Core-shell structured polymer, water-based undercoat slurry, secondary battery, electric device

Abstract

The core-shell structure polymer includes a core and a shell covering at least a part of the core, the core includes a structural unit derived from a monomer represented by formula I, the shell includes a structural unit derived from a monomer represented by formula I, a structural unit derived from a monomer represented by formula II, and a structural unit derived from a monomer represented by formula III, where R1, R2, and R3 are each independently hydrogen, fluorine, chlorine, or C 1 -containing at least one fluorine atom. 1~3 alkyl; R4, R5, R6, R7, R8, and R9 are each independently hydrogen or substituted or unsubstituted C 1~3 alkyl, and Ar is a substituted or unsubstituted aromatic group.

Description

[Technical field]

[0001] The present application relates to the field of secondary battery technology, in particular to core-shell polymers, preparation methods, aqueous undercoat slurries, secondary batteries, and electrical devices. [Background technology]

[0002] In the process of manufacturing a secondary battery sheet, a primer layer is coated between a current collector and an active material layer to provide electrical conduction between the active material layer and the current collector, and to reduce the contact resistance between the active material layer and the current collector. The primer layer is usually manufactured by coating a primer slurry containing a binder, a conductive agent, and an auxiliary agent on the surface of the current collector. However, in the conventional technology, the process window of the primer slurry is short, the filterability is poor, and the pipe clogging due to precipitation is easily caused, which seriously affects the productivity of the sheet. Therefore, there is an urgent need to develop a binder to improve the processing performance of the slurry. Summary of the Invention [Problem to be solved by the invention]

[0003] The present application has been made in consideration of the above-mentioned problems, and aims to provide a core-shell structure polymer and an aqueous undercoat slurry containing the core-shell structure polymer, which optimize the process window for preparing an aqueous undercoat slurry and improve the productivity of the aqueous undercoat slurry. [Means for solving the problem]

[0004] A first aspect of the present application provides a core-shell structure polymer including a core portion and a shell portion covering at least a part of the core portion, wherein the core portion includes a structural unit derived from a monomer represented by formula I, and the shell portion includes a structural unit derived from a monomer represented by formula I, a structural unit derived from a monomer represented by formula II, and a structural unit derived from a monomer represented by formula III. [ka] (where R 1 , R 2 , R 3 are each independently hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1~3 alkyl; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 each independently represents hydrogen, a substituted or unsubstituted C 1~5 alkyl, and Ar is a substituted or unsubstituted aromatic group.

[0005] The core-shell structure polymer provided in the present application can reduce the viscosity of the slurry, improve the filterability of the slurry, significantly expand the process window of the slurry, and improve the processability of the slurry, so that the production needs of the undercoat layer can be met without adding a dispersant to the slurry, which contributes to optimizing the production process of the undercoat layer and improving its productivity.

[0006] In any embodiment, the R 1 is fluorine, R 2 , R 3 are each independently selected from hydrogen, fluorine, chlorine, or trifluoromethyl; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from hydrogen or methyl.

[0007] In any embodiment, the mass content of the core portion is 40% to 50% based on the mass of the core-shell polymer.

[0008] By controlling the mass content of the core portion within an appropriate range, the core-shell structured polymer can achieve both the viscosity of the slurry and the adhesion of the sheet, thereby comprehensively improving the processing performance and use performance of the water-based undercoat slurry.

[0009] In any embodiment, the mass content of the structural unit derived from the monomer represented by formula II is 10% to 40% based on the mass of the core-shell polymer.

[0010] By controlling the mass content of the structural unit derived from the monomer shown in formula II within an appropriate range, it is possible to achieve a balance between the viscosity of the slurry and the adhesion of the sheet, thereby comprehensively improving the processing performance and use performance of the slurry.

[0011] In any embodiment, the mass content of the structural unit derived from the monomer represented by formula III is 10% to 40% based on the mass of the core-shell polymer.

[0012] By controlling the mass content of the structural unit derived from the monomer represented by formula III within an appropriate range, it is possible to achieve a balance between the viscosity of the slurry and the adhesive strength of the sheet, thereby comprehensively improving the processing performance and use performance of the slurry. In any embodiment, the weight average molecular weight of the core-shell polymer is 300,000 to 500,000.

[0013] By controlling the weight-average molecular weight of the core-shell structured polymer within an appropriate range, it is possible to achieve both the adhesive strength and the film resistance of the sheet, and to comprehensively improve the adhesive performance and dynamic performance of the sheet.

[0014] In any embodiment, the core-shell polymer has a Dv50 particle size of 100 nm to 10 μm.

[0015] In any embodiment, the monomer shown in formula I is one or more selected from vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene.

[0016] In any embodiment, the monomer represented by formula II is one or two selected from acrylic acid and methacrylic acid.

[0017] In any embodiment, the monomer represented by formula III is one or two selected from styrene and 4-methylstyrene.

[0018] A second aspect of the present application provides a method for preparing a core-shell structured polymer, the method comprising the steps of: preparing a core portion of the core-shell structured polymer by polymerizing a monomer represented by formula I under polymerizable conditions; and preparing a shell portion of the core-shell structured polymer that covers at least a part of the core portion by polymerizing a monomer represented by formula I, a monomer represented by formula II, and a monomer represented by formula III. [ka] (where R 1 , R 2 , R 3 are each independently hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1~3 alkyl; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 each independently represents hydrogen, a substituted or unsubstituted C 1~5 alkyl, and Ar is a substituted or unsubstituted aromatic group.

