Secondary battery binder, negative electrode slurry, electrode sheet, and secondary battery

Abstract

A secondary battery binder. The secondary battery binder comprises a component X and a component Y, wherein the component X is formed by mixing a raw material X1 and a raw material X2, and the component Y is obtained by subjecting a raw material Y1 and a raw material Y2 to a Schiff base reaction. The raw material X1, the raw material X2 and the raw material Y1 are all cellulose derivatives, which have been subjected to selective oxidation ring opening, and the raw material Y2 is an amine substance having at least two amino end groups. The secondary battery binder is tougher. When the secondary battery binder is used for preparing a battery slurry, a battery electrode sheet further prepared therefrom has a significantly lower warping degree during high-temperature baking, and a lower powder drop probability, and a higher electrode sheet surface density can be achieved, thereby improving the energy density of the battery.

Description

Secondary battery binder, negative electrode slurry, electrode sheet and secondary battery Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a secondary battery binder, a negative electrode slurry 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 activate the active materials for continued use, such as lithium-ion batteries and sodium-ion batteries. Drying the coated negative electrode sheets is a key challenge in the production of negative electrode sheets for secondary batteries. Drying can lead to warping, cracking, and powder loss. This phenomenon not only renders the sheet useless, increasing production costs and reducing efficiency, but also negatively impacts the battery's rate and cycle performance if these sheets are used in batteries.

[0003] At present, there are several ways to improve it: one is to add anti-cracking agents to the negative electrode slurry. Anti-cracking agents include polypropylene glycol, polyglycol aqueous solution and N-methylpyrrolidone (NMP). When these anti-cracking agents cannot fully volatilize, they will remain inside the electrode, causing certain losses to the initial effect and capacity of the battery, and NMP is toxic. Another way is to solve the problem by improving the coating and drying process. For example, the patent with publication number CN115394945A adopts different drying methods, time and temperature for single-sided coating and double-sided coating, and controls the drying degree of drying and blowing to make the electrode yield reach more than 95%; for example, the patent with publication number CN113991063A adopts a multiple coating method, by applying different slurry components multiple times, the raw materials of the first layer of slurry include 1.5wt% polyacrylonitrile, conductive agent and active substance, and the raw materials of the second layer of slurry include 0.5wt% polyacrylonitrile and 0.5wt% styrene-butadiene rubber, conductive agent and active substance. Although this method improves the cracking situation, it increases the process difficulty and reduces production efficiency.

[0004] Summary of the Invention

[0005] The object of the present invention is to provide a secondary battery adhesive that can solve the warping problem of the pole piece after drying, reduce the risk of pole piece cracking and powder loss, and does not introduce additional anti-cracking agents and does not increase the process difficulty.

[0006] The secondary battery binder provided by the present invention includes component X and component Y; component X is composed of a mixture of raw materials X1 and X2, and component Y is obtained by a Schiff base reaction of raw materials Y1 and Y2; raw materials X1, X2, and Y1 are all cellulose derivatives containing repeating units A and B.

[0007] The repeating unit A is:

[0008] The repeating unit B is:

[0009] In raw materials X1, X2 and Y1, when a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the following relationship is satisfied: R of repeating unit A and repeating unit B is independently selected from one or more of -OH or its derivative groups;

[0010] In the raw material X1, R1 of the repeating unit B is -CH2OH;

[0011] In the raw material X2, R1 of the repeating unit B is -COOH;

[0012] In the raw material Y1, R1 of the repeating unit B is -CHO;

[0013] The raw material Y2 is an amine substance containing at least two terminal amino groups.

[0014] In some preferred embodiments, the mass ratio of component X to component Y is 1-2:1-2.

[0015] In some further preferred embodiments, the mass ratio of component X to component Y is 1:1.

[0016] In some preferred embodiments, the mass ratio of raw material X1 to raw material X2 is 1-2:1-2.

[0017] In some further preferred embodiments, the mass ratio of raw material X1 to raw material X2 is 1:1.

