Negative electrode material sheet for non-aqueous secondary battery and method for manufacturing the same, negative electrode for non-aqueous secondary battery, and non-aqueous secondary battery

Abstract

To provide a negative electrode material sheet for a non-aqueous secondary battery capable of forming a negative electrode capable of imparting a good initial irreversible capacity to a non-aqueous secondary battery while maintaining sheet strength.SOLUTION: A negative electrode material sheet for a non-aqueous secondary battery according to the present invention includes a particulate carbon material, the particulate carbon material is oriented in a direction perpendicular to the surface of the negative electrode material sheet for the non-aqueous secondary battery, the content ratio of the resin-derived component in the negative electrode material sheet for the non-aqueous secondary battery is a predetermined value or less, and the surface roughness Sa of the negative electrode material sheet for non-aqueous secondary batteries is a predetermined value or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a negative electrode material sheet for a non-aqueous secondary battery, a method for producing the same, a negative electrode for a non-aqueous secondary battery, and a non-aqueous secondary battery. [Background technology]

[0002] Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes (positive and negative electrodes) have been studied with the aim of further improving the performance of secondary batteries.

[0003] Here, a negative electrode used in a secondary battery such as a lithium-ion secondary battery typically includes a current collector and an electrode mixture layer (negative electrode mixture layer) formed on the current collector. This negative electrode mixture layer (sometimes referred to as a "negative electrode active material layer") contains, for example, a negative electrode active material and a resin component such as a binder that is used as needed.

[0004] Therefore, in recent years, attempts have been made to further improve the performance of secondary batteries by improving the negative electrode mixture layer. For example, in Patent Document 1, in order to improve the input / output characteristics (rate characteristics) of a secondary battery, at least 50% by number of the total amount of negative electrode active material in the negative electrode active material layer is oriented so that the direction in which charge carriers are absorbed and released is 45° or more and 90° or less with respect to the surface of the current collector. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 088540 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when an electrode is fabricated using a resin binder as in Patent Document 1, it is expected that the binder component will inhibit the charge carrier absorption / release reaction of the negative electrode active material, resulting in a large initial irreversible capacity. For this reason, it is expected that battery performance can be improved by minimizing the binder component in the electrode.

[0007] Therefore, the inventors investigated removing the binder components by firing the electrode at high temperatures in the hope of obtaining a good initial irreversible capacity. Removing the binder components through high-temperature firing is expected to improve the initial irreversible capacity, but the loss of the binder components, which acted as glue, is expected to result in a decrease in sheet strength. If the firing conditions were changed to perform high-temperature firing in the hope of preventing a decrease in sheet strength, modified resin binders would remain. These residual modified resins would also function as a type of binder, and the presence of the residual modified resins would likely result in a high initial irreversible capacity. Therefore, a negative electrode material and a method for producing the same that can achieve both good initial irreversible capacity and maintain sheet strength were needed.

[0008] An object of the present invention is to provide a negative electrode material sheet for a non-aqueous secondary battery that can form a negative electrode that can impart a good initial irreversible capacity to a non-aqueous secondary battery while maintaining sheet strength. Another object of the present invention is to provide a negative electrode that maintains its strength and can impart a good initial irreversible capacity to a non-aqueous secondary battery. Another object of the present invention is to provide a non-aqueous secondary battery in which the strength of the negative electrode is maintained and which has a good initial irreversible capacity. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to achieve the above object, and have found that a negative electrode material sheet for a non-aqueous secondary battery, which includes a particulate carbon material, the particulate carbon material being oriented in a direction perpendicular to the surface of the negative electrode material sheet for a non-aqueous secondary battery, the content of a resin-derived component in the negative electrode material sheet for a non-aqueous secondary battery being a predetermined value or less, and further, the surface roughness Sa of the negative electrode material sheet for a non-aqueous secondary battery being a predetermined value or less, can, when bonded to a current collector as a negative electrode mixture layer to produce a negative electrode, impart a good initial irreversible capacity to a non-aqueous secondary battery including such a negative electrode while maintaining sheet strength as a negative electrode material sheet, and have completed the present invention.

[0010] That is, the present invention has an object to advantageously solve the above-mentioned problems, and provides a negative electrode material sheet for a non-aqueous secondary battery (hereinafter, may be simply referred to as "negative electrode material sheet") of the present invention, which is characterized in that it contains a particulate carbon material, the particulate carbon material is oriented in a direction perpendicular to the surface of the negative electrode material sheet, the content of a resin-derived component in the negative electrode material sheet is a predetermined value or less, and the surface roughness Sa of the negative electrode material sheet is a predetermined value or less. As described above, the negative electrode material sheet of the present invention contains particulate carbon material, the particulate carbon material is oriented in a direction perpendicular to the surface of the negative electrode material sheet, and the content of resin-derived components in the negative electrode material sheet is not more than a predetermined value, so that a negative electrode that can impart good initial irreversible capacity to a secondary battery can be formed. Furthermore, the negative electrode material sheet of the present invention has particulate carbon material oriented in a direction perpendicular to the surface of the negative electrode material sheet and has a surface roughness Sa not more than a predetermined value, so that the sheet strength of the negative electrode material sheet is well maintained. In the present invention, the orientation of the particulate carbon material in the negative electrode material sheet, the content ratio of the resin-derived component in the negative electrode material sheet, and the surface roughness Sa of the negative electrode material sheet can be measured by the method described in the examples of this specification.

[0011] Here, the negative electrode material sheet for a non-aqueous secondary battery of the present invention preferably has a thickness of 80 μm or more. If the thickness of the negative electrode material sheet for a non-aqueous secondary battery is equal to or greater than the above-mentioned predetermined value, a secondary battery manufactured using a negative electrode including the negative electrode material sheet can have a high capacity. In the present invention, the thickness of the negative electrode material sheet for a non-aqueous secondary battery can be measured by the method described in the examples of this specification.

[0012] In the negative electrode material sheet for a non-aqueous secondary battery of the present invention, the particulate carbon material preferably contains flake graphite. Using flake graphite as the particulate carbon material can further improve the strength of the negative electrode provided with the negative electrode material sheet, and can further improve the rate characteristics of a secondary battery produced using the negative electrode.

[0013] Furthermore, in the negative electrode material sheet for a non-aqueous secondary battery of the present invention, the aspect ratio of the particulate carbon material is preferably greater than 1.2 and not greater than 20. Use of particulate carbon material having an aspect ratio within the above-mentioned range can further improve the rate characteristics of a secondary battery produced using a negative electrode comprising the negative electrode material sheet. In the present invention, the "aspect ratio" can be determined by observing particulate carbon material with an SEM (scanning electron microscope), measuring the maximum diameter (long diameter) and the particle diameter (short diameter) in a direction perpendicular to the maximum diameter for 50 randomly selected particulate carbon material particles, and calculating the average ratio of the long diameter to the short diameter (long diameter / short diameter). In the above description, for example, when observing a flaky particulate carbon material with an SEM, the "long diameter" refers to the length in the direction of the long axis of the main surface of the flaky shape, and the "short diameter" refers to the length in the direction perpendicular to the long axis of the main surface on the same plane as the main surface.

