Binder for secondary batteries, negative electrode slurry composition, negative electrode, and secondary battery

Abstract

The present invention relates to the battery technology, and more specifically to a binder for secondary batteries, a negative electrode slurry composition, a negative electrode, and a secondary battery. The binder for secondary batteries contains a cellulose derivative and improves the problem of poor flexibility of cellulose derivatives when used as a dispersant, thickener, and binder in the secondary battery production process by selectively cleaving the -CC- bond between C2 and C3 in the cyclic structure of the cellulose derivative's main chain.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and particularly to a binder for secondary batteries, a negative electrode slurry composition, a negative electrode, and a secondary battery.

Background Art

[0002] A secondary battery, also called a rechargeable battery or a storage battery, refers to a battery that can continue to be used by activating an active material through charging after discharging the battery. A binder is an essential auxiliary material in the manufacturing process of a secondary battery, and many of the currently used binders are cellulose derivatives, such as carboxymethyl cellulose (CMC).

[0003] Taking CMC as an example, when CMC functions as a secondary battery binder, it has good dispersibility, thickening property, and adhesiveness. However, after film formation, it is hard and brittle, with poor flexibility, which is disadvantageous for the production and processing of secondary batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=​​​​​​​​​​​JPEG2026516417000003.jpg43125 In the repeating unit A and the repeating unit B, R is independently selected from one or more of -OH or its derivatives, and in the repeating unit B, R1 is independently selected from one or more of the groups derived from -CHO, where a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, The relationship JPEG2026516417000004.jpg28100 is satisfied.

[0006] When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, The relationship JPEG2026516417000005.jpg26102 is satisfied.

[0007] When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, The relationship JPEG2026516417000006.jpg25132 is satisfied.

[0008] In the repeating unit B, R1 is independently selected from at least one of -OH, -COOH, -COONa, and -COOLi.

[0009] In the repeating unit B, R1 is independently selected from at least one of -COOH, -COONa, and -COOLi.

[0010] In the repeating units A and B, R is independently selected from at least one of -OH, -OCH2COOH, -OCH2COONa, and -OCH2COOLi.

[0011] The secondary battery negative electrode slurry composition includes the binder for secondary batteries.

[0012] The negative electrode of the secondary battery has an electrode composite material layer manufactured from the secondary battery negative electrode slurry composition.

[0013] The secondary battery has the negative electrode of the secondary battery.

[0014] Use of the aforementioned secondary battery binder in a battery separator, a lithium iron phosphate positive electrode, or a carbon-coated copper foil current collector. [Effects of the Invention]

[0015] The binder for secondary batteries, negative electrode slurry composition, negative electrode, and secondary battery of the present invention provide a binder for secondary batteries with good flexibility, and the manufactured electrode sheets show no obvious breakage even after flexibility testing, significantly improving the processing performance of the electrode sheets. Furthermore, when used in secondary batteries, there is no degradation in the battery's first-cycle efficiency and cycle performance. This solves the problem of poor flexibility of cellulose derivatives when used as dispersants, thickeners, and binders in secondary battery production processes.

[0016] To more clearly explain the embodiments of this application or the technical concepts in the prior art, the drawings that need to be used in the description of the embodiments or the prior art are briefly described below. [Brief explanation of the drawing]

[0017] [Figure 1] This is a photograph of the flexibility test of the battery negative electrode sheet according to Example 7 of the present invention. [Figure 2] This is a photograph of the flexibility test of the battery negative electrode sheet of Comparative Example 1. [Modes for carrying out the invention]

[0018] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, and the embodiments described below with reference to the drawings are illustrative and intended to illustrate the present invention, and should not be understood as limitations of the present invention.

[0019] In addition, cellulose derivatives have various functions such as adhesion, dispersion, thickening, and suspension in the application of secondary batteries. The "binder for secondary batteries" according to the present invention should not be understood as having only an adhesive effect, but may also be understood as a dispersant for secondary batteries, a thickener for secondary batteries, a suspending agent for secondary batteries, and the like.

[0020] It should be understood that the numerical ranges in the present invention specifically disclose each intermediate value between the upper and lower limits of the range. Each small range between any stated value or intermediate value within the stated range, and any other stated value or intermediate value within that range is also included in the present invention. The upper and lower limits of these small ranges may be independently included within the range or excluded.

