Composite negative electrode active material, slurry for secondary battery negative electrode, negative electrode sheet, and secondary battery, and methods for manufacturing negative electrode sheet and secondary battery

Abstract

Provided is a composite negative electrode active material having a negative electrode active material capable of inserting metal ions of a Group 1 or a Group 2 of the periodic table, and a coating layer covering a surface of the negative electrode active material, wherein an amount of hydrogen gas generated per 1 g of the composite negative electrode active material is less than 0.30 cm3 / g when an aqueous dispersion containing the composite negative electrode active material at a concentration of 5 mass % is left to stand at 40°C for 24 hours. Also provided are a slurry for a secondary battery negative electrode, a negative electrode sheet, a secondary battery, and methods for manufacturing the negative electrode sheet and the secondary battery.

Description

Composite negative electrode active material, slurry for secondary battery negative electrode, negative electrode sheet and secondary battery, and method for manufacturing negative electrode sheet and secondary battery

[0001] The present invention relates to a composite negative electrode active material, a slurry for a secondary battery negative electrode, a negative electrode sheet and a secondary battery, and a method for manufacturing the negative electrode sheet and the secondary battery.

[0002] 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. Recently, against the backdrop of the global environmental challenge of reducing carbon dioxide emissions, they have become increasingly popular as power sources for transportation equipment such as automobiles, and for storing electricity such as nighttime power and electricity generated by natural energy sources.

[0003] The negative electrode of a lithium-ion secondary battery generally has a negative electrode active material layer, which contains electrode active material particles capable of absorbing or releasing lithium ions during charge and discharge, and optionally contains a conductive additive, etc. The negative electrode active material layer can be formed by coating a current collector with a slurry composition in which these solid particles are dispersed in an aqueous solvent, and then drying the coating.

[0004] In recent years, with the expansion of secondary battery applications, the use of silicon-based active materials as negative electrode active materials has been actively investigated to further increase the capacity of lithium-ion secondary batteries. However, silicon-based active materials react with aqueous solvents (moisture) in slurries to generate hydrogen gas. Similarly to the silicon-based active materials, metal-doped negative electrode active materials also tend to react with moisture to generate hydrogen gas. This hydrogen gas reduces the dispersion stability and coatability of the slurry, resulting in a decrease in the battery capacity of the resulting secondary battery. To address this issue, for example, Patent Document 1 proposes setting the pH of a slurry containing lithium-doped silicon oxide as the negative electrode active material, water as the solvent, a binder, and single-walled carbon nanotubes as a gas adsorbent to 10 or higher. It is claimed that this slurry improves the stability of the slurry, regardless of the type of lithium-doped silicon oxide, by allowing the gas adsorbent to adsorb the hydrogen gas generated by the reaction of lithium in the lithium silicate phase with water.

[0005] JP 2023-96785 A

[0006] The technology described in Patent Document 1 captures the generated hydrogen gas using a gas adsorbent, but does not suppress the generation of hydrogen itself. The inventors' investigations have revealed that when a negative electrode active material layer is formed using the slurry described in Patent Document 1, there are limitations to improving the battery capacity of the resulting secondary battery. This is thought to be due to hydrogen gas generated by the negative electrode active material layer reacting with trace amounts of moisture, affecting ionic conductivity, electronic conductivity, etc. The present invention aims to provide a composite negative electrode active material that can be used as a negative electrode active material component of a secondary battery to effectively increase the battery capacity of the secondary battery. Another objective of the present invention is to provide a slurry for a secondary battery negative electrode, a negative electrode sheet, and a secondary battery using this composite negative electrode active material. Another objective of the present invention is to provide a method for manufacturing these negative electrode sheets and secondary batteries.

[0007] The above-mentioned object of the present invention has been achieved by the following means: [1] A composite negative electrode active material having a negative electrode active material capable of inserting ions of a metal belonging to Group 1 or Group 2 of the periodic table, and a coating layer coating the surface of the negative electrode active material, wherein when an aqueous dispersion containing the composite negative electrode active material at a concentration of 5% by mass is allowed to stand at 40°C for 24 hours, the amount of hydrogen gas generated per 1 g of the composite negative electrode active material is 0.30 cm ３ [2] The composite negative electrode active material according to [1], wherein the coating layer contains a polymer having at least one of a component represented by the following general formula (A-1), a component represented by the following general formula (A-2), and a component represented by the following general formula (A-3): In the above general formula, R １１ ~R １３ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R １４ and R １５ represents a hydrogen atom, an alkyl group having 1 to 16 carbon atoms, or an aryl group having 6 to 12 carbon atoms. １６ represents an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 12 carbon atoms, -L １ -R １８or a counter ion. １ represents an alkylene group having 1 to 16 carbon atoms or a polyalkyleneoxy group having 1 to 16 carbon atoms. １ When is an alkylene group, R １８ represents a hydrogen atom, a hydroxy group, an alkoxy group, or a cyano group. １ When R is a polyalkyleneoxy group, １８ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a cyano group. １７represents a hydrogen atom, a hydroxy group, an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 12 carbon atoms, an acyloxy group having 2 to 16 carbon atoms, an alkoxycarbonyl group having 2 to 16 carbon atoms, or an aryloxycarbonyl group having 7 to 13 carbon atoms. * represents a bonding site for incorporation into the main chain of the polymer. [3] The composite negative electrode active material according to [2], wherein the total content of the component represented by general formula (A-1), the component represented by general formula (A-2), and the component represented by general formula (A-3) in the coating layer is 50 mass% or more. [4] The composite negative electrode active material according to [2] or [3], wherein the weight-average molecular weight of the polymer is 10,000 or more. [5] The composite negative electrode active material according to any one of [2] to [4], wherein the ratio of the content of the component represented by general formula (A-1) to the total content of the component represented by general formula (A-2) and the component represented by general formula (A-3) in the coating layer is 1 / 99 to 99 / 1 in mass ratio. [6] The composite negative electrode active material according to any one of [2] to [5], wherein the polymer contains the component represented by general formula (A-1) and the component represented by general formula (A-2) and / or the component represented by general formula (A-3). [7] The composite negative electrode active material according to any one of [2] to [6], wherein the coating layer contains a polymer having the component represented by general formula (A-1) and a polymer having the component represented by general formula (A-2) and / or the component represented by general formula (A-3). [8] The composite negative electrode active material according to any one of [1] to [7], wherein the coating layer has a content of 11.0 mass % or less. [9] The composite negative electrode active material according to any one of [1] to [8], wherein the negative electrode active material includes a silicon-based active material.

[10] A slurry for a secondary battery negative electrode, comprising the composite negative electrode active material according to any one of [1] to [9].

[11] A negative electrode sheet having a negative electrode active material layer formed using the slurry for a secondary battery negative electrode according to

[10] .

[12] A secondary battery including a negative electrode active material layer formed using the slurry for a secondary battery negative electrode according to

[10] .

[13] A method for producing a negative electrode sheet, comprising forming a negative electrode active material layer using the slurry for a secondary battery negative electrode according to

[10] .

[14] A method for producing a secondary battery, comprising incorporating the negative electrode active material layer of the negative electrode sheet obtained by the production method according to

[13] as a negative electrode active material layer of the secondary battery.

[0008] The composite negative electrode active material, secondary battery negative electrode slurry, and negative electrode sheet of the present invention can be used to form a negative electrode active material layer of a secondary battery, thereby further increasing the battery capacity of the resulting secondary battery. The negative electrode sheet of the present invention can be obtained by the method for producing a negative electrode sheet of the present invention. Furthermore, the secondary battery of the present invention can be obtained by the method for producing a secondary battery of the present invention.

[0009] FIG. 1 is a longitudinal sectional view showing a schematic diagram of a basic layer structure of an embodiment of a secondary battery according to the present invention.

[0010] In the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In the present invention, the expression of a compound, a constituent, or a substituent includes a partially modified structure within the scope of the effects of the present invention. Furthermore, in the present invention, a compound or a constituent that is not specified as substituted or unsubstituted means that it may have any substituent within the scope of the effects of the present invention. This also applies to substituents (e.g., groups expressed as "alkyl group," "methyl group," "methyl," etc.) and linking groups (e.g., groups expressed as "alkylene group," "methylene group," "methylene," etc.). Among such optional substituents, preferred substituents in the present invention are those selected from the substituent group T described below. In the present invention, when there are multiple substituents or linking groups, etc., represented by a specific symbol or formula (hereinafter referred to as "substituents, etc."), or when multiple substituents, etc., are specified simultaneously, the respective substituents, etc., may be the same or different from each other, unless otherwise specified. This also applies to the constituent components of a polymer. In the present invention, unless otherwise specified, each component may be contained in one type or in two or more types. For example, the components constituting the composite negative electrode active material of the present invention (the "negative electrode active material" and the "polymer constituting the coating layer") may each be contained in one type or in two or more types in the composite negative electrode active material of the present invention. In the present invention, the term "composition" includes not only mixtures with constant component concentrations (in which each component is uniformly dispersed) but also mixtures with non-uniform component concentrations within a range that does not impair the intended function. In the present invention, (meth)acrylic refers to one or both of acrylic and methacrylic. The same applies to (meth)acrylate. In the present invention, the term "secondary battery" refers to a general device in which ions move between positive and negative electrodes via an electrolyte upon charge and discharge, storing and releasing energy at the positive and negative electrodes. In other words, the term "secondary battery" in the present invention encompasses both batteries and capacitors (e.g., lithium ion capacitors). From the viewpoint of energy storage capacity, it is preferable that the secondary battery of the present invention be used for battery applications (not capacitors).Secondary batteries can be broadly classified into aqueous secondary batteries and nonaqueous secondary batteries depending on the electrolyte used, and nonaqueous secondary batteries are preferred in the present invention. In the present invention, "aqueous secondary battery" refers to a secondary battery using an aqueous electrolyte solution as the electrolyte. In the present invention, "nonaqueous secondary battery" includes nonaqueous electrolyte secondary batteries and all-solid-state secondary batteries. In the present invention, "nonaqueous electrolyte secondary battery" refers to a secondary battery using a nonaqueous electrolyte solution as the electrolyte. In the present invention, "nonaqueous electrolyte solution" refers to an electrolyte solution that is substantially free of water. An electrolyte solution that is substantially free of water means that the "nonaqueous electrolyte solution" may contain a trace amount of water as long as it does not impair the effects of the present invention. In the present invention, the "nonaqueous electrolyte solution" has a water concentration of 200 ppm (by mass) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. It is practically difficult to make a nonaqueous electrolyte solution completely anhydrous, and it usually contains 1 ppm or more of water. In the present invention, an "all-solid-state secondary battery" refers to a secondary battery that does not use a liquid electrolyte, but uses a solid electrolyte such as an inorganic solid electrolyte or a solid polymer electrolyte. In the present invention, when specifying the number of carbon atoms in a certain group, this carbon number refers to the number of carbon atoms in the group itself, unless otherwise specified in the present invention or this specification. In other words, if the group further has a substituent, the number of carbon atoms refers to the number of carbon atoms counted without including the carbon atoms of the substituent. In the present invention, the "solid content" used when describing the content or content ratio refers to components other than water and the liquid medium (solvent) described below. In the present invention, the "average particle size" refers to the volume-based median diameter D50. In the present invention, a "water-soluble polymer" refers to a polymer having a solubility in water of 10 g / L-H at 20°C. ２ The solubility of a "water-soluble polymer" is 100 g / L-H or more, that is, a polymer that dissolves 10 g or more in 1 liter of water. ２ It is preferably 0 or more.

[0011] [Composite Negative Electrode Active Material] The composite negative electrode active material of the present invention is a composite negative electrode active material having a negative electrode active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table, and a coating layer that coats the surface of the negative electrode active material, and is characterized in that, when an aqueous dispersion containing the composite negative electrode active material at a concentration of 5% by mass is allowed to stand at 40°C for 24 hours, the amount of hydrogen gas generated per 1 g of the composite negative electrode active material (referred to as the "amount of hydrogen gas generated under specific conditions") is 0.30 cm ３ Less than (0.30 cm ３ / g).

[0012] The composite negative electrode active material of the present invention can suppress the generation of hydrogen gas itself when it comes into contact with moisture, and can effectively increase the battery capacity of a secondary battery using it as a negative electrode active material component.

[0013] A known technique involves using a polymer as a binder during the preparation of a negative electrode slurry to improve the adhesion between particles of the negative electrode active material and the negative electrode active material. The negative electrode slurry prepared by this conventional technique contains a binder-adsorbed negative electrode active material in which the binder is physically or chemically adsorbed to a portion of the surface of the negative electrode active material. However, the binder content in the binder-adsorbed negative electrode active material obtained in this manner is quite low, typically less than 0.05% by mass. Furthermore, such binder-adsorbed negative electrode active materials are unable to suppress hydrogen gas generation to a desired level.

[0014] The amount of hydrogen gas generated under the above specific conditions is 0.20 cm ３ / g or less, and preferably 0.10 cm ３ / g or less is more preferable, and 0.05 cm ３ The lower limit is not particularly limited, but it is preferable that hydrogen gas is not generated, and it is more preferable that the lower limit is less than 0.03 cm ３ Therefore, the amount of hydrogen gas generated under the above specific conditions is 0.03 cm ３ / g or more 0.30cm ３ / g or less is preferred, and 0.03 cm ３ / g or more 0.20cm ３ / g or less is more preferable, and 0.03 cm３ / g or more 0.10cm ３ / g or less is more preferable, and 0.03 cm ３ / g or more 0.05cm ３ The amount of hydrogen gas generated under the above-mentioned specific conditions can be determined by measuring the specific gravity. Specifically, it can be determined by the method described in the Examples.

[0015] The components contained in the composite negative electrode active material of the present invention will be described below.

[0016] <Negative electrode active material> The negative electrode active material may be any active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table, and among these, those capable of reversibly inserting (occluding) and releasing lithium ions are preferred. The material is not particularly limited as long as it has the above-mentioned properties, and examples thereof include carbonaceous materials, silicon-based materials (meaning materials containing silicon), tin-based materials (meaning materials containing tin), metal oxides, metal composite oxides, lithium alone, and lithium alloys. Among these, carbonaceous materials or silicon-based materials are preferably used from the viewpoint of reliability.

