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

Abstract

Provided are: a composite negative electrode active material which has a negative electrode active material and a coating layer that covers the surface of the negative electrode active material and is composed of a polymer containing constituent components of general formula (A-1) and / or (A-2), wherein the content of the coating layer in the composite negative electrode active material is 0.05-5% by mass; a composition for secondary battery negative electrodes; a negative electrode sheet and a secondary battery; and methods for manufacturing a negative electrode sheet and a secondary battery.　In the formulae, R11 to R13 and R21 to R23 each represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, R14 and R15 each represent a hydrogen atom, an alkyl group having 1 to 16 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and * indicates the binding site to be incorporated into the main chain of the polymer.

Description

Composite negative electrode active material, composition 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 composition 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 battery generally has a negative electrode active material layer. This negative electrode active material layer contains electrode active material particles capable of inserting (preferably occluding) 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 desorption. ２ It is described that by using a silicon compound whose component part has been previously modified to another Li compound, it is possible to reduce the irreversible capacity that occurs during charging, and that by providing a coating layer made of an organic polymer on the surface of the silicon compound, it is possible to increase the battery capacity.

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

[0005] As a result of further investigations, the inventors have found that in addition to the cycle performance problem caused by the expansion and contraction range during charge and discharge described above, the following problems also exist. Specifically, when a silicon-based active material is mixed with graphite to form a composition (slurry), the silicon-based active material settles faster than the graphite, making the composition viscosity (slurry viscosity) prone to change over time (a dispersion stability problem). Furthermore, when the slurry is stored for a period of time after preparation, it becomes difficult to apply a negative electrode sheet with few defects (a coatability problem). As described above, negative electrode compositions (negative electrode slurries) obtained by mixing a silicon-based active material with graphite tend to have poor dispersion stability and poor coatability. For example, even the use of a negative electrode material for nonaqueous electrolyte secondary batteries having a coating layer made of polyacrylic acid on the surface of the silicon-based active material, as specifically described in Patent Document 1, does not sufficiently solve the above problems.

[0006] An object of the present invention is to provide a composite negative electrode active material that can be used as a component of a secondary battery negative electrode composition to impart excellent dispersion stability and coatability to the secondary battery negative electrode composition. Another object of the present invention is to provide a secondary battery negative electrode composition, 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] As a result of extensive investigations, the present inventors have found that a secondary battery negative electrode composition having excellent dispersion stability and coatability can be obtained by using a composite negative electrode active material in which a specific amount of a polymer containing an acrylamide-based component and / or a styrene-based component is coated on the surface of the negative electrode active material. Based on these findings, the present invention has been completed through further investigations.

[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 is made of a polymer containing a constituent component represented by the following general formula (A-1) and / or a constituent component represented by the following general formula (A-2), and the content of the coating layer in the composite negative electrode active material is 0.05 to 5 mass %. In the above formula, R １１ ~R １３ and R ２１ ~R ２３ 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 mass% or more. <3> The composite negative electrode active material according to <1> or <2>, wherein the polymer has a weight-average molecular weight of 10,000 or more. <4> The composite negative electrode active material according to any one of <1> to <3>, wherein the negative electrode active material contains a silicon-based active material. <5> A composition for a secondary battery negative electrode, comprising the composite negative electrode active material according to any one of <1> to <4> and a dispersion medium. <6> A negative electrode sheet having a layer formed using the composition for a secondary battery negative electrode according to <5>. <7> A secondary battery including a negative electrode active material layer formed using the composition for a secondary battery negative electrode according to <5>. <8> A method for producing a negative electrode sheet, comprising forming a negative electrode active material layer using the composition for a secondary battery negative electrode according to <5>. <9> A method for producing a secondary battery, comprising incorporating the negative electrode sheet obtained by the production method according to <8> as a negative electrode of the secondary battery.

[0009] By incorporating the composite negative electrode active material of the present invention into a secondary battery negative electrode composition, excellent dispersion stability and coatability can be imparted to the secondary battery negative electrode composition. Furthermore, the secondary battery negative electrode composition of the present invention has excellent dispersion stability and coatability. Therefore, a negative electrode sheet produced using the secondary battery negative electrode composition of the present invention has few defects, and a secondary battery incorporating this negative electrode sheet can achieve excellent battery capacity. According to the method for producing a negative electrode sheet of the present invention, the above-mentioned negative electrode sheet of the present invention can be obtained. Furthermore, according to the method for producing a secondary battery of the present invention, the above-mentioned secondary battery of the present invention can be obtained.

[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" in water at 20°C 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 Group 2 of the periodic table, and a coating layer that coats the surface of the negative electrode active material, wherein the coating layer is made of a polymer containing a constituent component represented by general formula (A-1) described below and / or a constituent component represented by general formula (A-2) described below, and the content of the coating layer in the composite negative electrode active material is 0.05 to 5 mass %.

[0013] The composite negative electrode active material of the present invention, when used as a component of a secondary battery negative electrode composition due to the above-described configuration, can achieve excellent dispersion stability and coatability. While the reason for this is unclear, it is presumed as follows: The surface of the negative electrode active material has hydrophobic and hydrophilic regions. The coating layer in the composite negative electrode active material of the present invention is composed of a polymer containing a hydrophilic component represented by the general formula (A-1) described below and / or a hydrophobic component represented by the general formula (A-2) described below, and therefore exhibits good affinity for at least one of the hydrophobic and hydrophilic regions on the surface of the negative electrode active material. By using a composite negative electrode active material in which the surface of the negative electrode active material is coated with a coating layer in a content of 0.05 to 5 mass %, the charge state of the particle surfaces of the negative electrode active material in the secondary battery negative electrode composition is adjusted, which is thought to contribute to dispersion stability. Furthermore, since the composition for secondary battery negative electrodes containing the composite negative electrode active material of the present invention has excellent dispersion stability, the composite negative electrode active material can maintain sufficiently high dispersibility even when stored for a period of time after preparation, making it possible to produce an electrode sheet with few defects.It is believed that if this negative electrode sheet is used as the negative electrode layer of a secondary battery, a secondary battery exhibiting excellent battery capacity can be produced.

