WO2024045471A1

WO2024045471A1 - Polymer with core-shell structure and preparation method therefor and use thereof, positive electrode paste, secondary battery, battery module, battery pack, and electric device

Info

Publication number: WO2024045471A1
Application number: PCT/CN2023/071572
Authority: WO
Inventors: 李�诚; 曾子鹏; 刘会会; 王景明
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-08-30
Filing date: 2023-01-10
Publication date: 2024-03-07
Also published as: CN115117356A; CN115117356B; CN115842130A

Abstract

Provided in the present application are a polymer with a core-shell structure and a preparation method therefor and the use thereof, a positive electrode paste, a secondary battery, a battery module, a battery pack, and an electric device. The polymer with a core-shell structure comprises: a core portion, which is a fluorine-containing polymer containing a structural unit derived from a monomer as represented by formula I; and a shell portion, which is a non-fluorine polymer containing structural units derived from monomers as represented by formula II and formula III, and at least partially covers the surface of the core portion. The polymer with a core-shell structure can improve the flexibility of a binder, and enhance the flexibility of an electrode sheet and the safety performance of a battery; moreover, the polymer can also ensure the adhesion force of the electrode sheet, thereby ensuring the performance and the service life of the battery.

Description

Core-shell structure polymer, preparation method and use, positive electrode slurry, secondary battery, battery module, battery pack and electrical device

cross reference

This application cites Chinese Patent No. 202211043832.2 titled "Core-shell structure polymer, preparation method and use, cathode slurry, secondary battery, battery module, battery pack and electrical device" submitted on August 30, 2022. application, which is incorporated by reference in its entirety.

Technical field

The present application relates to the technical field of secondary batteries, and in particular to a core-shell structure polymer, preparation methods and uses, positive electrode slurry, secondary batteries, battery modules, battery packs and electrical devices.

Background technique

In recent years, as the application range of secondary batteries has become more and more extensive, secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields. Due to the great development of lithium-ion batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance.

Existing technology often uses polyvinylidene fluoride (PVDF) as a binder. However, the crystallinity of PVDF homopolymer is relatively high, and the electrode piece is prone to brittle fracture during the battery preparation process, thus posing a greater safety risk. . How to improve the flexibility of the pole piece and ensure the bonding performance of the adhesive has become an urgent problem that needs to be solved.

Contents of the invention

This application was made in view of the above problems, and its purpose is to provide a core-shell structure polymer including: a core part, which is a fluorine-containing polymer containing a structural unit derived from the monomer represented by Formula I. ; And a shell part, the shell part is a non-fluoropolymer containing structural units derived from the monomers represented by formula II and formula III, the shell part at least partially covers the surface of the core part,

Among them, R ₁ and R ₂ are each independently selected from hydrogen, fluorine, chlorine or at least one fluoro-substituted C _1-3 alkyl group; R ₃ , R ₄ and R ₅ are each independently selected from hydrogen or substituted or unsubstituted C _1-5 alkyl.

The core-shell structure polymer can improve the flexibility of the binder, improve the flexibility of the pole piece and the safety performance of the battery; at the same time, it can also ensure the adhesive force of the pole piece, thereby ensuring the performance and service life of the battery.

In addition, the core-shell structure polymer helps to improve the dispersion of the cathode slurry, which can reduce the resistance of the electrode sheet film and improve the battery cycle performance. When the core-shell structure polymer is used in combination with a binder, the flexibility of the pole piece and the dispersion of the slurry can be improved at the same time, and the pole piece has good bonding properties.

In any embodiment, R ₁ and R ₂ are each independently selected from hydrogen, fluorine, or at least one fluoro-substituted C _1-3 alkyl group.

Compared with polychlorotrifluoroethylene and vinylidene fluoride-chlorotrifluoroethylene copolymer as the core of the core-shell polymer, the core in the core-shell polymer contains structural units derived from the monomer represented by Formula I. A fluoropolymer, and R ₁ and R ₂ are each independently selected from hydrogen, fluorine or at least one fluorine-substituted C _1-3 alkyl group, which can reduce the viscosity of the positive electrode slurry and the resistance of the positive electrode film layer, and improve the resistance of the electrode piece. The bonding force and the number of rolling cycles can be improved, as well as the capacity retention rate of the battery after 500 cycles.

In any embodiment, the mass content of the core part is 5% to 9%, and the mass content of the shell part is 91% to 95%, based on the total mass of the core-shell structure polymer.

When the content of the core and shell is within this range, it can increase the plastic strain stress of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery, and ensuring that the pole piece has sufficient adhesion, thereby ensuring Battery performance and lifespan.

In any embodiment, the molar content of the structural units derived from the monomer represented by Formula II is 20% to 50%, based on the total molar amount of the non-fluoropolymer. The core-shell structure polymer within this content range can ensure that the pole piece has good flexibility, thereby ensuring that the battery has excellent electrical performance and cycle performance while improving safety performance.

In any embodiment, the non-fluoropolymer further includes structural units derived from monomers represented by Formula IV,

Among them, R ₆ is selected from amide group or cyano group; R ₇ is selected from hydrogen, substituted or unsubstituted C _1-5 alkyl group.

In the non-fluorine polymer, the polar group contained in the monomer represented by formula IV can form better adsorption performance or affinity with the positive electrode active material, which helps to improve the agglomeration of the positive electrode active material, thereby improving the slurry It improves the stability of the material, improves the processing performance of the pole piece and improves the film resistance of the pole piece.

In any embodiment, the molar content of the structural units derived from the monomer represented by Formula IV is 40% to 50%, based on the total molar amount of the non-fluoropolymer.

The mass content of the monomer shown in Formula IV within a suitable range can have sufficient adsorption performance or affinity for the positive electrode active material, effectively improve the dispersion of the slurry, thereby reducing the electrode sheet film resistance and improving battery cycle performance.

In any embodiment, in the core-shell structure polymer, the weight average molecular weight of the fluorine-containing polymer is 20,000 to 200,000.

In any embodiment, in the core-shell structure polymer, the weight average molecular weight of the fluorine-containing polymer is 20,000 to 150,000.

In any embodiment, the fluoropolymer is polyvinylidene fluoride or a modified polymer thereof; the non-fluoropolymer is a copolymer of styrene and tert-butyl acrylate, acrylonitrile, styrene and Copolymer of tert-butyl acrylate, one or a combination of copolymers of acrylamide, styrene and methyl acrylate.

The fluorine-containing polymer has stable chemical properties, excellent electrical properties, and good mechanical properties. The non-fluorine polymer has relatively soft chain segments, which can significantly improve the flexibility of the binder and the plastic strain stress of the pole piece film layer, thereby improving the flexibility of the pole piece; at the same time, the polar functional groups of the non-fluorine polymer It also has good adsorption performance and/or affinity, and can be stably attached to the surface of cathode active materials including lithium iron phosphate and lithium nickel cobalt manganese oxide, thereby improving the dispersion of the slurry and the film resistance of the pole piece, and thus Improve battery cycle performance.

In any embodiment, the core-shell structure polymer has a median particle diameter Dv50 of 2 μm to 10 μm.

The particle size of the core-shell structure polymer within a suitable range is beneficial to dissolution in the positive electrode slurry solvent, such as N-methylpyrrolidone, reducing the processing difficulty of the binder glue and improving battery processing efficiency.

In any embodiment, when the core-shell structure polymer is dissolved to prepare a glue solution with a mass percentage of 7%, the viscosity of the glue solution is 50-180 mPa·s. Optionally, the core-shell structure The polymer is dissolved in N-methylpyrrolidone to prepare a glue solution. A core-shell structure polymer with a mass ratio of core and shell within a suitable range can have both good flexibility and adsorption of positive electrode active materials, which can improve the uniformity of the slurry coating on the pole piece and improve the pole piece. Flexibility, while taking into account the bonding performance of the adhesive, reducing battery safety hazards and improving the long-term cycle performance of the battery.

The second aspect of the application also provides a method for preparing a core-shell structure polymer, including:

Preparing the core part: at least one monomer represented by the following formula I is polymerized under the first polymerization condition to obtain an emulsion of fluorine-containing polymer;

Preparing a core-shell structure polymer: The emulsion of the fluorine-containing polymer and at least two monomers represented by the following formula V are polymerized under the second polymerization condition to prepare a non-fluorine polymer, and the non-fluorine polymer is polymerized as a core-shell structure The shell part of the object at least partially covers the surface of the core part;

Wherein, R ₁ and R ₂ are each independently selected from hydrogen, fluorine, chlorine or C _1-3 alkyl substituted by at least one fluoro group;

R ₈ and R ₉ are each independently selected from hydrogen, amide group, cyano group, substituted or unsubstituted phenyl group, or -CO ₂ R ₁₀ ; R ₁₀ is selected from substituted or unsubstituted C _1-5 alkyl group.

The polymerization conditions in this preparation method are safe and controllable, which is beneficial to the continuous production of the core-shell structure polymer. The core-shell structure polymer can improve the flexibility of the binder, improve the flexibility of the pole piece and the safety performance of the battery; at the same time, it can also ensure the adhesive force of the pole piece, thereby ensuring the performance and service life of the battery.

At the same time, the core-shell structure polymer prepared by this method has good affinity and/or adsorption properties for the cathode active material, which can help the cathode active material disperse in the slurry; and can also reduce the direct contact between the cathode active material and the electrolyte. contact, thereby improving the long-term cycle performance of the battery.

In any embodiment, the preparation of the non-fluoropolymer under the second polymerization conditions includes the following steps:

Under an inert gas atmosphere, the emulsion of the fluorine-containing polymer, at least two monomers represented by formula V and the second initiator are swollen in the second solvent, and polymerization ligands and catalysts are added to perform the polymerization reaction.

In an inert gas atmosphere, normal pressure, and 20°C to 30°C, the dispersed fluoropolymer emulsion, at least two monomers represented by formula V and the second initiator are swollen in the second solvent for 0.5 hours to 2 After an hour, the polymerization ligand and catalyst are added, and the polymerization reaction is carried out for 1 to 5 hours.

