An adhesive, a positive electrode, and a battery

Abstract

This invention provides an adhesive, a positive electrode, and a battery. The polyimide comprises a first structural unit derived from an amine monomer, a second structural unit derived from a first acid anhydride monomer and a functional compound, and a third structural unit derived from a second acid anhydride monomer. The second structural unit contains zwitterionic groups; the zwitterionic groups include positively charged quaternary ammonium groups and negatively charged anionic groups, the anionic groups including at least one of sulfonate groups and carboxylate groups. The first acid anhydride monomer contains tertiary amine groups, and at least a portion of the tertiary amine groups are grafted with functional compounds to generate the second structural unit containing zwitterionic groups. The adhesive provided by this invention introduces zwitterionic groups into the polyimide, thereby giving the adhesive hydrophilicity and ion exchange capacity, improving the interfacial stability between the electrode and the electrolyte, promoting lithium-ion transport, and enhancing the adhesive strength and ion conductivity of the adhesive through electrostatic interactions.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an adhesive, a positive electrode sheet, and a battery. Background Technology

[0002] Batteries are a vital energy source for human production and daily life. With increasing awareness of environmental protection and the energy crisis, coupled with the rapid development of mobile electronic devices and electric vehicles, the demand for energy storage devices is growing daily. The rapid development of various energy storage technologies, such as lithium-ion batteries, flow batteries, and sodium-ion batteries, has enabled batteries to play an increasingly important role in energy fields such as 3C energy storage components, power batteries, and energy storage batteries.

[0003] Electrodes are the most important component of a battery. Although the binder is used in small quantities, it plays a significant role as part of the electrode. It acts as a bond between the active material particles of the electrode and between the material and the current collector, maintaining the stability of the electrode during battery use and having a decisive impact on the battery's performance and safety.

[0004] Lithium iron phosphate cathode slurries typically use polyvinylidene fluoride (PVDF) as a binder. However, the organic solvent NMP (methylpyrrolidone) is expensive, environmentally unfriendly, and poses significant health risks. Water-based binders are environmentally friendly and inexpensive, making their replacement of PVDF a growing trend. However, water-based binders suffer from insufficient adhesion and interfacial compatibility in cathode materials. During charge and discharge, the binder detaches as the electrode expands and contracts, leading to decreased cycle performance.

[0005] Therefore, there is an urgent need for a new type of adhesive that can improve the bonding strength and interfacial compatibility of adhesives. Summary of the Invention

[0006] This invention addresses the shortcomings of existing adhesives in terms of adhesion strength and interfacial compatibility by providing an adhesive, a positive electrode sheet, and a battery.

[0007] To address the aforementioned technical problems, the present invention provides an adhesive comprising a polyimide, wherein the polyimide comprises a first structural unit derived from an amine monomer, a second structural unit derived from a first acid anhydride monomer and a functional compound, and a third structural unit derived from a second acid anhydride monomer; the second structural unit contains a zwitterionic group; the zwitterionic group comprises a positively charged quaternary ammonium group and a negatively charged anionic group, the anionic group comprising at least one of a sulfonate group and a carboxylate group; the first acid anhydride monomer contains a tertiary amine group, and at least a portion of the tertiary amine group is grafted with the functional compound to generate a second structural unit containing a zwitterionic group.

[0008] Preferably, the molar ratio of the quaternary ammonium group to the first structural unit is 8-18:10.

[0009] Preferably, the molar ratio of the second structural unit to the third structural unit is 4-9:6-1.

[0010] Preferably, the amount of substance of the first structural unit is n1, and the sum of the amounts of substance of the second structural unit and the third structural unit is n2, where n1:n2 = 1:0.95-1.05.

[0011] Preferably, the polyimide has a weight-average molecular weight of 50,000-300,000 g / mol.

[0012] Preferably, the functional compound includes at least one selected from chloroacetic acid, bromoacetic acid, 1,3-propanesulfonate lactone, and 1,4-butanesulfonate lactone.