[0021] Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art of the present invention. Although the present invention describes preferred methods and materials, any methods and materials similar or equivalent to those described in this specification may be used in the implementation or testing of the present invention. All documents described in this specification are incorporated by reference for the purpose of disclosing and describing the methods and / or materials related to that document. In case of conflict with any incorporated document, the content of this specification shall prevail. Terms such as "comprising", "including", "having", "containing", etc. used in this specification are all open terms, that is, they mean including but not limited to these.

[0022] The experimental methods used in the present invention are conventional methods unless otherwise explained.

[0023] The materials, reagents, etc. used in the present invention may be purchased or synthesized by known methods if not otherwise explained.

[0024] The present invention provides a binder for secondary batteries, the binder for secondary batteries contains a cellulose derivative, the cellulose derivative contains a repeating unit A and a repeating unit B, and the repeating unit A is as follows: JPEG2026516417000007.jpg45118 The repeating unit B is as follows: JPEG2026516417000008.jpg43125 In the repeating unit A and the repeating unit B, R is independently selected from one or more of -OH or its derivatives, and in the repeating unit B, R1 is independently selected from one or more of the groups derived from -CHO, where a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, The relationship JPEG2026516417000009.jpg28100 is satisfied.

[0025] When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, The relationship JPEG2026516417000010.jpg26102 is satisfied.

[0026] When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, The relationship JPEG2026516417000011.jpg25132 is satisfied.

[0027] In the repeating unit B, R1 is independently selected from at least one of -OH, -COOH, -COONa, and -COOLi.

[0028] In the repeating unit B, R1 is independently selected from at least one of -COOH, -COONa, and -COOLi.

[0029] In the repeating units A and B, R is independently selected from at least one of -OH, -OCH2COOH, -OCH2COONa, and -OCH2COOLi.

[0030] When using the secondary battery binder of this embodiment, R in the repeating unit A and the repeating unit B represents a hydroxyl group and / or its derivative group. In this embodiment of the present invention, R in the repeating unit A and the repeating unit B may independently represent different groups. As those skilled in the art will know, when cellulose is not modified, the R group represents all -OH, and in the prior art, -OH can be converted to a derivative functional group by etherification, esterification, grafting, etc., for example, -OH to -OCH2COOH, -OCH3, -OCH2CH3, -[OCH2CH(CH3)O] n The group is derived from CH3, -OCH2CH2OH, -ONO2, -OSO3Na, etc. For example, in one embodiment, the three R groups in repeating unit A represent -OH, -OCH2COONa, and -OCH2COOLi, respectively, and R in repeating unit B represents -OCH2COOLi. In another embodiment, the three R groups in repeating unit A represent -OH, -OCH2CH3COONa, and -OCH2OH, respectively, and R in repeating unit B represents -OSO3Na, with R1 in repeating unit B representing an aldehyde group derivative. However, in the embodiments of the present invention, R1 in repeating unit B may independently represent different groups. For example, the aldehyde group may be derived to a carboxyl group by a peroxy reaction, to a hydroxyl group by a reduction reaction, to both a hydroxyl group and a carboxyl group by a disproportionation reaction, or to other functional groups such as a hemiacetal. For example, in one embodiment, R1 in repeating unit B represents a hydroxyl group; in another embodiment, R1 in repeating unit B represents a functional group further derived from a hydroxyl group, the derivation method may similarly refer to the derivation method of the R group; and in yet another embodiment, R1 in repeating unit B is a carboxyl group, a carboxylate salt, such as sodium carboxylate or lithium carboxylate.

