CN117801295A

CN117801295A - BAB type block copolymer, preparation method, binder, positive electrode slurry, positive electrode plate, secondary battery and power utilization device

Info

Publication number: CN117801295A
Application number: CN202310512266.3A
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: 2024-04-02
Also published as: CN115286801B; CN115286801A

Abstract

The application relates to a BAB block copolymer, a preparation method, a binder, positive electrode slurry, a positive electrode sheet, a secondary battery and an electric device. In particular, the present application provides a BAB-type block copolymer comprising an A-block containing structural units of formula I and a B-block containing structural units of formula II or III, 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 groups, R ₄ 、R ₅ 、R ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1‑5 Alkyl, R ₇ Selected from one of hydroxyl, substituted or unsubstituted aryl.

Description

BAB type block copolymer, preparation method, binder, positive electrode slurry, positive electrode plate, secondary battery and power utilization device

The present application is a divisional application based on the invention application with application number 202211205128.2, application date 2022, 09 and 30, and the invention name "BAB block copolymer, preparation method, binder, positive electrode sheet, 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, positive electrode slurry, a positive electrode plate, a secondary battery and an electric device.

Background

In recent years, secondary batteries are widely used in energy storage power supply 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 automobiles, military equipment, aerospace, and the like.

The binder is a common material in secondary batteries and is widely applied to battery pole pieces, isolating films, packaging parts and the like. However, the traditional binder has high production cost, insufficient productivity and large environmental hazard, and gel is easy to appear in the preparation process, so that the slurry has poor stability and high processing cost, and the pole piece prepared by the binder has poor flexibility, low binding force, low liquid absorption rate, high resistance and low yield, and the direct current impedance of the battery has high growth rate, unstable circulation capacity retention rate and performance, and is difficult to meet the requirements of the market on the cost and performance of the battery. Thus, the existing adhesives remain to be improved.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a BAB-type block copolymer, in which a binder prepared from a BAB-type triblock copolymer can effectively slow down the gelation of a slurry, improve the stability of the slurry, improve the flexibility of a pole piece, improve the binding force, improve the imbibition rate of the pole piece, reduce the sheet resistance, reduce the rate of increase in the direct current resistance of a battery, and/or improve the retention rate of the circulating capacity of the battery.

A first aspect of the present application provides a BAB-type block copolymer comprising an A-block comprising structural units of formula I and a B-block comprising structural units of formula II or III,

-CH ₂ -CH ₂ -O-type III

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 groups, R ₄ 、R ₅ 、R ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1-5 Alkyl, R ₇ Selected from one of hydroxyl, substituted or unsubstituted aryl.

The adhesive prepared by the BAB type block copolymer 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 adhesive and the non-fluorine adhesive, and realize the effect of complementary advantages. The adhesive can effectively slow down the gelation phenomenon of the slurry, improve the stability of the slurry, improve the flexibility of the pole piece, improve the adhesive force, improve the liquid absorption rate of the pole piece, reduce the membrane resistance, reduce the direct current impedance growth rate of the battery and/or improve the circulation capacity retention rate of the battery.

In any embodiment, the molar content of the structural units represented by formula I is 30% to 70% based on the total moles of all structural units in the block copolymer.

The molar content of the structural unit shown in the control formula I is in a proper range, so that the gelation phenomenon of the slurry can be effectively slowed down, the stability of the slurry is improved, the flexibility of the pole piece is improved, the binding force is improved, the liquid absorption rate of the pole piece is improved, the membrane resistance is reduced, and the circulation capacity retention rate of the battery is improved.

In any embodiment, the block copolymer has a weight average molecular weight of 40 to 200, optionally 70 to 200, tens of thousands.

The weight average molecular weight of the block copolymer is controlled within a proper range, so that the binding force can be improved, and the cycle capacity retention rate of the battery can be improved.

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

The weight average molecular weight of the A-block in the block copolymer is controlled within a proper range, so that the gelation phenomenon of the slurry can be effectively slowed down, the stability of the slurry is improved, the flexibility of the pole piece is improved, the binding force is improved, the liquid absorption rate of the pole piece is improved, the membrane resistance is reduced, and the circulation capacity retention rate of the battery is improved.

In any embodiment, the weight average molecular weight of each B-block in the block copolymer is from 10 to 50 tens of thousands.

The weight average molecular weight of each B-block in the block copolymer is controlled within a proper range, so that the binding force can be improved, the DC resistance growth rate of the battery can be reduced, and the cycle capacity retention rate of the battery can be improved.

In any embodiment, the structural unit of formula I is

One or more of the following. In this case, the adhesion can be improved, the increase rate of the direct current resistance of the battery can be reduced, and the cycle capacity retention rate of the battery can be improved.

In any embodiment, the structural unit of formula II is

One or more of the following. At this time, the gel phenomenon of the slurry can be effectively slowed down, the stability of the slurry is improved, the flexibility of the pole piece is improved, the binding force is improved, the liquid absorption rate of the pole piece is improved, the membrane resistance is reduced, and the circulation capacity retention rate of the battery is improved.

The raw materials are simple and easy to obtain, and compared with the traditional adhesive, the adhesive can greatly reduce the production cost and improve the yield.

In any embodiment, the block copolymer is selected from one or more of a polyvinyl alcohol-polyvinylidene fluoride-polyvinyl alcohol triblock copolymer, a polyvinyl alcohol-polyvinyl fluoride-polyvinyl alcohol triblock copolymer, a polyvinyl alcohol-polytetrafluoroethylene-polyvinyl alcohol triblock copolymer, a polystyrene-polyvinylidene fluoride-polystyrene triblock copolymer, a polystyrene-polyvinyl fluoride-polystyrene triblock copolymer, a polystyrene-polytetrafluoroethylene-polystyrene triblock copolymer, a polyethylene oxide-polyvinylidene fluoride-polyethylene oxide triblock copolymer, a polyethylene oxide-polyvinyl fluoride-polyethylene oxide triblock copolymer, a polyethylene oxide-polytetrafluoroethylene-polyethylene oxide triblock copolymer, a poly 4-vinylbenzoic acid-polyvinylidene fluoride-poly 4-vinylbenzoic acid triblock copolymer, a poly 4-vinylbenzoic acid-polytetrafluoroethylene-poly 4-vinylbenzoic acid triblock copolymer. In this case, the cycle capacity retention rate of the battery can be improved.

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

preparation of the A-block: polymerizing at least one monomer shown in a formula IV to prepare an A-block,

wherein A is ₁ 、A ₂ 、A ₃ Each independently of the otherIs selected from hydrogen, fluorine, C containing at least one fluorine atom _1-3 One or more of alkyl groups;

preparation of the B-block: polymerizing at least one monomer shown in formula V to prepare a B-block, or ring-opening polymerizing a monomer shown in formula VI to prepare a B-block;

wherein A is ₄ 、A ₅ 、A ₆ Each independently selected from hydrogen, substituted or unsubstituted C _1-5 Alkyl, A ₇ One selected from ester groups and substituted or unsubstituted aromatic groups;

preparation of a BAB type block copolymer: joining the a-block and the B-block to produce 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-containing block, fully exert the respective advantages of the fluorine-containing binder and the non-fluorine binder, and realize the effect of complementary advantages. The adhesive of the BAB triblock copolymer prepared by the method can slow down the gelation phenomenon of slurry, improve the stability of the slurry, improve the flexibility of pole pieces, improve the adhesive force, reduce the resistance of the diaphragm, reduce the direct current impedance growth rate of the battery and improve the cycle capacity retention rate of the battery.

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

at least one monomer shown in formula IV and a first initiator are polymerized for 2.5-5 hours at the reaction temperature of 80-95 ℃, and substitution reaction is carried out on the end group of the product to prepare the A-block with azide groups or alkynyl groups at two ends as end groups.

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

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

and (3) carrying out reversible addition-fragmentation chain transfer polymerization on at least one monomer shown in formula V, a chain transfer agent and a second initiator at a reaction temperature of 65-80 ℃ for 4.5-6 hours to obtain the B-block with the terminal alkynyl or azido group as a terminal group.

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

polymerizing a monomer shown in a formula VI, an ionic initiator and water at a reaction temperature of 60-80 ℃ for 6-8 hours to obtain a product with a hydroxyl at the tail end;

and (3) carrying out functionalization reaction on the hydroxyl of the product to obtain the B-block with alkynyl or azido groups at the tail end.