[0013] Preferably, the first anhydride monomer comprises at least one of ethylenediaminetetraacetic acid dianhydride, N,N-bis(3,4-dicarboxyphenyl)aniline dianhydride, and N,N-bis(3,4-dicarboxyphenyl)-p-tert-butylaniline dianhydride;

[0014] Preferably, the amine monomer comprises at least one of the following C2-C18 alkane diamines, isophorone diamine, cyclohexanediamine, norbornene diamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, diaminodiphenylmethane, diaminodiphenyl ether, bisphenol A type diether diamine, diaminodiphenyl sulfone, diaminobiphenyl, diaminobenzophenone, lysine, and diaminobenzoic acid.

[0015] And / or, the second anhydride monomer comprises at least one of pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(4,4'-isopropyldienediphenoxy)diphthalic anhydride, butanetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, p-phenyl bis(trimethoxy) dianhydride, and trimellitic anhydride.

[0016] Secondly, this application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, wherein the positive active material layer includes the binder as described above.

[0017] Thirdly, this application provides a battery including the positive electrode plate as described above.

[0018] In this application, zwitterionic groups are introduced into the polyimide, forming a zwitterionic polymer. This imbues the binder with hydrophilicity and ion exchange capacity, improving the interfacial stability between the electrode and the electrolyte and promoting lithium-ion transport. It also exhibits water solubility and enhances the binder's adhesion and ion conductivity through electrostatic interactions. Furthermore, the polyimide segments in the binder have a stable structure and are not easily swollen by the electrolyte, improving the binder's stability in the electrolyte. Simultaneously, the polyimide segments form a dense structure through hydrogen bonding or π-π stacking, improving the adhesion to active materials and conductive agents, enhancing the bending and impact resistance of the positive electrode, and reducing active material shedding due to volume expansion during cycling. Additionally, the polyimide segments give the binder high thermal stability, reducing the risk of thermal runaway of the positive electrode. Detailed Implementation

[0019] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] One embodiment of this application provides an adhesive comprising a polyimide, the polyimide comprising a first structural unit derived from an amine monomer, a second structural unit derived from a first acid anhydride monomer and a functional compound, and a third structural unit derived from a second acid anhydride monomer; the second structural unit contains a zwitterionic group; the zwitterionic group comprises a positively charged quaternary ammonium group and a negatively charged anionic group, the anionic group comprising at least one of a sulfonate group and a carboxylate group; the first acid anhydride monomer contains a tertiary amine group, and at least a portion of the tertiary amine group is grafted with the functional compound to generate the second structural unit containing the zwitterionic group.

[0021] In this embodiment, zwitterionic groups are introduced into the polyimide, causing the polyimide to form a zwitterionic polymer. This gives the binder hydrophilicity and ion exchange capacity, improves the interfacial stability between the electrode and the electrolyte, and promotes lithium-ion transport. It is also water-soluble and can enhance the adhesive strength and ion conductivity of the binder through electrostatic interaction. Furthermore, the polyimide chain structure in the binder is stable and not easily swollen by the electrolyte, which improves the stability of the binder in the electrolyte.

[0022] The anionic and cationic groups of the zwitterionic group achieve dynamic coordination with lithium ions, which accelerates the migration of lithium ions in the electrolyte, improves the ionic conductivity of the positive electrode, reduces impedance, and improves the cycle stability and overcharge safety of the battery.

[0023] The polyimide segments in the binder have a stable structure and are not easily swollen by the electrolyte, thus improving the binder's stability in the electrolyte. Simultaneously, the polyimide segments form a dense cross-linked structure through hydrogen bonding or π-π stacking, enhancing the adhesion to active materials and conductive agents, improving the bending and impact resistance of the positive electrode, and reducing active material shedding due to volume expansion during cycling. Furthermore, the polyimide segments give the binder high thermal stability, reducing the risk of thermal runaway in the positive electrode.