[0017] The carbonaceous material used as the negative electrode active material is a material essentially composed of carbon. Examples include carbon black such as petroleum pitch and acetylene black, graphite (natural graphite such as flake graphite and block graphite, artificial graphite such as vapor-grown graphite and fibrous graphite, and expanded graphite obtained by specially processing flake graphite), activated carbon, carbon fiber, coke, soft carbon, hard carbon, and carbonaceous materials obtained by calcining various synthetic resins such as PAN (polyacrylonitrile)-based resins and furfuryl alcohol resins. Further examples include various carbon fibers such as PAN-based carbon fiber, cellulose-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, dehydrated PVA (polyvinyl alcohol)-based carbon fiber, lignin carbon fiber, glassy carbon fiber, and activated carbon fiber, mesophase microspheres, graphite whiskers, and tabular graphite.

[0018] Examples of tin-based materials (tin-based active materials) used as negative electrode active materials include Sn, SnO, and SnO ２ , SnS, SnS２ Examples include:

[0019] The metal oxides and metal composite oxides used as negative electrode active materials are not particularly limited as long as they are oxides capable of inserting and releasing (preferably absorbing and releasing) ions of a metal belonging to Group 1 or Group 2 of the periodic table (preferably lithium ions). Examples of metal oxides include oxides of metal elements (metal oxides) and oxides of metalloid elements (metalloid oxides). Examples of metal composite oxides include composite oxides of metal elements, composite oxides of metal elements and metalloid elements, and composite oxides of metalloid elements. These metal oxides and metal composite oxides are preferably amorphous oxides, and further preferred are chalcogenides, which are reaction products of metal elements and elements of Group 16 of the periodic table. The term "amorphous" as used herein refers to an oxide having a broad scattering band with a peak in the 2θ range of 20° to 40° when measured by X-ray diffraction using CuKα radiation, and may also have crystalline diffraction lines. Among the amorphous oxides and chalcogenides, amorphous oxides or chalcogenides of metalloid elements are more preferred, and oxides or composite oxides or chalcogenides of one or a combination of two or more of the elements of Groups 13 (IIIB) to 15 (VB) of the periodic table (e.g., Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) are particularly preferred. Specific examples of amorphous oxides and chalcogenides include, for example, Ga ２ O ３ , GeO, PbO, PbO ２ , Pb ２ O ３ , Pb ２ O ４ , Pb ３ O ４ , Sb ２ O ３ , Sb ２ O ４ , Sb ２ O ８ Bi ２ O ３ , Sb ２ O ８ Si ２ O ３ , Sb ２ O ５ , Bi ２ O３ , Bi ２ O ４ , GeS, PbS, PbS ２ , Sb ２ S ３ and Sb ２ S ５ are preferred.

[0020] The metal (composite) oxide and the chalcogenide preferably contain at least one of titanium and lithium as a constituent component from the viewpoint of charge / discharge characteristics at high current density. Examples of the lithium-containing metal composite oxide (lithium composite metal oxide) include, for example, composite oxides of lithium oxide and the metal (composite) oxide or the chalcogenide, more specifically, Li ２ SnO ２ Examples include:

[0021] The negative electrode active material preferably contains titanium element. More specifically, TiNb ２ O ７ (Niobium titanate oxide [NTO]), Li ４ Ti ５ O １２ Lithium titanate (LTO) is preferred because it has small volume fluctuations during absorption and desorption of lithium ions, has excellent rapid charge and discharge characteristics, suppresses electrode deterioration, and enables improved cycle characteristics of lithium ion secondary batteries.

[0022] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy that is commonly used as a negative electrode active material for secondary batteries, and an example thereof is a lithium aluminum alloy.

[0023] The silicon-based material is a negative electrode active material (silicon-based active material) containing silicon element, for example, Si, SiO ｘ (0<x≦1.5), and silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (e.g., LaSi ２ , VSi ２ ), or structured active materials (e.g., LaSi ２ / Si), as well as oxides or composite oxides containing silicon element in the above-mentioned metal oxides and metal composite oxides, SnSiO ３ , SnSiS ３ Examples of active materials include those containing silicon and tin, such as SiO ｘ can be used as a negative electrode active material (semi-metal oxide) by itself, and can also be used as an active material (precursor material) that can form an alloy with lithium because it produces Si during battery operation.

[0024] While the above description focuses on the components of the negative electrode active material, from the viewpoint of characteristics, the negative electrode active material is preferably a negative electrode active material capable of forming an alloy with lithium. The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is one typically used as a negative electrode active material for secondary batteries. Examples of such active materials include the above-mentioned negative electrode active materials containing silicon and / or tin, and metals such as Al and In. Silicon-based active materials are preferred because they enable higher battery capacities, and silicon-based active materials containing 40 mol% or more of silicon based on the total constituent elements are more preferred. Generally, negative electrodes containing these negative electrode active materials capable of forming an alloy with lithium (e.g., Si negative electrodes containing silicon-based active materials, Sn negative electrodes containing tin-based active materials) can absorb more Li ions than negative electrodes made solely of carbonaceous materials (e.g., graphite, carbon black, etc.). In other words, the amount of Li ions absorbed per unit mass is increased. This increases battery capacity (energy density). As a result, the battery operating time can be extended. Thus, a negative electrode active material containing silicon and / or tin is also called a high-capacity active material.

[0025] The surface of the negative electrode active material may be surface-coated with an oxide such as another metal oxide, a carbonaceous material, or the like (hereinafter, being surface-coated with a carbonaceous material may be referred to as being "carbon-coated"). Examples of surface-coating materials include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds. More specifically, examples include Li ４ Ti５ O １２ , Li ２ Ti ２ O ５ , LiTaO ３ , LiNbO ３ , LiAlO ２ , Li ２ ZrO ３ , Li ２ WO ４ , Li ２ TiO ３ , Li ２ B ４ O ７ , Li ３ P.O. ４ , Li ２ MoO ４ , Li ３ BO ３ , LiBO ２ , Li ２ CO ３ , Li ２ SiO ３ , SiO ２ , TiO ２ , ZrO ２ , Al ２ O ３ , B ２ O ３ and the like. Carbonaceous materials such as C, SiC, and carbon-added silicon oxides can also be used as surface coating materials. The effects of the composite negative electrode active material of the present invention are more effectively exhibited in negative electrode active materials, such as silicon-based active materials coated with carbonaceous materials, in which cracks occur in the surface coating layer (carbon coating layer) due to expansion and contraction during charge and discharge when conventional coatings are used.

[0026] The surface of the negative electrode active material may be surface-treated with sulfur or phosphorus. Furthermore, the particle surface of the negative electrode active material may be surface-treated with actinic rays or an active gas (plasma, etc.) before or after the above-mentioned surface coating. In the present invention, the surface coating with the above-mentioned oxide such as another metal oxide, material such as a carbonaceous material, sulfur, or phosphorus is not included in the coating with a polymer constituting the coating layer described below, but is included in the negative electrode active material.

[0027] The negative electrode active material may be doped with a metal element. In the negative electrode active material doped with a metal element, the doped metal element is preferably at least one of Li, Ni, and Ti, and more preferably Li.

[0028] The negative electrode active material preferably contains a silicon-based active material, which is a high-capacity active material. Examples of the silicon-based active material include silicon oxide (SiO ｘ (0<x≦1.5)) or carbon-coated silicon oxide (carbon-coated SiO ｘIt is preferable to use a silicon oxide (0<x≦1.5), and it is more preferable to use carbon-coated silicon oxide. The carbon-coated silicon oxide may be further doped with a metal element. The carbon content in the carbon-coated silicon oxide is not particularly limited and is, for example, preferably 0.5 to 5 mass% and more preferably 1 to 3 mass%. Commercially available silicon oxide or carbon-coated silicon oxide may be used. Carbon-coated silicon oxide can also be prepared by carbon-coating silicon oxide, for example, with reference to JP 2019-204686 A. The content of the silicon-based active material (preferably silicon oxide or carbon-coated silicon oxide) in the negative electrode active material is not particularly limited and can be, for example, 5 to 90 mass%, preferably 5 to 50 mass%, and more preferably 5 to 40 mass%. The entire negative electrode active material may be a silicon-based active material. When the negative electrode active material is silicon oxide or carbon-coated silicon oxide, the average particle size is preferably 5 to 20 μm. In the present invention, it is also preferable to use a silicon-based active material doped with a metal element as the negative electrode active material, with a silicon-based active material doped with at least one of Li, Ni, and Ti being more preferable, and a silicon-based active material doped with Li being even more preferable. As the silicon-based active material to be doped with a metal element, silicon oxide or carbon-coated silicon oxide is preferred. As silicon oxide doped with a metal element and silicon oxide doped with a metal element and carbon-coated, commercially available products may be used. Also, for example, with reference to JP 2022-121582 A, WO 14 / 188851 A, and JP 2021-150077 A, silicon oxide or carbon-coated silicon oxide can be doped with a metal element, or silicon oxide can be doped with a metal element and further carbon-coated as necessary. In the present invention, the phrase "both doped with a metal element and carbon coated" is used to mean both a material that has been doped with a metal element and then carbon coated, and a material that has been carbon coated and then doped with a metal element.In the present invention, it is also preferable to use, as the silicon-based active material, a silicon-based active material that is both doped with a metal element and coated with carbon. As such a silicon-based active material, silicon oxide that is both doped with a metal element and coated with carbon is more preferable, and silicon oxide that is both lithium-doped and coated with carbon is particularly preferable.

[0029] The shape of the negative electrode active material is not particularly limited, but particulate is preferred. The average particle size (volume-based median diameter D50) of the negative electrode active material is preferably 0.1 to 60 μm. To achieve the desired particle size, it can be prepared by a conventional method using a grinder or classifier. For example, a mortar, ball mill, sand mill, vibration ball mill, satellite ball mill, planetary ball mill, swirling airflow jet mill, or sieve is preferably used. Wet grinding in the presence of water or an organic solvent such as methanol can also be performed during grinding. Classification is preferred to achieve the desired particle size. The classification method is not particularly limited, and sieves, air classifiers, etc. can be used as desired. Classification can be performed using either dry or wet methods. When using commercially available negative electrode active materials, the average particle size of the negative electrode active material is determined from the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is unavailable or when a synthesized negative electrode active material is used, the negative electrode active material is dispersed in water, and the average particle size (volume-based median diameter D50 in water) obtained by measuring the particle size distribution using a laser diffraction / scattering particle size distribution measuring device (for example, Particle LA-960V2 (product name) manufactured by HORIBA Corporation) is used.

[0030] The negative electrode active material may be used alone or in combination of two or more.

[0031] In the present invention, from the viewpoint that hydrogen gas is easily generated in a configuration without a coating layer, it is preferable to use a silicon-based material, particularly a silicon-based material doped with a metal element, as the negative electrode active material. Also, a silicon-based material can be used in combination with other negative electrode active materials (e.g., carbonaceous materials).

[0032] As a combination of two or more negative electrode active materials, a combination including at least a silicon-based active material and a carbonaceous material is preferred, a combination including at least a silicon-based active material and graphite is more preferred, and a combination including at least silicon oxide or carbon-coated silicon oxide and graphite is even more preferred. The silicon oxide and carbon-coated silicon oxide may be silicon oxide doped with the above-mentioned metal element and silicon oxide doped with a metal element and carbon-coated, respectively. The doped metal element is preferably at least one of Li, Ni, and Ti, and more preferably Li. The total content of the silicon-based active material and carbonaceous material in the negative electrode active material can be, for example, 40 to 100% by mass, preferably 50 to 100% by mass, and more preferably 60 to 100% by mass. When a silicon-based active material and a carbonaceous material (preferably graphite) are used in combination, the mass ratio of the silicon-based active material to the carbonaceous material (preferably graphite) (silicon-based active material / carbonaceous material (preferably graphite)) is preferably 0.05 / 99.5 to 99 / 1, more preferably 1 / 99 to 99 / 1, even more preferably 1 / 99 to 90 / 10, even more preferably 1 / 99 to 80 / 20, even more preferably 1 / 99 to 70 / 30, even more preferably 1 / 99 to 50 / 50, and particularly preferably 3 / 97 to 30 / 70.

[0033] The specific surface area (BET specific surface area) of the negative electrode active material is 0.1 to 50 m ２ / g is preferred. When a commercially available negative electrode active material is used, the value listed in the manufacturer's catalog is used as the specific surface area of ​​the negative electrode active material. When the manufacturer's specific surface area information is unavailable or when a synthesized negative electrode active material is used, the negative electrode active material is packed into a sample tube, dried by flowing nitrogen, and the specific surface area (BET specific surface area) calculated by the BET (single point) method using a nitrogen adsorption method, measured using a specific surface area / pore distribution measuring device (e.g., BELSORP MINI manufactured by Microtrac-Bell), is used. When multiple types of negative electrode active materials are used, it is preferable that the specific surface area of ​​each negative electrode active material be within the above range.

[0034] The content of the negative electrode active material in the composite negative electrode active material is preferably 89.0% by mass or more, more preferably 90.0% by mass or more, even more preferably 91.0% by mass or more, even more preferably 92.0% by mass or more, even more preferably 93.0% by mass or more, and even more preferably 94.0% by mass or more. The content of the negative electrode active material in the composite negative electrode active material is preferably 89.0 to 99.9% by mass, more preferably 90.0 to 99.0% by mass, even more preferably 91.0 to 98.0% by mass, even more preferably 92.0 to 98.0% by mass, even more preferably 92.0 to 97.0% by mass, even more preferably 93.0 to 97.0% by mass, and even more preferably 94.0 to 96.0% by mass.

