Active material layer for negative electrode and method for producing the same, electrode mixture paste for negative electrode of power storage device, negative electrode for power storage device, and power storage device

Abstract

This power storage device uses a negative electrode active material layer that: contains a polyimide binder, and a negative electrode active material comprising silicon particles; and has a porosity of less than 20%. The power storage device has a high charge / discharge capacity and excellent cycle characteristics.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material layer and a method for producing the same, an electrode mixture paste for a negative electrode of an electricity storage device, a negative electrode for a electricity storage device, and an electricity storage device. [Background technology]

[0002] Energy storage devices are devices that store and extract electrical energy when needed. Typical examples of energy storage devices include secondary batteries such as lithium-ion secondary batteries, which are widely used as power sources for mobile information terminals. In recent years, efforts have been made to develop high-capacity energy storage devices, with a view to expanding their use in industrial applications such as electric and hybrid vehicles and unmanned aerial vehicles. One such attempt is to increase the charge / discharge capacity of energy storage devices by using, for example, silicon or tin, or alloys containing these, which have a high lithium storage capacity per unit volume, as the negative electrode active material.

[0003] However, active materials with large charge / discharge capacities, such as silicon, tin, or alloys containing these, undergo significant volume changes during charging and discharging. When general-purpose binders such as polyvinylidene fluoride or rubber-based resins are used in electrodes containing such active materials, the volume changes can cause damage to the active material layer or peeling at the interface between the current collector and the active material layer, resulting in a deterioration in the cycle performance of the energy storage device.

[0004] To solve this problem, a method has been proposed in which silicon particles with an average particle size of 1 to 10 microns are bound together using polyimide, which has excellent mechanical properties, and then subjected to a heat and pressure treatment to form a negative electrode active material layer (Patent Documents 1 to 5).

[0005] It has been pointed out that a negative electrode using the polyimide disclosed in the above patent document as a binder has cracks in the active material layer when it is charged and discharged, forming an island structure with spaces that can absorb the volume expansion during charging, thereby improving the capacity retention rate during repeated charging and discharging (Non-Patent Document 1).Recently, negative electrodes that focus on the shape of the active material layer have also been studied (Patent Document 6). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2004 / 004031 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-235057 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-203637 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-288520 [Patent Document 5] Japanese Patent Application Laid-Open No. 2004-022433 [Patent Document 6] Japanese Patent Application Publication No. 2017-092048 [Non-patent literature]

[0007] [Non-Patent Document 1] Proceedings of the 48th Battery Symposium, 2B23, p.238(2007) (Yasuo Takano et al.) Summary of the Invention [Problem to be solved by the invention]

[0008] However, with the negative electrodes that use the previously disclosed polyimides as binders, it has sometimes been difficult to achieve both high capacity and excellent cycle characteristics in industrial applications such as electric and hybrid vehicles.

[0009] Furthermore, the inventors conducted further tests and found that the negative electrode of Patent Document 6 could maintain a discharge capacity ratio of 0.9 only after 10 cycles in terms of cycle characteristics based on the second discharge / charge capacity. This means that simply specifying the porosity has not yet achieved both a high capacity sufficient for practical industrial use and excellent cycle characteristics.

[0010] Therefore, the present invention is intended to solve the above-mentioned problems, and has an object to provide an electrode mixture paste for a negative electrode of an electricity storage device, a negative electrode active material layer, a negative electrode for an electricity storage device, and an electricity storage device, which are capable of achieving both high charge / discharge capacity and excellent cycle characteristics. [Means for solving the problem]

[0011] The present invention particularly relates to the following items: 1. Silicon-based particles containing silicon as an ingredient and capable of absorbing and releasing lithium ions; Polyimide binder, an organic polymer with imide bonds in the main chain and a porosity of less than 20%. 2. The negative electrode active material layer according to item 1, wherein the silicon-based particles have an average particle size of less than 10 μm. 3. The negative electrode active material layer according to item 1 or 2, wherein the amount of the polyimide binder is 30% by mass or less based on the total mass of the negative electrode active material layer. 4. The negative electrode active material layer according to any one of items 1 to 3 above, wherein the precursor for forming the polyimide binder is a polyamic acid containing a repeating unit represented by the following chemical formula (I): [ka] (In the formula, A is one or more selected from the group consisting of tetravalent groups obtained by removing a carboxyl group from an aromatic tetracarboxylic acid, tetravalent groups obtained by removing a carboxyl group from an aliphatic tetracarboxylic acid, and tetravalent groups obtained by removing a carboxyl group from an alicyclic tetracarboxylic acid; and B is one or more selected from the group consisting of divalent groups obtained by removing an amino group from an aromatic diamine, divalent groups obtained by removing an amino group from an aliphatic diamine, and divalent groups obtained by removing an amino group from an alicyclic diamine.) 5. An electrode mixture paste for a negative electrode of an electricity storage device, used to form the negative electrode active material layer according to any one of items 1 to 4 above. 6. A method for producing a negative electrode active material layer, comprising casting or applying the electrode mixture paste for a negative electrode of an electricity storage device according to item 5 onto a current collector, and then heat treating the electrode mixture paste. 7. A negative electrode for an electricity storage device, comprising the negative electrode active material layer according to any one of items 1 to 4 above. 8. An electricity storage device having the negative electrode for an electricity storage device according to item 7 above. [Effects of the Invention]

[0012] The present invention can provide a negative electrode active material layer that has high charge / discharge capacity and also has excellent cycle characteristics, a method for producing the same, an electrode mixture paste for a negative electrode of an electricity storage device, a negative electrode for a electricity storage device, and an electricity storage device. DETAILED DESCRIPTION OF THE INVENTION

[0013] <<Negative electrode active material layer>> The negative electrode active material layer according to one embodiment of the present invention contains silicon-based particles capable of storing and releasing lithium ions and a polyimide-based binder, which is an organic polymer having imide bonds in its main chain. Additionally, the negative electrode active material layer according to the present invention is characterized in that its porosity is less than 20%.

