Anode slurry and method for manufacturing the same, and anode and method for manufacturing the same

Abstract

The present invention provides a negative electrode slurry that can suppress the increase in thickness of a secondary battery and suppress the swelling of the secondary battery when it is repeatedly charged and discharged. [Solution] The negative electrode slurry contains a negative electrode active material containing carbon particles, a water-soluble polymer, and water. The solid content of the negative electrode slurry is 40-60% by mass. The water-soluble polymer includes free water-soluble polymer that is not adsorbed on the negative electrode active material. The mass M1 of the negative electrode slurry, the mass M2 of the water-soluble polymer in the negative electrode slurry, and the mass M3 of the free water-soluble polymer in the negative electrode slurry satisfy the following relationships (i) and (ii). 0.0090 ≤ M2 / M1 ≤ 0.0095 (i) 0.18 ≤ M3 / M2 ≤ 0.25 (ii)

Description

Technical Field

[0001] The present invention relates to a negative electrode slurry, a method for manufacturing the same, a negative electrode, and a method for manufacturing the same.

Background Art

[0002] The negative electrode used in a secondary battery such as a lithium ion battery has a negative electrode active material layer on a negative electrode current collector. The negative electrode active material layer is formed by applying a negative electrode slurry containing carbon particles, a water-soluble polymer such as carboxymethyl cellulose (hereinafter also referred to as "CMC"), and water to the negative electrode current collector, drying it, and compressing it by pressing (for example, Patent Documents 1 and 2, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since internal stress due to compression remains in the negative electrode active material layer, it sometimes causes springback that gradually swells over time, increasing the thickness of the secondary battery. Also, the secondary battery sometimes swells when repeatedly charged and discharged.

[0005] The present disclosure aims to provide a negative electrode slurry, a method for manufacturing the same, a negative electrode, and a method for manufacturing the same that can suppress an increase in the thickness of a secondary battery and suppress swelling of the secondary battery when repeatedly charged and discharged.

Means for Solving the Problems

[0006] [1] A negative electrode slurry comprising a negative electrode active material containing carbon particles, a water-soluble polymer, and water, The solid content of the negative electrode slurry is 40-60% by mass. The water-soluble polymer includes free water-soluble polymers that are not adsorbed onto the negative electrode active material. A negative electrode slurry in which the mass M1 of the negative electrode slurry, the mass M2 of the water-soluble polymer in the negative electrode slurry, and the mass M3 of the free water-soluble polymer in the negative electrode slurry satisfy the following relationships (i) and (ii). 0.0090 ≤ M2 / M1 ≤ 0.0095 (i) 0.18 ≤ M3 / M2 ≤ 0.25 (ii) [2] The negative electrode slurry according to [1], wherein the negative electrode active material consists only of the carbon particles. [3] The negative electrode slurry according to [1] or [2], wherein the average particle size (D50) of the carbon particles is 12 to 18 μm. [4] The anode slurry according to any one of [1] to [3], wherein the water-soluble polymer contains cellulose. [5] The anode slurry according to any one of [1] to [4], wherein the water-soluble polymer comprises carboxymethylcellulose having a degree of etherification of 0.65 to 0.75 mol / C6. [6] A negative electrode slurry according to any one of [1] to [5], further comprising styrene-butadiene rubber. [7] A method for manufacturing a negative electrode slurry, The process includes a first kneading step in which a first mixture containing a negative electrode active material containing carbon particles, a water-soluble polymer, and water is kneaded using a planetary mixer to a solid content of 50-70% by mass. The above-mentioned first kneading step is, The process (1a) involves mixing the materials so that the rotational speed RP1 of the planetary mixer is 10 rpm or more and the cumulative power is 0.08 to 0.12 kWh, The process includes, after step (1a), a step (1b) in which the planetary mixer is kneaded so that the rotation speed RP2 is 35 rpm or more and the cumulative power is 0.32 to 0.40 kWh, A method for manufacturing a negative electrode slurry, wherein the ratio of the rotational speed RP1 to the rotational speed RP2 (RP1 / RP2) is 0.4 to 0.8. [8] A method for producing a negative electrode slurry according to [7], comprising a second mixing step of mixing a second mixture obtained by further adding water to the first mixture after the first mixing step in the planetary mixer. [9] The method for producing a negative electrode slurry according to [8], wherein the second mixing step is the rotation speed RP3 of the planetary mixer is 36 to 38 rpm.

[10] The method for producing a negative electrode slurry according to [7], wherein the negative electrode slurry is the negative electrode slurry described in any of [1] to [6].

[11] A negative electrode having a negative electrode current collector and a negative electrode active material layer, The negative electrode active material layer comprises a negative electrode active material containing carbon particles and a water-soluble polymer. The water-soluble polymer includes free water-soluble polymers that are not adsorbed onto the negative electrode active material. The negative electrode wherein the content of the free water-soluble polymer in the negative electrode active material layer is 0.18 to 0.26% by mass relative to the negative electrode active material.

[12] The water-soluble polymer further comprises an adsorbed water-soluble polymer adsorbed on the negative electrode active material. The negative electrode according to

[11] , wherein the content of the adsorbed water-soluble polymer in the negative electrode active material layer is 0.30 to 0.82% by mass relative to the negative electrode active material.

[13] The negative electrode according to

[11] or

[12] , wherein the negative electrode active material consists solely of the carbon particles.

[14] The negative electrode active material layer has, in order from the negative electrode current collector side, a first active material layer and a second active material layer, The first active material layer comprises a first negative electrode active material containing first carbon particles, a first water-soluble polymer, and a first styrene-butadiene rubber. The second active material layer comprises a second negative electrode active material containing second carbon particles, a second water-soluble polymer, and a second styrene-butadiene rubber. The negative electrode according to any one of

[11] to

[13] , wherein the ratio (C2 / C1) of the content C2 [mass%] of the second water-soluble polymer relative to the second negative electrode active material to the content C1 [mass%] of the first water-soluble polymer relative to the first negative electrode active material is 1.75 to 1.85.

[15] A method for manufacturing a negative electrode having a negative electrode current collector and a negative electrode active material layer, The process includes applying a negative electrode slurry to the negative electrode current collector, drying it, and compressing it to form the negative electrode active material layer. A method for manufacturing a negative electrode, wherein the negative electrode slurry is a negative electrode slurry described in any of [1] to [6], or a negative electrode slurry obtained by a method for manufacturing a negative electrode slurry described in any of [7] to

[10] .

