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

Abstract

A binder for a secondary battery, a negative electrode slurry composition, a negative electrode and a secondary battery. The binder comprises a cellulose derivative. By selectively breaking a -C-C- bond between C2 and C3 on a ring structure of the main chain of the cellulose derivative, the problem of poor flexibility of the cellulose derivative used as a dispersant, a thickener and a binder in a production process for secondary batteries is improved.

Description

Binder for secondary battery, negative electrode slurry composition, negative electrode and secondary battery Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a binder for a secondary battery, a negative electrode slurry composition, a negative electrode and a secondary battery. Background Art

[0002] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after discharge to reactivate the active materials and continue to be used. Binders are essential auxiliary materials in the production of secondary batteries. Currently, cellulose derivatives, such as carboxymethyl cellulose (CMC), are the most commonly used binders.

[0003] Taking CMC as an example, CMC has good dispersibility, thickening and adhesion when used as a binder for secondary batteries. However, after forming the film, it is hard and brittle and has poor flexibility, which is not conducive to the production and processing of secondary batteries.

[0004] Summary of the Invention

[0005] The object of the present invention is to provide a binder for secondary batteries, a negative electrode slurry composition, a negative electrode and a secondary battery, which improve the poor flexibility of cellulose derivatives when used as dispersants, thickeners and binders in the production process of secondary batteries.

[0006] To achieve the above object, the present invention provides a binder for a secondary battery, comprising a cellulose derivative, wherein the cellulose derivative comprises a repeating unit A and a repeating unit B, wherein the repeating unit A is:

[0007] The repeating unit B is,

[0008] Wherein, in the repeating unit A and the repeating unit B, R is independently selected from one or more of -OH or its derivative groups; in the repeating unit B, R1 is independently selected from one or more of -CHO derived groups; when a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the relationship is satisfied:

[0009] Wherein, when a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the relationship is satisfied:

[0010] Wherein, when a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the relationship is satisfied:

[0011] Wherein, in the repeating unit B, R1 is independently selected from at least one of —OH, —COOH, —COONa and —COOLi.

[0012] Wherein, in the repeating unit B, R1 is independently selected from at least one of —COOH, —COONa and —COOLi.

[0013] Wherein, in the repeating unit A and the repeating unit B, R is independently selected from at least one of —OH, —OCH2COOH, —OCH2COONa and —OCH2COOLi.

[0014] A secondary battery negative electrode slurry composition comprises the aforementioned binder for secondary batteries.

[0015] A secondary battery negative electrode comprises an electrode composite material layer made from the secondary battery negative electrode slurry composition.

[0016] A secondary battery comprises the secondary battery negative electrode.

[0017] The binder for secondary batteries is applied to battery separators, lithium iron phosphate positive electrodes, or carbon-coated copper foil current collectors.

[0018] The present invention provides a secondary battery binder, negative electrode slurry composition, negative electrode, and secondary battery. The provided secondary battery binder exhibits excellent flexibility, resulting in an electrode sheet with no apparent fracture after flexibility testing, significantly improving the sheet's processing performance. Furthermore, when used in a secondary battery, the battery's initial efficiency and cycle performance do not deteriorate. This solves the problem of poor flexibility of cellulose derivatives when used as dispersants, thickeners, and binders in secondary battery production processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art.

[0020] FIG1 is a photograph of the flexibility test of the negative electrode plate of the battery of Example 7 of the present invention.

[0021] FIG2 is a photograph showing the flexibility test of the negative electrode of the battery in comparative example 1. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0023] It should be noted that cellulose derivatives have multiple functions in the application of secondary batteries, such as bonding, dispersing, thickening and suspending. The "binder for secondary batteries" mentioned in the present invention should not only be understood as a bonding function, but can also be understood as a dispersant for secondary batteries, a thickener for secondary batteries, and a suspending agent for secondary batteries, etc.