[0014] The present invention also aims to advantageously solve the above-mentioned problems, and provides a method for producing a negative electrode material sheet for a non-aqueous secondary battery, comprising the steps of: a primary sheet-forming step of pressurizing a composition containing a resin and a particulate carbon material to form a sheet to obtain a primary sheet; a laminate-forming step of stacking a plurality of the primary sheets in the thickness direction or folding or rolling the primary sheets to obtain a laminate; a slicing step of slicing the laminate at an angle of 45° or less with respect to the stacking direction to obtain a secondary sheet; and a firing step of firing the secondary sheet under pressure at a firing temperature equal to or higher than a predetermined value. The method for producing a negative electrode material sheet for a non-aqueous secondary battery of the present invention makes it possible to produce a negative electrode material sheet for a non-aqueous secondary battery that can provide a secondary battery with good initial irreversible capacity while maintaining sheet strength.

[0015] In the method for producing a negative electrode material sheet for a non-aqueous secondary battery according to the present invention, the firing step is preferably carried out under a pressure equal to or greater than a predetermined value. If the pressure applied is equal to or greater than the predetermined value, smoothness can be imparted to the surface of the negative electrode material sheet during firing, thereby enabling the surface roughness Sa of the negative electrode material sheet to be adjusted to the above-mentioned upper limit or less, improving the packing of the particulate carbon material in the negative electrode material sheet and imparting excellent sheet strength to the negative electrode material sheet.

[0016] In the method for producing a negative electrode material sheet for a non-aqueous secondary battery of the present invention, the volume fraction of the particulate carbon material in the primary sheet is preferably 45% by volume or more. If the volume fraction of the particulate carbon material in the primary sheet is equal to or greater than the lower limit, the density of the produced negative electrode material sheet can be appropriately increased, improving the strength of the negative electrode material sheet and increasing the capacity of a secondary battery produced using a negative electrode including the negative electrode material sheet.

[0017] Furthermore, in the method for producing a negative electrode material sheet for a non-aqueous secondary battery of the present invention, the particulate carbon material preferably contains flake graphite. Using flake graphite as the particulate carbon material can further improve the strength of the negative electrode including the produced negative electrode material sheet, and can further improve the rate characteristics of a secondary battery produced using the negative electrode.

[0018] Furthermore, in the method of the present invention for producing a negative electrode material sheet for a non-aqueous secondary battery, the particulate carbon material preferably has an aspect ratio of more than 1.2 and not more than 20. Use of particulate carbon material having an aspect ratio within the above-mentioned range can further improve the rate characteristics of a secondary battery produced using a negative electrode comprising the produced negative electrode material sheet.

[0019] The present invention aims to advantageously solve the above-mentioned problems, and provides a negative electrode for a nonaqueous secondary battery comprising any one of the above-mentioned negative electrode material sheets for a nonaqueous secondary battery. The negative electrode for a nonaqueous secondary battery of the present invention maintains its strength and can impart a good initial irreversible capacity to the secondary battery.

[0020] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the nonaqueous secondary battery of the present invention is characterized by including the above-mentioned negative electrode for a nonaqueous secondary battery. Because the nonaqueous secondary battery of the present invention includes the above-mentioned negative electrode for a nonaqueous secondary battery, the strength of the negative electrode is maintained and the battery can have a good initial irreversible capacity. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a negative electrode material sheet for a non-aqueous secondary battery that can form a negative electrode that can impart a good initial irreversible capacity to a non-aqueous secondary battery while maintaining sheet strength. Furthermore, according to the present invention, it is possible to provide a negative electrode that maintains its strength and can impart a good initial irreversible capacity to a non-aqueous secondary battery. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery in which the strength of the negative electrode is maintained and which has a good initial irreversible capacity. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail. The negative electrode material sheet for a non-aqueous secondary battery of the present invention (hereinafter sometimes simply referred to as "negative electrode material sheet") can be used as a negative electrode mixture layer of a negative electrode for a non-aqueous secondary battery. The negative electrode material sheet of the present invention can be produced using the method for producing a negative electrode material sheet of the present invention. The negative electrode for a nonaqueous secondary battery of the present invention (hereinafter sometimes simply referred to as "negative electrode") includes the negative electrode material sheet of the present invention as a negative electrode mixture layer. That is, the negative electrode material sheet of the present invention can be used to manufacture the negative electrode of the present invention. For example, the negative electrode of the present invention can be manufactured by bonding the negative electrode material sheet of the present invention to a current collector. Furthermore, the nonaqueous secondary battery of the present invention (hereinafter sometimes simply referred to as "secondary battery") includes the negative electrode of the present invention. That is, the negative electrode of the present invention can be used to manufacture the secondary battery of the present invention.

[0023] (Negative electrode material sheet for non-aqueous secondary batteries) The negative electrode material sheet of the present invention contains a particulate carbon material and, optionally, further contains other components such as a resin-derived component and a fibrous carbon material. In the negative electrode material sheet of the present invention, the particulate carbon material is oriented perpendicular to the surface of the negative electrode material sheet. The content of the resin-derived component in the negative electrode material sheet of the present invention is a predetermined value or less. The surface roughness Sa of the negative electrode material sheet of the present invention is a predetermined value or less. The negative electrode material sheet of the present invention can form a negative electrode that maintains its strength and can impart a good initial irreversible capacity to a secondary battery.

[0024] <Carbon particle material> Particulate carbon materials are particulate materials formed from carbon-atom-containing substances that can absorb and release charge carriers such as lithium and serve as negative electrode active materials for nonaqueous secondary batteries. Examples of particulate carbon materials include, but are not limited to, graphite and carbon black. Graphite, depending on its origin, includes natural graphite and artificial graphite. Graphite, depending on its morphological characteristics, includes flake graphite, lump graphite (flake graphite), amorphous graphite, exfoliated graphite, and spherical graphite (ellipsoidal graphite). Graphite may or may not be treated. Examples of treated graphite include acid-treated graphite (e.g., expandable graphite, expanded graphite). Carbon black is an aggregate of several layers of graphitic carbon microcrystals forming a turbostratic structure, and specific examples include acetylene black, ketjen black, furnace black, channel black, and thermal lamp black. Furthermore, carbon black may contain a hetero element (e.g., silicon, nitrogen, boron, etc.) different from the carbon element that is the main component. These particulate carbon materials may be used alone or in combination of two or more.

[0025] Among the above-mentioned granular carbon materials, it is preferable to use granular carbon materials having a shape with a major axis (i.e., a shape with a major axis, a minor axis, and a thickness) from the viewpoint of obtaining a shape that provides excellent orientation. Examples of granular carbon materials having such shapes include graphite having a flat plate shape (e.g., flake graphite) and spherical graphite having a major axis (elliptical graphite). Among granular carbon materials having such shapes, it is more preferable to use graphite having a flat plate shape (e.g., flake graphite) from the viewpoint of improving the packing property and adhesion, thereby improving the bonding strength between the granular carbon materials and improving the strength of the negative electrode material sheet. The use of flake graphite as the granular carbon material can achieve excellent vertical orientation in the negative electrode material sheet, thereby further improving the rate characteristics of a secondary battery manufactured using a negative electrode including the negative electrode material sheet. The use of flake graphite as the granular carbon material also improves the packing property and adhesion, thereby further improving the bonding strength between the negative electrode active materials and further improving the strength of the negative electrode material sheet. Examples of flake graphite include "UP20α" manufactured by Nippon Graphite Industries Co., Ltd.