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

In any embodiment, the preparing a BAB-type block copolymer comprises:

mixing the A-block with azide groups or alkynyl groups at two ends as end groups with the B-block with alkynyl groups or azide groups at the ends as end groups, and performing click reaction to prepare the BAB type block copolymer, wherein the end 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 improves the yield of products.

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

In any embodiment, the first initiator is a symmetrical difunctional initiator selected from the group consisting of 4- (chloromethyl) benzoyl peroxide.

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

A third aspect of the present application provides the use of the BAB-type block copolymer of any embodiment or the BAB-type block copolymer prepared by the preparation method of any embodiment 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 electrode plate has excellent flexibility, binding force, liquid absorption rate and/or lower diaphragm resistance.

In any embodiment, the mass fraction of the binder is 0.1% to 3%, alternatively 1.03% 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, so that the flexibility of the pole piece can be improved, the binding force can be improved, the resistance of the diaphragm can be reduced, and the cycle capacity retention rate of the battery can be improved.

In any embodiment, the adhesion force between the positive electrode film layer and the positive electrode current collector per unit length is not less than 8N/m, optionally not less than 10N/m.

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

In any embodiment, after the positive electrode plate is subjected to bending test for at least 3 times, the positive electrode plate has a light transmission phenomenon.

The pole piece has excellent flexibility, is not easy to crack in the production process, and is beneficial to improving the yield.

In any embodiment, the positive electrode sheet has a liquid absorption rate of greater than 0.32 μg/s, optionally greater than 0.37 μg/s, to an electrolyte having a density of 1.1-1.2g/cm ³ 。

The pole piece has higher liquid absorption rate, can improve the infiltration efficiency of electrolyte to the pole piece, improve an ion transmission path, reduce interface resistance and improve the battery performance.

In any embodiment, the sheet resistance of the positive electrode sheet is 0.58 Ω or less, alternatively 0.48 Ω or less.

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

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

Drawings

FIG. 1 is a schematic illustration of the preparation of a BAB type block copolymer according to an 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 the secondary battery of the 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. 5 is 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 one embodiment of the present application shown in FIG. 5;

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

Reference numerals illustrate:

1, a battery pack; 2, upper box body; 3, lower box body; 4, a battery module; 5 a secondary battery; 51 a housing; 52 electrode assembly; 53 cover plates; a block copolymer of type 6 BAB; 61A-blocks; 611A-block; 612 structural units of formula I; 62B-block; end groups of 621B-blocks; 622 structural units of the formula II or III.

Detailed Description

Hereinafter, embodiments of the positive electrode active material and the method of manufacturing the same, the positive electrode tab, the secondary battery, the battery module, the battery pack, and the electrical device of the present application are specifically disclosed with reference to the accompanying drawings as appropriate. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of the actual same structure may be omitted. This is to avoid that the following description becomes unnecessarily lengthy, facilitating the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided for a full understanding of the present application by those skilled in the art, and are not intended to limit the subject matter recited in the claims.

The "range" disclosed herein is defined in terms of lower and upper limits, with a given range being defined by the selection of a lower and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges that are defined in this way can be inclusive or exclusive of the endpoints, and any combination can be made, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, 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 indicated, 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, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values. When a certain parameter is expressed as an integer of 2 or more, it is disclosed 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, unless specifically stated otherwise.

All technical features and optional technical features of the present application may be combined with each other to form new technical solutions, unless specified otherwise.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, unless otherwise indicated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), and the like.

Reference herein to "comprising" and "including" means open ended, as well as closed ended, unless otherwise noted. For example, the terms "comprising" and "comprises" may mean that other components not listed may be included or included, or that only listed components may be included or included.

The term "or" is inclusive in this application, unless 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 absent); a is false (or absent) and B is true (or present); or both A and B are true (or present).

Polyvinylidene fluoride (PVDF) is often used as a pole piece binder in the prior art, however, PVDF has a plurality of problems in the use process, such as sensitivity to water content in the production process; in the battery recycling process, a large amount of HF pollutes the environment, and the environment cannot be recycled in a large scale due to the limitation of environmental protection policy; in the process of preparing the positive electrode slurry by mixing the high-capacity positive electrode material (such as a high-nickel ternary material), the high-polarity groups on the PVDF can activate the residual hydroxyl groups on the positive electrode material, so that bonding reaction is carried out between the high-polarity groups and metal elements (such as nickel elements) in the positive electrode material, chemical crosslinking is formed, and finally slurry gel is caused, so that normal preparation of the slurry and subsequent pole piece processing are affected. In addition, PVDF is easy to crystallize, which is unfavorable for the transmission of electrons in the pole piece, thereby resulting in high resistance of the pole piece and poor electron transmission performance, and is unfavorable for the performance of the high-capacity positive electrode material.

[ adhesive ]

Based on this, the present application proposes a BAB-type block copolymer comprising an A-block containing structural units of formula I and a B-block containing structural units of formula II or III,

-CH ₂ -CH ₂ -O-type III

In this context, the term "binder" refers to a chemical compound, polymer or mixture that forms a colloidal solution or colloidal dispersion in a dispersing medium.

As used herein, the term "block copolymer" is a particular polymer prepared by joining together two or more polymer segments that differ in nature. Block polymers with a specific structure will exhibit properties that differ from simple linear polymers, as well as mixtures of many random copolymers and even homopolymers. There are commonly known AB and BAB types, of which A, B is a long segment; there are Also (AB) n-type multistage copolymers in which the A, 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 both sides. 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-blocks and B-blocks are covalently bonded in an ordered manner to form a BAB type block copolymer. Taking example 1 of the present application as an example, wherein the A-block is polyvinylidene fluoride having a weight average molecular weight of 45 ten thousand g/mol, formed by polymerization of vinylidene fluoride monomers; the B-block is polyvinyl alcohol, the weight average molecular weight is 40 ten thousand g/mol, and the polyvinyl alcohol is formed by polymerizing vinyl acetate monomer into polyvinyl acetate through alcoholysis (hydrolysis); the final BAB block copolymer is a polyvinyl alcohol-polyvinylidene fluoride-polyvinyl alcohol triblock copolymer with the weight average molecular weight of 120 ten thousand g/mol.

In this context, the term "polymer" includes on the one hand the collection of chemically homogeneous macromolecules prepared by polymerization, but differing in terms 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, i.e. compounds which can be obtained by reaction of functional groups in the macromolecules described above, for example addition or substitution, and which can be chemically homogeneous or chemically inhomogeneous.

In some embodiments, the dispersion medium of 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, polycarbonate. That is, the binder is dissolved in an oily solvent.

In some embodiments, a binder is used to secure the electrode materials and/or conductive agents in place and adhere them to the conductive metal components to form the electrode.

In some embodiments, the binder serves as a positive electrode binder for binding the positive electrode active material and/or the 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.

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

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

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

In this context, the term "hydroxy" refers to an-OH group.

In this context, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is substituted with another chemical moiety with a substituent, wherein each substituent is independently selected from the group consisting of: hydroxy, mercapto, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C _1-6 Alkyl, C _1-6 Alkoxy, carboxyl, ester groups.

In some embodiments, the molar content of structural units represented by formula I is 30% to 70% based on the total moles of all structural units in the block copolymer. In some embodiments, the molar content of the structural units represented by formula I may be selected from any of 30% -35%, 35% -40%, 40% -45%, 45% -50%, 50% -55%, 55% -60%, 60% -65%, 65% -70%, 30% -40%, 40% -50%, 50% -60%, 60% -70%, 35% -45%, 45% -55%, 55% -65%, 30% -45%, 45% -60%, 35% -50%, 50% -65%, 40% -55%, 55% -70%, 30% -50%, 50% -70%, 35% -55%, 40% -60%, 45% -65%, 30% -55%, 35% -60%, 40% -65%, 45% -70%, 30% -60%, 35% -65%, 40% -70%, 30% -65%, 35% -70% based on the total moles of all structural units in the block copolymer.

If the molar content of the structural unit shown in the formula I is too low, the adhesive force of the pole piece is reduced; if the molar content of the structural unit shown in the formula I is too high, the gelation phenomenon of the slurry is quickened, the stability of the slurry is reduced, and the membrane resistance is increased.

