Insulating glue, positive electrode sheet and secondary battery

Abstract

In order to overcome the problem in the prior art that the insulating glue at the edge of the pole piece is easy to interpenetrate with the positive electrode slurry, and the insulating glue has poor electrolyte resistance, the present invention provides an insulating glue, a positive pole piece and a secondary battery; the insulating glue includes a polyimide binder, and the polyimide binder is formed by dehydration after polymerization of a first amino monomer containing a side group, a second amino monomer and a carboxylic anhydride monomer, and the side group in the first amino monomer containing a side group is selected from an electron-withdrawing functional group and / or an electron-donating functional group; the first amino monomer containing a side group and the second amino monomer are both diamine monomers, and the first amino monomer containing a side group contains an aromatic group. The insulating glue provided by the present application uses a polyimide binder to avoid interpenetration with PVDF in the positive electrode slurry, and at the same time, the first amino monomer and the second amino monomer work together to make the insulating layer formed by the insulating glue have good electrolyte resistance and easy ductility.

Description

Technical Field

[0001] The invention belongs to the technical field of secondary batteries, and in particular relates to an insulating adhesive, a positive electrode sheet and a secondary battery. Background Art

[0002] Secondary batteries are widely used in various portable electronic devices, electric vehicles, energy storage systems, etc. due to their high energy density, long cycle life and environmental protection characteristics. In order to prevent the negative electrode from contacting the positive electrode and to avoid the positive and negative electrodes from short-circuiting due to defects such as striping burrs puncturing the diaphragm during the electrode cutting process, insulating glue is often applied to the edge of the electrode to increase the safety performance of the battery when preparing power lithium batteries.

[0003] In the prior art, polyvinylidene fluoride (PVDF) and inorganic fillers (such as boehmite, alumina, etc.) are slurried and then coated. However, PVDF is prone to produce fluorine-containing toxic gases during the cutting process. In addition, during the slurry coating process, the insulating slurry and the positive electrode slurry are prone to mutual penetration, resulting in coating abnormalities; in addition, as the electrode is immersed in the electrolyte for a longer time, the insulating coating prepared by PVDF will gradually fall off, and the long-term safety barrier properties cannot be achieved.

[0004] Therefore, how to reduce the interpenetration between the insulating glue and the positive electrode slurry at the edge of the electrode and improve the electrolyte resistance of the insulating glue is still a problem to be solved urgently. Summary of the invention

[0005] In order to solve the problem that the insulating glue at the edge of the electrode piece is easy to interpenetrate with the positive electrode slurry and the insulating glue has poor electrolyte resistance, the present invention provides an insulating glue, a positive electrode piece and a secondary battery.

[0006] In order to solve the above technical problems, on the one hand, the present invention provides an insulating adhesive, including a polyimide binder, which is formed by dehydration after polymerization of a first amino monomer containing a side group, a second amino monomer and a carboxylic anhydride monomer, and the side group in the first amino monomer containing a side group is selected from an electron-withdrawing functional group and / or an electron-donating functional group; the first amino monomer containing a side group and the second amino monomer containing a side group are both diamine monomers, and the first amino monomer containing a side group contains an aromatic group.

[0007] Preferably, the molar ratio of the first amino monomer to the second amino monomer is (5:5) to (9:1).

[0008] Preferably, the side group is selected from C1-C4 halogen-substituted or unsubstituted alkyl, halogen, C1-C4 halogen-substituted or unsubstituted alkoxy, methylthio, carboxyl or sulfonic acid, and the halogen is selected from chlorine and bromine.

[0009] Preferably, the first amino monomer includes one or more of 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,5-diethyltoluene-2,6-diamine, 3,5-diethyltoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,6-diamine, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-4,4'-diaminodiphenylmethane, 4,4'-methylenebis(2-chloroaniline), 4,4'-methylenebis(3-chloro-2,6-diethylaniline), 2,3-diaminobenzoic acid, 2,4-diaminobenzoic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, and 2,4-diaminobenzenesulfonic acid;

[0010] And / or, the second amino monomer includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, ethylene glycol bis(2-aminophenyl) ether, 1,3-bis(3-aminopropyl)-1,1',3,3'-tetramethyldisiloxane, dimeramine, and polyetheramine.