[0018] In some preferred embodiments, the mass ratio of raw material Y1 to raw material Y2 is 25-100:1.

[0019] In some possible embodiments, the raw material Y2 is selected from at least one of the following substances:

[0020] Polyolefins having at least two terminal amino groups and their derivatives,

[0021] Polyacrylamide and its derivatives having at least two terminal amino groups,

[0022] Polysilane ethers having at least two terminal amino groups and derivatives thereof,

[0023] Polyols having at least two terminal amino groups and their derivatives.

[0024] In some preferred embodiments, the raw material Y2 includes both a linear amine substance Y2-1 and a branched amine substance Y2-2.

[0025] In some further preferred embodiments, the amine substance Y2-1 is polyethylene glycol diamine, and the amine substance Y2-2 is amino-terminated trimethylolpropane tripropylene glycol ether.

[0026] The present invention also provides a secondary battery negative electrode slurry composition, comprising the secondary battery binder.

[0027] The present invention also provides a secondary battery negative electrode having an electrode composite material layer made from the secondary battery negative electrode slurry composition.

[0028] The present invention also provides a secondary battery having the secondary battery negative electrode.

[0029] The secondary battery adhesive provided by the present invention has higher toughness, and the film made from it has a higher elongation at break; the battery slurry prepared by using the secondary battery adhesive provided by the present invention has significantly lower warpage when baked at high temperature, the probability of powder loss of the electrode is lower, and a higher electrode surface density can be achieved, thereby improving the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] FIG1 is a diagram showing the warpage test results of a negative electrode sheet using the secondary battery binder provided in Example 1 of the present invention.

[0032] FIG2 is a diagram showing the warpage test results of a negative electrode sheet using the secondary battery binder provided in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention pertains. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All references mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials to which they relate. In the event of a conflict with any incorporated reference, the present specification controls. As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended, meaning inclusive but not limited to. Numerical ranges herein are understood to specifically disclose each intervening value between the upper and lower limits of the range. Intervening values ​​within any stated value or range, as well as any smaller ranges between any other stated value or intervening value within the stated range, are also encompassed within the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded within the range. Experimental methods used herein are conventional methods unless otherwise noted. Materials, reagents, and the like used herein, unless otherwise noted, can be purchased or synthesized by known methods.

[0034] The present invention provides a secondary battery binder, which comprises a component X and a component Y; the component X is formed by mixing raw materials X1 and X2, and the component Y is obtained by reacting raw materials Y1 and Y2 through a Schiff base; the raw materials X1, X2, and Y1 are all cellulose derivatives containing repeating units A and B.

[0035] Repeating unit A is:

[0036] Repeating unit B is:

[0037] In raw materials X1, X2 and Y1, when a represents the molar amount of the repeating unit A and b represents the molar amount of the repeating unit B, the following relationship is satisfied: R of repeating unit A and repeating unit B is independently selected from one or more of -OH or its derivative groups;

[0038] In the raw material X1, R1 of the repeating unit B is -CH2OH;

[0039] In the raw material X2, R1 of the repeating unit B is -COOH;

[0040] In the raw material Y1, R1 of the repeating unit B is -CHO;

[0041] The raw material Y2 is an amine substance containing at least two terminal amino groups.

[0042] During the drying process, the negative electrode slurry evaporates, causing the coating to shrink and generate internal stress. This can cause the electrode to warp upward. When the warping reaches a certain level, the electrode coating is prone to cracking. Unlike existing solutions that address this problem by adding anti-cracking agents or adjusting the coating and drying processes, the technical solution provided by the present invention aims to address the warping problem by reducing the internal stress of the coating material itself at high temperatures. In the negative electrode slurry, the binder serves as a bridge connecting the various materials and, therefore, bridges the interaction between them. As an organic polymer, the greater the rigidity of the binder's molecular chain, the more likely it is to generate internal stress. Compared to common cellulose derivatives, such as CMC (sodium carboxymethyl cellulose), the cellulose derivative used in the binder provided by the present invention has partially opened up its steel ring structure, significantly improving the flexibility of the cellulose derivative's molecular chain and thus reducing the material's internal stress. The greater the binder's toughness, the higher the elongation at break of the film-formed material, reducing the likelihood of cracking when used as a binder in battery coatings. The stronger the binder's bonding strength, the less likely the electrode will shed powder. In the technical solution provided by the embodiment of the present invention, component Y obtains high toughness through Schiff base crosslinking; X1 and X2 in component X have a large number of hydroxyl groups or carboxyl groups, which are strong polar groups and can greatly improve the bonding strength of the adhesive.

