WO2024066422A1

WO2024066422A1 - Bab type block copolymer, preparation method, binder, positive electrode plate, secondary battery, and electric device

Info

Publication number: WO2024066422A1
Application number: PCT/CN2023/096928
Authority: WO
Inventors: 曾子鹏; 李�诚; 刘会会; 孙成栋; 王景明
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-09-30
Filing date: 2023-05-29
Publication date: 2024-04-04
Also published as: CN117801296A; CN115286803A; CN115286803B

Abstract

The present application provides a BAB type block copolymer, a preparation method, a binder, a positive electrode plate, a secondary battery, and an electric device. The BAB type block copolymer comprises an A-block and a B-block. The B-block comprises a structural unit represented by formula I, and the A-block comprises one or more of structural units represented by formula II, formula III and formula IV, wherein R1, R2 and R3 are each independently selected from one or more of hydrogen, fluorine, and C1-3 alkyl containing at least one fluorine atom, R4 is each independently selected from a substituted C6-25 aromatic group, and R5, R6, R7, and R8 are each independently selected from substituted or unsubstituted C2-24 alkyl, and a substituted or unsubstituted C6-25 aromatic group. The block copolymer is used as a binder, such that the film resistance of the electrode plate can be reduced, the liquid absorption rate of the electrode plate is increased, and the dissolution of transition metal in a positive electrode active material is inhibited, thereby improving the cycle performance and the storage performance of the battery.

Description

BAB type block copolymer, preparation method, binder, positive electrode sheet, secondary battery and electrical device

cross reference

This application refers to Chinese Patent Application No. 202211205884.5 filed on September 30, 2022, entitled “BAB-type block copolymer, preparation method, binder, positive electrode plate, secondary battery and electrical device”, which is incorporated into this application in its entirety by reference.

Technical Field

The present application relates to the technical field of secondary batteries, and in particular to a BAB-type block copolymer, a preparation method, a binder, a positive electrode sheet, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. With the popularization of secondary battery applications, higher requirements have been put forward for their energy density and cycle performance.

Binders are commonly used materials in secondary batteries and are widely used in battery pole pieces, separators, packaging, etc. At present, the most widely used binder in the positive electrode of secondary batteries is polyvinylidene fluoride (PVDF), but it is expensive and has poor dispersibility. In addition, existing binders cannot meet the requirements of using and storing batteries under high voltage or extremely high temperature conditions. Therefore, existing binders still need to be improved.

Summary of the invention

The present application is made in view of the above-mentioned problems, and its purpose is to provide a BAB type block copolymer, which can reduce the membrane resistance of the electrode sheet, increase the liquid absorption rate of the electrode sheet, inhibit the dissolution of transition metals in the positive electrode active material, and thus improve the cycle performance and storage performance of the battery by using the block copolymer as a binder.

The first aspect of the present application provides a BAB type block copolymer comprising an A-block and B-block, B-block comprises the structural unit shown in formula I, A-block comprises one or more of the structural unit shown in formula II, the structural unit shown in formula III, and the structural unit shown in formula IV,

_R1 , _R2 , _R3 are each independently selected from one or more of hydrogen, fluorine, and _C1-3 alkyl containing at least one fluorine atom; _R4 is selected from substituted _C6-25 aromatic groups; and _R5 , _R6 , _R7 , _R8 are each independently selected from substituted or unsubstituted _C2-24 alkyl groups and substituted or unsubstituted _C6-25 aromatic groups.

The binder prepared with the BAB type block copolymer can maximize the weight average molecular weight of the fluorine-containing block and the non-fluorine block, give full play to the respective advantages of the fluorine-containing binder and the non-fluorine binder, and achieve the role of complementary advantages. At the same time, the BAB type block copolymer can utilize the steric hindrance between the B-block and the A-block to reduce the agglomeration of the binder and improve the uniformity of the dispersion of the material in the pole piece. The binder prepared with the above-mentioned BAB type block copolymer can reduce the membrane resistance of the pole piece, increase the liquid absorption rate of the pole piece, inhibit the dissolution of the transition metal in the positive electrode active material, and thus improve the cycle performance and storage performance of the battery. And compared with the simple blending of fluorine-containing polymers and non-fluorine polymers, the BAB type block copolymer can effectively inhibit the stratification of polymers of different structural units during the slurry preparation process through the interaction between the blocks.

In any embodiment, in the block copolymer, the mass percentage of each of the B-blocks 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 BAB type block copolymer with the mass percentage of B-block and A-block in a suitable range makes the electrode have excellent adhesion, good liquid absorption rate and low membrane resistance at the same time, and the battery has excellent cycle performance, high temperature storage performance and safety performance.

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

The BAB-type block copolymer with a weight-average molecular weight within a suitable range enables the electrode to have excellent liquid absorption rate, good adhesion and low membrane resistance, and the battery has both excellent cycle performance and storage performance.

In any embodiment, the A-block comprises a structural unit of Formula II containing a trifluoromethyl group.

In any embodiment, the structural unit represented by formula II containing a trifluoromethyl group comprises

One or more of .

The structural unit represented by formula II containing trifluoromethyl in the A-block enables the BAB-type block copolymer to further improve the adhesion and liquid absorption rate of the electrode, reduce the membrane resistance of the electrode, effectively inhibit 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.

In any embodiment, the A-block comprises a structural unit of Formula II comprising a sulfone group.

In any embodiment, the structural unit represented by formula II containing a sulfone group comprises

One or more of .

The structural unit shown in formula II containing a sulfone group in the A-block enables the BAB-type block copolymer to further improve the adhesion and liquid absorption rate of the electrode, reduce the membrane 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.

In any embodiment, the structural unit represented by Formula I comprises one or more of a structural unit derived from vinylidene fluoride, a structural unit derived from tetrafluoroethylene, a structural unit derived from vinyl fluoride, a structural unit derived from trifluoroethylene, and a structural unit derived from hexafluoropropylene.

In any embodiment, the structural unit shown in formula II comprises

One or more of , wherein n is any integer between 6 and 12.

The second aspect of the present application also provides a method for preparing a BAB type block copolymer, characterized in that it comprises the following steps:

Preparation of B-block: polymerizing at least one monomer represented by formula V to prepare B-block,

wherein A ₁ , A ₂ , and A ₃ are each independently selected from one or more of hydrogen, fluorine, and a C _1-3 alkyl group containing at least one fluorine atom;

Preparing the A-block: polymerizing at least one diamine and at least one dibasic anhydride or at least one dibasic acid to prepare the A-block, or ring-opening polymerizing a lactam monomer to prepare the A-block;

Preparation of BAB type block copolymer: B-block and A-block are joined to prepare BAB type block copolymer.

Compared with the traditional copolymerization method, this preparation method can maximize the weight average molecular weight of the fluorine-containing block and the non-fluorine block, give full play to the advantages of the fluorine-containing binder and the non-fluorine binder, and achieve the role of complementary advantages. The preparation method has cheap raw materials, can reduce costs, reduce environmental pollution, and is conducive to the increase of binder production. At the same time, the BAB type block copolymer prepared by this method as a binder can make the electrode have excellent liquid absorption ability. The good adhesion, low membrane resistance and the cycle performance, high temperature storage performance and safety performance of the battery are improved.

In any embodiment, the preparation of the B-block specifically comprises:

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

Reversible addition-fragmentation chain transfer polymerization is used to achieve controlled polymerization, and the molecular weight distribution of the product is relatively narrow. Moreover, through the above reaction, the B-block only has an alkynyl or azide group at the end, which is convenient for directing and bonding with the A-block in an efficient and mild manner to generate a BAB-type triblock copolymer.