[0026] <<Properties of particulate carbon materials>> The volume average particle diameter of the particulate carbon material is preferably 3 μm or more, more preferably 5 μm or more, even more preferably 8 μm or more, even more preferably 12 μm or more, even more preferably 16 μm or more, and preferably 200 μm or less, more preferably 150 μm or less, preferably 100 μm or less, and even more preferably 50 μm or less. If the volume average particle diameter of the particulate carbon material is above the above lower limit, the density of the negative electrode material sheet is appropriately reduced, facilitating the movement of charge carriers such as lithium, thereby further improving the rate characteristics of a secondary battery manufactured using a negative electrode comprising the negative electrode material sheet. On the other hand, if the volume average particle diameter of the particulate carbon material is below the above upper limit, the density of the negative electrode material sheet is appropriately increased, thereby enabling a secondary battery manufactured using a negative electrode comprising the negative electrode material sheet to have a high capacity. In the present invention, the "volume average particle size" can be measured in accordance with JIS Z8825, and represents the particle size at which the cumulative volume calculated from the smallest diameter side becomes 50% in the particle size distribution (volume basis) measured by a laser diffraction method.

[0027] Furthermore, as described above, the particulate carbon material is preferably a particulate carbon material having a shape with a major axis (i.e., a shape with a major axis, a minor axis, and a thickness). For particulate carbon materials having a shape with a major axis, the aspect ratio (major axis / minor axis) of the particulate carbon material is preferably greater than 1.2, more preferably greater than 2, even more preferably greater than 4, and even more preferably greater than 6, and is preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. When the aspect ratio of the particulate carbon material is within the above-mentioned range, excellent orientation of the particulate carbon material is obtained, and the effect of the particulate carbon material being oriented perpendicular to the surface of the negative electrode material sheet, as described below (i.e., the effect that charge carriers such as lithium can be easily moved, thereby further improving the rate characteristics of a secondary battery manufactured using a negative electrode comprising the negative electrode material sheet) is significantly exhibited.

[0028] <<Content of particulate carbon material>> The content of the particulate carbon material in the negative electrode material sheet is preferably 92% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more, and can be 100% by mass or less. If the content of the particulate carbon material in the negative electrode material sheet is equal to or greater than the above lower limit, the initial irreversible capacity of a secondary battery manufactured using a negative electrode including the negative electrode material sheet can be further improved, and the capacity of the secondary battery can be increased.

[0029] <Other ingredients> The negative electrode material sheet of the present invention may further contain components other than the particulate carbon material described above. Examples of other components that can be used include resin-derived components and fibrous carbon material.

[0030] <<Resin-derived ingredients>> The "resin-derived component" optionally contained in the negative electrode material sheet of the present invention is not particularly limited, but refers, for example, to a portion of the resin used to form the primary and secondary sheets, which are precursors of the negative electrode material sheet, in the manufacturing method of the negative electrode material sheet described below, which is not burned during the firing process and remains as the resin itself or a modified resin (e.g., a substance whose details are unknown but which is presumed to be tar). Specifically, the resin-derived component can be identified as a component that disappears (e.g., vaporizes or oxidizes) while the temperature of the negative electrode material sheet is raised from 30°C to 600°C, as in the method for measuring the content ratio of the resin-derived component described below. Specific examples of resins from which the resin-derived components that can be contained in the negative electrode material sheet are derived include the resins described below in the section "Method for producing negative electrode material sheet for non-aqueous secondary battery." The content of the resin-derived component in the negative electrode material sheet will be described later.

[0031] <<Carbon fiber materials>> The fibrous carbon material optionally contained in the negative electrode material sheet is a material that can improve the strength of the negative electrode material sheet. The fibrous carbon material is not particularly limited, and examples thereof include carbon nanotubes, vapor-grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, and cut products thereof. These may be used alone or in combination of two or more.

[0032] Among the above-mentioned materials, it is preferable to use a fibrous carbon nanostructure such as a carbon nanotube as the fibrous carbon material, and it is more preferable to use a fibrous carbon nanostructure containing a carbon nanotube. The use of a fibrous carbon nanostructure such as a carbon nanotube can further improve the strength of the negative electrode material sheet.

[0033] <Orientation of particulate carbon materials> The particulate carbon material is oriented perpendicular to the surface of the negative electrode material sheet for a nonaqueous secondary battery. "Oriented perpendicularly" means that the major axis of the particulate carbon material is oriented at an angle of a predetermined value or greater relative to the surface of the negative electrode material sheet. Orienting the particulate carbon material perpendicular to the surface of the negative electrode material sheet facilitates the movement of charge carriers such as lithium, thereby further improving the rate characteristics of a secondary battery manufactured using a negative electrode comprising the negative electrode material sheet. The orientation of the particulate carbon material can be evaluated, for example, using the measured value of the orientation angle of the particulate carbon material as an index. The orientation of the particulate carbon material can be adjusted, for example, by the steps performed in the method for manufacturing the negative electrode material sheet described below, the properties of the particulate carbon material used (e.g., aspect ratio), the molding conditions including the film thickness of the primary sheet described below, the cutting angle of the laminate, and the firing conditions (e.g., temperature, pressure load, and time).

[0034] <<Orientation angle of particulate carbon material>> When the orientation angle of the particulate carbon material is used as an indicator, the particulate carbon material is oriented perpendicular to the surface of the negative electrode material sheet. The orientation angle of the particulate carbon material in the negative electrode material sheet is preferably 60° or more, more preferably 65° or more, even more preferably 70° or more, and preferably 90° or less, relative to the surface of the negative electrode material sheet. If the orientation angle of the particulate carbon material is within the above-mentioned range relative to the surface of the negative electrode material sheet, the movement of charge carriers such as lithium is facilitated, thereby further improving the rate performance of a secondary battery manufactured using a negative electrode comprising the negative electrode material sheet. In the present invention, the orientation angle of the particulate carbon material relative to the surface of the negative electrode material sheet for a non-aqueous secondary battery can be measured by the method described in the Examples of this specification.

[0035] <Content of resin-derived components> The content of the resin-derived component in the negative electrode material sheet of the present invention must be 8% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and even more preferably 1% by mass or less. If the content of the resin-derived component in the negative electrode material sheet is equal to or less than the above-mentioned predetermined value, the amount of the resin-derived component that can function as a type of binder is reduced, which is thought to suppress an increase in initial irreversible capacity that may be caused by the presence of the resin-derived component, and therefore a secondary battery manufactured using a negative electrode including the negative electrode material sheet can have a good initial irreversible capacity. The content of the resin-derived component in the negative electrode material sheet is not particularly limited, and can be 0 mass % or more. From the viewpoint of further improving the initial irreversible capacity of the secondary battery, it is particularly preferable that the content of the resin-derived component in the negative electrode material sheet is 0 mass %. The content ratio of the resin-derived component in the negative electrode material sheet can be adjusted, for example, by the steps performed in the method for producing the negative electrode material sheet described below, the type and amount of the resin used, and the firing conditions (e.g., temperature, pressure load, and time). In the present invention, the content ratio of the resin-derived component in the negative electrode material sheet can be measured by subjecting the negative electrode material sheet to thermogravimetry (TGA measurement) in an oxygen atmosphere at a temperature range of 30°C to a temperature of 600°C or higher (e.g., 1000°C) at a heating rate of 10°C / min, determining the weight that is lost due to disappearance (e.g., vaporization or oxidation) between 30°C and 600°C as the weight of the resin-derived component, and determining the ratio of the weight of the resin-derived component to the initial weight of the negative electrode material sheet as the content ratio of the resin-derived component in the negative electrode material sheet.