[0035] <Coating Layer> In the composite negative electrode active material of the present invention, the coating layer is not particularly limited as long as it can suppress the amount of hydrogen gas generated as described above and the resulting composite negative electrode active material can function as a negative electrode active material in a secondary battery. The coating layer is preferably a resin layer. The coating layer preferably contains a polymer containing at least one of a component represented by the following general formula (A-1), a component represented by the following general formula (A-2), and a component represented by the following general formula (A-3) (hereinafter referred to as the "polymer constituting the coating layer"). The polymer constituting the coating layer may be any one of a polymer containing a constituent component represented by general formula (A-1), a polymer containing a constituent component represented by general formula (A-2), and a polymer containing a constituent component represented by general formula (A-3), or a mixture thereof, i.e., a mixture of a polymer containing a constituent component represented by general formula (A-1) and a polymer containing a constituent component represented by general formula (A-2), a mixture of a polymer containing a constituent component represented by general formula (A-1) and a polymer containing a constituent component represented by general formula (A-3), a mixture of a polymer containing a constituent component represented by general formula (A-2) and a polymer containing a constituent component represented by general formula (A-3), or a mixture of a polymer containing a constituent component represented by general formula (A-1), a polymer containing a constituent component represented by general formula (A-2), and a polymer containing a constituent component represented by general formula (A-3). The polymer may also be a copolymer containing a component represented by general formula (A-1) and a component represented by general formula (A-2) as copolymerization components, a copolymer containing a component represented by general formula (A-1) and a component represented by general formula (A-3) as copolymerization components, a copolymer containing a component represented by general formula (A-2) and a component represented by general formula (A-3) as copolymerization components, or a copolymer containing a component represented by general formula (A-1), a component represented by general formula (A-2), and a component represented by general formula (A-3) as copolymerization components. Furthermore, these polymers may be used in combination. In the present invention, the term "polymer containing a component represented by general formula (A-1)" refers to a polymer that does not contain a component represented by general formula (A-2) or a component represented by general formula (A-3).This polymer may be a homopolymer or a copolymer, preferably a homopolymer. In the present invention, when referring to a "polymer containing a constituent component represented by general formula (A-2)," it refers to a polymer that does not contain a constituent component represented by general formula (A-1) or a constituent component represented by general formula (A-3). This polymer may be a homopolymer or a copolymer, preferably a homopolymer. In the present invention, when referring to a "polymer containing a constituent component represented by general formula (A-3)," it refers to a polymer that does not contain a constituent component represented by general formula (A-1) or a constituent component represented by general formula (A-2). This polymer may be a homopolymer or a copolymer, preferably a homopolymer. In the case of a copolymer, the polymerization form may be either random or block. In addition, the polymer that constitutes the coating layer is a so-called chain polymerization polymer in which the constituent component represented by general formula (A-1), the constituent component represented by general formula (A-2), and / or the constituent component represented by general formula (A-3) are incorporated into the main chain of the polymer by *.

[0036] In the composite negative electrode active material of the present invention, a polymer containing at least one of the components represented by general formula (A-1), the component represented by general formula (A-2), and the component represented by general formula (A-3) physically adsorbs or adheres to the surface of the negative electrode active material, or is bonded by chemical adsorption (adsorption by the formation of chemical bonds, adsorption by the exchange of electrons, etc.) to form a coating layer. From the viewpoint of ion permeability and conductivity, it is preferable that the polymer constituting the coating layer is not chemically adsorbed to the surface of the negative electrode active material. As a method for chemically adsorbing a polymer to the surface of the negative electrode active material, for example, there is a method in which the surface of the composite negative electrode active material is treated with a silane compound and then coated with a polymer or the like to chemically bond the reactive groups of the polymer to the silane compound, but such chemical adsorption tends to decrease ion permeability and conductivity. Note that the coating layer may cover a portion or the entire surface of the negative electrode active material, as long as the effects of the present invention are achieved. The polymer constituting the coating layer is described below.

[0037] (Polymer constituting the coating layer)

[0038]

[0039] In the above general formula, R １１ ~R １３ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R １４ and R １５ represents a hydrogen atom, an alkyl group having 1 to 16 carbon atoms, or an aryl group having 6 to 12 carbon atoms. １６ represents an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 12 carbon atoms, -L １ -R １８ or a counter ion. １ represents an alkylene group having 1 to 16 carbon atoms or a polyalkyleneoxy group having 1 to 16 carbon atoms. １ When is an alkylene group, R １８ represents a hydrogen atom, a hydroxy group, an alkoxy group, or a cyano group. １ When R is a polyalkyleneoxy group, １８ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a cyano group. １７ represents a hydrogen atom, a hydroxy group, an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 12 carbon atoms, an acyloxy group having 2 to 16 carbon atoms, an alkoxycarbonyl group having 2 to 16 carbon atoms, or an aryloxycarbonyl group having 7 to 13 carbon atoms. * represents a bonding site for incorporation into the main chain of the polymer.

[0040] R １１ and R １２ is preferably a hydrogen atom. １３ is preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. １４ and R １５ is preferably a hydrogen atom or an alkyl group having 1 to 16 carbon atoms. １４ and R １５ The alkyl group having 1 to 16 carbon atoms that can be taken as R may be linear or branched. １４ and R １５The alkyl group having 1 to 16 carbon atoms that can be taken as R is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, even more preferably an alkyl group having 1 to 6 carbon atoms, particularly preferably an alkyl group having 1 to 4 carbon atoms, and even more preferably an alkyl group having 1 or 2 carbon atoms. １４ and R １５ The alkyl group having 1 to 16 carbon atoms and the aryl group having 6 to 12 carbon atoms that can be taken as R may further have a substituent. Such a substituent is preferably a substituent selected from the group T of substituents described below, and more preferably a hydroxy group. １４ and R １５ The combination of (R １４ , R １５ ) are preferably a combination in which both are hydrogen atoms, both are alkyl groups having 1 to 8 carbon atoms (the number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 or 2), or one is a hydrogen atom and the other is an alkyl group having 1 to 16 carbon atoms (the number of carbon atoms is preferably 1 to 12, more preferably 1 to 10, and even more preferably 1 to 8).

[0041] Specific examples of the constituent component represented by general formula (A-1) include (meth)acrylamide components; monoalkyl(meth)acrylamide components such as a methyl(meth)acrylamide component, an ethyl(meth)acrylamide component, an n-dodecyl(meth)acrylamide component, a 1,1,3,3-tetramethylbutyl(meth)acrylamide component, and a hydroxyethyl(meth)acrylamide component; and dialkyl(meth)acrylamide components such as a dimethyl(meth)acrylamide component and a diethyl(meth)acrylamide component.

[0042] R １６ The alkyl group having 1 to 16 carbon atoms that can be taken as R may be linear or branched. １６ The alkyl group having 1 to 16 carbon atoms that can be taken as R is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, even more preferably an alkyl group having 1 to 6 carbon atoms, and particularly preferably an alkyl group having 1 to 4 carbon atoms.１６ It can be taken as -L １ -R １８ In the group represented by １ The alkylene group having 1 to 16 carbon atoms that can be taken by L may be linear or branched. １ The alkylene group having 1 to 16 carbon atoms that can be taken by R is preferably an alkylene group having 2 to 12 carbon atoms, more preferably an alkylene group having 2 to 8 carbon atoms, and even more preferably an alkylene group having 2 to 4 carbon atoms. １６ It can be taken as -L １ -R １８ In the group represented by １ The alkylene group of the polyalkyleneoxy group having 1 to 16 carbon atoms that can be taken by is preferably an alkylene group having 1 to 12 carbon atoms, more preferably an alkylene group having 2 to 8 carbon atoms, even more preferably an alkylene group having 2 to 4 carbon atoms, and even more preferably an alkylene group having 2 carbon atoms (ethylene group). The number of repeating units of the polyalkyleneoxy group is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 4. １ The polyalkyleneoxy group having 1 to 16 carbon atoms is a group in which the oxygen atom in the polyalkyleneoxy group is R １８ Connect with. L １ When is an alkylene group, R １８ represents a hydrogen atom, a hydroxy group, an alkoxy group, or a cyano group. １ When R is a polyalkyleneoxy group, １８ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a cyano group. １６ When R is the counter ion, the constituent component represented by general formula (A-2) is a carboxylate. Therefore, the counter ion is a monovalent cation excluding a proton, and the carboxylate is preferably an alkali metal salt. １６ is a counter ion, O—R in general formula (A-2) １６ The bond is an ionic bond.

[0043] Specific examples of the constituent component represented by general formula (A-2) include a sodium (meth)acrylate component, a butyl (meth)acrylate component, a hydroxybutyl (meth)acrylate component, a hydroxyethyl (meth)acrylate component, a methoxyethyl (meth)acrylate component, an ethoxydiethylene glycol (meth)acrylate component, a methoxytriethylene glycol component, and a cyanoethyl (meth)acrylate component.

[0044] R １７ The alkyl group having 1 to 16 carbon atoms that can be taken as R may be linear or branched. １７ The alkyl group having 1 to 16 carbon atoms that can be taken as R is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, even more preferably an alkyl group having 1 to 6 carbon atoms, and particularly preferably an alkyl group having 1 to 4 carbon atoms. １７ The acyloxy group having 2 to 16 carbon atoms which can be taken as R may be either an alkylcarbonyloxy group or an arylcarbonyloxy group. The acyloxy group is preferably an acyloxy group having 2 to 12 carbon atoms, more preferably an acyloxy group having 2 to 8 carbon atoms, even more preferably an acyloxy group having 2 to 6 carbon atoms, and particularly preferably an acyloxy group having 2 to 4 carbon atoms. １７ The alkoxycarbonyl group having 2 to 16 carbon atoms that can be taken as R is preferably an alkoxycarbonyl group having 2 to 12 carbon atoms, more preferably an alkoxycarbonyl group having 2 to 8 carbon atoms, even more preferably an alkoxycarbonyl group having 2 to 6 carbon atoms, and even more preferably an alkoxycarbonyl group having 2 to 4 carbon atoms. １７ is preferably a hydrogen atom or a hydroxy group.

[0045] Specific examples of the constituent component represented by general formula (A-3) include a styrene component and a hydroxystyrene component.

[0046] From the viewpoint of more efficiently suppressing hydrogen gas generation, the polymer constituting the coating layer preferably contains at least a constituent component represented by general formula (A-1). In this case, the polymer constituting the coating layer may be a polymer containing a constituent component represented by general formula (A-1), or may be a copolymer containing a constituent component represented by general formula (A-1) and a constituent component represented by general formula (A-2) and / or a constituent component represented by general formula (A-3).

[0047] The polymer containing a constituent component represented by general formula (A-1) is preferably used in combination with a polymer containing a constituent component represented by general formula (A-2) and / or a polymer containing a constituent component represented by general formula (A-3), more preferably used in combination with a polymer having a constituent component represented by general formula (A-2) or a polymer having a constituent component represented by general formula (A-3), and even more preferably used in combination with a polymer having a constituent component represented by general formula (A-3).

[0048] The total content of the components represented by the general formula (A-1), the general formula (A-2), and the general formula (A-3) in the coating layer (when any of the components represented by the general formulas is not included, this refers to the total content of the remaining components) is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may even be 100% by mass. The total content (% by mass) of each of the above components in the coating layer is, for example, when the coating layer is composed of a polymer containing a component represented by the general formula (A-1) and a polymer containing a component represented by the general formula (A-2) (in the case of a mixed polymer), the proportion (% by mass) of the total content of the components represented by the general formula (A-1) and the general formula (A-2) that constitute this mixed polymer in the coating layer. Furthermore, when the coating layer is made of a copolymer containing a constituent component represented by general formula (A-1) and a constituent component represented by general formula (A-2), the total content of the constituent component represented by general formula (A-1) and the constituent component represented by general formula (A-2) that constitute this copolymer is the proportion (mass %) in the coating layer.

[0049] The content of the component represented by general formula (A-1) in the coating layer is, for example, preferably 1% by mass or more, more preferably 10% by mass or more, and from the viewpoint of more efficiently suppressing hydrogen gas generation, preferably 50% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 90% by mass or more.

[0050] When the coating layer contains a component represented by general formula (A-1), a component represented by general formula (A-2) and / or a component represented by general formula (A-3), the ratio of the content of the component represented by general formula (A-1) to the total content of the component represented by general formula (A-2) and the component represented by general formula (A-3) in the coating layer ([content of the component represented by general formula (A-1)] / [content of the component represented by general formula (A-2) + content of the component represented by general formula (A-3)], mass ratio) is not particularly limited, and is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 99 / 1, even more preferably 50 / 50 to 99 / 1, and particularly preferably 75 / 25 to 99 / 1. In addition, "when the coating layer contains a component represented by general formula (A-1), a component represented by general formula (A-2) and / or a component represented by general formula (A-3)" includes, for example, the following embodiments.When the polymer constituting the coating layer comprises a mixed polymer of a polymer containing a constituent component represented by general formula (A-1) and a polymer containing a constituent component represented by general formula (A-2) When the polymer constituting the coating layer comprises a mixed polymer of a polymer containing a constituent component represented by general formula (A-1) and a polymer containing a constituent component represented by general formula (A-3) When the polymer constituting the coating layer comprises a mixed polymer of a polymer containing a constituent component represented by general formula (A-1), a polymer containing a constituent component represented by general formula (A-2), and a polymer containing a constituent component represented by general formula (A-3) When the polymer constituting the coating layer comprises a copolymer containing, as copolymerization components, a constituent component represented by general formula (A-1) and a constituent component represented by general formula (A-2) When the polymer constituting the coating layer comprises a copolymer containing, as copolymerization components, a constituent component represented by general formula (A-1) and a constituent component represented by general formula (A-3) When the polymer constituting the coating layer comprises a copolymer containing, as copolymerization components, a component represented by general formula (A-1), a component represented by general formula (A-2), and a polymer containing a component represented by general formula (A-3) When the polymer constituting the coating layer comprises a mixed polymer of any of the above copolymers and a polymer containing a component represented by general formula (A-1) When the polymer constituting the coating layer comprises a mixed polymer of any of the above copolymers and a polymer containing a component represented by general formula (A-2) When the polymer constituting the coating layer comprises a mixed polymer of any of the above copolymers and a polymer containing a component represented by general formula (A-3) When the polymer constituting the coating layer comprises any of the above mixed polymers and any of the above copolymers.

[0051] The coating layer may contain components other than the component represented by general formula (A-1), the component represented by general formula (A-2), and the component represented by general formula (A-3) (hereinafter referred to as "other components"), as long as the effects of the present invention are not impaired. Examples of other components include an acrylic acid component, a methacrylic acid component, and a polyvinyl alcohol component. The other components may be contained in the coating layer as homopolymers of the other components, or may be contained as copolymers with the component represented by general formula (A-1), the component represented by general formula (A-2), and / or the component represented by general formula (A-3).

[0052] The weight-average molecular weight of the polymer constituting the coating layer is not particularly limited and can be, for example, 4,000 or more. From the viewpoint of more efficiently suppressing hydrogen gas generation, it is preferably 10,000 or more, more preferably 100,000 to 900,000, and even more preferably 200,000 to 500,000. When the polymer constituting the coating layer is a mixture of two or more polymers, it is preferable that the weight-average molecular weight of all polymers satisfy the above-mentioned preferred range. It is preferable that the polymer constituting the coating layer does not have a cross-linked structure, i.e., is a chain polymer. Furthermore, from the viewpoint of more efficiently suppressing hydrogen gas generation, it is preferable that the polymer constituting the coating layer does not have a carbon-carbon double bond in the main chain, i.e., is not rubber. Therefore, it is preferable that the polymer constituting the coating layer does not contain a styrene component-containing rubber such as styrene-butadiene rubber or styrene-isoprene-styrene rubber.