In any embodiment, the preparation of the A-block specifically comprises:

The catalyst, at least one diamine, at least one dibasic anhydride or at least one dibasic acid are stirred and reacted at room temperature for 4 to 10 hours, and the temperature is raised to 170 to 210° C. and reacted for 5 to 20 hours to obtain a product with both end groups being anhydride, carboxyl or amino groups;

The terminal groups of the product are subjected to functionalization reaction to obtain the A-block having alkynyl groups or azide groups at both ends.

In any embodiment, the preparation of the A-block specifically comprises:

Polymerizing an end group regulator, water and at least one lactam monomer at a reaction temperature of 250° C. to 280° C. for 12 to 24 hours to obtain a product having end groups at both ends being carboxyl groups or amino groups;

The A-block with azidation or alkyne at both ends prepared by the preparation method can be easily connected with the B-block in an efficient and mild manner to generate a BAB type block copolymer.

In any embodiment, the preparation of the BAB type block copolymer specifically comprises:

The A-block having alkynyl or azide groups at both ends is mixed with the B-block having an azide or alkyne group at one end and subjected to a click reaction to prepare a BAB type block copolymer, wherein the end groups of the B-block and the A-block are different.

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

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

In any embodiment, the end group modifier is a diamine or a dibasic acid.

The third aspect of the present application provides an application of a BAB type block copolymer in a secondary battery. Optionally, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

The fourth aspect of the present application provides a positive electrode plate, including a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material, a conductive agent and a binder, and the binder is a BAB type block copolymer in any embodiment or a BAB type block copolymer prepared by the preparation method in any embodiment.

The positive electrode sheet has excellent liquid absorption rate and good bonding force, and has excellent membrane resistance and transition metal dissolution amount.

In any embodiment, the binder has a mass percentage of 0.1% to 3% based on the total mass of the positive electrode active material.

Controlling the mass percentage of the binder within a suitable range can make the pole piece have excellent liquid absorption rate, good bonding force, and low membrane resistance. In addition, the binder in the pole piece can inhibit the dissolution of transition metals in the active material, and improve the cycle performance, high temperature storage performance and safety performance of the battery.

In any embodiment, the bonding 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 11.5-15 N/m.

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

In any embodiment, the electrolyte absorption rate of the positive electrode plate is greater than 0.31 μg/s, and may be 0.32-0.5 μg/s, and the electrolyte has a density of 1.1-1.2 g/cm ³ .

The electrode has a high liquid absorption rate, which can improve the electrolyte infiltration efficiency of the electrode, improve the ion transmission path, reduce the interface resistance, and improve the battery performance.

In a fifth aspect of the present application, a secondary battery is provided, comprising an electrode assembly and an The electrolyte is provided, and the electrode assembly comprises a separator, a negative electrode plate and a positive electrode plate according to the fourth aspect of the present application.

In a sixth aspect of the present application, an electrical device is provided, comprising the secondary battery of the fifth aspect of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a method for preparing a BAB type block copolymer according to an embodiment of the present application;

FIG2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

FIG3 is an exploded view of the secondary battery of one embodiment of the present application shown in FIG2 ;

FIG4 is a schematic diagram of a battery module according to an embodiment of the present application;

FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application;

FIG6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG5 ;

FIG. 7 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

Description of reference numerals:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate; 6BAB type block copolymer; 61A-block; 611A-terminal groups of the block; 612 structural unit shown in formula II, formula III or formula IV; 62B-block; 621B-terminal groups of the block; 622 structural unit shown in formula I.

Detailed ways

Below, the embodiments of the positive electrode active material and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack and electrical device of the present application are specifically disclosed with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. It is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope defined in this way can include or exclude end values, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 listed, and if the maximum range values 3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

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

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

If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or exists). A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

In the prior art, polyvinylidene fluoride (PVDF) is often used as a pole piece binder. However, the cost of PVDF binder is high and it cannot be recycled on a large scale due to restrictions of environmental protection policies. Moreover, PVDF binder is difficult to form an effective protective layer for the positive electrode active material, and cannot effectively inhibit the side reaction between the positive electrode active material and the electrolyte and the dissolution of transition metals in the positive electrode active material, resulting in problems such as gas generation, volume deformation, and deposition of transition metals at the negative electrode of the battery cell, which have a negative impact on the cycle performance and safety performance of the battery.

[Binder]

Based on this, the present application provides a BAB type block copolymer, comprising an A-block and a B-block, wherein the B-block comprises a structural unit shown in formula I, and the A-block comprises one or more of a structural unit shown in formula II, a structural unit shown in formula III, and a structural unit shown in formula IV.

In this article, the term "block copolymer" refers to a special type of polymer made by linking two or more polymer segments with different properties. Block polymers with specific structures will exhibit different properties from simple linear polymers, many random copolymers, and even mixtures of homopolymers. Common types include AB and BAB types, in which A and B are both long chain segments; there are also (AB)n type multi-segment copolymers, in which A and B segments are relatively short.

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

In this context, the term "polymer" includes, on the one hand, a collection of macromolecules that are chemically uniform but differ in degree of polymerization, molar mass and chain length, prepared by polymerization. The term also includes, on the other hand, derivatives of such a collection of macromolecules formed by polymerization, i.e. compounds that can be obtained by reaction, for example addition or substitution, of functional groups in the above-mentioned macromolecules and can be chemically uniform or chemically heterogeneous.

As used herein, the term "C _1-3 alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation in the radical, having from one to three carbon atoms, and attached to the remainder of the molecule by a single bond. Examples of C _1-3 alkyl include, but are not limited to, methyl, ethyl, n-propyl, 1-methylethyl (isopropyl). The term "C ₂ -C ₂₄ alkyl" should be interpreted accordingly.

In this context, the term "C _1-3 alkyl containing at least one fluorine atom" refers to an alkyl group containing 1 to 3 carbon atoms in which at least one H atom is replaced by a F atom. In the embodiment, the C _1-3 alkyl group containing one fluorine atom includes a -CF ₃ group and a -C ₂ F ₆ group.

As used herein, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is replaced by another chemical moiety with a substituent, wherein the substituent is independently selected from: hydroxyl, thiol, amino, cyano, nitro, aldehyde, halogen atom, alkenyl, alkynyl, aryl, heteroaryl, C _1-6 alkyl, C _1-6 alkoxy.

As used herein, the term "C _6-25 aromatic group" refers to an aromatic ring system in which at least one ring is aromatic, including but not limited to phenyl, biphenyl, indanyl, 1-naphthyl, 2-naphthyl and tetrahydronaphthyl.

Herein, the substituted C _6-25 aromatic group includes, but is not limited to, aralkyl, aralkyloxy, aryloxyalkyl, and a symmetrical or asymmetrical aromatic group linked via a carbonyl group or an ether group.

In some embodiments, the structural unit represented by Formula I comprises one or more of a structural unit derived from vinylidene fluoride, a structural unit derived from tetrafluoroethylene, a structural unit derived from vinyl fluoride, a structural unit derived from trifluoroethylene, and a structural unit derived from hexafluoropropylene.

In some embodiments, the structural unit shown in Formula II comprises

One or more of , wherein n is any integer between 6 and 12.

In some embodiments, the structural unit represented by formula III comprises

In some embodiments, the structural unit represented by formula IV comprises

In some embodiments, the BAB type block copolymer is used as a binder in a secondary battery. In some embodiments, the BAB type block copolymer is used as a pole piece binder in a secondary battery.

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

In some embodiments, the dispersion medium of the binder is an aqueous solvent, such as water, that is, the binder is dissolved in the aqueous solvent.

In some embodiments, the dispersion medium of the binder is an oily solvent, and examples of the oily solvent include but are not limited to dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate. Soluble in oily solvents.

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

In some embodiments, the binder is used as a positive electrode binder to bind the positive electrode active material and/or the conductive agent to form an electrode.

In some embodiments, the binder is used as a negative electrode binder to bind the negative electrode active material and/or the conductive agent to form an electrode.