[0024] The numerical ranges herein are understood to specifically disclose every intervening value between the upper and lower limits of the range. Each smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in that stated range is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0025] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art. Although the present invention has only described preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail. As used herein, "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0026] Unless otherwise specified, the experimental methods used in the present invention are all conventional methods.

[0027] Unless otherwise specified, the materials, reagents, etc. used in the present invention can be purchased or synthesized by known methods.

[0028] The present invention provides a binder for a secondary battery, comprising a cellulose derivative, wherein the cellulose derivative comprises a repeating unit A and a repeating unit B: the repeating unit A is,

[0029] The repeating unit B is,

[0030] Wherein, in the repeating unit A and the repeating unit B, R is independently selected from one or more of -OH or its derivative groups; in the repeating unit B, R1 is independently selected from one or more of -CHO derived groups; when a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the relationship is satisfied:

[0031] When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the relationship is satisfied:

[0032] When a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the relationship is satisfied:

[0033] In the repeating unit B, R1 is independently selected from at least one of —OH, —COOH, —COONa and —COOLi.

[0034] In the repeating unit B, R1 is independently selected from at least one of —COOH, —COONa and —COOLi.

[0035] In the repeating unit A and the repeating unit B, R is independently selected from at least one of —OH, —OCH 2 COOH, —OCH 2 COONa, and —OCH 2 COOLi.

[0036] A secondary battery binder according to the present embodiment is used, wherein R in the repeating unit A and the repeating unit B represents a hydroxyl group and / or a derivative group thereof. It should be noted that, in the embodiment of the present invention, R on the repeating unit A and the repeating unit B can independently represent different groups. It is known to those skilled in the art that, before modification, the R groups on the cellulose all represent -OH. In the prior art, -OH can be converted into a derivative functional group by etherification, esterification, grafting, etc., for example, -OH can be derived into -OCH2COOH, -OCH3, -OCH2CH3, -[OCH2CH(CH3)O] n CH3, -OCH2CH2OH, -ONO2, -OSO3Na, etc.; For example, in one embodiment, the three R groups in the repeating unit A represent -OH, -OCH2COONa and -OCH2COOLi, respectively, and the R in the repeating unit B represents -OCH2COOLi; in another embodiment, the three R groups in the repeating unit A represent -OH, -OCH2CH3COONa, -OCH2OH, respectively, and the R in the repeating unit B represents -OSO3Na; R1 in the above repeating unit B represents a group derived from an aldehyde group. It should be noted that in the present invention, In the embodiment, R1 on the repeating unit B can be independently represented by different groups. For example, the aldehyde group can be derived into a carboxyl group through an oxidation reaction, can be derived into a hydroxyl group through a reduction reaction, can be derived into a hydroxyl group and a carboxyl group at the same time through a disproportionation reaction, and can also be derived into other functional groups such as hemiacetal. For example, in one embodiment, R1 in the repeating unit B represents a hydroxyl group, and in another embodiment, R1 in the repeating unit B represents a functional group further derived from a hydroxyl group. The derivatization method can also refer to the derivatization method of the R group. In other embodiments, R1 in the repeating unit B represents a carboxyl group, a carboxylate, such as sodium carboxylate or lithium carboxylate.

