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

Abstract

Provided are a composite negative electrode active material, a slurry for a secondary battery negative electrode, a negative electrode sheet, a secondary battery, and a method for manufacturing a negative electrode sheet and a secondary battery, the composite negative electrode active material having a negative electrode active material, and a coating layer that covers the surface of the negative electrode active material and contains a polymer containing a constituent component represented by general formula (A-1), the coating layer content of the composite negative electrode active material being greater than 5.0 mass%. In the formula, R11 to R13 each denote a hydrogen atom or a C1-6 alkyl group, and R14 and R15 each denote a hydrogen atom, a C1-16 alkyl group, or a C6-12 aryl group. * indicates a bonding site to be incorporated into the main chain of the polymer.

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. This negative electrode active material layer contains electrode active material particles capable of absorbing or releasing lithium ions during charging and discharging, and optionally contains a conductive additive. 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. While the use of silicon-based active materials in negative electrodes enables higher energy density, the silicon-based active material also expands in its expansion and contraction range during charging and discharging. Therefore, negative electrode active material particles are prone to cracking, primarily in their surface layers. This cracking causes a decomposition reaction of the electrolyte on the newly formed surface of the negative electrode active material particles, and a coating made of the decomposed electrolyte is formed on the newly formed surface. Because this phenomenon consumes the electrolyte, the cracking leads to a deterioration in cycle characteristics. For example, Patent Document 1, regarding a negative electrode material for non-aqueous electrolyte secondary batteries, describes the SiO that becomes unstable during lithium insertion and extraction. ２ It describes that by using a silicon compound whose component part has been modified in advance to another Li compound, it is possible to reduce the irreversible capacity that occurs during charging, that by providing a coating layer made of an organic polymer on the surface of the silicon compound, it is possible to impart resistance to organic solvents and aqueous solvents, and to produce an anode material with excellent capacity retention and initial efficiency, and that by using an anode material mainly made of a silicon compound, it is possible to increase the battery capacity.

[0004] Japanese Patent Application Laid-Open No. 2015-156328

[0005] Through further investigations, the inventors have discovered that in addition to the cycle performance problem resulting from the expansion and contraction range during charge and discharge described above, the following problem also exists. Specifically, when a silicon-based active material is mixed with graphite and used to form a liquid composition (slurry), the silicon-based active material settles faster than graphite, making the slurry viscosity prone to change over time (leading to dispersion stability problems). Poor dispersion stability in the slurry is likely to result in defects in the negative electrode active material layer formed by applying and drying the slurry. Defects in the negative electrode active material layer impair ionic conductivity and directly lead to reduced battery performance. Therefore, a slurry containing a negative electrode active material is required to have high dispersion stability so that it can maintain a uniformly dispersed state for a long period of time. To improve dispersion stability in the slurry, coating the surface of the negative electrode active material to enhance dispersibility is considered. Increasing the amount of coating layer on the surface of the negative electrode active material tends to increase dispersion stability. On the other hand, increasing the amount of coating layer on the surface of the negative electrode active material leads to a problem of reduced battery capacity. In relation to this point, Patent Document 1 describes that the content of the coating layer is set to less than 5 mass % in order to maintain good electrical conductivity and ionic conductivity on the surface of the negative electrode active material particles and to suppress deterioration of battery characteristics.

[0006] An object of the present invention is to provide a composite negative electrode active material having a coating layer, which exhibits excellent dispersion stability when formed into a slurry and can achieve excellent battery capacity when used as a negative electrode active material for a secondary battery. Another object of the present invention is to provide a slurry for a secondary battery negative electrode, a negative electrode sheet, and a secondary battery that use this composite negative electrode active material. Another object of the present invention is to provide methods for manufacturing these negative electrode sheets and secondary batteries.

[0007] The present inventors have conducted extensive research into polymers that constitute coating layers for negative electrode active materials, and have found that by providing a coating layer containing a polymer containing an acrylamide-based component on the surface of a negative electrode active material in an amount exceeding a specific value, a slurry containing the resulting composite negative electrode active material can be formed, resulting in a slurry with excellent dispersion stability. Furthermore, by forming a negative electrode active material layer using this slurry, a secondary battery having excellent battery capacity can be obtained, even though the negative electrode active material contains a large amount of coating layer. The present invention was completed through further research based on these findings.

[0008] That is, the above-mentioned problems have been solved by the following means: <1> 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 2 of the periodic table, and a coating layer that coats the surface of the negative electrode active material, wherein the coating layer contains a polymer containing a constituent represented by the following general formula (A-1), and the content of the coating layer in the composite negative electrode active material is more than 5.0 mass%: In the above 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. * represents a bonding site for incorporation into the main chain of the polymer. <2> The composite negative electrode active material according to <1>, wherein the content of the component represented by general formula (A-1) in the coating layer is 50% by mass or more. <3> The composite negative electrode active material according to <1> or <2>, wherein the content of the component represented by general formula (A-1) in the coating layer is 5.1 to 15.0% by mass. <4> The composite negative electrode active material according to any one of <1> to <3>, wherein the weight-average molecular weight of the polymer containing the component represented by general formula (A-1) is 10,000 or more. <5> The composite negative electrode active material according to any one of <1> to <4>, wherein the coating layer contains the component represented by general formula (A-1) and a component represented by the following general formula (A-2): In the above formula, R ２１ ~R ２３represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. * represents a bonding site for incorporation into the main chain of the polymer. <6> The composite negative electrode active material according to <5>, in which the mass ratio of the content of the component represented by general formula (A-1) to the content of the component represented by general formula (A-2) in the coating layer is 1 / 99 to 99 / 1. <7> The composite negative electrode active material according to <5>, in which the polymer containing the component represented by general formula (A-1) contains the component represented by general formula (A-2). <8> The composite negative electrode active material according to <5>, in which the coating layer contains a polymer containing the component represented by general formula (A-2) in addition to the polymer containing the component represented by general formula (A-1). <9> The composite negative electrode active material according to <8>, in which the polymer containing the component represented by general formula (A-2) has a weight-average molecular weight of 10,000 or more. <10> The composite negative electrode active material according to any one of <1> to <9>, wherein the negative electrode active material comprises a silicon-based active material. <11> A slurry for a secondary battery negative electrode, comprising the composite negative electrode active material according to any one of <1> to <10> and a dispersion medium. <12> A negative electrode sheet having a negative electrode active material layer formed using the slurry for a secondary battery negative electrode according to <11>. <13> A secondary battery comprising a negative electrode active material layer formed using the slurry for a secondary battery negative electrode according to <11>. <14> 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 <11>. <15> A method for producing a secondary battery, comprising incorporating the negative electrode sheet obtained by the production method according to <14> as a negative electrode of the secondary battery.

