Binder, binder composition, preparation method, negative electrode slurry, negative electrode sheet, secondary battery, battery module, battery pack, and electrical device

Abstract

The present application relates to a binder, a binder composition, a preparation method, a negative electrode slurry, a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device, in which the binder includes a core material having a glass transition temperature of -50°C to 0°C and a shell material located on at least a part of the surface of the core material and having a glass transition temperature of 60°C to 100°C.

Description

[Technical Field] 【0001】 This application relates to the field of secondary battery technology, and specifically to binders, binder compositions, preparation methods, negative electrode slurries, negative electrode sheets, secondary batteries, battery modules, battery packs, and electrical devices. [Background technology] 【0002】 Due to their outstanding characteristics such as being lightweight, pollution-free, and having no memory effect, rechargeable batteries are widely used in various consumer electronic products and electric vehicles. With the development of the new energy industry, clients are presenting higher demand for rechargeable batteries. 【0003】 In related technologies, styrene-butadiene rubber and sodium carboxymethylcellulose are often used as binders to prepare negative electrode sheets. However, this method fails to provide both the processing performance of the negative electrode sheet and the kinetic performance of the corresponding battery cell. Therefore, there is room for improvement in the traditional binders used for negative electrode sheets. [Overview of the Initiative] [Problems that the invention aims to solve] 【0004】 In view of the challenges present in the background technology, this application aims to provide a binder, binder composition, preparation method, negative electrode slurry, negative electrode sheet, secondary battery, battery module, battery pack, and electrical device that simultaneously satisfy both the processing performance of the negative electrode sheet and the dynamic performance of the battery cell corresponding to the negative electrode sheet. [Means for solving the problem] 【0005】 To achieve the aforementioned objective, the first aspect of the present application is: A core material with a glass transition temperature of -50°C to 0°C, A shell material located on at least a portion of the surface of the core material, having a glass transition temperature of 60°C to 100°C. We provide a binder that includes [this]. 【0006】 Compared to the prior art, this invention includes at least the following advantageous effects. 【0007】 Regarding the binder according to this application, the shell material is located on at least a portion of the surface of the core material, the core material is a flexible material with a low glass transition temperature, and the shell material is a hard material with a high glass transition temperature. Therefore, the binder has a core-shell structure that is soft on the inside and hard on the outside. The flexible core material is advantageous for cold pressing of the negative electrode sheet, helping to reduce the cold pressing pressure, increasing the compaction window of the negative electrode active material, providing relatively good adhesion, and further reducing the amount of binder used. The relatively small amount of binder used reduces the coating on the surface of the negative electrode active material. The relatively hard shell material does not deform excessively after cold pressing of the negative electrode sheet, reducing the area of ​​binder coating on the negative electrode active material, effectively reducing the impedance when lithium ions are inserted and removed, and improving the dynamic performance of the battery cell corresponding to the negative electrode sheet. As described above, when the binder is applied to a battery cell, the DC internal resistance (DCR) of the battery cell is reduced by 5% to 12%, the charging interface is slightly increased, and the adhesive strength of the binder in this invention is more than 20% higher than that of styrene-butadiene rubber used in conventional technology, there is no film detachment or powder shedding, and the fully charged interface is good. 【0008】 In any embodiment of the present application, the shell material has polar groups. 【0009】 In any embodiment of the present application, the core material comprises a copolymer of styrene monomer units and butadiene monomer units. 【0010】 In any embodiment of the present application, the shell material comprises a copolymer of styrene monomer units, butadiene monomer units, unsaturated acid monomer units, and unsaturated ester monomer units. 【0011】 In any embodiment of the present application, the monomer corresponding to the unsaturated acid monomer unit contains an unsaturated acid that contains a substituted or unsubstituted -C=C- and has 3 to 6 carbon atoms. Optionally, the monomer corresponding to the unsaturated acid monomer unit includes one or more of acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. 【0012】 In any embodiment of the present application, the monomer corresponding to the unsaturated ester monomer unit includes a substituted or unsubstituted -C=C- containing unsaturated ester. Optionally, the monomer corresponding to the unsaturated ester monomer unit includes one or more of methyl methacrylate, ethyl hexyl ester, vinyl acetate, isooctyl acrylate, hydroxyethyl acrylate, isobornyl methacrylate, vinyl neodecanoate, butyl acrylate, acrylonitrile, ethyl acrylate, n-butyl acrylate, and isobutyl acrylate. 【0013】 In any embodiment of the present application, the viscosity of the aqueous solution of the binder at 45% solids content at 25°C is 10 mPa·s to 200 mPa·s. 【0014】 In any embodiment of the present application, the volume average particle diameter Dv50 of the binder is 100 nm to 1000 nm. 【0015】 The second aspect of the present application provides a method for preparing a binder including the following steps. 【0016】 S11: A step of preparing the core material by subjecting a styrene monomer and a butadiene monomer to a polymerization reaction. S12: A step of subjecting a styrene monomer, a butadiene monomer, an unsaturated acid-based monomer, and an unsaturated ester-based monomer to a polymerization reaction on the surface of the core material. In any embodiment of the present application, in the polymerization reaction for preparing the core material, the mass ratio of the styrene monomer to the butadiene monomer is 10:(4 to 8). 【0017】 In any embodiment of the present application, in the polymerization reaction for preparing the shell material, the mass ratio of the styrene monomer, the butadiene monomer, the unsaturated acid monomer, and the unsaturated ester monomer is 10:(4~8):(1~3):(2~4). 【0018】 A third aspect of the present application provides a binder composition comprising the binder of the first aspect of the present application or a binder prepared by the method of the second aspect of the present application, and high-viscosity sodium carboxymethylcellulose, wherein the viscosity of the aqueous solution of the high-viscosity sodium carboxymethylcellulose at a solid content of 1% at 25°C is 10,000 mPa·s to 20,000 mPa·s. 【0019】 In any embodiment of the present application, the mass ratio of the binder to the high-viscosity carboxymethylcellulose sodium is (1.1 to 3.5):1. 【0020】 In any embodiment of the present application, the hydrogen atoms of the hydroxyl groups in the high-viscosity sodium carboxymethylcellulose are substituted with a substitution agent, and the substitution agent and the hydroxyl groups react to form a hemiacetal. Optionally, the substitution agent comprises a dialdehyde monomer, and further optionally, the dialdehyde monomer comprises one or two of glyoxal and glutaraldehyde. 【0021】 A fourth aspect of the present application provides a negative electrode slurry comprising a binder according to the first aspect of the present application, a binder prepared by the method of the second aspect of the present application, or a binder composition according to the third aspect of the present application. 【0022】 A fifth aspect of the present application provides a method for preparing a negative electrode slurry comprising the following steps, wherein the negative electrode slurry comprises the binder composition. 【0023】 S21: A step of preparing a negative electrode active material aggregate from a negative electrode active material, a portion of the high viscosity sodium carboxymethylcellulose, a conductive agent, and a portion of the solvent. S22: Step of preparing the negative electrode slurry by adding the remaining portion of the high-viscosity sodium carboxymethylcellulose, the remaining portion of the solvent, and the binder to the aggregated negative electrode active material. 【0024】 In any embodiment of the present application, S201: Step of alkalizing cotton fibers and an alkalizing agent in a mixed solution of ethanol and water. S202: After the alkalization reaction is complete, an etherifying agent is added to the reaction system to carry out the etherification reaction. S203: A step to prepare the high viscosity sodium carboxymethylcellulose by replacing the product of the etherification reaction with a substitution agent. The method further comprises the step of preparing the high viscosity sodium carboxymethylcellulose containing the above, Optionally, the substitution agent comprises a dialdehyde monomer, and further optionally, the dialdehyde monomer comprises one or two of glyoxal and glutaraldehyde. 【0025】 In any embodiment of the present application, step S203 satisfies at least one of the following conditions I to III. 【0026】 I. The mass ratio of the product of the etherification reaction to the substitution agent is 100:(0.2~1.0). II. The temperature of the substitution reaction is 30°C to 70°C. III. The duration of the substitution reaction is 20 min to 120 min. 