Block copolymer of bab type, method of preparation, adhesive, positive electrode slurry, positive electrode sheet, secondary battery, and electric device

Abstract

The present application provides a BAB type block copolymer, a preparation method, an adhesive, a positive electrode slurry, a positive electrode sheet, a secondary battery and an electrical device. The BAB type block copolymer comprises an A-block and a B-block, the B-block comprises a structural unit shown in Formula I, and the A-block comprises one or more of structural units shown in Formula II, Formula III and Formula IV, wherein R1, R2 and R3 are each independently selected from one or more of hydrogen, fluorine, C 1‑3 alkyl containing at least one fluorine atom, R4 is each independently selected from substituted C 6‑25 aromatic group, R5, R6, R7 and R8 are each independently selected from substituted or unsubstituted C 2‑24 alkyl, substituted or unsubstituted C 6‑25 aromatic group. Using the block copolymer as an adhesive can reduce the sheet resistance of the electrode sheet, improve the liquid absorption rate of the electrode sheet, inhibit the dissolution of transition metals in the positive electrode active material, and further improve the cycle performance and storage performance of the battery.

Description

[0001] This application is a divisional application based on the invention application with application number 202211205884.5, application date September 30, 2022, entitled "BAB type block copolymer, preparation method, binder, positive electrode sheet, secondary battery and power device". Technical Field

[0002] This application relates to the field of secondary battery technology, and in particular to a BAB-type block copolymer, a preparation method, a binder, a positive electrode slurry, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0003] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the increasing application of rechargeable batteries, higher requirements have been placed on their energy density and cycle performance.

[0004] Binders are commonly used materials in secondary batteries, widely applied to battery electrodes, separators, and encapsulation. Currently, the most widely used binder in the positive electrode of secondary batteries is polyvinylidene fluoride (PVDF), but it is expensive, has poor dispersibility, and existing binders cannot meet the requirements for battery use and storage under high voltage or extreme high temperature conditions. Therefore, existing binders still need improvement. Summary of the Invention

[0005] This application was made in view of the above-mentioned problems, and its purpose is to provide a BAB-type block copolymer, which, when used as a binder, can reduce the film resistance of the electrode, increase the liquid absorption rate of the electrode, suppress the dissolution of transition metals in the positive electrode active material, and thereby improve the cycle performance and storage performance of the battery.

[0006] The first aspect of this application provides a BAB-type block copolymer comprising A-blocks and B-blocks, wherein the B-blocks comprise structural units represented by Formula I, and the A-blocks comprise one or more of structural units represented by Formula II, Formula III, and Formula IV.

[0007]

[0008] R1, R2, and R3 are each independently selected from hydrogen, fluorine, or C atoms containing at least one fluorine atom. 1-3 One or more of the alkyl groups, R4 is selected from substituted C. 6-25 The aromatic groups R5, R6, R7, and R8 are each independently selected from substituted or unsubstituted C4 groups. 2-24 Alkyl, substituted or unsubstituted C 6-25 Aromatic groups.

[0009] Binders prepared using BAB-type block copolymers can maximize the weight-average molecular weight of fluorinated and non-fluorinated blocks, fully leveraging the advantages of both fluorinated and non-fluorinated binders to achieve a complementary effect. Simultaneously, BAB-type block copolymers can utilize the steric hindrance between B-blocks and A-blocks to reduce binder aggregation and improve the uniformity of material dispersion in the electrode. Binders prepared using these BAB-type block copolymers can reduce the film resistance of the electrode, increase the electrolyte absorption rate, and inhibit the dissolution of transition metals in the positive electrode active material, thereby improving the cycle performance and storage performance of the battery. Furthermore, compared to simple blending of fluorinated and non-fluorinated polymers, BAB-type block copolymers can effectively suppress the stratification of polymers with different structural units during slurry preparation through the interaction between blocks.

[0010] In any embodiment, the block copolymer has each B-block having a mass percentage of 15% to 35% and each A-block having a mass percentage of 30% to 70%, based on the total mass of the block copolymer.

[0011] BAB-type block copolymers with appropriate mass percentages of B-blocks and A-blocks enable the electrodes to simultaneously possess excellent adhesion, good liquid absorption rate, and low membrane resistance, resulting in batteries with excellent cycle performance, high-temperature storage performance, and safety performance.

[0012] In any embodiment, the block copolymer has a weight-average molecular weight of 400,000 to 2,000,000.

[0013] BAB-type block copolymers with a suitable weight-average molecular weight enable the electrodes to simultaneously possess excellent liquid absorption rate, good adhesion, and low membrane resistance, resulting in batteries with both excellent cycle performance and storage performance.

[0014] In any embodiment, the A-block comprises a structural unit of formula II containing a trifluoromethyl group.

[0015] In any embodiment, the structural unit of formula II containing trifluoromethyl is

[0016]

[0017] One or more of them.

[0018] The A-block contains structural units of Formula II containing trifluoromethyl groups, which enables BAB-type block copolymers to further improve the adhesion and liquid absorption rate of the electrode, reduce the film resistance of the electrode, effectively suppress the dissolution of transition metals in the positive electrode active material, and improve the cycle performance, high-temperature storage performance and safety performance of the battery.

[0019] In any embodiment, the A-block comprises a structural unit of Formula II containing a sulfone group.

[0020] In any embodiment, the sulfone-containing structural unit of Formula II is selected from...

[0021] One or more of them.

[0022] The A-block contains structural units of Formula II containing sulfone groups, which enables BAB-type block copolymers to further improve the adhesion and liquid absorption rate of the electrode, reduce the film resistance of the electrode, inhibit the dissolution of transition metals in the positive electrode active material, and improve the cycle performance and high-temperature storage performance of the battery.

[0023] In any embodiment, the structural unit shown in Formula I is derived from one or more of vinylidene fluoride, tetrafluoroethylene, and vinyl fluoride.

[0024] A second aspect of this application also provides a method for preparing a BAB-type block copolymer, characterized by comprising the following steps:

[0025] Preparation of B-blocks: B-blocks are prepared by polymerizing at least one monomer of formula V.

[0026]

[0027] A1, A2, and A3 are each independently selected from hydrogen, fluorine, and C atoms containing at least one fluorine atom. 1-3 One or more of alkyl groups;

[0028] Preparation of A-block: A-block is prepared by polymerizing at least one diamine and at least one diacid or at least one diacid, or by ring-opening polymerization of lactam monomers;

[0029] Preparation of BAB-type block copolymers: B-blocks and A-blocks are joined to prepare BAB-type block copolymers.

[0030] Compared to traditional copolymerization methods, this preparation method maximizes the weight-average molecular weight of both fluorinated and non-fluorinated blocks, fully leveraging the advantages of both fluorinated and non-fluorinated binders to achieve a complementary effect. The raw materials used in this method are inexpensive, reducing costs and environmental pollution, and contributing to increased binder production. Furthermore, using the BAB-type block copolymer prepared by this method as a binder enables the electrode to possess excellent liquid absorption capacity, good adhesion, and low membrane resistance, thereby improving the battery's cycle performance, high-temperature storage performance, and safety performance.

[0031] In any embodiment, the preparation of the B-block specifically includes:

[0032] At least one monomer of formula V, a chain transfer agent, and an initiator are subjected to reversible addition-cracking chain transfer polymerization at a reaction temperature of 70–90 °C for 5–8.5 hours to obtain a B-block with an azide group or alkynyl group at one end.

[0033] Controlled polymerization is achieved using reversible addition-cracking chain transfer polymerization, resulting in a narrow molecular weight distribution of the product. Furthermore, through the above reaction, the B-block only has an alkynyl or azide group at its end, which facilitates efficient and mild directional bonding with the A-block to generate a BAB-type triblock copolymer.

[0034] In any embodiment, the preparation of the A-block specifically includes:

[0035] The catalyst, at least one diamine, at least one diacid or at least one diacid are stirred at room temperature for 4 to 10 hours, and then heated to 170 to 210°C for 5 to 20 hours to obtain a product with anhydride, carboxyl or amino groups at both ends.

[0036] The end groups of the product are functionalized to obtain the A-block having alkynyl or azide groups at both ends.

[0037] In any embodiment, the preparation of the A-block specifically includes:

[0038] The end-group regulator, water, and at least one lactam monomer are polymerized at a reaction temperature of 250°C to 280°C for 12 to 24 hours to obtain a product with carboxyl or amino end groups at both ends.

[0039] The end groups of the product are functionalized to obtain the A-block having alkynyl or azide groups at both ends.

[0040] The A-blocks prepared by this method, which are azidified or alkynylated at both ends, can be linked with B-blocks in a highly efficient and mild manner to form BAB-type block copolymers.

[0041] In any embodiment, the preparation of the BAB-type block copolymer specifically includes:

[0042] A-blocks with alkynyl or azido groups at both ends are mixed with B-blocks with azido or alkynyl groups at one end, and a click reaction is carried out to prepare BAB-type block copolymers, wherein the B-blocks and A-blocks have different end groups.