[16] The negative electrode active material layer has, in order from the negative electrode current collector side, a first active material layer and a second active material layer, The negative electrode slurry includes a first negative electrode slurry for forming the first active material layer and a second negative electrode slurry for forming the second active material layer. The first negative electrode slurry further comprises a first styrene-butadiene rubber, The second negative electrode slurry further comprises a second styrene-butadiene rubber, The ratio of the water-soluble polymer content Cs2 to the negative electrode active material content in the second negative electrode slurry and the water-soluble polymer content Cs1 to the negative electrode active material content in the first negative electrode slurry (Cs2 / Cs1) is 1.75 to 1.85. The step of forming the negative electrode active material layer is: The process involves applying a first negative electrode slurry to the negative electrode current collector to form a first layer, The process involves applying a second negative electrode slurry onto the first layer to form a second layer, A method for producing a negative electrode according to

[15] , comprising the steps of drying and compressing the first layer and the second layer. [Effects of the Invention]

[0007] According to the negative electrode slurry of the present disclosure, a negative electrode can be manufactured that can suppress an increase in the thickness of a secondary battery and suppress swelling of the secondary battery when the charge and discharge of the secondary battery are repeated.

Brief Description of the Drawings

[0008] [Figure 1] It is a flowchart for explaining the manufacturing process of the negative electrode slurry of the embodiment.

Embodiments for Carrying Out the Invention

[0009] In this specification, a numerical range such as "x to y" includes upper and lower limit values unless otherwise specified. That is, "x to y" represents a numerical range of "x or more and y or less". A numerical value arbitrarily selected from within the numerical range may be used as a new upper limit value or lower limit value. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described in another part of this specification, in a table, or in a figure, etc.

[0010] (Negative electrode slurry) The negative electrode slurry of the present embodiment (hereinafter also referred to as "this slurry (1)") can be used to form a negative electrode active material layer of a negative electrode of a non-aqueous electrolyte secondary battery (hereinafter also referred to as "secondary battery"). Examples of the secondary battery include a lithium-ion secondary battery that performs charge and discharge by intercalating and deintercalating lithium ions.

[0011] This slurry (1) contains a negative electrode active material containing carbon particles, a water-soluble polymer, and water. The water-soluble polymer includes free water-soluble polymer that is not adsorbed on the negative electrode active material (hereinafter also referred to as "free polymer (1-1)"). The water-soluble polymer usually also includes adsorbed water-soluble polymer that is adsorbed on the negative electrode active material (hereinafter also referred to as "adsorbed polymer (1-2)"). In this specification, free polymer (1-1) refers to the water-soluble polymer present in the supernatant when water is added to this slurry (1) and centrifuged to separate it into a precipitate and a supernatant, and adsorbed polymer (1-2) refers to the water-soluble polymer present in the precipitate. The free polymer (1-1) and adsorbed polymer (1-2) in this slurry (1) can be quantified by TG-DTA analysis as described in the examples.

[0012] The solid content of slurry (1) is 40-60% by mass, and the mass M1 of slurry (1), the mass M2 of the water-soluble polymer in slurry (1), and the mass M3 of the free polymer (1-1) in slurry (1) satisfy the following relationships (i) and (ii). 0.0090 ≤ M2 / M1 ≤ 0.0095 (i) 0.18 ≤ M3 / M2 ≤ 0.25 (ii)

[0013] As described above, in this slurry (1), the amount of free polymer (1-1) is moderately reduced while the content of water-soluble polymer is moderately increased. As a result, in the negative electrode active material layer formed using this slurry (1), the amount of adsorbent polymer (1-2) present between the negative electrode active materials can be moderately increased, thereby improving the bonding between the negative electrode active materials. The negative electrode active material layer can be formed by applying this slurry (1) to the negative electrode current collector, drying it, and compressing it. Internal stress due to compression remains in the negative electrode active material layer, which can cause springback, where the negative electrode active material layer gradually swells over time, increasing the thickness of the secondary battery. By using this slurry (1), the bonding between the negative electrode active materials in the negative electrode active material layer can be improved by the adsorbent polymer (1-2), thereby suppressing the increase in the thickness of the secondary battery caused by springback.

[0014] If the amount of adsorbent polymer (1-2) in the negative electrode active material layer increases too much, the water-soluble polymer will aggregate and become unevenly distributed between the negative electrode active materials. When the water-soluble polymer is unevenly distributed, repeated charging and discharging of the secondary battery causes the negative electrode active material to expand and contract, which can place a localized load on the negative electrode active material layer and cause the secondary battery to swell. By using this slurry (1), the uneven distribution of water-soluble polymer between the negative electrode active materials can be suppressed, thereby suppressing the swelling of the secondary battery when it is repeatedly charged and discharged.

[0015] When the amount of free polymer (1-1) in the negative electrode slurry decreases, the viscosity of the negative electrode slurry decreases, and its applicability onto the negative electrode current collector tends to decrease. Since this slurry (1) contains an appropriate amount of free polymer (1-1), the decrease in viscosity is suppressed, and this slurry (1) can have good applicability.

[0016] The solid content of this slurry (1) may be 42-58% by mass, 45-55% by mass, or 47-53% by mass.

[0017] M2 / M1 may be between 0.0091 and 0.0094, between 0.0092 and 0.0093, or between 0.0091 and 0.0092.

[0018] M3 / M2 may be 0.19-0.24, 0.20-0.23, or 0.21-0.22.

[0019] In this specification, the mass and content of each component contained in the slurry (1) refer to the total amount of two or more target components when the target component contains two or more target components.

[0020] The slurry (1) satisfies the above-mentioned solid content ratio and the relationship between formulas (i) and (ii), and the ratio (M4 / M2) of the mass M4 of the adsorbent polymer (1-2) to the mass M2 of the water-soluble polymer in the slurry (1) may be 0.75 to 0.82, 0.76 to 0.81, 0.77 to 0.80, or 0.78 to 0.79. By having the ratio (M4 / M2) within the above range, the increase in the thickness of the secondary battery is suppressed, and the swelling of the secondary battery when repeated charging and discharging is suppressed.

[0021] The slurry (1) satisfies the above-mentioned solid content ratio and the relationship between formulas (i) and (ii), and the ratio of the mass M2 of the water-soluble polymer to the mass M5 of the negative electrode active material in the slurry (1) (M2 / M5) may be between 0.003 and 0.020. The slurry (1) may also have a ratio (M4 / M2) within the above range. M2 / M5 may be between 0.004 and 0.018, between 0.005 and 0.015, between 0.006 and 0.012, or between 0.007 and 0.010. By having a ratio (M2 / M5) within the above range, it is possible to suppress the increase in the thickness of the secondary battery and to suppress the swelling of the secondary battery when charging and discharging is repeated.

[0022] The negative electrode active material preferably consists only of carbon particles, but may also contain other negative electrode active materials. Examples of other negative electrode active materials include metal-based particles. The carbon particle content is preferably 90% by mass or more relative to the negative electrode active material, but may also be 92% by mass or more, 95% by mass or more, 100% by mass, 90-99% by mass, 92-98% by mass, or 95-97% by mass. By having a carbon particle content within the above range, it is possible to suppress the increase in the thickness of the secondary battery and to suppress the swelling of the secondary battery when repeated charging and discharging occurs.