[0024] In some embodiments, the molar ratio of the quaternary ammonium group to the amine monomer is 8-18:10.

[0025] By limiting the content of quaternary ammonium groups in polyimide, the water solubility and ion exchange capacity of polyimide can be controlled, thereby improving the ionic conductivity of the binder. Specifically, the molar ratio of zwitterionic groups to amine monomers includes, but is not limited to, 8:10, 9:10, 10:10, 11:10, 12:10, 13:10, 14:10, 15:10, 16:10, 17:10, or 18:10.

[0026] In some embodiments, the molar ratio of the second structural unit to the third structural unit is 4-9:6-1. The second structural unit contains a flexible chain to improve the flexibility of the polyimide segments, while the third structural unit increases its structural strength by introducing more benzene rings into the polyimide segments. The second structural unit, containing a flexible chain, improves the flexibility of the polyimide segments and is water-soluble after zwitterionicization. The third structural unit increases its structural strength by introducing more benzene rings into the polyimide segments. By adjusting the molar ratio of the second and third structural units, water solubility, flexibility, and strength can be balanced.

[0027] Specifically, the ratio of the amount of substance of the second structural unit to the third structural unit includes, but is not limited to, 4:6, 5:5, 6:4, 7:3, 8:2 or 9:1.

[0028] In some embodiments, the amount of the first structural unit is n1, and the sum of the amounts of the second and third structural units is n2, where n1:n2 = 1:0.95-1.05. By limiting the ratio of the sum of the amounts of the second and third structural units to the amount of the first structural unit to be within the above range, the polyimide has a high molecular weight, meeting the adhesive's requirements for mechanical strength and heat resistance.

[0029] Specifically, n1:n2 includes, but is not limited to, 1:0.95, 1:0.97, 1:0.99, 1:1.01, 1:1.03, or 1:1.05.

[0030] In some embodiments, the polyimide has a weight-average molecular weight of 50,000-300,000 g / mol.

[0031] Specifically, the weight-average molecular weight of polyimide includes, but is not limited to, 50,000 g / mol, 100,000 g / mol, 150,000 g / mol, 200,000 g / mol, 250,000 g / mol, or 300,000 g / mol.

[0032] In some embodiments, the functional compound includes at least one selected from chloroacetic acid, bromoacetic acid, 1,3-propanesulfonate lactone, and 1,4-butanesulfonate lactone. The above functional compound undergoes a nucleophilic reaction with the tertiary amine group of the first anhydride monomer to form a positively charged quaternary ammonium group and a negatively charged carboxylic acid or sulfonic acid group, causing the polyimide to form a zwitterionic polymer, enhancing the hydrophilicity of the modified binder, and enabling the modified binder to be used in aqueous slurries.

[0033] In some embodiments, the first anhydride monomer comprises at least one selected from ethylenediaminetetraacetic acid dianhydride, N,N-bis(3,4-dicarboxyphenyl)aniline dianhydride, and N,N-bis(3,4-dicarboxyphenyl)-p-tert-butylaniline dianhydride. By selecting the aforementioned first anhydride monomer, it is convenient to introduce tertiary amine groups into the polyimide chain segment, thereby facilitating the grafting reaction between the functional compound and the polyimide to form a polyimide possessing both positive and negative charges.

[0034] In some embodiments, the amine monomer includes at least one of the following C2-C18 alkane diamines: isophorone diamine, cyclohexanediamine, norbornene diamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, diaminodiphenylmethane, diaminodiphenyl ether, bisphenol A type diether diamine, diaminodiphenyl sulfone, diaminobiphenyl, diaminobenzophenone, lysine, and diaminobenzoic acid. By selecting the above-mentioned amine monomers, the polyimide segments exhibit better structural stability, reducing the swelling of the binder in the electrolyte.