The preparation method of the polymer shell has low raw material cost and mild reaction conditions, and can obtain a core-shell structure polymer with a specific and stable structure.

In any embodiment, preparing the fluoropolymer under first polymerization conditions includes the steps of:

Polymerize at least one monomer represented by Formula I in an inert gas atmosphere, normal pressure, and a reaction temperature of 60°C to 70°C for 4 to 8 hours, then stop the reaction to obtain a fluoropolymer.

The preparation method of the polymer core has low raw material costs, relatively small environmental hazards to the reagents, and mild reaction conditions, which is conducive to the expanded production of the core.

A third aspect of the application also provides a cathode slurry, including a cathode active material, a conductive agent, a binder and the core-shell structure polymer described in the first aspect of the application.

The positive electrode slurry has good bonding performance, dispersibility and processability, which is beneficial to the processing of the electrode piece.

In any embodiment, the positive active material is a lithium-containing transition metal oxide with a carbon coating layer on the surface. The lithium-containing transition metal oxide can be selected from lithium iron phosphate and lithium nickel cobalt manganese oxide. one or more of them.

The carbon coating layer on the surface of the cathode active material can form a physical barrier to prevent or reduce the chemical erosion of the cathode active material by the electrolyte, thereby reducing the dissolution of transition metals; and it can also promote electronic and/or ion conductivity and improve conductive performance.

In any embodiment, the graphitization degree of the carbon coating layer is 0.2% to 0.35%, optionally 0.2% to 0.3%.

Controlling the graphitization degree of the carbon coating layer of the cathode active material within an appropriate range can make the cathode active material have appropriate conductivity, corrosion resistance and machining performance, and help improve the processing performance of the slurry and the performance of the pole piece. Conductive properties and long-term cycle performance of secondary batteries.

In any embodiment, in the cathode slurry, the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is 1% to 3%, optionally 1.4 %~2.4%.

The mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is within a suitable range, which helps to balance the bonding performance of the slurry and the flexibility of the pole piece.

In any embodiment, in the positive electrode slurry, the mass ratio of the core-shell structure polymer and the binder is 0.05-5, optionally 0.5-2.

The mass ratio of the core-shell structure polymer and the binder within an appropriate range helps to balance the dispersion of the cathode slurry and the flexibility of the pole piece, reduces the use of other additives in the slurry, and helps Improve the loading capacity of the positive active material of the pole piece and the energy density of the battery.

In any embodiment, when the solid content of the cathode slurry is 58%, the viscosity of the cathode slurry is 5000-50000 mPa·s, optionally 5000-32000 mPa·s, and the viscosity of the cathode slurry is The optional solvent used is N-methylpyrrolidone.

The viscosity of the positive electrode slurry within a suitable range helps to improve the processability of the pole piece and the bonding performance of the pole piece film layer.

In any embodiment, the binder is polyvinylidene fluoride or a modified polymer thereof, and the weight average molecular weight of the binder is 700,000 to 1.1 million.

The adhesive has good compatibility with the core-shell structure polymer provided in this application, and can maintain good bonding performance while improving flexibility.

A fourth aspect of the application also provides an application of the core-shell structure polymer described in the first aspect of the application or the core-shell structure polymer prepared by the method described in the second aspect of the application in secondary batteries.

The core-shell structure polymer can improve the dispersion, stability and processability of the cathode slurry, improve the flexibility of the pole piece, and improve the processing performance and battery cycle performance of the pole piece.

A fifth aspect of the present application provides a secondary battery, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a battery disposed on at least one surface of the positive electrode current collector. The positive electrode film layer is prepared from the positive electrode slurry described in the third aspect of the present application; optionally, the secondary battery is a lithium ion battery.

In any embodiment, the bonding force per unit length between the positive electrode film layer and the positive electrode current collector is 10 N/m to 35 N/m. The positive electrode film layer of the electrode piece has high bonding strength with the positive electrode current collector. During use, the positive electrode film layer is not easily detached from the positive electrode current collector, which helps to improve the cycle performance and safety of the battery.

In any embodiment, the membrane resistance of the positive electrode piece is 0.4Ω˜1Ω. The electrode piece has low diaphragm resistance, indicating that the materials in the positive electrode film layer are evenly dispersed, and the positive electrode film layer has good electron transmission efficiency, which is conducive to the performance of the battery.

In any embodiment, after the positive electrode piece undergoes no less than 2.3 bending tests, the positive electrode piece appears to be light-transmissive. The pole piece can pass no less than 2.3 bending tests, indicating that the pole piece has good flexibility and is not prone to cracking during the production process or brittle fracture during use, which helps improve the battery's performance. Yield rate and improve battery safety performance.

A sixth aspect of the present application provides a battery module including the secondary battery of the fifth aspect of the present application.

A seventh aspect of the present application provides a battery pack, including the battery module of the sixth aspect of the present application.

An eighth aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the fifth aspect of the present application, the battery module of the sixth aspect of the present application, or the battery pack of the seventh aspect of the present application. kind.

Description of drawings

Figure 1 is a schematic diagram of the core-shell structure polymer of the present application;

Figure 2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

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

Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application;

Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application;

Figure 6 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 5;

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

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover; 6 core-shell structure polymer; 61 core; 62 shell.

Detailed ways

Hereinafter, embodiments specifically disclosing the positive electrode active material and its manufacturing method, the positive electrode tab, the secondary battery, the battery module, the battery pack, and the electrical device of the present application will be described in detail with appropriate reference to the drawings. However, unnecessary detailed explanations may be omitted. For example, detailed descriptions of well-known matters may be omitted, or descriptions of substantially the same structure may be repeated. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless stated otherwise, the numerical range "a-b" represents an abbreviated 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 in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) 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 also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.

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

In this application, the term "or" is inclusive unless otherwise specified. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).

Cathode active materials, such as lithium iron phosphate, often have characteristics such as large specific surface area and small particle size. After coating treatment, they have poor compatibility with the binder, causing the prepared slurry to agglomerate and block the filter. Using this The surface of the pole piece prepared from the slurry is prone to defects such as cracking, peeling, particle scratches, pinholes, etc., and due to the uneven distribution of the positive active material in the pole piece, the film layer resistance is high and the cycle performance of the battery is reduced. At the same time, when the battery is processed by hot pressing and shaping, the electrode film layer at the corner of the innermost cathode is easily broken due to insufficient tensile strength, causing the electrode piece to transmit light, thereby causing the electrode piece to be brittle (or brittle). problem and reduce the safety of the battery. At the same time, during the battery cycle, the brittleness of the pole piece will also cause the positive active material to come into direct contact with the electrolyte, which will then be chemically corroded and reduce the cycle performance of the battery.

[Core-shell structure polymer]

Based on this, this application proposes a core-shell structure polymer, including: a core part, which is a fluoropolymer containing structural units derived from the monomer shown in Formula I; and a shell part, which The shell part is a non-fluorine polymer containing structural units derived from monomers represented by Formula II and Formula III, and the shell part at least partially covers the surface of the core part,

In this context, the term "polymer" includes on the one hand an assembly of macromolecules that are chemically homogeneous but differ in degree of polymerization, molar mass and chain length, prepared by polymerization reactions. The term on the other hand also includes derivatives of aggregates of macromolecules formed by polymerization reactions which are obtainable by reaction, for example addition or substitution, of functional groups in said macromolecules and which may be chemically homogeneous or chemically non-uniform compounds.

As used herein, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is replaced by a substituent of another chemical moiety, where each substituent is independently selected from: hydroxyl, mercapto, amino, cyano , nitro group, aldehyde group, halogen atom, alkenyl group, alkynyl group, aryl group, heteroaryl group, C _1-3 alkyl group or C _1-3 alkoxy group.

As used herein, the term "C _1-5 alkyl" refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, with no unsaturated bonds present in the group, and having from one to five carbon atoms, And attached to the rest of the molecule by a single bond, exemplary C _1-5 alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, n-pentyl.

As used herein, the term "C _1-3 alkyl" refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, with no unsaturated bonds present in the group, and having from one to three carbon atoms, And attached to the rest of the molecule by a single bond, exemplary C _1-3 alkyl groups such as methyl, ethyl, propyl, isopropyl.

In this article, the term "C _1-3 alkoxy" refers to a group formed by connecting a saturated alkyl group with one to three carbon atoms to an oxygen atom. Exemplary C _1-3 alkoxy groups such as methoxy , ethoxy.

In this article, hydrogen, fluorine, chlorine, amide group, cyano group, phenyl, -CO ₂ R ₅ , etc. are technical terms in the art and have meanings commonly understood in the art. For example, "cyano" refers to -CN group, "amide group" refers to the -CONH ₂ group, "-CO ₂ R ₅ " refers to the ester group with R ₅ group, R ₅ is selected from substituted or unsubstituted C _1-5 alkane base.

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

In this article, the term "core-shell polymer" can have the same meaning as "core-shell polymer" and "core-shell polymer", which means that the core and the shell are respectively enriched by two or more polymers. A layer-composite particulate polymer with a core covered by a shell. The force between the core and the shell is not limited to chemical cross-linking, but may also include physical deposition, hydrogen bonding force, etc. The schematic diagram of the core-shell structure polymer 6 is shown in FIG. 1 . The core portion 61 is inside the core-shell structure polymer 6 , and the outer periphery of the core portion 61 is wrapped with a shell portion 62 .

In some embodiments, the fluoro-substituted C _1-3 alkyl group is selected from -CF ₃ , -CHF ₂ , CH ₃ CF ₃ -, CH ₃ CHF ₂ -, or C ₂ F ₆ -. In some embodiments, the fluoro-substituted C _1-3 alkyl is -CF ₃ (or trifluoromethyl).

In some embodiments, R ₁ and R ₂ are each independently selected from hydrogen, fluorine, or at least one fluoro-substituted C _1-3 alkyl group.

In some embodiments, in the core-shell structure polymer, the weight average molecular weight of the fluoropolymer in the core is 20,000 to 200,000, optionally 20,000 to 150,000. The weight average molecular weight of the core polymer can be measured using measurement methods commonly used in this field, or using methods such as those in the examples.