[0031] The binder for secondary batteries according to the present invention can significantly improve upon the problem of poor flexibility of conventional cellulose derivatives when used as a dispersant, thickener, and binder in the secondary battery manufacturing process. Currently, cellulose derivatives used in the secondary battery manufacturing process mainly include carboxymethylcellulose, hydroxypropylcellulose, carboxymethylhydroxypropylcellulose, carboxymethylhydroxyethylcellulose, and carboxymethylethylcellulose. All of these cellulose derivatives have the problem of being rigid and having poor flexibility, making slurry coating difficult and resulting in easily cracked electrode sheets. In conventional technology, to solve this problem, cellulose derivatives are usually used in combination with other materials that have good flexibility. For example, CMC is mixed with SBR (styrene-butadiene rubber). Although SBR has more flexibility than CMC, it cannot meet the requirements of the lithium battery anode sheet manufacturing process. To improve the brittleness of the electrode sheet, most manufacturers add small molecule plasticizers to the formulation, but the addition of plasticizers consumes some lithium, leading to a decrease in battery capacity. There are also related technologies that modify cellulose derivatives in order to improve their flexibility. For example, by introducing weakly polar nonionic groups into the cellulose side chains, ferropolar groups such as hydroxyl groups and carboxyl ethers are partially substituted, improving the brittleness of carboxymethylcellulose. In this method, the hydrogen bonding action by polar groups within and between molecules is reduced, making relative motion between molecules easier and the material more flexible overall. However, the reason carboxymethylcellulose exhibits adhesive properties in secondary batteries is that its side chains contain a large number of ferropolar groups. Reducing the proportion of ferropolar groups leads to a decrease in adhesive strength, which manifests as powder shedding from electrode sheets in secondary battery applications.Furthermore, the flexibility of carboxymethylcellulose can be altered by adjusting the distribution ratio of carboxymethyl substitution positions, for example. However, C6 in cellulose has only one more methylene group than C2 and C3, and the advantage of the long chain is not very clear. The improvement in flexibility of carboxymethylcellulose is limited to the overall degree of substitution. Alternatively, the flexibility of the rigid cyclic group segment can be improved by cleaving the -COC- bond in the CMC using a strong acid and grafting a flexible material. -COC- is a bond in the repeating unit of the CMC main chain. When cleaved, the degree of polymerization and viscosity of the CMC decrease significantly, and when used in secondary battery slurries, the suspendability and thickening properties decrease significantly. Compared to the conventional technology, the cellulose derivatives according to the examples of the present invention selectively cleave the -CC- bond between C2 and C3 in the main chain cyclic structure, changing the rigid cyclic structure, which is originally not rotatable, into a flexible chain-like structure, thereby significantly improving the flexibility of the cellulose derivative.

[0032] In the embodiments of the present invention, when a represents the molar amount of repeating unit A and b represents the molar amount of repeating unit B, The filename is JPEG2026516417000012.jpg28100. In some specific examples, the relationship between a and b is: The JPEG2026516417000013.jpg19163 is satisfied. In some preferred embodiments, the relationship between a and b is further Satisfy the requirements for JPEG2026516417000014.jpg19170.

[0033] Embodiments of the present invention further provide a secondary battery negative electrode slurry composition containing the above-mentioned binder for secondary batteries, and a negative electrode having an electrode composite layer formed from the secondary battery negative electrode slurry composition, and further provide a secondary battery having the negative electrode. The secondary battery according to embodiments of the present invention has lower DC internal resistance and a better capacity retention rate after cycling.

[0034] The present invention will be described in detail by the following specific examples in order to fully understand it, but the present invention may also be carried out by other methods that can achieve similar dissemination without deviating from the scope of the present invention, and therefore the present invention is not limited to the specific examples disclosed below.

[0035] Example 1: <Preparation of reaction products> A 0.1 mol / L aqueous solution of carboxymethylcellulose sodium (CMC with a degree of substitution of 0.8-0.9) was prepared based on the molar amount of dehydrated glucose units in the CMC.

[0036] NaIO4 was dissolved in water under light-shielding conditions to prepare a 0.1 mol / L aqueous solution of NaIO4.

[0037] NaBH4 was dissolved in water at room temperature to prepare a 0.1 mol / L aqueous solution of NaBH4.

[0038] <Reaction process> Stage 1: The above CMC aqueous solution was placed in a light-shielded reaction vessel, heated to 40°C and maintained at this temperature, and an equal volume of NaIO4 aqueous solution (with a molar ratio of CMC to NaIO4 of 1:1) was slowly added dropwise to the reaction vessel. The mechanical stirring speed was adjusted to 500 rpm, and the pH of the reaction environment was adjusted to 4 using a 1 mol / L H2SO4 solution before starting the timer. The reaction was allowed to proceed for 2 hours, and once the reaction time was reached, the reaction pH was adjusted to 7 with 1 mol / L NaOH.