[0035] In some embodiments, the second anhydride monomer comprises at least one selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(4,4'-isopropyldienediphenoxy)phthalic anhydride, butanetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, p-phenyl bis(trimethoxy) dianhydride, and trimellitic anhydride. By selecting the above-mentioned second anhydride monomer, the polyimide segments exhibit better structural stability, reducing the swelling of the binder in the electrolyte.

[0036] Furthermore, one embodiment of this application provides a method for preparing an adhesive, comprising the following steps:

[0037] Under an argon atmosphere, amine monomers and solvents are added to a reactor, followed by the addition of first and second acid anhydride monomers in batches. The reaction is carried out at 0-60℃ for 1-6 hours to obtain a viscous polymer. Then, the temperature is raised to 120-200℃ for imidization reaction for 1-6 hours. Cyclohexane is then added and the temperature is raised to 150-200℃. The mixture is then refluxed to remove water for 1-6 hours to obtain a polyimide solution.

[0038] A functional compound was added to the above polyimide solution, and a grafting reaction was carried out at 20-100°C for 1-6 hours to obtain polyimide. After the reaction was completed, the above polyimide solution was precipitated in a precipitant and dried in a vacuum drying oven to obtain solid polyimide.

[0039] The solvent includes one of N,N-dimethylformamide, N-methylpyrrolidone, and dimethylacetamide.

[0040] Precipitating agents include toluene.

[0041] The solid content of the polyimide adhesive is 5%-40%.

[0042] As those skilled in the art will know, the reactions in the above steps are conventional methods for the synthesis of polyimide, and the specific methods and reaction conditions are commonly used in the prior art, and will not be described in detail in this invention.

[0043] In this invention, each of the aforementioned structural units represents the structural portion of the corresponding monomer present in the resulting polymer after the monomer participates in the polymerization reaction. The molar ratio of the first, second, and third structural units is based on the mass content of the corresponding monomer in the total amount of monomers participating in the polymerization.

[0044] One embodiment of this application also provides a positive electrode slurry, including the binder as described in any of the preceding claims.

[0045] Specifically, the cathode slurry using the above-mentioned binder can be either an aqueous slurry or an oil-based slurry.

[0046] In one embodiment, the positive electrode slurry comprises water and solids, and the solids, by mass percentage, comprise the following components: 90%-95% lithium iron phosphate, 0.1%-0.5% dispersant (polyvinylpyrrolidone), 1%-5% conductive agent (SP+CNT), and 1%-3% binder.

[0047] An embodiment of this application also provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer being formed from the positive electrode slurry as described above.

[0048] One embodiment of this application also provides a battery, including the positive electrode as described above.

[0049] The present invention will be further illustrated by the following examples.

[0050] Specifically, the binder, positive electrode slurry, positive electrode sheet, and battery disclosed in this invention are described.

[0051] Example 1

[0052] 1. Adhesive

[0053] Under argon protection, the reactor was kept in an ice bath. 1.0 mol of diaminodiphenyl ether (amine monomer) was added to the reactor. 0.6 mol of ethylenediaminetetracarboxylic dianhydride (the first anhydride monomer, each monomer having two tertiary amine groups) and 0.4 mol of butanetetracarboxylic dianhydride (the second anhydride monomer) were added in three batches. The reaction was continued for 5 hours. Cyclohexane was then added and the temperature was raised to 180°C. The mixture was refluxed to remove water for 6 hours to obtain a polyimide solution.

[0054] 1.2 mol of 1,3-propanesulfonate lactone (functional compound) was added to the above polyimide solution, and the mixture was stirred at 80°C for 4 h to carry out the reaction, thereby obtaining polyimide with zwitterionic groups. After the reaction was completed, the above polyimide solution with zwitterionic groups was precipitated in toluene as a precipitant, and then dried in a vacuum drying oven at 80°C for 12 h to obtain solid polyimide with zwitterionic groups.

[0055] The molar ratio of zwitterionic groups to diaminodiphenyl ether is 1.2:1.