[0043] The above preparation method has the advantages of high yield, harmless by-products, simple and mild reaction conditions, and readily available reaction raw materials. It can realize the controlled polymerization of block polymers, which is beneficial to improving the yield of products.

[0044] In any embodiment, the chain transfer agent is a RAFT chain transfer agent containing a terminal alkynyl group or an azide group.

[0045] In any embodiment, the end-group regulator is a diamine or a dicarboxylic acid.

[0046] A third aspect of this application provides an application of a BAB-type block copolymer in a secondary battery, wherein the secondary battery optionally includes at least one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, and a potassium-ion battery.

[0047] A fourth aspect of this application provides a positive electrode sheet, including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive active material, a conductive agent, and a binder, wherein the binder is a BAB-type block copolymer in any embodiment or a BAB-type block copolymer prepared by any method in any embodiment.

[0048] This positive electrode has excellent liquid absorption rate and good adhesion, as well as excellent film resistance and transition metal dissolution.

[0049] In any embodiment, the binder is 0.1% to 3% by mass, based on the total mass of the positive electrode active material.

[0050] By controlling the mass percentage of the binder within a suitable range, the electrode can exhibit excellent liquid absorption rate, good adhesion, and low film resistance. Furthermore, the binder in the electrode can inhibit the dissolution of transition metals from the active material, thereby improving the battery's cycle performance, high-temperature storage performance, and safety performance.

[0051] In any embodiment, the adhesion force per unit length between the positive electrode film layer and the positive electrode current collector is not less than 11.5 N / m, and can be selected as 11.5-15 N / m.

[0052] The positive electrode film layer of this electrode has high bonding strength with the positive electrode current collector. During use, the positive electrode film layer is not easy to fall off the positive electrode current collector, which helps to improve the cycle performance and safety of the battery.

[0053] In any embodiment, the positive electrode plate has an electrolyte absorption rate greater than 0.31 μg / s, optionally between 0.32 and 0.5 μg / s, and the electrolyte density is 1.1-1.2 g / cm³. 3 .

[0054] This electrode has a high liquid absorption rate, which can improve the electrolyte wetting efficiency of the electrode, improve the ion transport path, reduce the interface resistance, and improve battery performance.

[0055] In a fifth aspect of this application, a secondary battery is provided, comprising an electrode assembly and an electrolyte, wherein the electrode assembly includes a separator, a negative electrode, and a positive electrode according to a fourth aspect of this application.

[0056] In a sixth aspect of this application, a battery module is provided, including the secondary battery of the fifth aspect of this application.

[0057] In a seventh aspect of this application, a battery pack is provided, including the battery module of the sixth aspect of this application.

[0058] In an eighth aspect of this application, an electrical device is provided, comprising at least one of the secondary battery of the fifth aspect of this application, the battery module of the sixth aspect, or the battery pack of the seventh aspect. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of a method for preparing a BAB-type block copolymer according to an embodiment of this application;

[0060] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0061] Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0062] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0063] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0064] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0065] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0066] Explanation of reference numerals in the attached figures:

[0067] 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 BAB type block copolymer; 61A-block; 611A-terminal groups of block; 612 Structural unit shown in formula II, III or IV; 62B-block; 621B-terminal group of block; 622 Structural unit shown in formula I. Detailed Implementation

[0068] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0069] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0071] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0072] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0073] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0074] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0075] In current technologies, polyvinylidene fluoride (PVDF) is commonly used as an electrode binder. However, PVDF binders are expensive and cannot be recycled on a large scale due to environmental policy restrictions. Furthermore, PVDF binders are difficult to form an effective protective layer for the positive electrode active material, failing to effectively suppress side reactions between the positive electrode active material and the electrolyte, as well as the dissolution of transition metals from the positive electrode active material. This leads to problems such as cell gas generation, volume deformation, and transition metal deposition on the negative electrode, negatively impacting the battery's cycle performance and safety.

[0076] [Adhesive]

[0077] Based on this, this application provides a BAB-type block copolymer comprising A-blocks and B-blocks, wherein the B-blocks comprise the structural unit shown in Formula I, and the A-blocks comprise one or more of the structural units shown in Formula II, Formula III, and Formula IV.

[0078]

[0079] R1, R2, and R3 are each independently selected from hydrogen, fluorine, or C atoms containing at least one fluorine atom. 1-3 One or more of the alkyl groups, R4 is selected from substituted C. 6-25 The aromatic groups R5, R6, R7, and R8 are each independently selected from substituted or unsubstituted C4 groups.2-24 Alkyl, substituted or unsubstituted C 6-25 Aromatic groups.

[0080] In this paper, the term "block copolymer" refers to a special type of polymer prepared by linking two or more polymer segments with different properties together. Block polymers with specific structures exhibit properties different from simple linear polymers, as well as mixtures of many random copolymers and even homopolymers. Common types include AB and BAB types, where A and B are long segments; there are also (AB)n type multi-segment copolymers, where A and B segments are relatively short.

[0081] In this document, the term "BAB-type block copolymer" refers to a triblock copolymer with an A-block in the middle and B-blocks on both sides. The B-blocks and A-blocks are polymer segments with a predetermined degree of polymerization formed by polymerization of different monomers. In some embodiments, the B-blocks are long-sequence segments formed by polymerization of one or more fluorinated monomers, and the A-blocks are long-sequence segments formed by polymerization of one or more non-fluorinated monomers. The B-blocks and A-blocks are covalently bonded in an ordered manner to form the BAB-type block copolymer. As an example, in a BAB-type block polymer, the B-block is polyvinylidene fluoride, which is polymerized from vinylidene fluoride monomers and has a weight-average molecular weight of 100,000 to 500,000; the A-block is polyimide, which is polymerized from dianhydride monomers and diamine monomers and has a weight-average molecular weight of 200,000 to 1,000,000; the end groups on both sides of the B-block and A-block are bonded to obtain a polyvinylidene fluoride-polyimide-polyvinylidene fluoride block copolymer (BAB-type block copolymer), which has a weight-average molecular weight of 400,000 to 2,000,000.

[0082] In this document, the term "polymer" includes, on the one hand, an aggregate of chemically homogeneous macromolecules prepared by polymerization reactions, but differing in degree of polymerization, molar mass, and chain length. On the other hand, the term also includes derivatives of such aggregates of macromolecules formed by polymerization reactions, i.e., compounds that can be obtained through reactions of the functional groups in the aforementioned macromolecules, such as addition or substitution, and which may be chemically homogeneous or chemically heterogeneous.

[0083] In this article, the term "C" 1-3 "Alkyl" refers to a straight-chain or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms. The group is not unsaturated, has one to three carbon atoms, and is attached to the rest of the molecule by single bonds. C 1-3 Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl). The term "C2-C" is also relevant. 24 The term "alkyl" should be interpreted accordingly.

[0084] In this document, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is replaced by a substituent in another chemical moiety, wherein each substituent is independently selected from: hydroxyl, mercapto, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C 1-6 Alkyl, C 1-6 Alkyl group.

[0085] In this article, the term "C" 6-25 "Aromatic group" refers to an aromatic ring system with at least one aromatic ring, including but not limited to phenyl, biphenyl, indanyl, 1-naphthyl, 2-naphthyl and tetrahydronaphthyl.

[0086] In this article, C is replaced 6-25 The aromatic groups include, but are not limited to, aralkyl, aralkoxy, aryloxyalkyl, and symmetrical or asymmetrical aryl groups linked by carbonyl or ether groups.

[0087] In some embodiments, the structural unit shown in Formula I is selected from one or more of vinylidene fluoride, tetrafluoroethylene, and vinyl fluoride.

[0088] In some embodiments, the structural unit shown in Formula II is selected from...

[0089]

[0090] In some embodiments, the structural unit shown in Equation III is selected from...

[0091]

[0092] In some embodiments, the structural unit shown in Equation IV is selected from...

[0093]

[0094] In some embodiments, the BAB-type block copolymer is used as a binder in the secondary battery. In some embodiments, the BAB-type block copolymer is used as an electrode binder in the secondary battery.

[0095] In this document, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0096] In some embodiments, the dispersion medium of the binder is an aqueous solvent, such as water. That is, the binder is dissolved in an aqueous solvent.

[0097] In some embodiments, the dispersion medium for the binder is an oily solvent, examples of which include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate. That is, the binder is dissolved in an oily solvent.

[0098] In some embodiments, an adhesive is used to hold electrode materials and / or conductive agents in place and adhere them to a conductive metal component to form an electrode.

[0099] In some embodiments, the binder serves as a positive electrode binder, used to bond the positive electrode active material and / or conductive agent to form an electrode.

[0100] In some embodiments, the binder serves as a negative electrode binder, used to bond the negative electrode active material and / or conductive agent to form an electrode.

