Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one side of the positive current collector, the positive film layer comprises a binder, the binder comprises a polymer containing a structural unit A and a structural unit B, the structural unit A is derived from polyimide with carbon-carbon double bonds at at least one end, and the structural unit B is derived from polyimide with carbon-carbon double bonds at least one end. And the B structural unit is derived from an unsaturated carboxylic ester monomer. The positive pole piece of the secondary battery has excellent binding power and flexibility.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the widespread use of secondary batteries, higher requirements have been placed on their cycle performance and service life.

[0003] Binders are commonly used materials in secondary batteries. Currently, one of the most widely used binders in positive electrode sheets is polyvinylidene fluoride, but it has poor flexibility, poor environmental protection and its bonding performance is difficult to meet the further requirements of positive electrode sheets. Therefore, the existing binders still need to be improved. Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery, which includes a positive electrode plate, the positive electrode plate includes a positive electrode collector and a positive electrode film layer arranged on at least one side of the positive electrode collector, and the positive electrode film layer includes a binder prepared in the present application, which has good flexibility, bonding performance and environmental protection, so that the positive electrode plate has both excellent bonding strength and flexibility.

[0005] The first aspect of the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprising a binder, the binder comprising a polymer containing an A structural unit and a B structural unit, wherein the A structural unit is derived from a polyimide having a carbon-carbon double bond at at least one end, and the B structural unit is derived from an unsaturated carboxylic acid ester monomer.

[0006] The polymer contains structural units derived from polyimide having a carbon-carbon double bond at at least one end. The polyimide chain segment can improve the bonding strength between the polymer and the positive electrode active material and the current collector; the polymer contains structural units derived from unsaturated carboxylic acid ester monomers, which can weaken the rigidity brought by the polyimide chain segment and improve the flexibility of the polymer. The polymer has excellent environmental protection. As a positive electrode plate binder, the polymer enables the positive electrode plate to have both excellent bonding strength and flexibility, which is beneficial to improving the battery cycle stability.

[0007] In any embodiment, the polyimide having a carbon-carbon double bond at at least one end comprises a structure shown in Formula I,

[0008]

[0009] wherein R1 is selected from a substituted or unsubstituted tetravalent C6-C24 aromatic group, R2 is selected from substituted or unsubstituted divalent C6-C 24 An aromatic group, at least one of R3 and R4 is a residue of a capping agent containing an amino group and a carbon-carbon double bond, and 50≤n≤600.

[0010] R1, R2 are selected from substituted or unsubstituted tetravalent, divalent C6-C 24 The aromatic group helps to further improve the bonding properties of the polymer, and the positive electrode has excellent bonding properties.

[0011] In any embodiment, the capping agent containing an amino group and a carbon-carbon double bond includes one or more of amino polyethylene glycol acrylate, 2-aminoethyl methacrylate hydrochloride, and 3-amino methyl acrylate.

[0012] In any embodiment, the capping agent containing an amino group and a carbon-carbon double bond comprises amino polyethylene glycol acrylate.

[0013] Amino polyethylene glycol acrylate is selected as the end-capping agent. The residue of the end-capping agent enables the polyimide to have a carbon-carbon double bond at least at one end. At the same time, the flexibility of the polymer can be adjusted by changing the number of polyethylene glycol repeating units in the end-capping agent, which is beneficial to further enhance the flexibility of the polymer, so that the positive electrode has both good adhesion and better flexibility.

[0014] In any embodiment, the amino polyethylene glycol acrylate includes m CH2CH2O repeating units, 5≤m≤100.

[0015] The number m of CH2CH2O repeating units in amino polyethylene glycol acrylate is within a suitable range, which can not only further adjust the flexibility of the polymer, but also avoid the decrease in polymer bonding performance caused by excessively long polyethylene glycol chain segments. The positive electrode sheet has both excellent bonding and flexibility.

[0016] In any embodiment, based on the total mass of the polymer A structural units and the B structural units, the mass proportion of the A structural units is 10%-90%.

[0017] Based on the total mass of polymer structural units A and B, polymers with a suitable mass percentage of structural units A can achieve both superior bonding and flexibility. This avoids the poor polymer flexibility caused by an excessive mass percentage of polyimide segments, which in turn leads to poor positive electrode flexibility, prone to powder loss and cracking, and affects the processing performance of the electrode and subsequent battery safety during use. It also avoids the degradation of polymer bonding caused by an excessive mass percentage of structural units derived from unsaturated carboxylic acid ester monomers. Polymers with a suitable mass percentage of structural units A enable positive electrode sheets to possess better bonding, flexibility, and processing performance, which is conducive to further improving battery cycling stability.