In the core-shell structure polymer, the molecular weight of the non-fluorine polymer in the shell part can be estimated based on the degree of polymerization or the molecular weight can be theoretically calculated. The degree of polymerization is a measure of the size of the polymer molecules. Based on the number of repeating units, that is, the average number of repeating units contained in the polymer macromolecular chain,

Degree of polymerization = average molecular weight of polymer ÷ molecular weight of polymerized units

In the core-shell structure polymer, the degree of polymerization of the non-fluorine polymer in the shell can also be confirmed/estimated based on the weight average molecular weight.

In addition, the core-shell structure polymer helps to improve the dispersion of the cathode slurry, which can reduce the resistance of the electrode sheet film and improve the battery cycle performance. When the core-shell structure polymer is used in combination with a binder, it can simultaneously improve the flexibility of the pole piece and the dispersion of the slurry, and make the pole piece have good bonding properties, which helps to reduce the loss of other additives in the slurry. Used to improve battery safety and battery cycle performance, and help increase battery energy density.

The term "auxiliary agent" refers to auxiliary chemicals added to improve the production process of the pole piece and improve the quality of the pole piece. This article refers to other substances in the cathode slurry except the cathode active material, conductive agent and solvent.

In some embodiments, the mass content of the core part is 5% to 9%, and the mass content of the shell part is 91% to 95%, based on the total mass of the core-shell structure polymer.

In some embodiments, the mass content of the core part is 5% to 8.5%, 5% to 8%, 5% to 7.5%, 5.5% to 8.5% or 6% to 8.5%, based on the core-shell structure Total mass of polymer.

In some embodiments, the mass content of the shell part is 90% to 95%, 90% to 94.5%, 90% to 94%, 90.5% to 95% or 91% to 94%, based on the core-shell structure Total mass of polymer.

In some embodiments, the molar content of the structural units derived from the monomer represented by Formula III is 30% to 50%, based on the total molar amount of the non-fluoropolymer.

In some embodiments, the molar content of the structural units derived from the monomer represented by Formula III is 30% to 45%, 30% to 40%, 35% to 50% or 40% to 50%, based on the Total moles of non-fluoropolymers.

In some embodiments, the molar content of the structural units derived from the monomer represented by Formula II is 20% to 50%, based on the total molar amount of the non-fluoropolymer.

In some embodiments, the molar content of the structural units derived from the monomer represented by Formula II is 20% to 50%, 30% to 50%, or 20% to 30%, based on the total amount of the non-fluoropolymer. Molometer.

The core-shell structure polymer within this content range can ensure that the pole piece has good flexibility, thereby ensuring that the battery has excellent electrical performance and cycle performance while improving safety performance.

In some embodiments, the non-fluoropolymer further includes structural units derived from monomers represented by Formula IV,

In the non-fluorine polymer, the polar group contained in the monomer represented by formula IV can form better adsorption performance or affinity with the positive active material, which helps to improve the agglomeration of the positive active material, thereby improving the slurry stability, improve the processing performance of the pole piece and improve the film resistance of the pole piece.

In some embodiments, the molar content of the structural units derived from the monomer represented by Formula IV is 40% to 50%, based on the total molar amount of the non-fluoropolymer.

In some embodiments, the molar content of the structural units derived from the monomer represented by Formula IV is 40% to 47%, 40% to 45%, 43% to 50% or 45% to 50%, based on the Total moles of non-fluoropolymers.

The mass content of the structural units derived from the monomer shown in Formula IV within a suitable range can have sufficient adsorption performance or affinity for the positive electrode active material, effectively improve the dispersion of the slurry, thereby reducing the electrode sheet film resistance and improving the battery Cycle performance.

In some embodiments, the fluoropolymer is polyvinylidene fluoride or modified polymers thereof. In some embodiments, the fluoropolymer is polyvinylidene fluoride.

The core has stable chemical properties, excellent electrical properties, and good mechanical properties, which is helpful for preparing pole pieces with good electrical properties and mechanical properties.

The non-fluorine polymer is one or a combination of a copolymer of styrene and tert-butyl acrylate, a copolymer of acrylonitrile, styrene and tert-butyl acrylate, and a copolymer of acrylamide, styrene and methyl acrylate. .

In some embodiments, the non-fluoropolymer is a copolymer of styrene and t-butyl acrylate. In some embodiments, the non-fluoropolymer is a copolymer of acrylonitrile, styrene, and t-butyl acrylate. In some embodiments, the non-fluoropolymer is a copolymer of acrylamide, styrene, and methyl acrylate. In some embodiments, the non-fluoropolymer is polystyrene-t-butyl acrylate. In some embodiments, the non-fluoropolymer is polyacrylonitrile-styrene-t-butyl acrylate. In some embodiments, the non-fluoropolymer is polyacrylamide-styrene-t-butyl acrylate.

Without being bound by any theory, the structural units derived from the monomer shown in Formula II in the non-fluorine polymer have ester groups that can form soft segments that have large free volumes and can absorb external energy through segment motion. It has the effect of energy absorption and toughening; at the same time, its strong polarity can generate large intermolecular forces, making the core-shell structure polymer have excellent softening effect and bonding performance. The structural unit derived from the monomer represented by formula III in the non-fluorine polymer has a phenyl group, and the free volume of this chain segment is relatively limited, so that the core-shell structure polymer has good mechanical properties and processing strength. In addition, the polar functional groups of non-fluorine polymers also have good adsorption properties and/or affinity, and can be stably attached to the surface of cathode active materials including lithium iron phosphate and lithium nickel cobalt manganese oxide, thereby improving the dispersion of the slurry. and the film resistance of the electrode plate, thereby improving the cycle performance of the battery; it can also reduce the direct contact between the positive active material and the electrolyte, thereby improving the long-term cycle performance of the battery.

Without being bound by any theory, the non-fluoropolymer coats or partially coats the surface of the fluoropolymer, increasing the dispersion of the fluoropolymer in the non-fluoropolymer and interacting with the fluoropolymer. Forming a strong connection makes the structure of the core part and the shell part more stable, allowing the core-shell structure polymer to exert a long-lasting toughening effect. The force between the core and the shell of the core-shell structure polymer is not limited to chemical cross-linking, but may also include physical deposition, hydrogen bonding force, etc.

In some embodiments, when the core-shell structure polymer is dissolved in N-methylpyrrolidone to prepare a glue solution with a mass percentage of 7%, the viscosity of the glue solution is 50 to 180 mPa·s.

In some embodiments, when the mass percentage of the core-shell structure polymer in the glue is 7%, the viscosity of the glue prepared by dissolving the core-shell polymer in N-methylpyrrolidone 50~160mPa·s, 50~140mPa·s, 50~120mPa·s, 50~100mPa·s, 50~80mPa·s, 60~180mPa·s, 70~180mPa·s, 80~180mPa·s, 90 ~180mPa·s, 100~180mPa·s, 120~180mPa·s or 140~180mPa·s.

When the viscosity of the core-shell structure polymer is higher than 180 mPa·s (mass content is 7%), the chain segment movement of the core-shell structure polymer is restricted, which is not conducive to improving the flexibility of the pole piece; when the viscosity of the core-shell structure polymer When it is lower than 50 mPa·s (mass content is 7%), the bonding performance of the slurry will be affected, and the defect of pole piece defilming will easily occur. Controlling the viscosity of the core-shell structure polymer within a suitable range can take into account the flexibility of the pole piece and the adhesiveness of the binder, improve the uniformity and processability of the pole piece coating, maintain good flexibility while maintaining appropriate The adhesive force helps to reduce the resistance of the film layer and improve the cycle performance, and improves the safety of the long-term cycle of the battery.

The term "film layer" refers to the coating formed after the positive electrode or negative electrode slurry is coated and dried.

In some embodiments, the core-shell structure polymer has a median particle size Dv50 of 2 to 10 μm.

In some embodiments, the core-shell structure polymer has a median particle size Dv50 of 2 to 9 um, 2 to 7 um, 2 to 5 um, 3 to 7 um or 5 to 7 um.

In this article, the term "median particle size Dv50" refers to the particle size corresponding to when the cumulative particle size distribution percentage of the measured sample reaches 50%. Its physical meaning is that 50% of the particles have a particle size smaller (or larger) than it.

This application also provides a method for preparing a core-shell structure polymer, including:

Among them, R ₁ and R ₂ are each independently selected from hydrogen, fluorine, chlorine or at least one fluorine-substituted C _1-3 alkyl group; R ₈ and R ₉ are each independently selected from hydrogen, amide group, cyano group, substituted Or unsubstituted phenyl, or -CO ₂ R ₁₀ ; R ₁₀ is selected from substituted or unsubstituted C _1-5 alkyl.

In some embodiments, the C _1-5 alkyl group is selected from methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, or n-pentyl.

In some embodiments, each of R ₁ , R ₂ , and R ₉ is independently selected from hydrogen.

In some embodiments, R ₈ is selected from cyano, phenyl or -CO ₂ R ₁₀ ; R ₁₀ is selected from substituted or unsubstituted C _1-5 alkyl.

In some embodiments, the R ₈ is selected from cyano.

In some embodiments, the R ₈ is selected from phenyl.

In some embodiments, the R ₈ is selected from -CO ₂ R ₁₀ ; R ₁₀ is selected from substituted or unsubstituted C _1-5 alkyl. In some embodiments, R ₈ is selected from -CO ₂ R ₁₀ ; R ₁₀ is selected from n-butyl.

In some embodiments, the at least two monomers represented by the following formula V respectively include phenyl and -CO ₂ R ₁₀ ; R ₁₀ is selected from substituted or unsubstituted C _1-5 alkyl.

In some embodiments, the at least two monomers represented by the following formula V respectively include phenyl, -CO ₂ R ₁₀ and cyano; R ₁₀ is selected from substituted or unsubstituted C _1-5 alkyl.

In some embodiments, the at least two monomers represented by Formula V below include phenyl, -CO ₂ R ₁₀ and amide groups respectively; R ₁₀ is selected from substituted or unsubstituted C _1-5 alkyl groups.