[0014] (Polyimide binder) The polyimide-based binder contained in the negative electrode active material layer of the present invention is an organic polymer having an imide bond in its main chain. The polyimide-based binder is not particularly limited, and any known polyimide-based binder used as an electrode binder may be used. Specific examples include organic polymers having an imide bond in their main chain, such as polyimide, polyamideimide, and polyesterimide. In the present invention, a substance for forming the "polyimide-based binder" in the negative electrode active material layer is referred to as a "precursor," and a substance containing the "precursor," a solvent, and optionally other compounds is referred to as a "precursor composition." The precursor composition is sometimes called a "varnish."

[0015] A "precursor" is an organic polymer having an imide bond in its main chain, or a polymer or compound that can form an organic polymer having an imide bond in its main chain upon heating or chemical reaction. Examples of "precursors" that are organic polymers having an imide bond in their main chain include polyimides, polyamideimides, and polyesterimides, which are generally used in the form of precursor compositions (varnishes) dissolved in a solvent. These may be the same as the organic polymers that constitute "polyimide-based binders," or they may have a lower imidization rate or a lower molecular weight. Examples of "precursors" that are polymers or compounds that can form organic polymers having an imide bond in their main chain upon heating or chemical reaction include polyamic acids. These are also generally used in the form of precursor compositions (varnishes) dissolved in a solvent. The amic acid moieties of polyamic acids may be partially imidized. Furthermore, the organic polymers that constitute "polyimide-based binders" do not need to be completely imidized.

[0016] Such polyimide-based binders or precursors may be used alone or in combination of two or more. In the technical field, a "precursor" or a "precursor composition" may also be called a "binder." In the following description, a "precursor" may also be called a "polyimide-based binder." However, it is clear from the context in which the term is used whether it refers to the precursor or the polyimide-based binder in the negative electrode active material layer.

[0017] For example, as a precursor capable of forming an organic polymer having an imide bond in the main chain by heating or chemical reaction, polyamic acid, particularly polyamic acid containing a repeating unit represented by the following chemical formula (I), is preferred.

[0018] [ka] (In the formula, A is one or more selected from the group consisting of tetravalent groups obtained by removing a carboxyl group from an aromatic tetracarboxylic acid, tetravalent groups obtained by removing a carboxyl group from an aliphatic tetracarboxylic acid, and tetravalent groups obtained by removing a carboxyl group from an alicyclic tetracarboxylic acid; and B is one or more selected from the group consisting of divalent groups obtained by removing an amino group from an aromatic diamine, divalent groups obtained by removing an amino group from an aliphatic diamine, and divalent groups obtained by removing an amino group from an alicyclic diamine.)

[0019] For example, as a precursor that is an organic polymer having an imide bond in the main chain, a polyimide containing a repeating unit represented by the following chemical formula (II) is preferred.

[0020] [ka] (In the formula, X1 is one or more selected from the group consisting of tetravalent groups obtained by removing a carboxyl group from an aromatic tetracarboxylic acid, tetravalent groups obtained by removing a carboxyl group from an aliphatic tetracarboxylic acid, and tetravalent groups obtained by removing a carboxyl group from an alicyclic tetracarboxylic acid; and Y1 is one or more selected from the group consisting of divalent groups obtained by removing an amino group from an aromatic diamine, divalent groups obtained by removing an amino group from an aliphatic diamine, and divalent groups obtained by removing an amino group from an alicyclic diamine.)

[0021] A precursor for forming such a polyimide-based binder can be prepared by a known method from a tetracarboxylic acid component having the A structure of chemical formula (I) or the X1 structure of chemical formula (II), a diamine component having the B structure of chemical formula (I) or the Y1 structure of chemical formula (II), and, as essential components, other components as necessary.

[0022] The tetracarboxylic acid component is not particularly limited and can be appropriately selected in consideration of the porosity of the target negative electrode active material layer and the desired characteristics of the electricity storage device. Examples of the tetracarboxylic acid component include 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, diphenylsulfonetetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, m-terphenyltetracarboxylic dianhydride, and the like. Aromatic tetracarboxylic dianhydrides such as carboxylic dianhydrides, alicyclic tetracarboxylic acids such as cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid-1,2:4,5-dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3:5,6-tetracarboxylic dianhydride Dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 3,3'-(hexafluoroisopropylidene)diphthalic anhydride, 5,5'-[2,2,2-trifluoro-1-[3-(trifluoromethyl)phenyl]ethylidene]diphthalic anhydride, 5,5'-[2,2,3,3,3-pentafluoro-1-(trifluoromethyl)pyropylidene]diphthalic anhydride, 1H-difuro[3,4-b:3',4'-i]xanthene-1,3,7 Suitable examples include halogen-substituted tetracarboxylic acid dianhydrides such as 9(11H)-tetrone, 5,5'-oxybis[4,6,7-trifluoropyromellitic anhydride], 3,6-bis(trifluoromethyl)pyromellitic dianhydride, 4-(trifluoromethyl)pyromellitic dianhydride, 1,4-difluoropyromellitic dianhydride, and 1,4-bis(3,4-dicarboxytrifluorophenoxy)tetrafluorobenzene dianhydride. These may be used alone or in combination of two or more.

