer was 214 μm, and the porosity was 30% by volume. The battery capacity ratio was 1.9%.

<Measurement of discharge capacity of negative electrode active material>
The coated negative electrode active material particles prepared in Production Examples 2 and 3 and the negative electrode active material particles prepared in Production Example 4 were respectively mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) in a mixed solvent (volume ratio 1: 1) with LiN. (FSO ₂ ) ₂ was mixed with a non-aqueous electrolyte prepared by dissolving at a rate of 3 mol / L to form a slurry, which was applied to one side of an aramid separator [manufactured by Japan Vilene Co., Ltd.] and then 10 seconds at a pressure of 10 MPa. The electrode was produced by pressing and incorporated into the battery pack, and the discharge capacity when discharged from 0.0 V to 1.5 V was measured with a charge / discharge measuring device “Battery Analyzer 1470” [manufactured by Toyo Corporation], and The discharge capacity (0.0 V → 1.5 V discharge capacity) of the negative electrode active material was determined. As a result, the coated negative electrode active material prepared in Production Example 2 was 434 mAh / g, the coated negative electrode active material prepared in Production Example 3 was 300 mAh / g, and the negative electrode active material particles prepared in Production Example 4 was 492 mAh / g. It was.

<Measurement of charge capacity at high rate>
Using a charge / discharge measuring device “Battery Analyzer 1470” (manufactured by Toyo Technica Co., Ltd.) at room temperature, negative electrode evaluation lithium ion batteries 1 to 11 and negative electrode comparative evaluation lithium ion batteries 1, 3, and 4 were Evaluation was performed.

Under conditions of 45 ° C., the lithium ion batteries 1 to 11 for negative electrode evaluation and the lithium ion batteries 1, 3 and 4 for comparative evaluation of negative electrode were charged to 4.2 V at a current of 2.0 C, respectively, and the capacity at the time of charging (2.0 C charge capacity) was measured. 2.0 C charge for the battery capacity based on the total amount of negative electrode active material calculated from the discharge capacity (0.0 V → 1.5 V discharge capacity) of each negative electrode active material obtained in <Measurement of discharge capacity of negative electrode active material> above The capacity ratio [%] (hereinafter, also simply referred to as the ratio of the 2.0 C charge capacity to the battery capacity) is determined by [(2.0 C charge capacity) / (battery capacity based on the total amount of negative electrode active material) × 100]. The results are shown in Table 1. The larger the ratio of the 2.0 C charging capacity to the battery capacity, the better and faster charging is possible.

From Table 1, it can be seen that a lithium ion battery having a battery capacity ratio of 3 to 17% is excellent in a 2.0 C charge capacity with respect to the battery capacity. Further, from the comparison between Example 1 and Examples 6 to 8 in which the film thickness of the negative electrode active material layer was changed from Example 1 and Comparative Example 1, the ratio of the 2.0 charge capacity to the battery capacity was Although it decreased as the film thickness increased, all of Examples 1 and 6 to 8 had a 2.0 C charging capacity higher than that of Comparative Example 1.

Further, from the comparison between Examples 1 to 11 and Comparative Example 4 in which the porosity of the negative electrode active material layer or the type of the negative electrode active material was changed from Example 1 and Example 1, the porosity of the negative electrode active material layer or the negative electrode active material layer was compared. It can be seen that even when the type of substance is changed, good results can be obtained if the battery capacity ratio is 3 to 17%.

From the above, it can be seen that the lithium ion battery using the negative electrode for a lithium ion battery of the present invention has high energy density and excellent quick charge characteristics.

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 secondary batteries used for mobile phones, personal computers, hybrid vehicles and electric vehicles.

This application is based on Japanese Patent Application No. 2016-217173 filed on November 7, 2016 and Japanese Patent Application No. 2017-213671 filed on November 6, 2017, the disclosure of which is incorporated herein by reference. The contents are cited as a whole by reference.

Claims

A negative electrode for a lithium ion battery, comprising: a negative electrode current collector; a negative electrode active material layer formed on a surface of the negative electrode current collector; and a nonaqueous electrolyte solution containing an electrolyte containing lithium ions and a nonaqueous solvent. And
The negative electrode active material layer includes a negative electrode active material and voids,
The void is filled with the non-aqueous electrolyte,
The ratio of the battery capacity based on the total amount of lithium ions in the non-aqueous electrolyte present in the negative electrode active material layer to the battery capacity based on the total amount of the negative electrode active material is 3 to 17%. A negative electrode for a lithium ion battery.
The negative electrode for a lithium ion battery according to claim 1, wherein the thickness of the negative electrode active material layer is 100 to 1500 µm.
3. The negative electrode for a lithium ion battery according to claim 1, wherein the total volume of the voids is 35 to 60% by volume of the total volume of the negative electrode active material layer.
4. The negative electrode for a lithium ion battery according to claim 1, wherein the electrolyte concentration of the non-aqueous electrolyte is 1 to 5 mol / L.
The negative electrode for a lithium ion battery according to any one of claims 1 to 4, wherein the electrolyte is a sulfonylimide-based electrolyte having a fluorine atom.
The negative electrode for a lithium ion battery according to any one of claims 1 to 5, wherein the electrolyte contains at least LiN (FSO 2 ) 2 .
The negative electrode for a lithium ion battery according to any one of claims 1 to 6, wherein the electrolyte comprises only LiN (FSO 2 ) 2 .
The negative electrode for a lithium ion battery according to any one of claims 1 to 7, wherein the negative electrode current collector is a resin current collector containing a conductive material and a resin.
The negative electrode for a lithium ion battery according to any one of claims 1 to 8, wherein the negative electrode active material is a coated negative electrode active material in which part or all of the surface thereof is coated with a coating layer containing a polymer compound.
A lithium ion battery using the negative electrode for a lithium ion battery according to any one of claims 1 to 9.