[0039] Stage 2: An equal volume of NaBH4 aqueous solution (with a molar ratio of CMC, NaIO4, and NaBH4 of 1:1:1) was slowly added dropwise, the stirring speed was controlled to 300 rpm, the temperature of the reaction system was lowered to approximately 5°C, and the reaction was allowed to proceed for 2 hours. The pH was then adjusted to 7 using a 1 mol / L H2SO4 solution, at which point the reaction endpoint was reached.

[0040] <Separation and purification> After the reaction was complete, the resulting mixed liquid was slowly added to a large amount of frozen methanol to precipitate, filtered, and dried at room temperature to obtain a solid product, i.e., a binder for secondary batteries according to the embodiment of the present invention.

[0041] Example 2: <Preparation of reaction products> A 0.1 mol / L aqueous solution of carboxymethylcellulose sodium (CMC with a degree of substitution of 0.8-0.9) was prepared based on the molar amount of dehydrated glucose units in the CMC.

[0042] NaIO4 was dissolved in water under light-shielding conditions to prepare a 0.1 mol / L aqueous solution of NaIO4.

[0043] NaClO2 was dissolved in water at room temperature to prepare a 0.1 mol / L aqueous solution of NaClO2.

[0044] <Reaction process> Stage 1: The above CMC aqueous solution was placed in a light-shielded reaction vessel, heated to 40°C and maintained at this temperature, and an equal volume of NaIO4 aqueous solution (with a molar ratio of CMC to NaIO4 of 1:1) was slowly added dropwise to the reaction vessel. The mechanical stirring speed was adjusted to 500 rpm, and the pH of the reaction environment was adjusted to 4 using a 1 mol / L H2SO4 solution before starting the timer. The reaction was allowed to proceed for 2 hours, and once the reaction time was reached, the reaction pH was adjusted to 7 with 1 mol / L NaOH.

[0045] Stage 2: Slowly add the same volume of NaClO2 aqueous solution (with a molar ratio of CMC, NaIO4, and NaClO2 of 1:1:1) as the CMC aqueous solution from Stage 1, control the stirring speed to 300 rpm, lower the reaction system temperature to approximately 5°C, and allow the reaction to proceed for 2 hours. Adjust the pH to 7 using a 1 mol / L H2SO4 solution to reach the reaction endpoint.

[0046] <Separation and purification> After the reaction was complete, the reaction mixture was added dropwise to a large amount of anhydrous ethanol, and the precipitation of a cotton-like product was observed. The precipitate was filtered and the filtered cake was collected. The filtered cake was alternately washed with deionized water and anhydrous ethanol, and the washed filtered cake was dried at a constant temperature of 60°C for 12 hours to obtain a solid product, i.e., a binder for secondary batteries according to the embodiment of the present invention.

[0047] Example 3: The only difference from Example 2 was that direct separation and purification were performed after the first-step reaction to obtain a binder for secondary batteries according to the embodiment of the present invention.

[0048] Example 4 : The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.8, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.8V NaIO4 aqueous solution and a 0.2V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0049] Example 5: The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.6, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.6V NaIO4 aqueous solution and a 0.4V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0050] Example 6: The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.5, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.5V NaIO4 aqueous solution and a 0.5V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0051] Example 7: The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.4, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.4V NaIO4 aqueous solution and a 0.6V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0052] Example 8: The only difference from Example 7 was that direct separation and purification were performed after the first-step reaction to obtain a binder for secondary batteries according to the embodiment of the present invention.

[0053] Example 9 : The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.3, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.3V NaIO4 aqueous solution and a 0.7V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0054] Example 10: The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.2, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.2V NaIO4 aqueous solution and a 0.8V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0055] Example 11: The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.15, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.15V NaIO4 aqueous solution and a 0.5V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0056] Example 12: The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.1, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.1V NaIO4 aqueous solution and a 0.9V deionized water mixture were added slowly dropwise to the CMC aqueous solution.