[0014] A known technique involves mixing a negative electrode active material with a polymer binder during the preparation of a negative electrode composition to improve the adhesion between particles of the negative electrode active material. The negative electrode composition 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 c18 to c20 and c33 to c35 in the Examples described below, typical binder-adsorbed negative electrode active materials lack at least one of dispersion stability and coatability.

[0015] In the composite negative electrode active material of the present invention, the polymer containing the constituent component represented by the following general formula (A-1) and / or the constituent component represented by the following general formula (A-2) 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, with respect to the negative electrode active material, 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 exhibited.

[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 Si ２ O ３ , Sb ２ O ５ , Bi ２ O ３ , Bi ２ O４ , 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. 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 ３Examples 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 the dispersion stability and coatability 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 the desired particle size, it can be prepared by a conventional method using a grinder or classifier. For example, a mortar, ball mill, sand mill, vibration ball mill, satellite ball mill, planetary ball mill, swirling airflow jet mill, or sieve is preferably used. Wet grinding in the presence of water or an organic solvent such as methanol can also be performed during grinding. Classification is preferred to achieve the desired particle size. The classification method is not particularly limited, and sieves, air classifiers, etc. can be used as desired. Classification can be performed using either dry or wet methods. When using commercially available negative electrode active materials, the average particle size of the negative electrode active material is determined from the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is unavailable or when a synthesized negative electrode active material is used, the negative electrode active material is dispersed in water, and the average particle size (volume-based median diameter D50 in water) obtained by measuring the particle size distribution using a laser diffraction / scattering particle size distribution measuring device (for example, Particle LA-960V2 (product name) manufactured by HORIBA Corporation) is used.

[0031] The negative electrode active material may be used alone or in combination of two or more. The dispersion stability and coatability effects of the composite negative electrode active material of the present invention are 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 silicon-based active material has a specific gravity of 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 rate, and slurries containing silicon-based active materials and graphite tend to have poor dispersion stability. However, by providing a composite negative electrode active material of the present invention with a coating layer, as described below, the dispersion stability and coatability of the slurry can be more effectively improved. 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 is used, using a specific surface area / pore distribution measuring device (for example, BELSORP MINI (trade name) manufactured by Microtrac-Bell). 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 95 to 99.95% by mass, preferably 95 to 99.9% by mass, more preferably 95 to 99.8% by mass, and even more preferably 95 to 99.7% by mass. When the polymer constituting the coating layer contains only one of the constituent component represented by the general formula (A-1) and the constituent component represented by the general formula (A-2), the content of the negative electrode active material in the composite negative electrode active material is particularly preferably 95 to 99% by mass, and particularly preferably 95 to 98% by mass.

[0034] In the secondary battery of the present invention described below, 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 the battery can be used in combination. When the negative electrode active material layer is formed by charging the 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 the 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 is composed of a polymer containing a component represented by the following general formula (A-1) and / or a component represented by the following general formula (A-2) (hereinafter referred to as the "polymer constituting the coating layer"). The polymer constituting the coating layer may be either a polymer containing a component represented by the following general formula (A-1) or a polymer containing a component represented by the following general formula (A-2), or a mixture of both of these polymers. It may also be a copolymer containing the component represented by the following general formula (A-1) and the component represented by the following general formula (A-2) as copolymerization components. These polymers may also be mixed and used. In the present invention, the term "polymer containing a component represented by general formula (A-1)" refers to a polymer that does not contain a component represented by the following general formula (A-2). This polymer may be a homopolymer or a copolymer, and is preferably a homopolymer. In the present invention, the term "polymer containing a component represented by general formula (A-2)" refers to a polymer that does not contain a component represented by the following general formula (A-1). This polymer may be a homopolymer or a copolymer, and is preferably a homopolymer. 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 a constituent component represented by the following general formula (A-1) and / or a constituent component represented by the following general formula (A-2) is incorporated into the main chain of the polymer by *. The polymer constituting the coating layer will be described below.

[0036] (Polymer constituting the coating layer)

[0037] In the above formula, R １１ ~R １３ and R ２１ ~R ２３ 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 , R １２ , R ２１ and R ２２ is preferably a hydrogen atom. １３ and R ２３ is preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. １４ and R １５ is preferably a hydrogen atom or an alkyl group having 1 to 16 carbon atoms. １４ and R １５ The alkyl group having 1 to 16 carbon atoms that can be taken as R may be linear or branched. １４ and R 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] From the viewpoint of further improving dispersion stability and coatability, the polymer constituting the coating layer preferably contains at least a polymer containing at least a component represented by the general formula (A-1) above (this polymer may contain a component represented by the general formula (A-2) above in addition to the component represented by the general formula (A-1) above). Furthermore, from the viewpoint of further improving dispersion stability and coatability, the polymer constituting the coating layer more preferably contains a mixed polymer of a polymer containing a component represented by the general formula (A-1) above and a polymer containing a component represented by the general formula (A-2) above, or contains a copolymer containing the component represented by the general formula (A-1) above and the component represented by the general formula (A-2) above as copolymerization components. The total content of the component represented by the general formula (A-1) and the component represented by the general formula (A-2) in the coating layer (when one of the components is not included, this refers to the content of the other component) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, and of these, 95% by mass or more is preferable, and it may even be 100% by mass. Furthermore, when the coating layer contains the component represented by the general formula (A-1) and the component represented by the general formula (A-2), 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. In particular, from the viewpoint of further improving dispersion stability and coatability, 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, and particularly preferably 90% by mass or more. In the present invention, the content of a constituent component is the content of all constituent components constituting the polymer, excluding constituent components derived from the polymerization initiator.