In some embodiments, the preparation of the non-fluoropolymer under the second polymerization condition includes the following steps: under an inert gas atmosphere, an emulsion of the fluoropolymer, at least two monomers represented by Formula V and a second initiator Swell in the second solvent, add polymerization ligands and catalysts, and perform polymerization. The prepared non-fluoropolymer at least partially covers the surface of the fluoropolymer. The fluoropolymer serves as the core part and the non-fluoropolymer serves as the shell part. The prepared product is a core-shell structure polymer.

In some embodiments, the preparation method of the core-shell structure polymer includes the following steps: under an inert gas atmosphere, an emulsion of fluoropolymer, at least two monomers represented by formula V and a second initiator are added in a second Swell in the solvent, add polymerization ligands and catalysts, carry out polymerization, stop the reaction, collect the solid phase, and obtain a core-shell structure polymer.

The term "inert gas" refers to a gas that does not participate in the polymerization reaction. Exemplary inert gases include any or a combination of argon, helium, and nitrogen.

The term "initiator" refers to a substance that initiates the polymerization of monomers during a polymerization reaction.

The second initiator is selected from one or more of 2-bromopropionic acid methyl ester, 2-ethyl peroxydicarbonate and peroxytert-amyl pivalate.

In some embodiments, the second initiator is methyl 2-bromopropionate.

The second solvent is selected from deionized water, benzene or dimethylformamide. In some embodiments, the second solvent is deionized water, which is beneficial to reducing harm to the environment.

The term "swelling" refers to the phenomenon of volume expansion of polymers in solvents.

The term "polymerization ligand" refers to a compound that can form coordination with polymerized monomers and/or transition metals in a coordination polymerization reaction initiated by a complex catalyst composed of two or more components.

The polymerization reaction ligand is selected from one of N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine and pentamethyldiethylenetriamine.

In some embodiments, the polymerization ligand is pentamethyldiethylenetriamine.

The term "catalyst" refers to a substance that can change the chemical reaction rate (increase or decrease) of reactants in a chemical reaction without changing the chemical equilibrium, and its own quality and chemical properties do not change before and after the chemical reaction. The catalyst is selected from copper, titanium chloride or vanadium tetrachloride.

In some embodiments, the catalyst is copper.

At the same time, the core-shell structure polymer prepared by this method has good affinity and/or adsorption properties for the positive electrode active material, and can help the positive electrode active material to be dispersed in the slurry, thereby improving the film resistance and electrical properties of the electrode piece; it also It can reduce the direct contact between the positive active material and the electrolyte and improve the long-term cycle performance of the battery.

In some embodiments, the preparation of the non-fluoropolymer under the second polymerization conditions includes the following steps:

The term "normal pressure" refers to a standard atmospheric pressure, which is 101KPa.

In this article, dispersion processing methods include but are not limited to ultrasonic and stirring.

In some embodiments, the reaction temperature is 22°C to 30°C, 22°C to 28°C, or 23°C to 26°C, such as 25°C.

In some embodiments, the polymerization reaction time is 1 hour to 4 hours, 1 hour to 3 hours, 1 hour to 2 hours, 2 hours to 5 hours, 3 hours to 5 hours, or 3 hours to 4 hours.

The preparation method of the core-shell structure polymer has low raw material cost and mild reaction conditions; the shell part and the core part of the polymer have good binding force and stability, and the core-shell structure polymerization with a stable and specific structure can be obtained things.

In some embodiments, preparing the fluoropolymer under first polymerization conditions includes the steps of:

Polymerize at least one monomer represented by formula I in an inert gas atmosphere, normal pressure, and a reaction temperature of 60°C to 70°C for 4 to 8 hours, then stop the reaction to obtain an emulsion of fluoropolymer.

In the preparation method of the core part, the reaction temperature is 60°C to 68°C, 60°C to 66°C, 60°C to 64°C, 62°C to 70°C, 64°C to 70°C or 66°C to 70°C.

In the preparation method of the core part, the reaction time is 4 hours to 7 hours, 4 hours to 6 hours, 4 hours to 5 hours, 6 hours to 8 hours or 7 hours to 8 hours.

In some embodiments, preparing the core fluoropolymer under first polymerization conditions includes the steps of:

Add the first solvent and dispersion aid to the container, and fill the container with an inert gas;

Add the first initiator and pH adjuster to the container, then add the monomer represented by Formula I, stir for 30 to 60 minutes, and then raise the temperature to 60°C to 70°C to perform the polymerization reaction.

In some embodiments, the first initiator is selected from one or more of 2-ethyl peroxydicarbonate and peroxytert-amyl pivalate. In some embodiments, the first initiator is 2-ethylperoxydicarbonate.

The term "pH adjuster" refers to a substance that changes the pH of a solution or dispersion medium, including increasing the acidity or increasing the alkalinity. Exemplary pH adjusting agents include sodium bicarbonate, sodium carbonate and sodium hydroxide.

The term "dispersion aid" refers to substances that can promote the uniform dispersion of monomers in the medium during synthesis reactions. Exemplary dispersing aids include carboxyethyl cellulose ether.

In some embodiments, the first solvent is deionized water, which is beneficial to reducing harm to the environment.

In some embodiments, the pH is adjusted to 6.5, 6.8 or 7.

In some embodiments, the stirring time is 30 minutes to 55 minutes, 30 minutes to 50 minutes, 30 minutes to 45 minutes, 35 minutes to 60 minutes, 40 minutes to 60 minutes or 45 minutes to 60 minutes.

The preparation method of the core part has low raw material cost, controllable environmental hazards, and mild reaction conditions, which is beneficial to the expanded production of the core part.

In the core-shell structure polymer prepared by the method, the weight average molecular weight of the fluoropolymer in the core is 20,000 to 150,000.

Through step-by-step preparation, a core-shell polymer with a stable core-shell structure can be obtained, and the method has high repeatability.

[Cathode slurry]

This application also provides a positive electrode slurry, which includes a positive electrode active material, a conductive agent, a binder, and the core-shell structure polymer mentioned above in this application or the core-shell structure polymer prepared by the above method.

In some embodiments, the positive active material is a lithium-containing transition metal oxide with a carbon coating layer on the surface. The lithium-containing transition metal oxide can be selected from lithium iron phosphate and lithium nickel cobalt manganese oxide. of one or more.

The carbon coating layer can be coated with an organic carbon source. Exemplary organic carbon sources include glucose, tannic acid, polyvinylpyrrolidone, etc.

In some embodiments, the graphitization degree of the coating layer is 0.2% to 0.35%, optionally 0.2% to 0.3%.

In some embodiments, the graphitization degree of the coating layer is 0.2% to 0.3%, 0.2% to 0.25%, 0.25% to 0.35%, or 0.3% to 0.35%. In some embodiments, the coating layer has a degree of graphitization of 0.3%.

When the graphitization degree of the carbon coating layer of the positive active material is higher than 0.35%, the compatibility between the positive active material and the binder is further reduced, resulting in poor dispersion of the slurry; and the conductive properties of the positive active material will also be reduced. , thereby reducing the electrical performance of the battery. When the graphitization degree of the carbon coating layer of the cathode active material is less than 0.2%, the coating layer of the cathode active material is not enough to form a physical barrier and cannot prevent or mitigate the chemical erosion of the cathode active material by the electrolyte, resulting in the dissolution of the transition metal and the cathode Active material structure collapses. Controlling the graphitization degree of the carbon coating layer of the cathode active material within an appropriate range can make the cathode active material have appropriate conductivity, corrosion resistance and machining performance, and help improve the processing performance of the slurry and the performance of the pole piece. Conductive properties and long-term cycle performance of secondary batteries.

In some embodiments, the thickness of the coating layer of the positive active material does not exceed 100 nm.

In some embodiments, in the cathode slurry, the mass percentage of the composition consisting of the core-shell structure polymer and the binder and the cathode active material is 1% to 3%.

In some embodiments, in the cathode slurry, the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is 0.5% to 3%, 0.8% to 3% , 1% to 3%, 1.2% to 3%, 1.5% to 3%, 2% to 3%, 0.5% to 2.8%, 0.5% to 2.5%, 0.5% to 2.4%, 0.5% to 2% or 0.5 %~1.4%.

When the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is higher than 3%, the binding performance of the slurry is too high, resulting in reduced dispersion and processability of the slurry. ; Moreover, excessive dosage will also lead to increased brittleness of the pole piece. When the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is less than 0.5%, the bonding performance of the slurry is significantly reduced, resulting in a decrease in the bonding performance of the slurry. The adhesion of the prepared pole pieces is insufficient. It is easy to produce peeling defects. As the cycle proceeds, the electrolyte will decompose to produce hydrofluoric acid. Hydrofluoric acid will corrode the aluminum foil, causing great safety hazards. The mass percentage of the composition composed of the core-shell structure polymer and the binder and the positive electrode active material is within a suitable range, which helps to take into account the flexibility, dispersion and bonding properties of the slurry, so that the electrode piece has Good flexibility, adhesion and processability, thereby improving the electrical properties of the pole piece.

In some embodiments, in the cathode slurry, the mass ratio of the core-shell structure polymer and the binder is 0.05 to 5:1.

In some embodiments, in the cathode slurry, the mass ratio of the core-shell structure polymer and the binder is 0.1~5:1, 0.5~5:1, 0.5~2:1, 1~ 4:1, 1～3:1 or 1～2:1.

When the mass ratio of the core-shell structure polymer and the binder is higher than 5:1, the increase of the core-shell structure polymer in the slurry significantly improves the flexibility of the binder and the dispersion of the slurry, but This leads to a decrease in the bonding performance of the slurry, which is not conducive to the preparation of safe and stable pole pieces. When the mass ratio of the core-shell structure polymer and the binder is less than 0.05:1, the content of the soft segments in the core-shell structure polymer is insufficient, making it difficult to increase the plastic strain stress of the film layer; and, the core-shell structure polymer The adsorption capacity of the structural polymer to the cathode active material is limited, and it is unable to improve the dispersion of the slurry and effectively wrap/coat the cathode active material, resulting in a reduction in the flexibility and cycle performance of the pole piece, which is not conducive to improving the battery's performance. electrical properties. The mass ratio of the core-shell structure polymer and the binder within a suitable range helps to balance the flexibility of the pole piece and the dispersion of the cathode slurry, improve the processability of the pole piece, and reduce the film layer of the pole piece resistance and improve battery cycle performance.