[0018] In any embodiment, the unsaturated carboxylic acid ester monomer comprises a structure shown in Formula II,

[0019]

[0020] wherein R5, R6, and R7 are each independently hydrogen or substituted or unsubstituted C 1-5 Alkyl, R8 includes C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more alkoxy groups.

[0021] In any embodiment, the structure represented by Formula II includes one or more of methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 3-hydroxypropyl acrylate, 5-hydroxypentyl acrylate, and 6-methylheptyl acrylate.

[0022] The above monomers can effectively improve the flexibility of the polymer, making the positive electrode sheet have better adhesion and flexibility. 1-5 When a hydroxyalkyl group is added, the bonding performance of the polymer can be further improved, thereby improving the bonding strength of the positive electrode sheet.

[0023] In any embodiment, based on the total mass of the polymer A structural unit and the B structural unit, the mass proportion of the B structural unit is 10%-90%.

[0024] Based on the total mass of polymer A structural unit and B structural unit, the polymer with a mass proportion of B structural unit in an appropriate range takes into account the bonding performance and flexibility of the polymer. The positive electrode sheet has both better bonding strength and flexibility, which is conducive to further improvement of battery cycle stability.

[0025] In any embodiment, the weight average molecular weight of the polymer is 200,000 to 400,000.

[0026] Polymers with a weight-average molecular weight within an appropriate range exhibit excellent bonding strength with the active material and current collector, and can be readily dissolved and dispersed in the cathode slurry. This avoids the difficulties in dissolution and gel formation caused by excessively high polymer weight-average molecular weight, which can lead to excessive viscosity in the cathode slurry and difficulty in uniform coating, thus affecting subsequent electrode processing; and also avoids the ineffective bonding caused by too low a weight-average molecular weight. Polymers with a weight-average molecular weight within an appropriate range provide cathode electrodes with superior bonding strength, flexibility, and processing performance, further enhancing battery cycle stability.

[0027] In any embodiment, the method for preparing the polymer comprises the following steps: polymerizing a polyimide having a carbon-carbon double bond at at least one end with an unsaturated carboxylate monomer to obtain a polymer containing an A structural unit and a B structural unit.

[0028] The above preparation method has the advantages of high yield, few by-products, simple and mild reaction conditions, and readily available reaction raw materials. It can achieve controllable polymerization of polymers and prepare polymers with excellent adhesion, flexibility, environmental protection, electrolyte resistance and thermal stability.

[0029] In any embodiment, the preparation method of a polyimide having a carbon-carbon double bond at at least one end comprises the following steps: reacting at least one diamine, at least one dibasic anhydride, and at least one end-capping agent containing an amino group and a carbon-carbon double bond to obtain a polyamic acid having a carbon-carbon double bond at at least one end; and dehydrating the polyamic acid having a carbon-carbon double bond at at least one end to obtain the polyimide having a carbon-carbon double bond at at least one end.

[0030] The two-step method for preparing a polyimide having a carbon-carbon double bond at at least one end has the advantages of simple reaction conditions, a wide range of raw material options, and controllable polymerization, which is conducive to preparing a polyimide with a suitable molecular weight.

[0031] In any embodiment, based on the total mass of the positive electrode film layer, the mass proportion of the polymer is 0.5%-2%.

[0032] Based on the total mass of the positive electrode film layer, keeping the polymer mass percentage within an appropriate range can prevent the inadequate bonding effect caused by too low a polymer content, while also avoiding the reduction in battery energy density caused by too high a polymer content, as well as the gelation of the slurry and the impact on subsequent electrode processing. Controlling the polymer mass percentage within an appropriate range ensures that the positive electrode has superior bonding strength, flexibility, and processing performance, further improving the battery's cycle stability and energy density.

[0033] In any embodiment, the positive electrode film layer further includes a positive electrode active material, and the positive electrode active material includes lithium-containing phosphate, lithium transition metal oxide, and their respective modified materials.

[0034] A second aspect of the present application further provides an electrical device comprising the secondary battery of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application;

[0036] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0037] Figure 3 is a schematic diagram of a battery module according to one embodiment of the present application;

[0038] Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present application;

[0039] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0040] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0041] Description of reference numerals:

[0042] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0043] Below, the embodiments of the secondary battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0044] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0049] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] Binders are a key component of lithium-ion battery pole pieces. Although used in relatively small quantities, their performance directly impacts the stability and processability of the pole pieces, and thus the battery's cycling performance. Polyvinylidene fluoride (PVDF) is one of the most widely used binders in secondary battery positive pole pieces. However, its production and use produce fluoride, which is harmful to humans and the environment. Furthermore, PVDF has poor flexibility, poor adhesion, and high cost, making it difficult to meet the increased adhesion and flexibility requirements of positive pole pieces, negatively impacting battery cycling performance.