[0041] When the polymer constituting the coating layer contains a constituent component represented by the general formula (A-1) above and a constituent component represented by the general formula (A-2) above, the mass ratio of the content of the constituent component represented by the general formula (A-1) to the content of the constituent component represented by the general formula (A-2) above in the polymer constituting the coating layer (content of the constituent component represented by the general formula (A-1) above / content of the constituent 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 polymer constituting the coating layer contains a constituent component represented by the general formula (A-1) above and a constituent component represented by the general formula (A-2) above" means when the polymer constituting the coating layer contains a mixed polymer of a polymer containing a constituent component represented by the general formula (A-1) above and a polymer containing a constituent component represented by the general formula (A-2) above, and / or a copolymer containing the constituent component represented by the general formula (A-1) above and the constituent component represented by the general formula (A-2) above as copolymerization components.

[0042] The polymer constituting the coating layer may contain components other than the component represented by the general formula (A-1) above and / or the component represented by the general formula (A-2) above, within the range that does not impair the effects of the present invention.

[0043] 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 coatability, it is preferred to set the weight-average molecular weight to 10,000 (1.0 × 10 ４ ) or more, and 100,000 to 900,000 (1.0 × 10 ５ ~9.0 x 10 ５ ) is more preferable, and 200,000 to 500,000 (2.0 × 10 ５ ~5.0 x 10 ５) is more preferable. Note that, when the polymer constituting the coating layer is a mixture of two or more polymers, it is preferable that the average molecular weight of all of the polymers satisfy the above-mentioned preferable range. It is preferable that the polymer constituting the coating layer does not have a cross-linked structure, i.e., is a chain polymer. Furthermore, from the viewpoint of further improving dispersion stability and coatability, 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. Furthermore, from the viewpoint of further improving dispersion stability and coatability, it is preferable that the polymer constituting the coating layer is not a copolymer consisting of a sodium acrylate-derived component and a styrene-derived component, more preferably a copolymer consisting of a sodium (meth)acrylate-derived component and a styrene-derived component, and even more preferably a copolymer consisting of a sodium (meth)acrylate-derived component and a component represented by the above general formula (A-2). Therefore, the polymer constituting the coating layer preferably does not contain a copolymer consisting of a constituent component derived from sodium acrylate and a constituent component derived from styrene, more preferably does not contain a copolymer consisting of a constituent component derived from sodium (meth)acrylate and a constituent component derived from styrene, and even more preferably does not contain a copolymer consisting of a constituent component derived from sodium (meth)acrylate and a constituent component represented by the above general formula (A-2).

[0044] (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.

[0045] 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.

[0046] - 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 hydrofuran 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 groups (preferably alkoxycarbonyl groups having 2 to 20 carbon atoms, for example, ethoxycarbonyl, 2-ethylhexyloxycarbonyl, etc.), aryloxycarbonyl groups (preferably aryloxycarbonyl groups having 7 to 26 carbon atoms, for example, phenoxycarbonyl, 1-naphthyloxycarbonyl, 3-methylphenoxycarbonyl, 4-methoxyphenoxycarbonyl, etc.), amino groups (preferably amino groups having 0 to 20 carbon atoms, including amino groups substituted with a group selected from alkyl groups and aryl groups. For example, amino (—NH２ ), N,N-dimethylamino, N,N-diethylamino, N-ethylamino, anilino, etc.), sulfamoyl group (preferably a sulfamoyl group having 0 to 20 carbon atoms, including sulfamoyl groups substituted with 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, acyloxy groups, for example, formyloxy, acetyloxy, propionyloxy, butyryloxy, octanoyloxy, hexadecanoyloxy, acryloyloxy, methacryloyloxy, crotonoyloxy, benzoyloxy, naphthoyloxy, nicotinoyloxy, etc.), carbamoyl groups (preferably carbamoyl groups having 1 to 20 carbon atoms, including carbamoyl groups substituted with a group selected from alkyl groups and aryl groups; for example, N,N-dimethylcarbamoyl, N-phenylcarbamoyl, etc.), acylamino groups (preferably acylamino groups having 1 to 20 carbon atoms, and preferred examples of the acyl group in the acylamino group include the acyl groups described above.For example, acetylamino, benzoylamino, etc.), alkylthio groups (preferably alkylthio groups having 1 to 20 carbon atoms, for example, methylthio, ethylthio, isopropylthio, benzylthio, etc.), arylthio groups (preferably arylthio groups having 6 to 26 carbon atoms, for example, phenylthio, 1-naphthylthio, 3-methylphenylthio, 4-methoxyphenylthio, etc.), arylsilyl groups (preferably arylsilyl groups having 6 to 42 carbon atoms, for example, triphenylsilyl, etc.), heterocyclic thio groups (the above heterocyclic groups to which an -S- group is bonded), a group having 1 to 20 carbon atoms, such as a methylsulfonyl group, an ethylsulfonyl group, an alkylsulfonyl group (preferably an alkylsulfonyl group having 1 to 20 carbon atoms, such as a methylsulfonyl group, an ethylsulfonyl group, etc.), an arylsulfonyl group (preferably an arylsulfonyl group having 6 to 22 carbon atoms, such as a benzenesulfonyl group, etc.), an alkylsilyl group (preferably an alkylsilyl group having 1 to 20 carbon atoms, such as a monomethylsilyl group, a dimethylsilyl group, a trimethylsilyl group, a triethylsilyl group, etc.), a phosphite group (preferably a phosphite group having 0 to 20 carbon atoms, such as -OP(=O)(-OH)(R. Ｐ )), a hypophosphite group (preferably a hypophosphite group having 0 to 20 carbon atoms, for example, —OP(═O)(R Ｐ ) ２ ), a phosphoryl group (preferably a phosphoryl group having 0 to 20 carbon atoms, for example, —P(═O)(R Ｐ ) ２ ), a phosphinyl group (preferably a phosphinyl group having 0 to 20 carbon atoms, for example, —P(R Ｐ ) ２ ), a sulfo group, a phosphate group, a phosphonate group, a carboxy group, a hydroxy group, a sulfanyl group, a cyano group, and a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom). Ｐ is a hydrogen atom or a substituent (preferably a group selected from Substituent Group T). Each of the groups listed in Substituent Group T may further have, as a substituent, any of the groups listed in Substituent Group T above.