In some embodiments, the block copolymer has a weight average molecular weight of 40 ten thousand to 200 ten thousand. In some embodiments, the weight average molecular weight of the block copolymer may be selected from any of 40 to 60, 60 to 80, 80 to 100, 100 to 120, 120 to 140, 140 to 160, 160 to 180, 180 to 200, 60 to 90, 70 to 200, 90 to 120, 120 to 150, 150 to 180, 180 to 200, 120 to 200.

In this context, the term "weight average molecular weight" refers to the sum of the weight fractions of the polymer occupied by molecules of different molecular weights multiplied by their corresponding molecular weights.

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, the internal resistance of the membrane is increased, in addition, the viscosity of the slurry is larger, the dispersibility of the binder is reduced, and the flexibility of the pole piece is affected; if the weight average molecular weight of the block copolymer is too small, a three-dimensional network bonding structure is difficult to form, an effective bonding effect cannot be achieved, and in addition, the internal resistance of the membrane becomes large.

In some embodiments, the weight average molecular weight of the a-block in the block copolymer is 20 tens of thousands to 105 tens of thousands. In some embodiments, the weight average molecular weight of the A-block can be selected from any of 20-30, 30-40, 40-50, 50-60, 60-70, 70-80, 80-90, 90-105, 40-60, 40-80, 40-105.

If the weight average molecular weight of the A-block in the block copolymer is too large, the structural unit shown in the formula I has too many strong polar groups, so that the stability of the slurry is affected; if the weight average molecular weight of the A-block in the block copolymer is too small, the adhesion of the pole piece is lowered.

In some embodiments, the weight average molecular weight of each B-block in the block copolymer is from 10 ten thousand to 50 ten thousand. In some embodiments, the weight average molecular weight of each B-block can be selected from any of 10-20, 20-30, 30-40, 40-50, 20-40, 20-50.

In some embodiments, the structural unit of formula I is

One or more of the following.

In some embodiments, the building block of formula II is

One or more of the following.

In some embodiments, the block copolymer is selected from one or more of a polyvinyl alcohol-polyvinylidene fluoride-polyvinyl alcohol triblock copolymer, a polyvinyl alcohol-polyvinyl fluoride-polyvinyl alcohol triblock copolymer, a polyvinyl alcohol-polytetrafluoroethylene-polyvinyl alcohol triblock copolymer, a polystyrene-polyvinylidene fluoride-polystyrene triblock copolymer, a polystyrene-polyvinyl fluoride-polystyrene triblock copolymer, a polystyrene-polytetrafluoroethylene-polystyrene triblock copolymer, a polyethylene oxide-polyvinylidene fluoride-polyethylene oxide triblock copolymer, a polyethylene oxide-polyvinyl fluoride-polyethylene oxide triblock copolymer, a polyethylene oxide-polytetrafluoroethylene-polyethylene oxide triblock copolymer, a poly 4-vinylbenzoic acid-polyvinylidene fluoride-poly 4-vinylbenzoic acid triblock copolymer, a poly 4-vinylbenzoic acid-polytetrafluoroethylene-poly 4-vinylbenzoic acid triblock copolymer; optionally one or more selected from polyvinyl alcohol-polyvinylidene fluoride-polyvinyl alcohol triblock copolymer, polyvinyl alcohol-polyvinyl fluoride-polyvinyl alcohol triblock copolymer, polyvinyl alcohol-polytetrafluoroethylene-polyvinyl alcohol triblock copolymer, polystyrene-polyvinylidene fluoride-polystyrene triblock copolymer, polyethylene oxide-polyvinylidene fluoride-polyethylene oxide triblock copolymer, poly 4-vinylbenzoic acid-polyvinylidene fluoride-poly 4-vinylbenzoic acid triblock copolymer.

The fluorine element contained in the A-block forms hydrogen bond with the hydroxyl or/and carboxyl on the surface of the active material and the surface of the current collector, so that the pole piece has excellent adhesive force. The hydroxyl contained in the B-block forms a hydrogen bond with the hydroxyl on the surfaces of the positive electrode active substance and the conductive agent particles, so that on one hand, the binding force of the pole piece is improved, and on the other hand, the positive electrode active substance and the conductive agent particles are adsorbed on the B-block molecular chain, so that the surface states of the positive electrode active substance and the conductive agent particles can be changed, and the solid-liquid interface energy is reduced. Meanwhile, the molecular chain of the B-block can provide steric hindrance shielding to effectively prevent agglomeration of the positive electrode active material and the conductive agent. After the agglomerated positive electrode active material and the conductive agent adsorb the B-block molecular chain, the molecular chain of the B-block molecular chain is adsorbed on the defect and dangling bond on the surface of the particles, so that the interconnection among the particles is weakened, a certain rejection effect is achieved, the molecular chain of the B-block plays a certain role in dispersing, the gelation phenomenon of the slurry is slowed down, and the stability of the slurry is improved.

By forming the BAB block copolymer, the crystallinity of the polymer is reduced, the mobility of the chain segment is increased, and the flexibility of the pole piece is improved. Meanwhile, the structural units shown in the formula II or III can weaken intermolecular acting force between the structural units shown in the formula I, improve flexibility of the pole piece, reduce brittle failure risk of the high-load high-voltage dense pole piece and improve safety performance of the battery.

The adhesive prepared by the BAB type block copolymer 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 adhesive and the non-fluorine adhesive, and realize the effect of complementary advantages. And compared with the simple blending of the fluorine-containing copolymer and the non-fluorine copolymer, the BAB type block copolymer can effectively inhibit the layering phenomenon of the copolymer in the slurry preparation process through the interaction between the blocks.

In summary, the adhesive can effectively slow down the gelation phenomenon of the slurry, improve the stability of the slurry, improve the flexibility of the pole piece, improve the binding force, improve the liquid absorption rate of the pole piece, reduce the sheet resistance, reduce the direct current impedance growth rate of the battery, and/or improve the circulation capacity retention rate of the battery.

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

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

As used herein, the term "ester" refers to a-COO-group.

In some embodiments, a schematic diagram of a preparation method of the BAB type block copolymer 6 is shown in FIG. 1, wherein two end groups 611 of an A-block 61 comprising a structural unit 612 shown in formula I are active groups, a terminal group 621 of a B-block 62 comprising a structural unit 622 shown in formula II or formula III is active groups, and the two end groups 611 of the A-block react with the terminal group 621 of the B-block to achieve bonding of polymer segments, thereby preparing the BAB type block copolymer 6.

The preparation method has the advantages of cheap raw materials, reduced cost, reduced environmental pollution and contribution to the improvement of the yield of the binder. Meanwhile, the adhesive prepared by the method can effectively slow down the gelation phenomenon of the slurry, improve the stability of the slurry, improve the flexibility of the pole piece, improve the adhesive force, improve the liquid absorption rate of the pole piece, reduce the membrane resistance, reduce the direct current impedance growth rate of the battery and/or improve the circulation capacity retention rate of the battery.

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

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

In this context, the term "alkynyl" refers to a-C.ident.C group.

In some embodiments, the A-block is synthesized by polymerizing monomers of formula IV under the action of a first initiator to form the A-block as follows. Because the end groups at both sides of the first initiator are halogen substituted alkyl or trimethylsilyl ethynyl groups, the halogen or trimethylsilyl groups at both sides of the A-block are easily substituted, so that both ends of the A-block have azide groups.

The azide end-capped A-block prepared by the preparation method is convenient for the A-block to be connected with the B-block in an efficient and mild way to generate the BAB type block copolymer.

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

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 a RAFT reagent serving as a chain transfer reagent is added in free radical polymerization, so that free radicals which are easy to terminate are protected in a chain transfer mode, most of the free radicals in the polymerization reaction are converted into dormant species of free radicals, and a dormant chain segment and a reactive chain segment exist simultaneously in the reaction process and are continuously and rapidly switched with each other through dynamic reversible reaction, so that only a few polymer chains exist in the form of the reactive chain at any moment and are grown, and finally the growth probability of each polymer chain segment is approximately equal, and the characteristic of living polymerization is shown.

