CN115286804A

CN115286804A - BAB type block copolymer, preparation method, binder, positive pole piece, secondary battery and electric device

Info

Publication number: CN115286804A
Application number: CN202211206556.7A
Authority: CN
Inventors: 曾子鹏; 李�诚; 刘会会; 孙成栋; 王景明
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-09-30
Filing date: 2022-09-30
Publication date: 2022-11-04
Anticipated expiration: 2042-09-30
Also published as: CN117801293A; CN115286804B

Abstract

The application provides a BAB type block copolymer, a preparation method, a binder, a positive pole piece, a secondary battery and an electric device. The BAB-type block copolymer comprises an A-block comprising structural units derived from a monomer of formula I and a B-block comprising structural units derived from a monomer of formula II wherein R ₁ 、R ₂ 、R ₃ Each independently selected from hydrogen, fluorine, C containing at least one fluorine atom _1‑3 One or more of alkyl, R ₄ 、R ₅ 、R ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1‑5 An alkyl group. Preparation of adhesives from BAB-type block copolymersThe electrode plate has excellent binding power and flexibility, and the battery has high first-effect performance, cycle performance and high-temperature storage performance under the condition of low addition of the binding agent.

Description

BAB type block copolymer, preparation method, binder, positive pole piece, secondary battery and electric device

Technical Field

The application relates to the technical field of secondary batteries, in particular to a BAB type block copolymer, a preparation method, a binder, a positive pole piece, a secondary battery, a battery module, a battery pack and an electric device.

Background

In recent years, secondary batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power, and solar power stations, and in various fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the spread of secondary battery applications, higher demands are also made on energy density, cycle performance, and the like.

The adhesive is a common material in the secondary battery, and has great requirements on a pole piece, an isolating membrane, a packaging part and the like of the battery. However, the existing adhesive has poor adhesion, and the requirement of pole piece adhesion can be met by adding a large amount of the adhesive, so that the improvement of the energy density of the battery can be limited. Thus, the existing binders still need to be improved.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide a BAB type block copolymer which can give a high adhesive force and a low sheet resistance to a pole piece, a low amount of a transition metal eluted from a battery, and an excellent high-temperature storage property to a battery with a low addition amount of the BAB type block copolymer as an adhesive.

In a first aspect of the present application, there is provided a BAB-type block copolymer comprising an A-block comprising structural units derived from a monomer of formula I and a B-block comprising structural units derived from a monomer of formula II,

formula I

Formula II

Wherein R is ₁ 、R ₂ 、R ₃ Each independently selected from hydrogen, fluorine, C containing at least one fluorine atom _1-3 One or more of alkyl, R ₄ 、R ₅ 、R ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1-5 An alkyl group.

The adhesive prepared by the BAB type block copolymer can maximize the weight average molecular weight of a fluorine-containing block and a non-fluorine block, fully exert the respective advantages of the fluorine-containing adhesive and the non-fluorine adhesive and realize the complementary advantages. Compared with the traditional PVDF binder, the binder can reduce the membrane resistance of the pole piece, improve the binding power of the pole piece, reduce the dissolution amount of transition metal in the battery and improve the high-temperature storage performance of the battery. In addition, the performance of the pole piece and the battery can basically reach the level which can be reached only under the condition of high addition of the binder in the prior art under the condition of low addition of the binder, and the energy and the capacity of the battery are further promoted.

In any embodiment, the B-block further comprises structural units derived from a monomer of formula III,

formula III

Wherein R is ₇ 、R ₈ 、R ₉ Each independently selected from hydrogen, substituted or unsubstituted C _1-5 Alkyl radical, R ₁₀ One selected from ester group, aromatic group, hydroxyl group and amide group.

In any embodiment, the structural units derived from the monomer of formula I are present in a molar amount of from 40% to 60% based on the total moles of all structural units in the block copolymer.

The BAB type block copolymer with the mole content of the structural unit derived from the monomer shown in the formula I within a proper range can enable the pole piece to have excellent binding power and good flexibility, and the battery has excellent first-effect performance, cycle performance and high-temperature storage performance.

In any embodiment, the weight average molecular weight of the BAB type block copolymer is 40 to 200 ten thousand.

The BAB type block copolymer with the weight-average molecular weight within a proper range can reduce the sheet resistance of the pole piece, improve the cohesive force of the pole piece, inhibit the dissolution of transition metal in the positive active material, and improve the first-effect performance, the cycle performance and the high-temperature storage performance of the battery.

In any embodiment, the weight average molecular weight of the a-block in the block copolymer is 20 to 105 million.

The BAB type block copolymer with the weight average molecular weight of the A-block in a proper range can reduce the diaphragm resistance of the pole piece, improve the cohesive force of the pole piece, inhibit the dissolution of transition metal in the positive active material, and improve the first effect performance, the cycle performance and the high-temperature storage performance of the battery.

In any embodiment, each B-block in the block copolymer has a weight average molecular weight of 10 to 50 million.

The BAB type block copolymer with the weight average molecular weight of each B-block in a proper range can reduce the diaphragm resistance of the pole piece, improve the cohesive force of the pole piece and inhibit the dissolution of transition metal in the positive active material, thereby improving the first effect performance, the cycle performance and the high-temperature storage performance of the battery.

In any embodiment, the monomer of formula I is selected from one or more of vinylidene fluoride, tetrafluoroethylene, vinyl fluoride, and hexafluoropropylene.

In any embodiment, the monomer of formula II is selected from one or more of acrylonitrile and crotononitrile.

In any embodiment, the monomer represented by formula III is selected from one or more of styrene, vinyl alcohol, acrylamide, ethyl acrylate, and butyl methacrylate. The raw materials are simple and easy to obtain, and compared with the traditional binder, the production cost can be greatly reduced.

In any embodiment, the block copolymer is one of polyacrylonitrile-polyvinylidene fluoride-polyacrylonitrile block copolymer, polyacrylonitrile-polyvinyl fluoride-polyacrylonitrile block copolymer, polyacrylonitrile-polytetrafluoroethylene-polyacrylonitrile block copolymer, poly (acrylonitrile-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinyl fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polytetrafluoroethylene-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-butyl methacrylate-styrene) -polyvinylidene fluoride-poly (acrylonitrile-butyl methacrylate-styrene) block copolymer, poly (acrylonitrile-vinyl alcohol) -polyvinylidene fluoride-poly (acrylonitrile-vinyl alcohol) block copolymer.

The second aspect of the present application also provides a method for preparing a BAB-type block copolymer, comprising the steps of:

preparation of the A-block: polymerizing at least one monomer of formula I to prepare an A-block,

formula I

Wherein R is ₁ 、R ₂ 、R ₃ Each independently selected from hydrogen, fluorine, C containing at least one fluorine atom _1-3 One or more of alkyl;

preparation of the B-block: polymerizing monomer units comprising at least one monomer of formula II to produce a B-block,

formula II

Wherein R is ₄ 、R ₅ 、R ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1-5 An alkyl group.

Preparation of a BAB type Block copolymer: joining the A-block and the B-block to prepare a BAB type block copolymer.

Compared with the traditional copolymerization method, the preparation method can maximize the weight average molecular weight of the fluorine-containing block and the non-fluorine block, fully exert the respective advantages of the fluorine-containing binder and the non-fluorine binder and realize the complementary advantages. The BAB type triblock copolymer binder prepared by the method can reduce the diaphragm resistance of a pole piece, improve the binding power of the pole piece, and improve the cycle performance and high-temperature storage performance of a battery by reducing the dissolution amount of transition metal. In addition, the adhesive can ensure that the adhesive force and flexibility of the pole piece, the first-effect performance, the cycle performance and the high-temperature storage performance of the battery can basically reach the level which can be reached only under the condition of high addition of the adhesive in the prior art under the condition of low addition, and is beneficial to improving the energy density of the battery.

In any embodiment, the monomer unit further comprises at least one monomer of formula III,

formula III

In any embodiment, a method of making an a-block comprises:

at least one monomer shown in the formula I and a first initiator are subjected to polymerization reaction at the reaction temperature of 80-95 ℃ for 2.5-5 hours, the terminal group of the product is subjected to substitution reaction, and an A-block with azide groups or alkynyl groups at two ends is prepared.

By adopting the preparation method, the A block with azide at the tail end or alkynyl at the tail end is successfully prepared.

In any embodiment, a method of making a B-block comprises:

and (3) polymerizing the monomer unit, the chain transfer agent and the second initiator through reversible addition-fragmentation chain transfer at the reaction temperature of 60-75 ℃ for 4-8 hours to obtain the B-block with the alkynyl or azide group at the end.

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

In any embodiment, a method of making a BAB-type block copolymer comprises:

mixing an A-block with azide groups or alkynyl at both ends with a B-block with alkynyl or azide groups at the tail end, and carrying out click reaction to prepare the BAB type block copolymer, wherein the terminal groups of the A-block and the B-block are different.

The preparation method has the advantages of high efficiency, stability and high specificity, and the yield of the product is improved.

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

In any embodiment, the first initiator is a symmetric difunctional initiator.