[0023] The diamine component is not particularly limited and can be appropriately selected in consideration of the porosity of the target negative electrode active material layer and the desired characteristics of the power storage device. Examples of the diamine component include aromatic diamines such as p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 2,4-toluenediamine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, bis(4-amino-3-carboxyphenyl)methane, and 2,4-diaminotoluene; 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; 2,3,5,6-tetrafluoro-1,4-diaminobenzene; 2,4,5,6-tetrafluoro-1,3-diaminobenzene; and 2,3,5,6-tetrafluoro-1,4-benzene(dimethane). Preferred examples of the diamine include halogen-substituted diamines such as 2,2'-difluoro(1,1'-biphenyl)-4,4'-diamine, 4,4'-diaminooctafluorobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, and 4,4'-oxybis(2,3,5,6-tetrafluoroaniline), and aliphatic or alicyclic diamines such as trans-1,4-diaminocyclohexane, cis-1,4-diaminocyclohexane, 1,6-hexamethylenediamine, 1,10-decamethylenediamine, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane. These may be used alone or in combination.

[0024] In chemical formula (I) or (II), from the viewpoint of mechanical strength, battery characteristics, etc., it is preferable that X1 contains a tetravalent group obtained by removing a carboxyl group from an aromatic tetracarboxylic acid having a group that imparts a bent structure, such as an ether bond. Among these, it is particularly preferable that all of X1 and Y1 contain aromatic groups. In another embodiment, from the viewpoint of flexibility, formability of the negative electrode active material layer, battery characteristics, etc., it is preferable that Y1 contains an aliphatic group in chemical formula (I) or (II). Among these, it is particularly preferable that X1 contains an aromatic group and that Y1 contains an aliphatic group in an amount of about 30 to 80 mol %.

[0025] Commercially available precursor products that can be used include, for example, UPIA (registered trademark)-AT, UPIA (registered trademark)-ST, UPIA (registered trademark)-NF, and UPIA (registered trademark)-LB manufactured by Ube Industries, Ltd.

[0026] The molar ratio of the tetracarboxylic acid component to the diamine component constituting the polyamic acid and / or polyimide used in the present invention [tetracarboxylic acid component / diamine component] can be set to approximately equimolar, specifically 0.95 to 1.05, preferably 0.97 to 1.03. By setting the molar ratio within this range, the resulting polyimide has a high molecular weight, which often ensures the toughness required for use as a binder. Furthermore, the polyamic acid and / or polyimide used in the present invention has a high molecular weight, with an inherent viscosity measured at 30°C and a concentration of 0.5 g / 100 mL of 0.2 or greater, preferably 0.4 or greater, more preferably 0.6 or greater, and even more preferably 0.7 or greater. Setting the inherent viscosity within the above range may result in a polyamic acid and / or polyimide with a high molecular weight and mechanical properties suitable for use as a binder. The weight-average molecular weight determined by gel permeation chromatography (GPC) is preferably 1,000 to 1,000,000, particularly 5,000 to 500,000. Specifically, the weight-average molecular weight is, for example, 1,000 or more, preferably 5,000 or more, more preferably 7,500 or more, and even more preferably 9,000 or more, and is, for example, 1,000,000 or less, preferably 500,000 or less, more preferably 300,000 or less, even more preferably 100,000 or less, even more preferably 50,000 or less, and even more preferably 30,000 or less. These logarithmic viscosity and molecular weight can be set arbitrarily by adjusting the molar ratio of the tetracarboxylic acid component and the diamine component used, and can be appropriately set taking into consideration the mechanical strength of the negative electrode active material layer, the desired characteristics and application of the power storage device, and the like. In the present invention, the polyamic acid and / or polyimide have a sufficiently high molecular weight that they can function even in small amounts. Examples of products (polyimide precursor compositions; varnishes) containing polyamic acids and / or polyimides having the above molecular weights include UPIA (registered trademark)-LB-1001 and UPIA (registered trademark)-LB-2001 manufactured by Ube Industries, Ltd.

[0027] When the precursor is a polyamic acid, the polyamic acid can be easily prepared by reacting a tetracarboxylic acid component with a diamine component in a solvent according to a known method. When the polyimide binder used in the present invention is a polyimide, the polyimide is preferably prepared by adding a tetracarboxylic acid component all at once or in multiple stages to a solution in which a diamine component is dissolved in a solvent, and then polymerizing (imidizing reaction) the mixture by heating or adding a catalyst or chemical imidizing agent.

[0028] The amount of polyimide binder may be any amount that does not inhibit the formation of a negative electrode active material layer having a porosity within a specific range when the electrode mixture paste for a negative electrode of an electricity storage device of the present invention is used to form the negative electrode active material layer on a current collector. For example, the polyimide binder (solid content of precursor) is 0.5% by mass to 50% by mass, preferably 1% by mass to 45% by mass, based on the total solid content of the electrode mixture paste for a negative electrode of an electricity storage device. The upper limit can be more preferably 30% by mass or less, even more preferably less than 20% by mass, even more preferably less than 10% by mass, and even more preferably less than 5% by mass. In the present invention, a small binder content (solid content) can fully exhibit its binder function, thereby achieving the effects of the present invention, such as high discharge capacity and excellent cycle characteristics. The use of a polyamic acid and / or polyimide with a high molecular weight is presumed to be one of the reasons for the excellent effects of the present invention. Note that the solid content of the precursor refers to the mass when completely imidized.

[0029] (Negative electrode active material) The negative electrode active material layer of the present invention contains a negative electrode active material containing silicon-based particles. The silicon-based particles of the present invention are particles that contain silicon as a component and are capable of absorbing and releasing lithium ions. Examples of silicon-based particles include silicon, silicon-metal composites (including alloys of silicon and other metals), silicon oxide, and silicon-silicon dioxide composites, which may be used alone or in combination of two or more.

[0030] The shape of the negative electrode active material is not particularly limited and may be any shape, such as irregular, spherical, or fibrous. The average particle size of the negative electrode active material is preferably less than 10 μm, and from the viewpoint of ensuring better cycle characteristics, it is preferably 5 μm or less. The average particle size is, for example, 0.01 μm or more. The negative electrode active material having such an average particle size may consist of one type of material, or may be one in which the average particle size is adjusted by mixing two or more types of materials. Here, the average particle size refers to the value of the primary particles of the silicon-based particles that are the negative electrode active material, and refers to the average particle size of the silicon-based particle powder. It can be measured, for example, using a laser diffraction particle size distribution analyzer. This average particle size may also be confirmed from a scanning electron microscope (SEM) image of the surface of a negative electrode fabricated using the silicon-based negative electrode active material. When the particles are not spherical, the particle size refers to the longest part (major axis) of the particle.