The fluorine contained 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, making the pole piece have excellent adhesion. The A-block contains abundant carbonyl groups, which can form intermolecular hydrogen bonds. The hydrogen bonds interact with the hydroxyl groups on the surface of the positive electrode active material and the current collector, making the pole piece have excellent adhesion and improving the stability of the positive electrode. In addition, the abundant carbonyl groups make the binder have excellent flexibility, reducing the shedding of active materials that occurs as the pole piece volume changes during the charge and discharge process, thereby improving the battery's cycle capacity retention rate.

In some embodiments, the A-block comprises at least the structural unit represented by Formula II.

The imide bond contained in the A-block can improve the liquid absorption capacity of the electrode, improve the electrode's ability to infiltrate the electrolyte, help form a conductive network, and reduce the film resistance of the electrode. In addition, the highly polar imide bond can improve the electrochemical stability and thermal stability of the binder, and effectively inhibit the physical expansion of the electrode caused by the insertion and extraction of ions during the electrochemical reaction. At the same time, the surface energy of the A-block containing the imide bond is relatively low, and the film-forming performance is good. It can be evenly coated on the surface of the positive electrode active material, reducing the active sites on the surface of the positive electrode active material, reducing side reactions and the dissolution of transition metals, thereby improving the cycle performance and high-temperature storage performance of the electrode, and reducing the gas production of the battery at high temperature.

In some embodiments, the A-block comprises at least a structural unit represented by Formula III or Formula IV.

The amide bond contained in the A-block can improve the liquid absorption capacity of the electrode, improve the electrode's ability to infiltrate the electrolyte, help form a conductive network, and reduce the film resistance of the electrode. In addition, the strong polar amide bond can improve the electrochemical stability and thermal stability of the binder, and effectively inhibit the physical expansion of the electrode caused by the insertion and extraction of ions during the electrochemical reaction. At the same time, when the binder is coated on the surface of the active material, it can reduce The side reaction between the low-activity material and the electrolyte inhibits the dissolution of transition metals in the active material, thereby improving the cycle performance, high-temperature storage performance and gas production performance of the electrode.

In some embodiments, in the block copolymer, the mass percentage of each 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.

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%, and 35%, based on the total mass of the block copolymer.

In some embodiments, in the block copolymer, the mass percentage of the A-block may be any one of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70%, based on the total mass of the block copolymer.

If the mass percentage of the B-block is too high and the mass percentage of the A-block is too low, the A-block cannot fully exert its role in increasing the liquid absorption rate, reducing the membrane resistance, and inhibiting the dissolution of transition metals in the active material, and the battery's cycle performance and safety performance cannot be effectively improved; if the mass percentage of the B-block is too low and the mass percentage of the A-block is too high, the bonding strength of the electrode and the cycle stability of the battery will be reduced.

In some embodiments, the weight average molecular weight of the BAB type block copolymer is 400,000 In some embodiments, the weight average molecular weight of the BAB type block copolymer can be selected from any one of 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.

As used herein, the term "weight average molecular weight" refers to the sum of the products of the weight fractions of molecules with different molecular weights in a polymer and their corresponding molecular weights.

If the weight average molecular weight of the BAB type block copolymer is too large, the binder is difficult to dissolve and is easy to agglomerate with the conductive agent, resulting in excessive viscosity of the slurry, making it difficult to apply evenly, which is not conducive to the subsequent processing and production of the pole piece. If the weight average molecular weight of the BAB type block copolymer is too small, it is difficult to form a three-dimensional network bonding structure, and it cannot play an effective bonding and dispersion role, which is not conducive to the formation of a conductive network, resulting in an increase in the membrane resistance of the pole piece, and a decrease in the battery's cycle performance, high-temperature storage performance, and gas production performance.

In some embodiments, the A-block comprises a structural unit of Formula II containing a trifluoromethyl group.

In some embodiments, the structural unit represented by formula II containing a trifluoromethyl group comprises

One or more of .

As used herein, the term "trifluoromethyl" refers to a " _-CF3 " group.

As used herein, the term "sulfone" refers to a " _-SO2- " group.

As used herein, the term "ether bond" refers to "-O-".

The structural unit shown in Formula II containing trifluoromethyl in the A-block can enhance the ion transfer ability of the binder, improve the liquid absorption rate of the pole piece, and reduce the membrane resistance of the pole piece. At the same time, the fluorine element in the trifluoromethyl group can form hydrogen bonds with the carboxyl and hydroxyl groups remaining on the surface of the active material and the current collector to further improve the bonding force of the binder. In addition, the trifluoromethyl group in the A-block can improve the electrochemical stability and thermal stability of the binder, inhibit the dissolution of transition metals in the positive electrode active material, effectively inhibit the physical expansion of the pole piece caused by the insertion and removal of ions during the electrochemical reaction, and improve the battery's cycle performance, high-temperature storage performance and gas production performance.

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

In some embodiments, the structural unit represented by formula II containing a sulfone group comprises

One or more of .

The sulfone group has a strong electron-withdrawing effect, which can enhance the bonding ability between the electrode and the conductive ions in the active material, improve the bonding force of the electrode, and at the same time, the sulfone group can increase the electrolyte absorption rate of the electrode, so that the electrode has a lower membrane resistance. The sulfone group can also enhance the stability of the imide bond structure and improve the structural stability of the binder during the electrode charge and discharge process, thereby improving the battery's cycle performance, high-temperature storage performance and safety performance.

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

The structural unit shown in Formula II contains an ether bond, which helps to improve the flexibility of the binder and improve the cycle performance and gas production performance of the battery.

One embodiment of the present application provides a method for preparing a BAB type block copolymer, comprising the following steps:

Preparation of BAB type block copolymers: B-block and A-block are joined to prepare BAB type Block copolymers.

In some embodiments, a schematic diagram of a method for preparing a BAB-type block copolymer 6 is shown in FIG1 , wherein the end groups 611 of an A-block 61 comprising a structural unit 612 shown in Formula II, Formula III or Formula IV are active groups, and the terminal groups 621 of a B-block 62 comprising a structural unit 622 shown in Formula I are active groups, and the end groups 611 of the A-block react with the terminal groups 621 of the B-block to achieve bonding of polymer segments, thereby preparing a BAB-type block copolymer 6.

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

In some embodiments, the diamine is an aliphatic diamine or an aromatic diamine, comprising

One or more of , wherein n is any integer between 6 and 12.

As used herein, the term "dianhydride" refers to a monomer containing two anhydrides.

In some embodiments, the dibasic anhydride is an aromatic dianhydride, comprising
One or more of .

In this document, the term "diacid" refers to a monomer containing two carboxyl groups. The dibasic acid can be selected from aromatic dibasic acids or aliphatic dibasic acids, such as one or more of adipic acid, sebacic acid, terephthalic acid, and isophthalic acid.

The preparation method has cheap raw materials, can reduce costs, reduce environmental pollution, and is conducive to the improvement of binder production. At the same time, the BAB type block copolymer prepared by this method as a binder can make the pole piece have excellent liquid absorption capacity, good adhesion, and low membrane resistance, so that the battery's cycle performance, high temperature storage performance and safety performance are improved. to improvement.

In some embodiments, the preparation of the B-block specifically comprises:

At least one monomer represented by formula V, a chain transfer agent and an initiator are polymerized by reversible addition-fragmentation chain transfer to obtain a B-block having an azide group or an alkynyl group at one end.

In some embodiments, the reaction temperature of the reversible addition-fragmentation chain transfer polymerization is 70 to 90° C., and the reaction time is 5 to 8.5 hours.

In some embodiments, the preparation of the B-block specifically comprises:

As used herein, the term "azide group" refers to a _-N3 group.

As used herein, the term "alkynyl" refers to a -C≡CH group.