[0047] 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.

[0048] Preferred specific examples of the polymer constituting the coating layer include homopolymers containing the following components, mixed polymers of two or more of these homopolymers, and copolymers containing two or more of the following components. The above descriptions can be applied to the content of each component. The present invention should not be construed as being limited to these.

[0049]

[0050] In the present invention, the polymer constituting the coating layer may be used alone or in combination of two or more.

[0051] The content of the coating layer in the composite negative electrode active material is 0.05 to 5% by mass, preferably 0.1 to 5% by mass, more preferably 0.2 to 5% by mass, and even more preferably 0.3 to 5% by mass. When the polymer constituting the coating layer contains only one of the components represented by the general formula (A-1) and the components represented by the general formula (A-2), the content of the coating layer in the composite negative electrode active material is particularly preferably 1 to 5% by mass, more preferably 2 to 5% by mass, and even more preferably 3 to 5% by mass, from the viewpoint of further improving dispersion stability and coatability. On the other hand, when the polymer constituting the coating layer contains the components represented by the general formula (A-1) and the components represented by the general formula (A-2), the content of the coating layer in the composite negative electrode active material is less than when only one of the components represented by the general formula (A-1) and the components represented by the general formula (A-2) is contained, thereby achieving excellent dispersion stability and coatability. The content of the coating layer in the composite negative electrode active material can be measured by the method described in the Examples below. When two or more polymers are used in combination, the "content of the coating layer in the composite negative electrode active material" means the total amount of the two or more polymers.

[0052] (Method for Producing Composite Negative Electrode Active Material) The composite negative electrode active material of the present invention can be produced by coating at least a portion of the surface of the negative electrode active material with a polymer that constitutes a coating layer. For example, the negative electrode active material and the polymer that constitutes the coating layer are mixed in a solvent, and the polymer that constitutes the coating layer is physically or chemically adsorbed onto the surface of the negative electrode active material. The resulting negative electrode active material with the polymer that constitutes the coating layer adsorbed thereon (hereinafter referred to as the "composite negative electrode active material precursor") is then separated by filtration or other means and dried, thereby producing the composite negative electrode active material of the present invention. That is, by the above production method, a coating layer can be formed on at least a portion of the surface of the negative electrode active material such that the content of the coating layer in the composite negative electrode active material is in the range of 0.05 to 5 mass %. Examples of methods for mixing the negative electrode active material and the polymer that constitutes the coating layer in a solvent include preparing a solution in which the polymer that constitutes the coating layer is dissolved in a solvent, and then mixing the negative electrode active material in the resulting solution. Examples of solvents include water, tetrahydrofuran, and mixtures thereof. The negative electrode active material and the polymer constituting the coating layer are preferably mixed in a solvent by stirring at room temperature (25°C) to 40°C for 0.5 to 3 hours. After the composite negative electrode active material precursor is separated, it is also preferable to wash it before the drying step. Examples of the washing solvent include the solvents mentioned above. The composite negative electrode active material precursor is preferably dried under reduced pressure at room temperature (25°C) to 40°C for 0.5 to 1 day.

[0053] When preparing a composite negative electrode active material in which the coating layer is made of two or more polymers, it is preferable to perform the above-mentioned step I of "mixing the negative electrode active material and the polymer constituting the coating layer in a solvent, separating the composite negative electrode active material precursor by filtration or the like, and drying" for each type of polymer constituting the coating layer. For example, when preparing a composite negative electrode active material in which the polymer constituting the coating layer is made of two types of polymers, one type of polymer containing a component represented by the above-mentioned general formula (A-1) and one type of polymer containing a component represented by the above-mentioned general formula (A-2), first, the above-mentioned step I is performed using a polymer containing a component represented by the above-mentioned 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-mentioned 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.

[0054] [Composition for Secondary Battery Negative Electrode] The composition for secondary battery negative electrode of the present invention (hereinafter also simply referred to as "negative electrode composition of the present invention") contains the composite negative electrode active material of the present invention and a dispersion medium. The negative electrode composition of the present invention is preferably a slurry in which the composite negative electrode active material is dispersed in the dispersion medium. The content of the composite negative electrode active material in the negative electrode composition 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 composition. The negative electrode composition 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.

[0055] <Dispersion Medium> The dispersion medium contained in the negative electrode composition of the present invention may be any medium capable of dispersing or dissolving the solids contained therein, and preferably contains water. The negative electrode composition 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 composition 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 composition is preferably 20 to 99% by mass, more preferably 25 to 70% by mass, and even more preferably 30 to 60% by mass.

[0056] <Conductive Aid> The negative electrode composition 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, a conductive aid is preferably used 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 (e.g., acetylene black, ketjen black, furnace black, etc.), amorphous carbon (e.g., needle coke), carbon fibers (e.g., vapor-grown carbon fibers or carbon nanotubes), carbonaceous materials (e.g., graphene or fullerene), metal powders (e.g., copper, nickel, etc.), or conductive polymers (e.g., polyaniline, polypyrrole, polythiophene, polyacetylene, 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.

[0057] The content of the conductive additive in the negative electrode composition 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.