[0036] <Surface roughness Sa of negative electrode material sheet> The surface roughness Sa of the negative electrode material sheet is 10 μm or less, preferably 6 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. If the surface roughness Sa of the negative electrode material sheet is below the above upper limit, the surface smoothness of the negative electrode material sheet is increased, the filling of the particulate carbon material in the negative electrode material sheet is improved, and the negative electrode material sheet can be provided with excellent sheet strength. Furthermore, if the surface roughness Sa is below the above upper limit, the surface of the negative electrode using such a negative electrode material sheet is smooth, the distance between the opposing electrodes (negative electrode and positive electrode) is uniform, and problems such as output instability and inter-electrode short circuits in the secondary battery can be avoided. Furthermore, the surface roughness Sa of the negative electrode material sheet is preferably 1.0 μm or more. If the surface roughness Sa of the negative electrode material sheet is extremely small, excessive pressure is applied during firing in the production of the negative electrode material sheet, which is thought to be the cause, and the particulate carbon material is likely to be oriented in a horizontal direction. Therefore, if the surface roughness Sa of the negative electrode material sheet is equal to or greater than the above lower limit, the particulate carbon material can be prevented from being oriented in the horizontal direction, and it becomes easier to produce a sheet in which the particulate carbon material is oriented in the vertical direction. The surface roughness Sa of the negative electrode material sheet can be adjusted to fall within the above range, for example, by firing the secondary sheet under pressure when producing the negative electrode material sheet by the negative electrode material sheet production method described below.

[0037] <Thickness> The thickness of the negative electrode material sheet is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more, and is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. If the thickness of the negative electrode material sheet is equal to or greater than the above lower limit, a secondary battery manufactured using a negative electrode including the negative electrode material sheet can have a high capacity. On the other hand, if the thickness of the negative electrode material sheet is equal to or less than the above upper limit, a secondary battery manufactured using a negative electrode including the negative electrode material sheet can be made thinner.

[0038] (Method of manufacturing a negative electrode material sheet for a non-aqueous secondary battery) The method for producing a negative electrode material sheet of the present invention includes: (A) a primary sheet forming step of pressurizing a composition containing a resin and a particulate carbon material to form it into a sheet to obtain a primary sheet; (B) a laminate forming step of stacking a plurality of the primary sheets in the thickness direction or folding or rolling the primary sheets to obtain a laminate; (C) a slicing step of slicing the laminate at an angle of 45° or less with respect to the stacking direction to obtain a secondary sheet; and (D) a firing step of firing the secondary sheet under pressure at a firing temperature of a predetermined value or higher. The method for producing a negative electrode material sheet of the present invention may optionally further include steps other than the above steps (A) to (D).

[0039] According to the method for producing a negative electrode material sheet of the present invention, it is possible to produce a negative electrode material sheet capable of forming a negative electrode that can impart a good initial irreversible capacity to a non-aqueous secondary battery while maintaining sheet strength. According to the method for producing an anode material sheet of the present invention, the above-described anode material sheet of the present invention can be produced efficiently.

[0040] <(A) Primary sheet forming process> In the primary sheet forming step, a composition containing a resin and particulate carbon material is pressed into a sheet to obtain a primary sheet.

[0041] <<Composition>> The composition includes a resin and a particulate carbon material. The composition may or may not further include a fibrous carbon material (i.e., the content of the fibrous carbon material in the composition may be 0 parts by mass per 100 parts by mass of the resin, or 0 parts by mass or more per 100 parts by mass of the particulate carbon material). The composition may or may not further include components (other components) other than the above-mentioned resin, particulate carbon material, and fibrous carbon material.

[0042] -resin- The resin is not particularly limited, and any resin can be used. For example, either a liquid resin or a solid resin can be used. One type of resin may be used alone, or two or more types may be used in combination. For example, both a liquid resin and a solid resin can be used. When a liquid resin and a solid resin are used in combination, the mass ratio of the liquid resin to the solid resin can be adjusted within a range that achieves the desired effects of the present invention. The higher the proportion of liquid resin in the overall resin, the easier it is to increase the filling rate of the particulate carbon material in the primary sheet. On the other hand, the higher the proportion of solid resin in the overall resin, the greater the strength of the primary sheet.

[0043] = Liquid resin = The liquid resin is not particularly limited as long as it is liquid at room temperature and normal pressure, and for example, a thermoplastic resin that is liquid at room temperature and normal pressure can be used. In the present invention, "normal temperature" refers to 23° C., and "normal pressure" refers to 1 atm (absolute pressure).

[0044] Examples of liquid resins include fluororesins, silicone resins, acrylic resins, epoxy resins, and acrylonitrile-butadiene copolymers (nitrile rubbers). These may be used alone or in combination of two or more.

[0045] =Solid Resin= The solid resin is not particularly limited as long as it is not a liquid at room temperature and normal pressure, and for example, a thermoplastic resin that is solid at room temperature and normal pressure, or a thermosetting resin that is solid at room temperature and normal pressure can be used.

[0046] Examples of thermoplastic resins that are solid at room temperature and pressure include acrylic resins such as poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its esters, and polyacrylic acid or its esters; silicone resins; fluororesins; polyethylene; polypropylene; ethylene-propylene copolymers; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymers; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; and polyacrylonitrile. Examples of such copolymers include styrene-acrylonitrile copolymers, acrylonitrile-butadiene copolymers (nitrile rubbers), acrylonitrile-butadiene-styrene copolymers (ABS resins), styrene-butadiene block copolymers or hydrogenated products thereof, styrene-isoprene block copolymers or hydrogenated products thereof, polyphenylene ethers, modified polyphenylene ethers, aliphatic polyamides, aromatic polyamides, polyamideimides, polycarbonates, polyphenylene sulfides, polysulfones, polyethersulfones, polyethernitriles, polyetherketones, polyketones, polyurethanes, liquid crystal polymers, and ionomers. These may be used alone or in combination of two or more. In the present invention, rubber is included in the "resin".

[0047] Examples of thermosetting resins that are solid at room temperature and normal pressure include natural rubber, butadiene rubber, isoprene rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene propylene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, butyl rubber, halogenated butyl rubber, polyisobutylene rubber, epoxy resin, polyimide resin, bismaleimide resin, benzocyclobutene resin, phenolic resin, unsaturated polyester, diallyl phthalate resin, polyimide silicone resin, polyurethane, thermosetting polyphenylene ether, thermosetting modified polyphenylene ether, etc. These may be used alone or in combination of two or more.