[0031] In this way, the negative electrode active material can be used by appropriately combining the components, shapes and / or average particle diameters of silicon-based particles depending on the desired charge / discharge capacity and other properties of the electricity storage device.

[0032] The negative electrode active material of the present invention may also contain other active materials besides silicon-based particles, if necessary. Examples of other active materials include known active materials other than silicon-based particles, such as graphite particles (e.g., natural graphite, artificial graphite), particles of metals (e.g., tin, germanium, antimony, silver, copper, nickel), and alloys thereof. The average particle size of these other active materials is not particularly limited, but is preferably 5 μm or less. The blending ratio of the silicon-based particles to the other active materials is not particularly limited, and can be appropriately added taking into consideration the charge / discharge capacity and other characteristics of the electricity storage device. In one embodiment, however, the amount of the other active materials (particularly graphite particles) added is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, of the total negative electrode active material. It is also preferable that the amount of the other active materials other than the silicon-based particles is not included.

[0033] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited as long as it functions as a negative electrode active material layer. Typically, the content is 0.1 to 1,000 times, preferably 1 to 1,000 times, more preferably 5 to 1,000 times, and even more preferably 10 to 1,000 times, by mass, relative to the polyimide-based binder. The upper limit is preferably 500 times or less, more preferably 100 times or less, and even more preferably 50 times or less. If the amount of the negative electrode active material is too high, the negative electrode active material may not be sufficiently bonded to the current collector and may easily fall off. On the other hand, if the amount of the negative electrode active material is too low, the negative electrode active material layer formed on the current collector may have many inactive portions, resulting in insufficient function as a negative electrode for an electricity storage device.

[0034] (porosity) In the present invention, the porosity of the negative electrode active material layer is less than 20%, preferably 18% or less, more preferably 15% or less. The porosity is at least 3% or more, preferably 5% or more. By setting the porosity as described above, it is possible to increase the lithium conduction rate, thereby improving cycle characteristics, output characteristics, etc.

[0035] Here, the porosity in the present invention is a value calculated from the apparent density of the negative electrode active material layer and the true density (specific gravity) and blending amount of each component constituting the negative electrode active material layer (for example, the negative electrode active material (silicon-based particles), the polyimide-based binder, and optional materials (other active materials, polymer-based binders, etc.)). Specifically, it can be calculated using the following mathematical formula 1.

[0036] (Equation 1) Porosity (%)=100-N(WA1 / D A1 +W A2 / D A2 +···W An / D An +W B1 / D B1 +W B2 / D B2 +···+W Bm / D Bm )

[0037] For example, the negative electrode active material (true density D A1 (g / cm 3 )) to W A1 Mass%, other active materials (true density D A2 (g / cm 3 )) to W A2 Mass%, polyimide binder (true density D B1 (g / cm 3 )) to W B1 Mass%, other polymer binders (true density D B2 (g / cm 3 )) to W B2 The apparent density of the negative electrode active material layer mixed in mass% is N (g / cm 3 ) the porosity (%) is calculated using the following formula:

[0038] (Equation 2) Porosity (%)=100-N(W A1 / D A1 +W A2 / D A2 +W B1 / D B1 +W B2 / D B2 ) When two or more polyimide binders are used, the true density and mass of each component must be considered. Similarly, the true density and mass of other active materials and other polymers must be considered separately for each component. As demonstrated in this example, by satisfying the porosity specified in the present invention, it is possible to achieve both high capacity and excellent cycle characteristics.

[0039] (Polymer binder) In the present invention, a polymer binder other than the polyimide-based binder may be included. Such polymer binders are not particularly limited as long as they do not inhibit the functions of the polyimide-based binder and the negative electrode active material. Examples of such polymer binders include anionic polymers such as poly(meth)acrylic acid, polysulfonic acid, and salts thereof; water-soluble cellulose derivatives such as carboxyalkyl cellulose and hydroxyalkyl cellulose; water-soluble polymers such as polyvinyl alcohol, polyalkylene glycol, polyvinylpyrrolidone, salts thereof, and alginates; acrylic resins, synthetic rubbers, polyamides, and silicone-based resins (including silicone oils). Furthermore, without being limited to these, known electrode binders can also be used.

[0040] One or more polymer binders other than polyimide-based binders may be selected and used as appropriate depending on the desired functionality of the negative electrode active material layer, the power storage device, etc. Furthermore, depending on the solvent used, a water-soluble polymer may be selected for aqueous solvents, or a polymer soluble in organic solvents may be selected for organic solvents. The content of the polymer binder other than polyimide-based binders (solid content of precursor) can be appropriately set depending on the purpose. For example, the amount of the other polymer binder is 0 to 1,000 parts by mass (10 times the amount) per 100 parts by mass of the polyimide-based binder (solid content of precursor). In some embodiments, the amount of the other polymer binder is 50 parts by mass or less, preferably 20 parts by mass or less. It is also preferable that no polymer binder other than polyimide-based binders are contained (0 parts by mass). In a different embodiment, the amount of the other polymer binder is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and may be, for example, 300 parts by mass or less, per 100 parts by mass of the polyimide binder (solid content of precursor).