[0056] 2. Positive electrode slurry

[0057] The binder was mixed with lithium iron phosphate, dispersant (polyvinylpyrrolidone), and conductive agent (Super P+CNT) in a mass ratio of 3:94:0.5:2:0.5, and then added to water to obtain an aqueous positive electrode slurry.

[0058] 3. Positive electrode plate

[0059] The positive electrode slurry is coated onto carbon-coated aluminum foil, dried, rolled, and cut into electrode sheets.

[0060] 4. Negative electrode plate

[0061] CMC, SBR, graphite, and CNT are mixed in a mass ratio of 0.6:1.4:97.9:0.1 to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil, dried, rolled, and cut into electrode sheets.

[0062] 5. Battery

[0063] After assembling the positive electrode, negative electrode, and separator into a dry cell, a lithium battery is obtained by electrolyte injection. The electrolyte is 1M LiPF6, ethylene carbonate EC, ethyl methyl carbonate EMC, and diethyl carbonate DEC in a volume ratio of 3:5:2.

[0064] Example 2

[0065] Example 2 is similar to Example 1 in most steps, except that 0.8 mol of 1,3-propanesulfonate lactone is added and the molar ratio of quaternary ammonium group to diaminodiphenyl ether is 0.8:1.

[0066] Example 3

[0067] Most of the steps in Example 3 are the same as those in Example 1, except that 0.6 mol of 1,3-propanesulfonate lactone is added, and the molar ratio of quaternary ammonium group to diaminodiphenyl ether is 0.6:1.

[0068] Example 4

[0069] Example 4 is similar to Example 1 in most steps, except that the amount of the first anhydride monomer ethylenediaminetetracarboxylic dianhydride added is 0.9 mol, the amount of the second anhydride monomer added is 0.1 mol, 1.8 mol of 1,3-propanesulfonate lactone is added, and the molar ratio of quaternary ammonium group to diaminodiphenyl ether is 1.8:1.

[0070] Example 5

[0071] Most of the steps in Example 5 are the same as those in Example 1, except that the functional compound is chloroacetic acid.

[0072] Example 6

[0073] Most of the steps in Example 6 are the same as those in Example 1, except that the functional compound is 1,4-butanesulfonate lactone.

[0074] Example 7

[0075] Example 7 is similar to Example 1 in most steps, except that the amine monomer is p-phenylenediamine, the first acid anhydride monomer is N,N-bis(3,4-dicarboxyphenyl)aniline dianhydride, and the second acid anhydride monomer is pyromellitic dianhydride.

[0076] Example 8

[0077] Example 8 is similar to Example 1 in most steps, except that the amine monomer is cyclohexanediamine, the first anhydride monomer is N,N-(3,4-dicarboxyphenyl)-p-tert-butylaniline dianhydride, and the second anhydride monomer is 4,4'-(4,4'-isopropyldienediphenoxy)diphthalic anhydride.

[0078] Example 9

[0079] Example 9 is similar to Example 1 in most steps, except that the amino monomer is diaminodiphenyl ether and the second anhydride monomer is 3,3',4,4'-diphenylsulfone tetracarboxylic anhydride.

[0080] Example 10

[0081] Example 10 is similar to Example 1 in most steps, except that the amino monomer is lysine and the second anhydride monomer is p-phenyl di(triphenyl ester) dianhydride.

[0082] Example 11

[0083] Example 11 is similar to Example 1 in most steps, except that 0.4 mol of ethylenediaminetetracarboxylic dianhydride (first anhydride monomer), 0.6 mol of butanetetracarboxylic dianhydride (second anhydride monomer) and 0.8 mol of 1,3-propanesulfonate lactone (functional compound) are added in batches.

[0084] Example 12

[0085] Example 12 is similar to Example 1 in most steps, except that 0.2 mol of ethylenediaminetetracarboxylic dianhydride (first anhydride monomer), 0.8 mol of butanetetracarboxylic dianhydride (second anhydride monomer) and 0.4 mol of 1,3-propanesulfonate lactone (functional compound) are added in batches.