[0101] The fluorine in the B-block forms hydrogen bonds with the hydroxyl and carboxyl groups on the surface of the positive electrode active material and the current collector, giving the electrode excellent adhesion. The A-block contains abundant carbonyl groups, which can form intermolecular hydrogen bonds. These hydrogen bonds interact with the hydroxyl groups on the surface of the positive electrode active material and the current collector, resulting in excellent adhesion and improved stability of the positive electrode. In addition, the abundant carbonyl groups give the binder excellent flexibility, reducing the shedding of active material due to changes in electrode volume during charging and discharging, thereby improving the battery's cycle capacity retention.

[0102] In some implementations, the A-block includes at least the structural unit shown in Formula II.

[0103] The imide bonds in the A-block enhance the electrode's liquid absorption capacity and wettability with the electrolyte, facilitating the formation of a conductive network and reducing the electrode's film resistance. Furthermore, the highly polar imide bonds improve the electrochemical and thermal stability of the binder, effectively suppressing the physical expansion of the electrode caused by ion insertion and extraction during electrochemical reactions. Simultaneously, the A-block containing imide bonds has a relatively low surface energy, resulting in good film-forming properties. It can uniformly coat the surface of the positive electrode active material, reducing active sites on the surface, minimizing side reactions and transition metal dissolution, thereby improving the electrode's cycle performance, high-temperature storage performance, and reducing gas generation at high temperatures.

[0104] In some implementations, the A-block contains at least the structural unit shown in Formula III or Formula IV.

[0105] The amide bonds in the A-block enhance the electrode's liquid absorption capacity and wettability with the electrolyte, facilitating the formation of a conductive network and reducing the electrode's film resistance. Furthermore, the highly polar amide bonds improve the electrochemical and thermal stability of the binder, effectively suppressing the physical expansion of the electrode caused by ion insertion and extraction during electrochemical reactions. Simultaneously, when the binder coats the surface of the active material, it reduces side reactions between the active material and the electrolyte, inhibits the dissolution of transition metals from the active material, thereby improving the electrode's cycle performance, high-temperature storage performance, and gas generation performance.

[0106] Binders prepared using BAB-type block copolymers can maximize the weight-average molecular weight of fluorinated and non-fluorinated blocks, fully leveraging the advantages of both fluorinated and non-fluorinated binders to achieve a complementary effect. Simultaneously, BAB-type block copolymers can utilize the steric hindrance between B-blocks and A-blocks to reduce binder aggregation and improve the uniformity of material dispersion in the electrode. Binders prepared using these BAB-type block copolymers can reduce the film resistance of the electrode, increase the electrolyte absorption rate, and inhibit the dissolution of transition metals in the positive electrode active material, thereby improving the cycle performance and storage performance of the battery. Furthermore, compared to simple blending of fluorinated and non-fluorinated polymers, BAB-type block copolymers can effectively suppress the stratification of polymers with different structural units during slurry preparation through the interaction between blocks.

[0107] In some embodiments, the block copolymer contains 15% to 35% by mass of each B-block and 30% to 70% by mass of each A-block, based on the total mass of the block copolymer.

[0108] In some embodiments, the mass percentage of each B-block in the block copolymer can be selected as any one of 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, or 35%, based on the total mass of the block copolymer.

[0109] In some embodiments, the mass percentage of A-blocks in the block copolymer can be selected as any one of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, based on the total mass of the block copolymer.

[0110] If the mass percentage of B-block is too high and the mass percentage of A-block is too low, the A-block cannot fully play its role in increasing liquid absorption rate, reducing film resistance, and inhibiting the dissolution of transition metals in active materials, thus failing to effectively improve the cycle performance and safety performance of the battery. If the mass percentage of B-block is too low and the mass percentage of A-block is too high, the adhesion of the electrode and the cycle stability of the battery will decrease.

[0111] BAB-type block copolymers with appropriate mass percentages of B-blocks and A-blocks enable the electrodes to simultaneously possess excellent adhesion, good liquid absorption rate, and low membrane resistance, resulting in batteries with excellent cycle performance, high-temperature storage performance, and safety performance.

[0112] In some embodiments, the weight-average molecular weight of the BAB-type block copolymer is 400,000 to 2,000,000. In some embodiments, the weight-average molecular weight of the BAB-type block copolymer can be selected from any one of the following: 400,000 to 600,000, 600,000 to 800,000, 800,000 to 1,000,000, 1,000,000 to 1,200,000, 1,200,000 to 1,400,000, 1,400,000 to 1,600,000, 1,600,000 to 1,800,000, 1,800,000 to 2,000,000, 600,000 to 900,000, 900,000 to 1,200,000, 1,200,000 to 1,500,000, 1,500,000 to 1,800,000, and 1,200,000 to 2,000,000.

[0113] In this paper, the term "weight-average molecular weight" refers to the sum of the products of the weight fraction of molecules of different molecular weights in a polymer and their corresponding molecular weights.

[0114] If the weight-average molecular weight of the BAB-type block copolymer is too high, the binder will be difficult to dissolve and will easily agglomerate with the conductive agent, resulting in excessively high slurry viscosity, making it difficult to coat evenly and hindering subsequent electrode processing. If the weight-average molecular weight of the BAB-type block copolymer is too low, it will be difficult to form a three-dimensional network bonding structure, failing to provide effective bonding and dispersion, which is detrimental to the formation of the conductive network, leading to increased film resistance of the electrode and decreased cycle performance, high-temperature storage performance, and gas generation performance of the battery.

[0115] BAB-type block copolymers with a suitable weight-average molecular weight enable the electrodes to simultaneously possess excellent liquid absorption rate, good adhesion, and low membrane resistance, resulting in batteries with both excellent cycle performance and storage performance.

[0116] In some embodiments, the A-block comprises a structural unit of formula II containing a trifluoromethyl group.

[0117] In some embodiments, the structural unit of formula II containing trifluoromethyl groups may be selected from...

[0118]

[0119] One or more of them.

[0120] In this article, the term "trifluoromethyl" refers to the "-CF3" group.

[0121] In this paper, the term "sulfone group" refers to the "-SO2-" group.

[0122] In this article, the term "ether bond" refers to "-O-".

[0123] The inclusion of a trifluoromethyl group (Formula II) in the A-block enhances the ion transfer capability of the binder, improves the liquid absorption rate of the electrode, and reduces the film resistance of the electrode. Simultaneously, the fluorine in the trifluoromethyl group can form hydrogen bonds with residual carboxyl and hydroxyl groups on the surface of the active material and current collector, further improving the binder's adhesion. Furthermore, the trifluoromethyl group in the A-block improves the electrochemical and thermal stability of the binder, inhibits the dissolution of transition metals in the positive electrode active material, effectively suppresses the physical expansion of the electrode caused by ion insertion and extraction during electrochemical reactions, and improves the battery's cycle performance, high-temperature storage performance, and gas generation performance.

[0124] The A-block contains structural units of Formula II containing trifluoromethyl groups, which enables BAB-type block copolymers to further improve the adhesion and liquid absorption rate of the electrode, reduce the film resistance of the electrode, effectively suppress the dissolution of transition metals in the positive electrode active material, and improve the cycle performance, high-temperature storage performance and safety performance of the battery.

[0125] In some embodiments, the A-block comprises a structural unit of Formula II containing a sulfone group.

[0126] In some embodiments, the sulfone-containing structural unit of Formula II may be selected from...

[0127]

[0128] One or more of them.

[0129] The sulfone group has a strong electron-withdrawing effect, which can enhance the binding ability of the electrode and the conductive ions in the active material, improve the adhesion of the electrode, and at the same time, the sulfone group can increase the electrolyte absorption rate of the electrode, resulting in a lower film resistance. The sulfone group can also enhance the stability of the imide bond structure, improve the structural stability of the binder during electrode charge and discharge, and thus improve the battery's cycle performance, high-temperature storage performance, and safety performance.

[0130] The A-block contains structural units of Formula II containing sulfone groups, which enables BAB-type block copolymers to further improve the adhesion and liquid absorption rate of the electrode, reduce the film resistance of the electrode, inhibit the dissolution of transition metals in the positive electrode active material, and improve the cycle performance and high-temperature storage performance of the battery.

[0131] In some embodiments, the A-block comprises a structural unit of Formula II containing an ether bond.

[0132] The structural unit shown in Formula II contains ether bonds, which helps to improve the flexibility of the binder and enhance the cycle performance and gas generation performance of the battery.

[0133] One embodiment of this application provides a method for preparing a BAB-type block copolymer, comprising the following steps:

[0134] Preparation of B-blocks: B-blocks are prepared by polymerizing at least one monomer of formula V.