[0048] - Particulate carbon material - As the particulate carbon material, the particulate carbon material described above in the section "Negative electrode material sheet for non-aqueous secondary battery" can be used.

[0049] The content of the particulate carbon material in the composition is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, even more preferably 120 parts by mass or more, even more preferably 180 parts by mass or more, even more preferably 250 parts by mass or more, and preferably 500 parts by mass or less, more preferably 450 parts by mass or less, and even more preferably 400 parts by mass or less, relative to 100 parts by mass of the resin. When the content of the particulate carbon material in the composition is equal to or greater than the above-mentioned lower limit, the density of the produced negative electrode material sheet can be appropriately increased, improving the strength of the negative electrode material sheet and increasing the capacity of a secondary battery produced using a negative electrode comprising the negative electrode material sheet. On the other hand, when the content of the particulate carbon material in the composition is equal to or less than the above-mentioned upper limit, the density of the produced negative electrode material sheet can be appropriately decreased, further improving the rate characteristics of a secondary battery produced using a negative electrode comprising the negative electrode material sheet and increasing the electrolyte injectability of the secondary battery.

[0050] Furthermore, in the composition that becomes the primary sheet, the ratio (volume fraction) of the volume of the particulate carbon material to the total volume of the solid components (i.e., the total volume of the resin, particulate carbon material, optionally added fibrous carbon material, and other components) is preferably 25% by volume or more, more preferably 37% by volume or more, more preferably 45% by volume or more, even more preferably 53% by volume or more, and preferably 75% by volume or less, more preferably 70% by volume or less, and even more preferably 65% ​​by volume or less. If the volume fraction of the particulate carbon material to the total volume of the resin and particulate carbon material in the composition is equal to or greater than the above lower limit, the density of the produced negative electrode material sheet can be appropriately increased, improving the strength of the negative electrode material sheet and increasing the capacity of secondary batteries produced using negative electrodes that include the negative electrode material sheet. On the other hand, if the ratio of the volume of the particulate carbon material to the total volume of the resin and particulate carbon material in the composition is not more than the above upper limit, the density of the produced negative electrode material sheet can be appropriately reduced, thereby further improving the rate characteristics of a secondary battery produced using a negative electrode comprising the negative electrode material sheet and increasing the electrolyte injection properties of the secondary battery.

[0051] -Other ingredients- The composition may or may not further contain other components in addition to the resin, particulate carbon material, and fibrous carbon material described above. Examples of other components that can be used include a dispersant. The dispersant is not particularly limited, and known dispersants can be used. The content of the dispersant in the composition can be adjusted within a range that achieves the desired effects of the present invention.

[0052] -Preparation of composition- The composition is not particularly limited and can be prepared by mixing the above-mentioned components. The mixing of the above-mentioned components can be carried out using known mixing devices, such as kneaders; mixers such as Henschel mixers, Hobart mixers, and high-speed mixers; twin-screw kneaders; and roll mixers. Mixing can also be carried out in the presence of a solvent such as ethyl acetate. The resin can be dissolved or dispersed in a solvent to prepare a resin solution, which can then be mixed with the particulate carbon material and any added fibrous carbon material and other components. When using fibrous carbon nanostructures containing CNTs as the fibrous carbon material, a dispersion can be prepared by dispersing the fibrous carbon nanostructures containing CNTs and a dispersant in a solvent such as methyl ethyl ketone. A small amount of resin can then be added to the dispersion, and the solvent can be evaporated to obtain a masterbatch, which can then be mixed with the resin and particulate carbon material. The mixing time can be, for example, 5 minutes to 60 minutes. The mixing temperature can be, for example, 5°C to 150°C.

[0053] <<Molding of the composition>> The composition prepared as described above can be optionally degassed and crushed, and then pressed to form into a sheet. The sheet formed by pressing the composition in this manner can be used as a primary sheet. If a solvent is used during mixing, it is preferable to remove the solvent before forming into a sheet. For example, if degassing is performed using vacuum degassing, the solvent can be removed simultaneously during degassing.

[0054] Here, the composition can be formed into a sheet using any known forming method, such as press molding, rolling, or extrusion, as long as the forming method involves applying pressure. Among these, the composition is preferably formed into a sheet by rolling (primary processing), and more preferably by sandwiching the composition between protective films and passing it between rolls. The protective film is not particularly limited, and may be a sandblasted polyethylene terephthalate (PET) film or the like. The roll temperature may be 5°C to 150°C, the roll gap may be 50 μm to 2500 μm, the roll linear pressure may be 1 kg / cm to 3000 kg / cm, and the roll speed may be 0.1 m / min to 20 m / min.

[0055] <(B) Laminate formation process> In the laminate formation process, a plurality of primary sheets obtained in the primary sheet molding process are stacked in the thickness direction, or the primary sheets are folded or wound, to obtain a laminate in which a plurality of primary sheets containing a resin and a particulate carbon material are formed in the thickness direction. Here, the formation of the laminate by folding the primary sheets is not particularly limited and can be performed by folding the primary sheets at a constant width using a folding machine. Furthermore, the formation of the laminate by winding the primary sheets is not particularly limited and can be performed by winding the primary sheets around an axis parallel to the short or long direction of the primary sheets. Furthermore, the formation of the laminate by stacking the primary sheets can be performed using a lamination device, not particularly limited. For example, using a sheet lamination device (manufactured by Nikkiso Co., Ltd., product name "Hi-Stacker") can prevent air from entering between the layers, thereby efficiently obtaining a good laminate.

[0056] In the lamination step, it is preferable to apply pressure (secondary pressure) to the obtained laminate in the lamination direction while heating it. By applying secondary pressure to the laminate in the lamination direction while heating it, it is possible to promote fusion bonding between the laminated primary sheets.

[0057] Here, the pressure applied to the laminate in the lamination direction can be set to 0.05 MPa or more and 0.50 MPa or less. The heating temperature of the laminate is not particularly limited, but is preferably 50°C or higher and 170°C or lower. Furthermore, the heating time for the laminate can be, for example, 10 seconds or more and 30 minutes or less.

[0058] In the laminate obtained by stacking, folding, or rolling the primary sheet, the particulate carbon material is presumed to be oriented in a direction substantially perpendicular to the stacking direction. For example, when the particulate carbon material is flaky, the direction of the major axis of the main surface of the flaky shape is presumed to be substantially perpendicular to the stacking direction.

[0059] <(C) Slicing process> In the slicing step, the laminate is sliced ​​at an angle of 45° or less relative to the lamination direction to obtain secondary sheets consisting of slices of the laminate. The method for slicing the laminate is not particularly limited, and examples thereof include the multi-blade method, laser processing method, water jet method, and knife processing method. Among these, the knife processing method is preferred because it is easy to make the thickness of the secondary sheet uniform. The cutting tool used to slice the laminate is not particularly limited, and a slicing member having a smooth plate surface with a slit and a blade portion protruding from the slit portion (for example, a plane or slicer with a sharp blade) can be used.