[0086] Comparative Example 1

[0087] Comparative Example 1 and Example 1 follow most of the same steps, except that 1 mol of ethylenediaminetetracarboxylic dianhydride (the first anhydride monomer) is added in batches, and butanetetracarboxylic dianhydride (the second anhydride monomer) and 2.0 mol of 1,3-propanesulfonate lactone (the functional compound) are not added.

[0088] Comparative Example 2

[0089] Comparative Example 2 and Example 1 follow most of the same steps, except that no functional compound was added.

[0090] Comparative Example 3

[0091] Comparative Example 3 and Example 1 follow most of the same steps, except that the binder in the positive electrode slurry is polyacrylic acid.

[0092] Comparative Example 4

[0093] Comparative Example 4 and Example 1 follow most of the same steps, except that the binder in the positive electrode slurry is PVDF and NMP is used as the solvent.

[0094] Performance testing:

[0095] The binder, positive electrode slurry, positive electrode sheet, and battery prepared in the above embodiments and comparative examples were tested as follows.

[0096] 1. Steel needle winding flexibility test

[0097] The positive electrode sheets prepared in the above embodiments and comparative examples were tested for flexibility according to the method of GB / T 1731-2020. The minimum diameter of the coiled needle at which the electrode sheet cracked was recorded. The smaller the minimum diameter of the coiled needle, the better the flexibility of the electrode sheet.

[0098] 2. Adhesion test of positive electrode sheet

[0099] The bonding strength of the positive electrode was tested using a GBH-1 tensile testing machine with a 180° tape peel method. The test specimen size was 20mm×100mm, and the tensile rate was 50mm / min. The specific test method referred to GB / T2792-2014 Test Method for Peel Strength of Adhesive Tape.

[0100] 3. Electrochemical performance testing: The electrochemical performance of the prepared lithium-ion batteries was tested using the Blue Battery Testing System. The specific methods are as follows:

[0101] Internal resistance:

[0102] Charge to 3.4V using 0.03C for 240 minutes; charge to 3.75V using 0.1C for 420 minutes; charge to 4.2V using 0.5C with a cutoff current of 0.02C; discharge to 3.0V using 0.5C and record the discharge capacity; charge to 50% SOC using 0.5C and test the internal resistance.

[0103] (B) Initial efficiency:

[0104] Charging: Charge at a constant current of 0.5C to 4.2V, maintain constant voltage at 4.2V, cut off current at 0.05C, and record the charging capacity;

[0105] Discharge: Discharge at a constant current of 0.5C to 3V and record the discharge capacity.

[0106] Calculate the initial efficiency = (discharge capacity / charge capacity) × 100%;

[0107] Capacity retention rate:

[0108] The capacity of the pouch battery was tested at a temperature of 25℃±2℃ and recorded as the capacity before storage. The pouch battery was discharged at a constant current of 0.5C to a voltage of 2.7V. Then it was charged at a constant current of 1C to a voltage of 4.3V, and then charged at a constant voltage until the cutoff current was 0.05C. After charging was completed, it was discharged at a constant current of 1C to 2.75V.

[0109] Record the discharge capacity C1 for the first cycle; repeat this process until the 500th cycle, and record the discharge capacity C500 for the 500th cycle.

[0110] Cyclic capacity retention rate = (C500 / C1) × 100%.

[0111] The battery's cycle capacity retention at 45°C was tested using the same test method as in (C).