[0053] (Measurement of Weight-Average Molecular Weight) In the present invention, the weight-average molecular weight of a polymer is measured by gel permeation chromatography (GPC). The molecular weight refers to the molecular weight in terms of polyethylene oxide. The measurement method is basically a value measured by the method under Measurement Condition 1 below. However, depending on the type of polymer, an appropriate eluent may be selected and used. (Measurement Condition 1) Measurement equipment: HLC-8220GPC (trade name, manufactured by Tosoh Corporation) Column: TOSOH TSKgel 5000PWXL (trade name, manufactured by Tosoh Corporation), TOSOH TSKgel G4000PWXL (trade name, manufactured by Tosoh Corporation), and TOSOH TSKgel G2500PWXL (trade name, manufactured by Tosoh Corporation) are connected. Carrier: 200 mM sodium nitrate aqueous solution Measurement temperature: 40°C Carrier flow rate: 1.0 ml / min Sample concentration: 0.2 mass% Detector: RI (refractive index) detector If the molecular weight cannot be measured under Measurement Condition 1 above, such as in cases where crosslinking has occurred, measure the molecular weight by static light scattering under Measurement Condition 2 below. (Measurement Condition 2) Measuring instrument: DLS-8000 (trade name, manufactured by Otsuka Electronics Co., Ltd.) Measurement concentration: 0.25, 0.50, 0.75, 1.00 mg / mL Diluent: 0.1 M NaCl aqueous solution Laser wavelength: 633 nm Pinhole: PH1 = Open, PH2 = Slit Measurement angle: 60, 70, 80, 90, 100, 110, 120, 130 degrees Analysis method: Molecular weight is measured from the Zimm square root plot. The dn / dc required for analysis is measured using an Abbe refractometer.

[0054] The polymer constituting the coating layer may further have a substituent in each of the above-mentioned structures or partial structures, and examples of this substituent include substituents selected from the following substituent group T. Furthermore, for each substituent in the polymer constituting the coating layer, the description of the corresponding substituent in the following substituent group T can be applied unless otherwise specified.

[0055] - Substituent group T - alkyl groups (preferably alkyl groups having 1 to 20 carbon atoms, for example, methyl, ethyl, isopropyl, t-butyl, pentyl, heptyl, 1-ethylpentyl, benzyl, 2-ethoxyethyl, 1-carboxymethyl, etc.), alkenyl groups (preferably alkenyl groups having 2 to 20 carbon atoms, for example, vinyl, allyl, oleyl, etc.), alkynyl groups (preferably alkynyl groups having 2 to 20 carbon atoms, for example, ethynyl, butadiynyl, phenylethynyl, etc.), cycloalkyl groups (preferably cycloalkyl groups having 3 to 20 carbon atoms, for example, cycloalkyl groups), cyclopropyl, cyclopentyl, cyclohexyl, 4-methylcyclohexyl, etc.), aryl groups (preferably aryl groups having 6 to 26 carbon atoms, for example, phenyl, 1-naphthyl, 4-methoxyphenyl, 2-chlorophenyl, 3-methylphenyl, etc.), heterocyclic groups (preferably heterocyclic groups having 2 to 20 carbon atoms, more preferably 5- or 6-membered heterocyclic groups having at least one of oxygen atom, sulfur atom, and nitrogen atom as a ring-constituting atom. Heterocyclic groups include aromatic heterocyclic groups and aliphatic heterocyclic groups. For example, tetrahydropyran ring group, tetrahydropyran ring group, a tetrahydrofuran ring group, 2-pyridyl, 4-pyridyl, 2-imidazolyl, 2-benzimidazolyl, 2-thiazolyl, 2-oxazolyl, etc.), an alkoxy group (preferably an alkoxy group having 1 to 20 carbon atoms, for example, methoxy, ethoxy, isopropyloxy, benzyloxy, etc.), an aryloxy group (preferably an aryloxy group having 6 to 26 carbon atoms, for example, phenoxy, 1-naphthyloxy, 3-methylphenoxy, 4-methoxyphenoxy, etc.), a heterocyclic oxy group (a group in which an —O— group is bonded to the above heterocyclic group), an alkoxycarbonyl group, Examples of the alkyl group include an alkoxycarbonyl group (preferably an alkoxycarbonyl group having 2 to 20 carbon atoms, such as ethoxycarbonyl or 2-ethylhexyloxycarbonyl), an aryloxycarbonyl group (preferably an aryloxycarbonyl group having 7 to 26 carbon atoms, such as phenoxycarbonyl, 1-naphthyloxycarbonyl, 3-methylphenoxycarbonyl or 4-methoxyphenoxycarbonyl), an amino group (preferably an amino group having 0 to 20 carbon atoms, including an amino group bonded to a group selected from an alkyl group and an aryl group. For example, amino (-NH２ ), N,N-dimethylamino, N,N-diethylamino, N-ethylamino, anilino, etc.), sulfamoyl group (preferably a sulfamoyl group having 0 to 20 carbon atoms, including a sulfamoyl group to which a group selected from an alkyl group and an aryl group is bonded. For example, sulfamoyl (—SO ２ NH ２), N,N-dimethylsulfamoyl, N-phenylsulfamoyl, etc.), acyl groups (including alkylcarbonyl groups, alkenylcarbonyl groups, alkynylcarbonyl groups, arylcarbonyl groups and heterocyclic carbonyl groups, preferably acyl groups having 1 to 20 carbon atoms, for example, formyl, acetyl, propionyl, butyryl, octanoyl, hexadecanoyl, acryloyl, methacryloyl, crotonoyl, benzoyl, naphthoyl, nicotinoyl, etc.), acyloxy groups (including alkylcarbonyloxy groups, alkenylcarbonyloxy groups, alkynylcarbonyloxy groups, arylcarbonyloxy groups and heterocyclic carbonyloxy groups, preferably 1 to 20 carbon atoms, for example, acyloxy groups, for example, formyloxy, acetyloxy, propionyloxy, butyryloxy, octanoyloxy, hexadecanoyloxy, acryloyloxy, methacryloyloxy, crotonoyloxy, benzoyloxy, naphthoyloxy, nicotinoyloxy, etc.), carbamoyl groups (preferably carbamoyl groups having 1 to 20 carbon atoms, including carbamoyl groups to which a group selected from an alkyl group and an aryl group is bonded; for example, N,N-dimethylcarbamoyl, N-phenylcarbamoyl, etc.), acylamino groups (preferably acylamino groups having 1 to 20 carbon atoms, and preferred examples of the acyl group in the acylamino group include the acyl groups described above.For example, acetylamino, benzoylamino, etc.), alkylthio groups (preferably alkylthio groups having 1 to 20 carbon atoms, for example, methylthio, ethylthio, isopropylthio, benzylthio, etc.), arylthio groups (preferably arylthio groups having 6 to 26 carbon atoms, for example, phenylthio, 1-naphthylthio, 3-methylphenylthio, 4-methoxyphenylthio, etc.), arylsilyl groups (preferably arylsilyl groups having 6 to 42 carbon atoms, for example, triphenylsilyl, etc.), heterocyclic thio groups (the above heterocyclic groups to which an -S- group is bonded), a group having 1 to 20 carbon atoms, such as a methylsulfonyl group, an ethylsulfonyl group, an alkylsulfonyl group (preferably an alkylsulfonyl group having 1 to 20 carbon atoms, such as a methylsulfonyl group, an ethylsulfonyl group, etc.), an arylsulfonyl group (preferably an arylsulfonyl group having 6 to 22 carbon atoms, such as a benzenesulfonyl group, etc.), an alkylsilyl group (preferably an alkylsilyl group having 1 to 20 carbon atoms, such as a monomethylsilyl group, a dimethylsilyl group, a trimethylsilyl group, a triethylsilyl group, etc.), a phosphite group (preferably a phosphite group having 0 to 20 carbon atoms, such as -OP(=O)(-OH)(R. Ｐ )), a hypophosphite group (preferably a hypophosphite group having 0 to 20 carbon atoms, for example, —OP(═O)(R Ｐ ) ２ ), a phosphoryl group (preferably a phosphoryl group having 0 to 20 carbon atoms, for example, —P(═O)(R Ｐ ) ２ ), a phosphinyl group (preferably a phosphinyl group having 0 to 20 carbon atoms, for example, —P(R Ｐ ) ２ ), a sulfo group, a phosphate group, a phosphonate group, a carboxy group, a hydroxy group, a sulfanyl group, a cyano group, and a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom). Ｐ is a hydrogen atom or a substituent (preferably a group selected from Substituent Group T). Each of the groups listed in Substituent Group T may further have, as a substituent, any of the groups listed in Substituent Group T above.

[0056] The polymer constituting the coating layer can be obtained by a conventional polymer synthesis method. In synthesizing the polymer constituting the coating layer, the method and conditions for chain polymerization etc. are not particularly limited, and conventional methods and conditions can be appropriately applied depending on the purpose.

[0057] In the present invention, the polymer constituting the coating layer may be used alone or in combination of two or more.

[0058] The content of the coating layer in the composite negative electrode active material is preferably 11.0% by mass or less, more preferably 10.0% by mass or less, even more preferably 9.0% by mass or less, even more preferably 8.0% by mass or less, even more preferably 7.0% by mass or less, and even more preferably 6.0% by mass or less. The lower limit is not particularly limited, but a practical content is 0.1% by mass or more. Therefore, the content of the coating layer is preferably 0.1 to 11.0% by mass, more preferably 1.0 to 10.0% by mass, even more preferably 2.0 to 9.0% by mass, even more preferably 2.0 to 8.0% by mass, even more preferably 3.0 to 8.0% by mass, even more preferably 3.0 to 7.0% by mass, and even more preferably 4.0 to 6.0% by mass. The content of the coating layer in the composite negative electrode active material can be measured by the method described in the Examples below. Note that when two or more polymers are used in combination, the "content of the coating layer in the composite negative electrode active material" refers to the total amount of two or more polymers.

[0059] (Method for Producing Composite Negative Electrode Active Material) The composite negative electrode active material of the present invention can be produced by coating at least a portion of the surface of the negative electrode active material with a polymer that constitutes a coating layer. For example, the negative electrode active material and the polymer that constitutes the coating layer are mixed in a solvent, and the polymer that constitutes the coating layer is physically or chemically adsorbed onto the surface of the negative electrode active material. The resulting negative electrode active material with the polymer that constitutes the coating layer adsorbed thereon (hereinafter referred to as the "composite negative electrode active material precursor") is then separated by filtration or other means and dried, thereby producing the composite negative electrode active material of the present invention. Examples of methods for mixing the negative electrode active material and the polymer that constitutes the coating layer in a solvent include preparing a solution in which the polymer that constitutes the coating layer is dissolved in a solvent, and then mixing the negative electrode active material in the resulting solution. Examples of solvents include water, tetrahydrofuran, and mixtures thereof. Mixing the negative electrode active material and the polymer that constitutes the coating layer in the solvent is preferably performed by mixing and stirring at room temperature (25°C) to 40°C for 0.5 to 3 hours. It is also preferable to wash the composite negative electrode active material precursor after separation and before the drying step. Examples of the washing solvent include the solvents described above. The composite negative electrode active material precursor is preferably dried, for example, under reduced pressure at room temperature (25°C) to 40°C for 0.5 to 1 day.

[0060] In addition to the above, the composite negative electrode active material of the present invention can also be produced by, for example, mixing the negative electrode active material and the polymer that constitutes the coating layer in a solvent, physically or chemically adsorbing the polymer that constitutes the coating layer on the surface of the negative electrode active material, and then granulating the resulting dispersion by spray drying. The content of the coating layer can be controlled by the number of spray drying treatments. The solvents described above can be used as the solvent. The negative electrode active material and the polymer that constitutes the coating layer can be mixed in the same manner as described above.

[0061] When preparing a composite negative electrode active material in which two or more polymers constitute the coating layer, it is preferable to perform step I, which involves mixing the negative electrode active material and the polymers that constitute the coating layer in a solvent, separating the composite negative electrode active material precursor by filtration or the like, and drying, for each type of polymer that constitutes the coating layer. For example, when preparing a composite negative electrode active material in which the polymers that constitute the coating layer are two types, one polymer containing a component represented by general formula (A-1) and one polymer containing a component represented by general formula (A-2), first, step I is performed using a polymer containing a component represented by general formula (A-1), to obtain a composite negative electrode active material A-1 having a coating layer composed of a polymer containing a component represented by general formula (A-1). Thereafter, using a polymer containing a component represented by the general formula (A-2), the composite negative electrode active material A-1 obtained in the above step I is used instead of the negative electrode active material, and by performing the above step I, a composite negative electrode active material having a coating layer composed of a polymer containing a component represented by the general formula (A-1) and a polymer containing a component represented by the general formula (A-2) can be prepared. Note that when two or more polymers constitute the coating layer, there are no particular restrictions on the type of polymer used to coat the negative electrode active material by the above step I. For example, after performing step I using a polymer containing a component represented by the general formula (A-1), step I using a polymer containing a component represented by the general formula (A-2) may be performed, or after performing step I using a polymer containing a component represented by the general formula (A-2), step I using a polymer containing a component represented by the general formula (A-1) may be performed. In the present invention, after performing step I using a polymer containing a component represented by the general formula (A-1), it is preferable to perform step I using a polymer containing a component represented by the general formula (A-2) or a polymer containing a component represented by the general formula (A-3). Similarly, when preparing a composite negative electrode active material using a spray-drying method, the above-mentioned process of mixing the negative electrode active material and the polymer constituting the coating layer in a solvent and granulating by spray-drying can be performed for each type of polymer constituting the coating layer. Similarly, there is no limitation on the type of polymer used to coat the negative electrode active material.

[0062] [Slurry for Secondary Battery Negative Electrode] The slurry for a secondary battery negative electrode of the present invention (hereinafter also simply referred to as "negative electrode slurry of the present invention") is a slurry (liquid composition) containing the composite negative electrode active material of the present invention and a dispersion medium. The content of the composite negative electrode active material in the negative electrode slurry of the present invention is not particularly limited, and is preferably 10 to 99 mass %, more preferably 30 to 98 mass %, even more preferably 45 to 97 mass %, and particularly preferably 55 to 95 mass %, of the total solid content of the negative electrode slurry. The negative electrode slurry of the present invention can be preferably used as a molding material for a negative electrode sheet for a secondary battery or a negative electrode active material layer of a secondary battery.