[0135]

[0136] A1, A2, and A3 are each independently selected from hydrogen, fluorine, and C atoms containing at least one fluorine atom. 1-3 One or more of alkyl groups;

[0137] Preparation of A-block: A-block is prepared by polymerizing at least one diamine and at least one diacid or at least one diacid, or by ring-opening polymerization of lactam monomers;

[0138] Preparation of BAB-type block copolymers: B-blocks and A-blocks are joined to prepare BAB-type block copolymers.

[0139] In some embodiments, a schematic diagram of the preparation method of BAB-type block copolymer 6 is shown below. Figure 1 As shown, the two end groups 611 of the A-block 61 containing the structural unit 612 of Formula II, Formula III or Formula IV are active groups, and the end group 621 of the B-block 62 containing the structural unit 622 of Formula I is an active group. The two end groups 611 of the A-block react with the end group 621 of the B-block to achieve the bonding of polymer chain segments, thereby preparing the BAB type block copolymer 6.

[0140] In this article, the term "diamine" refers to an amine containing two amino groups.

[0141] In some embodiments, the diamine is an aliphatic diamine or an aromatic diamine, which may be selected as follows:

[0142]

[0143] One or more of them.

[0144] In this article, the term "dihydric anhydride" refers to a monomer containing two anhydrides.

[0145] In some embodiments, the dihydric anhydride is an aromatic dianhydride, which may be selected as...

[0146]

[0147] One or more of them.

[0148] In this article, the term "diacarboxylic acid" refers to a monomer containing two carboxyl groups. Diacarboxylic acids can be selected from aromatic or aliphatic diacarboxylic acids, such as one or more of adipic acid, sebacic acid, terephthalic acid, and isophthalic acid.

[0149] This preparation method uses inexpensive raw materials, which can reduce costs and environmental pollution, and is conducive to increasing binder production. Furthermore, using the BAB-type block copolymer prepared by this method as a binder enables the electrode to have excellent liquid absorption capacity, good adhesion, and low film resistance, thereby improving the battery's cycle performance, high-temperature storage performance, and safety performance.

[0150] In some embodiments, the preparation of the B-block specifically includes:

[0151] At least one monomer of Formula V, a chain transfer agent, and an initiator are subjected to reversible addition-cracking chain transfer polymerization to obtain B-blocks with azide or alkynyl groups at one end.

[0152] In some embodiments, the reaction temperature for reversible addition-cracking chain transfer polymerization is 70–90°C, and the reaction time is 5–8.5 hours.

[0153] In some embodiments, the preparation of the B-block specifically includes:

[0154] At least one monomer of formula V, a chain transfer agent, and an initiator are subjected to reversible addition-cracking chain transfer polymerization at a reaction temperature of 70–90 °C for 5–8.5 hours to obtain a B-block with an azide group or alkynyl group at one end.

[0155] In this paper, the term "azido group" refers to the -N3 group.

[0156] In this paper, the term "alkynyl" refers to the -C≡CH group.

[0157] In this paper, the term "reversible addition-fracture chain transfer polymerization" (RAFT polymerization) refers to a type of reversible deactivated free radical polymerization, also known as "living / controlled free radical polymerization." The main principle of RAFT polymerization is to add a RAFT reagent as a chain transfer agent during free radical polymerization. This protects easily terminated free radicals through chain transfer, transforming most free radicals into dormant free radicals during the polymerization reaction. During the reaction, dormant and active segments coexist and rapidly switch between each other through a dynamic and reversible reaction. This results in only a small number of polymer chains existing as active chains and growing at any given time, ultimately making the growth probability of each polymer chain segment approximately equal, thus exhibiting the characteristics of living polymerization.

[0158] In some embodiments, the monomer represented by Formula V is one or more of vinylidene fluoride, tetrafluoroethylene, and vinyl fluoride.

[0159] In some embodiments, the synthetic route of the B-block is shown in the schematic diagram below, wherein the chain transfer agent is a trithiocarbonate, Z' is an active group with a terminal alkynyl or azide group, and R is an alkyl group. The B-block with a terminal alkynyl or azide group was prepared by the following reaction.

[0160]

[0161] Reversible addition-cracking chain transfer polymerization enables controlled polymerization and produces products with a narrow molecular weight distribution. Furthermore, through the above reaction, the B-block only has an alkynyl or azide group at its end, which facilitates efficient and mild directional bonding with the A-block to generate BAB-type triblock copolymers.

[0162] This preparation method enables controlled polymerization and produces products with a narrow molecular weight distribution.

[0163] In some embodiments, the preparation of the A-block specifically includes:

[0164] Polymerize at least one diamine and at least one diacid or at least one diacid to obtain a product with anhydride, carboxyl or amino groups at both ends.

[0165] The end groups of the product are functionalized to obtain the A-block having alkynyl or azide groups at both ends.

[0166] In some embodiments, the polymerization conditions for at least one diamine and at least one diacid or at least one diacid are: stirring at room temperature for 4 to 10 hours, followed by further heating to 170 to 210°C for 5 to 20 hours.

[0167] In some embodiments, the preparation of the A-block specifically includes:

[0168] The catalyst, at least one diamine, and at least one diacid or at least one diacid are stirred and reacted at room temperature for 4 to 10 hours, and then heated to 170 to 210°C and reacted for 5 to 20 hours to obtain a product with anhydride, carboxyl or amino groups at both ends.

[0169] The end groups of the product are functionalized to obtain the A-block having alkynyl or azide groups at both ends.

[0170] In some embodiments, the synthetic route for the A-block involves polymerizing at least one diamine and at least one diacid in the presence of a catalyst to generate a polyimide, with the diamine or diacid in excess, resulting in a polyimide with amino or anhydride end groups at both ends. The amino or anhydride end groups then undergo a functionalization reaction with an active monomer containing an azide or alkynyl group to prepare an A-block with an azide or alkynyl group at both ends. It is understood that the active monomer containing an azide or alkynyl group refers to a monomer containing an azide or alkynyl group and an active functional group capable of reacting with the amino or anhydride end groups of the polyimide. The active functional group reacting with the amino group can be any one of epoxy, carboxyl, anhydride, isocyanate, or carbonyl chloride. The active functional group reacting with the anhydride can be an amino group.

[0171] In this article, the term "amino" refers to the -NH2 group.

[0172] In this article, the term "anhydride" refers to the -CO-O-CO- group.

[0173] In this article, the term "epoxy group" refers to the -CH-O-CH- group.

[0174] In this article, the term "carboxyl group" refers to the -COOH group.

[0175] In this article, the term "isocyanate group" refers to the -NCO group.

[0176] In this article, the term "carbonyl chloride" refers to the -COCl group.

[0177] In this article, the term "imino" refers to the "-NH-" group.

[0178] In some embodiments, the synthetic route for the A-block involves a polycondensation reaction of at least one diamine and at least one diacid in the presence of a catalyst to generate a polyamide, with the diamine or diacid in excess, resulting in a polyamide with amino or carboxyl groups at both ends. The amino or carboxyl groups at both ends then undergo a functionalization reaction with an active monomer containing an azide or alkynyl group to prepare an A-block with azide or alkynyl groups at both ends. It is understood that the active monomer containing an azide or alkynyl group refers to a monomer containing an azide or alkynyl group and an active functional group capable of reacting with the amino or carboxyl groups at both ends of the polyamide. The active functional group reacting with the amino group can be any one of epoxy, carboxyl, acid anhydride, isocyanate, or carbonyl chloride. The active functional group reacting with the carboxyl group can be an amino or imino group.

[0179] In some embodiments, the catalyst may be any one of quinoline, isoquinoline, or tertiary amine.

[0180] In some embodiments, the preparation of the A-block specifically includes:

[0181] The end-group regulator, water, and at least one lactam monomer are subjected to a polymerization reaction to obtain a product with carboxyl or amino end groups at both ends.

[0182] The end groups of the product are functionalized to obtain A-blocks with alkynyl or azide groups at both ends.

[0183] In some embodiments, the polymerization reaction of the end-group regulator, water, and at least one lactam monomer is carried out at a reaction temperature of 250°C to 280°C for 12 to 24 hours.

[0184] In some embodiments, the preparation of the A-block specifically includes:

[0185] The end-group regulator, water, and at least one lactam monomer are polymerized at a reaction temperature of 250°C to 280°C for 12 to 24 hours to obtain a product with carboxyl or amino end groups at both ends.

[0186] The end groups of the product are functionalized to obtain A-blocks with alkynyl or azide groups at both ends.

[0187] In some embodiments, the synthetic route for the A-block is as follows: Under water catalysis, a lactam monomer undergoes ring-opening polymerization to obtain a polyamide with an amino group at one end and a carboxyl group at the other. An end-group regulator is then added to react with the polyamide to obtain a polyamide with amino or carboxyl groups at both ends. The amino or carboxyl groups at both ends undergo a functionalization reaction with an active monomer containing an azide group or an alkynyl group to prepare an A-block with an azide or alkynyl group at both ends. It can be understood that the active monomer containing an azide or alkynyl group refers to a monomer containing an azide or alkynyl group and an active functional group capable of reacting with the amino or carboxyl groups at both ends of the polyamide. The active functional group reacting with the amino group can be any one of epoxy, carboxyl, acid anhydride, isocyanate, or carbonyl chloride. The active functional group reacting with the carboxyl group can be an amino or imino group.