[0023] Examples of carbon particles include graphite, hard carbon, soft carbon, and amorphous coated graphite. The graphite may be natural graphite or artificial graphite. The graphite particles may have an amorphous carbon film on their surface. The carbon particles are preferably graphite particles.

[0024] The average particle size (D50) of the carbon particles is preferably 12 to 18 μm, but may also be 13 to 17 μm or 14 to 16 μm. In this specification, the average particle size (D50) is the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution. The volume-based particle size distribution can be measured using a laser diffraction particle size distribution analyzer. By having the average particle size (D50) of the carbon particles within the above range, the increase in the thickness of the secondary battery is suppressed, and the swelling of the secondary battery when repeated charging and discharging is suppressed.

[0025] Examples of metallic particles include elements selected from the group consisting of silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge), such as elemental metals or metal oxides. Preferably, the metallic particles include one or more particles selected from the group consisting of Si, SiOx (x=0.5~1.5), Si-C composites (hereinafter also referred to as "SiC composites"), and Sn, or one or more particles selected from said group. More preferably, the metallic particles include one or more particles selected from the group consisting of Si, SiOx, and SiC composites, or one or more particles selected from said group. The metallic particles are even more preferably SiC composite particles. A SiC composite is, for example, a composite in which Si is dispersed in a carbon matrix.

[0026] Water-soluble polymers are polymers that are soluble in water. Water-soluble polymers may be polymers derived from natural products or synthetic polymers. Examples of water-soluble polymers include one or more selected from the group consisting of polysaccharides, polyacrylic acid (hereinafter also referred to as "PAA"), polyvinyl alcohol, water-soluble acrylic resins, water-soluble epoxy resins, water-soluble polyesters, water-soluble polyamides, derivatives thereof, and salts thereof. Examples of polysaccharides include starches such as starch acetate, starch phosphate, carboxymethyl starch, and hydroxyethyl starch; celluloses such as carboxymethylcellulose (hereinafter also referred to as "CMC"), methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose; polyuronides such as pectinic acid and alginic acid; pullulan; dextrin, etc. Of these, the water-soluble polymer is preferably one or more selected from celluloses and PAA, more preferably contains celluloses, and even more preferably contains CMC. The above water-soluble polymer may be in the form of an acid, in the form of a salt, or a mixture thereof. When CMC and PAA are in the form of salts, examples of such salts include alkali metal salts such as lithium and sodium, and ammonium salts.

[0027] The degree of etherification of the CMC contained in this slurry (1) is preferably 0.65 to 0.75 mol / C6, but may also be 0.67 to 0.73 mol / C6, 0.68 to 0.72 mol / C6, or 0.69 to 0.71 mol / C6. By keeping the degree of etherification of the CMC within the above range, it is possible to suppress the increase in the thickness of the secondary battery and to suppress the swelling of the secondary battery when repeated charging and discharging occurs.

[0028] The degree of etherification of CMC is measured by the following procedure: Prepare methanol nitrate by mixing 100 mL of special grade concentrated HNO3 with 1 L of anhydrous methanol. Place 2 g of CMC and 100 mL of methanol nitrate into a stoppered Erlenmeyer flask (capacity 300 mL) and shake for 2 hours. After shaking, filter the mixture in the stoppered Erlenmeyer flask by suction filtration using a glass filter, wash the residue with methanol aqueous solution (concentration 80%), add 50 mL of anhydrous methanol to the residue, and filter again by suction filtration. After drying the residue at 105°C for 2 hours, place 1 to 1.5 g of this dried residue into a stoppered Erlenmeyer flask (capacity 300 mL). Add 15 mL of methanol aqueous solution (concentration 80%) to this stoppered Erlenmeyer flask to wet the residue, then add 50 mL of NaOH aqueous solution (normality 0.1 N), and shake the stoppered Erlenmeyer flask at room temperature (25°C) for 2 hours. After shaking, the excess NaOH is back-titrated with H2SO4 (normality 0.1N). The indicator is phenolphthalein.

[0029] Based on the measurement results, the degree of etherification DS is calculated using the following formula. DS[mol / C6]=0.162A / (1-0.058A) In the above equation, A is represented by the following equation, where F represents the factor of 0.1N H2SO4 and F' represents the factor of 0.1N NaOH aqueous solution. A = 0.1 × (50 × F' - H2SO4 volume [mL] × F) / (mass of dried residue [g])

[0030] The water is preferably pure water. Examples of pure water include distilled water, ion-exchanged water, water produced by reverse osmosis (RO water), and purified water.

[0031] This slurry (1) may contain, in addition to the negative electrode active material, water-soluble polymer, and water, a binder other than the water-soluble polymer (hereinafter also simply referred to as "binder") and a conductive material, etc.

[0032] Examples of binders include styrene-butadiene rubber (hereinafter also referred to as "SBR"), polyvinyl acetate, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer and ethylene-propylene-butadiene copolymer, acrylonitrile-butadiene rubber (NBR), polyacrylonitrile (PAN), polyimide, polyamide, and acrylic resins such as ethylene-acrylic acid copolymer. This slurry (1) may contain one or more of the above binders, and it is preferable that it contains SBR.

[0033] In this slurry (1), the ratio of the binder mass M6 to the mass M5 of the negative electrode active material (M6 / M5) may be 0.005 to 0.015, 0.007 to 0.013, or 0.008 to 0.012.

[0034] Examples of conductive materials include carbon materials such as fibrous carbon, carbon black (acetylene black, Ketjenblack, etc.), coke, and activated carbon. Examples of fibrous carbon include carbon nanotubes (hereinafter also referred to as "CNTs"). CNTs may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes such as double-walled carbon nanotubes (DWCNTs).

[0035] In this slurry (1), the ratio of the mass M7 of the conductive material to the mass M5 of the negative electrode active material (M7 / M5) may be 0.005 to 0.025, 0.007 to 0.023, 0.008 to 0.022, 0.009 to 0.020, or 0.010 to 0.018.

[0036] (Method for manufacturing negative electrode slurry) Figure 1 is a flowchart illustrating the manufacturing process of the negative electrode slurry according to the embodiment. The negative electrode slurry produced by the negative electrode slurry manufacturing method (hereinafter also referred to as "this slurry (2)") can be used to form the negative electrode active material layer of the negative electrode of a secondary battery. This slurry (2) may be this slurry (1) described above, or it may be a negative electrode slurry other than this slurry (1).