[0041] (Conductive additive) The negative electrode active material layer of the present invention may contain a conductive additive as needed. Conventionally known conductive additives can be used as such conductive additives, and one or more types can be used depending on the characteristics of the desired negative electrode active material layer or power storage device. Such conductive additives are not particularly limited as long as they are conventionally known conductive additives. Examples of such conductive additives include carbon-based conductive additives such as graphite, acetylene black, and carbon black, and metal-based conductive additives such as silver, copper, nickel, and alloys thereof. As described above, in one embodiment of the present invention, it is preferable that the amount of active material other than silicon-based particles is small or that no active material is contained. In such cases, it is preferable to use materials that do not occlude lithium within particles, such as acetylene black and carbon black, rather than materials with charge / discharge capacity such as graphite.

[0042] (optional ingredient) The negative electrode active material layer of the present invention may contain other additives as needed. The other additives may be used within a range that does not impair the effects of the present invention, and specifically include catalysts (e.g., amine compounds, imidazole compounds); chemical imidizing agents (e.g., acid anhydrides such as acetic anhydride, and amine compounds such as pyridine and isoquinoline); antioxidants (e.g., phenolic and phosphorus-based antioxidants); light stabilizers (e.g., hindered amine-based stabilizers); antistatic agents (e.g., surfactants, carbon, metal oxides); plasticizers (e.g., ester-based plasticizers, epoxidized vegetable oils); oil-soluble solvents (e.g., 1-acetonaphthone, Acetophenone, benzyl acetone, methylacetophenone, dimethylacetophenone, propiophenone, valerophenone, anisole, methyl benzoate, benzyl benzoate); rust inhibitors (e.g., zinc compounds, lead compounds, diphenylamine, etc., adipic acid, ethanolamine and monoethanolamine, ethylene glycol monoethyl ether, trimethylamine, nonylphenol, hexamethylenediamine, pentaerythritol, etc., dicyclohexylammonium nitrite, diisopropylammonium nitrite Light and mixtures thereof, dicyclohexylammonium caprate, laurate, carbonate, etc., benzotriazole and alkylbenzotriazole, etc., amine salts, lower fatty acids and their salts, etc.; silane coupling agents; titanium coupling agents; flame retardants (e.g., bromine-based flame retardants, phosphorus-based flame retardants, antimony oxide, aluminum hydroxide, etc.); defoamers (e.g., silicone-based defoamers, acrylic defoamers, fluorine-based defoamers); leveling agents (e.g., silicone-based leveling agents, acrylic leveling agents); Leveling agents (e.g., benzyl alcohol, 2-phenylethyl alcohol, 4-methylbenzyl alcohol, 4-methoxybenzyl alcohol, 4-chlorobenzyl alcohol, 4-nitrobenzyl alcohol, phenoxy-2-ethanol, cinnamyl alcohol, furfuryl alcohol, and naphthyl carbinol, polyethylene glycol, coumarin, 2-butyne-1,4-diol, 2-propyn-1-ol, 3-phenylpropionic acid, etc.); rheology control agents (additives for flow control); viscosity modifiers; release agents;Examples of the surfactant include surfactants (for example, anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants); metal soaps (for example, salts of fatty acids such as stearic acid, lauric acid, ricinoleic acid, and octylic acid with metals such as lithium, magnesium, calcium, barium, and zinc); and supporting electrolytes (for example, halides and nitrates of alkali metals, and salts of strong acids such as tetraalkylammonium perchlorates and tetrafluoroboric acid).

[0043] The thickness of the negative electrode active material layer of the present invention can be appropriately set depending on the characteristics or shape of the target negative electrode or electricity storage device. For example, it can be about 0.5 μm to 300 μm, and preferably 1 μm or more. The thickness of the negative electrode active material layer is preferably 50 μm or less, more preferably 30 μm or less.

[0044] <<Electrode mixture paste for negative electrodes of energy storage devices>> The electrode mixture paste for a negative electrode of an electricity storage device, which is one embodiment of the present invention, is used to form the above-mentioned negative electrode active material layer. This electrode mixture paste for a negative electrode of an electric storage device contains a negative electrode active material, a polyimide-based binder, and other optional components. These components may be the same as those disclosed in the section on the negative electrode active material layer above. Furthermore, the electrode mixture paste for a negative electrode of an electric storage device of the present invention may contain various additives as needed.

[0045] (solvent) The electrode mixture paste for a negative electrode of an electricity storage device of the present invention may contain a solvent as needed. Such a solvent can be appropriately selected depending on the intended electricity storage device, electrode mixture paste, etc., and for example, an organic solvent, an aqueous solvent (water or a solvent containing water), or a mixture thereof can be used. Among these, solvents used in preparing polyimide-based binders (polyamic acid, polyimide resin, etc.) can be preferably used.

[0046] The organic solvent is not particularly limited, but examples thereof include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and N-vinyl-2-pyrrolidone; cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone; carbonate solvents such as ethylene carbonate and propylene carbonate; glycol-based solvents such as triethylene glycol; phenol-based solvents such as phenol, o-cresol, m-cresol, p-cresol, 3-chlorophenol, and 4-chlorophenol; acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, and dimethyl sulfoxide. Further, for example, alcohol solvents such as methanol and ethanol, ester solvents such as butyl acetate, ethyl acetate, isobutyl acetate, ethyl propionate, ethyl butyrate, butyl butyrate, butyl benzoate, ethyl benzoate, and methyl benzoate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexane, cyclohexane-1, cyclohexane-2, cyclohexane-3, cyclohexane-4, cyclohexane-5, cyclohexane-6, cyclohexane-7, cyclohexane-8, cyclohexane-9, cyclohexane-10, cyclohexane-11, cyclohexane-12, cyclohexane-13, cyclohexane-14, cyclohexane-15, cyclohexane-16, cyclohexane-17, cyclohexane-18, cyclohexane-19, cyclohexane-20, cyclohexane-21, cyclohexane-22, cyclohexane-23, cyclohexane-24, cyclohexane-25, cyclohexane-26, cyclohexane-27, cyclohexane-28, cyclohexane-29, cyclohexane-30, cyclohexane-31, cyclohexane-32, cyclohexane-33, cyclohexane-34, cyclohexane-35, cyclohexane-36, cyclohexane-37, cyclohexane-38, cyclohexane-39, cyclohexane-40, cyclohexane-41, cyclohexane-42, cyclohexane-43, cyclohexane-44, cyclohexane-45, cyclohexane-46, cyclohexane-47, cyclohexane-48, cyclohexane-49, cyclohexane-51, cyclohexane Other common organic solvents that can be used include hexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, toluene, chlorobenzene, N-methylcaprolactam, hexamethylphosphorotriamide, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, diphenyl sulfone, tetramethylurea, anisole, turpentine, mineral spirits, petroleum naphtha-based solvents, biodegradable methyl lactate, ethyl lactate, butyl lactate, and other common organic solvents. One or more organic solvents may be used.