[0058] The shape of the conductive additive is not particularly limited, but particulate is preferred. The average particle size (volume-based median diameter D50) of the conductive additive is not particularly limited, and is preferably 0.01 to 50 μm, and more preferably 0.02 to 10.0 μm. When a commercially available conductive additive is used, the average particle size of the conductive additive is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is not available or when a synthetic conductive additive is used, the average particle size of the conductive additive may be the value obtained by applying the above-mentioned method for measuring the average particle size of the negative electrode active material (volume-based median diameter D50 in water).

[0059] 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.

[0060] The conductive additives may be used alone or in combination of two or more.

[0061] <Binder> The negative electrode composition of the present invention may contain a binder. The binder may be contained in any form, for example, in the negative electrode composition, 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 that forms the polymer particles is not particularly limited. The "particulate" may be flat, amorphous, etc., and is preferably spherical or granular.

[0062] The average particle size of the polymer particles (volume-based median diameter in water) is not particularly limited, and is preferably 50 to 300 nm, more preferably 50 to 250 nm, and even more preferably 50 to 200 nm. When commercially available polymer particles are used, the average particle size of the polymer particles is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is not available or when synthetic polymer particles are used, the average particle size of the polymer particles is the particle size (volume-based median diameter in water) at which the cumulative volume calculated from the small diameter side in the particle size distribution measured by laser diffraction / scattering method becomes 50%.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] In the present invention, the polymer particles may be used alone or in combination of two or more kinds.

[0068] When the negative electrode composition of the present invention contains a binder, the content of the binder in the negative electrode composition 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.

[0069] <Water-Soluble Polymer> The negative electrode composition 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 compositions (slurries) for secondary batteries. Examples of the thickener include polysaccharides that function as thickeners, and these may be either natural or synthetic polysaccharides. Examples include the following: Examples of cellulose compounds that serve as thickening polysaccharides include methyl cellulose, ethyl cellulose, benzyl cellulose, triethyl cellulose, cyanoethyl cellulose, nitrocellulose, hydroxymethyl cellulose, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), hydroxybutyl methyl cellulose, carboxymethyl cellulose (CMC), aminomethyl hydroxypropyl cellulose, aminoethyl hydroxypropyl cellulose, cellulose nanofibers (CNF), and cellulose nanocrystals (CNC). The cellulose compound may also be in the form of a salt, such as an ammonium salt, sodium salt, or lithium salt. The degree of ether substitution in the cellulose compound is typically 0.5 to 1.5, preferably 0.5 to 1.0. The degree of ether substitution refers to the average number of hydroxyl groups substituted with ether groups 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.

[0070] 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.

[0071] (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.

[0072] 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 composition 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.

[0073] (Other Additives) The negative electrode composition 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.

[0074] [Method for Preparing Negative Electrode Composition] The negative electrode composition 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 other components, for example, using various commonly used mixers. In the case of the negative electrode composition of the present invention, in addition to the above, at least one of a conductive additive, a binder, and a water-soluble polymer is mixed, and optionally other additives are also mixed. The mixing method is not particularly limited, and the components may be mixed all at once or sequentially. The mixing environment is not particularly limited, and examples include dry air or an inert gas.

[0075] [Negative Electrode Sheet] The negative electrode sheet of the present invention has a negative electrode active material layer formed using the negative electrode composition 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 composition 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.

[0076] 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).

[0077] 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.

[0078] [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 composition 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 composition of the present invention. Specifically, a current collector or the like is used as a substrate, and the negative electrode composition 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 composition 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 as the negative electrode of the secondary battery.

[0079] [Secondary Battery] The secondary battery of the present invention includes a negative electrode active material layer formed using the negative electrode composition of the present invention.

[0080] 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.

[0081] A nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The positive electrode includes a positive electrode current collector and a positive electrode active material layer in contact with the positive electrode current collector, and the negative electrode includes a negative electrode current collector and a negative electrode active material layer in contact with the negative electrode current collector. In the nonaqueous electrolyte secondary battery of the present invention, the negative electrode active material layer is formed using the negative electrode composition of the present invention. The nonaqueous electrolyte secondary battery of the present invention also includes a nonaqueous electrolyte secondary battery having only a negative electrode active material layer, the negative electrode active material layer being formed using the negative electrode composition of the present invention. The nonaqueous electrolyte secondary battery of the present invention functions as a secondary battery upon charge and discharge by filling the space between the positive electrode and the negative electrode with a nonaqueous electrolyte.

[0082] 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 working electrodes 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 by 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.

[0083] 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 composition, and negative electrode active material layer with the positive electrode, positive electrode active material, positive electrode composition, and positive electrode active material layer, respectively. Furthermore, as for other components that may be contained in the positive electrode composition, the descriptions of the dispersion medium, conductive additive, binder, and other additives in the above-mentioned negative electrode composition can be applied.

[0084] (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 transition metal oxide as the positive electrode active material, and it is also preferred to use a transition metal element M ａ A transition metal oxide containing one or more elements 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 ) is 0.3 to 2.2 is more preferable. Specific examples of the transition metal oxide include (MA) a transition metal oxide having a layered rock salt structure, (MB) a 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. It is preferable that all of the above transition metal oxides are transition metal oxides containing lithium (lithium-containing transition metal oxides). The same applies to the following explanations of (MA) and (MB).

[0085] (MA) Specific examples of 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]), LiNi１／３ 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 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 MnSiO４ and Li ２ CoSiO ４ In the present invention, transition metal oxides having a layered rock salt structure (MA) are preferred, and LCO or NMC are more preferred.

[0086] The shape of the positive electrode active material is not particularly limited, but particulate is preferred. The average particle size (volume-based median diameter D50) of the positive electrode active material is not particularly limited. For example, it can be 0.1 to 50 μm. The positive electrode active material can be prepared to a predetermined particle size by a conventional method using a grinder or classifier. The above-mentioned method for preparing a negative electrode active material to a predetermined particle size can also be applied. The positive electrode active material obtained by the calcination method may be used after washing with water, an acidic aqueous solution, an alkaline aqueous solution, an organic solvent, or the like. When a commercially available positive electrode active material is used, the average particle size of the positive electrode active material is the value listed in the manufacturer's catalog. When the manufacturer's average particle size information is unavailable or when a synthesized positive electrode active material is used, the value measured and calculated using the method described above for negative electrode active materials is used.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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 ２The 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.