[0060] The angle at which the laminate is sliced ​​is preferably 30° or less with respect to the stacking direction, more preferably 15° or less with respect to the stacking direction, and preferably approximately 0° with respect to the stacking direction (i.e., in the direction along the stacking direction). In the secondary sheet obtained in this manner, the particulate carbon material is well oriented in the thickness direction. For example, when the particulate carbon material is flaky, the direction of the major axis of the main surface of the flaky shape is approximately aligned with the thickness direction of the secondary sheet.

[0061] <(D) Firing process> In the firing step, the secondary sheet is fired under pressure at a firing temperature equal to or higher than a predetermined value to burn and remove the resin contained in the secondary sheet, thereby obtaining a negative electrode material sheet. The resulting negative electrode material sheet is a sheet obtained by removing the resin from the secondary sheet described above. Therefore, in the negative electrode material sheet, the particulate carbon material is well oriented in the thickness direction. For example, when the particulate carbon material is flaky, the major axis of the main surface of the flaky shape is oriented perpendicular to the surface of the secondary sheet.

[0062] Here, the heating temperature when firing the secondary sheet is 600°C or higher, preferably 700°C or higher, more preferably 800°C or higher, and even more preferably 900°C or higher. Furthermore, the heating temperature when firing the secondary sheet is preferably 2000°C or lower, more preferably 1500°C or lower, and even more preferably 1200°C or lower. If the heating temperature when firing the secondary sheet is above the lower limit, the content of resin-derived components in the produced negative electrode material sheet can be reduced, thereby further improving the initial irreversible capacity of a secondary battery produced using a negative electrode including the negative electrode material sheet. On the other hand, if the heating temperature when firing the secondary sheet is below the upper limit, damage to the structure of the produced negative electrode material sheet due to excessive heating can be suppressed, and the strength of the negative electrode material sheet can be ensured to be sufficiently high.

[0063] The secondary sheet is fired under pressure. The pressure is preferably applied in the thickness direction of the secondary sheet, and more preferably uniformly. Pressure application methods include placing a weight on the secondary sheet or placing the secondary sheet under high-pressure gas. From the viewpoint of uniformly applying the load in the thickness direction of the secondary sheet, it is preferable to apply the load by placing a weight on the secondary sheet. Firing the secondary sheet under pressure can impart smoothness to the surface of the negative electrode material sheet during firing, thereby making it possible to adjust the surface roughness Sa of the negative electrode material sheet to the above-mentioned upper limit or less.

[0064] The pressure applied when firing the secondary sheet is preferably 0.001 MPa or more, more preferably 0.003 MPa or more, and even more preferably 0.005 MPa or more. The pressure applied when firing the secondary sheet is preferably 1 MPa or less, more preferably 0.5 MPa or less, and even more preferably 0.1 MPa or less. If the pressure applied when firing the secondary sheet is equal to or greater than the above-mentioned lower limit, smoothness can be imparted to the surface of the negative electrode material sheet during firing, thereby making it possible to adjust the surface roughness Sa of the negative electrode material sheet to equal to or less than the above-mentioned upper limit. This improves the packing of the particulate carbon material in the negative electrode material sheet, thereby providing the negative electrode material sheet with excellent sheet strength. On the other hand, if the pressure applied when firing the secondary sheet is below the above upper limit, excessive pressure will deteriorate the orientation of the particulate carbon material (i.e., the orientation angle will be biased horizontally rather than vertically, or the uniformity of the orientation angle will decrease), which will result in a decrease in rate characteristics when used in a secondary battery, and the sheet strength of the negative electrode material sheet will decrease due to the deterioration of orientation, which will prevent the negative electrode material sheet from becoming brittle.

[0065] The heating time when firing the secondary sheet can be adjusted depending on the heating temperature, but can be set to, for example, 30 minutes or more and 72 hours or less.

[0066] (Negative electrode for non-aqueous secondary batteries) The negative electrode for a non-aqueous secondary battery of the present invention is characterized by comprising the above-described negative electrode material sheet of the present invention. For example, the negative electrode of the present invention comprises the negative electrode material sheet of the present invention as a negative electrode mixture layer on a current collector. The negative electrode of the present invention maintains its strength and can impart a good initial irreversible capacity to a non-aqueous secondary battery.

[0067] The negative electrode of the present invention is not particularly limited, and can be produced, for example, by laminating a current collector and the negative electrode material sheet of the present invention. Here, the current collector can be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or other materials. Among these, copper foil is particularly preferred as the current collector for the negative electrode. The above-mentioned materials may be used alone or in any combination of two or more materials in any ratio. The current collector and the negative electrode material sheet can be attached to each other by any known method without any particular limitation. When attaching the current collector and the negative electrode material sheet to each other, an adhesive or the like may be used.

[0068] (Non-aqueous secondary battery) The non-aqueous secondary battery of the present invention is characterized by including the above-described negative electrode for a non-aqueous secondary battery of the present invention. For example, the nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator, and uses the negative electrode for a nonaqueous secondary battery of the present invention as the negative electrode. Furthermore, since the nonaqueous secondary battery of the present invention uses the negative electrode for a nonaqueous secondary battery of the present invention, the strength of the negative electrode is maintained and the battery can have a good initial irreversible capacity. Below, the positive electrode, electrolyte, and separator will be described using a case where the nonaqueous secondary battery is a lithium ion secondary battery as an example, but the present invention is not limited to these examples.

[0069] <Positive electrode> The positive electrode may be a known positive electrode used as a positive electrode for a lithium ion secondary battery. Specifically, the positive electrode may be, for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector. The current collector may be made of a metal material such as aluminum, etc. The positive electrode mixture layer may be a layer containing a known positive electrode active material, a conductive material, and a binder.

[0070] <Electrolyte> The electrolytic solution may be one in which an electrolyte is dissolved in a solvent. The solvent may be an organic solvent capable of dissolving the electrolyte. Specifically, the solvent may be an alkyl carbonate solvent such as ethylene carbonate, propylene carbonate, or γ-butyrolactone to which a viscosity adjusting solvent such as 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane, dioxolane, methyl propionate, or methyl formate has been added. Lithium salts can be used as the electrolyte. For example, those described in JP 2012-204303 A can be used as the lithium salt. Among these lithium salts, LiPF6, LiClO4, and CF3SO3Li are preferred as the electrolyte because they are easily soluble in organic solvents and exhibit a high degree of dissociation.

[0071] <separator> The separator is not particularly limited and may be any known separator, such as that described in JP 2012-204303 A. Among these, a microporous membrane made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the proportion of electrode active material in the lithium ion secondary battery and increasing the capacity per volume.

[0072] <Method of manufacturing non-aqueous secondary battery> The nonaqueous secondary battery of the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary according to the battery shape, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. To prevent internal pressure increases and overcharging and discharging, etc., a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. The shape of the secondary battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, etc. [Example]

[0073] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. In the examples, various measurements and evaluations were carried out according to the following methods.