[0051] [Secondary battery]

[0052] Based on this, the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprising a binder, the binder comprising a polymer containing an A structural unit and a B structural unit, wherein the A structural unit is derived from a polyimide having a carbon-carbon double bond at at least one end, and the B structural unit is derived from an unsaturated carboxylic acid ester monomer.

[0053] As used herein, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0054] In some embodiments, the binder dispersion medium is an oily solvent. Examples of such solvents include, but are not limited to, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate. That is, the binder is dissolved in the oily solvent.

[0055] In some embodiments, a binder is used to hold the electrode material and / or conductive agent in place and adhere them to the conductive metal component to form an electrode.

[0056] As used herein, the term "polymer" includes, on the one hand, a collection of chemically homogeneous macromolecules prepared by polymerization, but differing in degree of polymerization, molar mass, and chain length. The term also includes derivatives of such collections of macromolecules formed by polymerization, i.e., compounds that can be obtained by reaction, for example, addition or substitution, of functional groups in the aforementioned macromolecules and that can be chemically homogeneous or chemically heterogeneous.

[0057] As used herein, the term "polyimide" refers to a class of polymers containing an imide ring (-CO-NR-CO-) in the main chain.

[0058] As used herein, the term "unsaturated carboxylic acid ester monomer" refers to an unsaturated monomer containing a -COO- group in the molecule.

[0059] In some embodiments, a polymer is obtained by free radical polymerization of a polyimide having a carbon-carbon double bond at at least one end and an unsaturated carboxylate monomer.

[0060] The polymer contains structural units derived from polyimide having a carbon-carbon double bond at at least one end. The polyimide chain segment can improve the bonding strength between the polymer and the positive electrode active material and the current collector; the polymer contains structural units derived from unsaturated carboxylic acid ester monomers, which can weaken the rigidity brought by the polyimide chain segment and improve the flexibility of the polymer. The polymer has excellent environmental protection. As a positive electrode plate binder, the polymer enables the positive electrode plate to have both excellent bonding strength and flexibility, which is beneficial to improving the battery cycle stability.

[0061] In some embodiments, the polyimide having a carbon-carbon double bond at at least one end comprises a structure shown in Formula I,

[0062]

[0063] wherein R1 is selected from a substituted or unsubstituted tetravalent C6-C 24 aromatic group, R2 is selected from substituted or unsubstituted divalent C6-C 24 An aromatic group, at least one of R3 and R4 is a residue of a capping agent containing an amino group and a carbon-carbon double bond, and 50≤n≤600.

[0064] As used herein, the term "substituted" refers to a compound or chemical moiety in which at least one hydrogen atom is replaced by another chemical moiety, wherein the substituents are each independently selected from the group consisting of hydroxyl, thiol, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C 1-6 Alkyl, C 1-6 Alkoxy.

[0065] In this article, the term "C6-C 24 "Aryl" refers to an aromatic ring system in which at least one ring is aromatic, including but not limited to phenyl, biphenyl, indanyl, 1-naphthyl, 2-naphthyl, and tetrahydronaphthyl.

[0066] In this article, the substituted C6-C 24 Aryl groups include, but are not limited to, aralkyl, aralkyloxy, aryloxyalkyl, and aryl groups represented by -O-, -S-, -C(=O)-, -S(=O)2, -SO-, C 1-20Alkylene-linked symmetrical or unsymmetrical aryl groups.

[0067] As used herein, the term "amino" refers to a -NH2 group.

[0068] As used herein, the term "end-capping agent" refers to a compound added during the polymerization reaction that can react with the functional groups at both ends of the polymer, thereby terminating the polymerization reaction.

[0069] Herein, the term "residue of a capping agent containing an amino group and a carbon-carbon double bond" refers to the remaining portion after the amino group of the capping agent containing an amino group and a carbon-carbon double bond reacts with a functional group at at least one end of the polymer.

[0070] In some embodiments, R1 can be selected from

[0071]

[0072] One or more of .

[0073] In some embodiments, R2 can be selected from

[0074]

[0075] One or more of .

[0076] In some embodiments, n is 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, or any number therebetween.

[0077] R1, R2 are selected from substituted or unsubstituted tetravalent, divalent C6-C 24 The aromatic group helps to further improve the bonding properties of the polymer, and the positive electrode has excellent bonding properties.

[0078] In some embodiments, the capping agent containing an amino group and a carbon-carbon double bond includes one or more of amino polyethylene glycol acrylate, 2-aminoethyl methacrylate hydrochloride, and 3-amino methyl acrylate.

[0079] In some embodiments, the capping agent containing an amino group and a carbon-carbon double bond comprises amino polyethylene glycol acrylate.