[0009] The composite negative electrode active material of the present invention can impart excellent dispersion stability to a slurry containing the composite negative electrode active material. Furthermore, by incorporating the composite negative electrode active material of the present invention into the negative electrode active material layer of a secondary battery, excellent battery capacity can be achieved even when a large amount of coating layer is present on the surface of the negative electrode active material. By using the negative electrode sheet of the present invention as the negative electrode active material layer of a secondary battery, excellent battery capacity can be achieved even when a large amount of coating layer is present on the surface of the negative electrode active material. The secondary battery of the present invention has excellent battery capacity even when a large amount of coating layer is present on the surface of the negative electrode active material. The negative electrode sheet of the present invention can be obtained by the manufacturing method of the negative electrode sheet of the present invention. Furthermore, the secondary battery of the present invention can be obtained by the manufacturing method of the secondary battery of the present invention.

[0010] 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.

[0011] 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, which will be described later. 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.

[0012] [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 2 of the periodic table, and a coating layer that coats the surface of the negative electrode active material, wherein the coating layer contains a polymer containing a constituent component represented by general formula (A-1) described later, and the content of the coating layer in the composite negative electrode active material is more than 5.0% by mass (exceeds 5.0% by mass).

[0013] The composite negative electrode active material of the present invention, when used as a component of a slurry for a secondary battery negative electrode due to the above-described configuration, can achieve excellent dispersion stability in the slurry. While the reason for this is unclear, it is presumed as follows. The surface of a negative electrode active material typically contains hydrophobic and hydrophilic regions. The coating layer in the composite negative electrode active material of the present invention contains a polymer containing a hydrophilic component represented by the general formula (A-1) described below, and therefore exhibits good affinity for the hydrophilic regions on the surface of the negative electrode active material. Increasing the content of the coating layer to a range exceeding 5.0 mass% under these conditions is believed to adjust the charge state on the particle surface of the negative electrode active material in the slurry, contributing to dispersion stability. Furthermore, by incorporating the composite negative electrode active material of the present invention into the negative electrode layer of a secondary battery, a secondary battery with excellent battery capacity can be obtained. On the other hand, as shown in the comparative example described below, in a composite negative electrode active material using a resin such as polystyrene as the polymer constituting the coating layer, the coating layer leads to a decrease in battery capacity.

[0014] A known technique involves using a polymer as a binder during the preparation of a slurry for forming a negative electrode, with the aim of improving the adhesion between particles of the negative electrode active material and the negative electrode active material. The 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, as shown in Comparative Examples c138 to c140 in the Examples described below, even when a typical binder-adsorbed negative electrode active material is used, a decrease in battery capacity cannot be suppressed.

[0015] In the composite negative electrode active material of the present invention, the polymer containing the component represented by the following general formula (A-1) is physically adsorbed or attached 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. Note that the coating layer may cover a part or the entire surface of the negative electrode active material, as long as the effects of the present invention are achieved.

[0016] The components contained in the composite negative electrode active material of the present invention will be described below.

[0017] <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.

[0018] 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. Graphite is preferably used as the carbonaceous material.

[0019] Examples of tin-based materials (tin-based active materials) used as negative electrode active materials include Sn, SnO, and SnO ２ , SnS, SnS ２ Examples include:

[0020] 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 compound group consisting of the amorphous oxides and chalcogenides, amorphous oxides or the chalcogenides of metalloid elements are more preferred, and oxides or composite oxides or chalcogenides consisting of one element alone or a combination of two or more elements selected from 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 Si２ O ３ , Sb ２ O ５ , Bi ２ O ３ , Bi ２ O ４ , GeS, PbS, PbS ２ , Sb ２ S ３ and Sb ２ S ５ are preferred.

[0021] The metal (composite) oxide and the chalcogenide preferably contain at least one of titanium and lithium as a constituent component from the viewpoint of high current density charge / discharge characteristics. 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:

[0022] 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.

[0023] 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.

[0024] 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 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.

[0025] 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.

[0026] 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 Ti ５ 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, and dispersion stability can be further improved.

[0027] 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.

[0028] 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.

[0029] 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 ｘ(0<x≦1.5) is preferably used, and carbon-coated silicon oxide is more preferably used. 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%. 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 (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.

[0030] 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 a 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 preferably performed 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 a commercially available negative electrode active material, 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.

[0031] The negative electrode active material may be used alone or in combination of two or more. The dispersion stability effect of the composite negative electrode active material of the present invention is more effectively exhibited when two or more negative electrode active materials are used. A combination of two or more negative electrode active materials is preferably a combination including at least a silicon-based active material and a carbonaceous material, more preferably a combination including at least a silicon-based active material and graphite, and even more preferably a combination including at least silicon oxide or carbon-coated silicon oxide and graphite. The silicon oxide and carbon-coated silicon oxide may be silicon oxide doped with the above-mentioned metal element and silicon oxide doped with the 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 specific gravity of silicon-based active materials is about 2.1, which is significantly different from that of other negative electrode active materials such as graphite, which has a specific gravity of about 1.6. This results in differences in sedimentation rates, and slurries containing silicon-based active materials and graphite tend to have poor dispersion stability. However, even when a negative electrode active material containing a silicon-based active material and graphite is used as the negative electrode active material, the dispersion stability of the slurry can be more effectively improved by forming a composite negative electrode active material of the present invention with a coating layer, as described below. 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.

[0032] 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.

[0033] The content of the negative electrode active material in the composite negative electrode active material is usually less than 95.0% by mass, preferably 85.0 to 94.9% by mass, more preferably 85.0 to 94.5% by mass, even more preferably 86.0 to 94.0% by mass, still more preferably 87.0 to 93.0% by mass, even more preferably 88.0 to 92.0% by mass, even more preferably 89.0 to 92.0% by mass, even more preferably 90.0 to 92.0% by mass, and even more preferably 90.5 to 91.5% by mass. When the coating layer contains a component represented by the general formula (A-1) above and another component (for example, a component represented by the general formula (A-2) above as another component), the content of the anode active material in the composite anode active material is preferably 88.0 to 94.9 mass%, more preferably 89.0 to 93.0 mass%, even more preferably 89.5 to 92.0 mass%, and still more preferably 90.5 to 92.0 mass%. It is preferable that the other component is more hydrophobic than the component represented by the general formula (A-1).