[0188] In some embodiments, the lactam monomer may be selected from one or more of caprolactam, octyllactam, decanolactam, and dodecalactam.

[0189] The A-blocks prepared by this method, which are azidified or alkynylated at both ends, can be linked with B-blocks in a highly efficient and mild manner to form BAB-type block copolymers.

[0190] In some embodiments, the preparation of the BAB-type block copolymer specifically includes:

[0191] A-blocks with alkynyl or azido groups at both ends are mixed with B-blocks with azido or alkynyl groups at one end, and a click reaction is carried out to prepare BAB-type block copolymers, wherein the B-blocks and A-blocks have different end groups.

[0192] In this document, the term "click reaction" refers to a cycloaddition reaction between an alkynyl group and an azide group, resulting in the a-block and B-block linkage. In some embodiments, the click reaction is carried out at room temperature and pressure in the presence of a Cu(I) catalyst.

[0193] In some embodiments, the B-block is terminally an azide group, and the A-block is terminally an alkynyl group.

[0194] In some embodiments, the B-block is terminally alkynyl and the A-block is terminally azide.

[0195] The above preparation method has the advantages of high yield, harmless by-products, simple and mild reaction conditions, and readily available reaction raw materials. It can realize the controlled polymerization of block polymers, which is beneficial to improving the yield of products.

[0196] In some embodiments, the chain transfer agent is a RAFT chain transfer agent containing a terminal alkynyl or azide group. In some embodiments, the chain transfer agent is a trithiocarbonate containing a terminal alkynyl or azide group. In some embodiments, the structural formula of the chain transfer agent is selected from the following formula:

[0197]

[0198] RAFT chain transfer agents containing terminal alkynyl or azide groups can simultaneously induce the terminal alkynyl or azide groups of B-blocks during B-block synthesis, providing a basis for click reactions between A-blocks and B-blocks, avoiding complex post-processing steps, and improving reaction efficiency.

[0199] In some implementations, the end-group regulator is a diamine or a dicarboxylic acid.

[0200] End-group regulators of diamines or diacids can react with the end groups of the product to obtain products with amino or carboxyl groups at both ends, which facilitates subsequent transformations and enables the preparation of A-blocks with azide or alkynyl groups at both ends in a simple and efficient manner.

[0201] In some embodiments, BAB-type block copolymers can be used in secondary batteries, optionally including at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

[0202] [Positive electrode plate]

[0203] The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive active material, a conductive agent, and a binder. The binder is a BAB-type block copolymer in some embodiments or a BAB-type block copolymer prepared by the preparation method in some embodiments.

[0204] This positive electrode has excellent liquid absorption rate and good adhesion, low film resistance and low transition metal dissolution.

[0205] In some embodiments, the binder is present in a mass percentage of 0.1% to 3%, based on the total mass of the positive electrode active material. In some embodiments, the mass percentage of the binder may be selected from any one of 0.1% to 0.2%, 0.2% to 1%, 0.2% to 1.03%, 1% to 3%, or 1.03% to 3%.

[0206] When the binder content is too low, the binder cannot fully exert its bonding and dispersing effects, resulting in insufficient adhesion of the electrode and increased film resistance, which negatively impacts the battery's cycle performance and high-temperature storage performance. When the binder content is too high, the slurry viscosity is too high, leading to an excessively thick binder coating layer on the surface of the positive electrode active material. This affects the transport of electrons and ions during battery cycling, increasing the internal resistance of the electrode film and affecting the battery's cycle performance and high-temperature storage performance.

[0207] By controlling the mass percentage of the binder within a suitable range, the electrode can exhibit excellent liquid absorption rate, good adhesion, and low film resistance. Furthermore, the binder in the electrode can inhibit the dissolution of transition metals from the active material, thereby improving the battery's cycle performance, high-temperature storage performance, and safety performance.

[0208] In some embodiments, the adhesion force per unit length between the positive electrode film layer and the positive electrode current collector is not less than 11.5 N / m, and can be selected as 11.5-15 N / m. In some embodiments, the adhesion force per unit length between the positive electrode film layer and the positive electrode current collector can be selected as 11.5 N / m, 12 N / m, 12.5 N / m, 13 N / m, 13.5 N / m, 14 N / m, 14.5 N / m, or 15 N / m.

[0209] The adhesion strength per unit length between the positive electrode film and the positive electrode current collector can be tested using any method known in the art, such as referring to GB-T2790-1995 "Test Method for 180° Peel Strength of Adhesives". As an example, the positive electrode sheet is cut into 20*100mm pieces. 2Test specimens of various sizes are prepared for use. One side of the positive electrode film is adhered to the electrode sheet with double-sided tape and pressed firmly with a roller to ensure complete adhesion between the tape and the electrode sheet. The other side of the double-sided tape is adhered to the stainless steel surface. One end of the specimen is bent in the opposite direction at a bending angle of 180°. A high-speed rail tensile testing machine is used. One end of the stainless steel specimen is fixed to the lower clamp of the tensile testing machine, and the bent end of the specimen is fixed to the upper clamp. The specimen angle is adjusted to ensure that the upper and lower ends are in a vertical position. Then, the specimen is stretched at a speed of 50 mm / min until the positive current collector is completely peeled off from the positive electrode film layer. The displacement and force during the process are recorded. The force at equilibrium is divided by the width of the electrode sheet adhered to the double-sided tape (the width direction of the electrode sheet is perpendicular to the peeling direction) as the adhesive force per unit length of the electrode sheet. In this test, the width of the electrode sheet is 20 mm.

[0210] The positive electrode film layer of this electrode has high bonding strength with the positive electrode current collector. During use, the positive electrode film layer is not easy to fall off the positive electrode current collector, which helps to improve the cycle performance and safety of the battery.

[0211] In some embodiments, the positive electrode has an electrolyte absorption rate greater than 0.31 μg / s, optionally 0.32-0.5 μg / s, and the electrolyte density is 1.1-1.2 g / cm³. 3 In some embodiments, the electrolyte absorption rate of the positive electrode sheet can be selected as 0.32 μg / s, 0.33 μg / s, 0.34 μg / s, 0.35 μg / s, 0.36 μg / s, 0.37 μg / s, 0.38 μg / s, 0.39 μg / s, 0.40 μg / s, 0.41 μg / s, 0.42 μg / s, 0.43 μg / s, 0.44 μg / s, 0.45 μg / s, 0.46 μg / s, 0.47 μg / s, 0.484 μg / s, 0.49 μg / s, or 0.50 μg / s, and the density of the electrolyte is 1.1-1.2 g / cm³. 3 .

[0212] The electrolyte absorption rate of an electrode reflects its wettability in the electrolyte. This test can be performed using any method known in the art. As an example, a cold-pressed positive electrode sheet is cut into 5*5cm pieces. 2 For the size test sample: First, the sample was dried at 80℃ for 4 hours. After testing the electrode thickness, it was fixed on the sample stage. Then, a capillary tube with d = 200 μm was selected, and its end face was polished to a smooth finish using 5000-grit sandpaper. The state between the capillary tube and the electrode was observed using a microscope. Electrolyte was drawn up using the capillary tube, and the electrolyte height was controlled at h = 3 mm. The capillary tube was lowered to contact the electrode while a stopwatch was used to time the process. When the liquid level had completely dropped, the timer was stopped, and the absorption time t was read and recorded. The average absorption rate v of the electrode was calculated using the formula: v = π × (d / 2). 2×h×ρ / t. In this test, the density of the electrolyte used was 1.1-1.2 g / cm³. 3 As an example, the electrolyte can be prepared by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and methyl ethyl carbonate, wherein the mass content of the lithium hexafluorophosphate solution is 12.5%, and the volume ratio of ethylene carbonate to methyl ethyl carbonate in the solution is 3:7.

[0213] This electrode has a high liquid absorption rate, which can improve the electrolyte wetting efficiency of the electrode, improve the ion transport path, reduce the interface resistance, and improve battery performance.

[0214] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0215] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0216] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0217] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0218] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0219] [Negative electrode plate]

[0220] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0221] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0222] 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0223] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0224] In some embodiments, the negative electrode film layer may optionally 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).

[0225] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0226] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0227] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0228] [Electrolytes]

[0229] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0230] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0231] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0232] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0233] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0234] [Isolation membrane]

[0235] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0236] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0237] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0238] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0239] 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. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0240] [Rechargeable Battery]

[0241] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5. The secondary battery can also be a sodium-ion battery, a magnesium-ion battery, or a potassium-ion battery.