[0057] Example 13: The only difference from Example 1 was that the molar ratio of CMC to NaIO4 in the first reaction step was 1:0.05, and the volume of the CMC aqueous solution used as the reaction raw material was V. A 0.05V NaIO4 aqueous solution and a 0.95V deionized water mixture were mixed and slowly added dropwise to the CMC aqueous solution.

[0058] Example 14 : The only difference from Example 2 was that the degree of carboxymethylcellulose sodium substitution used in the first reaction step was 0.3 to 0.4.

[0059] Comparative Example 1: Unmodified CMC (degree of substitution 0.8-0.9).

[0060] 'a' represents the molar amount of repeating unit A, and 'b' represents the molar amount of repeating unit B. The value of b / a+b was measured. The solutions after the first step of the reaction in Examples 1-14 were collected, and the aldehyde group content in the solution was measured by the hydroxyamine hydrochloride method. The measurement method was based on the following reference: Wang Qinmei, Liao Yanhong, Teng Wei et al. Measurement of aldehyde group concentration in sodium alginate oxide by hydroxyamine hydrochloride-potential titration [J]. Analytical Laboratory, 2008, 27(S1):83-86.

[0061] Since the solid product after the reaction does not change in relation to the relative molecular mass of the repeating unit structure of the reactant CMC, b = measured molar amount of aldehyde group / 2.

[0062] Table 1: Comparison of reaction conditions for Examples 1-14 and Comparative Example 1 JPEG2026516417000015.jpg127146

[0063] <Performance Test> Battery cell manufacturing A negative electrode sheet was manufactured according to a conventional process. A negative electrode slurry was prepared using a negative electrode active material, conductive agent, binder, and SBR in a mass percentage ratio of 96.3%:0.7%:1.2%:1.8%. The negative electrode active material was artificial graphite, the conductive agent was conductive carbon black, and the binder was the solid product of Examples 1-14, while the binder in Comparative Example 1 was unmodified CMC (substitution degree 0.8-0.9). The single-sided density of the manufactured negative electrode sheet was 14-15 mg / cm³. 2 ​The negative electrode sheet had a thickness of 150-160 μm, and the size of the cut negative electrode sheet was 5*5 cm.

[0064] A positive electrode sheet was manufactured according to a conventional process. A positive electrode slurry was prepared with a positive electrode active material, conductive agent, and binder in a mass percentage ratio of 97%:2%:1%. The positive electrode active material was a nickel-cobalt-manganese ternary material (523 blending ratio: nickel 50%, cobalt 20%, manganese 30%), the conductive agent was conductive carbon super-p, and the binder was PVDF (Solvay 5130).

[0065] The separator used was a separator with a 7um base film, a 3um ceramic on one side, and a 1um adhesive coating on both sides. The electrolyte adopted a conventional formulation, with 1 mol / L of LiPF6 lithium salt, and a mass ratio of solvent EC (ethylene carbonate):PC (propylene carbonate):DEC (diethyl carbonate) of 3:1:3. The mass ratio of additive VC (vinylene carbonate) in the electrolyte was 0.3%, and the mass ratio of PS (1,3-propanesultone) in the electrolyte was 0.1%.

[0066] Battery structure: A small soft pack battery with tabs on both sides was assembled according to the above material system.

[0067] Performance testing The negative electrode sheet was placed in an 8mm diameter cylinder, bent, and the fracture of the sheet coating layer was observed to evaluate the flexibility of the electrode sheet.

[0068] The first-cycle efficiency and charge-discharge cycle performance of the above battery cells were tested in accordance with the Chinese national standard GB / T31486-2015. The test results are shown in Table 2.

[0069] Table 2: Results of Electrochemical Performance Tests JPEG2026516417000016.jpg135148