[0047] The electrode mixture paste for the negative electrode of the electricity storage device of the present invention can be prepared by a general preparation method, such as a method of mixing a negative electrode active material with a polyimide binder at a moderate temperature range (preferably 10°C to 60°C).

[0048] <<Method of manufacturing the negative electrode active material layer>> The method for producing a negative electrode active material layer, which is one embodiment of the present invention, is not particularly limited as long as it can produce the desired negative electrode active material layer. One example is a method in which an electrode mixture paste for a negative electrode of an electricity storage device is cast or applied onto a current collector, followed by heat treatment to form a negative electrode active material layer. Polyamic acid can easily be converted into polyimide by heat treatment or chemical treatment with an imidizing agent, etc. The method for producing a negative electrode active material layer will be described in detail below based on this example.

[0049] The current collector used in the present invention can be a general electron conductor that does not undergo chemical changes. Examples of materials for forming these current collectors include aluminum, copper, copper alloys, iron, stainless steel, nickel, and titanium. Aluminum, copper, copper alloys, iron, and stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like (thin films formed thereon) can also be used. Among these, aluminum, copper, copper alloys, nickel-plated steel, and stainless steel are preferred.

[0050] The current collector is usually in the form of a foil (sheet), but a net, a punched material, a porous material, a molded body of fibers, etc. may also be used depending on the intended electricity storage device. The current collector may also have an uneven surface formed by surface treatment.

[0051] The thickness of the current collector is not particularly limited and can usually be 1 μm to 500 μm. In the present invention, metal foils such as copper foil, stainless steel foil, and nickel foil can be suitably used as the current collector, and copper foils such as electrolytic copper foil and rolled copper foil can be suitably used. The thickness of these metal foils is not particularly limited and can usually be 5 to 50 μm, preferably 9 to 18 μm.

[0052] When a metal foil is used as the current collector, the foil surface may be roughened or rust-proofed to improve adhesion. A conductive adhesive layer may be laminated on the foil surface. The conductive adhesive layer can be formed by blending conductive particles such as graphite with an organic polymer compound.

[0053] The electrode mixture paste for a negative electrode of an electricity storage device can be applied to a current collector by a continuous roll-to-roll application method or a sheet-by-sheet application method, and examples of the application device that can be used include a die coater, a multilayer die coater, a gravure coater, a comma coater, a reverse roll coater, and a doctor blade coater.

[0054] The heat treatment is preferably carried out under conditions that allow for removing the solvent contained in the electrode mixture paste for the negative electrode of an electricity storage device, melting or imidizing the polyimide binder, integrating it with other components (e.g., the negative electrode active material) that form the negative electrode active material layer, and bonding the current collector and the negative electrode active material layer. For example, the heat treatment is preferably carried out at a temperature equal to or higher than the melting point of the polyimide binder used, and if necessary, under pressure. The heat treatment may be carried out once or multiple times.

[0055] The heat treatment temperature is not particularly limited as long as it allows the production of a negative electrode active material layer, and can be appropriately set depending on the type of polyimide binder (precursor) and the type of solvent contained in the electrode mixture paste for the negative electrode of an electricity storage device used. The heat treatment temperature is, for example, preferably 80°C to 350°C, more preferably 100°C to 300°C, and particularly preferably 120°C to 250°C. Heat treatment temperatures below 80°C are undesirable because they may require a long time to remove the solvent and may result in insufficient melting or a slow imidization reaction. Temperatures above 350°C are undesirable because they may cause deterioration of the current collector, polyimide binder, and / or polymer binder. The heat treatment may be performed at a temperature increased in multiple stages to prevent foaming or powdering.

[0056] The heat treatment time is not particularly limited as long as it can produce the desired negative electrode active material layer, but can be set, for example, in the range of 3 minutes to 48 hours. The above range allows the imidization reaction and solvent removal to be carried out sufficiently, and is also preferable from the viewpoint of productivity. During this time, most of the solvent is removed, and the polyamic acid is substantially converted into polyimide by the imidization reaction.

[0057] In the present invention, a pressurizing step may be added. For example, pressurizing may be performed before the heat treatment, after the heat treatment, or simultaneously with the heat treatment. Furthermore, when the heat treatment is performed multiple times, pressurizing may be performed between the heat treatments. Specific pressurizing conditions and pressurizing means are not particularly limited, but examples include a method of pressing using a roll press at a linear pressure of 100 to 2000 kg / cm. Here, the porosity of the negative electrode active material layer should be appropriately adjusted depending on the types of constituent components such as the polyimide binder and the negative electrode active material, and the necessary pressurizing conditions, etc., are also appropriately controlled so that the porosity is at a desired value, taking into consideration the types of each constituent component.

[0058] The porosity, which is one of the constituent elements of the present invention, tends to decrease as the applied pressure increases, but this tendency can be used as an indicator to adjust the manufacturing conditions. In addition, fine adjustments can be made by adjusting detailed conditions such as heat shrinkage and crosslink density.