[0037] The method for producing the slurry (2) includes a first kneading step in which a first mixture containing a negative electrode active material containing carbon particles, a water-soluble polymer, and water is kneaded using a planetary mixer to a solid content of 50 to 70% by mass. The first kneading step consists of the following steps (1a) and (1b): Process (1a): A process in which the planetary mixer is mixed so that the rotation speed RP1 is 10 rpm or more and the cumulative power is 0.08 to 0.12 kWh. Process (1b); a process performed after process (1a) in which the planetary mixer rotation speed RP2 is 35 rpm or higher and the integrated power is 0.32 to 0.40 kWh. Including this, the ratio of rotational speed RP1 to rotational speed RP2 (RP1 / RP2) is between 0.4 and 0.8.

[0038] In the method for producing slurry (2), the first mixture may contain at least one of a binder and a conductive material in addition to the negative electrode active material, water-soluble polymer, and water. The carbon particles, negative electrode active material, water-soluble polymer, water, binder, and conductive material contained in slurry (2) can be those described in slurry (1). Slurry (2) preferably contains CMC as the water-soluble polymer and preferably contains SBR as the binder.

[0039] Steps (1a) and (1b) are part of the first mixing step, in which the first mixture is kneaded with a solid content of 50-70% by mass using a planetary mixer. Therefore, both steps use the same planetary mixer and knead with the same solid content. Consequently, in steps (1a) and (1b), the shape, size, and number of blades of the planetary mixer are the same, the size and shape of the kettle of the planetary mixer are the same, and the amount of mixture in the kettle (filling amount) is also the same. The same applies to the operating conditions of the planetary mixer unless otherwise specified in this specification.

[0040] In the manufacturing method of this slurry (2), in the first kneading step, the first mixture is kneaded to a solid content of 50-70% by mass, so that the RP1 / RP2 ratio is 0.4-0.8. This breaks the chain structure of the water-soluble polymer, making it easier to uniformly disperse the negative electrode active material and the water-soluble polymer. In the negative electrode active material layer formed using this slurry (2), the amount of adsorbed water-soluble polymer adsorbed on the negative electrode active material can be appropriately increased, improving the binding properties between the negative electrode active materials. This suppresses the increase in thickness of the secondary battery due to springback of the negative electrode active material layer. Furthermore, according to the manufacturing method of this slurry (2), the aggregation and uneven distribution of water-soluble polymer between the negative electrode active materials can be suppressed. Therefore, in a secondary battery containing a negative electrode active material layer formed using this slurry (2), swelling during repeated charging and discharging can be suppressed.

[0041] The method for producing this slurry (2) makes it possible to produce a slurry (2) containing an appropriate amount of free water-soluble polymer. Therefore, it is possible to suppress the decrease in viscosity of this slurry (2) and provide a slurry (2) with good coatability onto the negative electrode current collector when forming the negative electrode active material layer.

[0042] On the other hand, if RP1 / RP2 becomes too small, the chain structure of the water-soluble polymer is less likely to be broken in the first kneading step, making it difficult to increase the amount of adsorbed water-soluble polymer in the negative electrode slurry. As a result, the thickness of the secondary battery tends to increase due to springback when the negative electrode active material layer is fabricated. If RP1 / RP2 becomes too large, the chain structure of the water-soluble polymer is more likely to be broken in the first kneading step, increasing the amount of adsorbed water-soluble polymer in the negative electrode slurry. As a result, the water-soluble polymer tends to aggregate and become unevenly distributed between the negative electrode active materials, and the secondary battery tends to swell when the secondary battery is repeatedly charged and discharged.

[0043] The solid content of the first mixture is 50-70% by mass, and may be 52-68% by mass, 53-65% by mass, 54-60% by mass, 54-57% by mass, 55-58% by mass, 58-70% by mass, 58-68% by mass, 59-67% by mass, 59-66% by mass, 60-64% by mass, or 61-63% by mass.

[0044] The rotational speed RP1 of the planetary mixer in process (1a) is 10 rpm or more, and may be 10-35 rpm, 12-34 rpm, 15-33 rpm, 17-32 rpm, 20-31 rpm, or 23-30 rpm. The rotational speed RP1 refers to the rotational speed of the planetary mixer blades.

[0045] The cumulative power of the planetary mixer in process (1a) may be 0.080 to 0.120 kWh, 0.090 to 0.110 kWh, or 0.095 to 0.105 kWh. The cumulative power in process (1a) can be calculated by multiplying the amount of energy used to rotate the blades of the planetary mixer in process (1a) by the mixing time. The mixing time in process (1a) may be, for example, 1 to 20 minutes, 2 to 15 minutes, or 3 to 12 minutes.

[0046] In process (1b), the rotational speed RP2 of the planetary mixer is 35 rpm or higher, and may be 35-40 rpm, 36-39 rpm, 36-38 rpm, or 36-37 rpm. The rotational speed RP2 refers to the rotational speed of the planetary mixer blades.

[0047] The cumulative power of the planetary mixer in process (1b) is 0.32 to 0.40 kWh, but may also be 0.33 to 0.39 kWh or 0.34 to 0.38 kWh. The cumulative power in process (1b) can be calculated by multiplying the amount of energy used to rotate the blades of the planetary mixer in process (1b) by the mixing time. The mixing time in process (1b) is, for example, 15 to 25 minutes, but may also be 18 to 22 minutes.

[0048] The method for producing the slurry (2) may further include a second mixing step in which a second mixture, obtained by adding water to the first mixture, is mixed in a planetary mixer. The second mixing step may be a step to adjust the slurry (2) to have the desired viscosity. In the method for producing the slurry (2), in the second mixing step, a binder may be added to the first mixture along with water and mixed.

[0049] The second mixing step is a mixing step using the same planetary mixer as the first mixing step. The solid content of the second mixture is smaller than that of the first mixture. The solid content of the second mixture is, for example, 40-60% by mass, but may also be 42-58% by mass, 45-55% by mass, 47-53% by mass, or 48-52% by mass. The solid content of the second mixture may also be the solid content of the slurry (2).

[0050] The rotational speed RP3 of the planetary mixer in the second mixing step may be different from the rotational speeds RP1 and RP2 of the planetary mixer in the first mixing step, but may be the same as at least one of the rotational speeds RP1 and RP2, for example, it may be the same as rotational speed RP2. The rotational speed RP3 in the second mixing step is 35 rpm or more, may be 35 to 40 rpm, may be 36 to 39 rpm, preferably 36 to 38 rpm, may be 37 to 38 rpm, or may be 36 to 37 rpm. By keeping the rotational speed RP3 within the above range, it is possible to suppress the increase in the thickness of the secondary battery and to suppress the swelling of the secondary battery when charging and discharging is repeated.