In addition, the composition of the core-shell structure polymer and the binder within the above range also helps to reduce the use of other additives in the slurry, and helps to increase the loading capacity of the positive active material of the electrode sheet and the energy density of the battery.

In some embodiments, when the solid content of the cathode slurry is 58%, the viscosity of the cathode slurry is 5,000 to 50,000 mPa·s.

In some embodiments, when the solid content of the positive electrode slurry is 58%, the viscosity of the positive electrode slurry is 5000~32000mPa·s, 8000~48000mPa·s, 10000~48000mPa·s, 12000~48000mPa·s , 13000～48000mPa·s, 15000～48000mPa·s, 16000～48000mPa·s, 18000～48000mPa·s, 20000～48000mPa·s, 25000～48000mPa·s, 30000～48000mPa·s, 35000～4800 0mPa·s, 40000 ~48000mPa·s or 45000～48000mPa·s.

In some embodiments, the solvent used in the cathode slurry is N-methylpyrrolidone.

When the viscosity of the cathode slurry is higher than 50,000 mPa·s, the dispersion and stability of the slurry are poor, which in turn leads to an increase in film layer resistance and a decrease in battery cycle performance. When the viscosity of the positive electrode slurry is lower than 5000 mPa·s, the viscosity of the slurry is too low, resulting in insufficient bonding force of the produced electrode piece, causing potential safety hazards for the battery. The viscosity of the positive electrode slurry within a suitable range helps to improve the processing performance of the pole piece and the bonding performance of the pole piece film layer.

In some embodiments, the binder is polyvinylidene fluoride or a modified polymer thereof, and the weight average molecular weight of the binder is 700,000 to 1.1 million.

In some embodiments, the binder is polyvinylidene fluoride.

In some embodiments, the weight average molecular weight of the binder is 700,000-1,000,000, 700,000-900,000, 800,000-1.1 million, 900,000-1.1 million or 1 million-1.1 million. In some embodiments, the binder has a weight average molecular weight of 700,000.

This application also provides the application of the above-mentioned core-shell structure polymer or the core-shell structure polymer prepared by the above-mentioned method in secondary batteries.

In some embodiments, the core-shell structure polymer or the core-shell structure polymer prepared by the above method is used to improve the dispersion of battery slurry.

In some embodiments, the core-shell structure polymer or the core-shell structure polymer prepared by the above method is used to improve the flexibility of the battery pole piece.

In the preparation of the slurry, if a variety of additives with different functions are added to improve the dispersion of the slurry and the flexibility of the pole piece, the additive content in the pole piece will be too high, resulting in a negative active material loading and Reduction in battery energy density. The core-shell structure polymer described in this application has the effect of improving the dispersion of the cathode slurry and the flexibility of the pole piece while taking into account the bonding performance. It helps to reduce the amount of additives in the slurry and improves the electrode performance. The processability and cycle performance of the sheet can be improved, as well as helping to improve the energy density of the battery.

In addition, the secondary battery, battery module, battery pack and electric device of the present application will be described below with appropriate reference to the drawings.

In one embodiment of the present application, a secondary battery is provided, and the secondary battery is a lithium-ion battery.

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

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

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the cathode active material may be a cathode active material known in the art for batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer optionally further 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 can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

[Negative pole piece]

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

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

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

In some embodiments, the negative active material may be a negative active material known in the art for batteries. As an example, the negative 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 selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.

In some embodiments, the negative electrode film layer optionally further includes a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

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

In some embodiments, the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.

[electrolyte]

The electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.

In some embodiments, the solvent may be selected from the group consisting 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 At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

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

[Isolation film]

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece, and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

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

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, FIG. 2 shows a square-structured secondary battery 5 as an example.

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 side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

Figure 4 is a battery module 4 as an example. Referring to FIG. 4 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

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

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

Figures 5 and 6 show the battery pack 1 as an example. Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

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

As the power-consuming device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

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, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

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

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Example 1

1) Preparation of core-shell structure polymer

Add 0.4kg of deionized water and 0.2g of carboxyethyl cellulose ether to a 1L four-necked flask, add nitrogen gas to remove dissolved oxygen in the solution, and then add 0.9g of 2-ethylperoxydicarbonate and 0.1 g of sodium bicarbonate, and filled with 0.1Kg of vinylidene fluoride, mixed and stirred for 30 minutes, heated to 64°C, and polymerized for 6 hours to obtain a PVDF emulsion with a final solid content of 30%.

Disperse 1.7g of the above PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water, sonicate for 40 minutes, stir at 150 rpm at 25°C, and pass in nitrogen to eliminate oxygen. Add 2.55g of purified styrene (St), 2.1g of tert-butyl acrylate (tBA), 2.2g of acrylonitrile (molar ratio 3:2:5), and 2% of the total monomer mass of the initiator 2-bromopropyl Methyl acid ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 2 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.

2) Preparation of positive electrode pieces

The composition consisting of the binder and the core-shell structure polymer, the conductive agent carbon black, and the carbon-coated lithium iron phosphate LFP are added according to the weight ratio of 2:4:100, and N-methylpyrrolidone is added to prepare a solid content of 58 % of the cathode slurry. Among them, the mass content of the carbon coating layer of lithium iron phosphate is 1.2%, and the graphitization degree G is 0.3%. The binder is PVDF (purchased from Arkema France Co., Ltd.) with a weight average molecular weight of 700,000. The mass ratio of the core-shell structure polymer to the binder is 0.5:1. The specific parameters are shown in Table 1. The positive electrode slurry is evenly coated on both surfaces of the aluminum foil positive electrode current collector, and then dried to obtain a film layer; it is then cold pressed and cut to obtain the positive electrode sheet.

2) Preparation of negative electrode piece

Dissolve the negative active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in the solvent and deionize according to the weight ratio of 96.2:0.8:0.8:1.2 In water, mix evenly and prepare a negative electrode slurry; apply the negative electrode slurry multiple times evenly on both surfaces of the negative electrode current collector copper foil, dry, cold press, and cut to obtain negative electrode sheets.

3)Isolation film

Use polypropylene film as the isolation film.

4) Preparation of electrolyte

In an argon atmosphere glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), mix the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3/7, and add LiPF ₆ Lithium salt is dissolved in an organic solvent to form a 12.5% solution to obtain an electrolyte.

5) Preparation of secondary batteries

The positive electrode sheet, isolation film and negative electrode sheet prepared in Example 1 are stacked in order so that the isolation film is between the positive and negative electrode sheets to play an isolation role. Then, the bare battery core is obtained by winding and welding to the bare battery core. The tabs are removed, and the bare battery core is put into an aluminum case, baked at 80°C to remove water, and then electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then undergoes processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.

The preparation method of the secondary batteries of Examples 2 to 5 is similar to that of the secondary battery of Example 1, but the mass content of the fluorine-containing polymer in the core-shell structure polymer is adjusted. The different product parameters are detailed in Table 1.

The preparation method of the secondary battery of Example 6 is similar to that of the secondary battery of Example 1, but the weight average molecular weight of the core-shell structure polymer core is adjusted to 200,000. The preparation method is as follows:

Add 0.4kg of deionized water and 0.2g of carboxyethyl cellulose ether to a 1L four-necked flask, add nitrogen to remove dissolved oxygen in the solution, and add 0.6g of 2-ethylperoxydicarbonate and 0.1g of sodium bicarbonate, and filled with 0.1Kg of vinylidene fluoride, mixed and stirred for 30 minutes, raised the temperature to 58°C, and carried out polymerization reaction for 8 hours to obtain a PVDF emulsion with a final solid content of 30%.

1.7g of the above PVDF emulsion was dispersed in 35g of deionized water, ultrasonic treated for 40 minutes, stirred at 25°C at 150rpm, and nitrogen was passed through to eliminate oxygen. Add 2.55g of purified styrene (St), 2.1g of tert-butyl acrylate (tBA), 2.2g of acrylonitrile (molar ratio 3:2:5), and 2% of the total monomer mass of the initiator 2-bromopropyl Methyl acid ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 5 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.

The preparation method of the secondary battery of Example 7 is similar to that of the secondary battery of Example 1, but the weight average molecular weight of the core-shell structure polymer core is adjusted to 150,000. The preparation method is as follows:

Add 0.4kg of deionized water and 0.2g of carboxyethyl cellulose ether to a 1L four-necked flask, pass in nitrogen to remove the dissolved oxygen in the solution, and then add 0.7g of 2-ethylperoxydicarbonate and 0.1g of sodium bicarbonate, and filled with 0.1Kg of vinylidene fluoride, mixed and stirred for 30 minutes, raised the temperature to 60°C, and carried out polymerization reaction for 8 hours to obtain a PVDF emulsion with a final solid content of 30%.

Disperse 1.7g of the above-mentioned PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water, sonicate for 40 minutes, stir at 25°C and 150rpm, and pass nitrogen gas to eliminate oxygen. Add 2.55g of purified styrene (St), 2.1g of tert-butyl acrylate (tBA), 2.2g of acrylonitrile (molar ratio 3:2:5), and 2% of the total monomer mass of the initiator 2-bromopropyl Methyl acid ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 4 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.

The preparation method of the secondary battery of Example 8 is similar to that of the secondary battery of Example 1, but the weight average molecular weight of the core-shell structure polymer core is adjusted to 20,000. The preparation method is as follows:

Add 0.4kg of deionized water to a 1L four-necked flask and pass in nitrogen to remove the dissolved oxygen in the solution. Then add 0.9g of 2-ethylperoxydicarbonate and 0.1g of sodium bicarbonate, and fill in 0.1Kg of Vinylidene fluoride, mix and stir for 30 minutes, raise the temperature to 66°C, and perform polymerization reaction for 4 hours to obtain a PVDF emulsion with a final solid content of 30%.

