JP7560656B2 - Composition for negative electrode, negative electrode sheet and non-aqueous secondary battery, and method for producing the negative electrode sheet and non-aqueous secondary battery - Google Patents

Description

The present invention relates to a negative electrode composition, a negative electrode sheet, a non-aqueous secondary battery, a method for manufacturing a negative electrode sheet, and a method for manufacturing a non-aqueous secondary battery.

Secondary batteries, such as lithium-ion secondary batteries, are used as power sources for portable electronic devices such as personal computers, video cameras, and mobile phones. In recent years, against the backdrop of the global environmental challenge of reducing carbon dioxide emissions, they have become increasingly popular as power sources for automobiles and other transportation equipment, and for storing electricity such as nighttime electricity and electricity generated by natural energy sources.

The electrodes (positive and negative electrodes) of a lithium-ion secondary battery have electrode active material layers (positive and negative active material layers), which contain electrode active material particles that can absorb or release lithium ions during charging and discharging. In addition, electrons are transported between the electrode active material particles, or between the electrode active material particles and the current collector, so it is necessary to ensure electronic conductivity. To improve the efficiency of this electronic conduction, the adhesion between the electrode active material particles, or between the electrode active material particles and the current collector, is important, and the electrode active material layers usually contain a binder.

In order to realize high-capacity lithium-ion secondary batteries, the use of silicon oxide as the negative electrode active material has been investigated. The theoretical capacity of silicon oxide is much higher than that of graphite, etc., and it is possible to achieve high energy density of the battery.
When silicon oxide is used as the negative electrode active material, it absorbs a large amount of lithium ions and expands significantly during charging, and the silicon oxide also contracts significantly during discharging. Therefore, in lithium ion batteries using silicon oxide as the negative electrode active material, the volume of the negative electrode active material changes significantly during charging and discharging, and the battery performance is easily degraded by repeated charging and discharging. In other words, there is a limit to improving the cycle life.
As a technique for dealing with such problems, for example, Patent Document 1 describes a slurry for the negative electrode of a lithium ion battery, which contains a negative electrode active material containing 20 mass% or more of silicon particles having a median diameter (D50) of 0.1 to 2 μm, poly(meth)acrylamide which is a radical copolymer of a monomer group including a (meth)acrylamide skeleton-containing monomer and a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer and exhibits a specific high viscosity in an aqueous solution state of a specific concentration, and water. According to the technique described in the Patent Document, it is said that a lithium ion secondary battery having excellent cycle life (cycle characteristics) can be obtained by using this negative electrode slurry.

It has also been proposed to use silicon oxide as a negative electrode active material by coating it with carbon. It is said that the electrical conductivity of silicon oxide particles can be increased by carbon coating, and that the side reaction between silicon oxide and an electrolyte can also be suppressed. Therefore, carbon-coated silicon oxide is expected to be a negative electrode active material for next-generation lithium-ion secondary batteries. For example, Patent Document 2 describes a lithium-ion battery negative electrode slurry containing carbon-coated silicon oxide, graphite having an R value of 0.2 to 1.5, which is the peak intensity ratio at 1360 cm ⁻¹ to the peak intensity at 1580 cm ⁻¹ in an argon ion laser Raman spectrum, a binder, carbon black, and water. According to the description in the same patent document, it is said that a lithium-ion secondary battery with excellent cycle life can be obtained by doping lithium ions into the negative electrode mixture layer formed using this negative electrode slurry.

Electrodes for lithium-ion secondary batteries are usually formed by applying an electrode-forming composition (slurry) onto a current collector and drying it. Therefore, the slurry for forming the electrode is prepared by dispersing an electrode active material and a binder in a liquid medium. With the recent increase in interest in environmental issues, there is a demand for aqueous liquid media.

JP 2018-6334 A JP 2018-81753 A

The present invention aims to provide a negative electrode composition that uses carbon-coated silicon oxide as a negative electrode active material, which, when used to form a negative electrode active material layer of a non-aqueous secondary battery, can provide a non-aqueous secondary battery with high capacity and low resistance while also sufficiently extending the cycle life. Another object of the present invention is to provide a negative electrode sheet and a non-aqueous secondary battery that use the negative electrode composition. Another object of the present invention is to provide a method for producing the negative electrode sheet and the non-aqueous secondary battery.

一般式（１）中、Ｒ^１は水素原子又はメチル基を示し、Ｌ^１は単結合又は連結基を示し、Ｒ^２は置換基を示す。＊は上記水溶性ポリマー中に組み込まれるための結合部位を示す。
一般式（２）中、Ｒ^３は水素原子又はメチル基を示し、Ｒ^４及びＲ^５は水素原子又は置換基を示す。＊は上記水溶性ポリマー中に組み込まれるための結合部位を示す。
＜４＞
上記水溶性ポリマーの含有量が、上記のカーボンコートされた酸化珪素１００質量部に対して、２質量部以上である、＜１＞～＜３＞のいずれか１つに記載の負極用組成物。
＜５＞
上記水溶性ポリマーが、上記一般式（１）又は（２）で表される２種以上の構成成分を含む、＜３＞に記載の負極用組成物。
＜６＞
分散媒体を含む負極用スラリーである、＜１＞～＜５＞のいずれか１つに記載の負極用組成物。
＜７＞
＜１＞～＜６＞のいずれか１つに記載の負極用組成物を用いて形成した層を有する負極シート。
＜８＞
正極活物質層とセパレータと負極活物質層とをこの順で有し、上記負極活物質層が＜１＞～＜６＞のいずれか１つに記載の負極用組成物を用いて形成した層である、非水二次電池。
＜９＞
＜１＞～＜６＞のいずれか１つに記載の負極用組成物を用いて成膜することを含む、負極シートの製造方法。
＜１０＞
＜９＞に記載の製造方法により得られた負極シートを非水二次電池の負極に組み込むことを含む、非水二次電池の製造方法。 The above problems were solved by the following means.
＜1＞
The binder includes a water-soluble polymer, and carbon-coated silicon oxide.
The negative electrode composition, wherein the water-soluble polymer has an adsorption rate of 5 to 25% with respect to the carbon-coated silicon oxide.
＜2＞
The negative electrode composition according to <1>, wherein the water-soluble polymer is a chain-polymerized polymer.
＜3＞
The negative electrode composition according to <1> or <2>, wherein the water-soluble polymer contains a component represented by the following general formula (1) or (2):

In formula (1), ^R1 represents a hydrogen atom or a methyl group, ^L1 represents a single bond or a linking group, and ^R2 represents a substituent. * represents a bonding site for incorporation into the water-soluble polymer.
In formula (2), ^R3 represents a hydrogen atom or a methyl group, ^R4 and ^R5 represent a hydrogen atom or a substituent, and * represents a bonding site for incorporation into the water-soluble polymer.
＜4＞
<4> The negative electrode composition according to any one of <1> to <3>, wherein the content of the water-soluble polymer is 2 parts by mass or more per 100 parts by mass of the carbon-coated silicon oxide.
＜5＞
The negative electrode composition according to <3>, wherein the water-soluble polymer contains two or more components represented by the general formula (1) or (2).
＜6＞
The negative electrode composition according to any one of <1> to <5>, which is a negative electrode slurry containing a dispersion medium.
＜７＞
<6> A negative electrode sheet having a layer formed using the negative electrode composition according to any one of <1> to <6>.
＜8＞
A non-aqueous secondary battery having a positive electrode active material layer, a separator, and a negative electrode active material layer in this order, the negative electrode active material layer being a layer formed using the negative electrode composition according to any one of <1> to <6>.
＜9＞
A method for producing a negative electrode sheet, comprising forming a film using the negative electrode composition according to any one of <1> to <6>.
＜10＞
A method for producing a non-aqueous secondary battery, comprising incorporating the negative electrode sheet obtained by the method for producing the non-aqueous secondary battery into a negative electrode of the non-aqueous secondary battery.