In some embodiments, the synthetic route to the B-block is shown below, wherein the chain transfer agent is a trithiocarbonate, A ₇ Is an ester group, Z' is an active group with an alkynyl or azido group at the end, B ₃ The B-block having an alkynyl or azido group at the end thereof is an alkyl group and is prepared by the following reaction.

In some embodiments, the monomer of formula v may be selected from any one of vinyl acetate, trimethylvinyl acetate, and methyl vinyl acetate.

In some embodiments, the synthetic route to the B-block is shown below, wherein the chain transfer agent is a trithiocarbonate, A ₇ Z' is an active group having an alkynyl or azido group at the end, B being a substituted or unsubstituted aromatic group ₃ The B-block having an alkynyl or azido group at the end thereof is an alkyl group and is prepared by the following reaction.

In some embodiments, the monomer of formula V may be selected from any one of styrene, 4-vinylbenzoic acid, 2-methylstyrene, and a-methylstyrene.

Controllable polymerization can be realized by adopting reversible addition-fragmentation chain transfer polymerization, and the molecular weight distribution of the product is narrower. Moreover, through the above reaction, the B-block only has alkynyl or azido groups at the terminal, which facilitates the bonding with the A-block in a highly efficient and gentle manner, resulting in a BAB type triblock copolymer.

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

In some embodiments, the synthetic route of the B-block is that under the action of an ionic initiator, the epoxy monomer undergoes ring-opening polymerization reaction to obtain the polyethylene oxide with hydroxyl at the tail end, and the hydroxyl at the tail end and an active monomer containing an azide group or an alkynyl group undergo functionalization reaction to prepare the B-block with the azide group or the alkynyl group at the tail end. It is understood that the reactive monomer containing an azide group or an alkyne group means a monomer containing an azide group or an alkyne group and containing a reactive functional group capable of reacting with a terminal hydroxyl group of polyethylene oxide, and the reactive functional group reacting with a hydroxyl group may be selected from any one of epoxy group, carboxyl group, acid anhydride, isocyanate group, carbonyl chloride.

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

In this context, the term "carboxyl" refers to a-COOH group.

In this context, the term "anhydride" refers to a-CO-O-CO-group.

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

In this context, the term "carbonyl chloride" refers to a-COCl group.

The preparation method is adopted to prepare the B-block with the terminal azido group or alkynyl, so that the connection between the B-block and the A-block can be conveniently carried out in a high-efficiency and mild mode, and the BAB type block copolymer is generated.

In some embodiments, preparing 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 azide group, such that the A-block is attached to the B-block. In some embodiments, the click reaction is performed in the presence of a Cu (I) catalyst at ambient temperature and pressure.

In some embodiments, the end groups of the A-block are azide groups and the end groups of the B-block are alkyne groups.

In some embodiments, the end groups of the A-block are alkynyl groups and the end groups of the B-block are azide groups.

The preparation method has the advantages of high yield, harmless byproducts, simple and mild reaction conditions and easily available 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 terminal alkynyl or azido groups. In some embodiments, the chain transfer agent is a trithiocarbonate containing terminal alkynyl or azido groups. In some embodiments, the chain transfer agent has a structural formula selected from the group consisting of,

The RAFT chain transfer agent containing the terminal alkynyl or azido group enables the terminal of the B-block to be provided with the alkynyl or azido group during the synthesis of the B-block, thereby providing a basis for the click reaction of the B-block and the A-block, avoiding complex post-treatment steps and improving the reaction efficiency.

In some embodiments, the first initiator is a symmetrical difunctional initiator selected from the group consisting of 4- (chloromethyl) benzoyl peroxide. The symmetrical bi-functionality initiator enables both sides of the A-block to carry the same active functional groups symmetrically, which is helpful for the simultaneous realization of the azide or alkyne of both side end groups of the A-block.

In some embodiments, the second initiator is an azo initiator selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile. 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 ionic initiator comprises a cationic initiator or an anionic initiator.

In some embodiments, the ionic initiator is any one of an alkoxide, hydroxide, amide, organometal, alkaline earth oxide of an alkali metal.

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, a potassium ion battery.

[ Positive electrode sheet ]

The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active substance, 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 a preparation method in some embodiments.

In some embodiments, the mass fraction of the binder is 0.1% -3% based on the total mass of the positive electrode active material. In some embodiments, the mass fraction of binder is 0.1% -0.2%, 0.1% -1.03%, 0.1% -1.2%, 0.2% -1.03%, 0.2% -1.2%, 0.2% -3%, 1.03% -1.2%, 1.03% -3%, 1.2% -3%.

When the content of the binder is too low, the binder cannot exert a sufficient binding effect. On one hand, the adhesive can not fully disperse the conductive agent and the active substance, so that the resistance of the membrane of the pole piece is increased; on the other hand, the positive electrode active material and the conductive agent in the slurry cannot be tightly combined with the binder, the positive electrode active material and the conductive agent particles are settled and agglomerated, and the stability of the slurry is reduced.

In contrast, when the binder content is too high, the viscosity of the slurry is too high, which results in too thick binder coating layer coating the surface of the positive electrode active material, which affects the transmission of electrons and ions during the battery cycle, and increases the internal resistance of the membrane.

In some embodiments, the adhesion per unit length between the positive electrode film layer and the positive electrode current collector is not less than 8N/m, alternatively not less than 10N/m.

The adhesion between the positive electrode film layer and the positive electrode current collector in unit length can be tested by any means known in the art, for example, by referring to GB-T2790-1995 national standard "180 DEG peel Strength test method of adhesive". As an example, the positive electrode sheet was cut into test specimens of 20mm×100mm size for use; the pole piece is adhered to one surface of the positive electrode film layer by double-sided adhesive tape, and is compacted by a pressing roller, so that the double-sided adhesive tape is completely adhered to the pole piece; the other surface of the double-sided adhesive tape is adhered to the surface of stainless steel, one end of the sample is reversely bent, and the bending angle is 180 degrees; and (3) testing by adopting a high-speed rail tensile machine, fixing one end of the stainless steel on a clamp below the tensile machine, fixing the bent tail end of the sample on the clamp above, adjusting the angle of the sample, ensuring that the upper end and the lower end are positioned at vertical positions, and then stretching the sample at the speed of 50mm/min until the positive electrode current collector is completely stripped from the positive electrode membrane, 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 faced adhesive tape (the width direction of the pole piece is perpendicular to the stripping direction) to be used as the adhesive force of the pole piece in unit length, and the width of the pole piece in the test is 20mm.

In some embodiments, the positive electrode sheet is subjected to bending test for at least 3 times, and the positive electrode sheet has a light transmission phenomenon.

Bending tests, also known as flexibility tests, may be used to test the flexibility of the pole piece, which may be performed by any means known in the art. As an example, the cold-pressed positive electrode sheet was cut into test specimens of 20mm×100mm size; after the light-transmitting slit is folded forward, flattening by using 2kg of pressing rollers, unfolding the light-transmitting slit to check whether light transmission occurs, and if not, folding the slit reversely, flattening by using 2kg of pressing rollers, checking the light again, repeating the steps until the light transmission phenomenon occurs in the slit, and recording folding times; at least three patterns are taken for testing, and an average value is taken as a test result of the bending test.

The pole piece can be subjected to bending tests for at least 3 times, so that the pole piece has good flexibility, the pole piece is not easy to crack in the production process, the pole piece is not easy to brittle fracture in the use process, the yield of the battery is improved, and the safety performance of the battery is improved.

In some embodiments, the positive electrode sheet has a imbibition rate of greater than 0.32 μg/s, optionally greater than 0.37. Mu.g/s, the density of the electrolyte is 1.1-1.2g/cm ³ 。

The imbibition rate of the pole piece can reflect the ability of the pole piece to wet in the electrolyte. The test may be performed by any means known in the art. As an example, the cold-pressed positive electrode sheet was cut into test samples of 5cm×5cm size; firstly, drying a sample at 80 ℃ for 4 hours, fixing the sample on a sample table after testing the thickness of a pole piece, selecting a capillary tube with d=200 mu m, polishing the end face of the capillary tube with 5000-mesh sand paper until the end face is flat, and observing the state between the capillary tube and the pole piece by using a microscope; sucking electrolyte by using a capillary, controlling the height h=3mm of the electrolyte, descending the capillary to be in contact with the pole piece, simultaneously using a stopwatch to count, stopping counting after the liquid level is descended, reading the liquid suction time t, and recording data; the average imbibition rate v, v=pi× (d/2) of the pole piece was calculated using the formula ² X h x ρ/t. In the test, the density of the electrolyte is 1.1-1.2g/cm ³ . As an example, the electrolyte may be prepared by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and methylethyl carbonate, the mass content of the lithium hexafluorophosphate solution being 12.5%, the volume ratio of ethylene carbonate and methylethyl carbonate in the solution being 3:7.