[0242] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0243] [Battery Template]

[0244] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0245] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0246] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0247] [Electrical appliances]

[0248] In one embodiment of this application, an electrical device is provided, including at least one of a secondary battery, a battery module, or a battery pack according to any embodiment.

[0249] The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0250] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0251] Figure 7 This is an example of an electrical device. The device could be 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 for this device, a battery pack or battery module can be used.

[0252] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0253] Example

[0254] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0255] I. Preparation Method

[0256] Example 1

[0257] 1) Preparation of adhesive

[0258] Preparation of A-blocks:

[0259] 10.5 mmol of 1,4-bis(2-trifluoromethyl-4-aminophenylsulfonyl)benzene was added to a 500 mL three-necked flask, followed by 250 mL of m-cresol. After stirring for a period of time until completely dissolved, 3% (by volume) of isoquinoline catalyst was added. 10 mmol of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was slowly added to the above solution in batches, resulting in a solid content of 15% in the reaction system. The mixture was stirred at room temperature under a nitrogen atmosphere for 6 hours. After stirring at room temperature, the temperature was raised to 180 °C, and stirring was continued for 8 hours under a nitrogen atmosphere. 5 mmol of 2-azido-2-methylpropionic acid was added, and the mixture was stirred for 3 hours under a nitrogen atmosphere. After purification and drying, polyimide-1 with azido groups at both ends, i.e., the A-block, was obtained.

[0260] The structural formula of 1,4-bis(2-trifluoromethyl-4-aminophenylsulfone)benzene is:

[0261]

[0262] The structural formula of 3,3',4,4'-benzophenone tetracarboxylic dianhydride is:

[0263]

[0264] The reaction process for preparing the A-block and the structural formula of the A-block are shown below.

[0265]

[0266] Wherein, A4 is a diamine residue, A5 is a dianhydride residue, and x is the degree of polymerization of the A-block. In the A-block polyimide-1 prepared in Example 1, A4 is...

[0267] A5 is

[0268] Preparation of B-blocks:

[0269] Vinylidene fluoride monomer, RAFT chain transfer agent (CTA-alkyne), and azobisisobutyronitrile (AIBN) in a molar ratio of 700:1:0.1 were added to 500 ml of tetrahydrofuran solution. The structural formula of the RAFT chain transfer agent is shown below.

[0270]

[0271] The mixture was subjected to at least three freeze-thaw cycles and placed in an oil bath preheated to 80°C. After 6 hours of reaction, the reaction was terminated by cooling in liquid nitrogen, and the solution precipitated in a large excess of methanol. The polymer was collected by filtration and reprecipitated twice from chloroform with methanol. The resulting product was vacuum dried overnight at room temperature to remove all trace amounts of residual solvent, yielding polyvinylidene fluoride with alkynyl groups at the ends, i.e., a B-block polymer.

[0272] The reaction process for preparing the B-block is shown below.

[0273]

[0274] Preparation of BAB-type block copolymers:

[0275] Polyvinylidene fluoride with alkynyl groups at the ends, polyimide with azido groups at both ends, and CuBr were added to a dry Schlenk tube in a molar ratio of 1:2.5:4. After degassing, 4 ml of anhydrous N,N-dimethylformamide (DMF) and 0.14 mmol of N,N,N',N,'N”-pentamethyldiethylenetriamine (PMDETA) were added. The reaction was stirred at 60 °C for 3 days, and the reaction was terminated by exposure to air. The reaction mixture was filtered through a neutral alumina column to remove the copper catalyst. The solution was concentrated under reduced pressure and precipitated in a 20-fold excess of a mixed solvent (methanol and water in a 1:1 volume ratio). The product was collected by filtration and vacuum dried to obtain a BAB-type block copolymer, which was used as a battery binder.

[0276] 2) Preparation of positive electrode sheet

[0277] Lithium nickel cobalt manganese (NCM) material, conductive carbon black, binder, and N-methylpyrrolidone (NMP) were mixed evenly in a weight ratio of 96.9:2.1:1:21 to obtain a positive electrode slurry with a solid content of 73%. The positive electrode slurry was then uniformly coated onto the positive electrode current collector, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0278] 3) Preparation of negative electrode sheet

[0279] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a weight ratio of 96.2:0.8:0.8:1.2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0280] 4) Separating membrane

[0281] Polypropylene film is used as the separator.

[0282] 5) Preparation of electrolyte

[0283] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7. 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent and stirred evenly to obtain the electrolyte of Example 1.

[0284] 6) Battery manufacturing

[0285] In Example 1, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.

[0286] Examples 2-11

[0287] The battery in Example 2 is prepared in a similar manner to the battery in Example 1. However, the degree of polymerization of the B-block and A-block is adjusted by adjusting the polymerization temperature and reaction time of the B-block, as well as the molar amounts of dianhydride and diamine in the A-block. The weight-average molecular weight of the B-block and A-block is also adjusted. The specific adjustment parameters are shown in Table 1.

[0288] Examples 12-15

[0289] The batteries in Examples 12-15 were prepared using a method similar to that in Example 1, but the mass percentage of the binder was adjusted. Based on the mass of the positive electrode active material, the specific parameters are shown in Table 1.

[0290] Example 16

[0291] The battery in Example 16 was prepared in a similar manner to the battery in Example 4, except that the diamine monomer was adjusted to 9.5 mmol of 1,4-bis(4-aminophenylsulfone)benzene, so that the prepared A-block was polyimide-2 containing only sulfone groups and having azide groups at both ends. The specific parameters are shown in Table 1.

[0292] The structural formula of 1,4-bis(4-aminophenylsulfone)benzene is shown below.

[0293]

[0294] In the A-block polyimide-2 prepared in Example 16, A4 is...

[0295]

[0296] A5 is

[0297] Example 17

[0298] The battery in Example 17 was prepared in a similar manner to the battery in Example 4, except that the diamine was adjusted to 9.5 mmol of 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, so that the prepared A-block was a polyimide containing only trifluoromethyl groups and azido groups at both ends. The specific parameters are shown in Table 1.

[0299] The structural formula of 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene is shown below.

[0300]

[0301] In the A-block polyimide-3 prepared in Example 17, A4 is... A5 is

[0302] Example 18

[0303] The battery in Example 18 was prepared using a similar method to the battery in Example 4, but the A-block was replaced with a polyamide having azide groups at both ends. Specific parameters are shown in Table 1, and the preparation method is as follows:

[0304] A 4 kg aqueous solution containing 0.3% oxalic acid, 5% ethylenediamine, and 85% caprolactam was added to a 5 L stirred reactor. A large amount of nitrogen gas was introduced to remove oxygen from the system. After stirring and reacting at 250 °C for 24 hours, 5 mmol of 4-acetaminobenzenesulfonyl azide was added. After stirring under a nitrogen atmosphere for 3 hours, the mixture was purified and dried to obtain a polyamide with azide groups at both ends, namely an A-block copolymer.

[0305] The above reaction process is illustrated below:

[0306]

[0307] Example 19

[0308] The battery in Example 19 was prepared in a similar manner to the battery in Example 4, except that the diamine was changed to 1,4-bis(4-aminophenoxy)benzene, and the specific parameters are shown in Table 1.

[0309] The structural formula of 1,4-bis(4-aminophenoxy)benzene is shown below.

[0310]

[0311] In the A-block polyimide-4 prepared in Example 19, A4 is... A5 is

[0312] Comparative Example 1

[0313] The battery of Comparative Example 1 was prepared in a similar manner to the battery of Example 1, but the binder was polyvinylidene fluoride with a weight-average molecular weight of 1.2 million. The specific parameters are shown in Table 1. It was purchased from Solvay Group 5130.

[0314] Comparative Example 2

[0315] The battery of Comparative Example 2 was prepared in a similar manner to that of Example 1, but the binder was polyimide-1 with a weight-average molecular weight of 1.2 million. The specific parameters are shown in Table 1. The preparation method was similar to that of polyimide-1 in Example 1, except that the diamine content was adjusted to 24 mmol and the dianhydride content was adjusted to 24.5 mmol. The solid content in the reaction system was 15%. The mixture was stirred at room temperature under a nitrogen atmosphere for 12 hours. After stirring at room temperature, the temperature was raised to 180°C and stirred for another 20 hours under a nitrogen atmosphere. The mixture was then purified and dried to obtain a polyimide containing trifluoromethyl and sulfone groups with a weight-average molecular weight of 1.2 million.

[0316] Comparative Example 3

[0317] The battery of Comparative Example 3 was prepared using a similar method to the battery of Example 1, but the binder was a blend of polyvinylidene fluoride and polyimide. Specific parameters are shown in Table 1, and the preparation method is as follows:

[0318] Blending: Polyimide-1 in Comparative Example 2 and polyvinylidene fluoride in Comparative Example 1 were blended at a mass ratio of 6:4 to obtain a polyvinylidene fluoride and polyimide-1 blend adhesive.