[0059] When evaluated under the conditions of the examples described later, the negative electrode active material layer of the present invention has a capacity retention rate calculated by dividing the discharge capacity after a cycle test by the initial discharge capacity of preferably more than 50%, more preferably 75% or more. Furthermore, when evaluated under the same conditions, the initial charge-discharge efficiency calculated by dividing the initial discharge capacity by the initial charge capacity of preferably more than 81%, more preferably 89% or more.

[0060] <<Anodes for energy storage devices>> An embodiment of the present invention is an anode for an electricity storage device, which has the above-described anode active material layer. More specifically, the anode has the anode active material layer of the present invention on a current collector. As a method for producing an anode for an electricity storage device, a method of forming an anode active material layer on a current collector, as described above, may be employed. Furthermore, the above-described anode for an electricity storage device may have one or more functional layers laminated on the anode active material layer depending on the configuration of the electricity storage device.

[0061] <<Electricity storage devices>> An electric storage device according to one embodiment of the present invention includes an electric storage device negative electrode having the above-described negative electrode active material layer. The above-described electric storage device negative electrode of the present invention can be suitably formed into an electric storage device according to a known method. For example, the obtained electric storage device negative electrode and positive electrode are wound into a cylindrical shape while sandwiching a separator such as a polyolefin porous body, and the cylindrical electrode body is left as is or crushed into a flattened shape, and the electrode body and a nonaqueous electrolyte solution are inserted into an exterior body, thereby suitably obtaining an electric storage device.

[0062] The positive electrode in the present invention has a layer containing at least a positive electrode active material formed on a current collector. A typical positive electrode active material can be used as the positive electrode active material. Examples include lithium-containing composite metal oxides, olivine-type lithium salts, chalcogen compounds, and manganese dioxide. The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal, or a metal oxide in which a portion of the transition metal in the metal oxide is substituted with a different element. Examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, with Mn, Al, Co, Ni, and Mg being preferred. The different element may be one type or two or more types. Among these, lithium-containing composite metal oxides are preferred. Examples of lithium-containing composite metal oxides include Li x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z , Li x Ni 1-y M y O z , Li x Mn2O4, Li x Mn 2-y M y Examples of the positive electrode active material include LiMPO4, LiMPO4, and Li2MPO4F (in the formulas, M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B; x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3). Here, the value of x, which represents the molar ratio of lithium, increases or decreases during charge and discharge. Examples of the olivine-type lithium salt include LiFePO4. Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide. One type of positive electrode active material can be used alone, or two or more types can be used in combination. The current collector used in the positive electrode may be a commonly used one.

[0063] The non-aqueous electrolyte is not particularly limited as long as it is one that is normally used in electricity storage devices, and a non-aqueous solvent in which a lithium salt is dissolved is preferably used. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, and ethyl propionate; lactones such as γ-butyrolactone and γ-valerolactone; chain ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, and ethoxymethoxyethane; and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran. These can be used alone or in combination of two or more.

[0064] Examples of lithium salts that dissolve in non-aqueous solvents include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCl, LiCF3SO3, LiCF3CO2, Li(CF3SO2)2, LiAsF6, LiN(CF3SO2)2, LiB 10 Cl 10 Examples of lithium salts include lithium carboxylates of lower aliphatic groups, LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, and lithium imide salts. These can be used alone or in combination of two or more. The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / L, and more preferably 0.5 to 1.5 mol / L.

[0065] In addition, various additives may be added to the non-aqueous electrolyte solution to improve the charge / discharge characteristics of the electricity storage device. Examples of such additives include vinylene carbonate, vinylethylene carbonate, phosphazene and fluorobenzene, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, pyridine, hexaphosphoric acid triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, and ethylene glycol dialkyl ether. These additives are preferably blended in an amount of about 0.5 to 10 mass % of the non-aqueous electrolyte solution.

[0066] In addition, in the present invention, an insulating microporous thin film conventionally used in lithium-ion batteries can be used as the separator. The microporous thin film preferably has a function of closing its pores at a certain temperature or higher, thereby increasing resistance. Polyolefins such as polypropylene and polyethylene, which have excellent organic solvent resistance and hydrophobicity, are preferably used as the material for the microporous thin film. Sheets, nonwoven fabrics, and woven fabrics made from glass fiber or the like can also be used.

[0067] The shape of the electricity storage device of the present invention is not particularly limited, and may be, for example, a coin, button, sheet, cylindrical, flat, or rectangular shape. When the electricity storage device is coin- or button-shaped, the negative electrode mixture is typically compressed into a pellet before use. The thickness and diameter of the pellet may be determined based on the size of the electricity storage device. The wound electrode body of the present invention does not necessarily have to be a perfect cylinder, and may have an elongated cylindrical shape with an elliptical cross section or a prismatic shape such as a rectangle.

[0068] The electricity storage device of the present invention has a high charge / discharge capacity and is equipped with a negative electrode that can achieve excellent cycle characteristics. Therefore, even in the form of a so-called all-solid-state battery that does not use an electrolyte solution, the device can fully demonstrate its capabilities and can be suitably used. [Example]

[0069] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0070] The abbreviations for compounds used in the following examples are explained below. Polyimide binder (precursor composition): UPIA (registered trademark)-LB-1001 (polyamic acid varnish (solvent: NMP) manufactured by Ube Industries, Ltd.) NMP: N-methyl-2-pyrrolidone EC: Ethylene carbonate DEC: Diethyl carbonate

[0071] (1) Preparation of negative electrode for evaluation Silicon (average particle size 5 μm) as the negative electrode active material, UPIA (registered trademark)-LB-1001, and acetylene black as the conductive additive were blended in a ratio of 80:2:18 (mass ratio; UPIA (registered trademark)-LB-1001 is the amount of solids (polyimide precursor)), and NMP was added to a slurry concentration of approximately 60 mass % to prepare a negative electrode mixture paste for a power storage device. This negative electrode mixture paste for a power storage device was applied to a nickel-plated steel foil (thickness 10 μm) as a current collector and pre-dried at 80°C for 10 minutes. Thereafter, it was roll-pressed and placed in a vacuum dryer and heat-treated at 350°C for 1 hour to produce a negative electrode for evaluation (capacity density: 3 mAh / cm 2 By changing the press line pressure, negative electrodes for evaluation having negative electrode active material layers with different porosities were prepared.