[0063] <Dispersion Medium> The dispersion medium contained in the negative electrode slurry of the present invention may be any medium capable of dispersing or dissolving the solid content, and preferably contains water. The negative electrode slurry of the present invention may contain a liquid medium other than water. Examples of liquid medium other than water include organic solvents that are miscible with water without phase separation when mixed with water (hereinafter referred to as water-soluble organic solvents), and preferred examples include N-methylpyrrolidone, methanol, ethanol, acetone, and tetrahydrofuran. The above-mentioned dispersion medium may be contained alone or in combination with two or more types. The content of the dispersion medium in the negative electrode slurry of the present invention is not particularly limited and can be set appropriately. For example, the content of the dispersion medium in the negative electrode slurry is preferably 20 to 99% by mass, more preferably 25 to 70% by mass, and particularly preferably 30 to 60% by mass.

[0064] <Conductive Aid> The negative electrode slurry of the present invention preferably contains a conductive aid. In particular, when a silicon-based active material is used as the negative electrode active material constituting the composite negative electrode active material, it is preferable to use a conductive aid in combination. The conductive aid is not particularly limited, and a commonly known conductive aid can be used. For example, it may be an electron conductive material such as carbon blacks such as acetylene black, ketjen black, 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 or nickel, or conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, or polyphenylene derivatives. In the present invention, when an active material and a conductive aid are used in combination, the conductive aid is one of the above conductive aids that does not undergo Li insertion and release during battery charging and discharging and does not function as an active material. Therefore, among the conductive additives, those that can function as an active material in the active material layer when the battery is charged and discharged are classified as active materials rather than as conductive additives. Whether or not a conductive additive functions as an active material when the battery is charged and discharged is not uniquely determined, but is determined by the combination with the active material.

[0065] The content of the conductive additive in the negative electrode slurry of the present invention is preferably 0.5 to 60 mass %, more preferably 1.0 to 50 mass %, still more preferably 1.5 to 40 mass %, and particularly preferably 2.5 to 35 mass %, based on the total solid content.

[0066] The shape of the conductive additive is not particularly limited, but particulate is preferred. The average particle size (volume-based median diameter D50) of the conductive additive is not particularly limited, and is preferably 0.01 to 50 μm, and more preferably 0.02 to 10.0 μm. When a commercially available conductive additive is used, the average particle size of the conductive additive is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is not available or when a synthetic conductive additive is used, the average particle size of the conductive additive may be the value obtained by applying the above-mentioned method for measuring the average particle size of the negative electrode active material (volume-based median diameter D50 in water).

[0067] The specific surface area (BET specific surface area) of the conductive additive is 10 to 100 m ２ / g is preferred. When a commercially available conductive additive is used, the value listed in the manufacturer's catalog is used as the specific surface area of ​​the conductive additive. When the manufacturer's specific surface area information is not available or when a synthetic conductive additive is used, the value obtained by applying the above-mentioned method for measuring the specific surface area (BET specific surface area) of the negative electrode active material (BET method using nitrogen adsorption) may be used.

[0068] The conductive additives may be used alone or in combination of two or more.

[0069] <Binder> The negative electrode slurry of the present invention may contain a binder. The binder may be contained in any form, for example, in the negative electrode slurry, negative electrode sheet, or secondary battery, and may be particulate or amorphous. The binder is preferably contained in the form of polymer particles from the viewpoint of further improving cycle characteristics. More preferably, the binder is contained in the form of resin particles containing a macromonomer component. When the binder used in the present invention is polymer particles, the polymer forming the polymer particles is not particularly limited. The "particulate" may be flat, amorphous, etc., and is preferably spherical or granular.

[0070] The average particle size of the polymer particles (volume-based median diameter in water) is not particularly limited, and is preferably 50 to 300 nm, more preferably 50 to 250 nm, and even more preferably 50 to 200 nm. When commercially available polymer particles are used, the average particle size of the polymer particles is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is not available or when synthetic polymer particles are used, the average particle size of the polymer particles is the particle size (volume-based median diameter in water) at which the cumulative volume calculated from the small diameter side in the particle size distribution measured by laser diffraction / scattering method becomes 50%.

[0071] The polymer particles may be either step-polymerized polymer particles or chain-polymerized polymer particles, with chain-polymerized polymer particles being preferred. The chain-polymerized polymer particles may be either a homopolymer or a copolymer. The copolymer may be polymerized in either a random or block form. Examples of components of the polymer particles (chain-polymerized polymers) include a conjugated diene component, an aromatic vinyl monomer component, an ethylenically unsaturated carboxylic acid component, a cyano group-containing ethylenic monomer component, an ethylenically unsaturated carboxylic acid ester component, and a vinyl fluoride monomer component. Preferably, the polymer particles contain at least one of a conjugated diene component, an ethylenically unsaturated carboxylic acid component, a cyano group-containing ethylenic monomer component, and an aromatic vinyl monomer component. Among the above components, the polymer particles preferably contain a conjugated diene component and an aromatic vinyl monomer component. In the above, the term "aromatic vinyl monomer component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one or two, more preferably one) and an aryl group (preferably one), the term "ethylenically unsaturated carboxylic acid component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one) and a carboxy group (preferably one or two), the term "cyano group-containing ethylenic monomer component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one) and a cyano group (preferably one or two, more preferably one), the term "ethylenically unsaturated carboxylic acid ester component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one) and a carboxylic acid ester moiety (esterified carboxy group) (preferably one), and the term "vinyl fluoride monomer component" refers to a component derived from ethylene having one to four (preferably two) fluorine atoms. Note that the term "carbon-carbon double bond" does not include the carbon-carbon double bond of an aromatic ring.

[0072] Conjugated dienes from which the conjugated diene component is derived include, for example, aliphatic conjugated dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene. Aromatic vinyl monomers from which the aromatic vinyl monomer component is derived include, for example, styrene, α-methylstyrene, 4-tert-butylstyrene, 4-tert-butoxystyrene, vinyltoluene (3-vinyltoluene, 4-vinyltoluene), and divinylbenzene (m-divinylbenzene, p-divinylbenzene). Ethylenically unsaturated carboxylic acids from which the ethylenically unsaturated carboxylic acid component is derived include, for example, (meth)acrylic acid, maleic acid, itaconic acid, and fumaric acid. Cyano-group-containing ethylenic monomers from which the cyano-group-containing ethylenic monomer component is derived include, for example, (meth)acrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and vinylidene cyanide. Examples of the ethylenically unsaturated carboxylic acid ester from which the ethylenically unsaturated carboxylic acid ester component is derived include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, ethylene glycol di(meth)acrylate, and 2,2,2-trifluoroethyl (meth)acrylate. Examples of the fluorinated vinyl monomer from which the fluorinated vinyl monomer component is derived include vinylidene fluoride.

[0073] The polymer particles used in the present invention can be obtained by a conventional polymer synthesis method. In the synthesis of the polymer particles used in the present invention, the method and conditions for chain polymerization and the like are not particularly limited, and conventional methods and conditions can be appropriately applied depending on the purpose. In addition, the polymer particles may be particles obtained by subjecting the above-mentioned step-polymerized polymer particles and chain-polymerized polymer particles to a modification treatment such as carboxy modification. The method and conditions for the modification treatment are not particularly limited, and the modification treatment can be carried out by a conventional method.

[0074] Specific examples of polymer particles include styrene / butadiene copolymers, acrylic polymers, and poly(vinylidene fluoride), with styrene / butadiene copolymers being preferred. The styrene / butadiene copolymer refers to a copolymer containing the aromatic vinyl monomer component and the conjugated diene component, and may be a modified copolymer such as a carboxyl-modified copolymer. The acrylic polymer refers to a polymer containing the ethylenically unsaturated carboxylic acid component and / or the ethylenically unsaturated carboxylic acid ester component. Examples of styrene / butadiene copolymers include those described in WO 2021 / 172208, WO 2021 / 153516, WO 2021 / 065457, WO 2019 / 188722, WO 2018 / 173717, WO 2017 / 056466, WO 2014 / 141721, JP 2014-203771 A, WO 2013 / 141140, JP 2014-116263 A, JP 2003-151560 A, JP 2000-123838 A, and JP 2000-100436, WO 1999 / 048953, WO 2020 / 226035, WO 2014 / 057749, JP 2019-179631, JP 2017-126456, JP 2017-084621, JP 2015-191876, JP 2012-169112, JP 2012-094506, JP 2011-108373, JP 2010-205722 or JP 2010-140684 It is possible to use those described in.Examples of acrylic polymers include those described in JP 2020-123590 A, WO 2018 / 173717 A, JP 2016-024985 A, WO 2015 / 107896 A, WO 2014 / 148064 A, WO 2014 / 073647 A, JP 2014-203805 A, JP 2014-116265 A, JP 2015-106488 A, and WO 2018 / 194101 A. No. 2015 / 012366, WO 2012 / 049971, JP 2012-212537, JP 2011-171181, JP 2010-245035, JP 2010-192434, JP 2010-182439, JP 2010-146870, JP 2010-146869 or JP 2002-319403 can be used. Examples of poly(vinylidene fluoride) that can be used include those described in JP 2014-229406 A, WO 2013 / 005796, WO 2011 / 040474, WO 2009 / 123168, WO 2014 / 057749, and WO 2012 / 117910. Other examples include those described in paragraphs 0120 to 0123 of WO 2013 / 005796.

[0075] In the present invention, the polymer particles may be used alone or in combination of two or more kinds.

[0076] When the negative electrode slurry of the present invention contains a binder, the content of the binder in the negative electrode slurry is preferably 0.5 to 50 mass %, more preferably 1.0 to 40 mass %, still more preferably 1.5 to 30 mass %, and particularly preferably 2.5 to 25 mass %, based on the total solid content.

[0077] <Water-Soluble Polymer> The negative electrode slurry of the present invention preferably contains a water-soluble polymer. A wide variety of water-soluble polymers can be used as thickeners for negative electrode slurries (slurries) for secondary batteries. Examples of the thickener include polysaccharides that function as thickeners, and these may be either natural or synthetic polysaccharides. Examples include the following: Examples of cellulose compounds that serve as thickening polysaccharides include methyl cellulose, ethyl cellulose, benzyl cellulose, triethyl cellulose, cyanoethyl cellulose, nitrocellulose, hydroxymethyl cellulose, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), hydroxybutyl methyl cellulose, carboxymethyl cellulose (CMC), aminomethyl hydroxypropyl cellulose, aminoethyl hydroxypropyl cellulose, cellulose nanofibers (CNF), and cellulose nanocrystals (CNC). The cellulose compound may also be in the form of a salt, such as an ammonium salt, sodium salt, or lithium salt. The degree of ether substitution in the cellulose compound is typically 0.5 to 1.5, preferably 0.5 to 1.0. The degree of ether substitution refers to the average number of hydroxyl groups bonded to an ether group per glucose ring unit of cellulose, and can be measured by titration or the like. Examples of natural polysaccharides other than the above-mentioned cellulose compounds include carrageenan, xanthan gum, guar gum, tamarind gum (tamarind seed gum), diutan gum, welan gum, gellan gum, locust bean gum, and tara gum. Among these, the water-soluble polymer preferably contains at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carrageenan, and xanthan gum, and more preferably contains at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan gum from the viewpoint of further improving cycle characteristics.

[0078] The weight average molecular weight (Mw) of the water-soluble polymer used in the present invention is not particularly limited, and is, for example, preferably 100,000 to 500,000, more preferably 150,000 to 500,000, and even more preferably 200,000 to 500,000.

[0079] (Measurement of Weight-Average Molecular Weight) In the present invention, the weight-average molecular weight of the water-soluble polymer is a value measured by the method described above for the polymer constituting the coating layer.

[0080] In the present invention, the water-soluble polymer may be used alone or in combination of two or more. The content of the water-soluble polymer in the negative electrode slurry of the present invention is preferably 0.5 to 60 mass %, more preferably 1.0 to 50 mass %, still more preferably 1.5 to 40 mass %, and particularly preferably 2.5 to 35 mass %, based on the total solid content.

[0081] (Other Additives) The negative electrode slurry of the present invention may contain, as desired, other components in addition to the above components, such as a lithium salt, an ionic liquid, a thickener, an antifoaming agent, a leveling agent, a dehydrating agent, an antioxidant, etc. For information on the active material, conductive aid, and other additives, see, for example, International Publication No. 2019 / 203334 and JP-A-2015-46389.

[0082] [Method for preparing a negative electrode slurry] The negative electrode slurry of the present invention can be prepared as a mixture, preferably as a slurry, by mixing the composite negative electrode active material, the dispersion medium, and optionally any other components, for example, using various commonly used mixers. In the case of the negative electrode slurry of the present invention, in addition to the above, at least one of a conductive additive, a binder, and a water-soluble polymer is mixed, and optionally other additives are also mixed. The mixing method is not particularly limited, and the components may be mixed all at once or sequentially. The mixing environment is not particularly limited, and examples include dry air or an inert gas.

[0083] [Negative Electrode Sheet] The negative electrode sheet of the present invention has a negative electrode active material layer formed using the negative electrode slurry of the present invention. The negative electrode sheet of the present invention may be a negative electrode sheet having a negative electrode active material layer formed using the negative electrode slurry of the present invention. The negative electrode sheet may be a sheet in which the negative electrode active material layer is formed on a substrate such as a current collector, or a sheet formed solely of the negative electrode active material layer without a substrate. This negative electrode sheet is typically a sheet configured by laminating the negative electrode active material layer on a current collector. The negative electrode sheet of the present invention may also have other layers, such as a protective layer or coating layer such as a release sheet. The negative electrode sheet of the present invention can be suitably used as a material for forming the negative electrode active material layer of a secondary battery, or as a laminate (negative electrode layer) of a negative electrode current collector and a negative electrode active material layer.

[0084] When the negative electrode sheet of the present invention has a current collector, the current collector constituting the negative electrode sheet of the present invention is an electron carrier and is usually in the form of a film sheet. The current collector can be appropriately selected depending on the active material. Examples of materials constituting the negative electrode current collector include aluminum, copper, copper alloy, stainless steel, nickel, and titanium, with aluminum, copper, copper alloy, or stainless steel being preferred. Examples of negative electrode current collectors include those in which the surface of aluminum, copper, copper alloy, or stainless steel is treated with carbon, nickel, titanium, or silver to form a coating layer (thin film).

[0085] The thickness of the negative electrode active material layer constituting the negative electrode sheet of the present invention is not particularly limited and may be, for example, 5 to 500 μm, preferably 20 to 200 μm. The thickness of the negative electrode current collector constituting the negative electrode sheet of the present invention is also not particularly limited and may be, for example, 10 to 100 μm, preferably 10 to 50 μm.