Disperse 1.7g of the above PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water, sonicate for 40 minutes, stir at 25°C and 150rpm, and pass nitrogen gas to eliminate oxygen. Add 2.55g of purified styrene (St), 2.1g of tert-butyl acrylate (tBA), 2.2g of acrylonitrile (molar ratio 3:2:5), and 2% of the total monomer mass of the initiator 2-bromopropionic acid. Methyl ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 1 hour, the copper wire was taken out and the reaction stopped to obtain a product with PVDF as the core and acrylonitrile-styrene-tert-butyl acrylate as the shell. Core-shell polymer.

The preparation method of the secondary battery of Example 9 is similar to that of the secondary battery of Example 1, but the median particle size Dv50 of the core-shell structure polymer is adjusted to 1 μm.

The preparation method of the secondary battery of Examples 10-11 is similar to the preparation method of the secondary battery of Example 1, but the graphitization degree is adjusted. The different product parameters are detailed in Table 1.

The preparation method of the secondary battery of Example 12 is similar to the preparation method of the secondary battery of Example 1, but the positive active material is adjusted to be lithium iron phosphate without a coating layer.

The preparation method of the secondary battery of Examples 13 to 17 is similar to the preparation method of the secondary battery of Example 1, but the mass ratio of the composition composed of the binder and the core-shell structure polymer and the positive electrode active material is adjusted. Different Product parameters are detailed in Table 1.

The preparation method of the secondary battery of Examples 18 to 23 is similar to the preparation method of the secondary battery of Example 1, but the mass ratio of the core-shell structure polymer and the binder is adjusted. The different product parameters are detailed in Table 1.

The preparation method of the secondary battery of Examples 24 to 25 is similar to the preparation method of the secondary battery of Example 1, but the weight average molecular weight of the PVDF binder in the core-shell structure is adjusted to 900,000 and 1.1 million respectively. Binder PVD with weight average molecular weights of 900,000 and 1.1 million was purchased from Solvay (Shanghai) Co., Ltd., see Table 1 for details. Among them, the positive active material in Example 25 is lithium nickel cobalt manganese oxide.

The secondary battery preparation method of Example 26 is similar to the secondary battery preparation method of Example 1, but the weight average molecular weight of the core-shell polymer core is 120,000 and the type of core-shell polymer is adjusted. See Table 1 for details. ; Its preparation method is as follows:

Add 0.4kg of deionized water and 0.2g of carboxyethyl cellulose ether to a 1L four-necked flask, add nitrogen to remove dissolved oxygen in the solution, and add 0.8g of 2-ethylperoxydicarbonate and 0.1g of sodium bicarbonate, and filled with 0.1Kg of vinylidene fluoride, mixed and stirred for 30 minutes, raised the temperature to 62°C, and carried out polymerization reaction for 7 hours to obtain a PVDF emulsion with a final solid content of 30%.

Disperse 1.7g of the above PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water, sonicate for 40 minutes, stir at 25°C and 150rpm, and pass nitrogen gas to eliminate oxygen. Add 2.55g of purified styrene (St), 3.2g of tert-butyl acrylate (tBA), 2.37g of acrylamide (molar ratio 3:3:4), and 2% of the total monomer mass of the initiator 2-bromopropyl Methyl acid ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 3 hours, the copper wire was taken out and the reaction was stopped to obtain a core with PVDF as the core and acrylamide-styrene-tert-butyl acrylate as the shell. Shell structure polymer.

The preparation method of the secondary battery in Example 27 is similar to that of Example 1, but the type of core-shell structure polymer is adjusted, as shown in Table 1 for details; the preparation method of the core-shell structure polymer is as follows:

The preparation method of PVDF emulsion is the same as the preparation method of PVDF emulsion in Example 1.

Disperse 1.7g of PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water. After ultrasonic treatment for 40 minutes, stir at 25°C and 150rpm, and pass in nitrogen to eliminate oxygen. Add 2.55g of purified styrene (St) and 3.24g of tert-butyl acrylate (tBA) (molar ratio 5:5), as well as 2% of the total monomer mass of the initiator methyl 2-bromopropionate (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 5 hours, the copper wire was taken out to stop the reaction, and a core-shell structure with PVDF as the core and styrene-tert-butyl acrylate as the shell was obtained. polymer.

The preparation method of the secondary battery in Example 28 is similar to that of Example 1, but the type of core-shell structure polymer is adjusted, as shown in Table 1 for details; the preparation method of the core-shell structure polymer is as follows:

Add 0.4kg of deionized water and 0.2g of carboxyethyl cellulose ether to a 1L four-necked flask, add nitrogen gas to remove dissolved oxygen in the solution, and then add 0.9g of 2-ethylperoxydicarbonate and 0.1 g of sodium bicarbonate, and add 0.1Kg of chlorotrifluoroethylene, mix and stir for 30 minutes, raise the temperature to 64°C, and perform a polymerization reaction for 6 hours to obtain a PVDF emulsion with a final solid content of 30%.

Disperse 1.7g of the above PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water, sonicate for 40 minutes, stir at 150 rpm at 25°C, and pass nitrogen to eliminate oxygen. Add 2.55g of purified styrene (St), 2.1g of tert-butyl acrylate (tBA), 2.2g of acrylonitrile (molar ratio 3:2:5), and 2-bromopropyl initiator of 2% of the total monomer mass. Methyl acid ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 2 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.

The preparation method of the secondary battery in Example 29 is similar to that of Example 1, but the type of core-shell structure polymer is adjusted, as shown in Table 1 for details; the preparation method of the core-shell structure polymer is as follows:

Add 0.4kg of deionized water and 0.2g of carboxyethyl cellulose ether to a 1L four-necked flask, add nitrogen gas to remove dissolved oxygen in the solution, and then add 0.9g of 2-ethylperoxydicarbonate and 0.1 g of sodium bicarbonate, and add 0.1Kg of chlorotrifluoroethylene and vinylidene fluoride (the molar ratio of vinylidene fluoride to chlorotrifluoroethylene is 1:1), mix and stir for 30 minutes, and raise the temperature to 64°C , the polymerization reaction was carried out for 6 hours, and a PVDF emulsion with a final solid content of 30% was obtained.

Disperse 1.7g of the above PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water, sonicate for 40 minutes, stir at 150 rpm at 25°C, and pass nitrogen to eliminate oxygen. Add 2.55g of purified styrene (St), 2.1g of tert-butyl acrylate (tBA), 2.2g of acrylonitrile (molar ratio 3:2:5), and 2% of the total monomer mass of the initiator 2-bromopropyl Methyl acid ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 2 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.

The secondary battery preparation method of Examples 30 to 31 is similar to the secondary battery preparation method of Example 1, but the mass ratio of the core-shell structure polymer and the binder is adjusted, and the binder and core-shell structure polymer are adjusted. The mass ratio of the composition and the positive active material is 3.0:100, see Table 1 for details.

The secondary battery preparation method of Example 32 is similar to the secondary battery preparation method of Example 1, but the weight average molecular weight of the core part of the core-shell structure polymer is adjusted to 200,000, and the binder and core-shell structure polymer are adjusted. The mass ratio of the composition and the positive active material is 3.0:100, see Table 1 for details; the preparation method is as follows:

Disperse 1.7g of the above PVDF emulsion in 35g of deionized water, sonicate for 40 minutes, stir at 25°C and 150rpm, and pass nitrogen gas to eliminate oxygen. Add 2.55g of purified styrene (St), 2.1g of tert-butyl acrylate (tBA), 2.2g of acrylonitrile (molar ratio 3:2:5), and 2% of the total monomer mass of the initiator 2-bromopropyl Methyl acid ester (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes. The reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 5 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.

The secondary battery preparation method of Example 33 is similar to the secondary battery preparation method of Example 10, but in the process of preparing the core-shell structure polymer, the molar ratio of acrylonitrile, styrene, and polytert-butyl acrylate is adjusted to 4 :3:3.

In Comparative Example 1, only a PVDF binder with a weight average molecular weight of 700,000 was used to prepare a secondary battery, and other steps were the same as the preparation method of the secondary battery in Example 1.

The preparation method of the secondary battery of Comparative Example 2 is the same as that of Example 1, but the shell part is adjusted to be polytert-butyl acrylate. See Table 1 for details. The shell preparation method was similar to Example 1, except that only 2.1 g of tert-butyl acrylate was added.

The preparation method of the secondary battery of Comparative Example 3 is the same as that of Example 1, but the shell part is adjusted to be polystyrene. See Table 1 for details. The shell preparation method is similar to Example 1, except that only 2.55g of styrene is added.

Performance Testing

1. Weight average molecular weight test method

Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141) was used. Use a polystyrene solution sample with a mass fraction of 3.0% as a reference and select a matching chromatographic column (oil: Styragel HT5 DMF7.8*300mm+Styragel HT4). Use purified N-methylpyrrolidone (NMP) solvent to prepare 3.0% adhesive glue solution, and let the prepared solution stand for one day for later use. When testing, first draw in tetrahydrofuran with a syringe, rinse, and repeat several times. Then draw 5 ml of the test solution, remove the air from the syringe, and dry the needle tip. Finally, slowly inject the sample solution into the injection port. Obtain the data after the display is stable.

2. Measurement of median particle size Dv50

Referring to the GB/T 19077-2016 particle size distribution laser diffraction method, weigh 0.1g to 0.13g of the polymer sample to be tested in a 50mL beaker, add 5g of absolute ethanol, put in a stirrer of about 2.5mm, and seal it with plastic wrap. After ultrasonic treatment for 5 minutes, the samples were transferred to a magnetic stirrer and stirred at 500 rpm for more than 20 minutes. Two samples were taken from each batch of products for testing. The test was carried out using the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the UK.

3. Viscosity test

Dissolve/disperse the sample to be measured in N-methylpyrrolidone (NMP) solvent, prepare glue with a solid content of 7%, select a suitable rotor, fix the viscometer rotor, and place the glue under the viscometer rotor. The glue liquid just covers the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 61# (0-500mPa·s), 62# (500-2500mPa·s), 63# (2500-10000mPa·s) , 64# (10000-50000mPa·s), rotation speed: 12r/min, test temperature: 25℃, test time is 5min, wait for the displayed number to be stable and read the data.