[0011] Preferably, the first amino monomer is selected from at least one of 3,5-diethyltoluene-2,6-diamine, 3,5-diethyltoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,6-diamine, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 2,2'-dimethyl-4,4'-diaminodiphenylmethane;

[0012] And / or, the second amino monomer is selected from at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,12-diaminododecane, 1,14-tetradecanediamine, 1,3-bis(4-aminophenoxy)benzene, ethylene glycol bis(2-aminophenyl) ether, and 1,3-bis(3-aminopropyl)-1,1',3,3'-tetramethyldisiloxane.

[0013] Preferably, the ratio of the total mole number of the first amino monomer and the second amino monomer to the mole number of the carboxylic anhydride monomer is 1:(0.95-1.05).

[0014] Preferably, the carboxylic acid anhydride monomer includes one or more of pyromellitic acid dianhydride, 3,3',4,4'-diphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-(4,4'-isopropyldiphenyldiphenoxy)diphthalic anhydride, butanetetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, p-phenylene di(trimellitic acid ester) dianhydride, and trimellitic acid anhydride.

[0015] Preferably, the carboxylic acid anhydride monomer is at least one selected from pyromellitic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 4,4'-biphenyl ether dianhydride.

[0016] In a second aspect, the present application provides a positive electrode sheet, comprising a positive electrode current collector, a positive electrode active material layer and an insulating layer, wherein the positive electrode active material layer and the insulating layer are both coated on at least one side of the positive electrode current collector, the insulating layer is located on both sides of the positive electrode active material layer, and the insulating layer is formed by coating with the insulating glue as described in any one of the above items.

[0017] In a third aspect, the present application provides a secondary battery, comprising a negative electrode sheet, a separator and the positive electrode sheet described above.

[0018] The insulating adhesive provided by the present application can avoid interpenetration with the positive electrode slurry, and the free volume of the polyimide is increased by introducing the first amino monomer containing a side group into the polyimide adhesive, so that the polyimide adhesive has good solubility in polar aprotic solvents, so as to facilitate the preparation of the adhesive solution of the insulating adhesive. At the same time, the first amino monomer and the second amino monomer work together to make the insulating layer formed by the insulating adhesive have good electrolyte resistance and easy ductility. In addition, the polyimide structure makes the insulating layer formed by the insulating adhesive have good thermal stability and mechanical strength. Moreover, the aromatic group in the first amino monomer is conducive to improving the thermal stability and mechanical strength of the insulating layer formed by the polyimide adhesive. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] On the one hand, an embodiment of the present application provides an insulating adhesive, including a polyimide adhesive, wherein the polyimide adhesive is formed by dehydration after polymerization of a first amino monomer containing a side group, a second amino monomer and a carboxylic anhydride monomer, wherein the side group in the first amino monomer containing a side group is selected from an electron-withdrawing functional group and / or an electron-donating functional group; the first amino monomer and the second amino monomer containing a side group are both diamine monomers, and the first amino monomer containing a side group contains an aromatic group.

[0021] The insulating adhesive provided by the present application uses a polyimide binder to avoid molecular diffusion with the PVDF in the positive electrode slurry, thereby avoiding interpenetration. The free volume of the polyimide is increased by introducing a first amino monomer containing a side group into the polyimide binder, so that the polyimide binder has good solubility in polar aprotic solvents, so as to facilitate the preparation of the adhesive solution of the insulating adhesive. At the same time, the first amino monomer and the second amino monomer work together to make the insulating layer formed by the insulating adhesive have good electrolyte resistance and easy ductility. In addition, the polyimide structure makes the insulating layer formed by the insulating adhesive have good thermal stability and mechanical strength.