In this article, the term "reversible addition-fragmentation chain transfer polymerization" (RAFT polymerization) is a type of reversibly deactivated free radical polymerization, also known as a "living/controlled free radical polymerization method". The main principle of RAFT polymerization is to add a RAFT agent as a chain transfer agent to the free radical polymerization, and protect the easily terminated free radicals through chain transfer, so that most of the free radicals in the polymerization reaction are converted into dormant free radicals. During the reaction, dormant segments and active segments exist at the same time and are constantly and rapidly switched to each other through dynamic reversible reactions, resulting in only a few polymer chains existing in the form of active chains and growing at any one time, and finally making the growth probability of each polymer segment roughly equal, thus showing the characteristics of living polymerization.

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

In some embodiments, the synthesis route of the B-block is shown in the figure below, wherein the chain transfer agent is trithiocarbonate, Z' is an active group having an alkynyl or azide group at the end, and R is an alkyl group. The B-block having an alkynyl or azide group at the end is prepared by the following reaction.

The reversible addition-fragmentation chain transfer polymerization can achieve controllable polymerization, and the molecular weight distribution of the product is relatively narrow. Moreover, through the above reaction, the B-block only has an alkynyl or azide group at the end, which is convenient for directing and bonding with the A-block in an efficient and mild manner to generate a BAB-type triblock copolymer.

By adopting the preparation method, controllable polymerization can be achieved, and the molecular weight distribution of the product is relatively narrow.

In some embodiments, the preparation of the A-block specifically comprises:

Polymerizing at least one diamine and at least one dibasic anhydride or at least one dibasic acid to obtain a product having end groups at both ends being anhydride, carboxyl or amino groups;

In some embodiments, the polymerization conditions of at least one diamine and at least one dibasic anhydride or at least one dibasic acid are stirring the reaction at room temperature for 4 to 10 hours, and then heating to 170 to 210° C. for 5 to 20 hours.

In some embodiments, the preparation of the A-block specifically comprises:

The catalyst, at least one diamine and at least one dibasic anhydride or at least one dibasic acid are stirred and reacted at room temperature for 4 to 10 hours, and the temperature is raised to 170 to 210° C. and reacted for 5 to 20 hours to obtain a product having end groups at both ends being anhydride, carboxyl or amino groups;

In some embodiments, the synthesis route of the A-block is that at least one diamine and at least one dibasic anhydride undergo a polymerization reaction under the action of a catalyst to generate a polyimide, so that the diamine or dibasic anhydride is in excess, and a polyimide with amino groups or acid anhydrides at both ends is obtained, and the amino groups or acid anhydrides at both ends are functionalized with an active monomer containing an azide group or an alkynyl group to prepare an A-block with an azide group or an alkynyl group at both ends. It is understood that the active monomer containing an azide group or an alkynyl group refers to a monomer containing an azide group or an alkynyl group and containing an azide group or an alkynyl group. The monomer having an active functional group that reacts with the amino group or acid anhydride at both ends of the polyimide, the active functional group that reacts with the amino group can be any one of epoxy, carboxyl, acid anhydride, isocyanate, and carbonyl chloride. The active functional group that reacts with the acid anhydride can be an amino group.

As used herein, the term "amino" refers to a _-NH2 group.

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

As used herein, the term "epoxy" refers to a -CH-O-CH- group.

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

As used herein, the term "isocyanate" refers to an -NCO group.

As used herein, the term "carbonyl chloride" refers to a -COCl group.

As used herein, the term "imino" refers to a "-NH-" group.

In some embodiments, the synthesis route of the A-block is that at least one diamine and at least one dibasic acid undergo a polycondensation reaction to generate polyamide under the action of a catalyst, so that the diamine or dibasic acid is excessive, and the end groups at both ends are amino or carboxyl polyamides, and the amino or carboxyl groups at both ends are functionalized with active monomers containing azide groups or alkynyl groups to prepare A-blocks with azide groups or alkynyl groups at both ends. It is understood that the active monomer containing azide groups or alkynyl groups refers to a monomer containing azide groups or alkynyl groups and containing active functional groups that can react with amino groups or carboxyl groups at both ends of the polyamide, and the active functional groups that react with amino groups can be selected from any one of epoxy groups, carboxyl groups, acid anhydrides, isocyanate groups, and carbonyl chloride. The active functional group that reacts with carboxyl groups can be selected from amino groups or imino groups.

In some embodiments, the catalyst may be any one of quinoline, isoquinoline, and tertiary amine.

In some embodiments, the preparation of the A-block specifically comprises:

A terminal group regulator, water and at least one lactam monomer are polymerized to obtain a product having terminal groups at both ends being carboxyl groups or amino groups;

The terminal groups of the product are functionalized to obtain an A-block having alkynyl or azide groups at both ends.

In some embodiments, the polymerization reaction conditions of the terminal group regulator, water and at least one lactam monomer are 250° C. to 280° C. for 12 to 24 hours.

In some embodiments, the preparation of the A-block specifically comprises:

The end group regulator, water and at least one lactam monomer are reacted at 250°C to 280°C. The polymerization reaction is carried out at a temperature of 12 to 24 hours to obtain a product having carboxyl or amino groups at both ends;

In some embodiments, the synthesis route of the A-block is as follows, under the catalysis of water, the lactam monomer undergoes a ring-opening polymerization reaction to obtain a polyamide with an amino group at one end and a carboxyl group at the other end, and then an end group regulator is added to react with the polyamide to obtain a polyamide with amino or carboxyl groups at both ends, and the amino or carboxyl groups at both ends are functionalized with an active monomer containing an azide group or an alkynyl group to prepare an A-block with an azide group or an alkynyl group at both ends. It is understood that the active monomer containing an azide group or an alkynyl group refers to a monomer containing an azide group or an alkynyl group and containing an active functional group that can react with the amino or carboxyl groups at both ends of the polyamide, and the active functional group that reacts with the amino group can be selected from any one of an epoxy group, a carboxyl group, an anhydride group, an isocyanate group, and a carbonyl chloride group. The active functional group that reacts with the carboxyl group can be selected from an amino group or an imino group.

In some embodiments, the lactam monomer may be selected from one or more of caprolactam, capryllactam, decanolactam, and laurolactam.

In some embodiments, the preparation of the BAB type block copolymer specifically comprises:

Herein, the term "click reaction" refers to a cycloaddition reaction between an alkynyl group and an azide group, so that the A-block is connected to the B-block. In some embodiments, the click reaction is carried out in the presence of a Cu(I) catalyst at room temperature and pressure.

In some embodiments, the terminal group of the B-block is an azide group and the terminal group of the A-block is an alkynyl group.

In some embodiments, the terminal group of the B-block is an alkynyl group and the terminal group of the A-block is an azide group.

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 achieve controlled polymerization of block polymers, which is beneficial to improving the yield rate of products.

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,

The RAFT chain transfer agent containing a terminal alkynyl or azide group allows the terminal of the B-block to carry an alkynyl or azide group during the synthesis of the B-block, providing a basis for the click reaction between the A-block and the B-block, avoiding complex post-processing steps, and improving the reaction efficiency.

In some embodiments, the end group modifier is a diamine or a dibasic acid.

The end group regulator of the diamine or dibasic acid can react with the end group of the product to obtain a product with both end groups being amino or carboxyl, which is convenient for subsequent conversion and can prepare A-blocks with both end groups being azido or alkynyl in a simple and efficient manner.

In some embodiments, the BAB type block copolymer may be used in a secondary battery. Optionally, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[Positive electrode]

The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material, a conductive agent and a binder, and 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.

The positive electrode sheet has excellent liquid absorption rate and good bonding force, low membrane resistance and transition metal dissolution amount.

In some embodiments, the mass percentage of the binder is 0.1% to 3%, based on the total mass of the positive electrode active material. In some embodiments, the mass percentage of the binder can be selected from any one of 0.1% to 0.2%, 0.2% to 1%, 0.2% to 1.03%, 1% to 3%, and 1.03% to 3%.