In some embodiments, the sheet resistance of the positive electrode sheet is 0.58 Ω or less, alternatively 0.48 Ω or less.

The sheet resistance test may be used to test the resistance of the pole piece, which may be performed by any means known in the art. As an example, a small wafer with the diameter of 20mm is cut at the left, middle and right parts of the pole piece; turning on a meta-energy science and technology pole piece resistance meter indicator lamp, placing the meta-energy science and technology pole piece resistance meter indicator lamp at a proper position of a probe of a diaphragm resistance meter, clicking a start button, and reading when the indication is stable; and testing two positions of each small wafer, and finally calculating the average value of six measurements, namely the diaphragm resistance of the pole piece.

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

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

In some embodiments, the positive electrode active material may employ a positive electrode 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 battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g. LiNiO) ₂ ) Lithium manganese oxide (e.g. LiMnO ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM) ₃₃₃ )、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM) ₅₂₃ )、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM) ₂₁₁ )、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM) ₆₂₂ )、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxide (e.g. LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) And at least one of its modified compounds 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 abbreviated as LFP)), composite material of lithium iron phosphate and carbon, and manganese lithium phosphate (such as LiMnPO) ₄ ) At least one of a composite material of lithium manganese phosphate and carbon, and a composite material of lithium 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 electrode 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 (3) coating the positive electrode slurry on a positive electrode current collector, and obtaining a positive electrode plate after the procedures of drying, cold pressing and the like.

[ negative electrode sheet ]

The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material.

As an example, the anode current collector has two surfaces opposing in its own thickness direction, and the anode film layer is provided on either one or both of the two surfaces opposing the anode 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 may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material 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 polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the anode active material may employ an anode active material for a battery, which is well 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 may be at least one selected from elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery anode active material may be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the negative electrode film layer 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 is at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

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

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

[ electrolyte ]

The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The type of electrolyte is not particularly limited in this application, and may be selected according to the need. For example, the electrolyte may be liquid, gel, or all solid.

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

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium difluorodioxaato phosphate, and lithium tetrafluorooxalato phosphate.

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

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

[ isolation Membrane ]

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

In some embodiments, the material of the isolating 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 outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.

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 exterior package of the secondary battery may also be a pouch type pouch, for example. The material of the flexible bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

Secondary battery

The shape of the secondary battery is not particularly limited in the present application, and may be cylindrical, square, or any other shape. For example, fig. 2 is a secondary battery 5 of a square structure as one 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 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a receiving chamber. The housing 51 has an opening communicating with the accommodation chamber, and the 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. The electrode assembly 52 is enclosed in the accommodating chamber. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art may select according to specific practical requirements.

[ Battery Module ]

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number may be selected by one 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 sequentially arranged in the longitudinal direction of the battery module 4. Of course, the arrangement may be performed in any other way. The plurality of secondary batteries 5 may be further fixed by fasteners.

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

[ Battery pack ]

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

Fig. 5 and 6 are battery packs 1 as an example. Referring to fig. 5 and 6, a battery case and a plurality of battery modules 4 disposed in the battery case may be included in the battery pack 1. The battery box includes an upper box body 2 and a lower box body 3, and 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. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[ electric device ]

In one embodiment of the present application, an electrical device is provided that includes at least one of any of the secondary battery of any embodiment, the battery module of any embodiment, or the battery pack of any embodiment.

The electricity utilization device comprises at least one of a secondary battery, a battery module or a battery pack. The secondary battery, the battery module, or the battery pack may be used as a power source of the power consumption device, and may also be used as an energy storage unit of the power consumption device. The power utilization device may include mobile devices (e.g., cell phones, notebook computers, etc.), electric vehicles (e.g., electric-only vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

As the electricity consumption device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirements thereof.

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

As another example, the device may be a cell phone, tablet computer, notebook computer, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

Examples

Hereinafter, embodiments of the present application are described. The embodiments described below are exemplary only for the purpose of illustrating the present application and are not to be construed as limiting the present application. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Example 1

1) Preparation of the adhesive

Preparation of the B-block: using alkynyl compound as chain transfer agent, and preparing alkynyl terminated polyvinyl alcohol through polymerization reaction;

vinyl acetate monomer, RAFT chain transfer agent (CTA-alkyne) and azobisisobutyronitrile were added in a molar ratio of 700:1:0.1 to 500ml of tetrahydrofuran solution. The mixture was subjected to at least three freeze-pump-thaw cycles and placed in an oil bath preheated to 75 ℃. After 6 hours of reaction, the reaction was stopped 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 polymer was dried in vacuo at room temperature for 10 hours to remove all traces of residual solvent. Dissolving the polyvinyl acetate obtained by the reaction in a mixed solvent (the volume ratio of methanol to water is 79.5:0.5), wherein the mass fraction of the polyvinyl acetate is 20%, adding a sodium hydroxide solution with the mass fraction of 1.5% for alcoholysis for 2 hours at the temperature of 30 ℃, fully washing and filtering to obtain a B-block polymer, and preparing the B-block polymer, wherein the reaction process is as follows

Preparation of the A-block: using azide as initiator, polymerization to prepare azide terminated polyvinylidene fluoride; 1% by mass of 4- (chloromethyl) benzoyl peroxide was dissolved in 300ml of anhydrous acetonitrile, and introduced into a high-pressure reactor, followed by nitrogen (N) ₂ ) Purging for 30 minutes. 4g of vinylidene fluoride monomer was transferred to the reactor at room temperature (20-25 ℃ C.) and pressurized to about 8 MPa. The temperature inside the reactor was raised to 90℃and the reaction mixture was stirred and reacted at a speed of 500 rpm for 3 hours. After the reaction was completed, the solvent was removed, and the resulting solid was washed with chloroform several times to remove the initiator residue, and dried in vacuo at 45℃to give a white product, i.e., chloro-terminated polyvinylidene fluoride (PVDF). 3mmol of chlorine-terminated PVDF and 60mmol of sodium azide (NaN ₃ ) Dissolved in 600ml of N, N-Dimethylformamide (DMF) and stirred at 60℃for 10 hours. The polymer solution was concentrated and precipitated three times in a mixed solvent (volume ratio of methanol to water 1:1). The pale yellow polymer was then dried under vacuum at 45℃to give an azide-terminated PVDF, namely, an A-block polymer, and the reaction procedure for preparing the A-block polymer was as follows

Preparation of a BAB type block copolymer:

Azide-terminated polyvinylidene fluoride, alkyne-terminated polyvinyl alcohol, and CuBr were added to a dry Schlenk tube in a molar ratio of 1:2.5:4, and after degassing, 4ml of anhydrous N, N-Dimethylformamide (DMF) and 0.14 mmole of N, N ', N, ' N ' -Pentamethyldiethylenetriamine (PMDETA) were added. 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 the product was precipitated using a 20-fold excess of a mixed solvent (volume ratio of methanol to water: 1:1), the product was collected by filtration, and vacuum-dried to obtain a polyvinyl alcohol-polyvinylidene fluoride-polyvinyl alcohol block copolymer, which was used as a battery binder, and the reaction process for preparing a BAB-type block copolymer was as follows

2) Preparation of positive electrode plate

The weight ratio of the lithium Nickel Cobalt Manganese (NCM) material, the conductive agent carbon black, the binder prepared in example 1 and N-methyl pyrrolidone (NMP) is 96.9:2.1:1:21, stirring and mixing uniformly to obtain positive electrode slurry, wherein the solid content of the slurry is 73%; and uniformly coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and cutting to obtain the positive electrode plate.