[0074] <Orientation angle of particulate carbon material> The orientation angle of the particulate carbon material in the negative electrode material sheet was determined by observing a cross section of the negative electrode material sheet cut into a regular octagon using a scanning electron microscope (SEM, Hitachi High-Technologies Corporation's "SU-3500") at a magnification that fit the entire sheet from top to bottom. The magnification was 700x. Fifty lines were drawn along the major axes of 50 randomly selected particles of carbon material in the cross section, and the average angle of the major axes relative to the surface of the negative electrode material sheet was calculated. This was performed for eight surfaces, and the largest value among the eight surfaces was taken as the orientation angle of the particulate carbon material in the negative electrode material sheet.

[0075] <Surface roughness Sa> The surface roughness Sa of the negative electrode material sheet was measured using a three-dimensional shape measuring device (manufactured by Keyence Corporation, product name "One-Shot 3D Measuring Macroscope"). Specifically, the three-dimensional shape was measured for five analysis ranges (1 cm x 1 cm) extracted from the surface of the negative electrode material sheet to be evaluated. It is desirable that the five analysis ranges be at least 0.5 cm apart when extracting the five points, but if the size of the negative electrode material sheet is small, it is acceptable for the analysis ranges to overlap partially. Furthermore, if the size of the negative electrode material sheet is too small to ensure a 1 cm x 1 cm analysis range, the analysis range may be reduced to 0.3 cm x 0.3 cm. Furthermore, the three-dimensional shape measurement results were filtered (2.5 mm) using software to remove waviness components, and the surface roughness Sa (μm) was automatically calculated. The average value of the five analysis points was taken as the surface roughness Sa of the negative electrode material sheet.

[0076] <Content of resin-derived components> The negative electrode material sheet was subjected to thermogravimetry (TGA measurement) in an oxygen atmosphere at a temperature range of 30 to 1000°C at a heating rate of 10°C / min. The weight loss rate from the starting point to 600°C (weight loss up to 600°C / sheet mass at the start of measurement × 100%) was defined as the content of resin-derived components in the negative electrode material sheet.

[0077] <Thickness> Using a film thickness meter (manufactured by Mitutoyo, product name "Digimatic Indicator ID-C112XBS"), the thickness was measured at five points, approximately the center and each of the four corners (squares), of the negative electrode material sheet, and the average value (μm) of the measured thicknesses was taken as the thickness of the negative electrode material sheet.

[0078] <Strength> A test specimen was prepared by cutting the negative electrode material sheet into a size of 1 cm x 5 cm. A 6 cm x 6 cm x 2 cm base was also prepared. The right half of the test specimen was placed on the base from the center, with the left half extending beyond the base. A 6 x 6 x 2 mm aluminum plate was then placed on the right half of the test specimen. Weights of 100 mg, 200 mg, and 300 mg were then alternately placed on the portion of the test specimen extending beyond the base until the test specimen broke. The strength of the negative electrode material sheet was evaluated according to the following criteria, based on the weight of the weight placed when the test specimen broke. 〇: The test piece broke under the weight of 300 mg △: The test piece broke under the weight of 200 mg ×: The test piece broke under the weight of 100 mg

[0079] <Irreversible capacity rate> <<Manufacturing cells for electrode evaluation>> A lithium-ion secondary battery half-cell for evaluation was fabricated with the following configuration: The half-cell was fabricated by punching out each component to a size of 17 mm diameter, vacuum drying (120°C x 10 hours), and then storing in a dry box with a dew point of -80°C or less.

[0080] [Half-cell configuration] Working electrode: negative electrode (negative electrode made by attaching a negative electrode material sheet to copper foil) Counter electrode: Li metal Reference pole: Li metal Separator: nonwoven glass fabric, polyethylene (PE) microporous membrane Electrolyte: 1.0M LiPF6 solution (solvent: ethylene carbonate (EC) / methyl ethyl carbonate (MEC) = 3 / 7 (volume ratio) mixed solvent, containing 1% by volume (solvent ratio) of vinylene carbonate (VC) as an additive)

[0081] <<Charge / Discharge Test>> The resulting half cell for evaluation was subjected to a charge-discharge test under the following condition 1. (Condition 1) Charging conditions: 0.2C, charging voltage 0.01V-CCCV (0.05C cut) Discharge conditions: 0.2C, final voltage 2.5V-CC Number of cycles: 10 cycles Test temperature: 25℃ Next, a charge-discharge test was further carried out under the following condition 2. (Condition 2) Charging conditions: 0.2C, charging voltage 0.01V-CCCV (0.05C cut) Discharge conditions: 2.0C, final voltage 2.5V-CC Number of cycles: 10 cycles Test temperature: 25℃ The ratio of the discharge capacity to the charge capacity in the first cycle was calculated as a percentage and used as the initial irreversible capacity rate. A: The initial irreversible capacity rate is between 85% and 100% B: Initial irreversible capacity rate is 75% or more and less than 85% C: Initial irreversible capacity rate is 65% or more and less than 75% It should be noted that the smaller the irreversible capacity rate, the more likely it is that lithium is not reacting properly due to the influence of components derived from the resin.

[0082] Example 1 <Preparation of Composition> 210 parts of liquid nitrile rubber (NBR) (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 1312", decomposition initiation temperature: 336 ° C.) and 90 parts of solid nitrile rubber (NBR) (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 3350", decomposition initiation temperature: 375 ° C.) and 820 parts of flake graphite (manufactured by Nippon Graphite Industries Co., Ltd., trade name "UP20α", volume average particle diameter: 20 μm, aspect ratio = 10) as a particulate carbon material (equivalent to 364 parts by volume relative to 300 parts by volume of the resin used) were mixed and stirred at 150 ° C. for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, the resulting mixture was placed in a crusher (manufactured by Osaka Chemical Co., Ltd., trade name "Wonder Crush Mill D3V-10") and crushed for 10 seconds to obtain a composition.

[0083] <Formation of primary sheet> Next, 50 g of the obtained composition was sandwiched between sandblasted PET films (protective films) having a thickness of 50 μm, and roll-molded (primary pressing) under the conditions of a roll gap of 1000 μm, a roll temperature of 50°C, a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min to obtain a primary sheet having a thickness of 0.8 mm.

[0084] <Formation of laminate> Next, the obtained primary sheet was cut into a size of 150 mm length x 150 mm width x 0.8 mm thickness, and 188 sheets were stacked in the thickness direction of the primary sheet.Furthermore, by pressing (secondary pressing) in the stacking direction at a temperature of 120°C and a pressure of 0.1 MPa for 3 minutes, a laminate with a height of approximately 150 mm was obtained.

[0085] <Secondary sheet formation> Then, while pressing the laminated side of the secondarily pressurized laminate with a pressure of 0.3 MPa, a woodworking slicer (manufactured by Marunaka Iron Works Co., Ltd., product name ``Super Finishing Planer Super Mecha S'') was used to slice at an angle of 0 degrees to the lamination direction (in other words, in the normal direction to the main surface of the laminated primary sheets), thereby obtaining a secondary sheet measuring 150 mm in length, 150 mm in width, and 0.10 mm in thickness.

[0086] <Preparation of negative electrode material sheet> The resulting secondary sheet was then subjected to uniform pressure of 0.003 MPa in the thickness direction and baked at 1000°C for 8 hours in a nitrogen atmosphere to burn off and remove the resin components, thereby obtaining a negative electrode material sheet. The obtained negative electrode material sheet was subjected to various measurements and evaluations, and the results are shown in Table 1.