In this specification, the term "water-soluble polymer" refers to a polymer that dissolves at least 7 g in 1 L of water at 25° C. (a polymer whose solubility at 25° C. is 7 [g/1L-H ₂ O] or more).
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
In this specification, the term "compound" is used to mean not only the compound itself, but also its salts and ions. It also means a derivative in which a part of the structure is changed, for example by introducing a substituent, within the range in which the desired effect is exhibited.
In the present specification, when a substituent has a dissociable hydrogen atom (a group in which the hydrogen atom dissociates due to the action of a base), the substituent includes the form of an ion or a salt.
For example, when a compound has a carboxy group, the carboxy group may be present as an anion with a hydrogen atom dissociated therefrom, and the anion may form a salt with a counter ion (cation). There are no particular limitations on the counter ion, and examples of the counter ion include alkali metal ions such as lithium ion, sodium ion, and potassium ion.
In the present specification, for substituents, linking groups, etc. (hereinafter referred to as "substituents, etc.") that are not specified as substituted or unsubstituted, this means that the group may have an appropriate substituent. Therefore, even when the term "group" (e.g., "alkyl group") is simply described in the present specification, this "group" (e.g., "alkyl group") includes not only an embodiment that does not have a substituent (e.g., "unsubstituted alkyl group"), but also an embodiment that further has a substituent (e.g., "substituted alkyl group"). This also applies to compounds that are not specified as substituted or unsubstituted.
In this specification, when there are multiple substituents etc. designated by a specific symbol, or when multiple substituents etc. are simultaneously or alternatively specified, it means that the respective substituents etc. may be the same or different from each other. In addition, even if not specified otherwise, when multiple substituents etc. are adjacent, it means that they may be linked to each other or condensed to form a ring.
In this specification, when a polymer has multiple components of the same designation (represented by the same general formula), each component may be the same or different from the others.
In this specification, the term "nonaqueous secondary battery" includes nonaqueous electrolyte secondary batteries and all-solid-state secondary batteries. In this specification, the term "nonaqueous electrolyte" means an electrolyte that does not substantially contain water. That is, the "nonaqueous electrolyte" may contain a small amount of water within a range that does not impede the effects of the present invention. In the present invention, the "nonaqueous electrolyte" has a water concentration of 200 ppm (by mass) or less, preferably 100 ppm or less, and more preferably 50 ppm or less. Note that it is practically difficult to make a nonaqueous electrolyte completely anhydrous, and it usually contains 1 ppm or more of water.
In this specification, the term "solid content" used when describing the content or content ratio means components other than the dispersion medium described below.

The negative electrode composition and negative electrode sheet of the present invention can be used to form a negative electrode active material layer, thereby imparting excellent cycle characteristics to a non-aqueous secondary battery using carbon-coated silicon oxide as a negative electrode active material, and therefore the non-aqueous secondary battery of the present invention has high capacity, low resistance, and excellent cycle characteristics.
According to the method for producing a negative electrode sheet of the present invention, the above-mentioned negative electrode sheet of the present invention can be obtained. Also, according to the method for producing a nonaqueous secondary battery of the present invention, the above-mentioned nonaqueous secondary battery of the present invention can be obtained.

FIG. 1 is a vertical cross-sectional view showing a schematic diagram of a basic layered structure of a nonaqueous electrolyte secondary battery.

[Negative electrode composition]
The negative electrode composition of the present invention contains a binder containing a water-soluble polymer and a negative electrode active material containing carbon-coated silicon oxide.
The water-soluble polymer has an adsorption rate of 5 to 25% to the carbon-coated silicon oxide. In the present invention, the adsorption rate is a value determined by the method described in the Examples below. When two or more water-soluble polymers are used, the value of the polymer with the highest adsorption rate is adopted. The adsorption rate is preferably 5 to 20%, and more preferably 10 to 20%.
By incorporating the negative electrode active material layer prepared using the negative electrode composition of the present invention into a secondary battery, the cycle life of the resulting secondary battery can be effectively increased. Although the reason for this is not yet clear, it is presumed that one of the reasons is that the water-soluble polymer is firmly bound to the negative electrode active material (carbon-coated silicon oxide) by, for example, fitting into the voids in the carbon coating layer (producing an anchor effect) when the polymer having the above adsorption rate is contained in the binder.
The negative electrode composition of the present invention can be prepared by mixing a binder containing a water-soluble polymer, a negative electrode active material containing carbon-coated silicon oxide, and, if necessary, a dispersion medium, a conductive assistant, and the like.

(binder)
The binder used in the present invention includes the water-soluble polymer described above.
From the viewpoint of improving the cycle characteristics of a nonaqueous secondary battery, the adsorption rate is preferably 8% or more, and more preferably 9% or more.
The structure of the water-soluble polymer is not particularly limited so long as it has the above-mentioned adsorption rate (5 to 25%).
The water-soluble polymer may be either a chain-polymerized polymer or a step-polymerized polymer, and is preferably a chain-polymerized polymer. The bonding form of the chain-polymerized polymer is not particularly limited, and may be either random or block.

The water-soluble polymer preferably contains, for example, a component represented by the following general formula (1) or (2):

In formula (1), ^R1 represents a hydrogen atom or a methyl group, ^L1 represents a single bond or a linking group (divalent), and ^R2 represents a substituent. * represents a bonding site for incorporation into a water-soluble polymer.
In formula (2), ^R3 represents a hydrogen atom or a methyl group, ^R4 and ^R5 represent a hydrogen atom or a substituent, and * represents a bonding site for incorporation into a water-soluble polymer.

The linking group that can be taken as ^L1 is not particularly limited as long as it does not have an acid group. The chemical formula weight of this linking group is preferably 14 to 1,000, more preferably 14 to 500, and even more preferably 26 to 250.
Examples of the linking group that can be taken as ^L1 include an alkylene group, -O-, a carbonyl group, an imino group, and a combination thereof. As these combinations, a linking group formed by combining 2 to 6 of the alkylene groups, -O-, carbonyl groups, and imino groups is preferable, and a linking group formed by combining 2 or 3 of them is more preferable.
Specifically, ^L1 is preferably any one of -C(=O)-O-, -O-C(=O)-, -NH-C(=O)-O-, -O-C(=O)-NH-, -NH-C(=O)-NH-, and an alkylene group, and more preferably an alkylene group.
The alkylene group that can be taken as ^L1 may be either linear or branched, and the alkylene group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, still more preferably 1 to 6 carbon atoms, particularly preferably 1 to 4 carbon atoms, and is most preferably any one of a methylene group, an ethylene group, an ethylethylene group, and a propylene group.
The chemical formula weight of ^L1 is preferably 14-200, more preferably 14-150, and even more preferably 14-100.