3) Preparation of negative electrode plate

The active material artificial graphite, conductive agent carbon black, binder Styrene Butadiene Rubber (SBR) and thickener sodium hydroxymethyl cellulose (CMC) are mixed according to the weight ratio of 96.2:0.8:0.8:1.2, dissolving in deionized water serving as a solvent, and uniformly mixing to prepare negative electrode slurry; and uniformly coating the negative electrode slurry on a negative electrode current collector copper foil once or a plurality of times, and drying, cold pressing and cutting to obtain a negative electrode plate.

4) Isolation film

A polypropylene film was used as a separator.

5) Preparation of electrolyte

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

6) Preparation of a Battery

The positive electrode plate, the isolating film and the negative electrode plate of the embodiment 1 are sequentially stacked, the isolating film is positioned between the positive electrode plate and the negative electrode plate to play a role of isolation, then the bare cell is obtained by winding, the tab is welded on the bare cell, the bare cell is arranged in an aluminum shell, baking and dewatering are carried out at 80 ℃, and then electrolyte is injected and sealed, so that the uncharged battery is obtained. The uncharged battery was subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity test and the like in sequence to obtain the lithium ion battery product of example 1.

Examples 2 to 11

The batteries of examples 2 to 11 were similar to the battery preparation method of example 1, but the polymerization temperatures and times of the a-block and B-block polymers were adjusted to adjust the polymerization degree (or molecular weight change of the fragments) of the different blocks, and specific adjustment parameters are shown in table 1 below, and the remaining parameters were the same as in example 1.

TABLE 1 examples 1-11 polymerization temperature and time parameters

Examples 12 to 15

The batteries of examples 12 to 15 were similar to the battery preparation method of example 1, but the mass fraction of the binder was adjusted, and specific parameters based on the total mass of the positive electrode active material were shown in table 2.

Example 16

The cell of example 16 was prepared similarly to the cell of example 4, except that the a-block was replaced with a polyvinyl fluoride block, the specific parameters are shown in table 2, and the preparation method was as follows:

a-block: 1% by mass of the monomers of 4- (chloromethyl) benzoyl peroxide was dissolved in 300ml of anhydrous acetonitrile and introduced into a high-pressure reactor and used with N ₂ Purging for 30 minutes. 4g of vinyl fluoride were transferred to the reactor at room temperature. The temperature inside the reactor was raised to 90℃and the reaction mixture was stirred at a speed of 500 rpm for 3 hours. Removing solvent after reaction, washing the obtained solid with chloroform for several times to remove initiator residue, and vacuum drying at 45deg.C to obtain white product, i.e. chlorine-terminated polyvinyl fluoride . 3mmol of chlorine-terminated polyvinyl fluoride and 60mmolNaN 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 (volume ratio of methanol to water 1:1). Followed by vacuum drying at 45℃to give azide-terminated polyvinyl fluoride, the A-block polymer.

Example 17

The cell of example 17 was prepared similarly to the cell of example 4, except that the a-block was replaced with a polytetrafluoroethylene block, the specific parameters are shown in table 2, and the preparation method is as follows:

a-block: 1% by mass of the monomers of 4- (chloromethyl) benzoyl peroxide was dissolved in 300ml of anhydrous acetonitrile, introduced into a high-pressure reactor and treated with N ₂ Purging for 30 minutes. 4g of tetrafluoroethylene was transferred to a reactor at room temperature, the temperature inside the reactor was increased to 90℃and the reaction mixture was stirred at 500 rpm for 3 hours. After the reaction was completed, the solvent was removed, and the resulting solid was washed with chloroform several times to remove the initiator residue, and dried in vacuo at 45℃to give a white product, i.e., chloro-terminated polytetrafluoroethylene. 3mmol of chlorine-terminated polytetrafluoroethylene and 60mmolNaN 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 (volume ratio of methanol to water 1:1) and dried in vacuo at 45 ℃ to give the azide-terminated polytetrafluoroethylene, the a-block polymer.

Example 18

The cell of example 18 was prepared similarly to the cell of example 4, except that the B-block was replaced with polystyrene, the specific parameters are shown in table 2, and the preparation method was as follows:

styrene monomer, RAFT chain transfer agent (CTA-alkyne) and azodiisobutyronitrile in a molar ratio of 700:1:0.1 are weighed 500ml tetrahydrofuran, a four-necked flask is added, a large amount of nitrogen is introduced, the stirring speed is gradually increased to 1200 revolutions per minute, RAFT chain transfer agent (CTA-alkyne) accounting for 1% of the mass of the monomer and azodiisobutyronitrile accounting for 0.1% of the mass of the monomer are added, and the temperature is increased to 75 ℃. After 6 hours of reaction, the reaction was stopped 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 polymer was vacuum dried at room temperature for 10 hours to remove all traces of residual solvent to obtain the target B-block, and the reaction process for preparing the B-block polymer was as follows

Example 19

The cell of example 19 was prepared similarly to the cell of example 4, except that the B-block was replaced with polyethylene oxide, the specific parameters are shown in table 2, and the preparation method was as follows:

adding ethylene oxide monomer, water and potassium hydroxide (KOH) in a molar ratio of 1:0.1:0.02 into a high-pressure stirring kettle, introducing a large amount of nitrogen to remove air, pressurizing to 0.3MPa, gradually increasing the stirring speed to 1000 revolutions per minute, and heating to 80 ℃. After the reaction for 6 hours, the pressure in the kettle is reduced, the excessive monomer is removed by short pressurization, and the polyethylene oxide is obtained after purification. Polyethylene oxide, glycidol propargyl ether and KOH in a molar ratio of 1:1.2:0.02 are pressurized with nitrogen, stirred and heated to 120 ℃ to activate the monomer, the reaction is carried out for 2 hours under high pressure, then the pressure is reduced to room temperature, the reaction product is stored and dried to obtain the target B-block polymer, and the reaction process for preparing the B-block polymer is as follows

Example 20

The cell of example 20 was prepared similarly to the cell of example 4, except that the B-block was replaced with poly 4-vinylbenzoic acid, the specific parameters are shown in table 2, and the preparation method is as follows:

taking 500ml of tetrahydrofuran, adding a large amount of nitrogen into a four-neck flask, gradually increasing the stirring speed to 1200 revolutions per minute, adding RAFT chain transfer agent (CTA-alkyne) accounting for 1% of the mass of the monomer and azodiisobutyronitrile accounting for 0.1% of the mass of the monomer, and heating to 75 ℃. After 6 hours of reaction, the reaction was stopped 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 polymer was dried in vacuo at room temperature for 10 hours to remove all traces of residual solvent to give the target 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, and specific parameters are shown in table 2, purchased from 5130 of the sor-wiry group.

Comparative example 2

The cell of comparative example 2 was similar to the cell of example 1, except that the binder was polyvinyl alcohol, synthesized as follows:

Vinyl acetate monomer, RAFT chain transfer agent (CTA-alkyne) and azobisisobutyronitrile were added in a molar ratio of 700:1:0.1 to 500ml of tetrahydrofuran solution. The mixture was subjected to at least three freeze-pump-thaw cycles and placed in an oil bath preheated to 60 ℃. After 12 hours of reaction, the reaction was stopped 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 polymer was dried in vacuo at room temperature for 10 hours to remove all traces of residual solvent. And dissolving the polyvinyl acetate obtained by the reaction in a mixed solvent (the volume ratio of methanol to water is 79.5:0.5), wherein the mass fraction of the polyvinyl acetate is 20%, and adding a sodium hydroxide solution with the mass fraction of 1.5% for alcoholysis for 2.5 hours at the temperature of 30 ℃, and fully washing and filtering to obtain the target binder.

Comparative example 3

The cell of comparative example 3 was similar to the cell of example 1, except that the binder was a blend of polyvinylidene fluoride and polyvinyl alcohol, and the specific parameters are shown in table 2, and the preparation method was as follows:

blending: the polyvinyl alcohol of comparative example 2 and the polyvinylidene fluoride of comparative example 1 were blended in a molar ratio of 4:6 to obtain a polyvinylidene fluoride and polyvinyl alcohol blend adhesive.

2. Performance testing

1. Slurry performance test

1) Slurry viscosity test

After the slurry was shipped, 500ml of the slurry was placed in a beaker, a rotor was selected using a rotary viscometer, the rotation speed was set at 12 rpm, the rotation time was set at 5 minutes, and after the values were stabilized, the viscosity values were read and recorded.