4. Graphitization degree test of lithium iron phosphate

The degree of graphitization was characterized using a French HORIBA Jobin Yvon high-resolution Raman spectrometer, model LabRAM HR Evlution. After subtracting the detection background, the following Gaussian function was used for fitting. Raman spectrum test conditions: wavelength 532nm, scanning range 200-4000cm ^-1 , accumulation twice, measuring 10 points for each sample, taking the average value for fitting:

In the above formula, G is the degree of graphitization, A _i , Vi _and w _i are the peak intensity, peak position and peak width respectively.

5. Determination of positive electrode film resistance:

Cut the dried positive electrode slurry (film layer) on the left, middle and right sides of the positive electrode piece into small discs with a diameter of 3mm. Turn on the power supply of Yuaneng Technology's pole piece resistance meter, place it in the appropriate position of the "probe" of the pole piece resistance meter, click the "Start" button, and wait until the reading is stable, then read it. Each small disc is tested at two positions, and finally the average value of the six measurements is calculated, which is the resistance of the film layer of the pole piece.

6. Pole piece brittleness test

Cut the prepared positive electrode piece into a test sample with a size of 20×100mm and set it aside. Bend the pole piece in half and fix it. Use a 2kg cylindrical roller to roll it once. Check whether there is light transmission and metal leakage at the folded part of the pole piece. If there is no light transmission and metal leakage, fold the pole piece in half and fix it again. Roll once to check whether light is transmitted and metal is leaking from the folded part of the pole piece. Repeat the above steps until light is transmitted and metal is leaked from the folded part of the pole piece and record the number of light-transmitting rolling operations. Take three samples for testing and take the average.

7. Cycle capacity retention test

The method for measuring the cycle capacity retention rate of lithium iron phosphate system is as follows:

Taking Example 1 as an example, the battery capacity retention rate test process is as follows: at 25°C, charge the battery corresponding to Example 1 with a constant current of 1/3C to 3.65V, and then charge with a constant voltage of 3.65V until the current is 0.05 C, leave it for 5 minutes, and then discharge it to 2.5V at 1/3C. The resulting capacity is recorded as the initial capacity C ₀ . Repeat the above steps for the same battery and record the discharge capacity C _n of the battery after the nth cycle. Then the battery capacity retention rate after each cycle is:

Pn＝C _n /C ₀ ×100%

During this test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and the 100th cycle corresponds to n=100. The battery capacity retention rate data corresponding to Example 1 in Table 1 is the data measured after 500 cycles under the above test conditions, that is, the value of P500. The testing procedures of Comparative Example 1 and other examples are the same as above;

When the positive active material is lithium nickel cobalt manganese oxide NCM, the measurement method is as follows:

Taking Example 25 as an example, the battery DC impedance DCR test process is as follows: at 25°C, charge the battery corresponding to Example 25 with a constant current of 1/3C to 4.4V, and then charge with a constant voltage of 4.4V until the current is 0.05 C. After leaving it for 5 minutes, record the voltage V1. Then discharge at 1/3C for 30 seconds and record the voltage V2, then (V2-V1)/1/3C, we get the internal resistance DCR1 of the battery after the first cycle. Other steps are the same as above.

8. Slurry viscosity test

The viscosity of the slurry was measured using a rotational viscometer. Select the appropriate rotor, fix the viscometer rotor, and place the positive slurry under the viscometer rotor so that the slurry just submerges the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 63# (2000-10000mPa· s), 64# (10000-50000mPa·s), rotation speed: 12r/min, test temperature: 25℃, test time is 5min, wait for the displayed number to be stable and read the data.

9. Determination of adhesive force:

Referring to the national standard GBT 2790-1995 "Test Method for 180° Peel Strength of Adhesives", the bonding force testing process of the examples and comparative examples of this application is as follows:

Use a blade to cut out a pole piece sample with a width of 30mm and a length of 100-160mm, and stick the special double-sided tape on the steel plate with a width of 20mm and a length of 90-150mm. Paste the pole piece sample intercepted earlier on the double-sided tape with the test side facing down, and then roll it three times in the same direction with a pressure roller.

Insert a paper tape with the same width as the pole piece sample and a length of 250 mm under the pole piece current collector, and fix it with wrinkle glue.

Turn on the power of the Sansi tensile machine (sensitivity is 1N), the indicator light is on, adjust the limit block to the appropriate position, and fix the end of the steel plate that is not attached to the pole piece sample with the lower clamp. Fold the paper tape upward and fix it with the upper clamp. Use the "up" and "down" buttons on the manual controller attached to the tensile machine to adjust the position of the upper clamp, then test and read the value. Divide the force of the pole piece when the force is balanced by the width of the tape as the bonding force of the pole piece per unit length to characterize the strength of the bonding force between the positive electrode film layer and the current collector.

3. Analysis of test results of each embodiment and comparative example

Batteries of each embodiment and comparative example were prepared according to the above method, and the specific parameters are shown in Table 1; various performance parameters were measured, and the results are shown in Table 2 below.

Table 1

Table 2

According to the above Table 1 and Table 2, it can be seen that in Examples 1 to 33, a core-shell structure polymer and a binder are used to prepare secondary batteries. The core of the core-shell structure polymer is polyvinylidene fluoride or its modified polymer. The shell structure polymer shell part is acrylonitrile-styrene-tert-butyl acrylate polymer, acrylamide-styrene-tert-butyl acrylate polymer or styrene-tert-butyl acrylate polymer. Compared with Comparative Example 1, The bonding force of the positive electrode piece is improved; at the same time, Comparative Example 2 shows that due to polytert-butyl acrylate, the electrode piece absorbs a large amount of liquid, and the battery capacity decays extremely quickly, making the capacity retention rate of the battery after 500 cycles lower than that of the Example 1 to 33, indicating that the combination of specific types of shell polymers in core-shell structure polymers can help improve battery cycle performance; in addition, Comparative Example 3 shows that polystyrene causes poor dispersion of the cathode slurry, resulting in poor dispersion of the cathode plate. The diaphragm resistance is higher than that of Examples 1 to 33, indicating that the combination of specific types of shell polymers in the core-shell structure polymer can help improve the conductive performance of the battery.

Comparing Example 1, Examples 3 to 4 with Example 2 and Example 5, it can be seen that the mass content of the core part in the core-shell structure polymer is controlled to be 5% to 9%, and the mass content of the shell part is 91% to 95%. , based on the total mass of the core-shell structure polymer, is conducive to further reducing the membrane resistance of the positive electrode piece, increasing the number of rolling times of the positive electrode piece and the capacity retention rate of the battery after 500 cycles.

Comparing Example 1, Examples 6 to 8 and Comparative Examples 1 to 3, it can be seen that controlling the weight average molecular weight of the fluoropolymer in the core-shell structure polymer to 20,000 to 200,000 can reduce the viscosity of the positive electrode slurry and the positive electrode film resistance, and improve the capacity retention rate of the battery after 500 cycles, indicating that the core-shell structure polymer containing a fluoropolymer with a weight average molecular weight of 20,000 to 200,000 is beneficial to improving the dispersion of the cathode slurry and improving the performance of the cathode. Conductive properties of pole pieces and battery cycle performance.

Comparison between Example 1, Examples 7-8 and Example 6 shows that controlling the weight average molecular weight of the fluoropolymer in the core-shell structure polymer to 20,000-150,000 can further reduce the viscosity of the positive electrode slurry and the positive electrode film. The layer resistance is greatly improved, and the bonding force of the positive electrode sheet, the number of rolling times and the capacity retention rate of the battery after 500 cycles are greatly improved, and the bonding force, flexibility, conductive performance and battery cycle performance of the positive electrode sheet are improved to a greater extent.

Comparing Example 1, Examples 7 to 8 with Examples 6 and 9, it can be seen that controlling the median particle size Dv50 of the core-shell structure polymer to 2 μm to 10 μm can further increase the number of rolling of the positive electrode sheet and the battery life. The capacity retention rate after 500 cycles improves the flexibility of the positive electrode sheet and the battery cycle performance to a greater extent.

The cathode active material in Example 12 was not coated. Compared with Examples 1 and 10 in which the cathode active material was coated with a carbon layer, the cycle performance and pole piece flexibility of the batteries in Example 1 and Example 10 were It is obviously better than Example 12, and the slurry viscosity in Example 1 and Example 10 is reduced, indicating that the core-shell structure polymer has good affinity to the carbon layer of the cathode active material and can coat the carbon layer of the cathode active material. The surface promotes the dispersion of positive active materials, thereby improving the cycle performance of the battery and the flexibility of the pole piece. In Example 11, a cathode active material with a graphitization degree of 0.5% was used to prepare a battery. Compared with Example 1 and Example 10, the viscosity of the slurry in Example 11 was significantly higher than that in Example 1 and Example 10. Viscosity, which leads to poor dispersion properties of the slurry, further increases the film resistance and reduces the adhesion and flexibility of the pole pieces, ultimately leading to reduced cycle performance of the battery.

Comparing Example 1, Examples 13 to 16 and Example 17, it can be seen that the mass percentage of the composition of the core-shell structure polymer and the binder and the cathode active material is controlled to be 1% to 3%. , the slurry viscosity and cathode film layer resistance were significantly reduced, and accordingly, the capacity retention rate of the battery after 500 cycles was significantly increased, indicating that the core-shell structure polymer can significantly improve the dispersion and stability of the cathode slurry, helping Improving the coating of the positive electrode slurry improves the cycle performance of the battery. At the same time, the number of rolling times of the positive electrode sheet is also improved, indicating that the core-shell structure polymer helps improve the flexibility of the electrode sheet; Examples 14-15 and Implementation Comparing Example 13 and Example 14, it can be seen that the mass percentage of the core-shell structure polymer and binder composition and the positive electrode active material can be controlled to 1.4% to 2.4%, which can take into account the viscosity of the positive electrode slurry and the flexibility of the electrode piece. , and battery cycle performance.