[0112] 4. Ionic conductivity test of adhesive:

[0113] Stainless steel sheet (SS) / film / stainless steel sheet (SS) blocked cells were assembled in an Ar atmosphere glove box. After the cells were allowed to stand for 12 hours, a 10mV perturbation voltage was applied to them using a Chenhua CHI660E electrochemical workstation with a frequency range of 1Hz-1MHz. The intercept of the measured AC impedance spectrum curve with the X-axis is the bulk resistance R. b The ionic conductivity at each temperature is calculated using the following formula:

[0114] Ionic conductivity = L / (R) b A)

[0115] The unit of ionic conductivity is S cm. -1 L represents the thickness of the sample electrolyte membrane, in cm; A represents the effective contact area between the stainless steel sheet and the sample electrolyte membrane, in cm². 2 .

[0116] Fill in the specific test results in Table 1.

[0117] Table 1

[0118]

[0119] Note: Examples 3 and 12, and Comparative Example 2, have poor water solubility and cannot meet the requirements for preparing aqueous lithium iron phosphate slurry samples.

[0120] As can be seen from the test results of the examples and comparative examples in Table 1, the binder in this application has good bonding performance, the prepared electrode has good flexibility, and the battery made with the binder in this application has excellent ionic conductivity, low impedance, and excellent cycle stability.

[0121] The test results from Examples 1-4, Example 11, Example 12, Comparative Example 1, and Comparative Example 2 show that if the polyimide does not contain zwitterionic groups, or the content of zwitterionic groups is low (i.e., the molar ratio of quaternary ammonium groups to the first structural unit is less than 8:10 or the molar ratio of the second structural unit to the third structural unit is less than 4:6), the binder has poor water solubility and cannot meet the requirements for the preparation of aqueous cathode slurry. When the molar ratio of quaternary ammonium groups to the first structural unit is higher than 18:10 or the binder does not contain the third structural unit, the peel strength decreases, and the cycle stability of the battery decreases.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A binder, characterized by The polyimide comprises a first structural unit from an amine-based monomer, a second structural unit from a first acid anhydride monomer and a functional compound, and a third structural unit from a second acid anhydride monomer; the second structural unit contains a zwitterionic group; the zwitterionic group comprises a quaternary ammonium group with a positive charge and an anionic group with a negative charge, the anionic group comprises at least one of a sulfonate group, a carboxylate group; the first acid anhydride monomer contains a tertiary amine group, and at least part of the tertiary amine groups are grafted with the functional compound to form the second structural unit with the zwitterionic group; The molar ratio of the quaternary ammonium group to the first structural unit is 8-18:10; The molar ratio of the second structural unit to the third structural unit is 4-9:6-1; The first acid anhydride monomer comprises at least one of ethylenediaminetetraacetic dianhydride, N,N-bis(3,4-dicarboxyphenyl)aniline dianhydride, and N,N-(3,4-dicarboxyphenyl)-p-tert-butylaniline dianhydride; The amine-based monomer comprises at least one of C2-C18 alkane diamine, isophorone diamine, cyclohexane diamine, norbornane diamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, diaminodiphenylmethane, diaminodiphenyl ether, bisphenol A type diether diamine, diaminodiphenyl sulfone, diaminobiphenyl, diaminobenzophenone, lysine, and diaminobenzoic acid; The second acid anhydride monomer comprises at least one of pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-diphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(4,4'-isopropyl diene diphenyloxy) di-phthalic anhydride, butane tetra-carboxylic dianhydride, 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride, p-phenyl bis (trimellitate) dianhydride, and trimellitic anhydride; The functional compound comprises at least one of chloroacetic acid, bromoacetic acid, 1,3-propane sulfonic acid lactone, and 1,4-butane sulfonic acid lactone.

2. The binder of claim 1, wherein, The molar amount of the first structural unit is n1, and the sum of the molar amounts of the second structural unit and the third structural unit is n2, n1:n2=1:0.95-1.

05.

3. The binder of claim 2, wherein, The weight average molecular weight of the polyimide is 50000-300000 g / mol.

4. A positive electrode sheet characterized by comprising: The positive electrode active material layer comprises the binder as claimed in any one of claims 1-3.

5. A battery, characterized by The positive electrode sheet comprises the positive electrode sheet as claimed in claim 4.

Images