2) Slurry stability test

And (3) after the slurry is stirred for 30 minutes again, pouring a certain amount of slurry into a sample bottle of the stability instrument, closing a test tower cover after the slurry is put into the sample bottle, opening the test tower cover, starting to generate a scanning curve on a test interface, starting to test the stability of the sample, and continuously testing for more than 48 hours to finish the test.

2. Pole piece performance test

1) Diaphragm resistance test

Cutting small discs with the diameter of 20mm at the left, middle and right parts of the pole piece. And (3) turning on the meta-energy science and technology pole piece resistance instrument indicator lamp, placing the meta-energy science and technology pole piece resistance instrument indicator lamp at a proper position of a probe of a diaphragm resistance instrument, clicking a start button, and reading after the indication is stable. And testing two positions of each small wafer, and finally calculating the average value of six measurements, namely the diaphragm resistance of the pole piece.

2) Adhesion test

Cutting the positive pole piece into a test sample with the size of 20mm multiplied by 100mm for later use; the surface of the pole piece, which needs to be tested, is glued by double-sided adhesive, and is compacted by a compression roller, so that the pole piece is completely attached to the pole piece; the other surface of the double faced adhesive tape of the sample is adhered to the surface of stainless steel, one end of the sample is reversely bent, and the bending angle is 180 degrees; and (3) testing by adopting a high-speed rail tensile machine, fixing one end of the stainless steel on a clamp below the tensile machine, fixing the bent tail end of the sample on the clamp above, adjusting the angle of the sample, ensuring that the upper end and the lower end are positioned at vertical positions, and then stretching the sample at a speed of 50mm/min until the sample is completely peeled off from the substrate, and recording displacement and acting force in the process, wherein the force when the stress is balanced is generally considered as the binding force of the pole piece.

3) Flexible test

Cutting the cold-pressed positive pole piece into a test sample with the size of 20mm multiplied by 100 mm; after the light-transmitting slit is folded forward, flattening by using 2kg of pressing rollers, unfolding the light-transmitting slit to check whether light transmission occurs, and if not, folding the slit reversely, flattening by using 2kg of pressing rollers, checking the light again, repeating the steps until the light transmission phenomenon occurs in the slit, and recording folding times; the test was repeated three times and averaged as reference data for pole piece flexibility.

3. Battery performance test

1) Battery cycle capacity retention (500 ds) test

The battery capacity retention test procedure was as follows: the prepared battery was charged to 4.3V at a constant current of 1/3C, charged to 0.05C at a constant voltage of 4.3V, left for 5min, and discharged to 2.8V at 1/3C, and the resulting capacity was designated as initial capacity C0. Repeating the above steps for the same battery, and recording the discharge capacity Cn of the battery after the nth cycle, wherein the battery capacity retention rate pn=cn/c0 after each cycle is 100%, the 500 point values of P1 and P2 … … P500 are taken as ordinate, and the corresponding cycle times are taken as abscissa, so as to obtain a graph of the battery capacity retention rate and the cycle times. In this test procedure, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and the 500 th cycle of … … corresponds to n=500. The battery capacity retention rate data corresponding to the examples or comparative examples in table 3 are data measured after 500 cycles under the above-described test conditions, i.e., the value of P500. The test procedure for the comparative example and the other examples is the same as above.

2) Battery DC impedance growth rate (100 cls) test

The DC impedance test process of the battery is as follows: the battery was charged to 4.3V at a constant current of 1/3C at 25C, and then charged to 0.05C at a constant voltage of 4.3V, and after resting for 5min, the voltage V1 was recorded. Then discharging for 30s at 1/3C, and recording the voltage V2, and obtaining the internal resistance DCR1 of the battery after the first circulation at (V2-V1)/1/3C. The above steps are repeated for the same battery, and the internal resistance DCRn (n=1, 2, 3 … … 100) of the battery after the nth cycle is recorded, and the graph of the battery discharge DCR and the cycle number is obtained by taking the 100 point values of the DCR1, DCR2, DCR3 … … DCR100 as the ordinate and the corresponding cycle number as the abscissa.

In this test procedure, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and … … the 100 th cycle corresponds to n=100. The battery internal resistance increase ratio of example 1= (DCRn-DCR 1)/DCR 1 in table 3 is 100%, and the test procedure of comparative example 1 and other examples is the same as above. The data in table 3 are measured after 100 cycles under the above test conditions.

4. Polymer detection

1) Weight average molecular weight (Wg/mol) test method

A Waters 2695 Isocric HPLC gel chromatograph (differential refractive detector 2141) was used. A sample of 3.0% by mass polystyrene solution was used as a reference and a matched column was selected (oiliness: styragel HT5 DMF 7.8. Times. 300mm+Styragel HT4). Preparing a 3.0% polymer glue solution by using a purified N-methyl pyrrolidone (NMP) solvent, and standing the prepared solution for one day for later use. During the test, tetrahydrofuran is firstly sucked by a syringe, and then the syringe is washed, and the test is repeated for several times. Then, 5ml of the test solution was aspirated, the air in the syringe was removed, and the needle tip was wiped dry. And finally, slowly injecting the sample solution into the sample inlet. And obtaining data after the indication is stable.

3. Analysis of test results for examples and comparative examples

Table 2 examples and comparative examples preparation parameters and weight average molecular weight test results

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Table 3 results of performance tests of examples and comparative examples

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From the above results, it is understood that the binders in examples 1 to 20 each comprise a polymer comprising an A-block containing structural units represented by formula I and a B-block containing structural units represented by formula II or formula III. As can be seen from a comparison of examples 1-7, 16-20 and comparative examples 1-3, the binder is effective in slowing down the gelation of the slurry, improving the stability of the slurry, improving the flexibility of the pole pieces, improving the adhesion, improving the wicking rate of the pole pieces, reducing the sheet resistance, reducing the rate of increase in the dc resistance of the battery, and/or improving the retention of the cycling capacity of the battery.

As can be seen from the comparison of examples 1-7 and 18-20 with comparative example 1, when the molar content of the structural unit shown in formula I is 30% -70%, the gel phenomenon of the slurry can be effectively slowed down, the stability of the slurry is improved, the flexibility of the pole piece is improved, the binding force is improved, the liquid absorption rate of the pole piece is improved, the membrane resistance is reduced, and the retention rate of the circulation capacity of the battery is improved based on the total molar number of all the structural units in the block copolymer.

As is clear from the comparison of examples 1 to 11 with comparative examples 1 to 3, the cycle capacity retention rate of the battery can be improved when the weight average molecular weight of the block copolymer is 40 to 200 tens of thousands. As can be seen from the comparison of examples 1 to 7 and 9 to 11 with comparative examples 1 to 3, the block copolymers have a weight average molecular weight of 70 to 200 tens of thousands, and are capable of improving the adhesion and improving the cycle capacity retention rate of the battery.

As can be seen from the comparison of examples 1-7 and 18-20 with comparative example 1, in the block copolymer, the A-block has a weight average molecular weight of 20 to 105 ten thousand, which can effectively slow down the gelation of the slurry, improve the stability of the slurry, improve the flexibility of the pole piece, improve the binding force, improve the liquid absorption rate of the pole piece, reduce the sheet resistance, and improve the cycle capacity retention rate of the battery.

As can be seen from the comparison of examples 1 to 7 and 16 to 17 with comparative example 1, in the block copolymer, each B-block has a weight average molecular weight of 10 to 50 ten thousand, it is possible to improve the adhesion, reduce the DC resistance increase rate of the battery, and improve the cycle capacity retention rate of the battery.

As can be seen from the comparison of examples 1 to 7 and 16 to 17 with comparative example 2, the structural units represented by formula I are

Can improve the adhesion, reduce the DC resistance increase rate of the battery, and improve the cycle capacity retention rate of the battery.

As can be seen from the comparison of examples 1 to 7 and 18 to 20 with comparative example 1, the B-block contains structural units of the formula II and the structural units of the formula II are

Or the B-block contains structural units shown in the formula III and the structural units shown in the formula III are-CH ₂ -CH ₂ When O-, in particular, when the B-block is selected from one or more of polystyrene, polyvinyl alcohol, poly-4-vinylbenzoic acid and polyalkylene oxide, the gel phenomenon of the slurry can be effectively slowed down, the stability of the slurry is improved, the flexibility of the pole piece is improved, the binding force is improved, the imbibition rate of the pole piece is improved, the membrane resistance is reduced, and the cycle capacity retention rate of the battery is improved.