[0034] In 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.

[0035] <Coating Layer> The coating layer in the composite negative electrode active material of the present invention comprises at least a polymer containing a constituent component represented by the following general formula (A-1) as the polymer constituting the coating layer. In the present invention, when referring to a "polymer containing a constituent component represented by the following general formula (A-1)," this polymer may be either a homopolymer or a copolymer, with a homopolymer being preferred, as long as it contains the constituent component represented by general formula (A-1). When it is a copolymer, the polymerization form may be either random or block. The polymer constituting the coating layer is a so-called chain polymerization polymer in which the constituent component represented by the following general formula (A-1) is incorporated into the main chain of the polymer via *. A polymer containing a constituent component represented by general formula (A-1) may be used in combination with a polymer that does not contain a constituent component represented by general formula (A-1). Therefore, in the present invention, "polymer constituting the coating layer" means a polymer containing a component represented by general formula (A-1) when the polymer contained in the coating layer is only a polymer containing a component represented by general formula (A-1), and means both of these polymers when the coating layer contains a polymer containing a component represented by general formula (A-1) and a polymer not containing a component represented by general formula (A-1). The polymer constituting the coating layer will be described in more detail below.

[0036] (Polymer constituting the coating layer)

[0037] In the above 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. * represents a bonding site for incorporation into the main chain of the polymer.

[0038] 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 １５is 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 １５ 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, 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 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).

[0039] Specific examples of the constituent component represented by the general formula (A-1) above 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, and a 1,1,3,3-tetramethylbutyl(meth)acrylamide component; and dialkyl(meth)acrylamide components such as a dimethyl(meth)acrylamide component and a diethyl(meth)acrylamide component.

[0040] The polymer containing the component represented by general formula (A-1) may contain other components as copolymerization components, such as the components represented by the following general formula (A-2):

[0041]

[0042] In the above formula, R ２１ ~R ２３represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. * represents a bonding site for incorporation into the main chain of the polymer. R ２１ and R ２２ is preferably a hydrogen atom. ２３ is preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom.

[0043] Since the component represented by the general formula (A-2) is highly hydrophobic, it is believed that a polymer containing the component represented by the general formula (A-2) exhibits good affinity for the hydrophobic region of the negative electrode active material. Therefore, from the viewpoint of further improving dispersion stability, it is preferable that a polymer containing a component represented by the general formula (A-1) also contains a component represented by the general formula (A-2).

[0044] The polymer constituting the coating layer may contain a polymer containing a component represented by the general formula (A-2) in addition to a polymer containing a component represented by the general formula (A-1). That is, the coating layer may contain two or more polymers. In the present invention, when referring to a "polymer containing a component represented by the general formula (A-2)," this polymer does not contain the component represented by the general formula (A-1). The polymer containing a component represented by the general formula (A-2) may be either a homopolymer or a copolymer as long as it contains the component represented by the general formula (A-2), and is preferably a homopolymer. The polymer containing a component represented by the general formula (A-2) may be a polystyrene resin or a styrene component-containing rubber, and is preferably a polystyrene resin.

[0045] The content of the component represented by the general formula (A-1) in the coating layer is, for example, preferably 1% by mass or more, more preferably 10% by mass or more. From the viewpoint of further improving dispersion stability, it is 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, particularly preferably 90% by mass or more, and may even be 100% by mass. When the content of the component represented by the general formula (A-1) in the coating layer is not 100% by mass, the remainder preferably contains a component that is more hydrophobic than the component represented by the general formula (A-1). An example of a highly hydrophobic component is a component represented by the general formula (A-2). In the present invention, the content of the component refers to the content of all the components constituting the polymer, excluding components derived from the polymerization initiator.

[0046] When the coating layer contains a component represented by the general formula (A-1) above and a component represented by the general formula (A-2) above, the mass ratio of the content of the component represented by the general formula (A-1) to the content of the component represented by the general formula (A-2) above in this coating layer (content of the component represented by the general formula (A-1) above / content of the component represented by the general formula (A-2) above) is not particularly limited, and is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 99 / 1, still more preferably 50 / 50 to 99 / 1, and particularly preferably 75 / 25 to 99 / 1. The phrase "when the coating layer comprises a constituent component represented by the general formula (A-1) and a constituent component represented by the general formula (A-2)" includes a case where the coating layer comprises a mixed polymer of a polymer containing a constituent component represented by the general formula (A-1) and a polymer containing a constituent component represented by the general formula (A-2), a case where the coating layer comprises a copolymer containing the constituent component represented by the general formula (A-1) and the constituent component represented by the general formula (A-2) as copolymerization components, a case where the coating layer comprises a mixed polymer of this copolymer and a polymer containing the constituent component represented by the general formula (A-1), a case where the coating layer comprises a mixed polymer of this copolymer and a polymer containing the constituent component represented by the general formula (A-2), and a case where the coating layer comprises a mixed polymer of this copolymer, a polymer containing the constituent component represented by the general formula (A-1), and a polymer containing the constituent component represented by the general formula (A-2).

[0047] The polymer constituting the coating layer may contain a component other than the component represented by the general formula (A-1) above and other than the component represented by the general formula (A-2) above, within a range that does not impair the effects of the present invention.

[0048] 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 further improving dispersion stability and enhancing the effect of suppressing the decrease in battery capacity, 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 (for example, a mixture of a polymer containing a component represented by general formula (A-1) and a polymer containing a component represented by general formula (A-2)), 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 crosslinked structure, i.e., is a chain polymer. Furthermore, from the viewpoint of further increasing battery capacity, 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.

[0049] In the present invention, a compound having a siloxane bond may or may not be included as a component of the coating layer. For example, International Publication No. 2020 / 262647 describes that a compound having a siloxane bond is essential to impart ionic conductivity to the coating layer of the negative electrode active material. However, by using the composite negative electrode active material of the present invention, a secondary battery having sufficient battery capacity can be obtained even if the coating layer does not contain the compound having the siloxane bond.

[0050] (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.

[0051] 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.