【0027】 The sixth aspect of this application is, Negative electrode current collector, and, The negative electrode active material layer located on at least one surface of the negative electrode current collector A negative electrode sheet including, The negative electrode active material layer comprises a binder according to the first aspect of this application, a binder prepared by the method according to the second aspect of this application, or a binder composition according to the third aspect of this application. We provide a negative electrode sheet. 【0028】 In any embodiment of the present application, the mass percentage of the binder in the negative electrode active material layer is 1.3% to 2.1%, arbitrarily 1.5% to 2.1%, and further arbitrarily 1.8% to 2.1%. 【0029】 In any embodiment of the present application, the negative electrode active material layer comprises the binder composition of the third embodiment of the present application, wherein the mass percentage of the high viscosity carboxymethylcellulose sodium in the negative electrode active material layer is 0.6% to 1.2%, optionally 0.8% to 1.2%, and optionally 0.9% to 1.2%. 【0030】 A seventh aspect of the present application provides a secondary battery including the negative electrode sheet of the sixth aspect of the present application. 【0031】 An eighth aspect of the present application provides a battery module including a secondary battery according to the seventh aspect of the present application. 【0032】 A ninth aspect of the present application provides a battery pack including the battery module of the eighth aspect of the present application. 【0033】 A tenth aspect of the present application provides an electrical device comprising at least one of the following: a secondary battery according to the seventh aspect of the present application, a battery module according to the eighth aspect of the present application, or a battery pack according to the ninth aspect of the present application. 【0034】 To more clearly explain the technical concept of this application, the drawings used in this application are briefly described below. Clearly, the drawings described below represent only some embodiments of this application, and those skilled in the art can obtain further drawings based on these drawings without any creative effort. [Brief explanation of the drawing] 【0035】 [Figure 1] Figure 1 is a viscosity-time curve diagram of the negative electrode slurry in Example 23 of the present invention. [Figure 2] Figure 2 is an adhesive force-time curve diagram of the negative electrode sheet in Embodiment 23 of the present invention. [Figure 3]Figure 3 shows the discharge DCR columnar diagrams of the battery cells in Examples 24, 25, 26, and Comparative Example 7 of this application. [Figure 4] Figure 4 is a schematic diagram of one embodiment of a secondary battery. [Figure 5] Figure 5 is an exploded view of Figure 4. [Figure 6] Figure 6 is a schematic diagram of one embodiment of a battery module. [Figure 7] Figure 7 is a schematic diagram of one embodiment of the battery pack. [Figure 8] Figure 8 is an exploded view of Figure 7. [Figure 9] Figure 9 is a schematic diagram of one embodiment of a device that uses a secondary battery as a power source. [Modes for carrying out the invention] 【0036】 The present application will be further described below with reference to specific embodiments. These specific embodiments should be understood to be merely illustrative of the present application and not to limit its scope. 【0037】 The “ranges” disclosed herein are limited in the form of lower and upper bounds, and a given range is limited by selecting a lower and an upper bound, and the selected lower and upper bounds define the boundaries of a particular range. Such limited ranges may or may not include the endpoints and may be in any combination; that is, any lower bound can be combined with any other upper bound to form a single range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Also, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4 and 5, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all expected. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed herein, and "0 to 5" is simply an abbreviation for combinations of these numbers. Also, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. 【0038】 In this specification, unless otherwise specified, "or more" and "or less" include the number of items, and "multiple types" in "one or more types" means two or more types. 【0039】 Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form novel technical inventions. 【0040】 Unless otherwise specified, all technical features and optional technical features of this application can be combined to form novel technical concepts. 【0041】 Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably in order. For example, if the method includes steps (a) and (b), it means that the method performs steps (a) and (b) in order, or steps (b) and (a) in order. For example, if the method referred to in the preceding paragraph may further include step (c), it means that step (c) may be added to the method in any order, for example, that the method includes steps (a), (b), and (c), steps (a), (c), and (b), or steps (c), (a), and (b). 【0042】 Unless otherwise specified, the terms “includes” and “contains” as used in this application mean open, but may also mean closed. For example, the terms “includes” and “contains” mean that other components not listed may be included or contained, and only the listed components may be included or contained. 【0043】 Unless otherwise specified, the term “or” in this application is inclusive. For example, the phrase “A or B” means “A, B, or both A and B.” More specifically, any of the following conditions also satisfy the “A or B” condition: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or A and B are true (or exist). Unless otherwise specified, the terms used in this application have the well-known meanings that are usually understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of each parameter mentioned in this application can be measured by various measurement methods common in the art (for example, by testing in the methods used in the embodiments of this application). 【0044】 In related technologies, styrene-butadiene rubber and sodium carboxymethylcellulose are often used as binders to prepare negative electrode sheets, but it is not possible to achieve both the processing performance of the negative electrode sheet and the dynamic performance of the battery cell. This is because, as the engineers of this application have discovered, negative electrode sheets prepared using styrene-butadiene rubber, a binder conventionally used at a rate of 2% to 2.5%, and sodium hydroxymethylcellulose, a binder conventionally used at a rate of 1% to 2%, result in poor dynamic performance in high-power systems for the corresponding battery cells. Furthermore, reducing the amount of styrene-butadiene rubber and sodium hydroxymethylcellulose added to improve the dynamic performance of the battery cell causes a series of processing performance problems, such as sedimentation due to decreased viscosity of the negative electrode slurry, decreased filterability, scratching of coated particles, and decreased adhesion strength of the negative electrode sheet, leading to further deterioration of the dynamic performance of the battery cell. 【0045】 The binder provided in this application comprises a core material having a glass transition temperature of -50°C to 0°C, and a shell material located on at least a portion of the surface of the core material, having a glass transition temperature of 60°C to 100°C. 【0046】 Not bound by any theory, the binder according to this application has a core-shell structure that is soft on the inside and hard on the outside, where the shell material is located on at least a portion of the surface of the core material, the core material is a flexible material with a lower glass transition temperature, and the shell material is a hard material with a higher glass transition temperature. The flexible core material is advantageous for cold pressing of the negative electrode sheet, helping to reduce the cold pressing pressure, increase the maximum value of the actual pressure window of the negative electrode active material, and provide relatively good adhesion. Furthermore, the amount of binder used can be reduced. The relatively small amount of binder used reduces the coating on the surface of the negative electrode active material. The relatively hard shell material does not deform excessively after cold pressing of the negative electrode sheet, reducing the area of ​​binder coating on the negative electrode active material, effectively reducing the impedance when lithium ions are inserted and removed, and improving the dynamic performance of the battery cell corresponding to the negative electrode sheet. Thus, when the above binder is applied to a battery cell, the DC internal resistance (DCR) of the battery cell is reduced by 5% to 12%, the charging interface is slightly increased, and compared to the styrene-butadiene rubber used in conventional technology, the adhesive strength of the binder in this application is increased by more than 20%, there is no film detachment or powder shedding, and the fully charged interface is good. 【0047】 The shell material may cover the entire surface of the core material or only a portion of the core material's surface, but it should be understood that it preferably covers the entire surface of the core material. The polar groups may include one or more of the following: carboxyl groups, hydroxyl groups, carbonyl groups, and ester groups. 【0048】 The glass transition temperatures of the core and shell materials mentioned earlier can be tested using a differential scanning calorimeter (DSC), and the specific procedure is as follows: 1. Sample preparation: Weigh 1-3 mg of the sample into an Al crucible and close the crucible lid; 2. Parameter setting: Nitrogen gas atmosphere, purge gas 50 ml / min, protective gas 100 ml / min; 3. Temperature rise sequence: 10°C / min, 35°C to -30°C, hold at -30°C for 3 min, 10°C / min, -30°C to 50°C; 4. Read the temperature at which the slope of the DSC curve is maximum as the glass transition temperature. 