[0086] In the negative electrode sheet of the present invention, in addition to the negative electrode active material layer formed using the composite negative electrode active material of the present invention, a negative electrode active material layer formed by charging a battery can be used in combination. When the negative electrode active material layer is formed by charging a battery, in addition to the composite negative electrode active material of the present invention, ions of a metal belonging to Group 1 or Group 2 of the periodic table that are generated in a secondary battery can be used. The negative electrode active material layer can be formed by bonding these ions with electrons and depositing them as a metal.

[0087] [Method for manufacturing a negative electrode sheet and method for manufacturing a secondary battery] The negative electrode sheet of the present invention can be obtained by forming a negative electrode active material layer using the negative electrode slurry of the present invention. For example, the negative electrode sheet of the present invention can be manufactured by forming a film using the negative electrode slurry of the present invention. Specifically, a current collector or the like is used as a substrate, and the negative electrode slurry of the present invention is applied thereon (optionally via other layers) to form a coating film, which is then dried to obtain a negative electrode sheet having a negative electrode active material layer (coated and dried layer) on the substrate. Furthermore, the secondary battery of the present invention can be obtained by incorporating the negative electrode active material layer of the negative electrode sheet obtained by the above-described method for manufacturing a negative electrode sheet as the negative electrode active material layer of the secondary battery.

[0088] [Secondary Battery] The secondary battery of the present invention includes a negative electrode active material layer formed using the negative electrode slurry of the present invention.

[0089] The secondary battery of the present invention will be described taking a non-aqueous electrolyte secondary battery as an example, but the secondary battery of the present invention is not limited to a non-aqueous electrolyte secondary battery and broadly includes secondary batteries in general.

[0090] 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 and negative electrodes. 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 negative electrode slurry of the present invention. The nonaqueous electrolyte secondary battery of the present invention also includes a nonaqueous electrolyte secondary battery having only a negative electrode active material layer, the negative electrode active material layer being formed using the negative electrode slurry of the present invention. The nonaqueous electrolyte secondary battery of the present invention functions as a secondary battery upon charge and discharge by filling the space between the positive electrode and the negative electrode with a nonaqueous electrolyte.

[0091] FIG. 1 is a cross-sectional view showing a schematic representation of the laminated structure of a typical nonaqueous electrolyte secondary battery 10, including the operating parts when the battery is in operation. The nonaqueous electrolyte secondary battery 10 has a laminated structure including, as viewed from the negative electrode side, 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, in this order. The space between the negative electrode active material layer 2 and the positive electrode active material layer 4 is filled with a nonaqueous electrolyte (not shown), and they are separated by the separator 3. The separator 3 has pores, and during normal battery use, it functions as a positive / negative electrode separator that insulates the positive and negative electrodes, allowing the electrolyte and ions to pass through the pores. With this structure, for example, in the case of a lithium-ion secondary battery, electrons (e － ) is supplied, and at the same time, lithium ions (Li ＋ ) moves and accumulates in the negative electrode. On the other hand, during discharge, the lithium ions (Li ＋ ) is 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 is turned on by discharge. 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.

[0092] In the secondary battery of the present invention, the positive electrode is not particularly limited, and a positive electrode used in a typical secondary battery can be appropriately applied. For example, it is preferable that the positive electrode has a configuration including a positive electrode current collector and a positive electrode active material layer in contact with the positive electrode current collector. Regarding the positive electrode active material layer, unless otherwise specified, the above descriptions of the negative electrode active material layer can be applied by replacing the negative electrode, composite negative electrode active material, negative electrode slurry, and negative electrode active material layer with positive electrode, positive electrode active material, positive electrode slurry, and positive electrode active material layer, respectively. Furthermore, as for other components that may be contained in the positive electrode slurry, the descriptions of the dispersion medium, conductive additive, binder, and other additives in the above-mentioned negative electrode slurry can be applied.

[0093] (Positive electrode active material) The positive electrode active material may be any active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table, and among these, those capable of reversibly inserting and releasing lithium ions are preferred. The material is not particularly limited as long as it has the above-mentioned properties, and examples thereof include transition metal oxides, organic substances, compounds containing an element such as sulfur that can be composited with Li, and composites of sulfur and metals. Among these, it is preferred to use a lithium-containing transition metal oxide as the positive electrode active material, and it is also preferred to use a transition metal element M ａ It is more preferable that the lithium-containing transition metal oxide contains at least one element selected from Co, Ni, Fe, Mn, Cu, and V. ｂ (metal elements of Group 1 (Ia) of the periodic table other than lithium, elements of Group 2 (IIa), elements such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, or B) may be mixed. ｂ The amount of the transition metal element M ａ The amount of the transition metal element M is preferably 0 to 30 mol % relative to 100 mol %. ａ The molar ratio of Li to ａ Specific examples of the lithium-containing transition metal oxide include (MA) a lithium-containing transition metal oxide having a layered rock salt structure, (MB) a lithium-containing transition metal oxide having a spinel structure, (MC) a lithium-containing transition metal phosphate compound, (MD) a lithium-containing transition metal halide phosphate compound, and (ME) a ​​lithium-containing transition metal silicate compound.

[0094] (MA) Specific examples of lithium-containing transition metal oxides having a layered rock salt structure include LiCoO ２ (Lithium cobalt oxide [LCO]), LiNi ２ O ２ (lithium nickel oxide), LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ (nickel cobalt lithium aluminum oxide [NCA]), LiNi １／３ Co １／３ Mn １／３ O２ (Lithium nickel manganese cobalt oxide [NMC]) and LiNi ０．５ Mn ０．５ O ２ (Lithium manganese nickel oxide). (MB) Specific examples of lithium-containing transition metal oxides having a spinel structure include LiMn ２ O ４ (LMO), LiCoMnO ４ , Li ２ FeMn ３ O ８ , Li ２ CuMn ３ O ８ , Li ２ CrMn ３ O ８ and Li ２ NiMn ３ O ８ Examples of the (MC) lithium-containing transition metal phosphate compound include LiFePO ４ and Li ３ Fe ２ (P.O. ４ ) ３ Olivine-type iron phosphate salts such as LiFeP ２ O ７ Iron pyrophosphate salts such as LiCoPO ４ Cobalt phosphate salts such as Li ３ V ２ (P.O. ４ ) ３ (MD) Examples of lithium-containing transition metal halide phosphate compounds include, for example, Li ２ FePO ４ Fluorophosphate iron salts such as F, Li ２ MnPO ４ Fluorophosphate manganese salts such as F and Li ２ CoPO ４ Examples of the (ME) lithium-containing transition metal silicate compound include cobalt fluorophosphate salts such as Li ２ FeSiO ４ , Li ２ MnSiO ４ and Li ２ CoSiO４ In the present invention, lithium-containing transition metal oxides having a layered rock salt structure (MA) are preferred, and LCO or NMC are more preferred.

[0095] The shape of the positive electrode active material is not particularly limited, but particulate is preferred. The average particle size (volume-based median diameter D50) of the positive electrode active material is not particularly limited. For example, it can be 0.1 to 50 μm. The positive electrode active material can be prepared to a predetermined particle size by a conventional method using a grinder or classifier. The above-mentioned method for preparing a negative electrode active material to a predetermined particle size can also be applied. The positive electrode active material obtained by the calcination method may be used after washing with water, an acidic aqueous solution, an alkaline aqueous solution, an organic solvent, or the like. When a commercially available positive electrode active material is used, the average particle size of the positive electrode active material is the value listed in the manufacturer's catalog. When the manufacturer's average particle size information is unavailable or when a synthesized positive electrode active material is used, the value measured and calculated using the method described above for negative electrode active materials is used.

[0096] The chemical formula of the compound obtained by the above calcination method can be measured by inductively coupled plasma (ICP) emission spectroscopy, or simply calculated from the difference in mass of the powder before and after calcination.

[0097] The surface of the positive electrode active material may be coated with an oxide such as another metal oxide, a carbonaceous material, etc. As the surface coating material, the oxide such as another metal oxide, a carbonaceous material, etc. described as the surface coating material that can be used to coat the surface of the negative electrode active material described above can be used.

[0098] The surface of the positive electrode active material may be treated with sulfur or phosphorus. Furthermore, the particle surfaces of the positive electrode active material may be treated with actinic rays or an active gas (plasma, etc.) before or after the surface coating.

[0099] The positive electrode active material may be used alone or in combination of two or more. When forming a positive electrode active material layer, the positive electrode active material layer has a unit area (cm ２ The mass (mg) (basis weight) of the positive electrode active material per unit area is not particularly limited and can be determined appropriately depending on the designed battery capacity.

[0100] The content of the positive electrode active material in the positive electrode slurry is not particularly limited, and is preferably 10 to 99 mass %, more preferably 30 to 98 mass %, still more preferably 50 to 97 mass %, and particularly preferably 55 to 95 mass %, based on the total solid content.

[0101] Examples of materials for the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, and titanium, and aluminum or aluminum alloys are preferred. Examples of the positive electrode current collector include those in which the surface of aluminum or stainless steel is treated with carbon, nickel, titanium, or silver to form a coating layer (thin film).

[0102] The thickness of the positive electrode active material layer constituting the positive electrode sheet is not particularly limited and may be, for example, 5 to 500 μm, preferably 20 to 200 μm. The thickness of the positive electrode current collector constituting the positive electrode sheet is not particularly limited and may be, for example, 10 to 100 μm, preferably 10 to 50 μm.

[0103] The secondary battery of the present invention is not particularly limited in terms of the electrolyte (aqueous electrolyte, non-aqueous electrolyte) or solid electrolyte material, separator, or other components, except that it comprises a negative electrode active material layer formed using the negative electrode slurry of the present invention. These materials and components can be appropriately applied to those used in conventional secondary batteries. Furthermore, for the method of producing the secondary battery of the present invention, conventional methods can be appropriately adopted, except for forming the negative electrode active material layer using the negative electrode slurry of the present invention. For details of the components and production methods typically used in these secondary batteries, see, for example, JP 2016-201308 A, JP 2005-108835 A, JP 2012-185938 A, and WO 2020 / 067106 A. A preferred embodiment of the non-aqueous electrolyte will now be described in more detail.

[0104] (Electrolyte) The electrolyte used in the non-aqueous electrolyte is preferably a salt of a metal ion belonging to Group 1 or Group 2 of the periodic table. The salt of the metal ion used is appropriately selected depending on the intended use of the non-aqueous electrolyte. Examples include lithium salt, potassium salt, sodium salt, calcium salt, magnesium salt, etc., and when used in a secondary battery, etc., lithium salt is preferred from the viewpoint of output. When the non-aqueous electrolyte is used as an electrolyte for a lithium ion secondary battery, lithium salt may be selected as the salt of the metal ion. As the lithium salt, lithium salts commonly used in electrolytes for lithium ion secondary batteries are preferred, and examples thereof include the following lithium salts.

[0105] (L-1) Inorganic lithium salt: LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF ６ Inorganic fluoride salts such as LiClO ４ , LiBrO ４ , LiIO ４ perhalogenates such as LiAlCl ４ Inorganic chloride salts, etc.

[0106] (L-2) Fluorine-containing organic lithium salt: LiCF ３ SO ３ perfluoroalkanesulfonates such as LiN(CF ３ SO ２ ) ２ , LiN(CF ３ CF ２ SO ２ ) ２ , LiN(FSO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ) or perfluoroalkanesulfonylimide salts, LiC(CF ３ SO ２ ) ３ perfluoroalkanesulfonylmethide salts such as Li[PF ５ (CF ２ CF ２ CF ３) )], Li[PF ４ (CF ２ CF ２ CF ３ ) ２ ], Li[PF ３ (CF ２ CF ２ CF ３ ) ３ ], Li[PF ５ (CF ２ CF ２ CF ２ CF ３ ) )], Li[PF ４ (CF ２ CF ２ CF ２ CF ３ ) ２ ], Li[PF ３ (CF ２ CF ２ CF ２ CF ３ ) ３ perfluoroalkyl fluorophosphates such as

[0107] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0108] Among these, LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF ６ , LiClO ４ , Li(R ｆ１ SO ３ ), LiN(R ｆ１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) is preferred, and LiPF ６ , LiBF ４ , LiN(R ｆ１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１ SO２ ) (R ｆ２ SO ２ ) is more preferred. ｆ１ and R ｆ２ Each of the groups represents a perfluoroalkyl group, and the carbon number thereof is preferably 1 to 6. The electrolytes used in the nonaqueous electrolytic solution may be used alone or in any combination of two or more.

[0109] The salt concentration of the electrolyte (preferably ions of a metal belonging to Group 1 or Group 2 of the periodic table or a metal salt thereof) in the non-aqueous electrolyte solution is appropriately selected depending on the intended use of the non-aqueous electrolyte solution, but is generally 10 to 50 mass % of the total mass of the non-aqueous electrolyte solution, and preferably 15 to 30 mass %. The molar concentration is preferably 0.5 to 1.5 M. When evaluating the ion concentration, it may be calculated in terms of the metal salt that is suitably applied.

[0110] (Non-aqueous Solvent) The non-aqueous electrolyte solution contains a non-aqueous solvent. The non-aqueous solvent is preferably an aprotic organic solvent, and more preferably an aprotic organic solvent having 2 to 10 carbon atoms. Examples of such non-aqueous solvents include linear or cyclic carbonate compounds, lactone compounds, linear or cyclic ether compounds, ester compounds, nitrile compounds, amide compounds, oxazolidinone compounds, nitro compounds, linear or cyclic sulfone or sulfoxide compounds, and phosphate ester compounds. Compounds having an ether bond, carbonyl bond, ester bond, or carbonate bond are preferred. These compounds may have a substituent, and examples of the substituent may include, for example, a substituent selected from the above-mentioned substituent group T.

[0111] Examples of non-aqueous solvents include ethylene carbonate, fluorinated ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, methyl acetate, Examples of suitable solvents include methyl acrylate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, etc. These may be used alone or in combination of two or more. Among these, at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone is preferred, and a combination of a high-viscosity (high-dielectric constant) solvent (e.g., relative dielectric constant ε≧30) such as ethylene carbonate or propylene carbonate with a low-viscosity solvent (e.g., viscosity≦1 mPa s) such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate is more preferred. By using a mixed solvent with such a combination, the dissociation of the electrolyte salt and the mobility of ions are improved. However, the nonaqueous solvent used in the present invention is not limited to these.

[0112] The secondary battery of the present invention can be installed in electronic devices such as notebook computers, pen-input PCs, mobile PCs, electronic book players, mobile phones, cordless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, headphone stereos, video camcorders, LCD televisions, handheld vacuum cleaners, portable CD players, mini-discs, electric shavers, transceivers, electronic organizers, calculators, portable tape recorders, radios, backup power supplies, and memory cards. It can also be installed in consumer electronic devices such as automobiles, electric vehicles, motors, lighting fixtures, toys, game devices, road conditioners, clocks, flash devices, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). It can also be used for various military and space applications. It can also be combined with solar cells.