[0052] - 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 having 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 groups (preferably sulfamoyl groups having 0 to 20 carbon atoms, including sulfamoyl groups having a group selected from an alkyl group and an aryl group. 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, Examples of suitable acyl groups include acyloxy groups having 1 to 20 carbon atoms, such as formyloxy, acetyloxy, propionyloxy, butyryloxy, octanoyloxy, hexadecanoyloxy, acryloyloxy, methacryloyloxy, crotonoyloxy, benzoyloxy, naphthoyloxy, and nicotinoyloxy; carbamoyl groups (preferably carbamoyl groups having 1 to 20 carbon atoms, including carbamoyl groups having a group selected from an alkyl group and an aryl group; for example, N,N-dimethylcarbamoyl and N-phenylcarbamoyl); and acylamino groups (preferably acylamino groups having 1 to 20 carbon atoms, and preferred examples of the acyl group in the acylamino group include the above-mentioned acyl groups.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.

[0053] 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.

[0054] Preferred specific examples of the polymer constituting the coating layer include homopolymers containing the following constituent components, mixed polymers of two or more of these homopolymers, and copolymers containing two or more of the following constituent components. The above descriptions can be applied to the content of each constituent component. The present invention should not be construed as being limited to these. First, specific examples of the constituent component represented by general formula (A-1) are shown below.

[0055]

[0056] Specific examples of the component represented by formula (A-2) are shown below.

[0057]

[0058] In the present invention, the polymer constituting the coating layer may be used alone or in combination of two or more.

[0059] The content of the coating layer in the composite negative electrode active material is greater than 5.0% by mass, preferably 5.1 to 15.0% by mass, more preferably 5.5 to 15.0% by mass, even more preferably 6.0 to 14.0% by mass, even more preferably 7.0 to 13.0% by mass, even more preferably 8.0 to 12.0% by mass, even more preferably 8.0 to 11.0% by mass, even more preferably 8.0 to 10.0% by mass, even more preferably 8.5 to 9.5% by mass. From the viewpoint of dispersion stability, a higher content tends to be preferable. Also, from the viewpoint of battery capacity, it tends to be better not to have too much. From this viewpoint, 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. When the polymer constituting the coating layer contains only the component represented by the general formula (A-1), the content of the coating layer in the composite negative electrode active material is preferably 5.1 to 12.0% by mass, more preferably 7.0 to 11.0% by mass, even more preferably 8.0 to 10.5% by mass, and even more preferably 8.0 to 9.5% by mass, from the viewpoint of further improving dispersion stability. On the other hand, when the polymer constituting the coating layer contains a component represented by the general formula (A-1) and a component represented by the general formula (A-2), the content of the coating layer in the composite negative electrode active material is smaller than when only one of the components represented by the general formula (A-1) and the component represented by the general formula (A-2) is contained, thereby achieving excellent dispersion stability. 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.

[0060] (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 constituting a coating layer. The method for producing the composite negative electrode active material is not particularly limited, as long as the content of the coating layer can be greater than 5.0% by mass. For example, the composite negative electrode active material of the present invention can be produced by mixing the negative electrode active material and the polymer constituting the coating layer in a solvent, physically or chemically adsorbing the polymer constituting 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. That is, the content of the coating layer can be increased by subjecting the spray-dried composite negative electrode active material to further spray drying. By using the above production method, a coating layer can be formed on the surface of the negative electrode active material so that the content of the coating layer in the composite negative electrode active material exceeds 5.0% by mass. Examples of methods for mixing the negative electrode active material and the polymer constituting the coating layer in a solvent include preparing a solution in which the polymer constituting the coating layer is dissolved in a solvent, and then mixing the negative electrode active material in the resulting solution. Examples of the solvent include water, tetrahydrofuran, and a mixture thereof. The negative electrode active material and the polymer constituting the coating layer are preferably mixed in the solvent by stirring at room temperature (25° C.) to 40° C. for 0.5 to 3 hours.

[0061] When preparing a composite negative electrode active material having two or more types of polymers constituting the coating layer, the above-mentioned step I 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 by mixing two or more types of polymers constituting the coating layer. It is also preferable to perform the above step I for each type of polymer constituting the coating layer. For example, when preparing a composite negative electrode active material having two types of polymers constituting the coating layer, namely, one type of polymer containing a component represented by the above general formula (A-1) and one type of polymer containing a component represented by the above general formula (A-2), first, the above step I is performed using a polymer containing a component represented by the above 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 the above general formula (A-1). Thereafter, using a polymer containing a component represented by the general formula (A-2) described above, and using the composite negative electrode active material A-1 obtained in the above step I instead of the negative electrode active material, 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) described above 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) described above, step I using a polymer containing a component represented by the general formula (A-2) described above may be performed, or after performing step I using a polymer containing a component represented by the general formula (A-2) described above, step I using a polymer containing a component represented by the general formula (A-1) described above may be performed. In the present invention, after performing step I using a polymer containing a component represented by the general formula (A-1) described above, it is preferable to perform step I using a polymer containing a component represented by the general formula (A-2) described above.

[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, and 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 is 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, an ethylenically unsaturated carboxylic acid amide component, and a vinyl fluoride monomer component. Preferably, the polymer particles contain at least one of the conjugated diene component, the aromatic vinyl monomer component, the ethylenically unsaturated carboxylic acid component, the cyano group-containing ethylenic monomer component, the ethylenically unsaturated carboxylic acid ester component, and the ethylenically unsaturated carboxylic acid amide 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); the term "ethylenically unsaturated carboxylic acid amide component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one) and a carboxylic acid amide moiety (amidated carboxy group) (preferably one); and the term "vinyl fluoride monomer component" refers to a component derived from ethylene having 1 to 4 (preferably 2) fluorine atoms. The above "carbon-carbon double bond" does not include carbon-carbon double bonds in aromatic rings.

[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 ethylenically unsaturated carboxylic acid esters from which ethylenically unsaturated carboxylic acid ester components are 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 ethylenically unsaturated carboxylic acid amides from which ethylenically unsaturated carboxylic acid amide components are derived include (meth)acrylamide, N-methylol (meth)acrylamide, and N,N-dimethyl (meth)acrylamide. Examples of fluorinated vinyl monomers from which fluorinated vinyl monomer components are 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. The acrylic polymer may further contain at least one component selected from the conjugated diene component, aromatic vinyl monomer component, cyano group-containing ethylenic monomer component, and ethylenically unsaturated carboxylic acid amide 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 in 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 substituted with ether groups (etherified) 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, it is preferable to mix at least one of a conductive additive, a binder, and a water-soluble polymer in addition to the above, and further optionally other additives. 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 thereof 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] [Method for Manufacturing Negative Electrode Sheet] The negative electrode sheet of the present invention can be obtained by forming a negative electrode active material layer using the negative electrode 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 another layer) 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. Regarding the method for manufacturing the negative electrode sheet of the present invention, any conventional method can be appropriately adopted, except for forming the negative electrode active material layer using the negative electrode slurry of the present invention. Furthermore, the secondary battery of the present invention can be obtained by incorporating the negative electrode sheet obtained by the above-described method for manufacturing a negative electrode sheet into the negative electrode of the secondary battery.