In any embodiment, the second initiator is selected from one or two of azobisisobutyronitrile, azobisisoheptonitrile.

In a third aspect of the present application, there is provided a use of a BAB-type block copolymer in a secondary battery.

The fourth aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, where 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 a preparation method in any embodiment.

The positive pole piece has excellent binding power and good flexibility, and simultaneously has low resistance of a pole piece diaphragm and low elution amount of transition metal.

In any embodiment, the mass fraction of the binder is 0.1% to 3%, and optionally 0.5% to 1.2%, based on the total mass of the positive electrode active material.

The mass fraction of the binder is controlled within a reasonable range, the binder can reduce the diaphragm resistance of the pole piece, improve the binding power of the pole piece, and simultaneously ensure that the pole piece has good flexibility. In addition, the binder can reduce the elution amount of transition metal and reduce the deposition of transition metal ions on the surface of the negative electrode, thereby improving the cycle performance and the high-temperature storage performance of the battery.

In any embodiment, the adhesion per unit length between the positive electrode film layer and the positive electrode current collector is not less than 11N/m. The positive pole film layer of the pole piece has high bonding strength with the positive pole current collector, and the positive pole film layer is not easy to fall off from the positive pole current collector in the using process, so that the cycle performance and the safety of the battery are improved.

In any embodiment, after the positive pole piece is subjected to bending test for not less than 3 times, the positive pole piece has a light transmission phenomenon. The pole piece can be through being no less than 3 times the test of buckling, shows that the pole piece has good pliability, is difficult for appearing the pole piece in the production process and bursts apart, the phenomenon that the pole piece appears brittle failure in the use, helps improving the yields of battery, improves the security performance of battery.

In any embodiment, the sheet resistance of the positive electrode sheet is 1 Ω or less. The pole piece has lower diaphragm resistance, which shows that the material in the anode film layer is uniformly dispersed, and the anode film layer has good electron transmission efficiency, thereby being beneficial to the performance of the battery.

In a fifth aspect of the present application, there is provided a secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a separator, a negative electrode tab, and the positive electrode tab of the fourth aspect of the present application.

In any embodiment, 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.

In a sixth aspect of the present application, there is provided a battery module including the secondary battery of the fifth aspect of the present application.

In a seventh aspect of the present application, there is provided a battery pack including the battery module of the sixth aspect of the present application.

In an eighth aspect of the present application, there is provided an electric device including at least one of the secondary battery of the fifth aspect of the present application, the battery module of the sixth aspect, or the battery pack of the seventh aspect.

Drawings

FIG. 1 is a schematic illustration of the preparation of a BAB type block copolymer according to one embodiment of the present application;

fig. 2 is a schematic view of a secondary battery according to an embodiment of the present application;

fig. 3 is an exploded view of a secondary battery according to an embodiment of the present application shown in fig. 2;

FIG. 4 is a schematic view of a battery module according to an embodiment of the present application;

fig. 5is a schematic view of a battery pack according to an embodiment of the present application;

fig. 6 is an exploded view of the battery pack of an embodiment of the present application shown in fig. 5;

fig. 7 is a schematic diagram of an electric device in which the secondary battery according to the embodiment of the present application is used as a power source.

Description of the reference numerals:

1, a battery pack; 2, putting the box body on the box body; 3, discharging the box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 cover plate; 6 BAB type block copolymers; 61 An A-block; 611 Both end groups of the A-block; 612 structural units derived from a monomer of formula I; 62 A B-block; 621 The terminal group of the B-block; 622 are derived from structural units of monomers represented by formula II.

Detailed Description

Hereinafter, embodiments of the positive electrode active material, the method for producing the same, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device according to the present application are specifically disclosed in detail with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually the same structures may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Further, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.

All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.

The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.

In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).

Polyvinylidene fluoride (PVDF) is one of the most widely used binder types in secondary batteries today. However, polyvinylidene fluoride synthesized by the traditional method has low viscosity, and a large amount of polyvinylidene fluoride is often added to ensure effective bonding of active materials, so that the pole piece can achieve effective bonding force. The increase of the dosage of the binder can reduce the loading of the active material in the pole piece, and has negative influence on the improvement of the power performance of the battery. Meanwhile, the low content of the PVDF binder is difficult to effectively relieve the phenomenon that transition metals in the positive active material are dissolved out, and is not beneficial to the improvement of the cycle performance of the battery.

[ Binder ]

Based on this, the present application provides a BAB type block copolymer comprising an A-block containing structural units derived from a monomer of formula I and a B-block containing structural units derived from a monomer of formula II,

formula I

Formula II

Wherein R is ₁ 、R ₂ 、R ₃ Each independently selected from hydrogen, fluorine, C containing at least one fluorine atom _1-3 One or more of alkyl radicals, R ₄ 、R ₅ 、R ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1-5 An alkyl group.

As used herein, the term "block copolymer" is a specialized polymer prepared by joining together two or more polymer segments of differing properties. Block polymers with a specific structure will exhibit properties that differ from simple linear polymers, as well as from a mixture of many random copolymers and even homopolymers. The AB type and the BAB type are common, wherein A and B are long chain segments; there are Also (AB) n type multistage copolymers in which the A and B segments are relatively short.

As used herein, the term "BAB-type block copolymer" refers to a triblock copolymer having an A-block in the middle and B-blocks on either side. Wherein the A-block and the B-block are each a polymer segment having a predetermined weight average molecular weight formed by polymerizing different monomers. In some embodiments, the A-block is a long sequence segment formed by polymerization of a fluoromonomer and the B-block is a long sequence segment formed by polymerization of one or more non-fluoromonomers. The A-block and B-block are covalently bonded in an ordered manner to form a BAB type block copolymer. Take the example of a BAB-type block polymer prepared in example 1, wherein the B-block poly (acrylonitrile-acrylamide-ethyl acrylate), formed by polymerization of acrylonitrile monomer, acrylamide monomer and acrylic acid monomer, has a weight average molecular weight of 45 ten thousand; the A-block is polyvinylidene fluoride and is formed by polymerizing a vinylidene fluoride monomer, and the weight average molecular weight is 40 ten thousand; the end groups on both sides of the B-block and the A-block are bonded to give a poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer (BAB type block copolymer) having a weight average molecular weight of 120 ten thousand.

In this context, the term "polymer" encompasses on the one hand a collection of chemically uniform macromolecules which are produced by polymerization and which differ in respect of degree of polymerization, molar mass and chain length. The term on the other hand also includes derivatives of such macromolecular assemblies formed by polymerization reactions, i.e. compounds which can be obtained by reactions, e.g. additions or substitutions, of functional groups in the macromolecules in question and which can be chemically homogeneous or chemically heterogeneous.

Herein, the term "C _1-3 Alkyl "refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, with no unsaturated bonds present in the group, having from one to three carbon atoms, and attached to the rest of the molecule by single bonds.C _1-3 Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl).

Herein, the term "C _1-5 Alkyl "refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, with no unsaturated bonds present in the group, having from one to five carbon atoms, and attached to the rest of the molecule by single bonds. C _1-5 Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, n-butyl, 1-methylethyl (isopropyl), n-butyl, t-butyl, isoamyl.

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

In some embodiments, the monomer of formula I is selected from one or more of vinylidene fluoride, tetrafluoroethylene, vinyl fluoride, and hexafluoropropylene.

In some embodiments, the monomer of formula II is selected from one or more of acrylonitrile and butenenitrile.

In some embodiments, the block copolymer may be selected from one or more of polyacrylonitrile-polyvinylidene fluoride-polyacrylonitrile block copolymer, polyacrylonitrile-polyvinyl fluoride-polyacrylonitrile block copolymer, polyacrylonitrile-polytetrafluoroethylene-polyacrylonitrile block copolymer, poly (acrylonitrile-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polytetrafluoroethylene-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-butyl methacrylate-styrene) -polyvinylidene fluoride-poly (acrylonitrile-butyl methacrylate-styrene) block copolymer, poly (acrylonitrile-vinyl alcohol) -polyvinylidene fluoride-poly (acrylonitrile-vinyl alcohol) block copolymer.

In some embodiments, the BAB type block copolymer serves as a binder in a secondary battery. In some embodiments, the BAB type block copolymer serves 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 dispersion in a dispersing medium.

In some embodiments, the dispersion medium for the binder is an aqueous solvent, such as water. I.e. the binder is dissolved in an aqueous solvent.

In some embodiments, the dispersion medium of the binder is an oily solvent, examples of which include, but are not limited to, dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethylcellulose, polycarbonates. I.e. the binder is dissolved in an oily solvent.

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

In some embodiments, the binder serves as a positive electrode binder for binding a positive electrode active material and/or a conductive agent to form an electrode.

In some embodiments, the binder serves as a negative electrode binder for binding a negative electrode active material and/or a conductive agent to form an electrode.