[0319] II. Performance Testing

[0320] 1. Electrode performance testing

[0321] 1) Diaphragm resistance test

[0322] Cut the dried positive electrode film into small round pieces with a diameter of 3mm from the left, center, and right sides of the positive electrode. Turn on the Yuaneng Technology electrode resistance meter, place it at the appropriate position of the "probe" on the meter, and click the "start" button. Once the reading stabilizes, take the reading. Test two positions for each small round piece, and finally calculate the average of the six measurements, which is the film resistance of the electrode.

[0323] 2) Adhesion test

[0324] Referring to GB-T2790-1995, "Test Method for 180° Peel Strength of Adhesives", the adhesion test process of the embodiments and comparative examples in this application is as follows:

[0325] Cut a sample with a width of 30mm and a length of 100-160mm using a blade. Apply special double-sided tape (20mm wide, 90-150mm long) to a steel plate. Place the positive electrode film layer of the previously cut electrode sample onto the double-sided tape, then roll it three times in the same direction using a 2kg roller. Fix a paper strip with a width equal to the electrode and a length of 250mm onto the current collector of the electrode, and secure it with wrinkle adhesive. Turn on the power of the tensile testing machine (sensitivity 1N), the indicator light will illuminate. Adjust the limit block to the appropriate position and secure the end of the steel plate without the electrode attached using the lower clamp. Fold the paper strip upwards and secure it with the upper clamp. Use the "up" and "down" buttons on the manual controller provided with the tensile testing machine to adjust the position of the upper clamp. Then perform the test and read the values. Divide the force when the electrode is in equilibrium by the width of the tape to obtain the adhesive force per unit length of the electrode, which characterizes the bonding strength between the positive electrode film layer and the current collector.

[0326] 3) Electrode liquid absorption rate test

[0327] The cold-pressed positive electrode sheet was cut into square test samples with a side length of 5 cm. First, the sample was dried at 80℃ for 4 hours. After testing the thickness of the electrode sheet, it was fixed on the sample stage. Then, a capillary tube with d = 200 μm was selected, and the end face was polished with 5000 grit sandpaper until it was smooth. The state between the capillary tube and the electrode sheet was observed using a microscope. Electrolyte was drawn up with the capillary tube, and the electrolyte height was controlled to be 3 mm. The capillary tube was lowered to contact the electrode sheet, and a stopwatch was used to time the process. When the liquid level was completely lowered, the timer was stopped, and the liquid absorption time t was read and recorded. The average liquid absorption rate v of the electrode sheet was calculated using the formula v = π × (d / 2)² × h × ρ / t.

[0328] 2. Battery performance test

[0329] 1) Metal dissolution test

[0330] At room temperature, the manufactured lithium-ion battery was first charged and discharged at a current of 0.5C (i.e., the current value at which the theoretical capacity is completely discharged within 2 hours). The charging was constant current and constant voltage charging, with a termination voltage of 4.2V, a cutoff current of 0.05C, and a discharge termination voltage of 2.8V. After the battery was left to stand for 24 hours, it was charged to 4.2V at a constant current and constant voltage of 0.5C. Then, the fully charged battery was discharged at a current of 1C, with a discharge termination voltage of 2.8V. The cell was disassembled, the negative electrode was removed, and the deposition amount of metals Co and Mn was tested using the ICP (inductively coupled plasma) method.

[0331] 2) Battery cycle capacity retention test

[0332] The battery cycle capacity retention rate test process is as follows: At 25℃, the prepared battery is charged to 4.3V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 4.3V, left to rest for 5 minutes, and then discharged to 2.8V at 1 / 3C. The resulting capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle is recorded. The battery capacity retention rate after each cycle is Pn = Cn / C0*100%. The battery capacity retention rate versus the number of cycles is plotted on the ordinate with the 500 points P1, P2...P500 as the abscissa.

[0333] During this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 500th cycle to n=500. The battery capacity retention rate data corresponding to the examples or comparative examples in Table 1 are the data measured after 500 cycles under the above test conditions, i.e., the values ​​of P500.

[0334] 3) Full cell capacity retention rate at 45℃

[0335] Charge the battery at a constant current of 1C to 4.2V, then charge it at a constant voltage of 4.2V to a current of 0.05C. Let it rest for 10 minutes, then discharge it at a constant current of 1C to a cutoff voltage of 2.8V. Record the capacity before storage as CAP1. Charge the battery at a constant current of 1C to a cutoff voltage of 4.2V, then charge it at a constant voltage of 4.2V to a current of 0.05C. Place the lithium-ion battery in an oven at 45℃ for 120 days, then remove it and discharge it at a constant current of 1C to 2.8V. Record the capacity after storage as CAP2. Calculate the storage capacity retention rate of the lithium-ion secondary battery according to the following formula:

[0336] Lithium-ion secondary battery storage capacity retention rate (%) = CAP2 / CAP1*100%.

[0337] 4) Gas production test of the entire battery at 70°C

[0338] Full cells at 100% State of Charge (SOC) were stored at 70°C. The open-circuit voltage (OCV) and internal resistance (IMP) of the cells were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. Every 48 hours of storage, the full cells were removed, allowed to stand for 1 hour, and then OCV and IMP were tested. After cooling to room temperature, the cell volume was measured using the displacement method. The displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion from the dial readings, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the process, the weight F2 of the battery cell is measured at this time, and the buoyancy F_buoyancy of the battery cell is F1-F2. Then, according to Archimedes' principle F_buoyancy = ρgV_displaced, the volume of the battery cell V = (F1-F2) / ρg is calculated.

[0339] After each volume test, the battery cell is recharged with a constant current of 1C to 4.25V, and then charged with a constant voltage of 4.25V until the current drops to 0.05C. After the recharge is completed, the cell is put into the furnace for further testing.

[0340] After 90 days of storage, the cell volume is measured, and the increase in cell volume after storage is calculated relative to the cell volume before storage, i.e., the amount of gas produced. The cell volume expansion rate is obtained by dividing the amount of gas produced by the initial cell volume.

[0341] 3. Polymer detection

[0342] 1) Weight-average molecular weight test method

[0343] A Waters 2695 Isocratic HPLC gel electrophoresis system (differential refractive index detector 2141) was used. A 3.0% (w / w) polystyrene solution was used as a reference, and a matched column (oil-based: Styragel HT5DMF7.8*300mm + Styragel HT4) was selected. A 3.0% polymer solution was prepared using purified N-methylpyrrolidone (NMP) solvent and allowed to stand for one day. For testing, tetrahydrofuran was first used to flush the syringe, repeated several times. Then, 5 ml of the experimental solution was drawn, air was expelled from the syringe, and the needle tip was dried. Finally, the sample solution was slowly injected into the injection port. Data was acquired after the reading stabilized.

[0344] The performance tests of the electrode and battery in the examples and comparative examples are shown in Tables 1 and 2.

[0345] Table 1

[0346]

[0347]

[0348] Table 2

[0349]

[0350]

[0351]

[0352] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0353] In Examples 1-19, the binders all comprise BAB-type block copolymers, wherein the B-blocks contain structural units derived from vinylidene fluoride, and the A-blocks contain imide or amide structural units. The binders prepared using the aforementioned polyvinylidene fluoride-polyimide-polyvinylidene fluoride block copolymers or polyvinylidene fluoride-polyamide-polyvinylidene fluoride block copolymers can reduce the film resistance of the electrode, increase the liquid absorption rate of the electrode, and inhibit the dissolution of transition metals in the positive electrode active material, thereby improving the cycle performance and storage performance of the battery.

[0354] As can be seen from the comparison between Examples 1-6 and Comparative Example 2, using BAB triblock copolymer as a binder can improve the cycle performance and high-temperature storage performance of the battery compared to non-fluoropolymers alone.

[0355] As can be seen from the comparison between Examples 1-6 and Comparative Example 3, compared with the simple blending of non-fluorinated polymers and fluorinated polymers, using BAB triblock copolymer as a binder can reduce the film resistance of the electrode, improve the adhesion of the electrode, and improve the cycle performance and high-temperature storage performance of the battery.

[0356] As can be seen from the comparison between Examples 1-7 and Comparative Example 1, in the block copolymer, based on the total mass of the block copolymer, when the mass percentage of each fluorinated block B-block is 15%-35% and the mass percentage of each non-fluorinated block A-block is 30%-70%, the BAB type block copolymer can reduce the film resistance of the electrode, effectively suppress the dissolution of transition metals in the positive electrode active material, improve the cycle performance and high-temperature storage performance of the battery, and reduce the amount of gas generated by the battery at high temperatures.