[0051] The cumulative power of the planetary mixer in the second mixing process may be 0.10 to 0.30 kWh, 0.12 to 0.28 kWh, or 0.15 to 0.25 kWh. The cumulative power in the second mixing process can be calculated by multiplying the amount of energy required to rotate the blades of the planetary mixer in the second mixing process by the mixing time. The mixing time in the second mixing process may be, for example, 5 to 15 minutes, or 8 to 12 minutes.

[0052] (Negative electrode) The negative electrode of this embodiment (hereinafter also referred to as "this negative electrode (1)") is, for example, the negative electrode of a secondary battery. This negative electrode (1) has a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer contains a negative electrode active material containing carbon particles and a water-soluble polymer. The water-soluble polymer includes free water-soluble polymer that is not adsorbed on the negative electrode active material (hereinafter also referred to as "free polymer (2-1)"). The content of free polymer (2-1) in the negative electrode active material layer is 0.18 to 0.26% by mass relative to the negative electrode active material.

[0053] The negative electrode current collector is a metal foil made of copper material such as copper and copper alloys, or iron material such as iron and iron alloys.

[0054] Water-soluble polymers typically contain, in addition to free polymers (2-1), adsorbed water-soluble polymers (hereinafter also referred to as "adsorbed polymers (2-2)") adsorbed onto the negative electrode active material.

[0055] The negative electrode active material layer may contain at least one of a binder and a conductive material in addition to the negative electrode active material and a water-soluble polymer. The carbon particles, negative electrode active material, water-soluble polymer, binder, and conductive material can each be those described in Slurry (1). The negative electrode active material layer preferably contains CMC as the water-soluble polymer and SBR as the binder.

[0056] In this specification, free polymer (2-1) refers to the water-soluble polymer present in the supernatant when the negative electrode active material layer is peeled off from the negative electrode current collector of the negative electrode (1), dispersed in water, and the resulting dispersion is centrifuged to separate it into precipitate and supernatant. Adsorbent polymer (2-2) refers to the water-soluble polymer present in the precipitate. The free polymer (2-1) and adsorbent polymer (2-2) in the negative electrode (1) can be quantified by TG-DTA analysis as described in the examples.

[0057] The negative electrode (1) may have a negative electrode active material layer on one or both sides of the negative electrode current collector. The negative electrode active material layer of the negative electrode (1) contains an appropriate amount of free polymer (2-1) and adsorbent polymer (2-2). Therefore, it is possible to suppress the increase in thickness of the secondary battery due to the springback of the negative electrode active material layer, and also to suppress the swelling of the secondary battery when repeated charging and discharging occurs.

[0058] The content of free polymer (2-1) in the negative electrode active material layer may be 0.18 to 0.25% by mass, 0.19 to 0.24% by mass, 0.20 to 0.23% by mass, 0.18 to 0.22% by mass, or 0.18 to 0.21% by mass, relative to the negative electrode active material.

[0059] The content of the adsorbent polymer (2-2) in the negative electrode active material layer is preferably 0.30 to 0.82% by mass relative to the negative electrode active material, but may also be 0.30 to 0.80% by mass, 0.35 to 0.75% by mass, 0.40 to 0.70% by mass, 0.45 to 0.65% by mass, or 0.50 to 0.60% by mass. In the negative electrode active material layer, the content of the adsorbent polymer (2-2) may be greater than the content of the free polymer (2-1). By keeping the content of the adsorbent polymer (2-2) within the above range, it is possible to suppress the increase in the thickness of the secondary battery and to suppress the swelling of the secondary battery when repeated charging and discharging occurs.

[0060] The negative electrode active material preferably consists only of carbon particles, but may also contain other negative electrode active materials such as metallic particles. As metallic particles, those described in this slurry (1) can be used. The carbon particle content is preferably 90% by mass or more relative to the negative electrode active material, but may also be 92% by mass or more, 95% by mass or more, 100% by mass, 90-99% by mass, 92-98% by mass, or 95-97% by mass.

[0061] In the negative electrode active material layer, the content of the water-soluble polymer may be 0.3 to 2.0% by mass, 0.4 to 1.8% by mass, 0.5 to 1.5% by mass, 0.6 to 1.2% by mass, or 0.7 to 1.1% by mass, relative to the negative electrode active material.

[0062] In the negative electrode active material layer, the binder content may be 0.5 to 1.5% by mass, 0.7 to 1.3% by mass, or 0.8 to 1.2% by mass relative to the negative electrode active material.

[0063] In the negative electrode active material layer, the content of the conductive material may be 0.5 to 2.5 mass%, 0.7 to 2.3 mass%, 0.8 to 2.2 mass%, 0.9 to 2.0 mass%, or 1.0 to 1.8 mass% relative to the negative electrode active material.

[0064] In this specification, the mass and content of each component contained in the negative electrode (1) refer to the total amount of two or more target components if the target component contains two or more target components.

[0065] The negative electrode (1) may have a first active material layer and a second active material layer in order from the negative electrode current collector side. If the negative electrode active material layer is formed on both sides of the negative electrode current collector, only the negative electrode active material layer on one side may have a first active material layer and a second active material layer, while the negative electrode active material layer on the other side may be a single layer.

[0066] Preferably, the first active material layer comprises a first negative electrode active material containing first carbon particles, a first water-soluble polymer, and a first SBR, and the second active material layer comprises a second negative electrode active material containing second carbon particles, a second water-soluble polymer, and a second SBR. In this case, the ratio (C2 / C1) of the content of the second water-soluble polymer relative to the content of the second negative electrode active material C2 [mass%] to the content of the water-soluble polymer relative to the content of the first negative electrode active material C1 [mass%] is preferably 1.75 to 1.85. The ratio (C2 / C1) may also be 1.76 to 1.84, 1.77 to 1.83, or 1.78 to 1.82.

[0067] When the content of free polymer (2-1) in the negative electrode active material layer decreases, the adhesion strength between the negative electrode current collector and the negative electrode active material layer tends to decrease. The reason for this is presumed to be as follows: A negative electrode active material layer with a low content of free polymer (2-1) is formed using a negative electrode slurry with a low content of free water-soluble polymer, resulting in a low viscosity of the negative electrode slurry. When such a negative electrode slurry is applied to the negative electrode current collector and dried, SBR moves along with the evaporation of water, promoting migration in which SBR is unevenly distributed on the surface of the negative electrode active material layer opposite to the negative electrode current collector side. As a result, the adhesion strength between the negative electrode current collector and the negative electrode active material layer tends to decrease. As described above, by forming a second active material layer on the first active material layer and increasing the content of water-soluble polymer in the second active material layer, the movement of SBR to the above surface can be suppressed, thereby suppressing migration and improving the adhesion strength between the negative electrode current collector and the negative electrode active material layer.