Comparison between Example 1, Examples 19-22, and Example 18 and Example 23 shows that by controlling the mass ratio of the core-shell structure polymer and the binder to 0.05-5:1, the slurry viscosity is improved, and the viscosity of the slurry is improved. Correspondingly, the resistance of the positive electrode film layer was significantly reduced, and the capacity retention rate of the battery after 500 cycles was significantly improved, indicating that the core-shell structure polymer and binder can significantly improve the dispersion and dispersion of the positive electrode slurry within the above mass ratio range. At the same time, the stability of the positive electrode plate has also been improved, indicating that the core-shell structure polymer helps to improve the flexibility of the binder and the flexibility of the electrode plate.

Comparison between Example 1, Examples 24-25 and Comparative Examples 1-3 shows that controlling the weight average molecular weight of the polyvinylidene fluoride binder to 700,000-1.1 million can be applied to different cathode active materials and reduce the cost of the cathode. The viscosity of the slurry and the resistance of the positive electrode film, the adhesion of the electrode piece and the number of rolling times, and the capacity retention rate of the battery after 500 cycles are improved.

Comparing Examples 26 to 27 with Comparative Example 1, it can be seen that the shell part in the core-shell polymer is polyacrylamide-styrene-tert-butyl acrylate or polystyrene-tert-butyl acrylate, which can reduce the density of the positive electrode slurry. viscosity and positive electrode film resistance, improve the adhesive force of the electrode piece and the number of rolling times, and improve the capacity retention rate of the battery after 500 cycles.

Comparison between Example 1 and Examples 28-29 shows that compared to the core in the core-shell polymer being polychlorotrifluoroethylene or vinylidene fluoride-chlorotrifluoroethylene copolymer, the core in the core-shell polymer is Partly composed of polyvinylidene fluoride, it can reduce the viscosity of the positive electrode slurry and the resistance of the positive electrode film, improve the adhesive force of the electrode piece and the number of rolling times, and improve the capacity retention rate of the battery after 500 cycles.

Comparing Example 16, Examples 30-31 and Example 32, it can be seen that the mass ratio of the core-shell structure polymer and the binder is controlled to be in the range of 0.5-2:1. The slurry of Example 16, Examples 30-31 The material viscosity, positive electrode film layer resistance, positive electrode sheet rolling times, and battery capacity retention rate after 500 cycles are all significantly better than those in Example 32, indicating that the polyvinylidene fluoride core with a weight average molecular weight of 80,000 has a core-shell structure. The core-shell structure polymer improves the cycle performance of secondary batteries and increases the flexibility of the pole piece.

It should be noted that the present application is not limited to the above-described embodiment. The above-mentioned embodiments are only examples. Within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same functions and effects are included in the technical scope of the present application. In addition, within the scope that does not deviate from the gist of the present application, various modifications to the embodiments that can be thought of by those skilled in the art, and other forms constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application. .

Claims

A core-shell structure polymer, characterized by containing:

A core that is a fluoropolymer containing structural units derived from the monomer represented by Formula I; and

a shell part, which is a non-fluoropolymer containing structural units derived from monomers represented by formula II and formula III, and the shell part at least partially covers the surface of the core part,

Among them, R 1 and R 2 are each independently selected from hydrogen, fluorine, chlorine or at least one fluoro-substituted C 1-3 alkyl group; R 3 , R 4 and R 5 are each independently selected from hydrogen, substituted or unsubstituted C 1-5 alkyl.
The core-shell structure polymer according to claim 1, characterized in that R 1 and R 2 are each independently selected from hydrogen, fluorine or at least one C 1-3 alkyl group substituted by fluoro group.
The core-shell structure polymer according to claim 1 or 2, characterized in that the mass content of the core part is 5% to 9%, and the mass content of the shell part is 91% to 95%. Based on the The total mass of the core-shell polymer.
The core-shell structure polymer according to any one of claims 1 to 3, characterized in that the molar content of the structural units derived from the monomer represented by formula II is 20% to 50%, based on the non- Total moles of fluoropolymer.
The core-shell structure polymer according to any one of claims 1 to 4, characterized in that the non-fluorine polymer also includes structural units derived from the monomer represented by Formula IV,

Among them, R 6 is selected from amide group or cyano group; R 7 is selected from hydrogen, substituted or unsubstituted C 1-5 alkyl group.
The core-shell structure polymer according to claim 5, wherein the molar content of the structural units derived from the monomer represented by Formula IV is 40% to 50%, based on the total moles of the non-fluorine polymer. Quantity meter.
The core-shell structure polymer according to any one of claims 1 to 6, wherein the weight average molecular weight of the fluorine-containing polymer is 20,000 to 200,000.
The core-shell structure polymer according to any one of claims 1 to 7, wherein the weight average molecular weight of the fluorine-containing polymer is 20,000 to 150,000.
The core-shell structure polymer according to claim 5, wherein the fluoropolymer is polyvinylidene fluoride or a modified polymer thereof;

The non-fluorine polymer is one or a combination of a copolymer of styrene and tert-butyl acrylate, a copolymer of acrylonitrile, styrene and tert-butyl acrylate, and a copolymer of acrylamide, styrene and methyl acrylate. .
The core-shell structure polymer according to any one of claims 1 to 9, wherein the core-shell structure polymer has a median particle diameter Dv50 of 2 μm to 10 μm.
The core-shell structure polymer according to any one of claims 1 to 10, characterized in that the core-shell structure polymer is dissolved in N-methylpyrrolidone to prepare a glue solution, based on the total mass of the glue solution, When the mass percentage of the core-shell structure polymer in the glue solution is 7%, the viscosity of the glue solution is 50 to 180 mPa·s.
A method for preparing a core-shell structure polymer, which is characterized by including:

Preparing the core part: at least one monomer represented by the following formula I is polymerized under the first polymerization condition to obtain an emulsion of fluorine-containing polymer;

Preparing a core-shell structure polymer: The emulsion of the fluorine-containing polymer and at least two monomers represented by the following formula V are polymerized under the second polymerization condition to prepare a non-fluorine polymer, and the non-fluorine polymer is polymerized as a core-shell structure The shell part of the object at least partially covers the surface of the core part;

Wherein, R 1 and R 2 are each independently selected from hydrogen, fluorine, chlorine or C 1-3 alkyl substituted by at least one fluoro group;

R 8 and R 9 are each independently selected from hydrogen, amide group, cyano group, substituted or unsubstituted phenyl group, or -CO 2 R 10 ; R 10 is selected from substituted or unsubstituted C 1-5 alkyl group.
The preparation method according to claim 12, characterized in that preparing the non-fluorine polymer under the second polymerization condition includes the following steps:

Under an inert gas atmosphere, the emulsion of the fluorine-containing polymer, at least two monomers represented by formula V and the second initiator are swollen in the second solvent, and polymerization ligands and catalysts are added to perform the polymerization reaction.
The preparation method according to claim 12 or 13, characterized in that preparing the non-fluorine polymer under the second polymerization condition includes the following steps:

In an inert gas atmosphere, normal pressure, and 20°C to 30°C, the emulsion of the fluoropolymer, at least two monomers represented by formula V and the second initiator are swollen in the second solvent for 0.5 to 2 hours. , add polymerization ligands and catalysts, and perform polymerization for 1 to 5 hours.
The preparation method according to any one of claims 12 to 14, wherein preparing the fluoropolymer under the first polymerization condition includes the following steps:

Polymerize at least one monomer represented by formula I in an inert gas atmosphere, normal pressure, and a reaction temperature of 60°C to 70°C for 4 to 8 hours, then stop the reaction to obtain the emulsion of the fluoropolymer.
A positive electrode slurry, characterized in that it includes a positive electrode active material, a conductive agent, a binder and the core-shell structure polymer according to any one of claims 1 to 11.
The cathode slurry according to claim 16, wherein the cathode active material is a lithium-containing transition metal oxide with a carbon coating layer on the surface, and the lithium-containing transition metal oxide is selected from lithium iron phosphate. and one or more of lithium nickel cobalt manganese oxide.
The cathode slurry according to claim 16, wherein the graphitization degree of the carbon coating layer is 0.2% to 0.35%.
The positive electrode slurry according to any one of claims 16 to 18, characterized in that, in the positive electrode slurry, the composition consisting of the core-shell structure polymer and the binder and the positive electrode active material The mass percentage is 1% to 3%.
The positive electrode slurry according to any one of claims 16 to 19, characterized in that, in the positive electrode slurry, a composition composed of the core-shell structure polymer and the binder The mass percentage of the cathode active material is 1.4% to 2.4%.
The positive electrode slurry according to any one of claims 16 to 20, wherein the mass ratio of the core-shell structure polymer and the binder in the positive electrode slurry is 0.05-5.
The positive electrode slurry according to any one of claims 16 to 21, characterized in that, in the positive electrode slurry, the mass ratio of the core-shell structure polymer and the binder is 0.5 ~2.
The positive electrode slurry according to any one of claims 16 to 22, characterized in that the positive electrode slurry is dispersed in N-methylpyrrolidone, and when the solid content of the positive electrode slurry is 58%, The viscosity of the positive electrode slurry is 5000-50000 mPa·s.
The cathode slurry according to any one of claims 16 to 23, wherein the binder is polyvinylidene fluoride or a modified polymer thereof, and the weight average molecular weight of the binder is 70 Ten thousand to 1.1 million.
Application of the core-shell structure polymer according to any one of claims 1 to 11 or the core-shell structure polymer prepared by the method according to any one of claims 12 to 15 in secondary batteries.
A secondary battery, characterized in that it includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. , the positive electrode film layer is prepared from the positive electrode slurry according to any one of claims 16 to 24.
The secondary battery according to claim 26, wherein the bonding force per unit length between the positive electrode film layer and the positive electrode current collector is 10 N/m to 35 N/m.
The secondary battery according to claim 26 or 27, wherein the membrane resistance of the positive electrode plate is 0.4Ω-1Ω.
The secondary battery according to any one of claims 26 to 28, characterized in that, after the positive electrode piece undergoes no less than 2.3 bending tests, the positive electrode piece appears light-transmissive.
A battery module comprising the secondary battery according to any one of claims 26 to 29.
A battery pack comprising the secondary battery according to any one of claims 26 to 29 or the battery module according to claim 30.
An electrical device, characterized by comprising at least one selected from the group consisting of the secondary battery according to any one of claims 26 to 29, the battery module according to claim 30, or the battery pack according to claim 31. kind.