^R2 is not particularly limited as long as it is a substituent that does not have an acid group. The chemical formula weight of ^R2 is preferably 15 to 200, more preferably 15 to 150, and even more preferably 15 to 100. Examples of ^R2 include a hydroxy group, an alkyloxy group, an alkyl group, an amide group, and a sulfonamide group, and is preferably a hydroxy group or an alkyloxy group.
The alkyl group in the alkyloxy group may be linear, branched or cyclic, and preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, further preferably 1 to 6 carbon atoms, particularly preferably 1 to 4 carbon atoms, and is most preferably a methyl group, an ethyl group or an isopropyl group.
The alkyl group has the same meaning as the alkyl group in the alkyloxy group, and the preferred range is also the same.

The chemical formula weight of each of R ⁴ and R ⁵ is preferably 1-200, more preferably 1-150, and even more preferably 1-60.
The substituents which can be taken as ^R4 and ^R5 are preferably alkyl groups.
The alkyl group has the same meaning as the alkyl group in the alkyloxy group which can be taken as R ² , and the preferred range is also the same. In addition, it is also preferable that the alkyl group which can be taken as R ⁴ and R ⁵ further has a substituent. Examples of such a substituent include a hydroxy group, an alkylcarbonyl group, an amide group, and a urethane bond-containing group (-NH-CO-O-R ^b (R ^b represents an alkyl group). Of these, a hydroxy group is preferable as the substituent of the alkyl group which can be taken as R ⁴ and R ⁵ .
The alkyl group in the alkylcarbonyl group has the same meaning as the alkyl group in the alkyloxy group which can be taken as the above ^R2 , and the preferred range is also the same. The alkyl group represented by ^Rb has the same meaning as the alkyl group in the alkyloxy group which can be taken as the above ^R2, and the preferred range is also the same.
It is preferable that ^R4 and ^R5 are both hydrogen atoms, or one of them is a hydrogen atom and the other is a hydroxyalkyl group.

It is preferable that the component represented by the above general formula (1) or (2) does not have an acid group.

The proportion of the component represented by the general formula (1) or (2) in the water-soluble polymer (the sum of the proportion of the component represented by the general formula (1) and the proportion of the component represented by the general formula (2) in the water-soluble polymer) is not particularly limited as long as the water-soluble polymer as a whole exhibits the above-mentioned adsorption rate. For example, the proportion of the component represented by the general formula (1) or (2) can be 30% by mass or more. In addition, the proportion of the component represented by the general formula (1) or (2) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.
From the viewpoint of improving the cycle characteristics of the secondary battery, the water-soluble polymer used in the present invention preferably contains two or more components represented by general formula (1) or (2), more preferably contains 2 to 6 components represented by general formula (1) or (2), and even more preferably contains 2 to 4 components represented by general formula (1) or (2). By containing two or more components represented by general formula (1) or (2), the water-soluble polymer can improve both the adsorption rate to the carbon-coated silicon oxide and the mechanical properties of the negative electrode sheet when used in the negative electrode sheet, and as a result, the cycle characteristics of the secondary battery can be further improved.
Examples of the form containing two or more components represented by general formula (1) or (2) include a form containing two or more components represented by general formula (1) and no component represented by general formula (2), a form containing two or more components represented by general formula (2) and no component represented by general formula (1), and a form containing both a component represented by general formula (1) and a component represented by general formula (2).

Preferred specific examples of the components represented by the above general formula (1) are shown below, but the present invention is not limited to these.

Preferred specific examples of the components represented by the above general formula (2) are shown below, but the present invention is not limited to these.

When the water-soluble polymer contains a component other than the component represented by the general formula (1) or (2) as a component not having an acid group, such a component is not particularly limited. For example, a component derived from a vinyl monomer such as styrene, maleimide, N-vinylacetamide, vinyl ester, or vinyl ether can be mentioned.

The water-soluble polymer may have a component having an acid group. The "acid group" of a component having an acid group means a group having a dissociable proton or a salt thereof. Examples include a carboxy group, a sulfo group, a phosphoric acid group (-OP(=O)(OH) ₂ ), a phosphonic acid group (-P(=O)(OH) ₂ ), and salts thereof. Carboxy groups and sulfo groups or salts thereof are preferred, and carboxy groups or salts thereof are more preferred. Examples of the salt form include alkali metal salts (e.g., lithium salts, sodium salts, potassium salts, etc.).

The component having an acid group is not particularly limited, and this component usually contains 1 to 3 acid groups, preferably 1 or 2, and more preferably 1. The component having an acid group that the water-soluble polymer may have is preferably, for example, a component represented by the following general formula (3).

In the formula, ^R6 represents a hydrogen atom or an acid group, ^R7 represents a hydrogen atom or a methyl group, ^L2 represents a single bond or a linking group (divalent), and ^R8 represents an acid group. * represents a bonding site for incorporation into a water-soluble polymer.

The linking group that can be taken as ^L2 is not particularly limited, and examples thereof include an alkylene group, an arylene group, a carbonyl group, -O-, an imino group, or a linking group that is a combination of two or more of these groups.

The alkylene group that can be taken as ^L2 may be either linear or branched, and the number of carbon atoms in the alkylene group is preferably 1 to 10, more preferably 1 to 8, still more preferably 1 to 6, and particularly preferably 1 to 4. Specific examples of this alkylene group include a methylene group, an ethylene group, a propylene group, and a dimethylethylene group.

The number of carbon atoms in the arylene group which can be taken as ^L2 is preferably 6 to 30, more preferably 6 to 20, even more preferably 6 to 15, and still more preferably 6 to 10. Specific examples of the arylene group include a phenylene group and a naphthylene group.

The above-mentioned "linking group combining two or more types" is a linking group combining at least two types of an alkylene group, an arylene group, a carbonyl group, -O-, and an imino group, and is preferably a linking group combining 2 to 10 types, more preferably a linking group combining 2 to 7 types, and even more preferably a linking group combining 2 to 4 types.
Specific examples of the above-mentioned "linking group combining two or more types" include "carbonyl group-imino group-alkylene group" and "carbonyl group-O-alkylene group".

The proportion of components having acid groups in the water-soluble polymer is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less, and it is most preferable that the water-soluble polymer does not have any components having acid groups.

Preferred specific examples of the components represented by the above general formula (3) are shown below, but the present invention is not limited to these.

The weight average molecular weight of the water-soluble polymer used in the present invention is preferably 900,000 or less, more preferably 800,000 or less, and particularly preferably 700,000 or less. On the other hand, the weight average molecular weight of the water-soluble polymer is preferably 10,000 or more, more preferably 40,000 or more, and even more preferably 100,000 or more.
From the viewpoint of the flex resistance of the negative electrode sheet, the weight average molecular weight of the water-soluble polymer is also preferably 350,000 or more.
In this specification, the weight average molecular weight of a polymer is a value obtained by measurement according to the method described in the Examples section below.

The above-mentioned adsorption rate of the water-soluble polymer used in the present invention is influenced by various factors. For example, physical interactions with the carbon coating layer, the anchoring effect on the voids in the carbon coating layer, and charged interactions with silicon oxide can be mentioned. Therefore, it is difficult to unequivocally explain whether such a polymer structure can achieve the desired adsorption rate, but it is presumed that the adsorption rate for carbon-coated silicon oxide can be changed into various ranges by controlling the type or amount of hydrophilic and hydrophobic groups in the polymer, or by controlling the molecular weight of the polymer.

In the binder used in the present invention, the content of the water-soluble polymer is preferably 5% by mass or more, and from the viewpoint of improving the cycle characteristics of the secondary battery, more preferably 10% by mass or more, and even more preferably 20% by mass or more. The binder used in the present invention may be made of the water-soluble polymer.