[0070] As can be seen from the test results in Table 1, in Examples 1-13 of the present invention, when CMC with a substitution degree of 0.8 to 0.9 was selected and modified, the measured b / (a+b) ratio was high at 0.63. In Example 14, when CMC with a substitution degree of 0.3 to 0.4 was used for modification, the measured b / (a+b) was 0.83. Figure 1 is a photograph of the flexibility test results of the battery anode sheet in Example 7 without breakage, and Figure 2 shows the situation in which clear breakage occurred during the flexibility test of the battery anode sheet in Comparative Example 1. The modified CMC according to Examples 1-14 of the present invention showed significantly improved flexibility compared to the unmodified CMC in Comparative Example 1, and the degree of improvement in CMC flexibility increased as the b / (a+b) ratio increased. However, in Examples 3 and 8, flexibility actually decreased as b / (a+b) increased. This suggests that in repeating unit B of Examples 3 and 8, all R1 groups are aldehyde groups, and as the aldehyde group concentration increases, hemiacetals are formed between the aldehyde groups, restricting molecular motion. This may result in the material's flexibility being lower than that when b / (a+b) is at an appropriate level. In addition to indirectly measuring the value of b by measuring the aldehyde group content using the hydrochloric acid hydroxyamine method, other methods such as nuclear magnetic measurement and infrared spectroscopy can be used in other specific examples. For example, the b / (a+b) ratio was determined by nuclear magnetic measurement of the main chain structure of repeating unit B.

[0071] Furthermore, from the test results in Table 2, it was found that, with the exception of Examples 3 and 8, the first-cycle efficiency of the batteries in the other examples was basically the same as that of Comparative Example 1. Examples 3 and 8 showed a clear decrease in first-cycle efficiency compared to Comparative Example 1, suggesting that they may have been affected by aldehyde groups in the modified CMC.

[0072] Finally, Table 2 shows that the capacity retention rate after 1500 battery cycles for most examples was essentially the same as that of Comparative Example 1, indicating that the adhesive strength of the binders in these examples did not decrease after modification. The battery capacity retention rates of Examples 2 and 14 were clearly superior to those of Comparative Example 1, suggesting that the binders in Examples 3 and 14 contained more carboxyl groups or carboxylate ions, and that the carboxyl groups were highly polar functional groups, potentially providing stronger adhesive strength. The battery capacity retention rates of Examples 3 and 8 were inferior to those of Comparative Example 1, suggesting that they may have been affected by aldehyde groups.

[0073] However, cellulose derivatives can be used in secondary batteries not only as binders, dispersants, and thickeners for the battery anode, but also as binders, dispersants, and thickeners for battery separator coating slurries, lithium iron phosphate cathode slurries, and carbon coating slurries for battery copper foil current collectors. In these application scenarios, the performance requirements for the binders are largely consistent.

[0074] The above disclosures represent only one or more preferred embodiments of this application and do not limit the scope of the rights of this application. A person skilled in the art will understand that implementing all or some of the processes of the above embodiments and making equivalent modifications in accordance with the claims of this application will still fall within the scope covered by this application.

Claims

1. A binder for secondary batteries containing a cellulose derivative, The cellulose derivative comprises repeating unit A and repeating unit B, and repeating unit A is as follows: The repeating unit B is as follows: In the repeating unit A and the repeating unit B, R is independently selected from one or more of -OH or its derivative groups, and in the repeating unit B, R １ independently, one or more groups derived from -CHO are selected, where a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, A binder for secondary batteries characterized by satisfying the following relationship.

2. When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, A binder for secondary batteries according to claim 1, characterized in that it satisfies the following relationship.

3. When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, A binder for secondary batteries according to claim 1, characterized in that it satisfies the following relationship.

4. In the repeating unit B, R １ The binder for secondary batteries according to claim 1, characterized in that the element is independently selected from at least one of -OH, -COOH, -COONa, and -COOLi.

5. In the repeating unit B, R １ The binder for secondary batteries according to claim 1, characterized in that the element is independently selected from at least one of -COOH, -COONa, and -COOLi.

6. In the repeating units A and B, R is independently -OH and -OCH. ２ COOH, -OCH ２ COONa and -OCH ２ A binder for secondary batteries according to claim 1, characterized in that it is selected from at least one of COOLi.

7. A secondary battery negative electrode slurry composition characterized by comprising a binder for secondary batteries according to any one of claims 1 to 6.

8. A secondary battery negative electrode, characterized in that it has an electrode composite material layer manufactured from the secondary battery negative electrode slurry composition described in claim 7.

9. A secondary battery characterized by having the secondary battery negative electrode described in claim 8.

10. Use of the secondary battery binder according to any one of claims 1 to 6 in a battery separator, a lithium iron phosphate positive electrode, or a carbon-coated copper foil current collector.

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