[0043] In some specific embodiments, R on the repeating unit A and the repeating unit B can be independently represented by different groups. Those skilled in the art know that when not modified, 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.

[0044] In some specific embodiments, in raw materials X1, X2, and Y1, when a represents the molar amount of repeating unit A and b represents the molar amount of repeating unit B, the relationship between a and b can also be: or or In some preferred embodiments, the relationship between a and b also satisfies or or

[0045] In some specific embodiments, the raw material Y2 can be a polyolefin containing at least two terminal amino groups and its derivatives, such as polypropylene amine shown in formula (1) and polyethyleneimine with a branched structure shown in formula (2):

[0046] The raw material Y2 can be a polyacrylamide or its derivatives containing at least two terminal amino groups, such as the polyacrylamide shown in formula (3):

[0047] The raw material Y2 can be a silane ether containing at least two terminal amino groups and its derivatives, such as aminopropyl polydimethylsiloxane represented by formula (4):

[0048] Raw material Y2 can also be polyols containing at least two terminal amino groups and their derivatives, such as polyethylene glycol diamine shown in formula (5), polypropylene glycol, 2-aminopropyl end-capping structure shown in formula (6), and amino-terminated trimethylolpropane tripropylene glycol ether shown in formula (7):

[0049] In formula (1) and formula (3), n is a positive integer greater than or equal to 2; in formula (2), formula (4), formula (5), formula (6) and formula (7), n is a positive integer greater than or equal to 1.

[0050] In some specific embodiments, the mass ratio of component X to component Y is 1-2:1-2, specifically 1:2, 1:1.6, 1:1.5, 1:1.2, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, etc.

[0051] In some specific embodiments, the mass ratio of raw material X1 to raw material X2 is 1-2:1-2, specifically 1:2, 1:1.6, 1:1.5, 1:1.2, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, etc.

[0052] In some specific embodiments, the mass ratio of raw material Y1 to raw material Y2 is 25-100:1, specifically 25:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, etc.

[0053] 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.

[0054] Example 1

[0055] <Preparation of Secondary Battery Binder>

[0056] Prepare the reactants: Based on the molar number of anhydroglucose units of sodium carboxymethyl cellulose (CMC, degree of substitution 0.8-0.9), with a weight-average molecular weight of 180,000 Da, prepare a 0.1 mol / L CMC aqueous solution.

[0057] Dissolve NaIO4 in water in a dark environment to prepare a 0.1 mol / L NaIO4 aqueous solution.

[0058] Dissolve (CH2OH)2 in water to prepare a 0.1 mol / L (CH2OH)2 aqueous solution.

[0059] Dissolve NaBH4 in water at room temperature to prepare a 0.1 mol / L NaBH4 aqueous solution.

[0060] Dissolve NaClO2 in water at room temperature to prepare a 0.1 mol / L NaClO2 aqueous solution.

[0061] (1) Preparation of raw material Y1

[0062] The CMC aqueous solution was placed in a light-proof reaction vessel. The reaction temperature was adjusted to 30°C and maintained there. An equal volume of NaIO4 aqueous solution was slowly added dropwise to the reaction vessel (the molar ratio of the anhydroglucose units of CMC to NaIO4 was 1:1). The mechanical stirring speed was adjusted to 500 rpm. The pH of the reaction environment was adjusted to 6 using a 1 mol / L H2SO4 solution, and the timer was started. After 30 minutes of reaction, the reaction was terminated by adding an equal volume of (CH2OH)2 solution to the CMC aqueous solution. After completion of the reaction, the reaction mixture was slowly poured into a large amount of ice-cold methanol to precipitate. After filtration, the solid product, i.e., raw material Y1, was obtained by drying at room temperature.