[0037] The secondary battery binder provided by the present invention can significantly improve the problem of poor flexibility of existing cellulose derivatives when used as dispersants, thickeners and binders in the production process of secondary batteries. At present, the cellulose derivatives used in the production process of secondary batteries mainly include carboxymethyl cellulose, hydroxypropyl cellulose, carboxymethyl hydroxypropyl cellulose, carboxymethyl hydroxyethyl cellulose, carboxymethyl ethyl cellulose, etc. These cellulose derivatives all have the problem of strong rigidity and poor flexibility, which makes the slurry coating process difficult and the electrode plates produced are easy to crack. In the prior art, in order to solve this problem, cellulose derivatives are usually used in combination with other materials with good flexibility, such as CMC and SBR (styrene-butadiene rubber). SBR has a certain flexibility compared to CMC, but it still cannot meet the production process requirements of lithium battery negative electrode plates. In order to improve the brittleness of the plates, most manufacturers add small molecule plasticizers to the formula, but the addition of plasticizers will consume some lithium, resulting in a decrease in battery capacity. In addition, there are also some related technologies for modifying cellulose derivatives in the hope of improving the flexibility of cellulose derivatives. For example, the brittleness of carboxymethyl cellulose can be improved by introducing weakly polar nonionic groups on the cellulose side chains to partially replace strong polar groups such as hydroxyl and carboxyl ether. This approach reduces the hydrogen bonding caused by polar groups within and between molecules, making the relative movement between molecules easier, resulting in a softer overall appearance. However, the reason why carboxymethyl cellulose acts as a binder in secondary batteries is that its side chains have a large number of strong polar groups. Reducing the proportion of strong polar groups will cause the bonding force to decrease, which manifests as powdering of the electrode in secondary battery applications. For example, the flexibility of carboxymethyl cellulose can be changed by adjusting the distribution ratio of the carboxymethyl substitution position. However, C6 on cellulose only has one more methylene group than C2 and C3, so the advantage of long chains is not very obvious. Moreover, due to the limitation of the overall degree of substitution, the improvement in the flexibility of carboxymethyl cellulose is limited. Another example is the use of a strong acid to break the -C-O-C- bond in CMC and then graft a flexible material onto it, improving the flexibility of the rigid cyclic group segments. -C-O-C- is the connecting bond between the repeating units in the CMC backbone. Breaking the bond significantly reduces the CMC's degree of polymerization and viscosity, significantly reducing its suspending and thickening properties in secondary battery slurries. Compared to existing technologies, the cellulose derivatives provided in the present invention selectively break the -C-C- bond between C2 and C3 in the main chain ring structure, transforming the previously rigid, non-rotatable ring structure into a flexible chain structure, significantly improving the cellulose derivative's flexibility.

[0038] 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, In some specific embodiments, the relationship between a and b satisfies or or In some preferred embodiments, the relationship between a and b also satisfies or or

[0039] The present invention also provides a secondary battery negative electrode slurry composition containing the aforementioned secondary battery binder, a negative electrode having an electrode composite layer formed from the secondary battery negative electrode slurry composition, and a secondary battery having the negative electrode. The secondary battery provided by the present invention has lower DC internal resistance and better capacity retention after cycling.

[0040] The present invention is described in many specific details through the following specific embodiments to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] Example 1:

[0042] <Reactant Configuration>

[0043] Based on the number of moles of anhydroglucose units in sodium carboxymethylcellulose (CMC, degree of substitution 0.8-0.9), a 0.1 mol / L CMC aqueous solution was prepared.

[0044] Dissolve NaIO4 in water in a dark environment to prepare a 0.1 mol / L NaIO4 aqueous solution.

[0045] Dissolve NaBH4 in water at room temperature to prepare a 0.1 mol / L NaBH4 aqueous solution.

[0046] <Reaction Process>

[0047] The first stage: take the above-mentioned CMC aqueous solution and place it in a light-proof reaction container, heat it to 40°C and maintain this temperature, slowly add a volume of NaIO4 aqueous solution equal to that of the CMC aqueous solution into the reaction container (the molar ratio of CMC and NaIO4 is 1:1), adjust the mechanical stirring speed to 500 rpm, use 1 mol / L H2SO4 solution to adjust the pH of the reaction environment to 4, start timing, react for 2 hours, and adjust the reaction pH to 7 with 1 mol / L NaOH after the reaction time is reached.

[0048] The second stage: slowly add an equal volume of NaBH4 aqueous solution to the CMC aqueous solution in the first stage (the molar ratio of CMC, NaIO4 and NaBH4 is 1:1:1), control the stirring speed at 300 rpm, reduce the temperature of the reaction system to about 5°C, react for 2 hours, and adjust the pH value to 7 with 1 mol / L H2SO4 solution, which means reaching the reaction end point.