[0087] [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.

[0088] 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 non-aqueous electrolyte secondary batteries and broadly encompasses secondary batteries in general.

[0089] 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. Typically, 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 the above-described configuration, but with only a negative electrode active material layer as the electrode active material layer, and this 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 functions as a secondary battery upon charge and discharge by filling the gap between the positive electrode and the negative electrode with a nonaqueous electrolyte.

[0090] 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.

[0091] 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.

[0092] (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 may be a transition metal oxide, an organic substance, a compound containing an element such as sulfur that can be composited with Li, a composite of sulfur and a metal, or the like. Among these, it is preferred to use a lithium-containing transition metal oxide as the positive electrode active material, and a transition metal element M ａ A transition metal oxide containing at least one element selected from Co, Ni, Fe, Mn, Cu, and V is more preferred. 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.

[0093] (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 O ２(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 CoSiO ４In the present invention, transition metal oxides having a layered rock salt structure (MA) are preferred, and LCO or NMC are more preferred.

[0094] 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. To obtain a predetermined particle size of the positive electrode active material, it may be prepared by a conventional method using a grinder or classifier. The above-mentioned method for preparing a predetermined particle size of the negative electrode active material 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 by the method described above for the negative electrode active material is used.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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).

[0101] 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.

[0102] 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 manufacturing method of 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 manufacturing 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.

[0103] (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.

[0104] (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.

[0105] (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

[0106] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0107] 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.

[0108] 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.

[0109] (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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] [Preparation of Silicon Oxide Doped with Lithium and Carbon Coating] Silicon oxide (LiSiOC) doped with lithium and carbon coating 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 coating was formed by performing 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 (SiOC). After the temperature reached room temperature, the temperature was lowered, and the powder was recovered. The carbon-coated silicon oxide was then modified by doping with lithium using a redox method. The carbon-coated silicon oxide was first immersed in a solution (Solution A) in which lithium flakes and naphthalene were dissolved in tetrahydrofuran (hereinafter referred to as THF). Solution A was prepared by dissolving naphthalene in 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 the carbon-coated silicon oxide was immersed was 20°C, and the immersion time was 20 hours. The solid matter was then filtered off. The carbon-coated silicon oxide was doped with lithium through the above process. 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 was modified to obtain silicon oxide (LiSiOC) that was both lithium-doped and carbon-coated.The carbon element content was 3 mass %, and the average particle size (volume-based median diameter D50) of the LiSiOC particles was 6.7 μm.

[0114] [Synthesis of Coating Layer Constituent Polymers] As coating layer constituent polymers, the homopolymers shown in the A-1 and A-2 columns of Table 1 below and the copolymer shown in the A-3 column of Table 1 below were synthesized as follows. Tables 1A to 1E are collectively referred to as Table 1.

[0115] (Synthesis of homopolymers listed in the A-1 column of Table 1) (1) Polyacrylamide used in 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., carboxyl group-containing water-soluble azo polymerization initiator) were mixed and stirred 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 valve. 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. (2) Homopolymers other than No. 101 Various homopolymers listed in the column A-1 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 the polyacrylamide described above.

[0116] (Synthesis of homopolymers listed in the A-2 column of Table 1) (1) Polystyrene No. c101 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, and the mixture was stirred and mixed at room temperature. Nitrogen gas was introduced at a flow rate of 200 mL / min for 30 minutes, and then 0.0046 g of V-601 (trade name, 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. (2) Polystyrene No. c101 Homopolymers other than 101 In the synthesis of the polystyrene described above, the type of monomer, the amount of polymerization initiator, the type of solvent, etc. were adjusted to synthesize various homopolymers listed in the column A-2 of Table 1.

[0117] (Synthesis of copolymers listed in column A-3 of Table 1) (1) No. 152 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 added to 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. After introducing nitrogen gas at a flow rate of 200 mL / min for 30 minutes, 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. As the reaction progressed, precipitation of a copolymer was confirmed in the reaction solution. After polymerization, the mixture was cooled to room temperature, and the precipitated copolymer was filtered, washed twice with dioxane, washed once with distilled water, and dried under reduced pressure to obtain a copolymer of acrylamide and styrene. The weight average molecular weight was 198,000. (2) Copolymers other than No. 152 Various copolymers shown in the column A-3 of Table 1 were synthesized by adjusting the type of monomers, composition ratio, amount of polymerization initiator, type of solvent, etc. in the synthesis of the above styrene and acrylamide copolymer.

[0118] <1> Preparation of Composite Negative Electrode Active Materials Composite negative electrode active materials Nos. 101 to 157, c101 to c130, c134 to c137, and c141 to c143 shown in Table 1 below were prepared using the coating layer-constituting polymers and negative electrode active materials shown in Table 1 below as follows.

[0119] (Preparation of Composite Negative Electrode Active Materials Described in Tables 1A, 1B, 1D, and 1E: When the Polymer Constituting the Coating Layer is Water-Soluble) (1) Preparation of Composite Negative Electrode Active Material No. 101 0.5 g of polyacrylamide described in No. 101 of Table 1 was dissolved in 60 g of distilled water to prepare Solution C. Graphite (trade name: MAG-D, manufactured by Resonac Co., Ltd. (formerly Showa Denko Materials Co., Ltd.), average particle size: 21 μm, specific surface area: 4 m) was added to the prepared Solution C. ２ 6 g of a polymer (100% by weight, 100% by weight, 100% by weight) was added to the dispersion and stirred at room temperature for 1 hour. After stirring, the resulting dispersion was spray-dried using a spray dryer (Mini Spray Dryer B-290 (trade name), manufactured by BUCHI) to produce composite negative electrode active material No. 101. The content (mass) of the coating layer was controlled by the number of spray-drying treatments. (2) Preparation of Composite Negative Electrode Active Materials Other than Composite Negative Electrode Active Material No. 101 In the preparation of the above composite negative electrode active material No. 101, 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, 1B, 1D, and 1E.