[0063] b / a+b test: a represents the number of moles of repeating unit A, b represents the number of moles of repeating unit B, and the value of b / a+b is determined. After the first reactant is redispersed and dissolved, the hydroxylamine hydrochloride method is used to determine the aldehyde content in the solution. The measurement method is 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]. Analysis Laboratory, 2008, 27 (S1): 83-86. Since the relative molecular mass of the solid product after the reaction does not change compared to the repeating unit structure of the reactant CMC, b = the measured number of moles of aldehyde groups / 2. The raw material Y1 prepared in this embodiment was measured In other specific embodiments, the value of b / a+b can be changed by adjusting the material ratio of sodium periodate and CMC. The adjustment method can refer to patent application CN2023107423260 or patent application CN2023110336003.

[0064] (2) Preparation of component Y

[0065] Raw material Y1 was prepared into a 20 g / L aqueous solution, placed in a reaction vessel, and the reaction temperature was adjusted to 60°C. Raw material Y2 was slowly added to the reaction vessel, the mechanical stirring speed was adjusted to 500 rpm, and the reaction was carried out for 6 hours. After the reaction was completed, the mixed liquid after the reaction was added dropwise to a large amount of a mixed solution of anhydrous ethanol and methanol. After the product precipitated, the precipitate was filtered and the filter cake was collected. The washed filter cake was placed at a constant temperature of 60°C and dried for 12 hours to obtain a solid product, namely component Y.

[0066] In Example 1, the raw material Y2 is composed of a linear amine substance Y2-1 and a branched amine substance Y2-2. The amine substance Y2-1 is represented by formula (5), and the amine substance Y2-2 is represented by formula (7), and the two are composed in a mass ratio of 1:1. The mass ratio of raw material Y1 to raw material Y2 is controlled to be 50:1.

[0067] For other preparation methods of component Y, please refer to patent application CN2023110335903.

[0068] (3) Preparation of raw material X1

[0069] Prepare a 0.1 mol / L aqueous solution of raw material Y1 in a reaction vessel. Slowly add an equal volume of NaBH4 aqueous solution to the Y1 aqueous solution. Stir at 300 rpm and maintain the reaction temperature at approximately 5°C for 1 hour. After completion, slowly pour the resulting mixture into a large amount of ice-cold methanol to precipitate. Filter and dry at room temperature to obtain a solid product, namely, raw material X1.

[0070] (IV) Preparation of raw material X2

[0071] A 0.1 mol / L aqueous solution of raw material Y1 was prepared and placed in a reaction vessel. An equal volume of NaClO2 aqueous solution was slowly added. The stirring speed was controlled at 300 rpm and the reaction temperature was maintained at approximately 5°C. The reaction was allowed to proceed for 1 hour. After the reaction was complete, the reaction mixture was added dropwise to a large amount of anhydrous ethanol. A flocculent product was observed to precipitate. The precipitate was filtered and the filter cake was collected. The filter cake was washed alternately with deionized water and anhydrous ethanol and dried at 60°C for 12 hours to obtain a solid product, namely raw material X2.

[0072] (V) Preparation of component X

[0073] The raw materials X1 and X2 were mixed in a mass ratio of 1:1 to obtain component X.

[0074] (6) Preparation of secondary battery binder

[0075] Component X was dissolved in deionized water, and the preliminarily dissolved mixture was placed in a dispersing mixer for stirring and dispersion, with the temperature controlled at about 90° C., and stirred for 6 hours.

[0076] Component Y is dissolved in deionized water, dispersed, and then mixed with the solution of component X. The mixture is then stirred and dispersed in a dispersing mixer at a temperature of approximately 60°C for 2 hours to obtain a gel-like secondary battery binder. In Example 1, the mass ratio of component X to component Y is 1:1.