【0049】 In the embodiments of this application, the glass transition temperature of the core material is -50°C to 0°C, and may be, for example, -50°C to -5°C, -50°C to -10°C, -50°C to -20°C, -50°C to -30°C, -50°C to -40°C, -30°C to -0°C, or -30°C to -10°C. The glass transition temperature of the shell material is 60°C to 100°C, and may be, for example, 60°C to 95°C, 65°C to 90°C, 70°C to 85°C, or 70°C to 80°C. 【0050】 As a result of diligent research, the inventors have discovered that if the binder according to the present invention satisfies the above-mentioned conditions and also satisfies one or more of the following conditions, the dynamic performance of the battery cell can be further improved. 【0051】 In some embodiments, the shell material has polar groups. The polar groups can adjust the swelling ability of the binder in the electrolyte, resulting in relatively high swelling characteristics for the binder in the electrolyte, improving the lithium ion transmission channel and further enhancing the dynamic performance of the battery cell. Furthermore, the polar groups of the shell material can provide hydrogen bonding action, further increasing the adhesion of the binder to the negative electrode active material and improving the processing performance of the negative electrode sheet. 【0052】 In some embodiments, the core material may include a copolymer of styrene monomer units and butadiene monomer units. 【0053】 In some embodiments, the shell material may include a copolymer of styrene monomer units, butadiene monomer units, unsaturated acid monomer units, and unsaturated ester monomer units. 【0054】 A copolymer of styrene monomer units, butadiene monomer units, unsaturated acid monomer units, and unsaturated ester monomer units represents a copolymer consisting of styrene monomer units, butadiene monomer units, unsaturated acid monomer units, and unsaturated ester monomer units. While the copolymer contains styrene monomer units, butadiene monomer units, unsaturated acid monomer units, and unsaturated ester monomer units, there is no restriction on the order in which the styrene monomer units, butadiene monomer units, unsaturated acid monomer units, and unsaturated ester monomer units are arranged in the copolymer. It should be understood that the styrene monomer units, butadiene monomer units, unsaturated acid monomer units, and unsaturated ester monomer units in the copolymer may be arranged in any order. 【0055】 Optionally, the monomer corresponding to the unsaturated acid monomer unit contains an unsaturated acid having 3 to 6 carbon atoms and containing a substituted or unsubstituted -C=C- group. "Substituted or unsubstituted" means that the unsaturated acid may or may not be substituted. If the defined unsaturated acid is substituted, it should be understood that it may optionally be substituted with a group permitted in the Art, including but not limited to silyl, carbonyl, alkoxycarbonyl, aryloxycarbonyl, carbamoyl, haloformyl, formyl, cyano, isocyano, isocyanate, thiocyanate, isothiocyanate, hydroxyl, trifluoromethyl, nitro, or halogen groups, and that these groups may be further substituted with substituents permitted in the Art. Furthermore, optionally, the monomer corresponding to the unsaturated acid monomer unit contains one or more of acrylic acid, methacrylic acid, maleic acid, fumaric acid, and iconic acid. 【0056】 Optionally, the monomer corresponding to the unsaturated ester monomer unit includes a substituted or unsubstituted -C=C- containing unsaturated ester. "Substituted or unsubstituted" means that the unsaturated ester may or may not be substituted. If the defined unsaturated ester is substituted, it should be understood that it may optionally be substituted with a group permitted in the Art, including but not limited to silyl, carbonyl, alkoxycarbonyl, aryloxycarbonyl, carbamoyl, haloformyl, formyl, cyano, isocyano, isocyanate, thiocyanate, isothiocyanate, hydroxyl, trifluoromethyl, nitro, or halogen, and that such group may be further substituted with substituents permitted in the Art. Furthermore, optionally, the monomer corresponding to the unsaturated ester monomer unit includes one or more of the following: methyl methacrylate, ethylhexyl ester, vinyl acetate, isooctyl acrylate, hydroxyethyl acrylate, isobornyl methacrylate, vinyl neodecanoate, butyl acrylate, acrylocyanine, ethyl acrylate, n-butyl acrylate, and isobutyl acrylate. 【0057】 In some examples, the viscosity of the aqueous solution of the binder at 25°C with a solid content of 45% is 10 mPa·s to 200 mPa·s, and may be, for example, 10 mPa·s to 150 mPa·s, 20 mPa·s to 150 mPa·s, 50 mPa·s to 100 mPa·s, or 80 mPa·s to 100 mPa·s. 【0058】 The viscosity of the binder aqueous solution with a solid content of 45% at 25°C, as mentioned earlier, can be measured by the following method. Specifically, 500g of the 45% solid content binder aqueous solution to be measured was weighed, stirred for 2 hours, and measured after the binder to be measured was completely and uniformly stabilized. Measurement temperature: 25±1°C, rotor and rotation speed used: 63# rotor, 12r / min, the value at the 6th minute was taken, device model: DV-2TLV Brookfield viscometer. In some embodiments, the volume-average particle diameter Dv50 of the binder is 100nm to 1000nm, and may be, for example, 100nm to 900nm, 200nm to 900nm, 300nm to 600nm, 400nm to 600nm, or 500nm to 600nm, etc. 【0059】 The aforementioned volume-average particle size Dv50 refers to the particle size corresponding to 50% of the volume-cumulative distribution. For example, Dv50 can be easily measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Marvin Instruments Co., Ltd. in the UK, in accordance with the GB / T 19077-2016 particle size distribution laser diffraction method. 【0060】 Embodiments of the present invention further provide a method for preparing the above-mentioned binder, comprising the following steps. 【0061】 S11: A step of preparing the core material by polymerizing styrene monomer and butadiene monomer. S12: A step of polymerizing styrene monomer, butadiene monomer, unsaturated acid monomer, and unsaturated ester monomer on the surface of the core material. In some examples, the mass ratio of styrene monomer to butadiene monomer in the polymerization reaction for preparing the core material is 10:(4-8), and may be, for example, 10:(4-7), 10:(5-8), or 10:(5-6). 【0062】 In some examples, in the polymerization reaction for preparing the shell material, the mass ratio of styrene monomer, butadiene monomer, unsaturated acid monomer, and unsaturated ester monomer is 10:(4~8):(1~3):(2~4), and may also be, for example, 10:(4~7):(2~3):(2~3) or 10:(5~8):(1~2):(2~3). 【0063】 In the embodiments of this application, both the polymerization reaction for preparing the core material and the polymerization reaction for preparing the shell material require the involvement of an emulsifier and an initiator. 【0064】 Optionally, the emulsifier may include one or more of the following: sodium alkyl sulfate, sodium alkyl sulfonate, sodium alkyl diphenyl ether disulfonate, ammonium alkylphenol ether sulfate, sodium alkylphenol ether sulfosuccinate, sodium p-styrene sulfonate, sodium 2-acrylamido-2,2-dimethylethanesulfonate, sodium allyl succinate alkyl ester sulfonate, sodium acrylamide isopropyl sulfonate, and sodium alkyl acrylic acid-2-ethanesulfonate. 【0065】 Optionally, the initiator may contain one or more of the following: sodium persulfate, ammonium persulfate, and potassium persulfate. 【0066】 The present invention further provides a binder composition comprising the above-mentioned binder or a binder prepared by the above-mentioned method and high-viscosity sodium carboxymethylcellulose, wherein the aqueous solution of high-viscosity sodium carboxymethylcellulose has a viscosity of 10,000 mPa·s to 20,000 mPa·s at 25°C with a solid content of 1%, and may be, for example, 10,000 mPa·s to 19,000 mPa·s, 10,000 mPa·s to 15,000 mPa·s, 13,000 mPa·s to 17,000 mPa·s, or 15,000 mPa·s to 20,000 mPa·s. 【0067】 In conventional technology, the carboxymethylcellulose sodium used in negative electrode sheets has a viscosity of 2000 mPa·s to 8000 mPa·s at 25°C in an aqueous solution with 1% solids. However, the aforementioned aqueous solution of high-viscosity carboxymethylcellulose sodium with 1% solids has a significantly increased viscosity at 25°C. By adopting high-viscosity carboxymethylcellulose sodium, it is possible to guarantee the processing performance of the negative electrode sheet, appropriately reduce the amount used, reduce the coating on the surface of the negative electrode active material, reduce the transition impedance of lithium ions, and improve the dynamic performance of the battery cell corresponding to the negative electrode sheet. 【0068】 The viscosity of the previously mentioned aqueous solution of high-viscosity carboxymethylcellulose sodium at 25°C with a solid content of 1% can be measured by the following method. Specifically, 5.0 g of the high-viscosity carboxymethylcellulose sodium to be measured is weighed out, and pure water is added so that the total weight of the high-viscosity carboxymethylcellulose sodium to be measured and the pure water is 500 g. After dissolving the high-viscosity carboxymethylcellulose sodium to be measured while stirring for 2 hours to completely and uniformly disperse it, the viscosity is measured, and different rotors correspond to different viscosities. Measurement temperature: 25±1°C, rotor and rotation speed used: 63# rotor, 12 r / min, the value at the 6th minute is taken, device model: DV-2TLV Brookfield viscometer. 【0069】 In some examples, the mass ratio of the binder to high-viscosity carboxymethylcellulose sodium is (1.1-3.5):1, and may be, for example, (1.1-3):1, (1.6-2.6):1, (1.8-2.2):1, or (2-2.2). Technical studies have found that when the mass ratio of the binder to high-viscosity carboxymethylcellulose sodium is within this range, it contributes to further improvement of the adhesive strength of the binder composition. 【0070】 In some examples, the hydrogen atoms of the hydroxyl groups in high-viscosity sodium carboxymethylcellulose are substituted with a substitution agent, which reacts with the hydroxyl groups to form hemiacetals. By substituting the hydrogen atoms of the hydroxyl groups in high-viscosity sodium carboxymethylcellulose with a substitution agent, the high-viscosity sodium carboxymethylcellulose temporarily loses its hydrophilicity, preventing the immediate sticky phenomenon that occurs when the high-viscosity sodium carboxymethylcellulose comes into contact with water, which is advantageous for the rapid dispersion of high-viscosity sodium carboxymethylcellulose in water. At the same time, the hemiacetals can be hydrolyzed during the process of dissolving in water to regenerate hydroxyl groups and restore hydrophilicity. 