[0080] Amino polyethylene glycol acrylate is selected as the end-capping agent. The residue of the end-capping agent enables the polyimide to have a carbon-carbon double bond at least at one end. At the same time, the flexibility of the polymer can be adjusted by changing the number of polyethylene glycol repeating units in the end-capping agent, which is beneficial to further enhance the flexibility of the polymer, so that the positive electrode has both good adhesion and better flexibility.

[0081] In some embodiments, the amino polyethylene glycol acrylate includes m CH2CH2O repeating units, 5≤m≤100.

[0082] In some embodiments, m is 5, 10, 15, 21, 25, 30, 35, 45, 55, 65, 75, 85, 95, 100, or any number therebetween.

[0083] The number m of CH2CH2O repeating units in amino polyethylene glycol acrylate is within a suitable range, which can not only further adjust the flexibility of the polymer, but also avoid the decrease in polymer bonding performance caused by excessively long polyethylene glycol chain segments. The positive electrode sheet has both excellent bonding and flexibility.

[0084] In some embodiments, based on the total mass of the polymer A structural units and the B structural units, the mass proportion of the A structural units is 10%-90%.

[0085] In some embodiments, based on the total mass of the polymer A structural unit and the B structural unit, the mass proportion of the A structural unit is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or any value therebetween.

[0086] Based on the total mass of polymer structural units A and B, polymers with a suitable mass percentage of structural units A can achieve both superior bonding and flexibility. This avoids the poor polymer flexibility caused by an excessive mass percentage of polyimide segments, which in turn leads to poor positive electrode flexibility, prone to powder loss and cracking, and affects the processing performance of the electrode and subsequent battery safety during use. It also avoids the degradation of polymer bonding caused by an excessive mass percentage of structural units derived from unsaturated carboxylic acid ester monomers. Polymers with a suitable mass percentage of structural units A enable positive electrode sheets to possess better bonding, flexibility, and processing performance, which is conducive to further improving battery cycling stability.

[0087] In some embodiments, the unsaturated carboxylate monomer comprises a structure shown in Formula II,

[0088]

[0089] wherein R5, R6, and R7 are each independently hydrogen or substituted or unsubstituted C 1-5 Alkyl, R8 includes C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more alkoxy groups.

[0090] In this article, the term “C 1-5"Alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present, having from one to five carbon atoms, and attached to the remainder of the molecule by a single bond. 1-5 Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, 1-methylethyl(isopropyl), n-butyl, isobutyl, tert-butyl, idenebutyl, and pentyl.

[0091] In this article, the term “C 1-5 "Hydroxyalkyl" refers to a group consisting of an alkyl group and a hydroxy group, with no unsaturation in the group, having from one to five carbon atoms, and attached to the rest of the molecule by a single bond, including but not limited to hydroxymethyl, hydroxyethyl, hydroxypropyl, and 4-hydroxybutyl.

[0092] In this article, the term “C 1-5 "Alkoxy" refers to a group consisting of an alkyl group and an oxygen atom, has from one to five carbon atoms, and is attached to the rest of the molecule by a single bond. Common examples include methoxy (CH3O-), ethoxy (C2H5O-), propoxy (C3H7O-), etc.

[0093] In some embodiments, the structure represented by Formula II includes one or more of methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 3-hydroxypropyl acrylate, 5-hydroxypentyl acrylate, and 6-methylheptyl acrylate.

[0094] The above monomers can effectively improve the flexibility of the polymer, making the positive electrode sheet have better adhesion and flexibility. 1-5 When a hydroxyalkyl group is added, the bonding performance of the polymer can be further improved, thereby improving the bonding strength of the positive electrode sheet.

[0095] In some embodiments, based on the total mass of the polymer A structural unit and the B structural unit, the mass proportion of the B structural unit is 10%-90%.

[0096] In some embodiments, based on the total mass of the polymer A structural unit and the B structural unit, the mass proportion of the B structural unit is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or any value therebetween.

[0097] Based on the total mass of polymer A structural unit and B structural unit, the polymer with a mass proportion of B structural unit in an appropriate range takes into account the bonding performance and flexibility of the polymer. The positive electrode sheet has both better bonding strength and flexibility, which is conducive to further improvement of battery cycle stability.

[0098] In some embodiments, the weight average molecular weight of the polymer is 200,000 to 400,000.

[0099] As used herein, the term "weight average molecular weight" refers to the sum of the weight fractions of molecules of different molecular weights in a polymer multiplied by their corresponding molecular weights.

[0100] In the present application, the weight-average molecular weight of the polymer can be tested using methods known in the art, such as gel chromatography, such as using a Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141). In some embodiments, the testing method is to use a polystyrene solution sample with a mass fraction of 3.0% as a reference and select a matching chromatographic column (oily: Styragel HT5DMF7.8*300mm+Styragel HT4). Use purified N-methylpyrrolidone (NMP) solvent to prepare a 3.0% polymer glue solution, and let the prepared solution stand for one day for use. During the test, first use a syringe to draw tetrahydrofuran, rinse, and repeat several times. Then draw 5 mL of experimental solution, expel the air in the syringe, and wipe the needle tip dry. Finally, slowly inject the sample solution into the injection port. After the reading stabilizes, obtain data and read the weight-average molecular weight.