[0068] The first active material layer may contain, in addition to the first negative electrode active material, the first water-soluble polymer, and the first SBR, at least one of a first binder other than the first SBR and a first conductive material. The second active material layer may contain, in addition to the second negative electrode active material, the second water-soluble polymer, and the second SBR, at least one of a second binder other than the second SBR and a second conductive material. The first and second negative electrode active materials, the first and second water-soluble polymers, the first and second binders, and the first and second conductive materials can each be those described in this slurry (1). The first and second negative electrode active materials are preferably composed solely of carbon particles, but may also contain negative electrode active materials other than carbon particles. It is preferable that the first and second water-soluble polymers include CMC.

[0069] The content [mass%] of the first carbon particles, first water-soluble polymer, first SBR, and first conductive material in the first negative electrode active material, and the content [mass%] of the second carbon particles, second water-soluble polymer, second SBR, and second conductive material in the second negative electrode active material, can be within the ranges described for the content [mass%] of carbon particles, water-soluble polymer, binder, and conductive material in the negative electrode active material layer, respectively.

[0070] The first water-soluble polymer may include a first free water-soluble polymer that is not adsorbed on the first anode active material, and may further include a first adsorbed water-soluble polymer that is adsorbed on the first anode active material. The second water-soluble polymer may include a second free water-soluble polymer that is not adsorbed on the second anode active material, and may further include a second adsorbed water-soluble polymer that is adsorbed on the second anode active material.

[0071] The first free water-soluble polymer and the second free water-soluble polymer refer to the water-soluble polymers present in the supernatant when the first active material layer and the second active material layer are dispersed in water, the resulting dispersion is centrifuged, and the precipitate and supernatant are separated. The first adsorbed water-soluble polymer and the second adsorbed water-soluble polymer refer to the water-soluble polymers present in the precipitates of the first active material layer and the second active material layer, respectively.

[0072] The content of the first free water-soluble polymer relative to the first anode active material in the first active material layer [mass%], and the content of the second free water-soluble polymer relative to the second anode active material in the second active material layer [mass%], can both be within the range described as the content of the free polymer (2-1) in the anode active material layer. The content of the first adsorbed water-soluble polymer relative to the first anode active material in the first active material layer [mass%], and the content of the second adsorbed water-soluble polymer relative to the second anode active material in the second active material layer [mass%], can both be within the range described as the content of the adsorbed polymer (2-2) in the anode active material layer. The above content of the second free water-soluble polymer is preferably the same as or greater than the above content of the first free water-soluble polymer. The above content of the second adsorbed water-soluble polymer is preferably the same as or greater than the above content of the second free water-soluble polymer.

[0073] (Method of manufacturing the negative electrode) The negative electrode manufactured by the negative electrode manufacturing method of this embodiment (hereinafter also referred to as "this negative electrode (2)") comprises a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer may have a first active material layer and a second active material layer in order from the negative electrode current collector side. This negative electrode (2) may be the above-described this negative electrode (1), or it may be a negative electrode other than this negative electrode (1).

[0074] A method for manufacturing the negative electrode (2), which has a negative electrode current collector and a negative electrode active material layer, includes the step of applying a negative electrode slurry to the negative electrode current collector, drying it, and compressing it to form a negative electrode active material layer. In the method for manufacturing the negative electrode (2), the negative electrode slurry is the slurry (1) or the slurry (2) obtained by the method for manufacturing the slurry (2).

[0075] According to the method for manufacturing the negative electrode (2), since the negative electrode active material layer is formed using the slurry (1) or the slurry (2), it is possible to suppress an increase in the thickness of the secondary battery having the negative electrode (2), and also to suppress swelling of the secondary battery when repeated charging and discharging occurs.

[0076] When the negative electrode active material layer has a first active material layer and a second active material layer, in the method for manufacturing the negative electrode (2), the negative electrode slurry includes a first negative electrode slurry for forming the first active material layer and a second negative electrode slurry for forming the second active material layer. The first negative electrode slurry further includes a first SBR, and the second negative electrode slurry further includes a second SBR. The first negative electrode slurry and the second negative electrode slurry are each independently the slurry (2) obtained by the method for manufacturing the slurry (1) or the slurry (2).

[0077] In the method for producing the negative electrode (2) described above, the ratio (Cs2 / Cs1) of the amount of water-soluble polymer Cs2 relative to the amount of negative electrode active material in the second negative electrode slurry to the amount of water-soluble polymer Cs1 relative to the amount of negative electrode active material in the first negative electrode slurry can be 1.75 to 1.85. The ratio (Cs2 / Cs1) may also be 1.76 to 1.84, 1.77 to 1.83, or 1.78 to 1.82.

[0078] When the negative electrode active material layer has a first active material layer and a second active material layer, the steps for forming the negative electrode active material layer may include: applying the first negative electrode slurry to the negative electrode current collector to form the first layer; applying the second negative electrode slurry on the first layer to form the second layer; and drying and compressing the first and second layers.

[0079] According to the manufacturing method of the negative electrode (2) described above, since the ratio (Cs2 / Cs1) is within the range described above, the adhesion strength between the negative electrode current collector and the negative electrode active material layer can be improved.

[0080] The process of forming the second layer is preferably carried out before the drying and compression of the first layer. For example, the process of forming the first layer and the process of forming the second layer can be carried out simultaneously, that is, by applying the second negative electrode slurry while applying the first negative electrode slurry onto the negative electrode current collector, the second layer can be formed before the drying and compression of the first layer. The drying and compression of the first and second layers are preferably carried out simultaneously for the first and second layers after the second layer has been formed on the first layer. This makes it easier to improve the adhesion strength between the negative electrode current collector and the negative electrode active material layer.

[0081] The solid content of the first anode slurry and the second anode slurry can be independently within the range described in Slurry (1). The water-soluble polymer content in the first anode slurry and the second anode slurry can be independently within the range of formula (i) and / or the ratio (M2 / M5) described in Slurry (1). The free water-soluble polymer content in the first anode slurry and the second anode slurry can be within the range of formula (ii) and / or the ratio (M2 / M5) described in Slurry (1). The first SBR content in the first anode slurry and the second SBR content in the second anode slurry can be independently within the ratio (M6 / M5) described in Slurry (1). The conductive material content in the first anode slurry and the second anode slurry can be independently within the ratio (M7 / M5) described in Slurry (1).

[0082] (Nonaqueous electrolyte secondary battery) A secondary battery may have an electrode body including a negative electrode and a non-aqueous electrolyte, and may also have a battery case that houses the electrode body and the non-aqueous electrolyte. The negative electrode is either the main negative electrode (1) or the main negative electrode (2). The battery case may include an outer casing having an opening and a sealing plate that seals the opening. The outer casing and the sealing plate are preferably made of metal and can be formed using aluminum, aluminum alloy, iron, or iron alloy, etc. A resin sheet as an electrode holder may be placed between the electrode body and the outer casing. The battery case may also be made of laminate film. The laminate film may have a laminated structure in which a metal layer and a resin layer are laminated together, for example. A pouch-shaped battery case can be formed by overlapping and welding the edges of the laminate film.