[0077] Example 2

[0078] The difference from Example 1 is that the mass ratio of component X to component Y is 1.5:1; and in component X, the mass ratio of raw material X1 to raw material X2 is 1:2.

[0079] Example 3

[0080] The difference from Example 1 is that the mass ratio of component X to component Y is 1.5:1; and in component X, the mass ratio of raw material X1 to raw material X2 is 2:1.

[0081] Example 4

[0082] The only difference from Example 1 is that the mass ratio of component X to component Y is 1.5:1.

[0083] Example 5

[0084] The only difference from Example 1 is that the mass ratio of component X to component Y is 1:2.

[0085] Example 6

[0086] The only difference from Example 1 is that in component Y, the mass ratio of raw material Y1 to raw material Y2 is 25:1.

[0087] Example 7

[0088] The only difference from Example 1 is that the mass ratio of component X to component Y is 2:1.

[0089] Example 8

[0090] The only difference from Example 1 is that in component Y, the mass ratio of raw material Y1 to raw material Y2 is 100:1.

[0091] Example 9

[0092] The only difference from Example 1 is that in component Y, all raw materials Y1 are linear amine substances Y2-1.

[0093] Example 10

[0094] The only difference from Example 1 is that in component Y, all raw materials Y1 are amine substances Y2-2 with branched structures.

[0095] Comparative Example 1

[0096] The binder of Comparative Example 1 is unmodified CMC with a degree of substitution of 0.8 to 0.9 and a weight-average molecular weight of 180,000 Da.

[0097] Comparative Example 2

[0098] The difference from Example 1 is that the secondary battery binder does not include component Y.

[0099] Comparative Example 3

[0100] The difference from Example 1 is that the secondary battery binder does not include component X.

[0101] Comparative Example 4

[0102] The difference from Example 1 is that component X consists only of raw material X1 and does not include raw material X2.

[0103] Comparative Example 5

[0104] The difference from Example 1 is that component X consists only of raw material X2 and does not include raw material X1.

[0105] The specific compositions of the secondary battery binders provided in Examples 1 to 10 and Comparative Examples 1 to 5 are shown in Table 1.

[0106] Table 1 Comparison table of relative proportions of components in Examples 1 to 10 and Comparative Examples 1 to 5

[0107] <Elongation at break test>

[0108] Preparation of adhesive film: Take the secondary battery adhesives of Examples 1-10 and Comparative Examples 1-5, prepare them into 1% solid content adhesive solution, put the adhesive solution into a Teflon mold and evaporate the water, and then completely remove the remaining water by drying under vacuum at 60°C for 12 hours to prepare an adhesive film.

[0109] Elongation at Break Test: Films prepared with the secondary adhesives of Examples 1-10 and Comparative Examples 1-5 were cut into dumbbell-shaped strips of equal size according to the national standard GB 13022-1991 and tested on a tensile testing machine. The deformation rate was 50 ± 5 mm / min. Three measurements were taken for each group, and the average was calculated. The test results are shown in Table 2.

[0110] <Electrode performance test>

[0111] Negative electrode slurry configuration: The negative electrode slurry is composed of an active material, a conductive agent, SBR (styrene-butadiene rubber), and a binder. The active material is artificial graphite, the conductive agent is conductive carbon black, and the binder is the secondary battery binder provided in Examples 1-10 and Comparative Examples 1-5 of the present invention. The mass percentages of graphite, conductive carbon black, SBR, and binder are: 96%: 1%: 1.5%: 1.5%.

[0112] (1) Pole warpage evaluation

[0113] Each of the above slurries was applied to the negative electrode current collector. After drying, the density of each electrode group was controlled to be 15 mg / cm². A 20mm x 20mm square area at the center of each electrode group was cut and baked in an oven at 80°C for 6 hours. After cooling, the area was transferred to a constant temperature heating table at 140°C. After the warpage height stabilized, the height difference between the four corners of the square electrode and the heating table was measured and the average value was obtained. Three measurements were taken for each electrode group, and the test results are shown in Table 2.