[0091] The content of the positive electrode active material in the positive electrode composition 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.

[0092] 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).

[0093] 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.

[0094] 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 composition of the present invention. These materials and components can be appropriately applied to those used in conventional secondary batteries. Furthermore, for the method of manufacturing 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 composition 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 form of the non-aqueous electrolyte will now be described in more detail.

[0095] (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.

[0096] (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.

[0097] (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

[0098] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0099] 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.

[0100] 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.

[0101] (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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] [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.

[0106] [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.

[0107] (Synthesis of homopolymer listed in column A-1 of Table 1) 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 stirred and mixed at room temperature to prepare solution A. 337.5 g of distilled water was added to a 1 L three-neck flask equipped with a reflux condenser and a gas inlet cock. Nitrogen gas was introduced at a flow rate of 200 mL / min for 60 minutes, and then the temperature was raised to 75°C. Solution A 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. In the synthesis of the polyacrylamide, the type of monomer, the amount of polymerization initiator, the type of solvent, etc. were adjusted to synthesize various homopolymers shown in the column A-1 of Table 1.

[0108] (Synthesis of homopolymers listed in the A-2 column of Table 1) 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. Various homopolymers listed in the A-2 column 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 above polystyrene.

[0109] (Synthesis of copolymer listed in column A-3 of Table 1) 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 valve, 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 0.004 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 stirred at 85°C for 5 hours. Precipitation of a copolymer was confirmed in the reaction solution as the reaction progressed. After polymerization, the mixture was cooled to room temperature, and the precipitated copolymer was filtered, washed twice with dioxane, 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. In the synthesis of the styrene-acrylamide copolymer, the type of monomer, the composition ratio, the amount of polymerization initiator, the type of solvent, etc. were adjusted to synthesize various copolymers shown in the column A-3 of Table 1.

[0110] <1> Synthesis of Composite Negative Electrode Active Materials Composite negative electrode active materials Nos. 101 to 181, c14 to c17, and c21 to c32 shown in Table 1 below were synthesized using the coating layer-constituting polymers and active materials shown in Table 1 below as follows.

[0111] (Preparation of each composite negative electrode active material listed in Tables 1A, 1B, 1D, and 1E) 0.5 g of polyacrylamide 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 100% ammonium hydroxide (1 / g) was added to the mixture, stirred at room temperature for 1 hour, filtered, and washed with 30 g of distilled water to obtain composite negative electrode active material precursor No. 101. The obtained composite negative electrode active material precursor No. 101 was dried under reduced pressure overnight to produce composite negative electrode active material No. 101. In the synthesis of composite negative electrode active material No. 101, the composition (type and / or amount) of the coating layer-constituting polymer, the type of solvent in which the polymer is dissolved, and the composition (type and / or amount) of the active material were adjusted to produce each of the composite negative electrode active materials listed in Tables 1A, 1B, 1D, and 1E.

[0112] (Preparation of each composite negative electrode active material listed in Table 1C) 0.3 g of polyacrylamide was dissolved in 60 g of distilled water 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 polystyrene (152-1 / g) was added, stirred at room temperature for 1 hour, filtered, and washed with 30 g of distilled water to obtain composite negative electrode active material precursor No. 152-1. The obtained composite negative electrode active material precursor No. 152-1 was dried under reduced pressure overnight to obtain composite negative electrode active material No. 152-1. Next, 0.15 g of polystyrene was dissolved in 30 g of tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare solution E. 3 g of composite negative electrode active material No. 152-1 was added to solution E, stirred at room temperature for 1 hour, filtered, and washed with 15 g of tetrahydrofuran to obtain composite negative electrode active material precursor No. 152. The obtained composite negative electrode active material precursor No. 152 was dried under reduced pressure overnight to produce composite negative electrode active material No. 152. In the synthesis of No. 152, the composition (type and / or amount) of the polymer constituting the coating layer, the type of solvent in which the polymer is dissolved, and the composition (type and / or amount) of the 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 two types of homopolymers constituting the coating layer, in the production of any of the composite negative electrode active materials, coating with the homopolymer listed in the A-1 column was performed, followed by coating with the homopolymer listed in the A-2 column.

[0113] Here, composite negative electrode active materials Nos. 101 to 181 shown in Table 1 below are composite negative electrode active materials of the present invention, and composite negative electrode active materials Nos. c14 to c17 and c21 to c32 are composite negative electrode active materials for comparison.

[0114] [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 from the second measurement. Specifically, in the thermogravimetry chart from the second measurement, the mass (W ｒ ) to mass at room temperature (W ｒ ) to the mass (W ５００ ) minus the mass percentage (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.

[0115] <2> Fabrication of Nonaqueous Electrolyte Secondary Battery (Coin Battery) (1) Preparation of Negative Electrode Composition To 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 foam 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 Foam Mixer (manufactured by THINKY Corporation) to prepare a negative electrode composition. In the resulting negative electrode composition 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 composition 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) Preparation 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 1M LiPF ６The separator was impregnated with 200 μL of ethylene carbonate / ethyl methyl carbonate (volume ratio 1:2). An additional 200 μL of electrolyte 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 Li foil, separator, negative electrode active material layer, and copper foil), which was a half-cell for evaluation.