[0083] The electrode body may include a positive electrode, a negative electrode, and a separator. In the electrode body, the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode face each other via a separator. The electrode body may be a laminated type in which the positive electrode, negative electrode, and separator are stacked, or a wound type in which a laminate of the positive electrode, negative electrode, and separator is wound. The wound type electrode body may have a flattened shape after the laminate is wound and pressed.

[0084] The positive electrode typically comprises a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector and the positive electrode active material layer can be formed using known materials. The separator has a substrate, and may have a functional layer on at least one side of the substrate. The functional layer may be, for example, an adhesive layer and a heat-resistant layer, and may have one or both of these. The separator and the functional layer can be formed using known materials. The non-aqueous electrolyte is preferably an electrolyte contained in a non-aqueous solvent such as an organic solvent. Known materials can be used as the electrolyte. [Examples]

[0085] The present disclosure will be further described below with reference to examples and comparative examples.

[0086] [Comparative Example 1] (Preparation of negative electrode slurry) Graphite particles (average particle size (D50): 15 μm), which are carbon particles, were prepared as the negative electrode active material; CMC (degree of etherification: 0.70 mol / C6), which is a water-soluble polymer; pure water; and SBR, which is a binder. The first mixture, which is a combination of the negative electrode active material, water-soluble polymer, and water (negative electrode active material: water-soluble polymer = 100:1 (mass ratio), solid content: 62.7 mass%), was put into a planetary mixer and mixed at a rotation speed (RP1) of 10 rpm for a mixing time of approximately 10 minutes until the cumulative power was 0.10 kWh (step (1a) of the first mixing process). Subsequently, the mixture was mixed at a rotation speed (RP2) of 37 rpm for a mixing time of approximately 20 minutes until the cumulative power was 0.36 kWh (step (1b) of the first mixing process). Water and SBR were added to the first mixture after mixing to obtain the second mixture. The composition ratio of the second mixture was negative electrode active material:water-soluble polymer:SBR = 100:1:1 (mass ratio) (solid content: 50.2 mass%). The second mixture was kneaded at a rotation speed (RP3) of 37 rpm for a kneading time of approximately 10 minutes, so that the accumulated power was 0.2 kWh (second kneading step), to obtain a negative electrode slurry. The ratio of the mass M2 of the water-soluble polymer to the mass M1 of the negative electrode slurry (M2 / M1) was 0.0092.

[0087] (Manufacturing of secondary battery cells) The negative electrode slurry obtained above was applied to a copper foil, which served as the negative electrode current collector, dried, and compressed to obtain the negative electrode. The negative electrode, positive electrode, and separator were stacked to obtain an electrode body, and the electrode body and non-aqueous electrolyte were housed in a battery case to obtain a secondary battery.

[0088] [Example 1] Except for setting the rotation speed (RP1) in step (1a) of the first kneading process to 25 rpm and the kneading time to approximately 4 minutes, the negative electrode slurry and secondary battery were obtained using the same procedure as in Comparative Example 1.

[0089] [Example 2] Except for setting the rotation speed (RP1) in step (1a) of the first kneading process to 30 rpm and the kneading time to approximately 2 minutes, the negative electrode slurry and secondary battery were obtained using the same procedure as in Comparative Example 1.

[0090] [Comparative Example 2] Except for setting the rotation speed (RP1) in step (1a) of the first kneading process to 37 rpm and the kneading time to approximately 1 minute, the negative electrode slurry and secondary battery were obtained using the same procedure as in Comparative Example 1.

[0091] [Content of free water-soluble polymers and adsorbed water-soluble polymers in the negative electrode slurry] Pure water was added to the negative electrode slurry, and centrifugation was performed using a centrifuge at a rotation speed of 50,000 rpm for 45 minutes. After centrifugation, the supernatant and precipitate were collected and dried, and the resulting dried materials were subjected to TG-DTA analysis (thermogravimetric differential thermal analysis) to calculate the amount of water-soluble polymer (CMC). The amount of water-soluble polymer obtained from the supernatant was defined as the amount of free water-soluble polymer, and the amount of water-soluble polymer obtained from the precipitate was defined as the amount of adsorbed water-soluble polymer. Based on the amount of free water-soluble polymer, the ratio of the mass of free water-soluble polymer (M3 / M2) to the mass of water-soluble polymer (M2) in the negative electrode slurry was calculated. The results are shown in Table 1.

[0092] [Content of free water-soluble polymers and adsorbed water-soluble polymers in the negative electrode active material layer] The negative electrode active material layer was peeled from the negative electrode current collector, and the negative electrode active material layer was dispersed in pure water to obtain a dispersion. The dispersion was centrifuged using a centrifuge at a rotation speed of 50,000 rpm for 45 minutes. The supernatant and precipitate after centrifugation were collected, and the amount of free water-soluble polymer and the amount of adsorbed water-soluble polymer in the negative electrode active material layer were determined using the procedure described in the section on the mass of free water-soluble polymer and adsorbed water-soluble polymer in the negative electrode slurry. The content of free water-soluble polymer relative to the negative electrode active material [mass %] and the content of adsorbed water-soluble polymer relative to the negative electrode active material [mass %] were calculated. The results are shown in Table 1.

[0093] [Measurement of the expansion rate of secondary batteries] The thickness of the secondary battery was measured and defined as the initial thickness. The results are shown in Table 1. Using the secondary battery after measuring the initial thickness, the battery was repeatedly charged and discharged so that the State of Charge (SOC) reached 15% and 95%. The thickness of the secondary battery was then measured and defined as the thickness after the charge-discharge cycle. The expansion rate of the secondary battery was calculated according to the following formula. The results are shown in Table 1. The expansion rate of a secondary battery [%] = (thickness after charge / discharge cycle - initial thickness / thickness after charge / discharge cycle) × 100

[0094] [Table 1]

[0095] [Example 3] (Preparation of the first and second negative electrode slurry) A negative electrode slurry was obtained in the same manner as in Example 2, and this was designated as the first negative electrode slurry. The composition ratio of the first mixture was set to negative electrode active material:water-soluble polymer = 100:1.8 (mass ratio) (solid content: 56 mass%), and the composition ratio of the second mixture was set to negative electrode active material:water-soluble polymer:SBR = 100:1.8:1 (mass ratio) (solid content: 52 mass%), but otherwise a negative electrode slurry was obtained in the same manner as in Example 2, and this was designated as the second negative electrode slurry.