[0087] Example 2 The same procedures as in Example 1 were carried out, except that spheroidized natural graphite (manufactured by Atomaxchem, trade name "DMGS", volume average particle size: 15 μm, aspect ratio = 2) was used instead of the flake graphite used in Example 1 (manufactured by Nippon Graphite Industries Co., Ltd., trade name "UP20α", volume average particle size: 20 μm, aspect ratio = 10).

[0088] Example 3 The amount of flake graphite in Example 1 was changed to 550 parts. Otherwise, the same procedure as in Example 1 was carried out.

[0089] Example 4 The firing temperature in Example 1 was changed to 600° C. Other than that, the same procedure as in Example 1 was carried out.

[0090] Example 5 The pressure during firing in Example 1 was set to 1 MPa, except that the procedure was the same as in Example 1.

[0091] (Comparative Example 1) The firing temperature in Example 1 was changed to 380° C., and firing was performed without applying pressure. Otherwise, the same procedures as in Example 1 were carried out.

[0092] (Comparative Example 2) The firing temperature in Example 1 was changed to 380° C. Other than that, the same procedure as in Example 1 was carried out.

[0093] (Comparative Example 3) The firing was carried out in the same manner as in Example 1, except that no pressure was applied.

[0094] [Table 1]

[0095] Table 1 shows that the negative electrodes of Examples 1 to 5, which were produced by bonding a negative electrode material sheet, which contained particulate carbon material and was oriented perpendicular to the surface of the negative electrode material sheet, had a content of resin-derived components in the negative electrode material sheet of a predetermined value or less, and further had a surface roughness Sa of a predetermined value or less, to a current collector as a negative electrode composite layer, were able to impart good initial irreversible capacity to a secondary battery while maintaining good sheet strength. On the other hand, the negative electrodes of Comparative Examples 1 to 3, which were produced by laminating a negative electrode material sheet, in which the content ratio of resin-derived components in the negative electrode material sheet was not equal to or less than a predetermined value, or the surface roughness Sa of the negative electrode material sheet was not equal to or less than a predetermined value, to a current collector as a negative electrode composite layer, were found to be inferior in either or both of the initial irreversible capacity for the secondary battery and the sheet strength relative to the negative electrode material sheet. [Industrial Applicability]

[0096] According to the present invention, it is possible to provide a negative electrode material sheet for a non-aqueous secondary battery that can form a negative electrode that can impart a good initial irreversible capacity to a non-aqueous secondary battery while maintaining sheet strength. Furthermore, according to the present invention, it is possible to provide a negative electrode that maintains its strength and can impart a good initial irreversible capacity to a non-aqueous secondary battery. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery in which the strength of the negative electrode is maintained and which has a good initial irreversible capacity.

Claims

1. A negative electrode material sheet for a non-aqueous secondary battery, comprising a particulate carbon material and a resin-derived component, the particulate carbon material is oriented at an orientation angle of 70° or more and 90° or less with respect to the surface of the negative electrode material sheet for a nonaqueous secondary battery, the resin-derived components include a component derived from a liquid resin that is liquid at 23°C and 1 atm and a component derived from a solid resin that is solid at 23°C and 1 atm, The content of the resin-derived component in the negative electrode material sheet for a nonaqueous secondary battery is 8% by mass or less, and The surface roughness Sa of the negative electrode material sheet for a nonaqueous secondary battery is 10 μm or less. Negative electrode material sheet for non-aqueous secondary batteries Here, the orientation angle is determined by drawing 50 lines along the major axes of any 50 particles of particulate carbon material in a cross section obtained by cutting a negative electrode material sheet for a non-aqueous secondary battery into a regular octagon, calculating the average angle of the major axes with respect to the surface of the sheet for eight faces, and determining the largest value among the eight faces as the orientation angle.

2. 2. The negative electrode material sheet for a nonaqueous secondary battery according to claim 1, having a thickness of 50 μm or more.

3. 3. The negative electrode material sheet for a non-aqueous secondary battery according to claim 1, wherein the particulate carbon material contains flake graphite.

4. 4. The negative electrode material sheet for a non-aqueous secondary battery according to claim 1, wherein the particulate carbon material has an aspect ratio of more than 1.2 and not more than 20.

5. The liquid resin is one or more selected from the group consisting of silicone resin, acrylic resin, epoxy resin, and acrylonitrile-butadiene copolymer, The solid resin may be an acrylic resin such as poly(2-ethylhexyl acrylate), a copolymer of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its ester, or polyacrylic acid or its ester; a silicone resin; polyethylene; polypropylene; an ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; polyvinyl acetate; an ethylene-vinyl acetate copolymer; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; a styrene-acrylonitrile copolymer; or an acrylic resin. at least one selected from the group consisting of acrylonitrile-butadiene copolymer (nitrile rubber); acrylonitrile-butadiene-styrene copolymer (ABS resin); styrene-butadiene block copolymer or hydrogenated product thereof; styrene-isoprene block copolymer or hydrogenated product thereof; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; polyamideimide; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyethernitrile; polyetherketone; polyketone; polyurethane; liquid crystal polymer; and ionomer, The negative electrode material sheet for a non-aqueous secondary battery according to any one of claims 1 to 4.

6. a primary sheet forming step of pressurizing a composition containing a resin and a particulate carbon material to form a sheet, thereby obtaining a primary sheet in which the particulate carbon material is oriented in a direction at an angle of 70° to 90° relative to the thickness direction; a laminate formation step of stacking a plurality of the primary sheets in a thickness direction or folding or rolling the primary sheets to obtain a laminate in which the orientation direction of the particulate carbon material in each layer is substantially the same; a slicing step of slicing the laminate at an angle of 15° or less with respect to the lamination direction to obtain a secondary sheet; and a firing step of firing the secondary sheet under pressure at a firing temperature of 600°C or higher. Here, the orientation angle is determined by drawing 50 lines along the long axes of any 50 particles of particulate carbon material in a cross section of a primary sheet cut into a regular octagon, calculating the average angle of the long axes relative to the surface of the sheet for eight surfaces, and using the largest value among the eight surfaces as the orientation angle.

7. The method for producing a negative electrode material sheet for a nonaqueous secondary battery according to claim 6 , wherein the firing step is carried out under a pressure of 0.001 MPa or more.

8. The method for producing a negative electrode material sheet for a non-aqueous secondary battery according to claim 6 or 7, wherein a volume fraction of the particulate carbon material in the primary sheet is 45% by volume or more.

9. The method for producing a negative electrode material sheet for a non-aqueous secondary battery according to any one of claims 6 to 8, wherein the particulate carbon material contains flake graphite.

10. The method for producing a negative electrode material sheet for a non-aqueous secondary battery according to any one of claims 6 to 9, wherein the particulate carbon material has an aspect ratio of more than 1.2 to 20 or less.

11. A negative electrode for a non-aqueous secondary battery comprising the negative electrode material sheet for a non-aqueous secondary battery according to any one of claims 1 to 5.

12. A non-aqueous secondary battery comprising the negative electrode for a non-aqueous secondary battery according to claim 11.

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