[0049] <Separation and purification>

[0050] After the reaction is completed, the mixed liquid after the reaction is slowly poured into a large amount of frozen methanol to precipitate, and after filtering, it is dried at room temperature to obtain a solid product, that is, the binder for secondary batteries provided by an embodiment of the present invention.

[0051] Example 2:

[0052] <Reactant Configuration>

[0053] Based on the number of moles of anhydroglucose units in sodium carboxymethylcellulose (CMC, degree of substitution 0.8-0.9), a 0.1 mol / L CMC aqueous solution was prepared.

[0054] Dissolve NaIO4 in water in a dark environment to prepare a 0.1 mol / L NaIO4 aqueous solution.

[0055] Dissolve NaClO2 in water at room temperature to prepare a 0.1 mol / L NaClO2 aqueous solution

[0056] <Reaction Process>

[0057] The first stage: take the above-mentioned CMC aqueous solution and place it in a light-proof reaction container, heat it to 40°C and maintain this temperature, slowly add a volume of NaIO4 aqueous solution equal to that of the CMC aqueous solution into the reaction container (the molar ratio of CMC and NaIO4 is 1:1), adjust the mechanical stirring speed to 500 rpm, use 1 mol / L H2SO4 solution to adjust the pH of the reaction environment to 4, start timing, react for 2 hours, and adjust the reaction pH to 7 with 1 mol / L NaOH after the reaction time is reached.

[0058] The second stage: slowly add an equal volume of NaClO2 aqueous solution to the CMC aqueous solution in the first stage (the molar ratio of CMC, NaIO4 and NaClO2 is 1:1:1), control the stirring speed at 300 rpm, reduce the temperature of the reaction system to about 5°C, react for 2 hours, and adjust the pH value to 7 with 1 mol / L H2SO4 solution, which means reaching the reaction end point.

[0059] <Separation and purification>

[0060] After the reaction is completed, the mixed liquid after the reaction is added dropwise to a large amount of anhydrous ethanol. The precipitation of flocculent products can be observed. The precipitate is filtered and the filter cake is collected. The filter cake is washed alternately with deionized water and anhydrous ethanol. The washed filter cake is placed at a constant temperature of 60°C and dried for 12 hours to obtain a solid product, namely the binder for secondary batteries provided in an embodiment of the present invention.

[0061] Example 3:

[0062] The only difference from Example 2 is that separation and purification are directly performed after the first-stage reaction to obtain the binder for secondary batteries provided by the embodiment of the present invention.

[0063] Example 4: The only difference from Example 1 is that the molar ratio of CMC and NaIO4 in the first reaction stage is 1:0.8; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.8V of NaIO4 aqueous solution and 0.2V of deionized water and slowly adding the mixture dropwise to the CMC aqueous solution.

[0064] Example 5:

[0065] The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.6; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.6V of NaIO4 aqueous solution and 0.4V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0066] Example 6:

[0067] The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.5; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.5V of NaIO4 aqueous solution and 0.5V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0068] Example 7:

[0069] The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.4; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.4V of NaIO4 aqueous solution and 0.6V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0070] Example 8:

[0071] The only difference from Example 7 is that separation and purification are directly performed after the first-stage reaction to obtain the binder for secondary batteries provided by this embodiment of the present invention.

[0072] Example 9: The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.3; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.3V of NaIO4 aqueous solution and 0.7V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0073] Example 10:

[0074] The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.2; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.2V of NaIO4 aqueous solution and 0.8V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0075] Example 11:

[0076] The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.15; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.15V of NaIO4 aqueous solution and 0.5V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0077] Example 12:

[0078] The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.1; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.1V of NaIO4 aqueous solution and 0.9V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0079] Example 13:

[0080] The only difference from Example 1 is that the molar ratio of CMC to NaIO4 in the first reaction stage is 1:0.05; the volume V of the CMC aqueous solution participating in the reaction is obtained by mixing 0.05V of NaIO4 aqueous solution and 0.95V of deionized water, and slowly adding the mixture dropwise to the CMC aqueous solution.