[0114] (2) Evaluation of electrode powder loss rate

[0115] Each of the above slurries was applied to the negative electrode current collector, and the density of each group of electrode sheets after drying was controlled to be 15 mg / cm2. The powder loss rate of each group of negative electrode sheets was tested. The electrode sheets were cut into 15mmx60mm specimens, weighed, and tested using a linear friction tester with the number of frictions set to 30. After the friction was completed, the powder on the surface was brushed off and the mass of the electrode sheet was weighed again. The powder loss rate = (pole sheet mass before friction - pole sheet mass after friction) / pole sheet mass before friction * 100%. Each group of electrode sheets was measured three times and the average value was taken. The test results are shown in Table 2.

[0116] (3) Evaluation of pole piece surface density

[0117] The flexibility of the adhesive material will affect the compaction density of the electrode. Improving the flexibility and adhesion of the material can increase the surface density of the electrode to a certain extent, thereby increasing the energy density of the battery.

[0118] The above-mentioned groups of slurries were applied on the negative electrode current collector, and the height of the electrode after rolling was controlled to be 160μm. A 20mm×20mm square area in the center of the electrode was cut out, and the mass of the electrode was weighed. A 20mm×20mm square area in the center of the copper foil not coated with the slurry was cut out, and the mass of the current collector was weighed. The surface density of the electrode = (mass of the electrode - mass of the current collector) / (2×2). Each group of electrode was measured three times and the average value was taken. The test results are shown in Table 2.

[0119] (IV) Battery energy density evaluation

[0120] Battery Preparation: The negative electrode was prepared using the same electrode as that used for the areal density evaluation. The positive electrode was prepared using conventional techniques, with the positive electrode active material, conductive agent, and binder mixed in a 97%:2%:1% (by mass) ratio 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). The separator consisted of a 7µm base film, a 3µm ceramic on one side, and a 1µm adhesive-coated separator on both sides. The electrolyte used a conventional formula: 1 mol / L LiPF6 lithium salt, and the solvents were EC (ethylene carbonate): PC (propylene carbonate): DEC (diethyl carbonate) in a 3:1:3 (by mass) ratio. The additives VC (vinylene carbonate) and PS (1,3-propane sultone) accounted for 0.3% and 0.1% of the electrolyte, respectively. The positive electrode sheet, the negative electrode sheet and the separator are wound into a battery cell, which is encapsulated with an aluminum-plastic film and a lithium-ion battery is manufactured according to a conventional soft-pack battery manufacturing process.

[0121] Energy density test: Each group of lithium-ion soft-pack batteries was charged at a constant current rate of 0.5C to a voltage of 4.35V. The batteries were then charged at a constant voltage rate of 4.35V to a current of 0.05C, reaching full charge. The batteries were then allowed to rest for 5 minutes and discharged at a constant current rate of 0.5C to a voltage of 2.8V. The batteries were allowed to rest for another 5 minutes. The capacity and voltage plateau of the lithium-ion battery during the 0.5C constant current discharge were recorded. Finally, the length, width, and thickness of the lithium-ion battery were measured. The energy density (Wh / L) of the lithium-ion battery is calculated as follows: (capacity of the lithium-ion battery during 0.5C constant current discharge × voltage plateau of the lithium-ion battery during 0.5C constant current discharge) / (length of the lithium-ion battery × width of the lithium-ion battery × thickness of the lithium-ion battery) * 100%. Three measurements were taken for each group of batteries, and the average value was obtained. The test results are shown in Table 2.

[0122] Table 2 Test results of adhesive application performance provided by Examples 1-10 and Comparative Examples 1-5

[0123] As can be seen from Table 2, the performance of each application test of Examples 1-10 and Comparative Examples 2-4 is better than that of Comparative Example 1 (normal CMC group).