The fluorine element contained in the A-block and the hydroxyl or/and carboxyl on the surface of the positive active material and the surface of the current collector are easy to form a hydrogen bond effect, so that the pole piece has excellent binding power. The B-block contains a strong polar group cyano group, and can form a hydrogen bond with strong acting force and a dipole-dipole effect with hydroxyl on the surface of the positive active material, so that the adhesive can play a role in maintaining stability and dispersing in slurry under a low addition amount, the adhesive is favorable for improving the adhesive force of the pole piece, and the sheet resistance of the pole piece is reduced. And the cyano group with strong polarity can enhance the stability of a molecular structure, improve the glass transition temperature of the block copolymer, improve the rigidity and the thermal stability of the block copolymer, contribute to improving the oxidation stability of a pole piece, and can improve the cycle and the rate capability of a battery. In addition, the cyano group enables the B-block to have a certain coating property on the positive active material, and the cyano group in the B-block can be complexed with the transition metal ions on the surface of the positive active material to prevent the dissolution of the transition metal ions, so that the deposition of the transition metal ions on the surface of the negative electrode is reduced, and the cycle performance and the high-temperature storage performance of the battery are improved.

In summary, the binder prepared from the BAB type block copolymer can maximize the weight average molecular weight of the fluorine-containing block and the non-fluorine-containing block, fully exert the respective advantages of the fluorine-containing binder and the non-fluorine-containing binder, and realize the complementary advantages. Compared with the traditional PVDF binder, the binder can reduce the diaphragm resistance of the pole piece, improve the binding power of the pole piece, reduce the dissolution amount of transition metal in the battery and improve the high-temperature storage performance of the battery. In addition, the performance of the pole piece and the battery can basically reach the level which can be reached only under the condition of high addition of the binder in the prior art under the condition of low addition of the binder, and the energy and the capacity of the battery are further promoted.

In some embodiments, the B-block also contains structural units derived from a monomer of formula III,

formula III

As used herein, the term "ester group" refers to the group-COOR ₁₁ Group, R ₁₁ Selected from alkyl groups substituted or unsubstituted with substituents.

As used herein, the term "aromatic group" refers to functional groups or substituents derived from simple aromatic rings, such as phenyl, o-tolyl, 1-naphthyl (or α -naphthyl).

As used herein, the term "hydroxy" refers to an-OH group.

As used herein, the term "amide group" refers to

，R ₁₂ 、R ₁₃ Each independently selected from hydrogen, substituted or unsubstituted alkyl.

In some embodiments, the monomer represented by formula III is selected from one or more of styrene, vinyl alcohol, acrylamide, ethyl acrylate, and butyl methacrylate.

In some embodiments, the B-block comprises structural units derived from monomers of formula III that contain an ester group.

The ester group contained in the B-block is beneficial to weakening the too strong dipole moment between the cyano groups, reducing the problem of pole piece brittleness caused by the obstruction of the free movement of the adhesive chain segment due to the too strong acting force between the cyano groups in the B-block and improving the safety performance of the battery. In addition, the ester group has good affinity with the electrolyte, and is beneficial to enhancing the contact between the electrolyte and the positive active material, thereby improving the ionic conductivity of the pole piece and reducing the resistance of the diaphragm.

In some embodiments, the B-block comprises structural units derived from monomers of formula III that contain an aromatic group.

The B-block contains aryl which is helpful to improve the mechanical strength of the pole piece so as to respond to the volume change of the positive active material in the charging and discharging process, keep the structural integrity of the electrode in the charging and discharging process and improve the first effect performance, the cycle performance and the high-temperature storage performance of the battery.

In some embodiments, the B-block comprises structural units derived from monomers of formula III that contain hydroxyl groups.

Hydroxyl contained in the B-block can form a hydrogen bond with the positive active material and the current collector, so that the adhesive force of the pole piece is improved; in addition, the hydroxyl groups are beneficial to weakening the over-strong dipole moment between the cyano groups, the problem of pole piece brittleness caused by the obstruction of free movement of an adhesive chain segment due to the over-strong acting force between the cyano groups is reduced, and the safety performance of the battery is improved.

In some embodiments, the B-block comprises structural units derived from a monomer of formula III that contain an amide group.

The amide group contained in the B-block and the hydroxyl group of the positive active material and the current collector are easy to form a hydrogen bond, and the adhesive force of the pole piece can be improved. In addition, the amide group contained in the B-block can improve the liquid absorption capacity of the pole piece, improve the infiltration capacity of the pole piece in electrolyte, contribute to the rapid formation of an ion transmission channel on the pole piece, contribute to reducing the sheet resistance of the pole piece and improve the first-effect performance of the battery.

In some embodiments, the structural units derived from the monomer of formula I are present in a molar amount of from 40% to 60% based on the total moles of all structural units in the block copolymer.

In some embodiments, the molar content of structural units derived from the monomer of formula I can be selected from any one of 40% to 45%, 45% to 50%, 50% to 55%, 55% to 60%, 40% to 50%, 50% to 60%, 45% to 55%, 45% to 60%, based on the total moles of all structural units in the block copolymer.

If the molar content of the structural unit derived from the monomer shown in the formula I is too high, the membrane resistance of the pole piece is increased, the flexibility of the pole piece is reduced, the dissolution amount of transition metal is increased, and the high-temperature storage performance of the battery is reduced; if the molar content of the structural unit derived from the monomer shown in the formula I is too low, the binding power of the pole piece is reduced, and the first-effect performance, the cycle performance and the high-temperature storage performance of the battery are reduced.

In some embodiments, the BAB type block copolymer has a weight average molecular weight of 40 to 200 ten thousand. In some embodiments, the weight average molecular weight of the BAB type block copolymer may be any one of 40 to 60 million, 60 to 80 million, 80 to 100 million, 100 to 120 million, 120 to 140 million, 140 to 160 million, 160 to 180 million, 180 to 200 million, 60 to 90 million, 90 to 120 million, 120 to 150 million, 150 to 180 million, 180 to 200 million, and 120 to 200 million.

As used herein, the term "weight average molecular weight" refers to the sum of the product of the weight fraction of molecules of different molecular weight in a polymer and their corresponding molecular weight.

If the weight average molecular weight of the block copolymer is too large, the binder is difficult to dissolve and is easy to agglomerate with the conductive agent, so that the viscosity of the slurry is too large, the slurry is difficult to be uniformly coated, and the subsequent processing production is not facilitated. If the weight average molecular weight of the block copolymer is too small, a three-dimensional network bonding structure is difficult to form, the bonding force of the bonding agent is reduced, an effective bonding effect cannot be achieved, a good conductive network is difficult to form, and the sheet resistance of the pole piece is increased. Meanwhile, the undersized weight average molecular weight of the block copolymer can cause that the binding agent can not be effectively coated on the surface of the positive active material, the complexation degree of cyano groups in the B-block and transition metal ions on the surface of the positive active material is reduced, the elution amount of the transition metal is increased, and the cycle performance and the high-temperature storage performance of the battery are reduced.

In some embodiments, the weight average molecular weight of the A-block is from 20 to 105 million. In some embodiments, the weight average molecular weight of the a-block may be any one of 20 to 30 ten thousand, 30 to 40 ten thousand, 40 to 50 ten thousand, 50 to 60 ten thousand, 60 to 70 ten thousand, 70 to 80 ten thousand, 80 to 90 ten thousand, 90 to 105 ten thousand, 40 to 60 ten thousand, 40 to 80 ten thousand, and 40 to 105 ten thousand.

In some embodiments, each B-block has a weight average molecular weight of 10 to 50 ten thousand. In some embodiments, the weight average molecular weight of each B-block may be any one of 10 to 20 ten thousand, 20 to 30 ten thousand, 30 to 40 ten thousand, 40 to 50 ten thousand, 20 to 40 ten thousand, and 20 to 50 ten thousand.

In one embodiment of the present application, there is provided a method for preparing a BAB type block copolymer, comprising the steps of:

formula I

formula II

Wherein R is ₄ 、R ₅ 、R ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1-5 An alkyl group;

preparation of a BAB type Block copolymer: the A-block and B-block are joined to prepare a BAB type block copolymer.

In some embodiments, the monomer unit further comprises at least one monomer of formula III,

formula III

In some embodiments, a schematic diagram of a preparation method of the BAB type block copolymer is shown in fig. 1, wherein both end groups 611 of the a-block 61 comprising the structural unit 612 derived from the monomer represented by formula I are active groups, the end groups 621 of the B-block 62 comprising the structural unit 622 derived from the monomer represented by formula II are active groups, and both end groups 611 of the a-block and the end groups 621 of the B-block react to achieve the joining of the polymer segments, thereby preparing the BAB type block copolymer 6.

The preparation method has cheap raw materials, can reduce the cost and the pollution to the environment, and is beneficial to the improvement of the yield of the binder. Meanwhile, the BAB type block copolymer prepared by the method is used as an adhesive, and the pole piece has high adhesive force and low sheet resistance under the condition of low addition amount, and the battery has low dissolution amount of transition metal and excellent high-temperature storage performance.

In some embodiments, a method of making an a-block comprises:

As used herein, the term "azido group" refers to-N ₃ A group.

As used herein, the term "alkynyl" refers to the-C.ident.C group.