[0022] It should be noted that the polyimide adhesive can be directly applied to the edge of the battery pole piece, or it can be prepared with boehmite or the like in an N-methylpyrrolidone (NMP) solvent system to form an insulating adhesive, which can be applied to the edge of the battery pole piece. This allows the insulating layer formed by the adhesive to have excellent adhesion and electrolyte resistance, and can play a role in coating and insulation, and avoid the generation of burrs and / or dust when the pole piece is cut, thereby improving the safety performance of the battery.

[0023] In some embodiments, the molar ratio of the first amino monomer to the second amino monomer is (5:5) to (9:1). When the proportion of the second amino monomer is too large, the flexibility of the insulating layer formed by the insulating adhesive is increased, the swelling of the insulating layer is high, it is easy to fall off, and the electrolyte resistance is poor. When the proportion of the first amino monomer is too large, the insulating layer formed by the insulating adhesive is hard.

[0024] Specifically, the molar ratio of the first amino monomer to the second amino monomer includes, but is not limited to, 5:5, 9:1, 6:4, 7:3 or 8:2.

[0025] In a preferred embodiment, the molar ratio of the first amino monomer to the second amino monomer is (40:60) to (95:5).

[0026] In some embodiments, the side groups are selected from C1-C4 halogen-substituted or unsubstituted alkyl, halogen, C1-C4 halogen-substituted or unsubstituted alkoxy, methylthio, carboxyl or sulfonic acid, and the halogen is selected from chlorine and bromine. By selecting the above side groups, the polyimide binder prepared from the first amino monomer has good solubility in polar aprotic solvents and is easy to form a glue to be coated on the electrode.

[0027] In some embodiments, the first amino monomer includes one or more of 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,5-diethyltoluene-2,6-diamine, 3,5-diethyltoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,6-diamine, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-4,4'-diaminodiphenylmethane, 4,4'-methylenebis(2-chloroaniline), 4,4'-methylenebis(3-chloro-2,6-diethylaniline), 2,3-diaminobenzoic acid, 2,4-diaminobenzoic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, and 2,4-diaminobenzenesulfonic acid;

[0028] The second amino monomer includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, ethylene glycol bis(2-aminophenyl) ether, 1,3-bis(3-aminopropyl)-1,1',3,3'-tetramethyldisiloxane, dimeramine, and polyetheramine.

[0029] By selecting the first amino monomer and the second amino monomer to react with the carboxylic anhydride monomer, the insulating layer formed by the insulating adhesive containing the polyimide adhesive has good electrolyte resistance and is easy to extend.

[0030] In some preferred embodiments, the first amino monomer is selected from at least one of 3,5-diethyltoluene-2,6-diamine, 3,5-diethyltoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,4-diamine, 3,5-dimethylthiotoluene-2,6-diamine, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 2,2'-dimethyl-4,4'-diaminodiphenylmethane;

[0031] The second amino monomer is selected from at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,12-diaminododecane, 1,14-tetradecanediamine, 1,3-bis(4-aminophenoxy)benzene, ethylene glycol bis(2-aminophenyl) ether, and 1,3-bis(3-aminopropyl)-1,1',3,3'-tetramethyldisiloxane.

[0032] In some embodiments, the ratio of the total molar number of the first amino monomer and the second amino monomer to the molar number of the carboxylic anhydride monomer is 1:(0.95-1.05), so that the polyimide adhesive contains units formed by the first amino monomer and the second amino monomer at the same time.

[0033] In some embodiments, the carboxylic acid anhydride monomer includes one or more of pyromellitic acid dianhydride, 3,3',4,4'-diphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-(4,4'-isopropyldiphenyldiphenoxy)diphthalic anhydride, butanetetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, p-phenylene di(trimellitic acid ester) dianhydride, and trimellitic acid anhydride.

[0034] In some preferred embodiments, the carboxylic anhydride monomer is selected from at least one of pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 4,4'-biphenyl ether dianhydride.