[0124] According to the data of Comparative Example 2, it can be seen that the elongation at break of the adhesive film containing only component X but no component Y is lower than that of other groups (except Comparative Example 1), indicating that component Y has the effect of improving the elongation at break of the adhesive material.

[0125] According to the data of Comparative Example 3, it can be seen that the warpage height of the electrode is the highest except for Comparative Example 1 when only component Y is present without component X, indicating that the addition of component X is beneficial to reducing the warpage height of the electrode during high-temperature baking. Furthermore, according to the data of Comparative Examples 4 and 5, it can be seen that the coexistence of raw materials X1 and X2 in component X can significantly reduce the warpage height of the electrode during high-temperature baking. It is speculated that the reason is that the hydroxyl groups of raw material X1 and the carboxyl groups of raw material X2 can form partial ester groups during stirring, reducing intramolecular and intermolecular hydrogen bonds. In addition, the ester groups are relatively softer, further improving the flexibility of the material, reducing the stress of the material, and reducing the warpage height of the electrode.

[0126] Comparing the data from Examples 1, 6, and 8 reveals that the optimal mass ratio of raw materials Y1 to Y2 is 50:1. At this ratio, the adhesive film achieves the highest elongation at break and minimizes powder shedding, resulting in a higher electrode surface density and, consequently, a higher battery energy density. This is presumably because excessive amounts of raw material Y2 can lead to excessive crosslinking of component Y, which in turn reduces material toughness. However, insufficient amounts of raw material Y2 can lead to insufficient crosslinking of component Y, resulting in insufficient improvement in material toughness.

[0127] Comparing the data from Examples 1, 9, and 10, it can be seen that the coexistence of raw materials Y2-1 and Y2-2 significantly improves the elongation at break of the adhesive film. This is presumably because the coexistence of linear and branched amines allows the formation of more complex and diverse cross-linking structures between the molecules of raw material Y1, increasing the number of intermolecular entanglements and thereby improving the material's elongation at break.

[0128] Comprehensive comparison shows that the application test performance of Example 1 is better than that of the above examples and comparative examples.

[0129] 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 secondary battery binder, characterized in that: The secondary battery binder comprises component X and component Y; component X is composed of a mixture of raw materials X1 and raw materials X2, and component Y is obtained by a Schiff base reaction of raw materials Y1 and raw materials Y2; raw materials X1, raw materials X2 and raw materials Y1 are all cellulose derivatives containing repeating units A and repeating units B at the same time, The repeating unit A is: The repeating unit B is: In raw materials X1, X2 and Y1, 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: R of repeating unit A and repeating unit B is independently selected from one or more of -OH or its derivative groups; In the raw material X1, R1 of the repeating unit B is -CH2OH; In the raw material X2, R1 of the repeating unit B is -COOH; In the raw material Y1, R1 of the repeating unit B is -CHO; The raw material Y2 is an amine substance containing at least two terminal amino groups.

2. The secondary battery binder according to claim 1, characterized in that: The mass ratio of component X to component Y is 1-2:1-2.

3. The secondary battery binder according to claim 2, characterized in that: In component X, the mass ratio of raw material X1 to raw material X2 is 1-2:1-2.

4. The secondary battery binder according to claim 2, characterized in that: In component Y, the mass ratio of raw material Y1 to raw material Y2 is 25 to 100:

1.

5. The secondary battery binder according to claim 1, characterized in that: The raw material Y2 is selected from at least one of the following substances: Polyolefins having at least two terminal amino groups and their derivatives, Polyacrylamide and its derivatives having at least two terminal amino groups, Polysilane ethers having at least two terminal amino groups and derivatives thereof, Polyols having at least two terminal amino groups and their derivatives.

6. The secondary battery binder according to claim 5, characterized in that: The raw material Y2 includes both the linear amine substance Y2-1 and the branched amine substance Y2-2.

7. The secondary battery binder according to claim 6, characterized in that: The amine substance Y2-1 is polyethylene glycol diamine, and the amine substance Y2-2 is amino-terminated trimethylolpropane tripropylene glycol ether.

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

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

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

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