When the binder content is too low, the binder cannot fully exert its bonding and dispersion effects, resulting in insufficient bonding force of the pole piece and increased membrane resistance, which has a negative impact on the battery's cycle performance and high-temperature storage performance. When the binder content is too high, the viscosity of the slurry is too high, which will cause the binder coating layer on the surface of the positive electrode active material to be too thick, affecting the transmission of electrons and ions during the battery cycle, increasing the internal resistance of the pole piece membrane, and affecting the battery's cycle performance and high-temperature storage performance.

In some embodiments, the bonding 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 11.5-15 N/m. In some embodiments, the bonding force per unit length between the positive electrode film layer and the positive electrode current collector can be 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.

The bonding force per unit length between the positive electrode film layer and the positive electrode current collector can be tested by any means known in the art, such as testing with reference to GB-T2790-1995 national standard "Adhesive 180° Peel Strength Test Method". As an example, the positive electrode plate is cut into a test specimen of 20* ^100mm2 size for use; the electrode is bonded to one side of the positive electrode film layer with double-sided tape, and compacted with a pressure roller to make the double-sided tape and the electrode completely fit; the other side of the double-sided tape is adhered to the stainless steel surface, and one end of the sample is bent in the opposite direction with a bending angle of 180°; the high-speed rail tensile machine is used for testing, one end of the stainless steel is fixed to the lower fixture of the tensile machine, and the bent end of the sample is fixed to the upper fixture, the angle of the sample is adjusted to ensure that the upper and lower ends are in a vertical position, and then the sample is stretched at a speed of 50mm/min until the positive current collector is completely removed from the positive electrode film. The layers are peeled off, and the displacement and force in the process are recorded. The force when the force is balanced is divided by the width of the electrode attached to the double-sided adhesive (the width direction of the electrode is perpendicular to the peeling direction) as the bonding force of the electrode per unit length. In this test, the width of the electrode is 20mm.

In some embodiments, the electrolyte absorption rate of the positive electrode plate is greater than 0.31 μg/s, and may be 0.32-0.5 μg/s, and the electrolyte has a density of 1.1-1.2 g/cm ³ . In some embodiments, the liquid absorption rate of the positive electrode plate to the electrolyte can be selected as 0.32μg/s, 0.33μg/s, 0.34μg/s, 0.35μg/s, 0.36μg/s, 0.37μg/s, 0.38μg/s, 0.39μg/s, 0.40μg/s, 0.41μg/s, 0.42μg/s, 0.43μg/s, 0.44μg/s, 0.45μg/s, 0.46μg/s, 0.47μg/s, 0.484μg/s, 0.49μg/s, 0.50μg/s, and the density of the electrolyte is 1.1-1.2g/ ^cm3 .

The liquid absorption rate of the electrode can reflect the ability of the electrode to wet in the electrolyte. The test can be performed by any means known in the art. As an example, the cold-pressed positive electrode is cut into a test sample of 5* ^5cm2 ; first, the sample is dried at 80℃ for 4h, and after the thickness of the electrode is tested, it is fixed on the sample table, and then a capillary with d=200μm is selected, and the end face is polished with 5000 mesh sandpaper to be flat, and the state between the capillary and the electrode is observed under a microscope; the electrolyte is absorbed by the capillary, and the electrolyte height is controlled to h=3mm, and the capillary is lowered to contact the electrode, and a stopwatch is used to time. When the liquid level drops, the timing is stopped, the liquid absorption time t is read, and the data is recorded; the average liquid absorption rate v of the electrode is calculated using the formula, v=π×(d/2) ² ×h×ρ/t. In this test, the density of the selected electrolyte is 1.1-1.2g/ ^cm3 . As an example, the electrolyte can be prepared by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and ethyl methyl carbonate, the mass content of the lithium hexafluorophosphate solution is 12.5%, and the volume ratio of ethylene carbonate to ethyl methyl carbonate in the solution is 3:7.

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to _, lithium cobalt oxide (such as _LiCoO2 ), lithium nickel oxide (such as _LiNiO2 ), lithium manganese oxide (such as _LiMnO2 , _LiMn2O4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel _cobalt manganese oxide (such as LiNi1 _/ 3Co1 _/ _3Mn1 _/ _3O2 (also referred to as _NCM333 ), _{LiNi0.5Co0.2Mn0.3O2} (also referred _to _as _NCM523 ₎ _, _{LiNi0.5Co0.25Mn0.25O2} (also referred _to as _NCM211 ₎ , _{LiNi0.6Co0.2Mn0.2O2} (also referred to as _NCM622 ), _{LiNi0.8Co0.1Mn0.1O2} (also referred to _as _NCM811 ), lithium _nickel _cobalt aluminum oxide ( _such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and at least one of modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

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

[Negative electrode]

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

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

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

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

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

In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent may At least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

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

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

[Electrolytes]

The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

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

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

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

[Isolation film]

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

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

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[Secondary battery]

The present application has no particular restrictions on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG2 is a secondary battery 5 of a square structure as an example. The secondary battery may also be a sodium ion battery, a magnesium ion battery, or a potassium ion battery.

In some embodiments, referring to FIG. 3 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[Battery Template]

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

FIG4 is a battery module 4 as an example. Referring to FIG4 , in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 are housed in the housing space.

[Electrical devices]

In one embodiment of the present application, there is provided an electric device, comprising at least one of a secondary battery of any embodiment, a battery module of any embodiment, or a battery pack of any embodiment.

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

As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

FIG7 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

Example

The following are examples of the present application. The examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If the specific technology or conditions are not specified, the technology or conditions described in the literature in this field or the product instructions shall be followed. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased from the market.

1. Preparation method

Example 1

1) Preparation of binder

Preparation of A-block:

10.5 mmol of 1,4-bis(2-trifluoromethyl-4-aminophenylsulfone)benzene was added into a 500 ml three-necked flask, and 250 ml of m-cresol was added. After stirring for a period of time to completely dissolve it, 3% of the solvent volume of the catalyst isoquinoline was added. 10 mmol of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was slowly added to the above solution in batches, and the solid content in the reaction system was 15%. Stirring was carried out at room temperature for 6 hours under a nitrogen atmosphere. 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 after stirring for 3 hours under a nitrogen atmosphere, the mixture was purified and dried to obtain polyimide-1 having azido groups at both ends, i.e., A-block.

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

The structural formula of 3,3',4,4'-benzophenone tetracarboxylic dianhydride is

The reaction process for preparing the A-block and the structural formula of the A-block are shown below:

Wherein, _A4 is the residue of diamine, _A5 is the residue of dianhydride, and x is the degree of polymerization of A _- block.

A ₅ is

Preparation of B-block:

Vinylidene fluoride monomer, RAFT chain transfer agent (CTA-alkyne) and azobisisobutyronitrile in a molar ratio of 700:1:0.1 were added to 500 ml of tetrahydrofuran solution, wherein the structural formula of the RAFT chain transfer agent is as follows:

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 was precipitated in a large excess of methanol. The polymer was collected by filtration and reprecipitated twice from chloroform with methanol. The resulting product was dried under vacuum at room temperature overnight to remove all traces of residual solvent to obtain polyvinylidene fluoride with alkynyl groups at the end, i.e., B-block polymer.

The reaction process for preparing the B-block is shown below,

Preparation of BAB type block copolymers:

Polyvinylidene fluoride with an alkynyl group at the end, polyimide with an azide group 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 N,N,N',N,'N"-pentamethyldiethylenetriamine (PMDETA) were added. The reaction was stirred at 60°C for 3 days and 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 (the volume ratio of methanol to water was 1:1), the product was collected by filtration, and vacuum dried to obtain a BAB-type block copolymer, which was used as a battery binder.