[0113] The present invention will be described in more detail below based on examples. Note that the present invention is not limited to these examples except as defined in the present invention. "Room temperature" means 25°C. "Parts" and "%" representing compositions are based on mass unless otherwise specified.

[0114] [Preparation of negative electrode active material] The following were used as negative electrode active materials. <Silicon (Si)> Silicon (trade name: Silgren e-Si, manufactured by Elkem, average particle size: 2.3 μm) was used. <Carbon-coated silicon oxide (SiOC)> Carbon-coated silicon oxide (carbon element content: 1.3 mass%, manufactured by Osaka Titanium Technologies Co., Ltd., grade: SiO NC, average particle size: 5 μm) was used.

[0115] <Preparation of Lithium-Doped and Carbon-Coated Silicon Oxide (Li-SiOC)> Silicon oxide (Li-SiOC) that was both lithium-doped and carbon-coated was prepared in the same manner as in Example 1-1 of JP 2022-121582 A. Specifically, it was prepared as follows. A raw material (vaporized starting material) containing a mixture of silicon metal and silicon dioxide was placed in a reactor, and the mixture was vaporized in a vacuum atmosphere of 10 Pa and deposited on an adsorption plate. After sufficient cooling, the deposit (silicon oxide) was removed and pulverized in a ball mill. After adjusting the particle size, a carbon coat was formed by thermal chemical vapor deposition (thermal CVD). During thermal CVD, the pulverized silicon oxide was placed in a silicon nitride tray and then placed in a processing furnace capable of maintaining the atmosphere. Next, argon gas was introduced into the furnace to replace the atmosphere with argon. Then, a methane-argon mixed gas was introduced at a rate of 2 NL (normal liter) / min while the temperature was increased at a rate of 300°C / hr. The temperature was then maintained at 600-1100°C for 3-10 hours, resulting in thermal CVD, which yielded carbon-coated silicon oxide (SiOC2). After the temperature was reduced, the temperature was lowered, and the powder was recovered after reaching room temperature. Subsequently, the carbon-coated silicon oxide (SiOC2) was modified by doping with lithium using a redox method. First, the carbon-coated silicon oxide (SiOC2) was immersed in a solution (Solution A) prepared by dissolving lithium flakes and naphthalene in tetrahydrofuran (hereinafter referred to as THF). Solution A was prepared by dissolving naphthalene in a THF solvent at a concentration of 0.2 mol / L, and then adding 10% by mass of lithium flakes to the mixture of THF solvent and naphthalene. The temperature of Solution A when immersing the carbon-coated silicon oxide (SiOC2) was 20°C, and the immersion time was 20 hours. The solid matter was then filtered off. Through the above process, the carbon-coated silicon oxide (SiOC2) was doped with lithium. The resulting solid matter was heat-treated at 600°C for 24 hours in an argon atmosphere to stabilize the Li compound. In this way, the carbon-coated silicon oxide (SiOC2) was modified to obtain a silicon oxide (Li-SiOC) that was both lithium-doped and carbon-coated.The proportion of carbon element in Li-SiOC was 3 mass %, and the average particle size (volume-based median diameter D50) of the Li-SiOC particles was 6.7 μm.

[0116] [Synthesis of Coating Layer Constituent Polymers] As coating layer constituent polymers, the homopolymers shown in columns A1, A2, and A3 of Table 1 below, and the copolymer shown in column A4 of Table 1 below, were synthesized as follows. Tables 1A to 1D are collectively referred to as Table 1.

[0117] <Synthesis of homopolymers listed in columns A1 and A2 of Table 1> (Synthesis of homopolymer (polyacrylamide) No. 101) 75.0 g of acrylamide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 75.0 g of distilled water, and 0.55 g of VA-057 (trade name, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., carboxy group-containing water-soluble azo polymerization initiator) were stirred and mixed at room temperature to prepare solution B. 337.5 g of distilled water was added to a 1 L three-neck flask equipped with a reflux condenser and a gas inlet cock. Nitrogen gas was introduced at a flow rate of 200 mL / min for 60 minutes, and then the temperature was raised to 75°C. Solution B prepared above was added dropwise to the distilled water in the 1 L three-neck flask over 1 hour. After completion of the dropwise addition, stirring was continued at 75°C for 3 hours. The mixture was cooled to room temperature, washed twice with ethanol, and dried under reduced pressure to obtain polyacrylamide. The weight-average molecular weight was 307,000. (Synthesis of Homopolymers Other Than No. 101) Various homopolymers shown in the A1 and A2 columns of Table 1 were synthesized by adjusting the type of monomer, the amount of polymerization initiator, the type of solvent, etc. in the synthesis of polyacrylamide described above.

[0118] Synthesis of Homopolymers Listed in Column A3 of Table 1 (Synthesis of Homopolymer No. 127 (Polystyrene)) 6.0 g of styrene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 24.0 g of propylene glycol monomethyl ether acetate were added to a 500 mL three-neck flask equipped with a reflux condenser and a gas inlet cock, followed by stirring and mixing at room temperature. Nitrogen gas was introduced into the flask at a flow rate of 200 mL / min for 30 minutes, after which 0.0046 g of V-601 (trade name, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., oil-soluble azo polymerization initiator) was added, the mixture was heated to 85°C, and stirring was continued at 85°C for 5 hours. The mixture was cooled to room temperature, washed twice with ethanol, washed once with distilled water, and dried under reduced pressure to obtain polystyrene. The weight-average molecular weight was 320,000. (Synthesis of Homopolymers Other Than No. 127) Various homopolymers shown in the column A3 of Table 1 were synthesized by adjusting the type of monomer, the amount of polymerization initiator, the type of solvent, etc. in the synthesis of polystyrene described above.

[0119] <Synthesis of Copolymers Listed in Column A4 of Table 1> (Synthesis of Copolymer No. 151 (Copolymer of Acrylamide and Styrene)) 3.5 g of acrylamide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 2.39 g of styrene (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 23.7 g of dioxane were placed in a 500 mL three-neck flask equipped with a reflux condenser and a gas inlet cock, and the mixture was stirred and mixed at room temperature. Nitrogen gas was introduced into the flask at a flow rate of 200 mL / min for 30 minutes, after which 0.004 g of V-601 (trade name, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., oil-soluble azo polymerization initiator) was added, the mixture was heated to 85°C, and stirring was continued at 85°C for 5 hours. Precipitation of a copolymer was confirmed in the reaction solution as the reaction progressed. After polymerization, the mixture was cooled to room temperature, and the precipitated copolymer was filtered, washed twice with dioxane and once with distilled water, and dried under reduced pressure to obtain an acrylamide-styrene copolymer. The weight-average molecular weight was 198,000. (Synthesis of copolymers other than No. 151) Various copolymers listed in column A4 of Table 1 were synthesized by adjusting the type of monomer, composition ratio, amount of polymerization initiator, type of solvent, etc. in the synthesis of the above acrylamide-styrene copolymer.

[0120] The structures of the obtained homopolymers are shown below, where n indicates the repeating number. Copolymers are not shown.

[0121]

[0122]

[0123]

[0124]

[0125] [Preparation of Composite Negative Electrode Active Materials] Composite negative electrode active materials Nos. 101 to 169, c1 to c7, and c17 shown in Table 1 below were prepared using coating layer-constituting polymers and negative electrode active materials as follows.

[0126] <Preparation of each composite negative electrode active material described in Tables 1A, 1C, and 1D: When the polymer constituting the coating layer is water-soluble> (Preparation of composite negative electrode active material No. 101) 0.5 g of polyacrylamide described in Table 1 No. 101 was dissolved in 60 g of distilled water to prepare solution C. 6 g of the silicon prepared above was added to the prepared solution C and stirred at room temperature for 1 hour. After stirring, the resulting dispersion was spray-dried using a spray dryer (manufactured by BUCHI, Mini Spray Dryer B-290 (trade name)) to prepare composite negative electrode active material No. 101. The content of the coating layer (polyacrylamide) was controlled by the number of spray-drying treatments. Specifically, the spray-drying treatment was performed in the same manner as above, except that silicon after spray drying was used instead of silicon when preparing solution C. This was repeated until the desired coating layer content was achieved (the same applies to the preparation of each subsequent composite negative electrode active material). (Preparation of Composite Negative Electrode Active Materials Other than No. 101) In the synthesis of the above composite negative electrode active material No. 101, the type and / or amount of the polymer used to form the coating layer, the type of solvent in which the polymer is dissolved, and the type and / or amount of the negative electrode active material were adjusted to prepare each of the composite negative electrode active materials listed in Tables 1A, 1C, and 1D.

[0127] <Preparation of Composite Negative Electrode Active Materials Described in Tables 1A, 1C, and 1D: Cases Where the Polymer Constituting the Coating Layer Is Not Dissolved in Water> (Preparation of Composite Negative Electrode Active Material No. 127) Solution D was prepared by dissolving 0.30 g of the polystyrene described in Table 1 No. 127 in 60 g of tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). 6 g of the lithium-doped and carbon-coated silicon oxide prepared above was added to the prepared Solution D and stirred at room temperature for 1 hour. After stirring, the resulting dispersion was spray-dried using a spray dryer (manufactured by Buchi, Mini Spray Dryer B-290 (trade name)) connected to an organic solvent recovery device (manufactured by Buchi, Inert Loop B-295 (trade name)) to prepare composite negative electrode active material No. 127. The content of the coating layer (polystyrene) was controlled by the number of spray-drying treatments. (Preparation of Composite Negative Electrode Active Materials Other than No. 127) In the synthesis of composite negative electrode active material No. 127, the type and / or amount of polymer used to form the coating layer, the type of solvent in which the polymer is dissolved, and the type and / or amount of negative electrode active material were adjusted to prepare each of the composite negative electrode active materials listed in Tables 1A, 1C, and 1D.

[0128] <Preparation of Composite Negative Electrode Active Materials Listed in Table 1B: Cases in which the Coating Layer is Made of Two Polymers> (Preparation of Composite Negative Electrode Active Material No. 129) 0.5 g of polyacrylamide listed in No. 129 of Table 1B was dissolved in 60 g of distilled water to prepare Solution E. 6 g of the silicon prepared above was added to the prepared Solution E and stirred at room temperature for 1 hour. After stirring, the resulting dispersion was spray-dried using a spray dryer (BUCHI, Mini Spray Dryer B-290 (trade name)) to prepare composite negative electrode active material No. 129a coated with polyacrylamide. The content of the coating layer (polyacrylamide) was controlled by the number of spray-drying treatments. Solution F was prepared by dissolving 0.30 g of polystyrene listed in No. 129 of Table 1B in 60 g of tetrahydrofuran (FUJIFILM Wako Pure Chemical Industries, Ltd.). 6 g of composite negative electrode active material No. 129a was added to the prepared solution F and stirred at room temperature for 1 hour. After stirring, the resulting dispersion was spray-dried using a spray dryer (Buchi Mini Spray Dryer B-290 (product name)) connected to an organic solvent recovery device (Buchi Inert Loop B-295 (product name)). The content of the coating layer (polystyrene) was controlled by the number of spray-drying treatments. In this manner, composite negative electrode active material No. 129 coated with polyacrylamide and polystyrene was prepared. (Preparation of Composite Negative Electrode Active Materials Other than No. 129) In the synthesis of composite negative electrode active material No. 129, the type and / or amount of polymer used to form the coating layer, the type of solvent in which the polymer was dissolved, and the type and / or amount of negative electrode active material were adjusted to prepare each of the composite negative electrode active materials listed in Table 1B. Regarding the mixing of the homopolymers used to form the coating layer, in the preparation of any of the composite negative electrode active materials, coating with the homopolymer described in column A1 was performed, and then coating with the homopolymer described in column A2 or A3 was performed.

[0129] Here, composite negative electrode active material Nos. 101 to 169 shown in Table 1 below are composite negative electrode active materials of the present invention, and composite negative electrode active material Nos. c1 to c7 and c17 are composite negative electrode active materials for comparison. Nos. c8 to c16 are negative electrode active materials without a coating layer.

[0130] [Content of coating layer in composite negative electrode active material] The content of the coating layer in the composite negative electrode active material prepared above was calculated by thermogravimetry under the following measurement conditions using a high-sensitivity differential thermobalance (product name: STA 2500 Regulus, manufactured by NETZSCH). The measurement was carried out twice using the same sample, and the calculation was carried out using the thermogravimetry chart of the second measurement. Specifically, in the thermogravimetry chart of the second measurement, the weight W ｒ Weight W at room temperature ｒ to weight W at 500 ° C ５００ The mass percentage of the value minus (i.e., [(W ｒ -W ５００ ) / W ｒ ]×100%) was defined as the content of the coating layer in the composite negative electrode active material. (Measurement conditions) Atmosphere in measurement chamber: nitrogen gas Temperature rise rate: 10° C. / min Measurement temperature: room temperature (25° C.) to 500° C.