[0357] A comparison of Examples 1-5 with Examples 6-7 shows that, based on the total mass of the block copolymer, when the mass percentage of each fluorinated block B-block is 17.5%-32.5% and the mass percentage of each non-fluorinated block A-block is 35%-65%, the BAB-type block copolymer can reduce the film resistance of the electrode, improve the cycle performance and high-temperature storage performance of the battery, while further taking into account the adhesion and liquid absorption rate of the electrode, thus improving the overall performance of the battery.

[0358] A comparison of Examples 1-11, Examples 16-19, and Comparative Example 1 shows that BAB-type block copolymers with a weight-average molecular weight of 400,000 to 2,000,000 result in electrode sheets with excellent liquid absorption rates and low film resistance. Furthermore, these block copolymers can suppress the dissolution of transition metals in the positive electrode active material, thereby improving the battery's cycle performance, high-temperature storage performance, and safety performance.

[0359] As can be seen from the comparison between Example 17 and Example 19, when the A-block contains an imide structural unit containing trifluoromethyl, the BAB-type block copolymer can further improve the adhesion and liquid absorption rate of the electrode, reduce the dissolution of transition metals, and improve the cycle performance and high-temperature storage performance of the battery.

[0360] As can be seen from the comparison between Example 16 and Example 19, when the A-block contains an imide structural unit containing a sulfone group, the BAB-type block copolymer can further improve the adhesion and liquid absorption rate of the electrode, reduce the dissolution of transition metals, and improve the cycle performance and high-temperature storage performance of the battery.

[0361] As can be seen from the comparison between Example 4 and Example 19, when the A-block contains an imide structural unit containing trifluoromethyl and sulfone groups, the BAB-type block copolymer can further improve the adhesion and liquid absorption rate of the electrode, reduce the dissolution of transition metals, and improve the cycle performance and high-temperature storage performance of the battery.

[0362] As can be seen from Examples 1 and 12-15, when the mass percentage of the binder is 0.1% to 3%, based on the mass of the positive electrode active material, the binder enables the electrode to have excellent liquid absorption rate and low film resistance, resulting in high cycle performance and high-temperature storage performance of the battery.

[0363] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A BAB-type block copolymer, characterized in that, It comprises an A-segment and two B-segments, each of the B-segments comprising a structural unit shown in Equation I, and the A-segment comprising one or more of the structural units shown in Equation II, Equation III, and Equation IV. Equation I Formula II Formula III Formula IV R1, R2, and R3 are each independently selected from hydrogen, fluorine, or C atoms containing at least one fluorine atom. 1-3 One or more of the alkyl groups, R4 is selected from substituted or unsubstituted C4 groups. 6-25 The aromatic group, R5 is selected from substituted or unsubstituted C 6-25 The aromatic groups, R6, R7, and R8, are each independently selected from substituted or unsubstituted C groups. 2-24 alkyl; In the BAB-type block copolymer, the mass percentage of any B-block is 15% to 35%, and the mass percentage of the A-block is 30% to 70%, based on the total mass of the block copolymer; The weight-average molecular weight of the BAB-type block copolymer is 400,000 to 2,000,000.

2. The BAB-type block copolymer according to claim 1, characterized in that, The A-block comprises a structural unit of Formula II containing trifluoromethyl groups.

3. The BAB-type block copolymer according to claim 2, characterized in that, The structural unit of Formula II containing trifluoromethyl groups is selected from... 、 、 、 、 One or more of them.

4. The BAB-type block copolymer according to claim 1, characterized in that, The A-block comprises a structural unit of Formula II containing a sulfone group.

5. The BAB-type block copolymer according to claim 4, characterized in that, The structural unit of Formula II containing a sulfone group is selected from... 、 、 、 、 One or more of them.

6. The BAB-type block copolymer according to claim 1, characterized in that, The structural unit shown in Formula I is derived from one or more of vinylidene fluoride, tetrafluoroethylene, and vinyl fluoride.

7. A method for preparing a BAB-type block copolymer, characterized in that, Includes the following steps: Preparation of B-blocks: B-blocks are prepared by polymerizing at least one monomer of formula V. Formula V A1, A2, and A3 are each independently selected from hydrogen, fluorine, and C atoms containing at least one fluorine atom. 1-3 One or more of alkyl groups; Preparation of A-blocks: A-blocks are prepared by polymerizing at least one diamine with at least one diacid or at least one diacid, or by ring-opening polymerization of a lactam monomer; the A-blocks comprise one or more of the structural units shown in Formula II, Formula III, and Formula IV. Formula II Formula III Formula IV R4 is selected from substituted or unsubstituted C. 6-25 The aromatic group, R5 is selected from substituted or unsubstituted C 6-25 The aromatic groups, R6, R7, and R8, are each independently selected from substituted or unsubstituted C groups. 2-24 alkyl; Preparation of BAB-type block copolymers: BAB-type block copolymers are prepared by joining the B-block and the A-block, wherein in the BAB-type block copolymer, the mass percentage of any B-block is 15% to 35%, and the mass percentage of the A-block is 30% to 70%, based on the total mass of the block copolymer; The weight-average molecular weight of the BAB-type block copolymer is 400,000 to 2,000,000.

8. The method for preparing the BAB-type block copolymer according to claim 7, characterized in that, The preparation of the B-block specifically includes: At least one monomer of formula V, a chain transfer agent, and an initiator are subjected to reversible addition-cleavage chain transfer polymerization at a reaction temperature of 70-90°C for 5-8.5 hours to obtain a B-block with an azide group or alkynyl group at one end.

9. The method for preparing the BAB-type block copolymer according to claim 7, characterized in that, The preparation of the A-block specifically includes: The catalyst, at least one diamine, and at least one diacid or at least one diacid are stirred and reacted at room temperature for 4 to 10 hours, and then heated to 170 to 210°C and reacted for 5 to 20 hours to obtain a product with anhydride, carboxyl or amino groups at both ends. The end groups of the product are functionalized to obtain the A-block having alkynyl or azide groups at both ends.

10. The method for preparing the BAB-type block copolymer according to claim 7, characterized in that, The preparation of the A-block specifically includes: The end-group regulator, water, and at least one lactam monomer are polymerized at a reaction temperature of 250℃~280℃ for 12~24 hours to obtain a product with carboxyl or amino end groups at both ends. The end groups of the product are functionalized to obtain the A-block having alkynyl or azide groups at both ends.

11. The method for preparing the BAB-type block copolymer according to claim 7, characterized in that, The preparation of the BAB-type block copolymer specifically includes: A-blocks with alkynyl or azide groups at both ends are mixed with B-blocks with alkynyl or azide groups at one end, and a click reaction is carried out to prepare BAB-type block copolymers, wherein the B-blocks and A-blocks have different end groups.

12. The method for preparing the BAB-type block copolymer according to claim 8, characterized in that, The chain transfer agent is a RAFT chain transfer agent containing a terminal alkynyl group or an azide group.

13. The method for preparing the BAB-type block copolymer according to claim 10, characterized in that, The end-group regulator is a diamine or a dicarboxylic acid.

14. The application of the BAB-type block copolymer according to any one of claims 1 to 6 in secondary batteries.

15. The application according to claim 14, characterized in that, The secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

16. A positive electrode slurry, characterized in that, The positive electrode slurry includes a positive electrode active material, a conductive agent, and a binder, wherein the binder is a BAB-type block copolymer according to any one of claims 1 to 6 or a BAB-type block copolymer prepared by any one of claims 7 to 13.

17. The positive electrode slurry according to claim 16, characterized in that, The binder has a mass percentage of 0.1% to 3%, based on the total mass of the positive electrode active material.

18. A positive electrode plate, characterized in that, The invention includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, a conductive agent, and a binder. The binder is a BAB-type block copolymer according to any one of claims 1 to 6 or a BAB-type block copolymer prepared by the preparation method according to any one of claims 7 to 13.

19. The positive electrode sheet according to claim 18, characterized in that, The binder has a mass percentage of 0.1% to 3%, based on the total mass of the positive electrode active material.

20. The positive electrode sheet according to claim 18 or 19, characterized in that, The adhesion force per unit length between the positive electrode film and the positive electrode current collector is not less than 11.5 N / m.

21. The positive electrode sheet according to claim 18 or 19, characterized in that, The adhesion force per unit length between the positive electrode film and the positive electrode current collector is 11.5 N / m-15 N / m.

22. The positive electrode sheet according to claim 18 or 19, characterized in that, The positive electrode has an electrolyte absorption rate greater than 0.31 μg / s, and the electrolyte density is 1.1-1.2 g / cm³. 3 .

23. The positive electrode sheet according to claim 18 or 19, characterized in that, The positive electrode has an electrolyte absorption rate of 0.32-0.5 μg / s, and the electrolyte has a density of 1.1-1.2 g / cm³. 3 .

24. A secondary battery, characterized in that, It includes an electrode assembly and an electrolyte, wherein the electrode assembly includes a separator, a negative electrode, and a positive electrode as described in any one of claims 18 to 23.

25. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 24.

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