【0071】 Optionally, the substitution agent may contain a dialdehyde monomer, and further optionally, the dialdehyde monomer may contain one or two of glyoxal and glutaraldehyde. 【0072】 The present invention further provides a method for preparing high-viscosity carboxymethylcellulose sodium, comprising the following steps. 【0073】 S201: Step of alkalizing cotton fibers and an alkalizing agent in a mixed solution of ethanol and water. In some examples, the mass ratio of water to cotton fibers is (0.3~0.8):1, and may be, for example, (0.3~0.7):1, (0.4~0.6):1, or (0.5~0.7):1. The mass ratio of ethanol to cotton fibers is (1.0~2.0):1, and may be, for example, (1.0~1.8):1, (1.1~1.7):1, (1.3~1.6):1, or (1.4~1.5):1. The alkalizing agent may be an aqueous sodium hydroxide solution with a mass percentage concentration of 30%~55%, and the mass ratio of the alkalizing agent to cotton fibers is (0.6~1.0):1, and may be, for example, (0.6~0.9):1, (0.7~1.0):1, or (0.7~0.8):1. The alkalizing reaction time may be 30 min to 80 min, and the alkalizing reaction temperature may be 10°C to 40°C. 【0074】 S202: After the alkalization reaction is complete, an etherifying agent is added to the reaction system to carry out the etherification reaction. In some examples, the etherifying agent may be an ethanol solution of chloroacetic acid with a mass percentage concentration of 50% to 80%. The mass ratio of the etherifying agent to the cotton fibers is (1.0 to 1.5):1, and may be, for example, (1.0 to 1.4):1 or (1.2 to 1.3):1. The etherification reaction time may be 40 min to 70 min, and the temperature of the etherification reaction may be 60°C to 90°C. 【0075】 S203: A step to prepare the high viscosity carboxymethylcellulose by replacing the product of the etherification reaction with a substitution agent. Optionally, the substitution agent comprises a dialdehyde monomer, and further optionally, the dialdehyde monomer comprises one or two of glyoxal and glutaraldehyde. 【0076】 In some examples, the mass ratio of the etherification reaction product to the substitution agent is 100:(0.2~1.0), and may be, for example, 100:(0.2~0.8), 100:(0.3~0.7), or 100:(0.4~0.6). 【0077】 In some examples, the temperature of the substitution reaction is 30°C to 70°C, and may be, for example, 30°C to 60°C, 40°C to 70°C, or 50°C to 60°C. 【0078】 In some examples, the duration of the substitution reaction is 20 min to 120 min, and may be, for example, 20 min to 110 min, 30 min to 90 min, 40 min to 70 min, or 50 min to 60 min. 【0079】 The embodiments of this application further provide a negative electrode slurry containing the above-described binder, a binder prepared by the above-described method, or the above-described binder composition. 【0080】 The present embodiment provides a method for preparing a negative electrode slurry comprising the following steps, wherein the negative electrode slurry comprises a binder composition: S21: A step of preparing a negative electrode active material aggregate from a negative electrode active material, a portion of the high viscosity sodium carboxymethylcellulose, a conductive agent, and a portion of the solvent. S22: A step of preparing the negative electrode slurry by adding the remaining portion of the high-viscosity sodium carboxymethylcellulose, the remaining portion of the solvent, and the binder to the aggregated negative electrode active material. 【0081】 In the embodiments of this invention, when preparing the anode slurry, high-viscosity sodium carboxymethylcellulose is added in two stages. First, a portion of the high-viscosity sodium carboxymethylcellulose is added to impregnate the anode active material in the aqueous slurry to promote uniform dispersion of the anode active material, and then the mixture is stirred and kneaded to obtain agglomerates of the anode active material. Finally, the remaining portion of the high-viscosity sodium carboxymethylcellulose is added and the anode active material is stirred. The high-viscosity sodium carboxymethylcellulose was able to suspend and disperse the anode active material. Since high-viscosity sodium carboxymethylcellulose can disperse rapidly in water, it is understood that, compared to sodium carboxymethylcellulose used in conventional anode slurries, the stirring time can be shortened, fulfilling the 2-hour anode slurry stirring preparation process and improving the stirring productivity. 【0082】 In some examples, high viscosity carboxymethylcellulose sodium is added in two separate additions, and the mass ratio of the high viscosity carboxymethylcellulose sodium added in the first addition to the high viscosity carboxymethylcellulose sodium added in the second addition is (0.25~1):1, and may be, for example, (0.25~0.9):1, (0.3~0.8):1, or (0.5~0.7):1. 【0083】 Negative electrode sheet An embodiment of the present invention is a negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, The present invention further provides a negative electrode sheet in which the negative electrode active material layer comprises the above-mentioned binder, a negative electrode binder prepared by the above-mentioned method, or the above-mentioned binder composition. 【0084】 In some examples, the mass percentage of the binder in the negative electrode active material layer is 1.3% to 2.1%, and may be arbitrarily 1.5% to 2.1%, or even arbitrarily 1.8% to 2.1%. The amount of binder used in the negative electrode active material layer is clearly lower than the amount of styrene-butadiene rubber binder used in the conventional technology. 【0085】 The mass percentage of the binder in the negative electrode active material layer mentioned above can be measured by the following method. Specifically, first, the mass M1 of the binder in the negative electrode active material layer is measured, then the mass M0 of the negative electrode active material layer is measured, and the mass percentage of the binder in the negative electrode active material layer is calculated according to the formula M1 / M0 * 100%. 【0086】 In some embodiments, the negative electrode active material layer contains the above-mentioned binder composition, and the mass percentage of high-viscosity carboxymethylcellulose sodium in the negative electrode active material layer is 0.6% to 1.2%, optionally 0.8% to 1.2%, and even more optionally 0.9% to 1.2%. The mass percentage of carboxymethylcellulose sodium in the negative electrode active material layer used in the prior art is usually 1% to 2%, but the mass percentage of high-viscosity carboxymethylcellulose sodium in the negative electrode active material layer of the embodiments of this application is clearly reduced. 【0087】 The mass percentage of high-viscosity carboxymethylcellulose sodium in the negative electrode active material layer mentioned above can be measured by the following method. Specifically, first, the mass M2 of high-viscosity carboxymethylcellulose sodium in the negative electrode active material layer is measured, and then the mass M0 of the negative electrode active material layer is measured. The mass percentage of high-viscosity carboxymethylcellulose sodium in the negative electrode active material layer is then calculated according to the formula M2 / M0*100%. 【0088】 The negative electrode current collector may be a conventional metal foil sheet or a composite current collector. For example, the metal foil sheet may be copper foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). 【0089】 The negative electrode active material layer typically further comprises a negative electrode active material, a conductive agent, and other optional auxiliary agents. 【0090】 For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be at least one selected from elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloy. However, this application is not limited to these materials, and other traditional materials used as negative electrode activators in batteries may be used. These negative electrode activators may be used individually or in combination of two or more. 【0091】 For example, the conductive agent may be one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. 【0092】 For example, other optional additives may include PTC thermistor material, etc. 【0093】 For example, a negative electrode sheet can be manufactured using the following method. That is, the components for manufacturing the negative electrode sheet, such as a negative electrode activator, a conductive agent, a binder, and optionally other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry. The negative electrode slurry is then applied onto a negative electrode current collector, and a negative electrode sheet can be obtained through processes such as drying and cold rolling. 【0094】 Unless otherwise specified, all of the above ingredients are commercially available. 【0095】 secondary battery A secondary battery refers to a battery that can be used again after being discharged and recharged by activating an active material. 【0096】 Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet provided above according to the present application, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions are repeatedly inserted into and removed from between the positive electrode sheet and the negative electrode sheet. The separator is provided between the positive electrode sheet and the negative electrode sheet and plays a role in isolation. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. 【0097】 Positive electrode sheet In a secondary battery, the positive electrode sheet typically includes a positive electrode current collector and a positive electrode film layer containing a positive electrode activator provided on at least one surface of the positive electrode current collector. 【0098】 For example, a positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector. 