2) Preparation of positive electrode

Lithium nickel cobalt manganese (NCM) material, conductive agent carbon black, binder, and N-methylpyrrolidone (NMP) are stirred and 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 is then evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

3) Preparation of negative electrode sheet

The active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium hydroxymethyl cellulose (CMC) are dissolved in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2, and the negative electrode slurry is prepared after being evenly mixed; the negative electrode slurry is evenly coated on the negative electrode collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

4) Isolation film

Polypropylene film is used as the isolation film.

5) Preparation of electrolyte

In an argon atmosphere glove box (H ₂ O<0.1ppm, O ₂ <0.1ppm), organic solvents ethylene carbonate (EC)/ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3/7, 12.5% LiPF ₆ lithium salt was added and dissolved in the organic solvent, and stirred uniformly to obtain the electrolyte of Example 1.

6) Preparation of batteries

The positive electrode sheet, the separator, and the negative electrode sheet of Example 1 are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, and the bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the lithium-ion battery product of Example 1.

Embodiments 2 to 11

The battery of Example 2 is prepared in a similar manner to the battery of Example 1, but the polymerization reaction temperature and reaction time of the B-block, the molar amounts of the dianhydride and diamine of the A-block, the polymerization degrees of the B-block and the A-block, and the weight average molecular weights of the B-block and the A-block are adjusted. The specific adjustment parameters are shown in Table 1.

Embodiments 12 to 15

The preparation methods of the batteries of Examples 12 to 15 are similar to those of the battery of Example 1, but the mass percentage of the binder is adjusted. The specific parameters are shown in Table 1 based on the mass of the positive electrode active material.

Example 16

The battery of Example 16 is prepared in a similar manner to the battery of Example 4, except that the diamine The 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.

The structural formula of 1,4-bis(4-aminophenylsulfone)benzene is shown below:

In the A-block polyimide-2 prepared in Example 16, _A4 is

A ₅ is

Embodiment 17

The preparation method of the battery of Example 17 is similar to that of the battery of Example 4, but the diamine is adjusted to 9.5 mmol of 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, so that the prepared A-block is a polyimide containing only trifluoromethyl groups and having azide groups at both ends. The specific parameters are shown in Table 1.

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

In the A-block polyimide-3 prepared in Example 17, _A4 is A ₅ is

Embodiment 18

The preparation method of the battery of Example 18 is similar to that of the battery of Example 4, but the A-block is replaced with polyamide-6 having azide groups at both ends. The specific parameters are shown in Table 1, and the preparation method is as follows:

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

The above reaction schematic process is as follows:

Embodiment 19

The preparation method of the battery of Example 19 is similar to that of the battery of Example 4, but the diamine is adjusted to 1,4-bis(4-aminophenoxy)benzene. The specific parameters are shown in Table 1.

The structural formula of 1,4-bis(4-aminophenoxy)benzene is shown below:

In the A-block polyimide-4 prepared in Example 19, _A4 is A ₅ is

Embodiment 20

The preparation method of the battery of Example 20 is similar to that of the battery of Example 4, but the dianhydride is adjusted to 2,2'-bis(trifluoromethyl)-3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and the diamine is adjusted to 4,4'-diaminodiphenyl ether. The specific parameters are shown in Table 1.

The structural formula of 2,2'-bis(trifluoromethyl)-3,3',4,4'-diphenylether tetracarboxylic dianhydride is as follows:

The structure of 4,4'-diaminodiphenyl ether is shown below.

A4 in the A-block polyimide-5 prepared in Example 20 is

A5

Embodiment 21

The preparation method of the battery of Example 21 is similar to that of the battery of Example 4, but the dianhydride is adjusted to 2,2'-bis(trifluoromethyl)-3,3',4,4'-diphenylethertetracarboxylic dianhydride, and the diamine is adjusted to 1,4-(bis-2-trifluoromethyl-4-aminophenoxy)benzene. The specific parameters are shown in Table 1.

The structure of 1,4-(bis-2-trifluoromethyl-4-aminophenoxy)benzene is shown below.

A4 in the A-block polyimide-6 prepared in Example 21 is

A5

Embodiment 22

The preparation method of the battery of Example 22 is similar to that of the battery of Example 4, but the diamine is adjusted to 4,4'-diaminodiphenyl sulfone. The specific parameters are shown in Table 1.

The structure of 4,4'-diaminodiphenyl sulfone is shown below:

A4 in the A-block polyimide-7 prepared in Example 22 is

A5

Embodiment 23

The preparation method of the battery of Example 23 is similar to that of the battery of Example 4, but the dianhydride is adjusted to 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, and the diamine is adjusted to 1,4-bis(2-trifluoro methyl-4-aminophenone)benzene, the specific parameters are shown in Table 1.

The structure of 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride is shown below:

The structure of 1,4-bis(2-trifluoromethyl-4-aminophenyl)benzene is shown below.

A4 in the A-block polyimide-8 prepared in Example 23 is

A5

Embodiment 24

The preparation method of the battery of Example 24 is similar to that of the battery of Example 4, but the dianhydride is adjusted to 2,2'-bis(trifluoromethyl)-3,3',4,4'-diphenylethertetracarboxylic dianhydride, and the diamine is adjusted to 4,4'-diaminodiphenyl sulfone. The specific parameters are shown in Table 1.

The structure of 2,2'-bis(trifluoromethyl)-3,3',4,4'-diphenylether tetracarboxylic dianhydride is shown below:

The structure of 4,4'-diaminodiphenyl sulfone is shown below,

A4 in the A-block polyimide-9 prepared in Example 24 is

A5

Embodiment 25

The preparation method of the battery of Example 25 is similar to that of the battery of Example 4, but the A-block is replaced with polyamide-66 having azide groups at both ends. The specific parameters are shown in Table 1, and the preparation method is as follows:

10.5 mmol of hexamethylenediamine was added to a 500 ml three-necked flask, and 250 ml of m-cresol was added. After stirring for a period of time to completely dissolve it, 3% of the solvent volume of the catalyst isoquinoline was added; 10 mmol of adipic acid was slowly added to the above solution in batches, and the solid content in the reaction system was 15%. Stirring was carried out at room temperature for 6 hours under a nitrogen atmosphere; stirring at room temperature was completed. Then, 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, and then purified and dried to obtain polyamide-66 having azido groups at both ends, namely, A-block.

The above reaction schematic process is as follows:

Comparative Example 1

The preparation method of the battery of Comparative Example 1 is similar to that of the battery of Example 1, but the binder is polyvinylidene fluoride with a weight average molecular weight of 1.2 million. The specific parameters are shown in Table 1 and are purchased from Solvay Group's 5130.

Comparative Example 2

The preparation method of the battery in Comparative Example 2 is similar to that of the battery in Example 1, but the binder is polyimide-1 with a weight average molecular weight of 1.2 million. The specific parameters are shown in Table 1. The preparation method is similar to that of the polyimide-1 in Example 1, except that the diamine content is adjusted to 24 mmol; the dianhydride content is adjusted to 24.5 mmol, wherein the solid content in the reaction system is 15%, and stirring is carried out at room temperature for 12 hours under a nitrogen atmosphere. After stirring at room temperature, the temperature is raised to 180°C, and stirring is continued for 20 hours under a nitrogen atmosphere. The polyimide containing trifluoromethyl and sulfone groups is purified and dried, and the weight average molecular weight thereof is 1.2 million.

Comparative Example 3

The preparation method of the battery of Comparative Example 3 is similar to that of the battery of Example 1, but the binder is a blend of polyvinylidene fluoride and polyimide. The specific parameters are shown in Table 1. The preparation method is as follows:

Blending: The polyimide-1 in comparative example 2 and the polyvinylidene fluoride in comparative example 1 were blended in a mass ratio of 6:4 to obtain a polyvinylidene fluoride and polyimide-1 blend adhesive. dose.