In some embodiments, the A-block is synthesized by polymerizing a monomer of formula I with a first initiator to form the A-block. Because the end groups on both sides of the first initiator are halogen-substituted alkyl groups or trimethylsilyl acetylene groups, the halogen groups or trimethylsilyl groups on both sides of the A-block are easily substituted, so that both ends of the A-block have azide groups or alkynyl groups.

The A-block with azide or alkynyl at the tail ends of both sides, which is prepared by the preparation method, is convenient to be connected with the B-block in a high-efficiency and mild way to generate the BAB type block copolymer.

In some embodiments, a method of making a B-block comprises:

and (2) carrying out reversible addition-fragmentation chain transfer polymerization on the monomer unit, the chain transfer agent and the second initiator at the reaction temperature of 60-75 ℃ for 4-8 hours to obtain a B-block with an alkynyl or azide group at the end.

Herein, the term "reversible addition-fragmentation chain transfer polymerization" (RAFT polymerization) is a reversible deactivation radical polymerization, also referred to as "living/controlled radical polymerization process". The main principle of RAFT polymerization is that RAFT reagent serving as chain transfer reagent is added in free radical polymerization, easily terminated free radicals are protected in a chain transfer mode, most free radicals in polymerization reaction are converted into dormant free radicals, dormant chain segments and active chain segments exist simultaneously in the reaction process, and rapid mutual switching is continuously carried out through dynamic reversible reaction, so that only a few polymer chains exist in an active chain form at any time and grow, finally, the growth probability of each polymer chain segment is approximately equal, and the characteristic of active polymerization is shown.

In some embodiments, the B-block is schematically synthesized as shown in the following figure, wherein the chain transfer agent is trithiocarbonate, Z' is a reactive group having an alkynyl or azido group at the terminus, and R is an alkyl group. A B-block having an alkynyl or azido group at the terminal is prepared by the following reaction, wherein m is the degree of polymerization of a structural unit derived from a monomer represented by formula II. In some embodiments, the B-block is formed by copolymerization of monomers of formula II and III, either in random or alternating copolymerization.

The reversible addition-fragmentation chain transfer polymerization is adopted, controllable polymerization can be realized, and the molecular weight distribution of the product is narrow. Furthermore, by the above reaction, the B-block has an alkynyl group or an azide group only at the terminal, and is conveniently and directionally bonded with the A-block in an efficient and mild manner to produce a BAB type block copolymer.

The preparation method can realize controllable polymerization, and the molecular weight distribution of the product is narrow.

In some embodiments, a method of making a BAB-type block copolymer comprises:

As used herein, the term "click reaction" refers to a reaction in which an alkynyl group undergoes a cycloaddition reaction with an azido group, resulting in the attachment of an A-block to a B-block. In some embodiments, the click reaction is carried out in the presence of a Cu (I) catalyst at ambient temperature and pressure.

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

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

The preparation method has the advantages of high yield, harmless by-products, simple and mild reaction conditions and easily obtained reaction raw materials, can realize the controllable polymerization of the block polymer, and is beneficial to improving the yield of products.

In some embodiments, the chain transfer agent is a RAFT chain transfer agent containing a terminal alkynyl or azido group. In some embodiments, the chain transfer agent is a trithiocarbonate containing a terminal alkynyl or azido group. In some embodiments, the chain transfer agent has a formula selected from the group consisting of,

、

。

the RAFT chain transfer agent containing the terminal alkynyl or the azide group enables the terminal of the B-block to have the alkynyl or the azide group while the B-block is synthesized, so that a foundation is provided for the click reaction of the B-block and the A-block, a complex post-treatment step is avoided, and the reaction efficiency can be improved.

In some embodiments, the first initiator is a symmetric difunctional initiator. In some embodiments, the first initiator is 4- (chloromethyl) benzoyl peroxide. The symmetric bifunctional initiator enables both sides of the A-block to conveniently carry active functional groups, and is beneficial to realizing the end group azidation or alkynylation of the A-block.

In some embodiments, the second initiator is an azo initiator selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile. The azo initiator is a common free radical polymerization initiator, is easy to decompose to form free radicals, and is convenient to initiate free radical polymerization.

In some embodiments, the BAB-type block copolymer may be applied in a secondary battery, optionally including at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[ Positive electrode sheet ]

The positive pole piece comprises a positive pole current collector and a positive pole film layer arranged on at least one surface of the positive pole current collector, wherein the positive pole film layer comprises a positive pole 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 pole piece has excellent binding power and good flexibility, and simultaneously has low sheet resistance and low dissolution of transition metal.

In some embodiments, the mass fraction of the binder is from 0.1% to 3% based on the total mass of the positive electrode active material. In some embodiments, the mass fraction of the binder can be selected from any one of 0.1% -0.2%, 0.2% -1.2%, 0.2% -1%, 0.2% -1.03%, 0.5% -1.2%, 1% -3%, and 1.03% -3%.

When the content of the binder is too low, on one hand, the binder cannot fully disperse the conductive agent and the positive active material, so that the resistance of the diaphragm of the pole piece is increased; on the other hand, the binder can not be effectively coated on the surface of the positive active material, and the effects of slowing down the dissolution of transition metal and improving the cycle performance and the high-temperature storage performance are difficult to achieve.

On the contrary, when the content of the binder is too high, the viscosity of the slurry is too high, so that the binder coating layer coated on the surface of the positive active material is too thick, the transmission of electrons and ions is influenced in the battery circulation process, the resistance of the diaphragm is increased, and the improvement of the energy density of the battery is also not facilitated.

The mass fraction of the binder is controlled within a reasonable range, the binder can reduce the diaphragm resistance of the pole piece, improve the binding power and flexibility of the pole piece, reduce the deposition of transition metal on the surface of a negative electrode, and improve the cycle performance and high-temperature storage performance of the battery.

In some embodiments, the adhesion per unit length between the positive electrode film layer and the positive electrode current collector is not less than 11N/m. In some embodiments, the adhesion force per unit length between the positive electrode film layer and the positive electrode current collector is 11 to 20N/m. In some embodiments, the adhesion per unit length between the positive electrode film layer and the positive electrode current collector can be selected from 11.5N/m, 12N/m, 12.5N/m, 13N/m, 13.5N/m, 14N/m, 14.5N/m, 15N/m, 15.5N/m, 16N/m, 16.5N/m, 17N/m, 17.5N/m, 18N/m, 18.5N/m, 19N/m, 19.5N/m, and 20N/m.

The adhesive 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, for example, by referring to GB-T2790-1995 national standard, adhesive 180 DEG peel strength test method. As an example, the positive electrode sheet was cut to 20 x 100mm ² Testing samples with the size for standby; the pole piece is adhered to one side of the positive pole film layer by using a double-sided adhesive tape and is compacted by using a compression roller, so that the double-sided adhesive tape is completely attached to the pole piece; the other side of the double-sided adhesive tape is stuck to the surface of the stainless steel, and one end of the sample is reversely bent, wherein the bending angle is 180 degrees; adopting a high-speed rail tensile machine for testing, fixing one end of the stainless steel on a clamp below the tensile machine, and fixing the bent tail end of the sampleAnd adjusting the angle of the sample by using an upper clamp, ensuring that the upper end and the lower end are positioned at vertical positions, stretching the sample at the speed of 50mm/min until the positive current collector is completely stripped from the positive film layer, and recording the displacement and acting force in the process. The force in the stress balance is divided by the width of the pole piece attached to the double-sided adhesive tape (the width direction of the pole piece is vertical to the peeling direction) to serve as the bonding force of the pole piece with unit length, and the width of the pole piece in the test is 20mm.

The positive pole film layer of the pole piece has high bonding strength with the positive pole current collector, and the positive pole film layer is not easy to fall off from the positive pole current collector in the using process, so that the cycle performance and the safety of the battery are improved.

In some embodiments, after the positive pole piece is subjected to bending test for not less than 3 times, the positive pole piece has a light transmission phenomenon. In some embodiments, after the positive electrode sheet is subjected to bending tests for not less than 3.1, 3.3, 3.5, 3.7, 4, 4.3 or 4.5 times, the positive electrode sheet has a light transmission phenomenon.

A bending test, also known as a flexibility test, may be used to test the flexibility of the pole piece by any means known in the art. As an example, the positive pole piece after cold pressing is cut into 20X 100mm ² A test specimen of a size; folding the steel wire in the forward direction, flattening the steel wire by using a 2kg compression roller, unfolding the steel wire to face light to check whether the gap is transparent, if the gap is not transparent, folding the steel wire in the reverse direction, flattening the steel wire by using the 2kg compression roller, checking the gap again when the gap is opposite to the light, repeating the steps until the gap is transparent, and recording the folding times; at least three samples are taken for testing, and the average value is taken as the test result of the bending test.

The pole piece can be through being no less than 3 times bending test, show that the pole piece has good pliability, is difficult for appearing the pole piece and bursting apart in the production process, the phenomenon that the pole piece is brittle failure appears in the use, helps improving the yields of battery, improves the security performance of battery.

In some embodiments, the sheet resistance of the positive electrode sheet is 1 Ω or less. In some embodiments, the sheet resistance of the positive electrode sheet is 0.1 Ω, 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω, 0.6 Ω, 0.7 Ω, 0.8 Ω, 0.9 Ω, or 1 Ω.