[0101] In some embodiments, the weight average molecular weight of the polymer is 200,000, 220,000, 240,000, 260,000, 280,000, 300,000, 320,000, 340,000, 360,000, 380,000, 400,000, or any value therebetween.

[0102] Polymers with a weight-average molecular weight within an appropriate range exhibit excellent bonding strength with the active material and current collector, and can be readily dissolved and dispersed in the cathode slurry. This avoids the difficulties in dissolution and gel formation caused by excessively high polymer weight-average molecular weight, which can lead to excessive viscosity in the cathode slurry and difficulty in uniform coating, thus affecting subsequent electrode processing; and also avoids the ineffective bonding caused by too low a weight-average molecular weight. Polymers with a weight-average molecular weight within an appropriate range provide cathode electrodes with superior bonding strength, flexibility, and processing performance, further enhancing battery cycle stability.

[0103] In some embodiments, the method for preparing a polymer comprises the following steps: polymerizing a polyimide having a carbon-carbon double bond at at least one end with an unsaturated carboxylate monomer to obtain a polymer containing an A structural unit and a B structural unit.

[0104] The above preparation method has the advantages of high yield, few by-products, simple and mild reaction conditions, and readily available reaction raw materials. It can achieve controllable polymerization of polymers and prepare polymers with excellent adhesion, flexibility, environmental protection, electrolyte resistance and thermal stability.

[0105] In some embodiments, the preparation method of a polyimide having a carbon-carbon double bond at at least one end includes the following steps: reacting at least one diamine, at least one dibasic anhydride, and at least one end-capping agent containing an amino group and a carbon-carbon double bond to obtain a polyamic acid having a carbon-carbon double bond at at least one end; and dehydrating the polyamic acid having a carbon-carbon double bond at at least one end to obtain the polyimide having a carbon-carbon double bond at at least one end.

[0106] As used herein, the term "diamine" refers to an amine containing two amino groups.

[0107] In some embodiments, the diamine is an aromatic diamine, which may be

[0108] One or more of .

[0109] As used herein, the term "dianhydride" refers to a monomer containing two anhydride groups.

[0110] In some embodiments, the dibasic anhydride is aromatic dianhydride, which may be

[0111]

[0112] One or more of .

[0113] When the diamine and the dianhydride are selected from one or more compounds represented by the above structural formula, the polymer has better flexibility, bonding performance and environmental friendliness, and the positive electrode sheet has better bonding strength and flexibility.

[0114] In some embodiments, the synthesis route of the polyamic acid having a carbon-carbon double bond at at least one end is as follows: at least one diamine and at least one dibasic anhydride undergo a polymerization reaction to generate polyamic acid, so that the dibasic anhydride is in excess, thereby obtaining a polyamic acid having carboxyl groups at both ends; the carboxyl group at at least one end reacts with a capping agent comprising an amino group and a carbon-carbon double bond to prepare a polyamic acid having a carbon-carbon double bond at at least one end.

[0115] As used herein, the term "anhydride" refers to a -CO-O-CO- group.

[0116] As used herein, the term "carboxyl" refers to a -COOH group.

[0117] The two-step method for preparing a polyimide having a carbon-carbon double bond at at least one end has the advantages of simple reaction conditions, a wide range of raw material options, and controllable polymerization, which is conducive to preparing a polyimide with a suitable molecular weight.

[0118] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the polymer is 0.5%-2%.

[0119] Based on the total mass of the positive electrode film layer, keeping the polymer mass percentage within an appropriate range can prevent the inadequate bonding effect caused by too low a polymer content, while also preventing excessively high content from reducing the battery's energy density and causing the slurry to gel, impacting subsequent electrode processing. Keeping the polymer mass percentage within an appropriate range ensures that the positive electrode has superior bonding strength, flexibility, and processing performance, further improving the battery's cycle stability and energy density.

[0120] In some embodiments, the polymer may be used in a secondary battery. Optionally, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0121] [Positive electrode]

[0122] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and including a positive electrode active material.

[0123] For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0124] In some embodiments, the positive electrode active material may adopt the positive electrode active material for secondary batteries well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the embodiments of the present application are not limited to these materials, and other traditional materials that can be used as positive electrode active materials for lithium-ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include but are not limited to lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0125] In some embodiments, the positive electrode active material includes lithium-containing phosphates, lithium transition metal oxides, and their respective modified materials.