From the viewpoint of improving the cycle characteristics of the secondary battery, the content of the water-soluble polymer in the negative electrode composition is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and even more preferably 8 parts by mass or more, relative to 100 parts by mass of the carbon-coated silicon oxide, while the content of the water-soluble polymer in the negative electrode composition is preferably 30 parts by mass or less, more preferably 24 parts by mass or less, and even more preferably 18 parts by mass or less, relative to 100 parts by mass of the carbon-coated silicon oxide.
By including the water-soluble polymer in the negative electrode composition in an amount of 2 parts by mass or more per 100 parts by mass of carbon-coated silicon oxide, the carbon-coated silicon oxide can be coated, and the cycle characteristics of the secondary battery can be improved.

The binder used in the present invention may contain a polymer other than the above-mentioned water-soluble polymer, within a range that does not impair the effects of the present invention. Examples of such polymers include water-insoluble polymers and polymers whose adsorption rate to carbon-coated silicon oxide is less than 5% or more than 20%. Specific examples of such polymers include, but are not limited to, polymer B described in Table 1 below.

(Negative Electrode Active Material)
The negative electrode active material used in the present invention contains carbon-coated silicon oxide (SiOx (0<x≦1.5)). Carbon-coated silicon oxide can reversibly absorb and release lithium ions.
The silicon oxide may have a carbon-coated surface entirely or may have a portion not coated with carbon. Even if the silicon oxide has a carbon-coated surface entirely, the carbon-coated layer itself has many voids.
The proportion of carbon atoms in the carbon-coated silicon oxide (in the total of the carbon coating layer and silicon oxide) is not particularly limited, and from the viewpoint of achieving both electrical conductivity and electric capacity, for example, it is preferably 0.2 to 5 mass%, more preferably 0.5 to 5 mass%, even more preferably 0.5 to 3 mass%, and particularly preferably 1 to 3 mass%.
The carbon-coated silicon oxide may be a commercially available product, or may be prepared by coating silicon oxide with carbon, for example, by referring to JP-A-2019-204686.

The negative electrode active material used in the present invention may contain a negative electrode active material other than carbon-coated silicon oxide. In the following description of the negative electrode active material used in the present invention, the negative electrode active material other than carbon-coated silicon oxide is referred to as "other negative electrode active material."
The other negative electrode active material is preferably one that can reversibly absorb and release lithium ions. The material is not particularly limited as long as it has the above-mentioned characteristics, and examples of the material include carbonaceous materials, metal oxides, metal composite oxides, lithium alloys, and negative electrode active materials that can form alloys with lithium.
The lithium alloy is not particularly limited as long as it is an alloy that is usually used as a negative electrode active material for secondary batteries, and an example thereof is a lithium aluminum alloy.
The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is a material that is commonly used as a negative electrode active material for secondary batteries. Examples of such active materials include negative electrode active materials having tin atoms, and metals such as Al and In.
Examples of the negative electrode active material having tin atoms include Sn, SnO, _SnO2 , SnS, _SnS2 , and the above-mentioned active materials containing silicon atoms and tin _atoms . Also included are composite oxides with lithium oxide, such as _Li2SnO2 .
Among these, as the other negative electrode active material, carbonaceous materials are preferably used from the viewpoint of reliability.

Other carbonaceous materials used as negative electrode active materials are materials that are essentially made of carbon. Examples include carbon black such as petroleum pitch, graphite (natural graphite, artificial graphite such as vapor-grown graphite, etc.), and carbonaceous materials obtained by baking various synthetic resins such as PAN (polyacrylonitrile)-based resins or furfuryl alcohol resins. In addition, various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, mesophase microspheres, graphite whiskers, and plate-shaped graphite can also be mentioned.

Other metal oxides and metal composite oxides that can be used as negative electrode active materials are not particularly limited as long as they are oxides that can absorb and release lithium, and amorphous oxides are preferred, and chalcogenides that are reaction products of metal elements and elements of group 16 of the periodic table are also preferred. The term "amorphous" as used herein means that the oxide has a broad scattering band with a peak in the 2θ value range of 20° to 40° in an X-ray diffraction method using CuKα radiation, and may have crystalline diffraction lines.
Among the compound group consisting of the above-mentioned amorphous oxides and chalcogenides, amorphous oxides of metalloid elements and the above-mentioned chalcogenides are more preferred, and oxides consisting of one kind alone or a combination of two or more kinds of elements of Groups 13 (IIIB) to 15 (VB) of the periodic table, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi (however, oxides containing Si are excluded), or chalcogenides are particularly preferred. Specific examples of preferred amorphous oxides and chalcogenides include _Ga2O3 , _GeO , _PbO , _PbO2 , _Pb2O3 , Pb2O4, _{Pb3O4 , Sb2O3 , Sb2O4 , Sb2O8Bi2O3 , Sb2O5 , Bi2O3 , Bi2O4 , GeS} , _{PbS , PbS2 , Sb2S3 and Sb2S5 .}

The metal (composite) oxide and the chalcogenide preferably contain at least one of titanium and lithium as a component from the viewpoint of high current density charge/discharge characteristics. Examples of the metal composite oxide containing lithium (lithium composite metal oxide) include composite oxides of lithium oxide and the metal (composite) oxide or the chalcogenide, more specifically Li ₂ SnO ₂ .

Other negative electrode active materials are also preferably those containing titanium atoms. More specifically, TiNb ₂ O ₇ (niobium titanate oxide [NTO]) and Li ₄ Ti ₅ O ₁₂ (lithium titanate [LTO]) are preferred because they have small volume fluctuations during the absorption and release of lithium ions, and therefore have excellent rapid charge and discharge characteristics, suppress electrode deterioration, and enable an improvement in the life of the lithium ion secondary battery.

The shape of the carbon-coated silicon oxide and other negative electrode active materials is not particularly limited, but particulate is preferred. The volume-based median diameter D50 of the carbon-coated silicon oxide and other negative electrode active materials is preferably 0.1 to 60 μm. To obtain a desired particle size, a conventional grinder or classifier is used. For example, a mortar, a ball mill, a sand mill, a vibration ball mill, a satellite ball mill, a planetary ball mill, a swirling airflow type jet mill, or a sieve is preferably used. During grinding, wet grinding in the presence of water or an organic solvent such as methanol can also be performed. In order to obtain a desired particle size, it is preferable to perform classification. The classification method is not particularly limited, and a sieve, a wind classifier, etc. can be used as desired. Classification can be performed both dry and wet.

The median diameter D50 of the carbon-coated silicon oxide is preferably from 0.1 to 30 μm, more preferably from 0.5 to 20 μm, and particularly preferably from 2 to 8 μm.
The median diameter D50 can be determined by a laser diffraction method, for example, using SALD-2300 (product name) manufactured by Shimadzu Corporation.

When carbon-coated silicon oxide is used in combination with other negative electrode active materials, a combination of carbon-coated silicon oxide and a carbonaceous material is preferred, and a combination of carbon-coated silicon oxide and graphite is particularly preferred. The blending ratio (carbon-coated silicon oxide/graphite, mass basis) when carbon-coated silicon oxide and graphite are combined is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. There is no particular upper limit to the blending ratio of carbon-coated silicon oxide to graphite, but 4 or less is practical, preferably 3 or less, and more preferably 2 or less.
The content of the carbon-coated silicon oxide in the negative electrode active material is not particularly limited and can be, for example, 10 to 90 mass %, preferably 10 to 50 mass %, and more preferably 15 to 40 mass %.
When forming the negative electrode active material layer, the mass (mg) (weight per unit area) of the carbon-coated silicon oxide and other negative electrode active materials per unit area (cm ² ) of the negative electrode active material layer is not particularly limited and can be appropriately determined depending on the designed battery capacity.