[0081] Example 14: The only difference from Example 2 is that the degree of substitution of sodium carboxymethyl cellulose used in the first reaction stage is 0.3-0.4.

[0082] Comparative Example 1: CMC without modification (degree of substitution 0.8-0.9).

[0083]

[0084] ​Denote the number of moles of repeating unit A by a, and the number of moles of repeating unit B by b by b / a+b. The aldehyde content of the solution after the first stage reaction of Example 1-14 was determined using the hydroxylamine hydrochloride method. The measurement method is described in the literature referenced by Wang Qinmei, Liao Yanhong, Teng Wei, et al. Determination of the aldehyde concentration on oxidized sodium alginate by hydroxylamine hydrochloride-potentiometric titration [J]. Analytical Laboratory, 2008, 27(S1): 83-86.

[0085] Since the relative molecular mass of the repeating unit structure of the solid product after the reaction is unchanged compared to that of the reactant CMC, b = the measured number of moles of aldehyde groups / 2.

[0086] Table 1 Comparison of reaction conditions for Examples 1-14 and Comparative Example 1

[0087] <Performance Test>

[0088] Battery cell production

[0089] A negative electrode sheet was prepared according to conventional techniques. The negative electrode active material, conductive agent, binder, and SBR were mixed in a mass ratio of 96.3%:0.7%:1.2%:1.8% to form a negative electrode slurry. The negative electrode active material was artificial graphite, the conductive agent was conductive carbon black, and the binder was the solid products of Examples 1-14, respectively. In Comparative Example 1, the binder used unmodified CMC (degree of substitution 0.8-0.9). The resulting negative electrode sheet had a single-sided density of 14-15 mg / cm², a thickness of 150-160 μm, and a cut sheet size of 5 x 5 cm.

[0090] The positive electrode sheet was prepared using conventional techniques. The positive electrode active material, conductive agent, and binder were mixed in a 97%:2%:1% ratio by mass to form a positive electrode slurry. The positive electrode active material was a nickel-cobalt-manganese ternary material (523 ratio: 50% nickel, 20% cobalt, 30% manganese), the conductive agent was conductive carbon Super-P, and the binder was PVDF (Solvay 5130).

[0091] The diaphragm adopts 7um base film + 3um ceramic on one side + 1um glue-coated diaphragm on both sides; the electrolyte adopts a conventional formula, 1mol / L LiPF6 lithium salt, solvent EC (ethylene carbonate): PC (propylene carbonate): DEC (diethyl carbonate) mass ratio is 3:1:3; the additive VC (vinylene carbonate) accounts for 0.3% of the electrolyte mass ratio, and PS (1,3-propane sultone) accounts for 0.1% of the electrolyte mass ratio.

[0092] Battery structure: According to the above material system, assemble a small soft-pack battery with tabs on both sides.

[0093] Performance Testing

[0094] The negative electrode was placed on an 8mm diameter cylinder and bent, and the fracture of the electrode coating was observed to evaluate the flexibility of the electrode.

[0095] The initial efficiency and charge-discharge cycle performance of the above-mentioned battery cells were tested in accordance with the national standard "GB / T31486-2015". The test results are shown in Table 2:

[0096] Table 2 Electrochemical performance test results

[0097] The test results in Table 1 show that in Examples 1-13 of the present invention, CMC with a degree of substitution of 0.8-0.9 was used for modification, and the measured b / (a+b) ratio was as high as 0.63. Example 14, using CMC with a degree of substitution of 0.3-0.4, achieved a measured b / (a+b) of 0.83. Figure 1 exemplifies the results of the flexibility test of the negative electrode plate of the battery in Example 7, showing no fracture. Figure 2 shows the negative electrode plate of the battery in Comparative Example 1, showing significant fracture during the flexibility test. The modified CMC provided in Examples 1-14 of the present invention has significant improvement in flexibility compared to the unmodified CMC in Comparative Example 1, and as the b / (a+b) ratio increases, the degree of improvement in the flexibility of the CMC increases. However, in Examples 3 and 8, the flexibility decreases as b / (a+b) increases. This is presumably because the R1 in the repeating unit B in Examples 3 and 8 are all aldehyde groups. As the aldehyde group concentration increases, hemiacetals are formed between the aldehyde groups, restricting molecular motion, thereby showing that the flexibility of the material is lower than when b / (a+b) is at an appropriate level. In addition, in addition to indirectly determining the value of b by measuring the aldehyde content using the hydroxylamine hydrochloride method, in other specific embodiments, other methods such as nuclear magnetic resonance and infrared spectroscopy can also be used for determination. For example, the ratio of b / (a+b) can be determined by measuring the main chain structure of the repeating unit B using nuclear magnetic resonance.