[0116] Coin batteries Nos. 102 to 181, c14 to c17, and c21 to c32 were fabricated in the same manner as in the fabrication of coin battery No. 101, except that composite negative electrode active material No. 101 was replaced with composite negative electrode active material Nos. 102 to 181, c14 to c17, and c21 to c32. Coin batteries Nos. c11 to c13 were fabricated in the same manner as in the fabrication of coin battery No. 101, except that composite negative electrode active material No. 101 was replaced with active materials listed in Table 1 below. In Nos. c11 to c13, the active materials (graphite, SiOC, and LiSiOC) were used without being coated with a polymer.

[0117] Coin batteries Nos. c18 to c20 were prepared in the same manner as in the preparation of coin battery No. 101, except that instead of composite negative electrode active material No. 101, active materials shown in Nos. c18 to c20 in Table 1 below were used, and when adding active materials in the preparation of the negative electrode composition (1) above, 0.3 g of polyacrylamide shown in Nos. c18 to c20 in Table 1 below was further added, and the blending ratio was adjusted so that the mass ratio of each solid content in the negative electrode composition was as follows. In the obtained negative electrode compositions Nos. c18 to c20, the mass ratio of each solid content was negative electrode active material: acetylene black: CMC: polymer particles: polyacrylamide = 89.7:3:3:4:0.3. Coin battery No. Coin batteries Nos. c33 to c35 were produced in the same manner as in the production of c18 to c20, except that the amounts of the negative electrode active material and polyacrylamide were changed so that the mass ratio of the solid contents in the negative electrode composition was negative electrode active material:acetylene black:CMC:polymer particles:polyacrylamide=87.3:3:3:4:2.7.

[0118] The negative electrode compositions, negative electrode sheets, and secondary batteries prepared as described above were evaluated as follows. The evaluation results are shown in Table 1.

[0119] [2] Slurry Stability In the above-mentioned <2> nonaqueous electrolyte secondary battery (coin battery) fabrication, a negative electrode composition (slurry) I immediately after preparation and a negative electrode composition (slurry) II obtained by allowing the immediately prepared negative electrode composition I to stand for one day were prepared. The ratio of the storage modulus II of the negative electrode composition II at a shear strain of 0.01% to the storage modulus I of the negative electrode composition I at a shear strain of 0.01% (i.e., [storage modulus II] / [storage modulus I]) was used to evaluate the slurry stability according to the following evaluation criteria. A smaller storage modulus ratio indicates better slurry stability. (Measurement of Storage Modulus) The storage modulus of each negative electrode composition 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). Regarding negative electrode composition II, the composition was re-stirred for 1 minute at 500 rpm using a planetary mixer (trade name: Awatori Rentaro ARE-310, manufactured by THINKY Corporation), and then the storage modulus was measured. - Evaluation Criteria - 7: Less than 1.02 6: 1.02 or more, less than 1.04 5: 1.04 or more, less than 1.06 4: 1.06 or more, less than 1.08 3: 1.08 or more, less than 1.10 2: 1.10 or more, less than 1.12 1: 1.12 or more

[0120] [3] Dispersibility In the above-mentioned <2> nonaqueous electrolyte secondary battery (coin battery) production, a negative electrode composition (slurry) I immediately after preparation and a negative electrode composition (slurry) II obtained by allowing the immediately prepared negative electrode composition I to stand for one day were prepared. The ratio of the difference between the storage modulus II and the loss modulus II of the negative electrode composition II at a shear strain of 0.01% (i.e., [storage modulus II - loss modulus II]) to the difference between the storage modulus I and the loss modulus I of the negative electrode composition I at a shear strain of 0.01% (i.e., [storage modulus I - loss modulus I]) was calculated, i.e., [storage modulus II - loss modulus II] / [storage modulus I - loss modulus I]. Dispersibility was evaluated using [storage modulus II - loss modulus II] / [storage modulus I - loss modulus I] according to the following evaluation criteria. The smaller the ratio of [storage modulus II - loss modulus II] / [storage modulus I - loss modulus I], the more excellent the dispersibility. (Measurement of storage modulus and loss modulus) The storage modulus and loss modulus of each negative electrode composition I and II at a shear strain of 0.01% were 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). Regarding negative electrode composition II, the composition was stirred again at 500 rpm for 1 minute using a planetary mixer (trade name: Awatori Rentaro ARE-310, manufactured by THINKYO Corporation), and then the storage modulus and loss modulus were measured. - Evaluation criteria - 7: 1.0 or more, less than 1.1 6: 1.1 or more, less than 1.2 5: 1.2 or more, less than 1.3 4: 1.3 or more, less than 1.4 3: 1.4 or more, less than 1.5 2: 1.5 or more, less than 1.6 1: 1.6 or more

[0121] [4] Coatability: Negative electrode composition I prepared in the above-mentioned <2> Preparation of non-aqueous electrolyte secondary battery (coin battery) was left standing for one day immediately after preparation, to obtain a negative electrode composition II, which was used as a sample. This sample was re-stirred for one minute at 500 rpm using a planetary centrifugal mixer (product name: Awatori Rentaro ARE-310, manufactured by THINKY Corporation), and then a negative electrode sheet was produced by the method described in the above-mentioned <2> Preparation of non-aqueous electrolyte secondary battery (coin battery). The obtained negative electrode sheet was visually inspected for defects (the number of voids found in the negative electrode active material layer of the negative electrode sheet) present within a 5 cm × 5 cm area, and the coatability was evaluated according to the following evaluation criteria. - Evaluation criteria - 6: No defects or one defect. 5: Two defects. 4: Three defects. 3: Four defects. 2: Five defects. 1: Six or more defects.