The content of carbon-coated silicon oxide and other negative electrode active materials in the negative electrode composition is not particularly limited, but is preferably 10 to 98 mass% in total, and more preferably 15 to 95 mass%, based on 100 mass% solids.

(Dispersion Medium)
The negative electrode composition of the present invention can also contain a dispersion medium to form a negative electrode slurry.
When a non-aqueous electrolyte secondary battery is produced using the negative electrode composition of the present invention, an aqueous medium containing water can be used as the dispersion medium. The "aqueous medium containing water" refers to water or a mixture of water and a water-soluble organic solvent. The "water-soluble organic solvent" refers to an organic solvent that is compatible with water, such as N-methylpyrrolidone, methanol, ethanol, acetone, and tetrahydrofuran.

(Conductive assistant)
The negative electrode composition of the present invention may also contain a conductive assistant.
The conductive assistant is not particularly limited, and may be any known conductive assistant. For example, it may be an electron conductive material such as graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, and furnace black, amorphous carbon such as needle coke, carbon fibers such as vapor-grown carbon fibers or carbon nanotubes, carbonaceous materials such as graphene or fullerene, metal powders or metal fibers such as copper and nickel, or conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives.
In the present invention, when a negative electrode active material and a conductive assistant are used in combination, among the above conductive assistants, those that do not insert or release Li when the secondary battery is charged and discharged and do not function as a negative electrode active material are considered to be conductive assistants. Therefore, among the conductive assistants, those that can function as a negative electrode active material in the negative electrode active material layer when the secondary battery is charged and discharged are classified as negative electrode active materials rather than conductive assistants. Whether or not a conductive assistant functions as a negative electrode active material when the secondary battery is charged and discharged is not unique, but is determined by the combination with the negative electrode active material.

The conductive assistant may be used alone or in combination of two or more kinds.
The content of the conductive assistant in the negative electrode composition is preferably 1 to 30 mass %, more preferably 1 to 15 mass %, and even more preferably 3 to 10 mass %, based on 100 mass % of the solid content.

The shape of the conductive additive is not particularly limited, but particulate is preferred. The median diameter D50 of the conductive additive is not particularly limited, but is preferably 0.01 to 50 μm, and more preferably 0.02 to 10.0 μm.

(Other Additives)
The negative electrode composition of the present invention may contain, as desired, other components in addition to the above-mentioned components, such as a lithium salt, an ionic liquid, a thickener, an antifoaming agent, a leveling agent, a dehydrating agent, an antioxidant, etc. In addition, the composition may contain a crosslinking agent (such as one that undergoes a crosslinking reaction by radical polymerization, condensation polymerization, or ring-opening polymerization) for chemically crosslinking the water-soluble polymer, and further a polymerization initiator (such as one that generates an acid or radicals by heat or light).
With regard to the conductive assistant and other additives, for example, International Publication No. 2019/203334 and JP-A-2015-46389 can be referred to.

[Negative electrode sheet]
The negative electrode sheet of the present invention has a layer (negative electrode active material layer) that is constructed (formed) using the negative electrode composition of the present invention. The negative electrode sheet of the present invention may have a negative electrode active material layer, and may be a sheet in which the negative electrode active material layer is formed on a substrate (current collector), or may be a sheet formed only of the negative electrode active material layer without a substrate. This negative electrode sheet is usually a sheet having a configuration in which the negative electrode active material layer is laminated on the current collector. The negative electrode sheet of the present invention may have other layers such as a protective layer (release sheet) and a coating layer.
The negative electrode sheet of the present invention can be suitably used as a material constituting the negative electrode active material layer of a secondary battery.

[Method of manufacturing negative electrode sheet]
The negative electrode sheet of the present invention can be obtained by forming a negative electrode active material layer using the negative electrode composition of the present invention. For example, a current collector or the like is used as a substrate, and the negative electrode composition of the present invention is applied thereon (with or without another layer) to form a coating film, which is then dried to obtain an electrode sheet having a negative electrode active material layer (coated and dried layer) on the substrate.

[Non-aqueous secondary battery]
The nonaqueous secondary battery of the present invention refers to any device in which ions pass between positive and negative electrodes via an electrolyte upon charging and discharging, and energy is stored and released at the positive and negative electrodes. That is, the nonaqueous secondary battery of the present invention includes both batteries and capacitors (e.g., lithium ion capacitors). From the viewpoint of the amount of energy stored, it is preferable that the nonaqueous secondary battery of the present invention is used for battery applications (not as a capacitor).

The nonaqueous secondary battery of the present invention will be described taking a nonaqueous electrolyte secondary battery as an example, but the secondary battery of the present invention is not limited to a nonaqueous electrolyte secondary battery and broadly includes all nonaqueous secondary batteries including all-solid-state secondary batteries.
A nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer in contact with the positive electrode current collector, and the negative electrode includes a negative electrode current collector and a negative electrode active material layer in contact with the negative electrode current collector. In the nonaqueous electrolyte secondary battery of the present invention, the negative electrode active material layer is formed using the electrode composition of the present invention.

FIG. 1 is a cross-sectional view showing a typical laminated structure of a nonaqueous electrolyte secondary battery 10, including a working electrode when the battery is operated. The nonaqueous electrolyte secondary battery 10 has a laminated structure having, in this order, a negative electrode current collector 1, a negative electrode active material layer 2, a separator 3, a positive electrode active material layer 4, and a positive electrode current collector 5, as seen from the negative electrode side. The space between the negative electrode active material layer and the positive electrode active material layer is filled with a nonaqueous electrolyte (not shown), and is separated by the separator 3. The separator 3 has pores, and in a normal battery use state, it functions as a positive and negative electrode separator that insulates between the positive and negative electrodes while allowing the electrolyte and ions to pass through. With this structure, for example, in the case of a lithium ion secondary battery, electrons (e ⁻ ) are supplied to the negative electrode side through an external circuit during charging, and at the same time, lithium ions (Li ⁺ ) move from the positive electrode through the electrolyte and are accumulated in the negative electrode. On the other hand, during discharging, the lithium ions (Li ⁺ ) stored in the negative electrode are returned to the positive electrode side via the electrolyte, and electrons are supplied to the operating part 6. In the illustrated example, a light bulb is used as the operating part 6, and this is turned on by discharging.
In the present invention, the negative electrode current collector 1 and the negative electrode active material layer 2 are collectively referred to as the negative electrode, and the positive electrode active material layer 4 and the positive electrode current collector 5 are collectively referred to as the positive electrode.

The nonaqueous secondary battery of the present invention is not particularly limited in terms of the positive electrode active material material, nonaqueous electrolyte, solid electrolyte material, and other components, except that the negative electrode active material layer is formed using the negative electrode composition of the present invention. These materials and components can be appropriately applied to those used in normal nonaqueous secondary batteries. In addition, for the method of producing the nonaqueous secondary battery of the present invention, a normal method can be appropriately adopted, except that the negative electrode active material layer is formed using the negative electrode composition of the present invention. For example, JP 2016-201308 A, JP 2005-108835 A, JP 2012-185938 A, and WO 2020/067106 A can be appropriately referred to.