[0126] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0128] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0129] [Negative electrode]

[0130] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0131] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0132] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0133] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0134] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0135] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0136] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0137] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0138] [Electrolytes]

[0139] The electrolyte conducts ions between the positive and negative electrodes. The present invention does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, solid, or gel.

[0140] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0141] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0142] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0143] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0144] [Isolation film]

[0145] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0146] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0147] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0148] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0149] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0150] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 1 As an example, a secondary battery 5 with a square structure is shown. Optionally, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0151] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0152] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0153] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0154] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0155] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0156] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0157] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0158] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0159] Figure 6 This is an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0160] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0161] Example

[0162] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0163] 1. Preparation method

[0164] Example 1:

[0165] 1) Synthesis of copolymer

[0166] Synthesis of polyamic acid having a carbon-carbon double bond at at least one end: 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed at a molar ratio of 1.01:1. 5 mmol of 4,4'-diaminodiphenyl ether, 0.03 mmol of aminopolyethylene glycol acrylate, and 0.033 mmol of ethanolamine were dissolved in 100 mL of N-methylpyrrolidone (NMP) at room temperature. Nitrogen was continuously introduced and mechanically stirred until the raw materials were dissolved in the solvent. 5.05 mmol of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added, and the mixture was stirred in an ice-water bath at low temperature for 12 hours to obtain a precursor polyamic acid polymer solution. The precursor solution was precipitated in ethanol, washed, filtered, and dried to obtain a polyamic acid solid powder having a carbon-carbon double bond at at least one end.

[0167] The number of CH2CH2O repeating units in amino polyethylene glycol acrylate is 21, and the structural formulas of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether are:

[0168]

[0169] Synthesis of a polyimide having a carbon-carbon double bond at at least one end: Using the above-mentioned polyamic acid as a reactant, 0.02 mmol of the above-synthesized polyamic acid solid powder is dissolved in 150 mL of the organic solvent NMP, 8 mL of acetic anhydride and 10 mL of triethylamine are added to the solution, and the temperature is raised to 120°C and the reaction is continued for 10 hours. After the reaction is completed, the reaction product is precipitated in anhydrous ethanol, centrifuged, and washed with ethanol until the centrifuge liquid is clear and transparent. The solid obtained by centrifugation is vacuum dried to obtain a polyimide solid having a carbon-carbon double bond at at least one end, wherein n is 450.

[0170] Synthesis of a polymer containing structural units A and B: 20 ​​g of deionized water, 0.15 g of ammonium persulfate, 0.3 g of sodium lauryl sulfate, and 0.3 g of emulsifier alkylphenol polyoxyethylene ether OP-10 were added to a reactor and stirred to dissolve them; 0.02 mmol of the above-mentioned polyimide solid having a carbon-carbon double bond at at least one end and 14 mmol of hydroxypropyl acrylate were added to the reactor and mixed thoroughly to emulsify to obtain a monomer pre-emulsion; 0.7 g of dodecane was added to the polymerization kettle. The mixture was stirred until fully mixed; the monomer emulsion was weighed and added to a polymerization kettle, and 0.3 g of ammonium persulfate was weighed and dissolved in 5 g of deionized water, which was then slowly added to the polymerization kettle; when the temperature of the reaction kettle reached 80°C, the monomer emulsion was added dropwise at a constant rate of 2 h, and after the addition was completed, the mixture was kept warm for 1 h, and then cooled to obtain a polymer containing structural units A and B, and the molecular weight of the polymer was 300,000.

[0171] 2) Preparation of positive electrode sheet

[0172] The positive electrode active material NCM811, the conductive agent Super P, and the aforementioned polymers were mixed in a mass ratio of 96.5:2.0:1.5. N-methylpyrrolidone was added as a solvent and stirred in a blender until the mixture was homogeneous, resulting in a positive electrode slurry with a solid content of 75wt%. The positive electrode slurry was evenly coated on the current collector, dried at high temperature, and then cold pressed to produce the positive electrode sheet.

[0173] Example 2-3

[0174] The preparation method of the positive electrode sheet of Example 2-3 is basically the same as that of the positive electrode sheet of Example 1. The difference is that the mass ratio of the A structural unit and the B structural unit based on the total mass of the polymer A structural unit and the B structural unit is changed. See Table 1 for details.

[0175] Example 4

[0176] The preparation method of the positive electrode sheet of Example 4 is basically the same as that of the positive electrode sheet of Example 1, except that the type of the capping agent is changed, as shown in Table 1.

[0177] Examples 5-6

[0178] The preparation method of the positive electrode sheets of Examples 5-6 is basically the same as that of the positive electrode sheet of Example 1, except that the number m of CH2CH2O repeating units in amino polyethylene glycol acrylate is changed, as shown in Table 1 for details.