[0122] [5] Initial Battery Capacity Retention Rate In the above-mentioned <2> Non-aqueous Electrolyte Secondary Battery (Coin Battery), a secondary battery I was prepared using a negative electrode composition I immediately after preparation, and a secondary battery II was prepared using a negative electrode composition II obtained by leaving the immediately prepared negative electrode composition I stationary for one day. 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 battery II] / [initial battery capacity of battery I]) was applied to the following evaluation criteria, and the initial battery capacity retention rate was evaluated. The results are shown in the "Initial Battery Capacity" column in the table below. (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. Discharge was performed at a C rate of 0.2C (a rate at which the battery is completely discharged in 5 hours) until the battery voltage reached 1.5V. Three cycles of charge and discharge, each consisting of one charge and one discharge, were repeated to initialize the secondary battery. After initialization, the secondary battery was charged at 0.5C until it reached 0.02V, and then discharged at 0.5C until it reached 1.5V. The discharge capacity was taken as the "initial battery capacity." All charge and 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

[0123]

[0124]

[0125]

[0126]

[0127]

[0128] (Coating layer constituent polymers) PAAm: polyacrylamide PDAAm: polydimethylacrylamide PTMBAAm: poly1,1,3,3-tetramethylbutylacrylamide PDEAAm: polydiethylacrylamide PAA: polyacrylic acid PSt: polystyrene SBR: styrene-butadiene rubber Content: This refers to the content of each homopolymer constituent component (excluding components derived from the polymerization initiator) in the coating layer, and is expressed in % by mass. Molecular weight: weight average molecular weight measured by the above-mentioned method. AAm / St = 90 / 10: copolymer consisting of 90% by weight of acrylamide-derived components and 10% by weight of styrene-derived components. AAm / St = 50 / 50: copolymer consisting of 50% by weight of acrylamide-derived components and 50% by weight of styrene-derived components. AAm / St = 10 / 90: copolymer consisting of 10% by weight of acrylamide-derived components and 90% by weight of styrene-derived components. AANa / St = 50 / 50: copolymer consisting of 50% by weight of sodium acrylate-derived components and 50% by weight of styrene-derived components. More than 50% of the acrylic acid-derived components in the copolymer are neutralized to form sodium acrylate-derived components. In the copolymers listed in Table 1D, the content of each component (excluding the polymerization initiator-derived components) in the coating layer corresponds to the content of each component (excluding the polymerization initiator-derived components) constituting the copolymer. (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: the lithium-doped and carbon-coated silicon oxide prepared above (carbon element content: 3 mass%, average particle size: 6.7 μm)

[0129] A "-" in the "Coating layer constituent polymer" column indicates that the constituent component is not contained. The columns for graphite, SiOC, and LiSiOC indicate the percentage of each active material in the total active material, in units of mass %. Mass percentage of coating layer: 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 mass percentage" column indicates that the negative electrode active material is used without being coated. Note that, as described above, Nos. c18 to c20 and c33 to c35 are examples in which the negative electrode active material and the polymer were used directly to prepare the negative electrode composition without coating the negative electrode active material with a polymer. Therefore, No. The "Polymer Constituting Coating Layer" column for c18 to c20 and c33 to c35 shows polyacrylamide corresponding to a polymer containing a component represented by general formula (A-1) and / or a component represented by general formula (A-2) that was added directly during the preparation of the negative electrode composition, rather than a polymer that constitutes the coating layer of the negative electrode active material as a composite negative electrode active material. Furthermore, the "Mass Percentage of Coating Layer" column for Nos. c18 to c20 and c33 to c35 shows the amount of polyacrylamide added during the preparation of the negative electrode composition relative to the total amount of the negative electrode active material and polyacrylamide, in units of mass%, rather than the mass percentage of the coating layer calculated by the above-mentioned measurement method.

[0130] As is clear from Table 1, all of the negative electrode compositions containing composite negative electrode active materials Nos. c14 to c17 and c21 to c32, which do not satisfy the requirements of the present invention, were inferior in at least one of slurry stability, dispersibility, and coatability. Furthermore, all of the negative electrode compositions Nos. c11 to c13, which contained negative electrode active materials without a coating layer, were inferior in all of slurry stability, dispersibility, and coatability. Furthermore, all of the negative electrode compositions Nos. c18 to c20 and c33 to c35, which were obtained by adding and mixing the respective components during the mixing of the negative electrode compositions without coating the negative electrode active material with a polymer containing the component represented by general formula (A-1) and / or the component represented by general formula (A-2), were inferior in at least one of slurry stability, dispersibility, and coatability. In contrast, all of the negative electrode compositions containing composite negative electrode active materials Nos. 101 to 181 of the present invention were excellent in dispersion stability (slurry stability and dispersibility) and coatability. Furthermore, all of the composite negative electrode active materials Nos. When the negative electrode compositions containing Nos. 101 to 181 were used, even when the compositions were allowed to stand for one day after preparation, the initial battery capacity of the resulting secondary battery showed a sufficiently reduced decrease in initial battery capacity compared to the initial battery capacity of a secondary battery produced using a composition immediately after preparation.

[0131] This application claims priority based on Japanese Patent Application No. 2023-141286, filed on August 31, 2023, the contents of which are incorporated herein by reference as part of the present specification.

[0132] 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 is made of a polymer containing a component represented by the following general formula (A-1) and / or a component represented by the following general formula (A-2), and the content of the coating layer in the composite negative electrode active material is 0.05 to 5 mass %. In the above formula, R １１ ~R １３ and R ２１ ~R ２３ 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 of claim 1, wherein the polymer has a weight average molecular weight of 10,000 or more.

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

5. A secondary battery negative electrode composition comprising the composite negative electrode active material according to any one of claims 1 to 4 and a dispersion medium.

6. A negative electrode sheet having a layer formed using the secondary battery negative electrode composition according to claim 5.

7. A secondary battery comprising a negative electrode active material layer formed using the composition for a secondary battery negative electrode according to claim 5.

8. A method for producing a negative electrode sheet, comprising forming a negative electrode active material layer using the composition for a secondary battery negative electrode according to claim 5.

9. A method for producing a secondary battery, comprising incorporating the negative electrode sheet obtained by the method according to claim 8 as the negative electrode of the secondary battery.

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