The nonaqueous secondary battery of the present invention can be mounted in electronic devices such as notebook computers, pen-input computers, mobile computers, electronic book players, mobile phones, cordless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, headphone stereos, video movie machines, liquid crystal televisions, handheld cleaners, portable CDs, mini-discs, electric shavers, transceivers, electronic organizers, calculators, portable tape recorders, radios, backup power sources, and memory cards. It can also be mounted in consumer devices such as automobiles, electric vehicles, motors, lighting equipment, toys, game equipment, road conditioners, watches, strobes, cameras, and medical equipment (pacemakers, hearing aids, shoulder massagers, etc.). It can also be combined with solar cells.

The present invention will be described in more detail with reference to examples. Note that the present invention is not to be construed as being limited by these examples except as provided for in the present invention.

[Synthesis of Polymer A]
<Synthesis of Polymer 1 (Polymer No. 1 in Table 1 below)>
Polymer 1 shown in Table 1 below was synthesized as follows.
A 500 mL separable flask was charged with 108.1 g of ion-exchanged water, and while stirring under a nitrogen atmosphere at 75° C., a mixture containing 17.5 g of 2-hydroxyethyl acrylate, 52.5 g of N-(2-hydroxyethyl)acrylamide, and 24.9 g of ion-exchanged water and a mixture containing 1.26 g of 2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate and 33.3 g of ion-exchanged water were simultaneously added dropwise over 1 hour. After completion of the dropwise addition, the mixture was stirred at 75° C. for 2 hours to obtain a polymer solution with a solid content of 29.8% by mass.

<Synthesis of polymers 2 to 19 and c1 to c3 (synthesis of polymers No. 2 to 19 and c1 to c3 in Table 1 below)
Polymers 2 to 19 and c1 to c3 were synthesized in the same manner as in the synthesis of Polymer 1, except that the monomers shown in Table 1 below were used in the mass ratios shown in Table 1 below as monomers from which the constituent components were derived.

<Synthesis of Polymers 20 to 23, c4, and c5 (Synthesis of Polymers No. 20 to 23, c4, and c5 in Table 3 below)
Polymers 20 to 23, c4 and c5 were synthesized in the same manner as in the synthesis of Polymer 1, except that the monomers shown in Table 3 below were used in the mass ratios shown in Table 3 below as monomers from which the constituent components were derived.

<Synthesis of Polymers 25 to 28, c6, and c7 (Synthesis of Polymers No. 25 to 28, c6, and c7 in Table 5 below)
Polymers 25 to 28, c6 and c7 were synthesized in the same manner as in the synthesis of Polymer 1, except that the monomers shown in Table 3 below were used in the mass ratios shown in Table 5 below as monomers from which the constituent components were derived.

[Carbon-coated silicon oxide]
In preparing the negative electrode composition described below, active materials 1 to 3 (all manufactured by Osaka Titanium Co., Ltd.) shown in Table A below were used as the carbon-coated silicon oxide.

(Measurement of weight average molecular weight)
The weight average molecular weight (Mw) of the polymer shown in Table 1 below is a weight average molecular weight calculated as sodium polyacrylate by gel permeation chromatography (GPC), and is a value measured under the following conditions.
Measuring instrument: HLC-8220GPC (product name, manufactured by Tosoh Corporation)
Columns: TOSOH TSKgel 5000PWXL (product name, manufactured by Tosoh Corporation), TOSOH TSKgel G4000PWXL (product name, manufactured by Tosoh Corporation), and TOSOH TSKgel G2500PWXL (product name, manufactured by Tosoh Corporation) were connected.
Guard column: TSKgel guard column PWXL (product name, manufactured by Tosoh Corporation)
Carrier: 200 mM sodium nitrate aqueous solution Rinse: ultrapure water Carrier flow rate: Sample pump 1.0 ml/min
Reference pump 0.223mL/min
Initial pump pressure: Sample pump 4.4MPa
Reference pump 0.8MPa
Sample concentration: 0.10% by mass
Column temperature: 40°C
Detector temperature: 40°C
Collection time: 45 minutes (runtime 47.0 minutes)
Detector: RI (refractive index) detector

(Measurement of Adsorption Rate)
40 mg of the aqueous polymer solution was poured into a 50 mL sample bottle in terms of solid content, and diluted with ion-exchanged water to 40.00 g including the polymer to obtain an aqueous polymer solution with a polymer concentration of 0.1% by mass.
800 mg of carbon-coated silicon oxide was placed in a 15 mL sample bottle. 8 g of the above-mentioned polymer aqueous solution with a polymer concentration of 0.1% by mass was added to the sample bottle, and then the mixture was stirred at 80 rpm at 25° C. for 1 hour using a mix rotor. After standing at 25° C. for 30 minutes, the supernatant was filtered through a 0.45 μm filter to obtain a filtrate. GPC measurement was performed under the above conditions, and the peak height (1) of the polymer aqueous solution and the peak height (2) of the filtrate were applied to the following formula to calculate the adsorption rate (%). The adsorption rate is shown in Table 2 below, together with the weight average molecular weight (adsorption molecular weight) obtained by GPC measurement.

Adsorption rate (%)=100−{100×peak height (2)/peak height (1)}

The adsorption molecular weight was calculated from the difference between the GPC data of the aqueous polymer solution and the GPC data of the filtrate. The carbon-coated silicon oxide was the same as that used in the negative electrode composition.

[Preparation of negative electrode composition 1 (composition No. 1 in Table 2 below)]
In a 60 mL ointment container (manufactured by Umano Chemical Co., Ltd.), 30 parts by mass of the active material 1 described in Table A above, 70 parts by mass of graphite (product name: MAG-D, manufactured by Hitachi Chemical Co., Ltd.), 5 parts by mass of acetylene black (product name: Denka Black, manufactured by Denka Co., Ltd.), 5 parts by mass of polymer 1, and 22.5 parts by mass of distilled water were added, and dispersed for 10 minutes at 2000 rpm using a foaming mixer (product name, manufactured by THINKY Co., Ltd.). 27 parts by mass of distilled water was added to the dispersed liquid, and dispersed for 10 minutes at 2000 rpm using a foaming mixer, to obtain a negative electrode composition 1.

[Preparation of Non-aqueous Electrolyte Secondary Battery (2032 Type Coin Battery) 1 (Battery No. 1 in Table 2 below)]
The obtained negative electrode composition 1 was applied onto a copper foil having a thickness of 20 μm using an applicator and dried for 1 hour at 80° C. Thereafter, the composition was pressed using a press machine and then dried in a vacuum at 150° C. for 6 hours to obtain a negative electrode sheet having a negative electrode active material layer having a thickness of 25 μm.
A disk having a diameter of 13.0 mm was cut out from the negative electrode sheet and used to form a negative electrode.
Lithium foil (thickness 50 μm, 14.5 mmφ) and a polypropylene separator (thickness 25 μm, 16.0 mmφ) were stacked in this order, and 200 μL of 1M LiPF ₆ ethylene carbonate/ethyl methyl carbonate (volume ratio 1:2) electrolyte was impregnated into the separator. 200 μL of electrolyte was further impregnated into the separator, and the negative electrode sheet was stacked so that the negative electrode active material layer surface was in contact with the separator. Then, a 2032-type coin case was crimped to prepare a nonaqueous electrolyte secondary battery 1 (a battery having a laminate consisting of Li foil-separator-negative electrode active material layer-copper foil).