[0035] In a second aspect, the present application provides a method for preparing the above-mentioned insulating adhesive, comprising the following steps:

[0036] The first amino monomer and the second amino monomer are dissolved in a first organic solvent, stirred at a certain temperature in a nitrogen atmosphere, and then carboxylic anhydride monomers are added in batches, and a polyamic acid solution is obtained after a period of reaction.

[0037] After the polyamic acid solution is heated and reacted for a period of time, it is dehydrated to obtain a brown viscous adhesive solution, which is a polyimide adhesive solution.

[0038] In some embodiments, the reaction temperature for preparing the polyamic acid solution is 0 to 80°C;

[0039] The reaction temperature of dehydrating the polyamic acid solution to form the polyimide adhesive is 120~200℃.

[0040] In some preferred embodiments, the reaction temperature for preparing the polyamic acid solution is preferably 20 to 40°C;

[0041] The reaction temperature for dehydrating the polyamic acid solution to form the polyimide binder is preferably 140-180°C.

[0042] In some embodiments, the first organic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, cyclohexanone, toluene, xylene, and cyclohexane.

[0043] In some preferred embodiments, the first organic solvent is selected from N-methylpyrrolidone and xylene.

[0044] In a third aspect, the present application provides a positive electrode sheet, comprising a positive electrode current collector, a positive electrode active material layer and an insulating layer, wherein the positive electrode active material layer and the insulating layer are both coated on at least one side of the positive electrode current collector, and the insulating layer is located on both sides of the positive electrode active material layer, and the insulating layer is formed by coating with the insulating glue as described in any of the above embodiments.

[0045] The positive electrode sheet provided in the present application has an insulating glue coated on the edge, so that the insulating layer formed by the insulating glue has excellent adhesion and electrolyte resistance, can play a role of coating and insulation, and avoids the generation of burrs and / or dust when the electrode sheet is cut, thereby improving the safety performance of the battery.

[0046] Specifically, the positive electrode current collector includes aluminum foil, carbon-coated aluminum foil, etc., and the positive electrode current collector is preferably aluminum foil. The positive electrode active material layer is obtained by coating the positive electrode slurry on the surface of the positive electrode current collector and drying it. The positive electrode slurry includes positive electrode active materials, positive electrode conductive agents, adhesives and a second organic solvent. The positive electrode active materials include lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, etc. The positive electrode conductive agents include conductive carbon black, carbon nanotubes, conductive graphite, carbon fiber, graphene, etc. The adhesive is PVDF, and the second organic solvent includes NMP.

[0047] In a fourth aspect, the present application provides a secondary battery, comprising a negative electrode sheet, a separator and the positive electrode sheet described above.

[0048] Specifically, the secondary battery includes a negative electrode sheet, a positive electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet is the positive electrode sheet described above, and the negative electrode sheet includes a negative electrode active material, wherein the negative electrode active material includes graphite, a silicon-based negative electrode, and the like.

[0049] The present invention is further described below by way of examples.

[0050] The insulating adhesive, positive electrode sheet and secondary battery disclosed in the present invention are specifically described.

[0051] Example 1

[0052] 1) Preparation of insulating adhesive

[0053] The first amino monomer 2,2'-dimethyl-4,4'-diaminobiphenyl 0.90 mol (191.1 g) and the second amino monomer ethylene glycol bis(2-aminophenyl) ether 0.10 mol (24.4 g) were dissolved in a mixed solution of 2995.4 g N-methylpyrrolidone and 352.4 g xylene. Under a nitrogen atmosphere, the mixture was stirred at 30°C until dissolved. The carboxylic anhydride monomer 4,4'-biphenyl ether dianhydride 1.01 mol (313.3 g) was added in batches. After reacting for 12 hours, a viscous polyamic acid solution was obtained.

[0054] The polyamic acid solution was heated to 160° C., refluxed for 6 hours to separate water, and then xylene was evaporated to obtain brown viscous polyimide insulating adhesive.