[0120] (Preparation of each composite negative electrode active material described in Tables 1A, 1B, 1D, and 1E: Cases in which the polymer constituting the coating layer is not soluble in water) (1) Preparation of composite negative electrode active material No. c101 0.30 g of polystyrene described in No. c101 of Table 1 was dissolved in 60 g of tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare solution D. Graphite (trade name: MAG-D, manufactured by Resonac Co., Ltd. (formerly Showa Denko Materials Co., Ltd.), average particle size: 21 μm, specific surface area: 4 m) was added to the prepared solution D. ２6 g of a soluble polymer (100%) (1 / g) was added 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)), to produce composite negative electrode active material No. c101. The mass of the coating layer was controlled by the number of spray-drying treatments. (2) Preparation of Composite Negative Electrode Active Materials Other than Composite Negative Electrode Active Material No. c101 In the preparation of the above composite negative electrode active material No. c101, 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, 1B, 1D, and 1E.

[0121] (Preparation of Composite Negative Electrode Active Materials Described in Table 1C) (1) Preparation of Composite Negative Electrode Active Material No. 131 0.5 g of polyacrylamide No. 131 in Table 1C was dissolved in 60 g of distilled water to prepare Solution E. Graphite (trade name: MAG-D, manufactured by Resonac Co., Ltd. (formerly Showa Denko Materials Co., Ltd.), average particle size: 21 μm, specific surface area: 4 m) was added to the prepared Solution E. ２6 g of polystyrene (No. 131a) was added to the dispersion 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 polyacrylamide-coated composite negative electrode active material No. 131a. The mass of the coating layer was controlled by the number of spray-drying treatments. Solution F was prepared by dissolving 0.30 g of polystyrene (No. 131 in Table 1) in 60 g of tetrahydrofuran (FUJIFILM Wako Pure Chemical Industries, Ltd.). 6 g of composite negative electrode active material No. 131a 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)). This produced composite negative electrode active material No. 131 coated with polyacrylamide and polystyrene. The mass of the coating layer was controlled by the number of spray-drying treatments. (2) Preparation of Composite Negative Electrode Active Materials Other than Composite Negative Electrode Active Material No. 131 In the preparation of the above composite negative electrode active material No. 131, 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 produce each of the composite negative electrode active materials listed in Table 1C. Note that, with regard to the mixing of the homopolymer used to form the coating layer, in the preparation of all composite negative electrode active materials, coating with the homopolymer listed in column A-1 was first performed, followed by coating with the homopolymer listed in column A-2.

[0122] Here, composite negative electrode active material Nos. 101 to 157 shown in Table 1 below are composite negative electrode active materials of the present invention, and composite negative electrode active material Nos. c101 to c130, c134 to c137, and c141 to c143 are composite negative electrode active materials for comparison.

[0123] [1] 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 mass W at room temperature was calculated. ｒ Mass W at room temperature ｒ Mass 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.

[0124] <2> Preparation of Negative Electrode Slurry, Negative Electrode Sheet, and Nonaqueous Electrolyte Secondary Battery (Coin Battery) (Preparation of No. 101 Negative Electrode Slurry, Negative Electrode Sheet, and Coin Battery) (1) Preparation of Negative Electrode Slurry Into a 60 mL ointment container (manufactured by Umano Chemical Co., Ltd.), 4.5 g of composite negative electrode active material No. 101, 0.15 g of acetylene black (trade name: Denka Black, manufactured by Denka Co., Ltd.), 1.5 g of a carboxymethyl cellulose (CMC) aqueous solution (solid content: 0.15 g), and 1.79 g of distilled water were added, and the mixture was dispersed for 10 minutes at 2000 rpm (rotations per minute) using a Mixer (manufactured by THINKY Corporation). To the resulting dispersion, 0.4 g (solid content: 0.2 g) of an aqueous dispersion of polymer particles (synthesized according to the synthesis example of copolymer latex (B-2) described in paragraph 0044 of JP 2011-171181 A, corresponding to the aqueous dispersion of the binder in the present invention) was added, and the mixture was dispersed at 2000 rpm for 2 minutes using a mixer (manufactured by THINKY Corporation) to prepare a negative electrode slurry. In the resulting negative electrode slurry No. 101, the mass ratio of the solid components was: composite negative electrode active material No. 101: acetylene black: CMC: polymer particles = 90:3:3:4. (2) Preparation of a negative electrode sheet The resulting negative electrode slurry was applied to a 20 μm-thick copper foil using an applicator and dried at 80 ° C for 1 hour. The sheet was then pressed using a press and dried in a vacuum at 150°C for 6 hours to obtain a negative electrode sheet No. 101 with a negative electrode active material layer thickness of 25 μm. (3) Fabrication of Secondary Battery The negative electrode sheet was cut into a disk shape with a diameter of 13.0 mm and used as a negative electrode. A lithium foil (thickness 50 μm, diameter 14.5 mm) and a polypropylene separator (thickness 25 μm, diameter 16.0 mm) were stacked in this order, and LiPF ６ The separator was impregnated with 200 μL of an ethylene carbonate / ethyl methyl carbonate (volume ratio 1:2) electrolyte solution containing 1 M of ethylene carbonate. An additional 200 μL of the electrolyte solution was added to the separator, and the negative electrode was placed on top of the separator so that the active material layer surface was in contact with the separator. A 2032-type coin case was then crimped to prepare coin battery No. 101 (a laminate consisting of lithium foil, separator, negative electrode active material layer, and copper foil), which was a half-cell for evaluation.

[0125] (Preparation of Negative Electrode Slurries, Negative Electrode Sheets, and Coin Batteries Nos. 102 to 157, c101 to c130, c134 to c137, and c141 to c143) Negative electrode slurries, negative electrode sheets, and coin batteries Nos. 102 to 157, c101 to c130, c134 to c137, and c141 to c143 were prepared in the same manner as in the preparation of the negative electrode slurry, negative electrode sheet, and coin battery of Battery No. 101, except that composite negative electrode active material No. 101 was replaced with composite negative electrode active material Nos. 102 to 157, c101 to c130, c134 to c137, and c141 to c143.

[0126] (Preparation of negative electrode slurries, negative electrode sheets, and coin batteries Nos. c131 to c133) Furthermore, negative electrode slurries, negative electrode sheets, and coin batteries Nos. c131 to c133 were prepared in the same manner as in the preparation of the negative electrode slurry, negative electrode sheet, and coin battery No. 101 above, except that the negative electrode active materials Nos. c131 to c133 in Table 1 below were used instead of composite negative electrode active material No. 101. In Nos. c131 to c133, the negative electrode active materials (graphite, SiOC, and LiSiOC) were all used without being coated with a polymer.