[Preparation of negative electrode compositions 2 to 19 and c1 to c3 (compositions No. 2 to 19 and c1 to c3 in Table 2 below)]
Negative electrode compositions 2 to 19 and c1 to c3 were prepared in the same manner as in the preparation of the negative electrode composition 1, except that polymers 2 to 19 and c1 to c3 shown in Table 1 below were used instead of polymer 1.

[Preparation of Nonaqueous Electrolyte Secondary Batteries 2 to 19 and c1 to c3 (Batteries No. 2 to 19 and c1 to c3 in Table 2 below)]
Non-aqueous electrolyte secondary batteries 2 to 19 and c1 to c3 were produced in the same manner as in the production of the non-aqueous electrolyte secondary battery 1, except that negative electrode compositions 2 to 19 and c1 to c3 shown in Table 2 below were used instead of the negative electrode composition 1.

[Test Example 1] Evaluation of cycle characteristics The discharge capacity retention rate of each coin battery was measured using a charge/discharge evaluation device: TOSCAT-3000 (product name, manufactured by Toyo Systems Co., Ltd.). Charging was performed at a C rate of 0.2 C (a rate at which the battery is fully charged in 5 hours) until the battery voltage reached 0.02 V. Discharging was performed at a C rate of 0.2 C until the battery voltage reached 1.5 V. Each coin battery was initialized by repeating three cycles of charging and discharging, with one charge and one discharge constituting one charge/discharge cycle.
After the initialization, charging was performed at 0.5 C until the voltage reached 0.02 V. Discharging was performed at 0.5 C until the voltage reached 1.5 V. This one charge and one discharge constituted one charge/discharge cycle, and 50 charge/discharge cycles were repeated to evaluate the cycle characteristics. When the discharge capacity at the first cycle after initialization (initial discharge capacity) was taken as 100%, the discharge capacity retention rate at the 50th cycle (100 x "discharge capacity at the 50th cycle"/"initial discharge capacity") was calculated, and the cycle characteristics were evaluated according to the following evaluation rank. Table 1 shows the polymer types and their characteristics, and Table 2 shows the test evaluation results using each composition.

-Evaluation rank of discharge capacity retention rate (cycle characteristics)-
1: 95% or more 2: 90% or more, but less than 95% 3: 85% or more, but less than 90% 4: Less than 85%

Notes for Tables 1 and 2
The abbreviations of the monomers from which the components are derived are explained. Also, the structures of the components derived from the monomers are described.
(Components not having an acid group)
HEA: 2-hydroxyethyl acrylate HEAA: N-(2-hydroxyethyl)acrylamide Aam: acrylamide MEA: 2-methoxyethyl acrylate

(Component having an acid group)
AA: Sodium acrylate AMPS: 2-acrylamido-2-methylpropanesulfonic acid

Latex: copolymer latex of styrene/2-ethylhexyl acrylate/acrylic acid=40/55/5 (mass ratio), Mw=1.2 million, average primary particle size on a volume basis of 3 μm (solid content 15 mass %), this latex is water-insoluble.
High acid group polymer: a random copolymer synthesized in the same manner as polymer 1 above ("HEAA/HEA/AA", HEAA:HEA:AA = 70:20:10 (mass ratio), Mw = 150,000)
High molecular weight polymer: a random copolymer synthesized in the same manner as polymer 1 above ("HEAA/HEA", HEAA:HEA = 50:50 (mass ratio), Mw = 400,000)

"Content in polymer A (% by mass)" means the content in polymer A of a component having an acid group.
"Content 1 (parts by mass)": means the content of polymer A relative to 100 parts by mass of carbon-coated silicon oxide, assuming that the content of carbon-coated silicon oxide in the negative electrode composition is 100 parts by mass.
"Content in binder (% by mass)" means the percentage of the content of the water-soluble polymer defined in the present invention relative to the total polymer contained in the binder.
"Content 2 (parts by mass)": when the content of carbon-coated silicon oxide in the negative electrode composition is taken as 100 parts by mass, this refers to the content of polymer B relative to 100 parts by mass of carbon-coated silicon oxide. The content of "latex" is the content of solids.
"Water-soluble/water-insoluble": "Water" means that 7 g or more was dissolved in 1 L of water at 25° C., and "Non-water" means that less than 7 g was dissolved in 1 L of water at 25° C. All of the polymers A, including those used in the comparative examples, are water-soluble.

The polymer A used in the negative electrode compositions No. c1 to c3 had an adsorption rate of less than 5% on the carbon-coated silicon oxide. The batteries No. c1 and c3 made using the negative electrode compositions No. c1 to c3 had poor cycle characteristics.
In contrast, it is clear that the batteries (Nos. 1 to 19) produced using the negative electrode compositions of the present invention (Nos. 1 to 19) have excellent cycle characteristics.

[Preparation of negative electrode compositions 20 to 24, c4, and c5 (compositions No. 20 to 24, c4, and c5 in Table 4 below)]
Negative electrode compositions 20 to 24, c4, and c5 were prepared in the same manner as the negative electrode composition 1, except that the active material 1 and polymer 1 used in the preparation of the negative electrode composition 1 were replaced with the polymers and active materials shown in Table 4 below.

[Preparation of Nonaqueous Electrolyte Secondary Batteries 20 to 24, c4, and c5 (Batteries No. 20 to 24, c4, and c5 in Table 4 below)]
Non-aqueous electrolyte secondary batteries 20 to 24, c4, and c5 were produced in the same manner as in the production of the non-aqueous electrolyte secondary battery 1, except that in the production of the non-aqueous electrolyte secondary battery 1, negative electrode compositions 20 to 24, c4, and c5 shown in Table 4 below were used instead of the negative electrode composition 1.

[Preparation of negative electrode sheets 20 to 24, c4 and c5 (negative electrode sheets Nos. 20 to 24, c4 and c5 in Table 4 below)]
The negative electrode composition 20 was applied onto a copper foil having a thickness of 20 μm using an applicator and dried at 80° C. for 1 hour. The negative electrode composition 20 was further dried at 100° C. for 6 hours under vacuum to obtain a negative electrode sheet 20. The negative electrode sheet 20 was 50 mm wide, 150 mm long, and 90 μm thick, and the thickness of the negative electrode active material layer was 70 μm.
In the preparation of the negative electrode sheet 20, negative electrode compositions 21 to 24, c4, and c5 shown in Table 4 below were used instead of the negative electrode composition 20. The negative electrode sheets 21 to 24, c4, and c5 were prepared in the same manner as in the preparation of the negative electrode sheet 20.

The nonaqueous electrolyte secondary batteries 20 to 24, c4, and c5 were used to evaluate cycle characteristics according to the above-mentioned Test Example 1. In addition, the negative electrode sheets 20 to 24, c4, and c5 were used to evaluate bending resistance according to the later-described Test Example 2.
The polymer types and their properties are shown in Table 3 below, and the results of the cycle characteristic evaluation and flex resistance evaluation are shown in Table 4 below.

Test Example 2 Evaluation of flex resistance A test piece measuring 10 mm in width, 100 mm in length, and 90 μm in thickness was cut out from the produced negative electrode sheet, and this test piece was set in a cylindrical mandrel flex tester (BEVS 1603 (product name, manufactured by Allgood Corporation). The test piece was wrapped around a mandrel rod so that the current collector of the test piece was in contact with the mandrel rod. The diameter of the mandrel rod was gradually reduced from 32 mm, and the diameter at which a crack first occurred in the negative electrode active material layer of the test piece was assigned to the following evaluation rank to evaluate the flex resistance.