[0055] Preparation of insulating adhesive paste: using NMP to dilute the above polyimide adhesive to a viscosity of 1000-5000 cp to obtain insulating adhesive paste.

[0056] 2) Preparation of positive electrode:

[0057] Prepare positive electrode slurry: the mass ratio of lithium iron phosphate, dispersant (polyvinyl pyrrolidone), conductive carbon black, conductive graphite and PVDF is 97.2:0.2:0.5:0.4:1.7.

[0058] The dispersant (polyvinyl pyrrolidone), conductive carbon black and conductive graphite are dispersed in NMP according to the above ratio, and then PVDF and lithium iron phosphate are added, stirred and dispersed to obtain the positive electrode slurry.

[0059] The positive electrode slurry and insulating adhesive slurry are extruded and coated on the carbon-coated aluminum foil, and the positive electrode edge coating is located on both sides of the positive electrode. After drying at 100° C., the positive electrode sheet is obtained by rolling and cutting.

[0060] 3) Secondary battery preparation:

[0061] A negative electrode sheet is obtained, wherein the negative electrode active material in the negative electrode sheet is graphite; a positive electrode sheet, a negative electrode sheet and a separator are stacked to obtain a winding core, the winding core, an aluminum-plastic film and a commercially available secondary battery electrolyte are assembled, and aging, formation and other processes are performed to prepare a secondary battery.

[0062] Example 2

[0063] Most of the steps of this embodiment are the same as those of embodiment 1, except that: 0.50 mol of 2,2'-dimethyl-4,4'-diaminobiphenyl and 0.50 mol of the second amino monomer ethylene glycol bis(2-aminophenyl) ether.

[0064] Example 3

[0065] Most of the steps of this embodiment are the same as those of embodiment 1, except that: 0.70 mol of 2,2'-dimethyl-4,4'-diaminobiphenyl and 0.30 mol of the second amino monomer ethylene glycol bis(2-aminophenyl) ether.

[0066] Example 4

[0067] Most of the steps of this embodiment are the same as those of Embodiment 1, except that the first amino monomer is 3,5-diethyltoluene-2,6-diamine and 3,5-diethyltoluene-2,4-diamine, the second amino monomer is 1,3-bis(3-aminopropyl)-1,1',3,3'-tetramethyldisiloxane, and the carboxylic anhydride monomer is 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride.

[0068] Example 5

[0069] Most of the steps of this embodiment are the same as those of embodiment 1, except that the amount of the carboxylic anhydride monomer 4,4'-biphenyl ether dianhydride is 1.05 mol.

[0070] Example 6

[0071] Most of the steps of this embodiment are the same as those of embodiment 1, except that the amount of the carboxylic anhydride monomer 4,4'-biphenyl ether dianhydride is 0.95 mol.

[0072] Example 7

[0073] Most of the steps of this embodiment are the same as those of Embodiment 1, except that: preparing the positive electrode edge insulating slurry: mixing the polyimide binder and boehmite in a mass ratio of 15 / 85, and filtering to obtain the positive electrode edge slurry.

[0074] Comparative Example 1

[0075] The insulating adhesive of this comparative example is prepared by dispersing commercially available PVDF and boehmite in N-methylpyrrolidone. The preparation method of the battery is the same as that of Example 1.

[0076] Comparative Example 2

[0077] This comparative example is similar to Example 1 in most steps, except that the second amino monomer is not contained.

[0078] Comparative Example 3

[0079] This comparative example is similar to Example 1 in most steps, except that the first amino monomer is not contained.

[0080] Performance Test:

[0081] The positive electrode sheets and secondary batteries prepared in the above examples and comparative examples were subjected to the following tests.

[0082] 1) Peel strength test

[0083] The insulating adhesive is applied to the aluminum foil, dried, peeled upward at 180°, and the peeling strength is tested using a universal mechanical tensile machine.