The sheet resistance refers to the resistance of the positive film layer of the pole piece, and can be tested by any means known in the art. As an example, a resistance meter may be used for testing.

The pole piece has lower diaphragm resistance, which shows that the material in the anode film layer is uniformly dispersed, and the anode film layer has good electron transmission efficiency, thereby being beneficial to the performance of the battery.

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

In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum 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 base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive active material may employ a positive active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g., liNiO) ₂ ) Lithium manganese oxides (e.g., liMnO) ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxideOxides, lithium nickel cobalt manganese oxides (e.g. LiNi) _1/3 Co _1/3 Mn _1/3 O ₂ (may also be abbreviated as NCM) ₃₃₃ ）、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (may also be abbreviated as NCM) ₅₂₃ ）、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (may also be abbreviated as NCM) ₂₁₁ ）、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (may also be abbreviated as NCM) ₆₂₂ ）、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (may also be abbreviated as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxides (e.g., liNi) _0.85 Co _0.15 Al _0.05 O ₂ ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) ₄ (also referred to as LFP for short)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., liMnPO) ₄ ) At least one of 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 further optionally includes a conductive agent. As an example, the conductive agent may include 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 may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.

[ negative electrode sheet ]

The negative pole piece includes the negative pole mass flow body and sets up the negative pole rete on the negative pole mass flow body at least one surface, the negative pole rete includes negative pole active material.

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

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

In some embodiments, the negative active material may employ a negative active material for a battery known in the art. As an example, the anode 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 and the like. The silicon-based material can be at least one selected from the group consisting of elemental silicon, a silicon oxy compound, a silicon carbon compound, a silicon nitrogen compound and a silicon alloy. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. The present application is not limited to these materials, however, and other conventional materials that can be used as a battery negative active material may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the anode film layer further optionally includes a binder. The binder may be at least one selected from 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 further optionally includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative electrode film layer may also optionally include other adjuvants, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In some embodiments, the negative electrode sheet can be prepared by: dispersing the components for preparing the negative electrode plate, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (such as deionized water) to form negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and performing the procedures of drying, cold pressing and the like to obtain the negative electrode piece.

[ electrolyte ]

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The kind of the electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be liquid, gel, or all solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte 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-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate.

In some embodiments, the solvent may 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, sulfolane, dimethylsulfone, methylethylsulfone, and diethylsulfone.

In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.

[ isolation film ]

In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In some embodiments, the material of the isolation film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and electrolyte.

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

The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other shape. For example, fig. 2 is a secondary battery 5 of a square structure as an example. The secondary battery may 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 housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodation chamber, and a cover plate 53 can be provided to cover the opening to close the accommodation chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. An electrode assembly 52 is enclosed within the receiving cavity. The electrolyte wets the electrode assembly 52. The number of the electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to specific practical needs.

[ Battery Module ]

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

Fig. 4 is a battery module 4 as an example. Referring to fig. 4, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series in the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other way. The plurality of secondary batteries 5 may be further fixed by a fastener.

Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

[ Battery pack ]

In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and the capacity of the battery pack.

Fig. 5 and 6 are a battery pack 1 as an example. Referring to fig. 5 and 6, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.

[ electric device ]

In one embodiment of the present application, there is provided an electric device including at least one of the secondary battery according to any one of the embodiments, the battery module according to any one of the embodiments, and the battery pack according to any one of the embodiments.

The electricity utilization device comprises at least one of the secondary battery, the battery module or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirement thereof.

Fig. 7 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.

As another example, the device may be a cell phone, tablet, laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.

Examples

Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples do not specify particular techniques or conditions, and are performed according to techniques or conditions described in literature in the art or according to the product specification. The reagents or instruments used are conventional products which are commercially available, and are not indicated by manufacturers.

1. Preparation method

Example 1

1) Preparation of the Binder

Preparation of the B-block: preparing alkynyl-terminated polyacrylonitrile-acrylamide-ethyl acrylate by using an alkynyl compound as a chain transfer agent through a polymerization reaction;

respectively weighing acrylonitrile, ethyl acrylate and acrylamide according to the molar ratio of 8,

；

the system was warmed to 75 ℃ and after 6 hours of reaction, the reaction was stopped by cooling in liquid nitrogen and the solution precipitated in excess methanol. The polymer was collected by filtration and reprecipitated twice from chloroform with methanol. The resulting product was dried under vacuum at room temperature for 10 hours to remove all traces of residual solvent to give poly (acrylonitrile-acrylamide-ethyl acrylate) with alkynyl group at end having weight average molecular weight of 40 ten thousand, i.e., B-block polymer;

preparation of the A-block: using azide as an initiator, and carrying out polymerization reaction to prepare azide-terminated polyvinylidene fluoride;

4- (chloromethyl) benzoyl peroxide at 1% by mass of vinylidene fluoride monomer was dissolved in 300ml of anhydrous acetonitrile, and the solution was introduced into a high-pressure reactor and purged with nitrogen (N) ₂ ) Purge for 30 minutes. 4g of vinylidene fluoride monomer were subsequently transferred to the reactor at room temperature. The temperature inside the reactor was raised to 90 ℃ and the reaction mixture was stirred at 500rpm for another 3 hours. The reactor was cooled to room temperature with water and depressurized to remove unreacted monomers. The solvent was removed in vacuo and the resulting solid was washed several times with chloroform to remove initiator residue. Finally the polymer was dried under vacuum at 45 ℃ to give a white product. 3mmol of chlorine-terminated polyvinylidene fluoride and 60mmol of sodium azide (NaN) ₃ ) Dissolved in 600ml of N, N-Dimethylformamide (DMF) and stirred at 60 ℃ for 10 hours. Concentrating the polymer solution and dissolving in mixtureThree times in an agent (methanol to water volume ratio of 1). Then, vacuum drying the light yellow product at 45 ℃ to obtain polyvinylidene fluoride with weight average molecular weight of 45 ten thousand and azide groups at two ends, namely an A-block polymer;

preparation of a BAB type Block copolymer:

polyvinylidene fluoride having azide groups at both ends, poly (acrylonitrile-acrylamide-ethyl acrylate) having an alkynyl group at the terminal, and cuprous bromide were added to a dried Schlenk tube in a molar ratio of 1. The reaction was stirred at 60 ℃ 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 (volume ratio of methanol to water 1), the product was collected by filtration and dried under vacuum to obtain a poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer having a weight average molecular weight of 120 ten thousand, which was used as a battery binder.

2) Preparation of positive pole piece

Uniformly stirring and mixing a lithium Nickel Cobalt Manganese (NCM) material, a conductive agent carbon black, the binder prepared in example 1 and N-methylpyrrolidone (NMP) according to a weight ratio of 96.9; and then uniformly coating the positive electrode slurry on a positive electrode current collector, and then drying, cold pressing and cutting to obtain the positive electrode piece.

3) Preparation of negative electrode plate

Dissolving active substance artificial graphite, conductive agent carbon black, binder Styrene Butadiene Rubber (SBR) and thickener carboxymethylcellulose sodium (CMC) in solvent deionized water according to a weight ratio of 96.2; and uniformly coating the negative electrode slurry on the copper foil of the negative current collector for one time or multiple times, and drying, cold pressing and slitting to obtain the negative electrode pole piece.

4) Isolation film

Polypropylene film was used as the separator.

5) Preparation of the electrolyte

In an argon atmosphere glove box (H) ₂ O<0.1ppm，O ₂ <0.1 ppm), mixing organic solvent Ethylene Carbonate (EC)/Ethyl Methyl Carbonate (EMC) at volume ratio of 3/7, adding LiPF 12.5% ₆ The lithium salt was dissolved in the organic solvent and uniformly stirred to obtain an electrolyte of example 1.

6) Preparation of the Battery

The positive pole piece, the isolation film and the negative pole piece in the embodiment 1 are sequentially stacked, the isolation film is positioned between the positive pole piece and the negative pole piece to achieve the isolation effect, then the bare cell is obtained by winding, a tab is welded on the bare cell, the bare cell is arranged in an aluminum shell, the bare cell is baked at 80 ℃ to remove water, and then the electrolyte is injected and sealed, so that the uncharged battery is obtained. The lithium ion battery product of the embodiment 1 is obtained by sequentially carrying out the working procedures of standing, hot and cold pressing, formation, shaping, capacity testing and the like on the uncharged battery.

Examples 2 to 11

The batteries of examples 2 to 11 were prepared in a similar manner to the battery of example 1, except that the weight average molecular weights of the a-block and the B-block were adjusted by adjusting the polymerization temperature and the polymerization time of the a-block and the B-block, respectively, and the weight average molecular weight of the poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer was adjusted, and the preparation parameters were as shown in table 1.

Examples 12 to 16

The batteries of examples 12 to 16 were prepared in a similar manner to the battery of example 1, except that the mass fraction of the binder based on the mass of the positive electrode active material was adjusted, and the specific parameters are shown in table 2.