[0127] (Preparation of negative electrode slurries, negative electrode sheets, and coin batteries No. c138 to c140) In the preparation of the negative electrode slurry, negative electrode sheet, and coin battery No. 101 above, the negative electrode active materials No. c138 to c140 in Table 1 below were used instead of composite negative electrode active material No. 101, and when adding the negative electrode active material in the above (1) preparation of the negative electrode slurry, 5.5 g of polyacrylamide shown in Table 1 was further added, and the blending ratio was adjusted so that the content ratio of each solid content in the negative electrode slurry was the following ratio on a mass basis. Negative electrode slurries, negative electrode sheets, and coin batteries No. c138 to c140 were prepared in the same manner. In No. c138 to c140, the negative electrode active material was not coated with a polymer, and the negative electrode active material and the polymer were used as they were in the preparation of the negative electrode slurry. The obtained negative electrode slurry No. In c138 to c140, the mass ratio of the solid contents was negative electrode active material: acetylene black: CMC: polymer particles: polyacrylamide = 84.5:3:3:4:5.5.

[0128] The negative electrode slurry, negative electrode sheet, and secondary battery prepared as described above were evaluated as follows. The evaluation results are shown in Table 1.

[0129] [2] Slurry Stability In the above <2> (1) Preparation of Negative Electrode Slurry, a negative electrode slurry I was prepared immediately after preparation, and a negative electrode slurry II was prepared by allowing the immediately prepared negative electrode slurry I to stand for one day. The storage modulus I of the negative electrode slurry I at a shear strain of 0.01% and the storage modulus II of the negative electrode slurry II at a shear strain of 0.01% were measured under the conditions described below (Measurement of Storage Modulus). Then, the ratio of the storage modulus II of the negative electrode slurry II at a shear strain of 0.01% to the storage modulus I of the negative electrode slurry I at a shear strain of 0.01% (i.e., [Storage Modulus II] / [Storage Modulus I]) was obtained. The obtained ratio was applied to the following evaluation criteria to evaluate the slurry stability. A smaller storage modulus ratio indicates better slurry stability. (Measurement of storage modulus) The storage modulus of each of negative electrode slurries I and II at a shear strain of 0.01% was measured using a rheometer (trade name: Modular Compact Rheometer MCR102, manufactured by Anton Paar) under conditions of 25°C, 10 rad / s, and a rheometer jig PP50 (parallel plate, diameter 50 mm). Note that, for negative electrode slurry II, the storage modulus was measured after re-stirring at 500 rpm for 1 minute using a planetary centrifugal mixer (trade name: Awatori Rentaro ARE-310, manufactured by THINKY Corporation). - Evaluation criteria - 8: Less than 1.010 7: 1.010 or more, less than 1.012 6: 1.012 or more, less than 1.014 5: 1.014 or more, less than 1.016 4: 1.016 or more, less than 1.018 3: 1.018 or more, less than 1.020 2: 1.020 or more, less than 1.040 1: 1.040 or more

[0130] [3] Initial Battery Capacity Retention Rate The effect of the coating layer on battery capacity was confirmed as follows, using the initial battery capacity retention rate as an index. The initial battery capacity of each coin battery obtained by fabricating the nonaqueous electrolyte secondary battery (coin battery) described in <2> above was measured under the following conditions. Secondary batteries Nos. c131 to c133, which were fabricated using a negative electrode slurry containing a negative electrode active material without a coating layer, were designated as secondary batteries I. Secondary batteries Nos. 101 to 157, c101 to c130, and c134 to c143, which were fabricated using a negative electrode slurry containing a composite negative electrode active material or a negative electrode slurry containing a polymer and a negative electrode active material, were designated as secondary batteries II. For secondary batteries I and II, which had the same type and amount of negative electrode active material, the ratio of the initial battery capacity of secondary battery II to the initial battery capacity of secondary battery I (i.e., [initial battery capacity of secondary battery II] / [initial battery capacity of secondary battery I]) was calculated. The obtained ratio was applied to the following evaluation criteria to evaluate the retention rate of the initial battery capacity. The results are shown in the "Initial Battery Capacity" column in the table below. When evaluating secondary batteries No. c131 to c133 containing a negative electrode active material without a coating layer, the above ratio was calculated for secondary battery II as well as secondary batteries No. c131 to c133. Therefore, the retention rate of the initial battery capacity for these comparative examples is 1.00. (Measurement of Initial Battery Capacity) The initial battery capacity (initial discharge capacity) of each secondary battery I and II was measured as follows using a charge / discharge evaluation device: TOSCAT-3000 (trade name, manufactured by Toyo Systems Co., Ltd.). Specifically, charging was performed at a C rate (capacity rate) of 0.2 C (a rate at which the battery is fully charged in 5 hours) until the battery voltage reached 0.02 V. Discharging was performed at a C rate of 0.2 C (a rate at which the battery is fully discharged in 5 hours) until the battery voltage reached 1.5 V. This one charge and one discharge constitute one charge / discharge cycle, and three charge / discharge cycles were repeated to initialize the secondary battery. The secondary battery after initialization was charged at 0.5 C until it reached 0.02 V, and then discharged at 0.5 C until it reached 1.5 V, and the discharge capacity was recorded as "initial battery capacity." All charge / discharge operations were performed at 25°C. - Evaluation criteria - 5: 0.97 or more 4: 0.95 or more, less than 0.97 3: 0.93 or more, less than 0.95 2: 0.91 or more, less than 0.93 1: Less than 0.91

[0131]

[0132]

[0133]

[0134]

[0135]

[0136] <Notes for the table> (Coating layer constituent polymers) PAAm: polyacrylamide PDAAm: polydimethylacrylamide PTMBAAm: poly1,1,3,3-tetramethylbutylacrylamide PDEAAm: polydiethylacrylamide PSt: polystyrene PAANa: sodium polyacrylate (50% or more of the acrylic acid-derived components in the homopolymer are neutralized to form sodium acrylate-derived components) PVA: polyvinyl alcohol SBR: styrene-butadiene rubber PAA: polyacrylic acid Content: This refers to the content of the constituent 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 AAm / St = 90 / 10: copolymer consisting of 90% by mass of acrylamide-derived components and 10% by mass of a styrene-derived components AAm / St = 50 / 50: copolymer consisting of 50% by mass of acrylamide-derived components and 50% by mass of a styrene-derived components AAm / St = 10 / 90: copolymer consisting of 10% by mass of acrylamide-derived components and 90% by mass of a styrene-derived components AANa / St = 50 / 50: copolymer consisting of 50% by mass of sodium acrylate-derived components and 50% by mass of styrene-derived components (50% or more of the acrylic acid-derived components in the copolymer are neutralized to form sodium acrylate-derived components) Note that in the copolymers listed in Table 1D, the content of each component (excluding components derived from the polymerization initiator) in the coating layer corresponds to the content of each component (excluding components derived from the polymerization initiator) constituting the copolymer. (Negative electrode active material) Graphite: MAG-D (trade name, manufactured by Resonac Co., Ltd. (formerly Showa Denko Materials Co., Ltd.), average particle size: 21 μm, specific surface area: 4 m ２ / g) 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, specific surface area: 2.6 m ２ / g) LiSiOC: silicon oxide prepared above that was both lithium-doped and carbon-coated (carbon element content: 3 mass%, average particle size: 6.7 μm)