[0131] [Evaluation of Hydrogen Gas Generation Amount Under Specific Conditions] <For Composite Negative Electrode Active Materials Nos. 101-169, c1-c7, and c17> 1 g of the negative electrode active material used above or the prepared composite negative electrode active material was added to water to a concentration of 5% by mass, and the mixture was stirred at 2000 rpm for 3 minutes using a planetary centrifugal mixer (product name: Awatori Rentaro ARV-310P, manufactured by THINKY Corporation) to prepare a uniform slurry (gas measurement slurry, hereinafter sometimes simply referred to as "slurry"). 10 g of the prepared slurry was filled into an aluminum laminate container (length: 10 cm, width: 10 cm, thickness: 0.1 cm) (product name: D-EL40H / consumer use, manufactured by Hosen Co., Ltd.), and vacuum-sealed to obtain a gas-free sealed body. The sealed body was left to stand at 40°C for 24 hours. The amount of hydrogen gas generated within the sealed body was calculated by specific gravity measurement. All of the above operations were carried out under atmospheric pressure. The amount of hydrogen gas was determined as follows: First, the weight of the sealed body (the weight of the slurry including the aluminum laminated container) (M Ａ＋Ｓ Separately, the weight of the aluminum laminate container itself was measured, and the weight of the aluminum laminate container was subtracted from the weight of the sealed body to obtain the slurry weight (M ｓ Furthermore, the specific gravity ρ of the sealed body at 25°C was determined.０ was measured using a hydrometer (product name: EW-300SG, manufactured by Alpha Mirage). The sealed body was then left to stand at 40°C for 24 hours. The sealed body was returned to room temperature, and the specific gravity ρ of the sealed body at 25°C after standing for 24 hours was measured using a hydrometer. From the weight and specific gravity of the obtained sealed body, the amount of hydrogen gas generated (cm ３ The amount of hydrogen gas generated (cm ３ ) = M Ａ＋Ｓ / ρ ０ × (ρ ０ The obtained amount of hydrogen gas generated was converted into the amount of hydrogen gas generated per 1 g of the composite negative electrode active material. The weight of the negative electrode active material sealed in the aluminum laminate container was calculated by multiplying the weight of the slurry by M Ｓ The hydrogen gas generation rate was calculated from the formula (1). Evaluation was performed according to the following evaluation criteria. <In the case of negative electrode active materials No. c8 to c16 having no coating layer> The hydrogen gas generation rate from the negative electrode active material having no coating layer was determined in the same manner as the measurement method for the hydrogen gas generation rate from the composite negative electrode active material, except that, in the determination of the hydrogen gas generation rate from the composite negative electrode active material, a total of 1 g of a mixture of the negative electrode active material and the coating layer-constituting polymer shown in Table 1D was added instead of 1 g of the composite negative electrode active material when preparing the slurry for gas measurement. More specifically, when preparing the slurry, the negative electrode active material was mixed with the polymer or carbon nanotubes shown in the "Coating layer-constituting polymer" column so that the content of the polymer or carbon nanotubes (CNTs) shown in the "Coating layer content" column in Table 1 was the content (mass %) shown in the "Coating layer content" column in Table 1 relative to the total content of the negative electrode active material and the content of the polymer or carbon nanotubes shown in the "Coating layer-constituting polymer" column, and this mixture was used in place of 1 g of the negative electrode active material. As the carbon nanotubes, single-walled carbon nanotubes (trade name: Lamfil WPB-030, manufactured by Kusumoto Chemicals Co., Ltd.) were used. The pH of the gas measurement slurries containing negative electrode active materials Nos. c14 to c16 was all 12. When evaluating the amount of hydrogen gas generated per 1 g of the composite negative electrode active material, if the negative electrode active material did not have a coating layer, the amount of hydrogen gas generated was converted into the amount of hydrogen gas generated per 1 g of negative electrode active material and evaluated. - Evaluation Criteria - 7: 0.05 cm ３ / g or less 6: 0.05 cm ３ / g or more, 0.10cm ３ / g or less 5: 0.10 cm ３ / g or more, 0.20cm ３ / g or less 4: 0.20 cm ３ / g or more, 0.30cm ３ / g or less 3: 0.30 cm ３ / g or more, 0.40cm ３ / g or less 2: 0.40 cm ３ / g or more, 0.50cm ３ / g or less 1: 0.50 cm ３ / g or more

[0132]

[0133]

[0134]

[0135]

[0136] (Coating layer constituent polymers) PAAm: Polyacrylamide PDMAAm: Polydimethylacrylamide PTMBAAm: Poly 1,1,3,3-tetramethylbutylacrylamide PDEAAm: Polydiethylacrylamide PDAAm: Polydodecylacrylamide PHEAAm: Polyhydroxyethylacrylamide PAANa: Sodium polyacrylate PBA: Polybutyl acrylate PHBA: Polyhydroxybutyl acrylate PHEA: Polyhydroxyethyl acrylate PMEA: Polymethoxyethyl acrylate PEDEGA: Polyethoxydiethylene glycol acrylate PMTEGA: Polymethoxytriethylene glycol acrylate PCEA: Polycyanoethyl acrylate PSt: Polystyrene PHSt: Polyhydroxystyrene SBR: Styrene-butadiene rubber PAA: Polyacrylic acid AAm: Acrylamide AAm / St = 90 / 10: Copolymer consisting of 90% by mass of a component derived from acrylamide and 10% by mass of a component derived from styrene. AAm / St = 50 / 50: Copolymer consisting of 50% by mass of a component derived from acrylamide and 50% by mass of a component derived from styrene. AAm / St = 10 / 90: Copolymer consisting of 10% by mass of a component derived from acrylamide and 90% by mass of a component derived from styrene. AANa / St = 50 / 50: Copolymer consisting of 50% by mass of a component derived from sodium acrylate and 50% by mass of a component derived from styrene. AAm / HSt = 90 / 10: Copolymer consisting of 90% by mass of a component derived from acrylamide and 10% by mass of a component derived from hydroxystyrene. AAm / AA = 90 / 10: Copolymer consisting of 90% by mass of a component derived from acrylamide and 10% by mass of a component derived from acrylic acid. AAm / AA = 70 / 30: A copolymer consisting of 70% by weight of a component derived from acrylamide and 30% by weight of a component derived from acrylic acid. AAm / AA = 60 / 40: A copolymer consisting of 60% by weight of a component derived from acrylamide and 40% by weight of a component derived from acrylic acid. AAm / AANa = 90 / 10: A copolymer consisting of 90% by weight of a component derived from acrylamide and 10% by weight of a component derived from sodium acrylate.AAm / PBA=90 / 10: Copolymer consisting of 90% by mass of a component derived from acrylamide and 10% by mass of a component derived from butyl acrylate AAm / HEAAm=90 / 10: Copolymer consisting of 90% by mass of a component derived from acrylamide and 10% by mass of a component derived from hydroxyethyl acrylamide CNT: Single-walled carbon nanotubes PVA: Polyvinyl alcohol Content: This refers to the content of the components of each homopolymer in the coating layer (excluding components derived from the polymerization initiator), and is expressed in % by mass. Molecular weight: weight average molecular weight measured by the method described above Si: silicon (trade name: Silgren e-Si, manufactured by Elkem, average particle size: 2.3 μm) SiOC: carbon-coated silicon oxide (carbon element content: 1.3 mass%, manufactured by Osaka Titanium Technologies Co., Ltd., grade: SiO NC, average particle size: 5 μm) Li-SiOC: lithium-doped and carbon-coated silicon oxide prepared above (carbon element content: 3 mass%, average particle size: 6.7 μm)

[0137] The "-" in the "Coating Layer Constituent Polymer" column indicates that no constituent component is contained. The "Coating Layer Content" column indicates the content (mass %) of the coating layer in the composite negative electrode active material (100 mass %) calculated by the measurement method described above. The "Coating Layer Content" column indicates that the negative electrode active material was used without being coated. Note that, as described above, Nos. c11 to c13 are examples in which the negative electrode active material was not coated with a polymer, and the negative electrode active material and the polymer were used directly to prepare the slurry for gas measurement. Therefore, the "Coating Layer Constituent Polymer" column for Nos. c11 to c13 indicates polyacrylamide, which corresponds to a polymer containing a constituent component represented by general formula (A-1), a constituent component represented by general formula (A-2) and / or a constituent component represented by general formula (A-3), which was added directly during the preparation of the slurry, rather than a polymer constituting the coating layer of the negative electrode active material as the composite negative electrode active material. Also, Nos. The "Coating Layer Content" column for c11 to c13 shows not the mass percentage value of the coating layer calculated by the above-mentioned measurement method, but the amount of polyacrylamide added when preparing the negative electrode slurry, relative to the total amount of the negative electrode active material and polyacrylamide, in units of mass %. Furthermore, Nos. c14 to c16 are examples in which the negative electrode active material and carbon nanotubes were used directly to prepare the gas measurement slurry without coating the negative electrode active material with a polymer. Therefore, the "Coating Layer Constituent Polymer" column for Nos. c14 to c16 shows the carbon nanotubes that were directly added when preparing the gas measurement slurry, rather than the polymer that constitutes the coating layer of the negative electrode active material as a composite negative electrode active material. Furthermore, Nos. The "Content of coating layer" columns c14 to c16 show not the mass percentage value of the coating layer calculated by the above-mentioned measurement method, but the amount of carbon nanotubes added when preparing the gas measurement slurry relative to the total amount of negative electrode active material and carbon nanotubes, in units of mass %.

[0138] As is clear from Table 1, all of the composite negative electrode active materials Nos. c1 to c7 and c17 had a hydrogen gas generation rate of 0.30 cm3 when prepared into slurries for gas measurement. ３In the composite negative electrode active materials Nos. c1 and c17 having a coating layer of polyacrylic acid or polyvinyl alcohol on Li-SiOC, the hydrogen gas generation rate was 0.30 cm ３ / g or more, and the amount of hydrogen gas generated is suppressed compared to the case where there is no coating layer (No. c10), but it is not sufficient. Similarly, in the case of composite negative electrode active materials Nos. c2 to c7, in which the coating layer polymer contains a large amount of acrylic acid component, the amount of hydrogen gas generated is suppressed compared to the case where there is no coating layer (No. c10), but it is not sufficient. As shown in Nos. c8 to c10, the negative electrode active materials without a coating layer all have a hydrogen gas generation rate of 0.40 cm ３ / g or more, and among them, the lithium-doped negative electrode active material (Li-SiOC) has a hydrogen gas generation rate of 0.50 cm ３ As shown in Nos. c11 to c13, the negative electrode active materials without a coating layer had a hydrogen gas generation rate of 0.40 cm3 or more, even when polyacrylamide was added during the preparation of the slurry for gas measurement. ３ As shown in Nos. c14 and c15, the negative electrode active material having no coating layer had a hydrogen gas generation rate of 0.40 cm3 even when the slurry for gas measurement was prepared by adding carbon nanotubes. ３ / g or more. It is thought that the amount of hydrogen gas adsorbed by the carbon nanotubes is limited. In addition, in No. c16, the amount of hydrogen gas generated was not measured because the slurry gelled. It was determined that if the slurry gelled, the amount of hydrogen gas generated could not be accurately evaluated because uniform mixing was not achieved. In contrast, in all of the composite negative electrode active materials Nos. 101 to 169 of the present invention, the amount of hydrogen gas generated was 0.30 cm ３ / g. It can be seen that the composite negative electrode active material of the present invention is less likely to generate hydrogen gas when made into a negative electrode slurry. Therefore, it can be seen that forming a negative electrode active material layer using the composite negative electrode active material of the present invention can increase the battery capacity of a secondary battery.

[0139] When a component represented by general formula (A-1) and a component represented by general formula (A-3) are contained (when a polymer containing a component represented by general formula (A-1) and a polymer containing a component represented by general formula (A-3) are used in combination, and when a copolymer of a component obtained by general formula (A-1) and a component represented by general formula (A-3) is used), the amount of hydrogen gas generated tends to be further reduced. The reason for this is unclear, but it is thought to be as follows. The surface of the negative electrode active material has hydrophobic regions and hydrophilic regions. The components represented by general formula (A-1) and general formula (A-2) are relatively hydrophilic components, and the component represented by general formula (A-3) is a relatively hydrophobic component. When these components are present in a balanced manner, it is thought that the coating state of the active material layer surface will be favorable for suppressing hydrogen gas generation.

[0140] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0141] This application claims priority based on Japanese Patent Application No. 2024-084931, filed on May 24, 2024, the contents of which are incorporated herein by reference as part of the present specification.

[0142] REFERENCE SIGNS LIST 10 Non-aqueous 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

A composite negative electrode active material having a negative electrode active material into which ions of a metal belonging to Group 1 or 2 of the periodic table can be inserted, and a coating layer that coats the surface of the negative electrode active material, When an aqueous dispersion containing the composite negative electrode active material at a concentration of 5% by mass was allowed to stand at 40° C. for 24 hours, the amount of hydrogen gas generated per 1 g of the composite negative electrode active material was 0.30 cm ３ / g or less of the composite negative electrode active material. 　 The composite negative electrode active material according to claim 1, wherein the coating layer contains a polymer having at least one of a component represented by the following general formula (A-1), a component represented by the following general formula (A-2), and a component represented by the following general formula (A-3): In the above general formula, R １１ ~R １３ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R １４ and R １５ represents a hydrogen atom, an alkyl group having 1 to 16 carbon atoms, or an aryl group having 6 to 12 carbon atoms. R １６ represents an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 12 carbon atoms, -L １ -R １８ or a counter ion. １ represents an alkylene group having 1 to 16 carbon atoms or a polyalkyleneoxy group having 1 to 16 carbon atoms. １ When is an alkylene group, R １８ represents a hydrogen atom, a hydroxy group, an alkoxy group, or a cyano group. １ When R is a polyalkyleneoxy group, １８ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a cyano group. R １７ represents a hydrogen atom, a hydroxy group, an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 12 carbon atoms, an acyloxy group having 2 to 16 carbon atoms, an alkoxycarbonyl group having 2 to 16 carbon atoms, or an aryloxycarbonyl group having 7 to 13 carbon atoms. * indicates a binding site for incorporation into the backbone of the polymer.

3. The composite negative electrode active material according to claim 2, wherein the total content of the component represented by general formula (A-1), the component represented by general formula (A-2), and the component represented by general formula (A-3) in the coating layer is 50 mass% or more.

3. The composite negative electrode active material of claim 2, wherein the polymer has a weight average molecular weight of 10,000 or greater.

3. The composite negative electrode active material according to claim 2, wherein in the coating layer, a ratio of the content of the component represented by general formula (A-1) to the total content of the component represented by general formula (A-2) and the component represented by (A-3) is 1 / 99 to 99 / 1 in mass ratio. 　 The composite negative electrode active material according to claim 2, wherein the polymer contains a component represented by the general formula (A-1), a component represented by the general formula (A-2), and / or a component represented by the general formula (A-3). 　 The composite negative electrode active material according to claim 2, wherein the coating layer comprises a polymer having a component represented by general formula (A-1), and a polymer having a component represented by general formula (A-2) and / or a polymer having a component represented by general formula (A-3). 　 The composite negative electrode active material according to claim 1 , wherein the coating layer has a content of 11.0% by mass or less.

10. The composite negative electrode active material of claim 1, wherein the negative electrode active material comprises a silicon-based active material. 　 A slurry for a secondary battery negative electrode, comprising the composite negative electrode active material according to any one of claims 1 to 9. 　 A negative electrode sheet having a negative electrode active material layer formed using the slurry for a secondary battery negative electrode according to claim 10. 　 A secondary battery comprising a negative electrode active material layer formed using the slurry for a secondary battery negative electrode according to claim 10. 　 A method for producing a negative electrode sheet, comprising forming a negative electrode active material layer using the slurry for a secondary battery negative electrode according to claim 10. 　 A method for producing a secondary battery, comprising incorporating the negative electrode active material layer of the negative electrode sheet obtained by the production method according to claim 13 as a negative electrode active material layer of the secondary battery.

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