Example 17

The cell of example 17 was prepared similarly to the cell of example 4, but with the substitution of the a-block for the polyvinyl fluoride block, with the specific parameters shown in table 2, as follows:

a-block: 4- (chloromethyl) benzoyl peroxide, 1% of the mass of the monomer, was dissolved in 300ml of anhydrous acetonitrile, introduced into a high-pressure reactor and reacted with N ₂ Purge for 30 minutes. 5g of vinyl fluoride are transferred into the reactor at room temperature. The temperature inside the reactor was raised to 90 ℃ and the reaction mixture was stirred at 500rpm for 3 hours. After the reaction is finished, the solvent is removed, the obtained solid is washed by chloroform for a plurality of times to remove the initiator residue, and the white product, namely the chlorine-terminated polyvinyl fluoride, is obtained after vacuum drying at the temperature of 45 ℃. 3mmol of chlorine-terminated polyvinyl fluoride and 60mmol of NaN ₃ Dissolved in 600ml of DMF and stirred at 60 ℃ for 10 hours, the polymer solution was concentrated and precipitated three times in a mixed solvent (methanol to water volume ratio 1. Then vacuum drying is carried out at 45 ℃ to obtain the polyfluoroethylene with azide groups at both ends, namely the A-block polymer.

Example 18

The cell of example 18 was prepared similarly to the cell of example 4, but with the substitution of the a-block for the polytetrafluoroethylene block, with the specific parameters shown in table 2, as follows:

A-Block: 4- (chloromethyl) benzoyl peroxide, 1% of the monomer mass, was dissolved in 300ml of anhydrous acetonitrile, introduced into a high-pressure reactor and reacted with N ₂ Purge for 30 minutes. 5g of tetrafluoroethylene was transferred to a reactor at room temperature, the temperature inside the reactor was raised to 90 ℃ and the reaction mixture was stirred at 500rpm for 3 hours. After the reaction was completed, the solvent was removed, and the obtained solid was washed with chloroform several times to remove the initiator residue, and dried in vacuo at 45 ℃ to obtain a white product, i.e., chlorine-terminated polytetrafluoroethylene. 3mmol of chlorine-terminated polytetrafluoroethylene and 60mmol of NaN ₃ Dissolved in 600ml DMF and stirred at 60 ℃ for 10 hours. The polymer solution was concentrated and precipitated three times in a mixed solvent (methanol to water volume ratio of 1), and vacuum-dried at 45 ℃ to obtain polytetrafluoroethylene having azide groups at both ends, i.e., an a-block polymer.

Example 19

The cell of example 19 was prepared similarly to the cell of example 4, but with the B-block replaced with poly (acrylonitrile-ethyl acrylate), with the specific parameters shown in table 2, as follows:

respectively weighing acrylonitrile and ethyl acrylate according to a molar ratio of 8, measuring 500ml of tetrahydrofuran, adding the tetrahydrofuran into a four-neck flask, introducing a large amount of nitrogen, gradually increasing the stirring speed to 1200rpm, adding a RAFT chain transfer agent (CTA-alkyne) accounting for 1% of the mass of a monomer and azobisisobutyronitrile accounting for 0.1% of the mass of the monomer, wherein the chain transfer agent is trithiocarbonate containing alkynyl at the tail end, and the structural formula is shown as follows,

the reaction was warmed to 75 ℃ and after 6 hours of reaction, the reaction was terminated by cooling in liquid nitrogen and the solution was precipitated in excess methanol. The polymer was collected by filtration and reprecipitated twice from chloroform with methanol. The resulting product was dried under vacuum at room temperature for 10 hours to remove all traces of residual solvent, yielding poly (acrylonitrile-ethyl acrylate) having an alkynyl group at the end, i.e., a B-block polymer.

Example 20

The cell of example 20 was prepared similarly to the cell of example 4, but with the B-block replaced by polyacrylonitrile, with the specific parameters as shown in table 2, as follows:

acrylonitrile monomer, RAFT chain transfer agent (CTA-alkyne) and azobisisobutyronitrile at a molar ratio of 700. 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 for 10 hours to remove all traces of residual solvent to obtain polyacrylonitrile having an alkynyl group at the end, i.e., a B-block polymer.

Example 21

The cell of example 21 was prepared similarly to the cell of example 4, but with the B-block replaced with poly (acrylonitrile-butyl methacrylate-styrene), with the specific parameters shown in table 2, as follows:

respectively weighing acrylonitrile, butyl methacrylate and styrene according to a molar ratio of 8. The polymer was collected by filtration and reprecipitated twice from chloroform with methanol. The resulting product was dried under vacuum at room temperature for 10 hours to remove all traces of residual solvent to give an alkynyl end capped poly (acrylonitrile-butyl methacrylate-styrene), i.e., a B-block.

Example 22

The cell of example 22 was prepared similarly to the cell of example 4, but with the B-block replaced with poly (acrylonitrile-vinyl alcohol), with the specific parameters shown in table 2, as follows:

1.65g of polyvinyl alcohol was added to 265.1g of dimethyl sulfoxide, and the mixture was dissolved by stirring at 60 ℃ for 2 hours. Then, 30.3g of acrylonitrile, 1% by mass of monomer of RAFT chain transfer agent (CTA-alkyne), 0.1% by mass of monomer of azobisisobutyronitrile and 3g of dimethyl sulfoxide were added, wherein the chain transfer agent was trithiocarbonate containing alkynyl at the end, and the mixture was copolymerized for 6 hours under stirring, cooled to room temperature to stop the polymerization, and filtered and washed in excess methanol to obtain poly (acrylonitrile-vinyl alcohol) having alkynyl at the end, i.e., a B-block.

Comparative example 1

The cell of comparative example 1 was prepared similarly to the cell of example 1, except that the binder was polyvinylidene fluoride, purchased from solvay group under the designation 5130, and the specific parameters are shown in table 2.

Comparative example 2

The cell of comparative example 2 was prepared similarly to the cell of example 1, but with the binder being poly (acrylonitrile-acrylamide-ethyl acrylate) and was synthesized in the following manner:

the system was warmed to 65 ℃ and after 12 hours of reaction, the reaction was terminated by cooling in liquid nitrogen and the solution was precipitated in excess methanol. The polymer was collected by filtration and reprecipitated twice from chloroform with methanol. The resulting product was dried under vacuum at room temperature for 10 hours to remove all traces of residual solvent to give poly (acrylonitrile-acrylamide-ethyl acrylate) with a weight average molecular weight of 120 ten thousand.

Comparative example 3

The cell of comparative example 3 was prepared similarly to the cell of example 1, except that the binder was a blend of polyvinylidene fluoride and poly (acrylonitrile-acrylamide-ethyl acrylate) prepared as follows:

blending: the poly (acrylonitrile-acrylamide-ethyl acrylate) of comparative example 2 was blended with the polyvinylidene fluoride of comparative example 1 in a monomer molar ratio of 6.

Comparative example 4

The battery of comparative example 4 was prepared similarly to the battery of comparative example 1, except that the mass fraction of the binder was adjusted to 2.0%.

2. Performance testing

1. Polymer Property testing

1) Weight average molecular weight test method

A Waters2695Isocratic hour PLC type gel chromatograph (differential refractometer 2141) was used. A sample of polystyrene solution with a mass fraction of 3.0% is used as a reference and a matching column is selected (oily: styragel hours T5DMF7.8. Multidot. 300mm + Styragel hours T4). Preparing a 3.0% polymer glue solution by using a purified N-methylpyrrolidone (NMP) solvent, and standing the prepared solution for one day for later use. When in testing, the tetrahydrofuran is firstly absorbed by a syringe and washed for several times. Then 5ml of the test solution was aspirated, the air in the syringe was removed and the tip of the needle was wiped dry. And finally, slowly injecting the sample solution into the sample inlet. And acquiring data after the readings are stable.

2. Pole piece performance testing

1) Diaphragm resistance test

Small round pieces with the diameter of 20mm are respectively cut at the left, middle and right parts of the pole piece. And (3) opening the indicator lamp of the pole piece resistance meter of the meta-energy science and technology, placing the indicator lamp in a proper position of a probe of the diaphragm resistance meter, clicking a start button, and reading when the number is stable. And testing two positions of each small wafer, and finally calculating the average value of six measurements to obtain the film resistance of the electrode sheet.

2) Adhesion test

Cutting the positive pole piece into a test sample with the size of 20mm multiplied by 100mm for later use; the pole piece is adhered to one surface of the positive pole film layer by using a double-faced adhesive tape and is compacted by using a compression roller, so that the double-faced adhesive tape is completely attached to the pole piece; the other side of the double-sided adhesive tape is stuck to the surface of the stainless steel, and one end of the sample is reversely bent, wherein the bending angle is 180 degrees; and (3) testing by adopting a high-speed rail tensile machine, fixing one end of stainless steel on a clamp below the tensile machine, fixing the bent tail end of the sample on a clamp above, adjusting the angle of the sample, ensuring that the upper end and the lower end are positioned at vertical positions, stretching the sample at a speed of 50mm/min until the current collector is completely stripped from the anode membrane, and recording the displacement and acting force in the process. The force when the force was balanced divided by the width of the pole piece attached to the double-sided tape (the width direction of the pole piece was perpendicular to the peeling direction) as the adhesive force of the pole piece per unit length, the width of the pole piece in this test was 20mm.