[0072] (2) Preparation of evaluation battery Using the negative electrode for evaluation obtained in (1) above, a battery for evaluation was fabricated with the following configuration. Counter electrode: Lithium foil (metallic lithium) Electrolyte: 1M LiPF6 / EC:DEC = 1:1 (volume%)

[0073] (3) Battery evaluation Charge and discharge were repeated under the following conditions to evaluate the cycle characteristics. ·Measurement temperature: 30℃ Charge / discharge range: SOC (battery charge rate) 30-90% Charge / discharge current: 0.1C The initial charge / discharge efficiency was calculated by (initial discharge capacity) / (initial charge capacity). The capacity retention rate was calculated by dividing the discharge capacity after the cycle test by the initial discharge capacity. Here, the absorption of Li into the "negative electrode for evaluation" is referred to as "charging," and the release of Li from the "negative electrode for evaluation" is referred to as "discharging."

[0074] [Example 1] The charge-discharge cycle characteristics of the fabricated test battery (negative electrode active material layer porosity: 5%) were examined, and the capacity retention rate after 40 cycles was 95%. The initial charge-discharge efficiency was 90%.

[0075] [Example 2] The charge-discharge cycle characteristics of the fabricated test battery (negative electrode active material layer porosity: 10%) were examined, and the capacity retention rate after 40 cycles was 88%, and the initial charge-discharge efficiency was 89%.

[0076] [Example 3] The charge-discharge cycle characteristics of the fabricated test battery (negative electrode active material layer porosity: 18%) were examined, and the capacity retention rate after 40 cycles was 75%, and the initial charge-discharge efficiency was 94%.

[0077] [Comparative Example 1] The charge-discharge cycle characteristics of the fabricated test battery (negative electrode active material layer porosity: 25%) were examined, and the capacity retention rate after 40 cycles was 50%, and the initial charge-discharge efficiency was 81%.

[0078] Comparative Example 2 The charge-discharge cycle characteristics of the fabricated test battery (negative electrode active material layer porosity: 30%) were examined, and the capacity retention rate after 40 cycles was 44%, and the initial charge-discharge efficiency was 67%.

[0079] Comparative Example 3 The charge-discharge cycle characteristics of the fabricated test battery (negative electrode active material layer porosity: 35%) were examined, and the capacity retention rate after 40 cycles was 48%, and the initial charge-discharge efficiency was 44%.

Claims

1. Silicon-based particles containing silicon as an ingredient and capable of absorbing and releasing lithium ions; Polyimide binder, an organic polymer with imide bonds in the main chain A method for producing a negative electrode active material layer containing a negative electrode mixture paste containing the silicon particles and a precursor for forming the polyimide binder, the negative electrode mixture paste being heat-treated at a temperature in the range of 80 to 350°C; a negative electrode active material layer having a porosity of 3% or more and less than 20%, an amount of the polyimide-based binder of 0.5% by mass or more and 30% by mass or less with respect to the total mass of the negative electrode active material layer, and an amount of the silicon-based particles of 90% by mass or more with respect to the total mass of the negative electrode active material; Method for manufacturing negative electrode active material layer (however, The method for producing the negative electrode active material layer includes the steps of producing composite particles as a negative electrode active material having a plurality of particles containing Si element and a binder, and binding the composite particles and a sulfide solid electrolyte to produce a negative electrode active material layer having a porosity of 15% or less, and 18% or less, except for the steps of: The negative electrode active material layer includes secondary particles including an active material having a volume expansion coefficient of 5% or more, a conductive additive, and a first binder, and a second binder having an elastic modulus different from that of the first binder, except for the negative electrode active material layer including secondary particles including an active material having a volume expansion coefficient of 5% or more, a conductive additive, and a first binder, The polyimide binder excludes polyimides obtained from a tetracarboxylic acid component consisting of benzophenonetetracarboxylic dianhydride and a diamine component consisting of oxydianiline and metaphenylenediamine.

2. The method for producing a negative electrode active material layer according to claim 1 , wherein the silicon-based particles have a volume-based average particle size of less than 10 μm as measured with a laser diffraction particle size distribution analyzer.

3. 3. The method for producing a negative electrode active material layer according to claim 1, wherein the precursor for forming the polyimide-based binder is a polyamic acid containing a repeating unit represented by the following chemical formula (I): 【Chemistry 1】 (In the formula, A is one or more selected from the group consisting of tetravalent groups obtained by removing a carboxyl group from an aromatic tetracarboxylic acid, tetravalent groups obtained by removing a carboxyl group from an aliphatic tetracarboxylic acid, and tetravalent groups obtained by removing a carboxyl group from an alicyclic tetracarboxylic acid; and B is one or more selected from the group consisting of divalent groups obtained by removing an amino group from an aromatic diamine, divalent groups obtained by removing an amino group from an aliphatic diamine, and divalent groups obtained by removing an amino group from an alicyclic diamine.)

4. The method for producing a negative electrode active material layer according to any one of claims 1 to 3, comprising casting or applying the negative electrode mixture paste on a current collector, and performing a heat treatment on the current collector.

5. A method for producing a negative electrode for an electricity storage device, comprising the method for producing a negative electrode active material layer according to any one of claims 1 to 4 as one step.

6. A method for producing an electricity storage device, comprising the step of assembling the electricity storage device negative electrode produced by the method according to claim 5 as a negative electrode.

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