2. Performance Test

1. Pole performance test

1) Diaphragm resistance test

Cut the dried positive electrode film layer at the left, middle and right of the positive electrode piece into small discs with a diameter of 3mm. Turn on the power of Yuanneng Technology's electrode piece resistor meter, place it in the appropriate position of the "probe" of the electrode piece resistor meter, click the "start" button, wait for the reading to stabilize, and then read it. Test two positions of each small disc, and finally calculate the average value of the six measurements, which is the film resistance of the electrode piece.

2) Adhesion test

With reference to GB-T2790-1995 national standard "Adhesive 180° Peel Strength Test Method", the adhesion test process of the embodiments and comparative examples of the present application is as follows:

Use a blade to cut a sample with a width of 30mm and a length of 100-160mm, and stick a special double-sided tape on the steel plate. The tape is 20mm wide and 90-150mm long. Stick the positive electrode film layer of the electrode sample cut earlier on the double-sided tape, and then roll it three times in the same direction with a 2kg roller. Fix a paper tape with a width equal to the electrode and a length of 250mm on the electrode collector and fix it with wrinkled glue. Turn on the power of the Sansi tensile machine (sensitivity is 1N), the indicator light is on, adjust the limit block to the appropriate position, and fix the end of the steel plate without the electrode with the lower clamp. Fold the paper tape upwards and fix it with the upper clamp. Use the "up" and "down" buttons on the manual controller attached to the tensile machine to adjust the position of the upper clamp. Then test and read the value. The force when the electrode is balanced divided by the width of the tape is taken as the bonding force of the electrode per unit length to characterize the bonding strength between the positive electrode film layer and the current collector.

3) Electrode liquid absorption rate test

The cold-pressed positive electrode was cut into a square test sample with a side length of 5 cm; first, the sample was dried at 80°C for 4 h, and after the thickness of the electrode was tested, it was fixed on the sample table, and then a capillary with d = 200 μm was selected, and the end face was polished with 5000 mesh sandpaper until it was flat, and the state between the capillary and the electrode was observed under a microscope; the electrolyte was absorbed by the capillary, and the electrolyte height was controlled to h = 3 mm, and the capillary was lowered to contact the electrode, and a stopwatch was used at the same time. When the liquid level was completely lowered, the timing was stopped, the liquid absorption time t was read, and the data was recorded; the average liquid absorption rate v of the electrode was calculated using the formula, v = π × (d/2)2 × h × ρ/t.

2. Battery performance test

1) Metal dissolution test

At room temperature, the prepared lithium-ion battery was charged and discharged for the first time with a current of 0.5C (i.e., the current value that completely discharges the theoretical capacity within 2 hours). The charging was constant current and constant voltage charging, the termination voltage was 4.2V, the cut-off current was 0.05C, and the discharge termination voltage was 2.8V. After the battery was left for 24 hours, it was charged to 4.2V with a constant current and constant voltage of 0.5C, and then the fully charged battery was discharged with a current of 1C. The discharge termination voltage was 2.8V. The battery cell was disassembled, the negative electrode plate was taken out, and the ICP (inductively coupled plasma) method was used to test the deposition of metal Co and Mn.

2) Battery cycle capacity retention test

The test process of battery cycle capacity retention rate is as follows: at 25°C, 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 for 5 minutes, and then discharged to 2.8V at 1/3C. The obtained capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery, and record the discharge capacity Cn of the battery after the nth cycle at the same time. Then the battery capacity retention rate after each cycle is Pn = Cn/C0*100%, with the 500 point values of P1, P2...P500 as the vertical coordinates and the corresponding number of cycles as the horizontal coordinates, to obtain a curve graph of battery capacity retention rate and cycle number.

In the test process, the first cycle corresponds to n=1, the second cycle corresponds to n=2, ... the 500th cycle corresponds to n=500. The battery capacity retention rate data corresponding to the embodiments or comparative examples in Table 1 are the data measured after 500 cycles under the above test conditions, that is, the value of P500.

3) Full battery capacity retention rate at 45°C

Charge to 4.2V with a constant current of 1C, then charge to a current of 0.05C with a constant voltage of 4.2V, leave for 10 minutes, then discharge to a cut-off voltage of 2.8V with a constant current of 1C, and record the capacity before storage CAP ₁ ; charge to a cut-off voltage of 4.2V with a constant current of 1C, then charge to a current of 0.05C with a constant voltage of 4.2V, place the lithium-ion battery in an oven at 45°C for 120 days, take it out and discharge to 2.8V with a constant current of 1C, record the capacity after storage CAP ₂ , and calculate the storage capacity retention rate of the lithium-ion secondary battery according to the following formula:

Lithium ion secondary battery storage capacity retention rate (%) = CAP ₂ /CAP ₁ * 100%.

4) Full battery 70℃ gas generation test

Full batteries with 100% state of charge (SOC) are stored at 70°C. The open circuit voltage (OCV) and AC internal resistance (IMP) of the battery cells are measured before, during and after storage to monitor the SOC, and the volume of the battery cells is measured. The full battery is taken out after every 48 hours of storage, and the OCV and IMP are tested after standing for 1 hour. The volume of the battery cells is measured by the water displacement method after cooling to room temperature. The water displacement method is to first use a balance that automatically converts units using dial data to measure the gravity F1 of the battery cell separately, and then place the battery cell completely in deionized water (density is known to be 1g/ ^cm3 ), and measure the gravity F2 of the battery cell at this time. The buoyancy Ffloat on the battery cell is F1-F2, and then according to the Archimedean principle Ffloat=ρgV_排, the battery cell volume V=(F1-F2)/ρg is calculated.

After each volume test, the battery cell is recharged at a constant current of 1C to 4.25V, and then charged at a constant voltage of 4.25V until the current drops to 0.05C. After the recharging is completed, the battery cell is put into the furnace to continue testing.

After 90 days of storage, the volume of the battery cells was measured, and the increase in the volume of the battery cells after storage relative to the volume of the battery cells before storage, i.e. the gas production, was calculated. The gas production/initial volume of the battery cells gave the battery volume expansion rate.

3. Polymer detection

1) Weight average molecular weight test method

A Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141) was used. A 3.0% polystyrene solution sample was used as a reference, and a matching chromatographic column (oily: Styragel HT5 DMF7.8*300mm+Styragel HT4) was selected. A 3.0% polymer solution was prepared with purified N-methylpyrrolidone (NMP) solvent, and the prepared solution was allowed to stand for one day for use. During the test, tetrahydrofuran was first drawn with a syringe and rinsed, and repeated several times. Then 5 ml of the experimental solution was drawn, the air in the syringe was removed, and the needle tip was wiped dry. Finally, the sample solution was slowly injected into the injection port. Data was obtained after the indication stabilized.

The performance tests of the pole pieces and the batteries in the embodiments and comparative examples are shown in Tables 1 and 2.

Table 1

Table 2

III. Analysis of test results of various embodiments and comparative examples

The binders in Examples 1 to 25 all include BAB type block copolymers, wherein the B-blocks all include structural units derived from vinylidene fluoride, and the A-blocks include imide or amide structural units. The binders prepared with the above polyvinylidene fluoride-polyimide-polyvinylidene fluoride block copolymers or polyvinylidene fluoride-polyamide-polyvinylidene fluoride block copolymers can reduce the film resistance of the pole piece, increase the liquid absorption rate of the pole piece, inhibit the dissolution of transition metals in the positive electrode active material, and thus improve the cycle performance and storage performance of the battery.

From the comparison between Examples 1 to 6 and Comparative Example 2, it can be seen that, compared with the single non-fluorinated polymer, using the BAB triblock copolymer as a binder can improve the cycle performance and high-temperature storage performance of the battery.