3) Flexibility test

Cutting the cold-pressed positive pole piece into 20 multiplied by 100mm ² A test specimen of a size; folding the film in the forward direction, flattening the film by using a 2kg compression roller, unfolding the film to face the light to check whether the gap is transparent, if the gap is not transparent, folding the film in the reverse direction, flattening the film by using a 2kg compression roller, checking the film to face the light again, and repeating the steps until the gap is transparentThe light transmission phenomenon is realized, and the folding times are recorded; and repeating the test for three times, and taking an average value as reference data of the flexibility of the pole piece.

3. Battery performance testing

1) First efficiency performance test of battery

Charging the button cell to 3.25V at 2.8-3.25V according to 0.1C, then charging the button cell to a current of less than or equal to 0.05mA at 4.3V at a constant voltage, standing for 2min, recording the charging capacity as C0, then discharging the button cell to 2.8V according to 0.1C, and recording the discharging capacity as D0 at the initial gram capacity. The first effect is calculated according to D0/C0 multiplied by 100%.

2) Battery cycling capacity retention rate test

The battery capacity retention rate test procedure is as follows: at 25 ℃, the prepared battery is charged to 4.3V at a constant current of 1/3C, then charged at a constant voltage of 4.3V until the current is 0.05C, left for 5min, and then discharged to 2.8V at 1/3C, and the obtained capacity is marked as initial capacity C0. When the steps are repeated for the same battery and the discharge capacity Cn of the battery after the nth cycle is recorded, the battery capacity retention rate Pn = Cn/C0 x 100% after each cycle is obtained, and a graph of the battery capacity retention rate and the cycle number is obtained by taking the 500 point values of P1, P2 \8230;, 500 as ordinate and the corresponding cycle number as abscissa. In the test process, the first cycle corresponds to n =1, the second cycle corresponds to n =2, \8230, and the 500 th cycle corresponds to n =500. The battery capacity retention rate data corresponding to the examples or comparative examples in table 1 is data measured after 500 cycles under the above-described test conditions, i.e., the value of P500. The test procedure of the comparative example and other examples was the same as above.

3) Retention ratio of high temperature storage capacity

Charging to 4.2V with 1C constant current, charging to 0.05C with 4.2V constant voltage, standing for 10min, discharging to cut-off voltage of 2.8V with 1C constant current, and recording the capacity before storage (CAP) ₁ (ii) a Charging with 1C constant current until 4.2V is cut off, charging with 4.2V constant voltage until the current is 0.05C, placing the lithium ion battery in a 45 ℃ oven for 120 days, taking out, performing 1C constant current discharge to 2.8V, and recording the stored capacity CAP ₂ The storage capacity retention rate of the lithium ion secondary battery was calculated according to the following equation：

Storage capacity retention (%) of lithium ion secondary battery = CAP ₂ /CAP ₁ ×100％。

4) Metal dissolution test

At normal temperature, the manufactured lithium ion battery is charged and discharged for the first time by using a current of 0.5C (namely a current value which completely discharges theoretical capacity within 2 hours), the charging is constant-current constant-voltage charging, the termination voltage is 4.2V, the cut-off current is 0.05C, and the discharge termination voltage is 2.8V, then the battery is placed for 24 hours and then is charged to 4.2V by using a constant-current constant-voltage charging of 0.5C, then the fully-charged battery is discharged by using a current of 1C, the discharge termination voltage is 2.8V, the battery core is disassembled, a negative pole piece is taken out, and the deposition amounts of metal Co and metal Mn are tested by adopting an Inductive Coupling Plasma (ICP) method.

The results of the performance tests of the above examples and comparative examples are shown in tables 2 and 3.

3. Analysis of test results of examples and comparative examples

From the results, it is understood that the binders in examples 1 to 22 are BAB type block copolymers comprising an A-block and a B-block, the A-block containing a structural unit derived from vinylidene fluoride, vinyl fluoride or tetrafluoroethylene, the B-block containing a structural unit derived from acrylonitrile, and the B-blocks in examples 1 to 19 and examples 21 to 22 further contain at least one structural unit derived from acrylamide, ethyl acrylate, butyl methacrylate, styrene or vinyl alcohol. As can be seen from the comparison of examples 1 to 7, examples 17 to 22 and comparative example 1, polyacrylonitrile-polyvinylidene fluoride-polyacrylonitrile block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polytetrafluoroethylene-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinyl fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-ethyl acrylate) block copolymer, poly (acrylonitrile-butyl methacrylate-styrene) -polyvinylidene fluoride-poly (acrylonitrile-butyl methacrylate-styrene) block copolymer or poly (acrylonitrile-vinyl alcohol) -polyvinylidene fluoride-poly (acrylonitrile-vinyl alcohol) block copolymer as a binder can reduce the electrical resistance of the pole piece, improve the adhesion of the pole piece, reduce the deposition of transition metal on the negative electrode, and improve the cycle performance and high temperature storage performance of the battery.

The binders in examples 1 to 16 were BAB type block copolymers comprising an A-block containing structural units derived from vinylidene fluoride and a B-block containing structural units derived from acrylonitrile, acrylamide and ethyl acrylate. As can be seen from the comparison between examples 1 to 7 and comparative example 1, the poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer binder can reduce the sheet resistance of the pole piece, improve the flexibility and the binding power of the pole piece, reduce the deposition of transition metal on the surface of the negative electrode, and further improve the high-temperature storage performance and the cycle performance of the battery.

The binders in examples 17 to 18 were BAB type block copolymers comprising an A-block containing structural units derived from vinyl fluoride or tetrafluoroethylene and a B-block containing structural units derived from acrylonitrile, acrylamide and ethyl acrylate. From the comparison between examples 17 to 18 and comparative example 1, it can be seen that the poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinyl fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polytetrafluoroethylene-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer binder can reduce the sheet resistance of the pole piece, improve the flexibility and the binding power of the pole piece, and reduce the deposition of transition metal on the surface of the negative electrode, thereby improving the high-temperature storage performance, the cycle performance and the first efficiency performance of the battery.

The binder in example 19 was a BAB type block copolymer comprising an a-block containing structural units derived from vinylidene fluoride and a B-block containing structural units derived from acrylonitrile and ethyl acrylate. From a comparison of example 19 with comparative example 1, it can be seen that the poly (acrylonitrile-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-ethyl acrylate) block copolymer binder can reduce the sheet resistance of the pole piece, and improve the flexibility and adhesion of the pole piece. In addition, the BAB type block copolymer can improve the high-temperature storage performance and the cycle performance of the battery by reducing the elution amount of the transition metal and reducing the deposition of transition metal ions on the surface of the negative electrode.

The binder in example 21 is a BAB type block copolymer comprising an a-block containing structural units derived from vinylidene fluoride and a B-block containing structural units derived from acrylonitrile, butyl methacrylate and styrene. It can be seen from the comparison of example 21 and comparative example 1 that the poly (acrylonitrile-butyl methacrylate-styrene) -polyvinylidene fluoride-poly (acrylonitrile-butyl methacrylate-styrene) block copolymer can reduce the sheet resistance of the pole piece, improve the flexibility and the binding power of the pole piece, reduce the deposition of transition metal on the surface of the negative electrode, and thus improve the high-temperature storage performance, the cycle performance and the first-effect performance of the battery.

The binder in example 22 was a BAB type block copolymer comprising an a-block containing structural units derived from vinylidene fluoride and a B-block containing structural units derived from propylene and vinyl alcohol. From the comparison between example 22 and comparative example 1, it can be seen that the binder of the poly (acrylonitrile-vinyl alcohol) -polyvinylidene fluoride-poly (acrylonitrile-vinyl alcohol) triblock copolymer can reduce the sheet resistance of the pole piece, improve the flexibility and the binding power of the pole piece, and reduce the deposition of transition metal on the surface of the negative electrode, thereby improving the high-temperature storage performance, the cycle performance and the first-efficiency performance of the battery.

As can be seen from the comparison among examples 1 to 7, examples 17 to 18 and comparative example 2, the BAB type block copolymer contains an A-block derived from a structural unit of vinylidene fluoride, vinyl fluoride or tetrafluoroethylene, which is helpful for improving the flexibility of a pole piece, reducing the resistance of a diaphragm and improving the first efficiency performance, the cycle performance and the high-temperature storage performance of a battery.

As can be seen from the comparison between example 1 and comparative example 3, the block copolymer of poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) as the binder can improve the binding power and flexibility of the pole piece, reduce the resistance of the membrane, and improve the first-efficiency performance and high-temperature storage performance of the battery.

As can be seen from the comparison among examples 1 to 7, examples 19 to 22 and comparative example 4, the BAB type block copolymer provided by the application can effectively reduce the film resistance of a pole piece and the deposition amount of transition metal on a negative electrode under a low addition amount, so that the cohesiveness, the flexibility, the first effect performance, the cycle performance and the high-temperature storage performance of the pole piece basically reach the level which can be reached under a high addition amount of a binder in the prior art, and the energy density of a battery is further improved.