【0099】 As an example, a positive electrode current collector may use a metal foil sheet or a composite current collector. For example, an aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). 【0100】 When the secondary battery is a lithium-ion battery, the positive electrode active material may use a positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other traditional materials used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides include lithium cobalt oxide (for example, LiCoO2), lithium nickel oxide (for example, LiNiO2), lithium manganese oxide (for example, LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM 333 as well), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM 523 as well), LiNi 0.5 Co 0.25 Mn 0.25 O2 (abbreviated as NCM 211 as well), LiNi 0.6 Co 0.2 Mn 0.2O2(NCM 622 (Also abbreviated as LiNi) 0.8 Co 0.1 Mn 0.1 O2(NCM 811 (Also abbreviated as LiNi)), Lithium nickel cobalt aluminum oxide (for example, LiNi 0.85 Co 0.15 Al 0.05 It may include, but is not limited to, at least one of O2) and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure include, but is not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (also abbreviated as LFP)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), composite materials of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon. 【0101】 When the secondary battery is a sodium-ion battery, the positive electrode active material may be a positive electrode active material for sodium-ion batteries known in this art. For example, the positive electrode active material may be used alone or in combination of two or more types. Among these, the positive electrode active material may be sodium iron composite oxide (NaFeO2), sodium cobalt composite oxide (NaCoO2), sodium chromium composite oxide (NaCrO2), sodium manganese composite oxide (NaMnO2), sodium nickel composite oxide (NaNiO2), or sodium nickel titanium composite oxide (NaNi 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O2), sodium iron manganese complex oxide (Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), sodium iron phosphate compounds (NaFePO4), sodium manganese phosphate compounds (NaMn PThe material may be selected from O4, sodium cobalt phosphate compounds (NaCoPO4), Prussian blue-based materials, polyanionic materials (phosphates, fluorophosphates, pyrophosphates, sulfates), etc., but this invention is not limited to these materials, and other traditional materials used as positive electrode active materials for sodium-ion batteries may also be used. 【0102】 The positive electrode film layer may, in principle, optionally contain a binder, a conductive agent, and other optional auxiliary agents. 【0103】 For example, the binder may include at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. 【0104】 For example, the conductive agent may include at least one of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. 【0105】 For example, a positive electrode sheet can be manufactured by the following method: The components for manufacturing the positive electrode sheet described above, such as a positive electrode activator, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then applied to a positive electrode current collector, and a positive electrode sheet can be obtained through processes such as drying and cold rolling. 【0106】 Separator In some embodiments, the secondary battery further includes a separator. The present application is not particularly limited to the type of separator, and any known porous separator having good chemical and mechanical stability can be selected. 【0107】 In some embodiments, the material of the separator may be at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. If the separator is a multilayer composite film, the materials of each layer may be the same or different, and is not particularly limited. 【0108】 In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be fabricated into an electrode assembly by a winding process or a lamination process. 【0109】 electrolyte A secondary battery may contain an electrolyte, which plays a role in conducting ions between the positive and negative electrodes. The electrolyte may contain an electrolyte salt and a solvent. 【0110】 For example, the electrolyte salt may be one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiDFOB), lithium difluoro(oxalate)borate (LiBOB), lithium bis(oxalate)borate (LiPO2F2), lithium difluorobis(oxalate)phosphate (LiDFOP), and lithium tetrafluoro(oxalate)phosphate (LiTFOP). 【0111】 For example, the solvent may include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). 【0112】 In some embodiments, the electrolyte may further contain additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve the overcharge performance of the battery or additives that improve the high-temperature and low-temperature performance of the battery. 【0113】 In some embodiments, the secondary battery according to the present invention is a lithium-ion secondary battery. 【0114】 Secondary batteries can be manufactured according to conventional methods in this field, for example, by sequentially winding (or stacking) a positive electrode sheet, a separator, and a negative electrode sheet so that the separator is positioned between the positive electrode sheet and the negative electrode sheet to act as an separator to obtain a battery cell, placing the battery cell in an outer casing, injecting an electrolyte, and sealing the opening to obtain a secondary battery. 【0115】 The embodiments of this invention are not particularly limited in shape, and may be cylindrical, rectangular, or any other shape. For example, Figure 4 shows a rectangular secondary battery 5 as one example. 【0116】 In some embodiments, the secondary battery may include an outer casing. This casing is used to seal the electrode assembly and the electrolyte. 【0117】 In some embodiments, the casing of the secondary battery may be a rigid case such as a hard plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft bag such as a pouch-type soft bag. The material of the soft bag may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate. 【0118】 In some embodiments, referring to Figure 5, the exterior may include a case 51 and a lid plate 53. The case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates may be enclosed to form a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the lid plate 53 can be fitted over the opening so as to close the housing cavity. 【0119】 The positive electrode sheet, negative electrode sheet, and separator can be formed into the electrode assembly 52 by a winding or lamination process. The electrode assembly 52 is sealed within the aforementioned housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted according to the needs. 【0120】 In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, with the specific number being adjusted according to the application and capacity of the battery module. 【0121】 Figure 6 shows a battery module 4 as one example. In the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery joule 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed in place by fasteners. 【0122】 Optionally, the battery module 4 may include a housing having a space for accommodating multiple secondary batteries 5. 【0123】 In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack. 【0124】 Figures 7 and 8 show a battery pack 1 as an example. The battery pack 1 may include a battery housing and a plurality of battery modules 4 provided in the battery housing. The battery housing includes an upper housing 2 and a lower housing 3, the upper housing 2 being able to cover the lower housing 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in any manner within the battery housing. 【0125】 Electrical equipment The present invention further provides an electrical device comprising at least one of the secondary battery, battery module, or battery pack described above. The secondary battery, battery module, or battery pack may be used as a power source for the device, or as an energy storage unit for the device. The device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships and satellites, energy storage systems, etc. 【0126】 The device can be configured to use a secondary battery, battery module, or battery pack, depending on the user's needs. 【0127】 Figure 9 shows an example of an electrical device 6. This electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements for the lithium-ion battery of this device, a battery pack or battery module may be employed. 【0128】 Another example of an electrical device could be a mobile phone, tablet, or laptop computer. Such devices are typically required to be thin and may use rechargeable batteries as their power source. 【0129】 The beneficial effects of this application will be further explained below with reference to the examples. [Examples] 【0130】 To further clarify the problems, technical solutions, and beneficial effects that this application aims to solve, the following descriptions will be made in more detail with reference to examples and drawings. Clearly, the described examples are only a selection of examples of this application, not all of them. The following descriptions of at least one exemplary example are merely illustrative and do not limit this application or its application. All other examples obtained by those skilled in the art without expending creative effort based on the examples of this application are within the scope of protection of this application. 【0131】 All materials used in the embodiments of this application are commercially available. 【0132】 1. Preparation of the binder Example 1: The binder in question contained a core material and a shell material that coated the surface of the core material. The glass transition temperature of the core material was -30°C, the glass transition temperature of the shell material was 80°C, the viscosity of the aqueous solution of the binder at 25°C with a solid content of 1% was 100 mPa·s, and the volume-average particle size Dv50 of the binder was 500 nm. Specifically, the preparation method was as follows. 【0133】 1) Add 110g of water, 0.65g of initiator, and 1.5g of emulsifier to a reaction kettle, then add 50g of styrene and 25g of butadiene, adjust the pH to 5, raise the temperature of the reaction kettle to 70°C, and allow the reaction to proceed for 40 minutes to prepare a core layer emulsion containing the core material. 