[0084] 2) Material channeling resistance test

[0085] Use a straw to suck up the insulating glue slurry and the positive electrode slurry, make the two slurries contact, observe their penetration phenomenon, and record the time when obvious penetration occurs.

[0086] 3) Electrolyte resistance test:

[0087] The insulating adhesive slurry is coated on the aluminum foil and dried to obtain the positive electrode edge adhesive coating; the coating is immersed in an electrolyte at 85°C for 72 hours to observe whether there is cracking or falling off.

[0088] 4) Electrolyte swelling rate test:

[0089] The insulating adhesive was coated on a smooth glass plate and dried. After peeling off, a pure adhesive film was obtained. The adhesive film was immersed in an electrolyte at 85°C for 72 hours, and its mass swelling rate was tested.

[0090] Fill in the results of the above tests in Table 1.

[0091] Table 1

[0092]

[0093] It can be seen from the experimental results in Table 1 that compared with the existing PVDF insulating glue, the insulating glue of the present application has excellent peel strength and excellent electrolyte resistance, will not fall off, and has a low electrolyte swelling rate; at the same time, it has excellent resistance to material leakage, and the leakage time is at least more than 6 minutes, which is higher than the time of the prior art.

[0094] Comparing the results of Examples 2 and 3, it can be seen that increasing the content of the first amino monomer is beneficial to improving the anti-channeling performance and maintaining a low electrolyte swelling rate.

[0095] Comparing the results of Example 1 with Comparative Examples 2 and 3, it can be seen that when the second amino monomer is not included, the peel strength and electrolyte resistance of the insulating adhesive are poor. If the first amino monomer is not included, the adhesive will precipitate and cannot be dissolved.

[0096] 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 in the protection scope of the present invention.

Claims

1. An insulating adhesive for a positive electrode sheet, characterized in that: The insulating adhesive is a polyimide adhesive, which is formed by random copolymerization of a first amino monomer containing a side group, a second amino monomer and a carboxylic anhydride monomer and then dehydration; the first amino monomer containing a side group and the second amino monomer are both diamine monomers, and the first amino monomer containing a side group contains an aromatic group; The first amino monomer is selected from one or more of 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,5-diethyltoluene-2,6-diamine, 3,5-diethyltoluene-2,4-diamine, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 2,2'-dimethyl-4,4'-diaminodiphenylmethane; The second amino monomer is selected from one or more of ethylene glycol bis(2-aminophenyl) ether and 1,3-bis(3-aminopropyl)-1,1',3,3'-tetramethyldisiloxane; The molar ratio of the first amino monomer to the second amino monomer is 9:1; The ratio of the total mole number of the first amino monomer and the second amino monomer to the mole number of the carboxylic anhydride monomer is 1:(0.95-1.05).

2. The insulating adhesive according to claim 1, characterized in that: The carboxylic acid anhydride monomer includes one or more of pyromellitic acid dianhydride, 3,3',4,4'-diphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-(4,4'-isopropyldiphenyldiphenoxy)diphthalic anhydride, butanetetracarboxylic acid dianhydride, 3,3',4,4'-diphenyl sulfonetetracarboxylic acid dianhydride, p-phenylene di(trimellitic acid ester) dianhydride, and trimellitic acid anhydride.

3. The insulating adhesive according to claim 2, characterized in that: The carboxylic anhydride monomer is selected from at least one of pyromellitic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-biphenyl ether dianhydride.

4. A positive electrode sheet, characterized in that: It comprises a positive electrode current collector, a positive electrode active material layer and an insulating layer, wherein the positive electrode active material layer and the insulating layer are both coated on at least one side of the positive electrode current collector, the insulating layer is located on both sides of the positive electrode active material layer, and the insulating layer is formed by coating the insulating glue according to any one of claims 1 to 3.

5. A secondary battery, characterized in that: The invention comprises a negative electrode sheet, a separator and the positive electrode sheet as claimed in claim 4.

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