[0179] Examples 7-8

[0180] The preparation methods of the positive electrode sheets of Examples 7-8 are basically the same as those of the positive electrode sheets of Example 1, except that in Examples 7-8, hydroxypropyl acrylate is replaced by methyl methacrylate and butyl acrylate, respectively, during the polymer synthesis process. See Table 1 for details.

[0181] Examples 9-10

[0182] The preparation methods of the positive electrode sheets of Examples 9-10 are basically the same as those of the positive electrode sheet of Example 1, except that the weight average molecular weight of the polymer is changed, as shown in Table 1.

[0183] Examples 11-13

[0184] The preparation methods of the positive electrode sheets of Examples 11-13 are basically the same as those of Example 1. The difference is that the amount of polymer added is adjusted in Examples 11-13, and the content of the positive electrode active material changes accordingly:

[0185] In Example 11, the positive electrode active material NCM811, the conductive agent Super P, and the polymer are mixed in the positive electrode slurry at a mass ratio of 97.5:2.0:0.5.

[0186] In Example 12, the positive electrode active material NCM811, the conductive agent Super P, and the polymer are mixed in the positive electrode slurry at a mass ratio of 97.0:2.0:1.0.

[0187] In Example 13, the positive electrode active material NCM811, the conductive agent Super P, and the polymer are mixed in the positive electrode slurry at a mass ratio of 96.0:2.0:2.0.

[0188] Comparative Example 1

[0189] The preparation method of the positive electrode sheet of Comparative Example 1 is basically the same as the preparation method of the positive electrode sheet of Example 1, except that the polymer in the positive electrode slurry of Comparative Example 1 is replaced by polyvinylidene fluoride with a molecular weight of 1 million, which is commonly used in the production line.

[0190] Comparative Example 2

[0191] The preparation method of the positive electrode sheet of Comparative Example 2 is basically the same as the preparation method of the positive electrode sheet of Example 1, except that the polymer in the positive electrode slurry is replaced by polyimide with a molecular weight of 300,000.

[0192] 2. Battery performance test

[0193] 1. Adhesion of positive electrode

[0194] The prepared positive electrode sheet was cut into test specimens of 20*100mm size for later use; the side of the electrode to be tested was adhered with double-sided tape and compacted with a pressure roller to make it completely fit the electrode; the other side of the double-sided tape of the specimen was adhered to the surface of the steel plate, and one end of the current collector was bent in the opposite direction with a bending angle of 180°; a high-speed rail tensile testing machine was used for testing, one end of the steel plate was fixed to the lower fixture of the tensile testing machine, and the bent end of the current collector was fixed to the upper fixture, the angle of the current collector was adjusted to ensure that the upper and lower ends were in a vertical position, and then the specimen was stretched at a speed of 50mm / min until the current collector was completely peeled off from the surface of the current collector, and the displacement and force during the process were recorded. The force when the force was balanced was taken as the bonding force of the electrode, and the bonding strength was taken as the force divided by the adhesion length of the sample.

[0195] 2. Flexibility of the positive electrode

[0196] Take a 20mm×100mm (longitudinal) sample of the prepared positive electrode and sample along the rolling direction of the electrode; place the pre-folded experimental electrode on the plane of the experimental table and roll it with a 2kg cylindrical roller. After each rolling, observe whether the electrode is translucent. When the electrode is translucent, record the corresponding number of rolling times. The number of rolling times represents the flexibility of the electrode.

[0197] 3. Analysis of test results of various embodiments and comparative examples

[0198] The positive electrode sheets of each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1.

[0199] Table 1

[0200]

[0201]

[0202]

[0203] As can be seen from Examples 1-13, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer includes a binder, and the binder includes a polymer containing an A structural unit and a B structural unit, wherein the A structural unit is derived from a polyimide having a carbon-carbon double bond at at least one end, and the B structural unit is derived from an unsaturated carboxylic acid ester. The positive electrode plate has both excellent bonding strength and flexibility.

[0204] From the comparison of Examples 1-13 and Comparative Example 1, it can be seen that the positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector. The positive electrode film layer includes a binder. Compared with the polyvinylidene fluoride binder, the polymer binder containing a structural unit derived from a polyimide having a carbon-carbon double bond at at least one end and a structural unit derived from an unsaturated carboxylic acid ester monomer enables the positive electrode plate to have both excellent bonding strength and flexibility.

[0205] From the comparison of Examples 1-13 and Comparative Example 2, it can be seen that when the polymer contains structural units derived from polyimide having a carbon-carbon double bond at at least one end and structural units derived from unsaturated carboxylic acid ester monomers, the bonding strength and flexibility of the positive electrode sheet can be improved.

[0206] As can be seen from Examples 1-3, based on the total mass of the polymer A structural unit and the B structural unit, the mass proportion of the A structural unit is 10%-90%, and the positive electrode sheet has excellent bonding strength and flexibility.