As can be seen from the comparison of examples 1 to 7 with comparative example 4, the poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer can make the pole piece have excellent flexibility, good adhesive force, lower film resistance and lower transition metal dissolution under low addition, so that the first efficiency performance and the cycle performance of the battery basically reach the level which can be reached only under the high addition of the adhesive in the prior art, and the improvement of the energy density of the battery is facilitated.

As can be seen from the comparison of examples 17 to 18 with comparative example 4, the poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinyl fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer and the poly (acrylonitrile-acrylamide-ethyl acrylate) -polytetrafluoroethylene-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer can enable the pole piece to have excellent flexibility and binding power and lower film resistance and transition metal dissolution amount under the condition of low addition amount, so that the cycle performance and the high-temperature storage performance of the battery basically reach the level which can be reached under the condition of high addition amount of the binding agent in the prior art, and the improvement of the energy density of the battery is facilitated.

As can be seen from the comparison of examples 1 to 5 and examples 6 to 7, the mole content of the structural unit derived from the vinylidene fluoride monomer in the BAB type block copolymer is 40-60%, and when the total mole number of all the structural units in the block copolymer is counted, the adhesive can enable the pole piece to have excellent adhesive force, good flexibility, lower diaphragm resistance and lower dissolution amount of transition metal, and enable the battery to have excellent comprehensive performances including cycle performance, high-temperature storage performance and first performance.

From examples 1 to 11 and examples 17 to 22, it can be seen that when the weight average molecular weight of the BAB type block copolymer is 40 to 200 ten thousand, compared with the PVDF binder in the prior art, the block copolymer can enable the pole piece to have low sheet resistance, high binding power and flexibility, and enable the battery to have good first efficiency, cycle performance and high-temperature storage performance.

As can be seen from examples 1 to 11 and examples 17 to 22, when the weight average molecular weight of the fluorinated block A-block in the BAB type block copolymer is 20 to 105 ten thousand, the BAB type block copolymer enables the pole piece to have low sheet resistance, high cohesive force and flexibility, and the battery has good first effect, cycle performance and high-temperature storage performance.

From examples 1 to 11 and examples 17 to 22, it can be seen that when the weight average molecular weight of the non-fluorine block B-block in the BAB type block copolymer is 10 to 50 ten thousand, the BAB type block copolymer enables the pole piece to have low sheet resistance, high cohesive force and flexibility, and the battery has good first effect, cycle performance and high-temperature storage performance.

From the embodiment 1 and the embodiments 12 to 16, the mass fraction of the binder is 0.1 to 3 percent, based on the mass of the positive electrode active material, the binder can reduce the diaphragm resistance of a pole piece, improve the binding power of the pole piece, reduce the deposition of transition metal on the surface of a negative electrode, and improve the cycle performance and the high-temperature storage performance of a battery. As can be seen from the comparison of the examples 1, 14 to 15 and 12 to 13, the mass fraction of the binder is 0.5 to 1.2%, and based on the mass of the positive electrode active material, the binder can further reduce the film resistance of the pole piece, improve the binding power and flexibility of the pole piece, improve the first efficiency performance of the battery, reduce the deposition of transition metal on the surface of the negative electrode, and thus improve the cycle performance and the high-temperature storage performance of the battery.

The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are included in the technical scope of the present application. In addition, various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.

Claims

1. A BAB-type block copolymer comprising an A-block comprising structural units derived from a monomer of formula I and a B-block comprising structural units derived from a monomer of formula II,

formula I

Formula II

2. The BAB-type block copolymer of claim 1, wherein the B-block further comprises structural units derived from a monomer of formula III,

formula III

3. The BAB-type block copolymer of claim 1, wherein the molar content of the structural units derived from the monomer represented by formula I is 40% to 60% based on the total moles of all structural units in the BAB-type block copolymer.

4. A BAB-type block copolymer according to any one of claims 1 to 3, characterized in that the weight average molecular weight of said BAB-type block copolymer is 40 to 200 ten thousand.

5. The BAB type block copolymer according to any one of claims 1 to 3, wherein the weight average molecular weight of the A-block in the BAB type block copolymer is 20 to 105 ten thousand.

6. A BAB-type block copolymer according to any one of claims 1 to 3, wherein the weight average molecular weight of each of said B-blocks in said BAB-type block copolymer is 10 to 50 ten thousand.

7. A BAB-type block copolymer according to any of claims 1 to 3, wherein said monomer of formula I is selected from one or more of vinylidene fluoride, tetrafluoroethylene, vinyl fluoride, hexafluoropropylene.

8. The BAB block copolymer according to any one of claims 1 to 3, wherein the monomer of formula II is selected from one or more of acrylonitrile and butenenitrile.

9. The BAB-type block copolymer according to claim 2, wherein the monomer represented by formula III is selected from one or more of styrene, vinyl alcohol, acrylamide, ethyl acrylate, and butyl methacrylate.

10. The BAB-type block copolymer according to any one of claims 1 to 3, wherein the BAB-type block copolymer is one of polyacrylonitrile-polyvinylidene fluoride-polyacrylonitrile block copolymer, polyacrylonitrile-polyvinyl fluoride-polyacrylonitrile block copolymer, polyacrylonitrile-polytetrafluoroethylene-polyacrylonitrile block copolymer, poly (acrylonitrile-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinylidene fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polyvinyl fluoride-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-acrylamide-ethyl acrylate) -polytetrafluoroethylene-poly (acrylonitrile-acrylamide-ethyl acrylate) block copolymer, poly (acrylonitrile-butyl methacrylate-styrene) -polyvinylidene fluoride-poly (acrylonitrile-butyl methacrylate-styrene) block copolymer, poly (acrylonitrile-vinyl alcohol) -polyvinylidene fluoride-poly (acrylonitrile-vinyl alcohol) block copolymer.

11. A method for preparing a BAB type block copolymer, comprising the steps of:

formula I

formula II

preparation of a BAB type Block copolymer: the A-block and the B-block are joined to prepare a BAB type block copolymer.

12. The method of preparing a BAB-type block copolymer of claim 11, wherein said monomer units further comprise at least one monomer of formula III,

formula III

13. Process for the preparation of a BAB-type block copolymer according to claim 11 or 12, characterized in that it comprises:

at least one monomer shown in the formula I and a first initiator are subjected to polymerization reaction at the reaction temperature of 80-95 ℃ for 2.5-5 hours, and the terminal group of the product is subjected to substitution reaction to prepare the A-block with azide groups or alkynyl groups at two ends.

14. Process for the preparation of a BAB-type block copolymer according to claim 11 or 12, characterized in that it comprises:

and (2) carrying out reversible addition-fragmentation chain transfer polymerization on the monomer unit, the chain transfer agent and the second initiator at the reaction temperature of 60-75 ℃ for 4-8 hours to obtain the B-block with the alkynyl or azide group at the end.

15. The method for preparing a BAB-type block copolymer according to claim 11 or 12, comprising:

mixing the A-block having an azide group or an alkyne group at both ends with the B-block having an alkyne group or an azide group at the terminal, and performing a click reaction to prepare a BAB type block copolymer, wherein the terminal groups of the A-block and the B-block are different.

16. The method of producing a BAB-type block copolymer according to claim 14, wherein the chain transfer agent is a RAFT chain transfer agent containing a terminal alkynyl or azide group.

17. The method of preparing a BAB-type block copolymer as claimed in claim 13, wherein said first initiator is a symmetric bifunctional initiator.

18. The method of producing a BAB-type block copolymer according to claim 14, wherein the second initiator is one or two selected from the group consisting of azobisisobutyronitrile, azobisisoheptonitrile.

19. Use of the BAB-type block copolymer as claimed in any one of claims 1 to 10 in a secondary battery.

20. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, a conductive agent and a binder, and the binder is the BAB type block copolymer of any one of claims 1 to 10 or the BAB type block copolymer prepared by the method of preparing the BAB type block copolymer of any one of claims 11 to 18.

21. The positive electrode sheet according to claim 20, wherein the mass fraction of the binder is 0.1% to 3% based on the total mass of the positive electrode active material.

22. The positive electrode sheet according to claim 20 or 21, wherein the mass fraction of the binder is 0.5% to 1.2% based on the total mass of the positive electrode active material.

23. The positive electrode sheet according to claim 20 or 21, wherein the adhesive force per unit length between the positive electrode film layer and the positive electrode current collector is not less than 11N/m.

24. The positive pole piece of claim 20 or 21, wherein the positive pole piece is transparent after being subjected to bending test not less than 3 times.

25. The positive electrode tab of claim 20 or 21, wherein the sheet resistance of the positive electrode tab is 1 Ω or less.

26. A secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a separator, a negative electrode tab, and the positive electrode tab of any one of claims 20 to 25.

27. The secondary battery of claim 26, wherein the secondary battery comprises at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

28. A battery module characterized by comprising the secondary battery according to claim 26 or 27.

29. A battery pack comprising the battery module according to claim 28.

30. An electric device comprising at least one selected from the secondary battery according to claim 26 or 27, the battery module according to claim 28, and the battery pack according to claim 29.