【0134】 2) 50 g of styrene, 25 g of butadiene, 10 g of methacrylic acid, and 15 g of methyl methacrylate were added dropwise to a reaction kettle. 1.5 g of emulsifier, 0.65 g of initiator, and 110 g of deionized water were added dropwise, and the mixture was stirred thoroughly for 1.5 hours. The reaction kettle was then heated to 80°C and the mixture was reacted with stirring for 6 hours. After cooling, the product was collected to prepare an emulsion containing the binder. 【0135】 Examples 2-14: Examples 2 to 14 were basically the same as Example 1, but differed in at least one of the following parameters: the type and / or amount of monomer used when preparing the core material, the type and / or amount of monomer used when preparing the shell material, the glass transition temperature of the core material, the glass transition temperature of the shell material, the viscosity of the aqueous solution of the binder at 25°C with a solid content of 1%, and the volume average particle size Dv50 of the binder. Details are shown in Table 1 below. 【0136】 Examples 2 and 3 further adjusted the reaction kettle pH value, reaction kettle temperature and reaction time in step 1), and / or the reaction kettle temperature in step 2). 【0137】 Specifically, in Example 2, the reaction kettle pH value in step 1) was 4.5, the reaction kettle temperature was 60°C, and the reaction time was 50 min, while the reaction kettle temperature in step 2) was 85°C. 【0138】 Specifically, in Example 3, the reaction kettle pH value in step 1) was 5.5, the reaction kettle temperature was 80°C, and the reaction time was 30 min, while the reaction kettle temperature in step 2) was 83°C. 【0139】 Comparative Example 1 In Comparative Example 1, only the core material was prepared, and the binder for Comparative Example 1 was obtained using the same preparation method as in step 1) of Example 1. 【0140】 Comparative Example 2 In Comparative Example 2, the shell material was prepared directly, and the binder for Comparative Example 2 was obtained using the same preparation method as in step 2) of Example 1. 【0141】 Comparative Examples 3-4 Comparative Examples 3 and 4 were basically the same as Example 1, except for the amount of monomer used when preparing the shell material, the details of which are shown in Table 1 below. 【0142】 Binder performance test The solid content of the binder-containing emulsions in Examples 1-14 and Comparative Examples 1-4 was calculated. Specifically, the total mass W1 of all materials excluding the deionized water added during the preparation process and the total mass W2 of all materials including the deionized water added during the preparation process were calculated, and the solid content of the binder contained in the emulsion was calculated according to the formula W1 / W2 * 100%. 【0143】 The core material glass transition temperature, shell material glass transition temperature, viscosity of the binder aqueous solution at 25°C with a solid content of 1%, and volume-average particle size Dv50 were tested for Examples 1-14 and Comparative Examples 1-4. Dv50 represents the particle size corresponding to when the cumulative volume distribution percentage of the binder reaches 50%. The test methods were as follows: Core material glass transition temperature: The glass transition temperature of the core material was tested using a differential scanning calorimeter (DSC), and the specific procedure was as follows: 1. Sample preparation: 1-3 mg of core material was weighed into an aluminum crucible and the crucible lid was closed. 2. Parameter setting: Nitrogen gas atmosphere, purge gas 50 ml / min, protective gas 100 ml / min. 3. Temperature rise sequence: 10°C / min, 35°C to -30°C, hold at -30°C for 3 minutes, 10°C / min, -30°C to 50°C. 4. The temperature at which the slope of the DSC curve was maximum was read as the glass transition temperature of the core material. 【0144】 Shell material glass transition temperature: The glass transition temperature of the shell material was tested using a differential scanning calorimeter (DSC), and the specific procedure was as follows: 1. Sample preparation: 1-3 mg of shell material was weighed into an aluminum crucible and the crucible lid was closed. 2. Parameter setting: Nitrogen gas atmosphere, purge gas 50 ml / min, protective gas 100 ml / min; 3. Temperature rise sequence: 10°C / min, 35°C to -30°C, hold at -30°C for 3 minutes, 10°C / min, -30°C to 50°C; 4. The temperature at which the slope of the DSC curve was maximum was read as the glass transition temperature of the shell material. 【0145】 Viscosity of binder-containing emulsion at 25°C: 500g of the binder emulsion to be measured was weighed and dissolved with stirring for 2 hours until the binder was completely and uniformly stable before measurement. Measurement temperature: 25±1°C, rotor and rotation speed used: 63# rotor, 12 r / min, the value at the 6th minute was taken; device model: DV-2TLV Brookfield viscometer. 【0146】 The volume-average particle size Dv50:GB / T 19077-2016 was measured using a laser particle size analyzer (e.g., Mastersizer 2000E laser particle size analyzer), referring to the particle size distribution laser diffraction method. 【0147】 Some of the parameters of the binders prepared in Examples 1-14 and Comparative Examples 1-4, as well as the types and amounts of monomers used when preparing the core material and the types and amounts of monomers used when preparing the shell material, are shown in Table 1 below. 【0148】 [Table 1-1] [Table 1-2] [Table 1-3] 【0149】 In Table 1, Tg1 represents the glass transition temperature of the core material, and Tg2 represents the glass transition temperature of the shell material. Viscosity represents the viscosity of an aqueous solution of a 1% solids binder at 25°C. 【0150】 2. Preparation of high-viscosity carboxymethylcellulose sodium Example 15: 1) The cotton fibers were crushed, and the crushed cotton fibers were mixed with ethanol and water and added to the reactor. A sodium hydroxide solution was added, and after the addition was complete, the air in the reactor was discharged so that the vacuum level of the reactor was -0.08 MPa, and the reactor was filled with inert gas so that the internal pressure of the reactor exceeded 0.02 MPa. The process of vacuuming and filling with inert gas was repeated 2 to 3 times to remove the air from the reactor, and the mixture was alkalized while stirring for 70 minutes. The alkalization temperature was 30°C, the mass ratio of water to cotton fibers was 0.5:1, the mass ratio of ethanol to cotton fibers was 1.5:1, the mass percentage concentration of the sodium hydroxide solution was 40%, and the mass ratio of the sodium hydroxide solution to cotton fibers was 0.8:1. 【0151】 2) A chloroacetic acid ethanol solution was uniformly sprayed into the reactor, the air in the reactor was removed so that the vacuum of the reactor was -0.08 MPa, and the reactor was filled with inert gas so that the internal pressure of the reactor exceeded 0.02 MPa. The reactor temperature was raised to 80°C and the etherification reaction was carried out for 50 minutes. The mass percentage concentration of the chloroacetic acid ethanol solution was 70%, and the mass ratio of the chloroacetic acid ethanol solution to the cotton fibers was 1.2:1. 【0152】 3) After the etherification reaction was complete, the material was cooled to 50°C, added to 60% volume alcohol, the pH was adjusted to neutral with hydrochloric acid, and after two washes and two centrifugations, the material was dried in a vacuum rake dryer. The measured moisture content of the material was 33%. A glyoxal alcohol solution was uniformly sprayed and added. The alcohol used was 65% volume alcohol, and the substitution reaction was carried out for 60 minutes while controlling the temperature to 55°C. The residual alcohol was collected under vacuum negative pressure (-0.02 MPa), and after post-processing such as drying and grinding, high viscosity carboxymethylcellulose sodium was obtained. The mass ratio of the product after the etherification reaction to glyoxal was 100:0.6. 【0153】 Examples 16-20 Examples 16-20 were basically the same as Example 15, but differed in at least one of the following: the amount of ethanol used, the amount of water used, the concentration of the sodium hydroxide aqueous solution, the amount of the sodium hydroxide aqueous solution used, the alkalization reaction time, the alkalization reaction temperature, and / or the concentration of the chloroacetic acid ethanol solution, the amount of the chloroacetic acid ethanol solution used, the etherification reaction time, the etherification reaction temperature, and / or the type / or amount of substitution agent used, the substitution reaction time, and the substitution reaction temperature, in step 3). Details are shown in Table 2 below. 【0154】 Example 21 Example 21 differed from Example 15 in that it only carried out alkalization and etherification reactions, and did not perform substitution reactions. The alkalization reaction followed the same alkalization method as in step 1) of Example 15, and the etherification reaction followed the same etherification method as in step 2) of Example 15. Details are shown in Table 2 below. 【0155】 High-viscosity carboxymethylcellulose sodium performance test The viscosity of aqueous solutions of high-viscosity carboxymethylcellulose sodium in Examples 15-21 was tested at 25°C with a solid content of 1%. The test method was as follows. 【0156】 5.0 g of high-viscosity sodium carboxymethylcellulose to be measured was weighed out, and pure water was added until the total weight of the sodium carboxymethylcellulose to be measured and the pure water reached 500 g. The mixture was stirred for 2 hours to dissolve the sodium carboxymethylcellulose to be measured, ensuring complete and uniform dispersion. After dissolving, the viscosity was measured, with different rotors corresponding to different viscosities. Measurement temperature: 25 ± 1°C, rotor and rotation speed used: 63# rotor, 12 r / min, the value at the 6th minute was taken; device model: DV-2TLV Brookfield viscometer. 【0157】 The viscosity, amount used in the preparation process, and parameter settings of the high-viscosity sodium carboxymethylcellulose prepared in Examples 15-20 and Comparative Examples 5-6 are shown in Table 2 below. 