-Bending resistance evaluation rank-
1: Less than 10 mm 2: 10 mm to less than 20 mm 3: 20 mm to less than 25 mm 4: 25 mm or more

Notes for Tables 3 and 4
The meanings of "HEA", "AA", "HEAA", "Aam", "Content in polymer A (% by mass)", "Content 1 (parts by mass)", "Content in binder (% by mass)", and "Water" are the same as those in the "Notes to Tables 1 and 2" above.

The polymer A used in the negative electrode compositions of No. c4 and No. c5 has an adsorption rate of less than 5% on the carbon-coated silicon oxide. The batteries of No. c4 and No. c5 made using the negative electrode compositions of No. c4 and No. c5 had poor cycle characteristics. The electrode sheet of No. c4 also had poor bending resistance.
In contrast, it is found that the batteries (Nos. 20 to 24) produced using the negative electrode composition of the present invention (Nos. 20 to 24) have excellent cycle characteristics. In addition, a comparison of the negative electrode sheets 22 and 24 with the negative electrode sheets 20, 21, and 23 shows that the use of a water-soluble polymer with a larger weight average molecular weight can further improve flex resistance.

It was confirmed that in negative electrode compositions 20 to 24, even if the content of active material 2 (30 parts by mass) and the content of graphite (70 parts by mass) were changed to "active material 2 (10 parts by mass), graphite (90 parts by mass)", "active material 2 (20 parts by mass), graphite (80 parts by mass)", "active material 2 (40 parts by mass), graphite (60 parts by mass)", "active material 2 (50 parts by mass), graphite (50 parts by mass)", or "active material 2 (60 parts by mass), graphite (40 parts by mass)", a battery with excellent cycle characteristics and a negative electrode sheet with excellent flex resistance could be obtained.

[Preparation of negative electrode compositions 25 to 29, c6, and c7 (compositions No. 25 to 29, c6, and c7 in Table 6 below)]
Negative electrode compositions 25 to 29, c6, and c7 were prepared in the same manner as in the preparation of the negative electrode composition 1, except that the active material 1 and polymer 1 used in the preparation of the negative electrode composition 1 were replaced with the polymers and active materials shown in Table 6 below.

[Preparation of Nonaqueous Electrolyte Secondary Batteries 25 to 29, c6, and c7 (Batteries No. 25 to 29, c6, and c7 in Table 6 below)]
Non-aqueous electrolyte secondary batteries 25 to 29, c6, and c7 were produced in the same manner as in the production of the non-aqueous electrolyte secondary battery 1, except that negative electrode compositions 25 to 29, c6, and c7 shown in Table 6 below were used instead of negative electrode composition 1.

[Preparation of negative electrode sheets 25 to 29, c6 and c7 (negative electrode sheets Nos. 25 to 29, c6 and c7 in Table 6 below)]
Negative electrode sheets 25 to 29, c6, and c7 were produced in the same manner as in the production of the negative electrode sheet 20, except that negative electrode compositions 25 to 29, c6, and c7 were used instead of the negative electrode composition 20.

The nonaqueous electrolyte secondary batteries 25 to 29, c6, and c7 were used to evaluate the cycle characteristics according to the above-mentioned Test Example 1. The negative electrode sheets 25 to 29, c6, and c7 were used to evaluate the flex resistance according to the above-mentioned Test Example 2.
The polymer types and their properties are shown in Table 5 below, and the results of the cycle characteristic evaluation and flex resistance evaluation are shown in Table 6 below.

Notes for Tables 5 and 6
The meanings of "HEA", "AA", "HEAA", "Aam", "Content in polymer A (% by mass)", "Content 1 (parts by mass)", "Content in binder (% by mass)", and "Water" are the same as those in the "Notes to Tables 1 and 2" above.

The polymer A used in the negative electrode compositions of No. c6 and No. c7 has an adsorption rate of less than 5% on the carbon-coated silicon oxide. The batteries of No. c6 and No. c7 made using the negative electrode compositions of No. c6 and No. c7 had poor cycle characteristics.
In contrast, the batteries (Nos. 25 to 29) made using the negative electrode compositions of the present invention (Nos. 25 to 29) are excellent in cycle characteristics and flex resistance. In addition, a comparison of the negative electrode sheets 27 and 29 with the negative electrode sheets 25, 26, and 28 shows that the flex resistance can be further improved by using a water-soluble polymer with a larger weight average molecular weight.

It was confirmed that in negative electrode compositions 25 to 29, even if the content of active material 3 (30 parts by mass) and the content of graphite (70 parts by mass) were changed to "active material 3 (10 parts by mass), graphite (90 parts by mass)," "active material 3 (20 parts by mass), graphite (80 parts by mass)," "active material 3 (40 parts by mass), graphite (60 parts by mass)," "active material 3 (50 parts by mass), graphite (50 parts by mass)," or "active material 3 (60 parts by mass), graphite (40 parts by mass)," batteries with excellent cycle characteristics and negative electrode sheets with excellent flex resistance could be obtained.

Although the present invention has been described in conjunction with its embodiments, we do not intend to limit our invention to any of the details of the description unless specifically stated otherwise, and believe that the appended claims should be interpreted broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

This application claims priority to Patent Application No. 2021-060334, filed in Japan on March 31, 2021, and Patent Application No. 2021-159546, filed in Japan on September 29, 2021, the contents of which are incorporated herein by reference as part of the present specification.

Reference Signs List 10: nonaqueous electrolyte secondary battery 1: negative electrode current collector 2: negative electrode active material layer 3: separator 4: positive electrode active material layer 5: positive electrode current collector 6: operating part (light bulb)

Claims (8)

The binder contains a water-soluble polymer that is a chain-polymer , and carbon-coated silicon oxide.
the water-soluble polymer has an adsorption rate of 5 to 25% with respect to the carbon-coated silicon oxide;
the water-soluble polymer contains a component represented by the following general formula (1) or (2), and the component represented by the general formula (1) or (2) does not have an acid group,
A composition for a negative electrode , wherein the proportion of the component represented by the general formula (1) or (2) in the water-soluble polymer is 95 mass % or more .

In formula (1), R1 ^represents a hydrogen atom or a methyl group, L1 ^represents a single bond or a linking group, and R2 ^represents a substituent. * represents a bonding site for incorporation into the water-soluble polymer.
In formula (2), R3 ^represents a hydrogen atom or a methyl group, R4 ^and R5 ^represent a hydrogen atom or a substituent, and * represents a bonding site for incorporation into the water-soluble polymer. 2. The negative electrode composition according to claim 1 , wherein the content of the water-soluble polymer is 2 parts by mass or more based on 100 parts by mass of the carbon-coated silicon oxide. The negative electrode composition according to claim 1 or 2 , wherein the water-soluble polymer contains two or more components represented by the general formula (1) or (2). The negative electrode composition according to any one of claims 1 to 3 , which is a negative electrode slurry containing a dispersion medium. A negative electrode sheet having a layer formed using the negative electrode composition according to any one of claims 1 to 4 . A non-aqueous secondary battery comprising a positive electrode active material layer, a separator, and a negative electrode active material layer in this order, the negative electrode active material layer being a layer formed using the negative electrode composition according to any one of claims 1 to 4 . A method for producing a negative electrode sheet, comprising forming a film using the negative electrode composition according to any one of claims 1 to 4 . A method for producing a non-aqueous secondary battery, comprising incorporating the negative electrode sheet obtained by the method according to claim 7 into a negative electrode of the non-aqueous secondary battery.

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