[0207] It can be seen from Examples 1 and 4-6 that when the capping agent includes one or more of aminopolyethylene glycol acrylate, 2-aminoethyl methacrylate hydrochloride, and 3-aminomethyl acrylate, the positive electrode sheet has excellent bonding strength and flexibility.

[0208] From the comparison between Examples 1, 5, and 6 and Example 4, it can be seen that when the capping agent includes amino polyethylene glycol acrylate and the number m of CH2CH2O repeating units satisfies 5≤m≤100, the positive electrode sheet has excellent bonding strength and is conducive to further improving the flexibility of the positive electrode sheet.

[0209] It can be seen from Examples 1, 7-8 that when the unsaturated carboxylic acid ester monomer includes one or more of methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 3-hydroxypropyl acrylate, 5-hydroxypentyl acrylate, and 6-methylheptyl acrylate, the positive electrode sheet has excellent adhesion and flexibility.

[0210] It can be seen from Examples 1, 9-10 that when the weight average molecular weight of the polymer is 200,000-400,000, the positive electrode sheet has both excellent bonding strength and flexibility.

[0211] It can be seen from Examples 1 and 11-13 that when the mass proportion of the polymer is 0.5%-2% based on the total mass of the positive electrode film layer, the positive electrode sheet has both excellent bonding strength and flexibility.

[0212] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, characterized in that: The positive electrode film layer includes a binder, and the binder includes a polymer containing an A structural unit and a B structural unit. The A structural unit is derived from a polyimide having a carbon-carbon double bond at at least one end, and the B structural unit is derived from an unsaturated carboxylic acid ester monomer.

2. The secondary battery according to claim 1, wherein The polyimide having a carbon-carbon double bond at at least one end includes a structure shown in Formula I, wherein R1 is selected from a substituted or unsubstituted tetravalent C6-C 24 aromatic group, R2 is selected from substituted or unsubstituted divalent C6-C 24 An aromatic group, at least one of R3 and R4 is a residue of a capping agent containing an amino group and a carbon-carbon double bond, and 50≤n≤600.

3. The secondary battery according to claim 2, wherein The end-capping agent containing an amino group and a carbon-carbon double bond includes one or more of amino polyethylene glycol acrylate, 2-aminoethyl methacrylate hydrochloride, and 3-aminomethyl acrylate.

4. The secondary battery according to claim 2 or 3, characterized in that The end-capping agent containing amino group and carbon-carbon double bond includes amino polyethylene glycol acrylate, The amino polyethylene glycol acrylate contains m CH2CH2O repeating units, 5≤m≤100.

5. The secondary battery according to any one of claims 1 to 4, characterized in that Based on the total mass of the A structural unit and the B structural unit of the polymer, the mass proportion of the A structural unit is 10%-90%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that The unsaturated carboxylate monomer includes the structure shown in Formula II, wherein R5, R6, and R7 are each independently hydrogen or substituted or unsubstituted C 1-5 Alkyl, R8 includes C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more alkoxy groups.

7. The secondary battery according to claim 6, characterized in that The structure shown in formula II includes one or more of methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 3-hydroxypropyl acrylate, 5-hydroxypentyl acrylate, and 6-methylheptyl acrylate.

8. The secondary battery according to any one of claims 1 to 7, characterized in that Based on the total mass of the A structural unit and the B structural unit of the polymer, the mass proportion of the B structural unit is 10%-90%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that The weight average molecular weight of the polymer is 200,000-400,000.

10. The secondary battery according to any one of claims 1 to 9, characterized in that The preparation method of the polymer comprises the following steps: The polymer containing the A structural unit and the B structural unit is obtained by polymerizing a polyimide having a carbon-carbon double bond at at least one end with an unsaturated carboxylic acid ester monomer.

11. The secondary battery according to claim 10, wherein The preparation method of the polyimide having a carbon-carbon double bond at at least one end comprises the following steps: reacting at least one diamine, at least one dibasic anhydride, and at least one end-capping agent containing an amino group and a carbon-carbon double bond to obtain a polyamic acid having a carbon-carbon double bond at at least one end; The polyamic acid having a carbon-carbon double bond at at least one end is dehydrated to obtain the polyimide having a carbon-carbon double bond at at least one end.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: Based on the total mass of the positive electrode film layer, the mass proportion of the polymer is 0.5%-2%.

13. The secondary battery according to any one of claims 1 to 12, characterized in that: The positive electrode film layer further comprises a positive electrode active material, and the positive electrode active material comprises lithium-containing phosphate, lithium transition metal oxide and their respective modified materials.

14. An electrical device, characterized in that: The electric device includes the secondary battery according to any one of claims 1 to 13.

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