[0137] A "-" in the "Coating Layer Constituent Polymer" column indicates that the component is not contained. The columns for graphite, SiOC, and LiSiOC indicate the proportion of each negative electrode active material in the total negative electrode active material, expressed in mass %. Coating layer content: This refers to the content (mass %) of the coating layer in the composite negative electrode active material (100 mass %), calculated using the measurement method described above. A "-" in the "Coating Layer Content" column indicates that the negative electrode active material is used without being coated. Note that, as described above, Nos. c138 to c140 are examples in which the negative electrode active material and the polymer were used directly to prepare the negative electrode slurry without coating the negative electrode active material with a polymer. Therefore, the "Coating Layer Constituent Polymer" column for Nos. c138 to c140 indicates polyacrylamide, which corresponds to a polymer containing a component represented by general formula (A-1), that was directly added during the preparation of the negative electrode slurry, rather than the polymer that constitutes the coating layer of the negative electrode active material as the composite negative electrode active material. Further, in the column "Content of coating layer" of Nos. c138 to c140, instead of the content of the coating layer calculated by the above-mentioned measurement method, the amount of polyacrylamide added when preparing the negative electrode slurry is shown relative to the total amount of the negative electrode active material and polyacrylamide, and the unit is % by mass.

[0138] As is clear from Table 1, composite negative electrode active materials Nos. c101 to c130, c134 to c137, and c141 to c143, which do not satisfy the requirements of the present invention, all had storage modulus ratios of 1.018 or more when used as negative electrode slurries, resulting in poor slurry stability, or when used as secondary batteries, had initial discharge capacity retention rates of less than 0.93, resulting in insufficient suppression of the decrease in battery capacity due to the coating layer. In particular, composite negative electrode active materials in which the polymer constituting the coating layer is a polymer (polystyrene (PSt), sodium polyacrylate (PAANa), polyvinyl alcohol (PVA), and polyacrylic acid (PAA)) that does not contain a component represented by general formula (A-1) had slurry stability comparable to or slightly higher than negative electrode active materials Nos. c131 to c133 that did not have a coating layer, but were unable to sufficiently suppress the decrease in battery capacity when used as secondary batteries. Furthermore, negative electrode active materials Nos. All of the composite negative electrode active materials c131 to c133 had poor slurry stability when used as a negative electrode slurry. Furthermore, when the negative electrode active material was mixed without being coated with a polymer containing the component represented by general formula (A-1) (Nos. c138 to c140), the decrease in battery capacity could not be sufficiently suppressed when used as a secondary battery. In contrast, all of the composite negative electrode active materials Nos. 101 to 157 of the present invention had excellent slurry stability when used as a negative electrode slurry. Furthermore, the initial battery capacity of the secondary batteries produced using the composite negative electrode active materials Nos. 101 to 157 of the present invention was sufficiently suppressed compared to the initial battery capacity of secondary batteries produced using a negative electrode active material without a coating layer. It can be seen that the use of the composite negative electrode active material of the present invention makes it possible to obtain a negative electrode slurry with excellent dispersion stability, and to obtain secondary batteries that contain a large amount of coating layer while suppressing the decrease in battery capacity.

[0139] 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.

[0140] This application claims priority based on Japanese Patent Application No. 2023-189428, filed on November 6, 2023, the contents of which are incorporated herein by reference as part of the present specification.

[0141] 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

1. 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 coating a surface of the negative electrode active material, wherein the coating layer contains a polymer containing a component represented by the following general formula (A-1), and the content of the coating layer in the composite negative electrode active material is more than 5.0 mass%. In the above formula, R １１ ~R １３ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; 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. * represents a bonding site for incorporation into the main chain of the polymer.

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

3. The composite negative electrode active material according to claim 2, wherein the coating layer has a content of 5.1 to 15.0 mass %.

4. The composite negative electrode active material according to claim 3, wherein the polymer containing the component represented by the general formula (A-1) has a weight average molecular weight of 10,000 or more.

5. The composite negative electrode active material according to claim 1, wherein the coating layer contains a component represented by the general formula (A-1) and a component represented by the following general formula (A-2): In the above formula, R ２１ ~R ２３ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. * represents a bonding site for incorporation into the main chain of the polymer.

6. The composite negative electrode active material according to claim 5, wherein in the coating layer, a mass ratio of the content of the component represented by general formula (A-1) to the content of the component represented by general formula (A-2) is 1 / 99 to 99 / 1.

7. The composite negative electrode active material according to claim 5, wherein the polymer containing the component represented by general formula (A-1) contains the component represented by general formula (A-2).

8. The composite negative electrode active material according to claim 5, wherein the coating layer contains a polymer containing a component represented by general formula (A-2) in addition to the polymer containing a component represented by general formula (A-1).

9. The composite negative electrode active material according to claim 8, wherein the polymer containing the component represented by the general formula (A-2) has a weight average molecular weight of 10,000 or more.

10. The composite anode active material of claim 1, wherein the anode active material comprises a silicon-based active material.

11. A slurry for a secondary battery negative electrode, comprising the composite negative electrode active material according to any one of claims 1 to 10 and a dispersion medium.

12. A negative electrode sheet having a negative electrode active material layer formed using the slurry for secondary battery negative electrodes according to claim 11.

13. A secondary battery comprising a negative electrode active material layer formed using the slurry for a secondary battery negative electrode according to claim 11.

14. A method for producing a negative electrode sheet, comprising forming a negative electrode active material layer using the slurry for secondary battery negative electrodes according to claim 11.

15. A method for producing a secondary battery, comprising incorporating the negative electrode sheet obtained by the method according to claim 14 as the negative electrode of the secondary battery.