[0096] (Manufacturing of secondary battery cells) A first negative electrode slurry was applied to a copper foil serving as a negative electrode current collector, and a second negative electrode slurry was applied simultaneously. This formed a first layer with the applied first negative electrode slurry, and a second layer was formed on top of the first layer by applying the second negative electrode slurry. The first and second layers on the negative electrode current collector were dried simultaneously and compressed to obtain a negative electrode in which the first active material layer and the second active material layer were formed in that order on the negative electrode current collector. A secondary battery was obtained in the same manner as in Example 1, except for the use of this negative electrode. The ratio (C2 / C1) of the water-soluble polymer content C2 [mass%] relative to the negative electrode active material in the second active material layer and the water-soluble polymer content C1 [mass%] relative to the negative electrode active material in the first active material layer was calculated from the amounts of negative electrode active material and water-soluble polymer in the first and second negative electrode slurries.

[0097] [Measurement of adhesion strength] The negative electrode was cut out, double-sided tape was attached to the negative electrode current collector side, and it was fixed to a tensile testing machine. The negative electrode active material layers (first active material layer and second active material layer) were gripped with a jig on the tensile testing machine, and the load was measured when they were pulled up at a constant speed. This was defined as the adhesion strength [N / m (unit)]. The results measured for the negative electrodes obtained in Example 2 and Example 3 are shown in Table 2.

[0098] [Table 2]

Claims

1. A negative electrode slurry containing a negative electrode active material containing carbon particles, a water-soluble polymer, and water, The solid content of the negative electrode slurry is 40 to 60% by mass. The water-soluble polymer includes free water-soluble polymers that are not adsorbed onto the negative electrode active material. The anode slurry is such that the mass M1 of the anode slurry, the mass M2 of the water-soluble polymer in the anode slurry, and the mass M3 of the free water-soluble polymer in the anode slurry satisfy the following relationships (i) and (ii). 0.0090≦M2 / M1≦0.0095 (i) 0.18≦M3 / M2≦0.25 (ii)

2. The negative electrode slurry according to claim 1, wherein the negative electrode active material consists solely of the carbon particles.

3. The negative electrode slurry according to claim 1, wherein the average particle size (D50) of the carbon particles is 12 to 18 μm.

4. The anode slurry according to claim 1, wherein the water-soluble polymer comprises cellulose.

5. The anode slurry according to claim 1, wherein the water-soluble polymer comprises carboxymethylcellulose having a degree of etherification of 0.65 to 0.75 mol / C6.

6. Furthermore, the negative electrode slurry according to claim 1, further comprising styrene-butadiene rubber.

7. A method for manufacturing a negative electrode slurry, The process includes a first kneading step in which a first mixture containing a negative electrode active material containing carbon particles, a water-soluble polymer, and water is kneaded using a planetary mixer to a solid content of 50 to 70% by mass. The above-mentioned first kneading step is, The process (1a) involves mixing the materials so that the rotational speed RP1 of the planetary mixer is 10 rpm or more and the cumulative power is 0.08 to 0.12 kWh, The process includes, after step (1a), a step (1b) in which the planetary mixer is kneaded so that the rotational speed RP2 is 35 rpm or more and the cumulative power is 0.32 to 0.40 kWh, A method for manufacturing a negative electrode slurry, wherein the ratio of the rotational speed RP1 to the rotational speed RP2 (RP1 / RP2) is 0.4 to 0.

8.

8. A method for producing a negative electrode slurry according to claim 7, comprising a second mixing step of mixing a second mixture, which is obtained by further adding water to the first mixture after the first mixing step, in the planetary mixer.

9. The method for producing a negative electrode slurry according to claim 8, wherein the second mixing step is performed in which the rotational speed RP3 of the planetary mixer is 36 to 38 rpm.

10. The method for producing a negative electrode slurry according to claim 7, wherein the negative electrode slurry is the negative electrode slurry according to any one of claims 1 to 6.

11. A negative electrode having a negative electrode current collector and a negative electrode active material layer, The negative electrode active material layer comprises a negative electrode active material containing carbon particles and a water-soluble polymer. The water-soluble polymer includes free water-soluble polymers that are not adsorbed onto the negative electrode active material. The negative electrode wherein the content of the free water-soluble polymer in the negative electrode active material layer is 0.18 to 0.26% by mass relative to the negative electrode active material.

12. The aforementioned water-soluble polymer further includes an adsorbed water-soluble polymer adsorbed onto the negative electrode active material. The negative electrode according to claim 11, wherein the content of the adsorbed water-soluble polymer in the negative electrode active material layer is 0.30 to 0.82% by mass relative to the negative electrode active material.

13. The negative electrode according to claim 11, wherein the negative electrode active material consists solely of the carbon particles.

14. The negative electrode active material layer has, in order from the negative electrode current collector side, a first active material layer and a second active material layer. The first active material layer comprises a first negative electrode active material containing first carbon particles, a first water-soluble polymer, and a first styrene-butadiene rubber. The second active material layer comprises a second negative electrode active material containing second carbon particles, a second water-soluble polymer, and a second styrene-butadiene rubber. The negative electrode according to claim 11, wherein the ratio (C2 / C1) of the content C2 [mass%] of the second water-soluble polymer relative to the second negative electrode active material to the content C1 [mass%] of the first water-soluble polymer relative to the first negative electrode active material is 1.75 to 1.

85.

15. A method for manufacturing a negative electrode having a negative electrode current collector and a negative electrode active material layer, The process includes applying a negative electrode slurry to the negative electrode current collector, drying it, and compressing it to form the negative electrode active material layer. A method for manufacturing a negative electrode, wherein the negative electrode slurry is a negative electrode slurry according to any one of claims 1 to 6, or a negative electrode slurry obtained by a method for manufacturing a negative electrode slurry according to any one of claims 7 to 9.

16. The negative electrode active material layer has, in order from the negative electrode current collector side, a first active material layer and a second active material layer. The negative electrode slurry includes a first negative electrode slurry for forming the first active material layer and a second negative electrode slurry for forming the second active material layer. The first negative electrode slurry further comprises a first styrene-butadiene rubber, The second negative electrode slurry further comprises a second styrene-butadiene rubber, The ratio of the water-soluble polymer content Cs2 to the negative electrode active material content in the second negative electrode slurry and the water-soluble polymer content Cs1 to the negative electrode active material content in the first negative electrode slurry (Cs2 / Cs1) is 1.75 to 1.

85. The step of forming the negative electrode active material layer is: The process involves applying a first negative electrode slurry to the negative electrode current collector to form a first layer, The process involves applying a second negative electrode slurry onto the first layer to form a second layer, A method for manufacturing a negative electrode according to claim 15, comprising the steps of drying and compressing the first layer and the second layer.

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