From the comparison of Examples 1 to 6 with Comparative Example 3, it can be seen that compared with the simple blending of non-fluorinated polymers and fluorinated polymers, using BAB triblock copolymer as a binder can reduce the membrane resistance of the electrode, improve the adhesion of the electrode, and improve the cycle performance and high-temperature storage performance of the battery.

From the comparison of Examples 1 to 7 with Comparative Example 1, it can be seen that in the block copolymer, based on the total mass of the block copolymer, when the mass percentage of each fluorine-containing block B-block is 15% to 35%, and the mass percentage of the non-fluorine block A-block is 30% to 70%, the BAB-type block copolymer can reduce the diaphragm resistance of the electrode, effectively inhibit 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 gas production of the battery at high temperature.

From the comparison between Examples 1 to 5 and Examples 6 to 7, it can be seen that in the block copolymer, based on the total mass of the block copolymer, when the mass percentage of each fluorine-containing block B-block is 17.5% to 32.5%, and the mass percentage of the non-fluorine block A-block is 35% to 65%, the BAB-type block copolymer can reduce the diaphragm 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, thereby improving the overall performance of the battery.

From the comparison of Examples 1 to 11, Examples 16 to 25 and Comparative Example 1, it can be seen that the BAB type block copolymer with a weight average molecular weight of 400,000 to 2,000,000 enables the electrode to have an excellent liquid absorption rate and a low membrane resistance. In addition, the block copolymer can inhibit the positive electrode active material The dissolution of transition metals improves the battery's cycle performance, high-temperature storage performance and safety performance.

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

From the comparison between Example 16 and Example 19, it can be seen that 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 amount of transition metals, and improve the cycle performance and high-temperature storage performance of the battery.

From the comparison between Example 4 and Example 19, it can be seen that when the A-block contains an imide structural unit containing a trifluoromethyl group and a sulfone group, the BAB-type block copolymer can further improve the adhesion and liquid absorption rate of the electrode, reduce the dissolution amount of transition metals, and improve the cycle performance and high-temperature storage performance of the battery.

It can be seen from Examples 1 and 12 to 15 that 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 an excellent liquid absorption rate and a lower membrane resistance, so that the battery has high cycle performance and high temperature storage performance.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

A BAB type block copolymer, characterized in that it comprises an A-block and a B-block, wherein the B-block comprises a structural unit represented by formula I, and the A-block comprises one or more of a structural unit represented by formula II, a structural unit represented by formula III, and a structural unit represented by formula IV.

R1 , R2 , R3 are each independently selected from one or more of hydrogen, fluorine, and C1-3 alkyl containing at least one fluorine atom; R4 is selected from substituted or unsubstituted C6-25 aromatic groups; and R5 , R6 , R7 , R8 are each independently selected from substituted or unsubstituted C2-24 alkyl groups and substituted or unsubstituted C6-25 aromatic groups.
The BAB type block copolymer according to claim 1, characterized in that, in the BAB type block copolymer, the mass percentage of each of the B-blocks 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 BAB type block copolymer according to claim 1 or 2, characterized in that the weight average molecular weight of the BAB type block copolymer is 400,000 to 2,000,000.
The BAB type block copolymer according to any one of claims 1 to 3, characterized in that the A-block comprises a structural unit of formula II containing a trifluoromethyl group.
The BAB type block copolymer according to claim 4, characterized in that the structural unit represented by formula II containing a trifluoromethyl group comprises

One or more of .
The BAB type block copolymer according to any one of claims 1 to 5, characterized in that the A-block comprises a structural unit represented by formula II containing a sulfone group.
The BAB type block copolymer according to claim 6, characterized in that the structural unit represented by formula II containing a sulfone group comprises

One or more of .
The BAB-type block copolymer according to any one of claims 1 to 7, characterized in that the structural unit represented by formula I comprises one or more of a structural unit derived from vinylidene fluoride, a structural unit derived from tetrafluoroethylene, a structural unit derived from vinyl fluoride, a structural unit derived from trifluoroethylene, and a structural unit derived from hexafluoropropylene.
The BAB type block copolymer according to any one of claims 1 to 8, characterized in that the structural unit represented by formula II comprises

One or more of , wherein n is any integer between 6 and 12.
A method for preparing a BAB type block copolymer, characterized in that it comprises the following steps:

Preparation of B-block: polymerizing at least one monomer represented by formula V to prepare B-block,

wherein A 1 , A 2 , and A 3 are each independently selected from one or more of hydrogen, fluorine, and a C 1-3 alkyl group containing at least one fluorine atom;

Preparation of A-block: polymerizing at least one diamine with at least one dibasic anhydride or at least one dibasic acid to prepare A-block, or ring-opening polymerization of lactam monomer to prepare A-block;

Preparation of BAB type block copolymer: The B-block and the A-block are joined to prepare a BAB type block copolymer.
The method for preparing a BAB type block copolymer according to claim 10, characterized in that the preparation of the B-block specifically comprises:

At least one monomer represented by formula V, a chain transfer agent and an initiator are subjected to reversible addition-fragmentation chain transfer polymerization at a reaction temperature of 70 to 90° C. for 5 to 8.5 hours to obtain a B-block having an azide group or an alkynyl group at one end.
The method for preparing a BAB type block copolymer according to claim 10 or 11, characterized in that the preparation of the A-block specifically comprises:

The catalyst, at least one diamine and at least one dibasic anhydride or at least one dibasic acid are stirred and reacted at room temperature for 4 to 10 hours, and then heated to 170 to 210° C. for 5 to 20 hours. A product is obtained in which both end groups are anhydride, carboxyl or amino;

The terminal groups of the product are subjected to functionalization reaction to obtain the A-block having alkynyl groups or azide groups at both ends.
The method for preparing a BAB type block copolymer according to claim 10 or 11, characterized in that the preparation of the A-block specifically comprises:

Polymerizing an end group regulator, water and at least one lactam monomer at a reaction temperature of 250° C. to 280° C. for 12 to 24 hours to obtain a product having end groups at both ends being carboxyl or amino groups;

The terminal groups of the product are subjected to functionalization reaction to obtain the A-block having alkynyl groups or azide groups at both ends.
The method for preparing the BAB type block copolymer according to any one of claims 10 to 13, characterized in that the preparation of the BAB type block copolymer specifically comprises:

The A-block having alkynyl or azide groups at both ends and the B-block having an azide or alkyne group at one end are mixed and subjected to a click reaction to prepare a BAB type block copolymer, wherein the terminal groups of the B-block and the A-block are different.
The method for preparing a BAB type block copolymer according to any one of claims 11 to 14, characterized in that the chain transfer agent is a RAFT chain transfer agent containing a terminal acetylenic group or an azide group.
The method for preparing a BAB type block copolymer according to any one of claims 13 to 15, characterized in that the terminal group regulator is a diamine or a dibasic acid.
Use of the BAB type block copolymer according to any one of claims 1 to 9 in a secondary battery.
The use according to claim 17, characterized in that the secondary battery It includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.
A positive electrode plate, characterized in that it includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, a conductive agent and a binder, and the binder is a BAB type block copolymer as described in any one of claims 1 to 9 or a BAB type block copolymer prepared by the preparation method as described in any one of claims 10 to 16.
The positive electrode sheet according to claim 19 is characterized in that the mass percentage of the binder is 0.1% to 3%, based on the total mass of the positive electrode active material.
The positive electrode plate according to claim 19 or 20 is characterized in that the bonding 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 optionally 11.5-15 N/m.
The positive electrode plate according to any one of claims 19 to 21, characterized in that the electrolyte absorption rate of the positive electrode plate is greater than 0.31 μg/s, and can be 0.32-0.5 μg/s, and the electrolyte density is 1.1-1.2 g/cm 3 .
A secondary battery, characterized in that it comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a separator, a negative electrode sheet and a positive electrode sheet according to any one of claims 19 to 23.
An electrical device, characterized by comprising the secondary battery as claimed in claim 23.