[0098] Secondly, it can be seen from the test results in Table 2 that, except for Example 3 and Example 8, the initial efficiency of the batteries in other examples is basically the same as that of Comparative Example 1; the initial efficiency of Example 3 and Example 8 is significantly lower than that of Comparative Example 1, which may be affected by the aldehyde groups on the modified CMC.

[0099] Finally, the capacity retention rates of the batteries of most examples in Table 2 after 1500 cycles are basically the same as those of Comparative Example 1, indicating that the adhesive strength of the binders provided in these examples has not decreased after modification; the battery capacity retention rates of Examples 2 and 14 are significantly better than those of Comparative Example 1, presumably because the binders provided in Examples 3 and 14 have more carboxyl groups or carboxyl groups, which are highly polar functional groups and provide stronger adhesive strength; while the battery capacity retention rates of Examples 3 and 8 are poorer than those of Comparative Example 1, presumably because they are affected by the aldehyde group.

[0100] When it is necessary to specify, cellulose derivatives can be used in secondary batteries not only as binders, dispersants and thickeners for battery negative electrodes, but also as binders, dispersants and thickeners for battery separator coating slurries, lithium iron phosphate positive electrode slurries, and carbon coating slurries for battery copper foil current collectors. The performance requirements for binders in these application scenarios are basically the same.

[0101] The above disclosure is merely one or more preferred embodiments of the present application and is not intended to limit the scope of the present application. A person skilled in the art will understand that all or part of the processes of the above embodiments and equivalent changes made in accordance with the claims of the present application are still within the scope of the present application.

Claims

1. A binder for a secondary battery, comprising a cellulose derivative, characterized in that: The cellulose derivative comprises a repeating unit A and a repeating unit B, wherein the repeating unit A is: The repeating unit B is, Wherein, in the repeating unit A and the repeating unit B, R is independently selected from one or more of -OH or its derivative groups; in the repeating unit B, R1 is independently selected from one or more of -CHO derived groups; when a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the relationship is satisfied:

2. The binder for secondary batteries according to claim 1, wherein: When a represents the molar amount of the repeating unit A, and b represents the molar amount of the repeating unit B, the relationship is satisfied:

3. The binder for secondary batteries according to claim 1, wherein: When a represents the molar amount of the repeating unit A, and b represents the molar amount of the repeating unit B, the relationship is satisfied:

4. The binder for secondary batteries according to claim 1, wherein: In the repeating unit B, R1 is independently selected from at least one of —OH, —COOH, —COONa and —COOLi.

5. The binder for secondary batteries according to claim 1, wherein: In the repeating unit B, R1 is independently selected from at least one of —COOH, —COONa and —COOLi.

6. The binder for secondary batteries according to claim 1, wherein: In the repeating unit A and the repeating unit B, R is independently selected from -OH, - At least one of OCH2COOH, -OCH2COONa and -OCH2COOLi.

7. A secondary battery negative electrode slurry composition, characterized in that: The invention comprises the binder for secondary battery according to any one of claims 1 to 6.

8. A secondary battery negative electrode, characterized in that: The invention provides an electrode composite material layer prepared by using the secondary battery negative electrode slurry composition according to claim 7.

9. A secondary battery, characterized in that: A secondary battery negative electrode according to 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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