【0158】 [Table 2] 【0159】 In Table 2, viscosity refers to the viscosity of a 1% solids aqueous solution of high-viscosity carboxymethylcellulose sodium at 25°C. 【0160】 2. Preparation of the negative electrode slurry Example 22: 95.9 g of graphite, the negative electrode active material, 0.16 g of high-viscosity sodium carboxymethylcellulose prepared in Example 15, and 2.0 g of carbon black (SP), the conductive agent, were mixed at 200 rpm for 15 minutes and stirred uniformly. 43.54 g of deionized water was added, and the mixture was stirred and kneaded at 300 rpm for 60 minutes to obtain well-impregnated graphite aggregates. Then, 0.64 g of high-viscosity sodium carboxymethylcellulose was added, and the mixture was stirred at 300 rpm for 5 minutes. After adding 43.54 g of deionized water, the mixture was dispersed at 1200 rpm for 60 minutes. Finally, 2.89 g of the binder-containing emulsion prepared in Example 1 was added, and the mixture was stirred at 800 rpm for 30 minutes to obtain a negative electrode slurry. 【0161】 Examples 23-32 and Examples 34-56 Examples 23-32 and 34-56 were basically the same as Example 21, but differed in at least one of the following: the amount of negative electrode active material used, the type and / or amount of binder used, and the type and / or amount of high viscosity carboxymethylcellulose sodium used. Details are shown in Table 3 below. 【0162】 Example 33 Example 33 differed from Example 22 in that it employed a 2-hour stirring process, and the details of the preparation process were as follows. 【0163】 95.9g of graphite, the negative electrode active material, 0.16g of high-viscosity sodium carboxymethylcellulose, and 2.0g of carbon black, the conductive agent, were mixed at 200 rpm for 5 minutes and stirred uniformly. 43.54g of deionized water was added, and the mixture was stirred and kneaded at 800 rpm for 30 minutes to obtain well-impregnated graphite aggregates. 0.64g of high-viscosity sodium carboxymethylcellulose was then added, and the mixture was stirred at 300 rpm for 5 minutes. After adding another 43.54g of deionized water, the mixture was dispersed at 1200 rpm for 50 minutes, and then 4.0g of binder-containing emulsion was added and stirred at 800 rpm for 30 minutes to obtain a negative electrode slurry. The solid content of the binder-containing emulsion was 45%. 【0164】 Comparative Examples 7-11 Comparative Examples 7 to 11 were basically the same as Example 22, but differed in at least one of the following: the amount of negative electrode active material used, the type and / or amount of binder used, and the type and / or amount of high viscosity carboxymethylcellulose sodium used. Details are shown in Table 3 below. 【0165】 Anode slurry performance test Slurry stability tests were performed on the negative electrode slurries prepared in Examples 22-56 and Comparative Examples 7-11, and the specific test procedures are shown below. 【0166】 At 25°C, the negative electrode slurry was set to a viscosity matching the coating specification of 3000-20000 mPa.s. A 500 mL sample of the slurry was then taken out and allowed to stand. The viscosity of the negative electrode slurry was measured every 4 hours, and the amount of main material settled at the bottom of the slurry was measured every 12 hours by scraping it with a steel plate. The measurement process was stopped 24 hours after the completion of each measurement. 【0167】 Figure 1 shows the viscosity-time curve of the negative electrode slurry in Example 23, where the horizontal axis represents the test time and the vertical axis represents the viscosity value of the negative electrode slurry. As can be seen from Figure 1, when the negative electrode slurry was left to stand for 24 hours, the viscosity of the negative electrode slurry remained almost unchanged, indicating good viscosity stability of the negative electrode slurry. 【0168】 Table 3 shows the parameter settings for the preparation process of the negative electrode slurry in Examples 22-56 and Comparative Examples 7-11, as well as the slurry stability test results. 【0169】 [Table 3-1] [Table 3-2] [Table 3-3] 【0170】 In Table 3, "high viscosity CMC" refers to high viscosity carboxymethylcellulose sodium, and "general-purpose CMC" refers to general-purpose carboxymethylcellulose sodium. The general-purpose process refers to the negative electrode slurry preparation process used in Example 22, and the 2h stirring process refers to the negative electrode slurry preparation process used in Example 33. The viscosity of the general-purpose CMC was 5000 mPa·s. 【0171】 3. Fabrication of the negative electrode sheet The negative electrode slurries from Examples 22-56 and Comparative Examples 7-11 were uniformly applied to copper foil, which served as the negative electrode current collector, with a weight of 60-80 mg / 1540.25 mm² per side. 2The process was controlled, and then the negative electrode sheet was obtained through drying, cold pressing, and slitting. 【0172】 Anode sheet performance test Adhesion strength tests were performed on the negative electrode sheets in Examples 22-56 and Comparative Examples 7-11, and the results of the adhesion strength tests are shown in Table 4 below. The specific test method was as follows. 【0173】 At 25°C, the negative electrode sheet is used as a test sheet. Sheet samples measuring 30mm in width and 100-160mm in length are cut with a blade. Special double-sided tape is applied to a steel plate (the tape is 20mm wide and 90-150mm long). The cut sheet sample is attached to the double-sided tape with the test surface facing downwards, and rolled three times in the same direction with a press roller. Paper tape, whose width is the same as the sheet sample and whose length is 80-200mm longer than the sheet sample, is inserted under the sheet sample and fixed with wrinkle glue. The tensioning machine is then powered on. The following steps were performed: turn on the power, the lamp lit up, adjust the limit block to the appropriate position, secure the unattached end of the steel plate sheet sample with the lower jig, fold the paper tape upwards and secure it with the upper jig, adjust the position of the upper jig using the "up" and "down" buttons on the manual controller attached to the tensioner, open the dedicated computer linked to the tensioner, double-click the software icon on the desktop to perform the test, the tensile speed was 50 m / min, the test distance was 50 mm, and the software took data points every 10 seconds. 【0174】 The adhesive strength of the negative electrode sheet in Example 23 was tested three times in parallel. The adhesive strength-time curve for the negative electrode sheet in Example 23 is shown in Figure 2. The vertical axis represents adhesive strength, and the horizontal axis represents test distance. As can be seen from Figure 2, the average value of the adhesive strength of the negative electrode sheet in Example 23, tested three times, was higher than 15 N / m, indicating that the adhesive strength of the negative electrode sheet was good. 【0175】 IV. Manufacturing of battery cells 1. Preparation of the positive electrode sheet: LiNi, which is the positive electrode active material. 0.8 Co0.1 Mn 0.1 O2 (NCM811), polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent were dissolved in N-methylpyrrolidone (NMP) as a solvent in a mass ratio of 97%:1.5%:1.5%. After thorough stirring and homogeneous mixing, a positive electrode slurry was prepared. The positive electrode slurry was then uniformly applied to aluminum foil, which served as the positive electrode current collector, and subsequently dried, cold-pressed, and slit to obtain a positive electrode sheet. 【0176】 2. Separator: A polyethylene film (PE) with a thickness of 12 μm was used as the separator. 【0177】 3. Preparation of the electrolyte: Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and LiPF6 was uniformly dissolved in the above solution to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L. 【0178】 4. Manufacturing of battery cells: The positive electrode sheet, separator, negative electrode sheet manufactured in Examples 22-56 and Comparative Examples 7-11, and electrolyte were assembled into small soft bag battery cells. 【0179】 Battery cell performance test Battery DC impedance tests were performed on the battery cells prepared in Examples 22-56 and Comparative Examples 7-11, and the specific test procedure was as follows. 【0180】 At 25°C, the battery corresponding to Example 1 was charged to 4.2V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.2V, left for 5 minutes, then discharged for 12 minutes with a constant current of 1C, and the voltage V1 was recorded. After leaving for 5 minutes, it was left at -10°C for 2 hours, then discharged for 10 seconds at 15C, and the voltage V2 was recorded. (V2-V1) / 15C was obtained as the DCR of the battery cell. 【0181】 Using the DCR of the battery cell in Comparative Example 7 as a reference, the increase ratio of the internal resistance of the battery cells in Examples 22-56 and Comparative Examples 7-11 was calculated. Taking Example 22 as an example, the increase ratio of the internal resistance of the battery cell in Example 22 = DCR(Example 22) / DCR(Comparative Example 7)*100%, and the calculation method for the increase ratio of the internal resistance of the battery cells in the other examples was the same as above. The results of the increase ratio of the internal resistance of the battery cells in Examples 22-56 and Comparative Examples 7-11 are shown in Table 4 below. 【0182】 Figure 3 shows the discharge DCR barometric sections of the battery cells in Examples 24, 25, 26, and Comparative Example 7. As can be seen from Figure 3, the DCR of the battery cells clearly decreased, indicating a significant improvement in the dynamic performance of the battery cells. 【0183】 The performance test results for the negative electrode sheets and battery cell performance test results for Examples 22-56 and Comparative Example 7-11 are shown in Table 4 below. 【0184】 [Table 4-1] [Table 4-2] 【0185】 In Table 4, the weight excluding the negative electrode tearweight refers to the weight per unit area of ​​the negative electrode sheet. 