As can be seen from the comparison of examples 1 to 7 and 16 to 20 with comparative examples 1 to 3, the block copolymer is selected from one or more of polyvinyl alcohol-polyvinylidene fluoride-polyvinyl alcohol triblock copolymer, polyvinyl alcohol-polyvinyl fluoride-polyvinyl alcohol triblock copolymer, polyvinyl alcohol-polytetrafluoroethylene-polyvinyl alcohol triblock copolymer, polystyrene-polyvinylidene fluoride-polystyrene triblock copolymer, polyethylene oxide-polyvinylidene fluoride-polyethylene oxide triblock copolymer, and poly 4-vinylbenzoic acid-polyvinylidene fluoride-poly 4-vinylbenzoic acid triblock copolymer, and can improve the cycle capacity retention rate of the battery.

As can be seen from the comparison of examples 1 to 7 and 12 to 15 with comparative example 3, the binder has a mass fraction of 0.1% to 3%, alternatively 1.03% to 1.2%, based on the total mass of the positive electrode active material, which can improve the cycle capacity retention rate of the battery. From comparison of examples 1 to 7 and 14 to 15 with comparative example 3, it is apparent that the flexibility of the electrode sheet, the adhesion, and the retention of the cycle capacity of the battery can be improved based on the total mass of the positive electrode active material when the mass fraction of the binder is 1.03% to 3%. From comparison of examples 1 to 7 and 12 to 15 with comparative example 3, it is apparent that when the mass fraction of the binder is 1.03% to 1.2%, the flexibility of the electrode sheet can be improved, the binding force can be improved, the sheet resistance can be reduced, and the cycle capacity retention rate of the battery can be improved based on the total mass of the positive electrode active material.

The present application is not limited to the above embodiment. The above embodiments are merely examples, and embodiments having substantially the same configuration and the same effects as those of the technical idea within the scope of the present application are included in the technical scope of the present application. Further, various modifications that can be made to the embodiments and other modes of combining some of the constituent elements in the embodiments, which are conceivable to those skilled in the art, are also included in the scope of the present application within the scope not departing from the gist of the present application.

Claims

1. A BAB-type block copolymer comprising an A-block containing structural units represented by formula I and a B-block containing structural units represented by formula II or formula III,

-CH ₂ -CH ₂ -O-type 11I

2. The BAB-type block copolymer as claimed in claim 1, characterized in that the molar content of the structural units of formula I is 30-70% based on the total number of moles of all structural units in the block copolymer.

3. The BAB-type block copolymer according to claim 1 or 2, characterized in that the weight average molecular weight of the block copolymer is 40-200 ten thousand.

4. A BAB-type block copolymer according to any of claims 1 to 3, characterized in that the weight average molecular weight of the block copolymer is 70-200 tens of thousands.

5. The BAB-type block copolymer as claimed in any of claims 1 to 4, wherein the weight average molecular weight of the a-block in the block copolymer is 20 to 105 tens of thousands.

6. The BAB-type block copolymer as claimed in any one of claims 1 to 5, characterized in that the weight average molecular weight of each B-block in the block copolymer is 10 to 50 tens of thousands.

7. The BAB-type block copolymer as claimed in any one of claims 1 to 6, characterized in that the structural unit represented by formula I is

One or more of (a) and (b).

8. The BAB-type block copolymer as claimed in any one of claims 1 to 7, characterized in that the structural unit represented by the formula II is

One or more of the following.

9. The BAB-type block copolymer according to any of claims 1 to 8, characterized in that the block copolymer is selected from one or more of polyvinyl alcohol-polyvinylidene fluoride-polyvinyl alcohol triblock copolymer, polyvinyl alcohol-polyvinyl fluoride-polyvinyl alcohol triblock copolymer, polyvinyl alcohol-polytetrafluoroethylene-polyvinyl alcohol triblock copolymer, polystyrene-polyvinylidene fluoride-polystyrene triblock copolymer, polystyrene-polyvinyl fluoride-polystyrene triblock copolymer, polystyrene-polytetrafluoroethylene-polystyrene triblock copolymer, polyethylene oxide-polyvinylidene fluoride-polyethylene oxide triblock copolymer, polyethylene oxide-polyvinyl fluoride-polyethylene oxide triblock copolymer, polyethylene oxide-polytetrafluoroethylene-polyethylene oxide triblock copolymer, poly 4-vinylbenzoic acid-polyvinylidene fluoride-poly 4-vinylbenzoic acid triblock copolymer, poly 4-vinylbenzoic acid-polyvinyl fluoride-poly 4-vinylbenzoic acid triblock copolymer, poly 4-vinylbenzoic acid-polytetrafluoroethylene-poly 4-vinylbenzoic acid triblock copolymer.

10. A process for the preparation of a BAB-type block copolymer comprising the steps of:

wherein A is ₁ 、A ₂ 、A ₃ Each independently selected fromHydrogen, fluorine, C containing at least one fluorine atom _1-3 One or more of alkyl groups;

11. The method of preparing according to claim 10, characterized in that the method of preparing a-block comprises:

12. The process according to claim 10 or 11, characterized in that it comprises:

13. The process according to claim 10 or 11, characterized in that it comprises:

14. The production method according to any one of claims 10 to 13, characterized in that the production of a BAB-type block copolymer comprises:

15. The method of preparation according to claim 12 or 13, wherein the chain transfer agent is a RAFT chain transfer agent containing terminal alkynyl or azido groups.

16. The method of any one of claims 11 to 15, wherein the first initiator is a symmetrical difunctional initiator.

17. The method of any one of claims 11 to 15, wherein the first initiator is 4- (chloromethyl) benzoyl peroxide.

18. The method of claim 12, wherein the second initiator is an azo initiator.

19. The method of claim 12, wherein the second initiator is selected from one or both of azobisisobutyronitrile and azobisisoheptonitrile.

20. Use of the BAB-type block copolymer as defined in any one of claims 1 to 9 in a secondary battery.

21. A positive electrode slurry comprising a positive electrode active material, a conductive agent, and a binder, the binder being the BAB-type block copolymer according to any one of claims 1 to 9 or the BAB-type block copolymer produced by the production method according to any one of claims 10 to 19.

22. The positive electrode slurry according to claim 21, wherein the mass fraction of the binder is 0.1% -3%, optionally 1.03% -3%, more optionally 1.03% -1.2% based on the total mass of the positive electrode active material.

23. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, a conductive agent and a binder, the binder being the BAB-type block copolymer as claimed in any one of claims 1 to 9 or the BAB-type block copolymer produced by the production method as claimed in any one of claims 10 to 19.

24. The positive electrode sheet according to claim 23, wherein the mass fraction of the binder is 0.1-3%, optionally 1.03-3%, more optionally 1.03-1.2% based on the total mass of the positive electrode active material.

25. The positive electrode tab of claim 23 or 24, wherein the adhesion per unit length between the positive electrode film layer and the positive electrode current collector is not less than 8N/m.

26. The positive electrode sheet according to any one of claims 23 to 25, wherein a binding force per unit length between the positive electrode film layer and the positive electrode current collector is not less than 10N/m.

27. The positive electrode sheet according to any one of claims 23 to 26, wherein the positive electrode sheet exhibits a light transmission phenomenon after being subjected to a bending test no less than 3 times.

28. The positive electrode sheet according to any one of claims 23 to 27, wherein the sheet resistance of the positive electrode sheet is 0.58 Ω or less.

29. The positive electrode sheet according to any one of claims 23 to 28, wherein the sheet resistance of the positive electrode sheet is 0.48 Ω or less.

30. The positive electrode sheet of any one of claims 23 to 29, wherein the positive electrode sheet has a liquid absorption rate of greater than 0.32 μg/s to an electrolyte having a density of 1.1-1.2g/cm ³ 。

31. The positive electrode sheet of any one of claims 23 to 30, wherein the positive electrode sheet has a liquid absorption rate of greater than 0.37 μg/s to an electrolyte having a density of 1.1-1.2g/cm ³ 。

32. 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 23 to 31.

33. The secondary battery of claim 32, 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.

34. An electric device comprising the secondary battery according to claim 32 or 33.