【0186】 As can be seen from Example 1 and Comparative Examples 3-4 in Table 1, by optimizing the amounts of unsaturated acid monomers and unsaturated ester monomers used when preparing the binder shell material, the glass transition temperature of the shell material could be brought within the required range for the binder. 【0187】 As can be seen from Example 39 and Comparative Examples 7-11 in Tables 1-4, by providing the binder of the present invention in the negative electrode active material layer of the negative electrode sheet, the sheet adhesion strength of the negative electrode sheet is increased, the processing performance of the negative electrode sheet is satisfied, and the DC internal resistance of the battery cell is reduced, thereby improving the dynamic performance of the battery cell. 【0188】 As can be seen from Examples 22-38 and 40-56, by simultaneously providing the binder of the present invention and high-viscosity sodium carboxymethylcellulose in the negative electrode active material layer of the negative electrode sheet, the sheet adhesion strength of the negative electrode sheet is further enhanced, satisfying the processing performance of the negative electrode sheet, and the DC internal resistance of the battery cell is further reduced, thereby further improving the dynamic performance of the battery cell. In particular, by further optimizing the amount of binder and high-viscosity sodium carboxymethylcellulose used in the negative electrode active material layer of the present invention, higher sheet adhesion strength and lower DC internal resistance of the battery cell were obtained. 【0189】 The difference between Examples 22-25 and Examples 35-36 lies in the mass percentage of the binder in the negative electrode active material layer. Preferably, the binder mass percentage is 1.3% to 2.1%, in which case the negative electrode sheet has good processing performance and the battery cell has excellent dynamic performance. More preferably, the binder mass percentage is 1.5% to 2.1%, and even more preferably, it is 7.8% to 2.1%. 【0190】 The difference between Examples 26-33 and Examples 37-38 lies in the mass percentage of high-viscosity carboxymethylcellulose sodium in the negative electrode active material layer. Preferably, the mass percentage of high-viscosity carboxymethylcellulose sodium is 0.6% to 1.0%, in which case the negative electrode sheet has good processing performance and the battery cell has excellent kinetic performance. More preferably, the mass percentage of high-viscosity carboxymethylcellulose sodium is 0.6% to 1.0%, and even more preferably, it is 0.9% to 1.0%. 【0191】 The difference between Example 24 and Example 33 lies in the stirring process. By preparing the anode slurry using the binder and high-viscosity sodium carboxymethylcellulose of the present invention, the 2-hour stirring preparation process for the anode slurry can be met, thereby increasing the production capacity of the stirring. 【0192】 The foregoing describes only specific embodiments of the present application, and the scope of protection of the present application is not limited thereto. A person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the art disclosed herein, and such modifications or substitutions should be included within the scope of protection of the present application. Accordingly, the scope of protection of the present application should be subject to the scope of protection of the claims. [Explanation of symbols] 【0193】 1 Battery pack 2 Upper cabinet 3 Lower cabinet 4 Battery Modules 5 Secondary battery 51 cases 52 Electrode Assembly 53 Lid plate 6. Electrical equipment.

Claims

[Claim 1] A core material with a glass transition temperature of -50°C to 0°C, A shell material located on at least a portion of the surface of the core material and having a glass transition temperature of 60°C to 100°C A binder that includes, A binder having a viscosity of 10 mPa·s to 200 mPa·s when the solid content of the aqueous solution of the binder is 45% at 25°C. [Claim 2] The binder according to claim 1, wherein the shell material has polar groups. [Claim 3] The binder according to claim 1, wherein the core material comprises a copolymer of styrene monomer units and butadiene monomer units. [Claim 4] The binder according to claim 1, wherein the shell material comprises a copolymer of styrene monomer units - butadiene monomer units - unsaturated acid monomer units - unsaturated ester monomer units. [Claim 5] The binder according to claim 4, wherein the monomer corresponding to the unsaturated acid monomer unit contains a substituted or unsubstituted -C=C- and an unsaturated acid having 3 to 6 carbon atoms. [Claim 6] The binder according to claim 4, wherein the monomer corresponding to the unsaturated ester monomer unit comprises a substituted or unsubstituted -C=C- containing unsaturated ester. [Claim 7] The binder according to claim 1, wherein the volume-average particle diameter Dv50 of the binder is 100 nm to 1000 nm. [Claim 8] A method for preparing a binder according to claim 4, comprising the following steps: S11: A step of preparing the core material by polymerizing a styrene monomer and a butadiene monomer. S12: A step of polymerizing styrene monomer, butadiene monomer, unsaturated acid monomer, and unsaturated ester monomer onto the surface of the core material. [Claim 9] The method for preparing a binder according to claim 8, wherein in the polymerization reaction for preparing the core material, the mass ratio of the styrene monomer to the butadiene monomer is 10:(4-8). [Claim 10] A method for preparing a binder according to claim 8, wherein in the polymerization reaction for preparing the shell material, the mass ratio of the styrene monomer, the butadiene monomer, the monomer corresponding to the unsaturated acid monomer unit, and the monomer corresponding to the unsaturated ester monomer unit is 10:(4-8):(1-3):(2-4). [Claim 11] A binder composition comprising the binder described in claim 1 and high viscosity carboxymethylcellulose sodium, wherein the viscosity of the aqueous solution of the high viscosity carboxymethylcellulose sodium at 25°C with a solid content of 1% is 10,000 mPa·s to 20,000 mPa·s, and the mass ratio of the binder to the high viscosity carboxymethylcellulose sodium is (1.1 to 3.5):

1. [Claim 12] The binder composition according to claim 11, wherein the mass ratio of the binder to the high-viscosity sodium carboxymethylcellulose is (1.1 to 3):

1. [Claim 13] The binder composition according to claim 11, wherein the hydrogen atoms of the hydroxyl groups in the high viscosity sodium carboxymethylcellulose are substituted with a substitution agent, and the substitution agent and the hydroxyl groups react to produce a hemiacetal. [Claim 14] A negative electrode slurry comprising the binder according to any one of claims 1 to 7 and sodium carboxymethylcellulose. [Claim 15] A negative electrode slurry comprising the binder composition according to any one of claims 11 to 13. [Claim 16] A method for preparing a negative electrode slurry according to claim 15, comprising the following steps, wherein the negative electrode slurry comprises the binder composition: S21: Step of preparing a negative electrode active material aggregate from the negative electrode active material, a portion of the high viscosity sodium carboxymethylcellulose, a conductive agent, and a portion of the solvent. S22: A step of preparing the negative electrode slurry by adding the remaining portion of the high-viscosity sodium carboxymethylcellulose, the remaining portion of the solvent, and the binder to the aggregated negative electrode active material. [Claim 17] The process further includes the step of preparing the high viscosity sodium carboxymethylcellulose, the step of which is: S201: A step in which cotton fibers and an alkalizing agent are subjected to an alkalizing reaction in a mixed solution of ethanol and water. S202: After the alkalization reaction is complete, add an etherifying agent to the reaction system to carry out the etherification reaction. S203: A step of preparing the high viscosity sodium carboxymethylcellulose by replacing the product of the etherification reaction with a substitution agent. A method for preparing a negative electrode slurry according to claim 16, comprising: [Claim 18] Step S203 is the method for preparing a negative electrode slurry according to claim 17, satisfying at least one of the following conditions I to III: I: The mass ratio of the product of the etherification reaction to the substitution agent is 100:(0.2 to 1.0). II: The temperature of the substitution reaction is between 30°C and 70°C. III: The duration of the substitution reaction is 20 min to 120 min. [Claim 19] Negative electrode current collector, and, The negative electrode active material layer located on at least one surface of the negative electrode current collector A negative electrode sheet including, The negative electrode active material layer comprises the binder and sodium carboxymethylcellulose described in claim 1, and is a negative electrode sheet. [Claim 20] Negative electrode current collector, and, The negative electrode active material layer located on at least one surface of the negative electrode current collector A negative electrode sheet including, A negative electrode sheet comprising the binder composition according to claim 11. [Claim 21] The negative electrode sheet according to claim 19 or 20, wherein the mass percentage of the binder in the negative electrode active material layer is 1.3% to 2.1%. [Claim 22] The negative electrode sheet according to claim 20, wherein the negative electrode active material layer comprises the binder composition, and the mass percentage of the high viscosity carboxymethylcellulose sodium in the negative electrode active material layer is 0.6% to 1.2%. [Claim 23] A secondary battery comprising the negative electrode sheet according to claim 19 or 20. [Claim 24] A battery module including the secondary battery described in claim 23. [Claim 25] A battery pack comprising the battery module described in claim 24. [Claim 26] An electrical device including a secondary battery as described in claim 23.

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