[0019] The core-shell structure polymer prepared by this method can reduce the viscosity of the slurry, improve the filterability of the slurry, significantly expand the process window of the slurry, and improve the processability of the slurry. The production needs of the undercoat layer can be met without adding a dispersant to the slurry, which contributes to optimizing the production process of the undercoat layer and improving its productivity.

[0020] In any embodiment, the R 1 is fluorine, R 2 , R 3 are each independently one or more selected from hydrogen, fluorine, chlorine, and trifluoromethyl; R 4 , R 5 , R6 , R 7 , R 8 , R 9 each independently represents one or two selected from hydrogen and methyl.

[0021] In any embodiment, the mass content of the core portion is 40% to 50% based on the mass of the core-shell polymer.

[0022] In any embodiment, the mass content of the monomer represented by formula II is 10% to 40% based on the total mass of the monomer represented by formula I, the monomer represented by formula II, and the monomer represented by formula III.

[0023] In any embodiment, the mass content of the monomer represented by formula III is 10% to 40% based on the total mass of the monomer represented by formula I, the monomer represented by formula II, and the monomer represented by formula III.

[0024] In either embodiment, the preparation method includes a first stage polymerization and a second stage polymerization. First stage polymerization: providing an initiator, a first emulsifier, at least one monomer of formula I, and an aqueous medium, conducting a first stage polymerization reaction to obtain a core portion, and continuously feeding the monomer of formula I during the first stage polymerization reaction. Second-stage polymerization: after reacting for a certain time, add initiator, second emulsifier, at least one monomer represented by formula II and monomer represented by formula III, and aqueous medium into the reaction vessel to carry out second-stage polymerization reaction to obtain core-shell structure polymer, and continuously introduce monomer represented by formula I during the second-stage polymerization reaction.

[0025] The method provided in the present application first forms a fluorine-containing core portion by continuously feeding the monomer shown in formula I, makes the core portion have high thermal stability, and then forms a core-shell structure polymer by feeding the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III. In an emulsion system, monomers with different hydrophilicity are added stepwise and polymerized to obtain a core-shell structure polymer, which exists as a core-shell structure in an aqueous medium, and compared with a non-core-shell structure polymer prepared by simultaneously feeding all monomers into a reaction vessel, the stability and dispersibility of the core-shell structure polymer are greatly improved, the filterability and dispersibility of the aqueous undercoat slurry are improved, the film resistance of the sheet is reduced, and the process window of the slurry is further expanded, which contributes to improving the productivity of the aqueous undercoat layer. In addition, the structural units derived from the monomer shown in formula II are all distributed in the shell portion, and the carboxyl of the shell portion can improve the adhesion of the core-shell structure polymer and further increase the adhesion of the sheet. In addition, when the monomer represented by formula II and the monomer represented by formula III are fed into the reaction vessel to carry out the second stage polymerization, the monomer represented by formula I is subsequently fed into the reaction vessel to increase the compatibility between the core and shell parts and improve the stability of the core-shell structured polymer.

[0026] In any embodiment, the second stage polymerization comprises: After adding the initiator to the reaction vessel, a premix including a second emulsifier, at least one monomer represented by Formula II, a monomer represented by Formula III, and an aqueous medium is further added. In any embodiment, the mass of the monomer shown in formula I supplied to the first stage polymerization reaction is 70% to 85% of the total mass of the monomer shown in formula I supplied to the polymerization reaction, and the mass of the monomer shown in formula I supplied to the second stage polymerization reaction is 15% to 30% of the total mass of the monomer shown in formula I supplied to the polymerization reaction.

[0027] In any embodiment, the initiator provided in the first stage polymerization and the initiator provided in the second stage polymerization are both persulfates, and based on the total mass of the monomer shown in Formula I, the monomer shown in Formula II, and the monomer shown in Formula III, the mass percentage of the initiator provided in the first stage polymerization is 0.05% to 0.075%, and the mass percentage of the initiator provided in the second stage polymerization is 0.05% to 0.075%.

[0028] In any embodiment, the mass percentage of the first emulsifier is 0.28% to 0.42% based on the total mass of the monomer represented by formula I, the monomer represented by formula II, and the monomer represented by formula III.

[0029] In any embodiment, the mass percentage of the second emulsifier is 0.8% to 1.2% based on the total mass of the monomer represented by formula I, the monomer represented by formula II, and the monomer represented by formula III.

[0030] In any embodiment, based on the total mass of the monomer represented by formula I, the monomer represented by formula II, and the monomer represented by formula III, the mass percentage of the aqueous medium provided in the first stage polymerization is 200% to 500%, and the mass percentage of the aqueous medium provided in the second stage polymerization is 100% to 200%.

[0031] In any embodiment, the reaction pressure in the first stage polymerization is 5.5 MPa to 7.5 MPa, and the reaction temperature is 75°C to 85°C.

[0032] In any embodiment, the second stage polymerization is carried out at a reaction pressure of 4.5 MPa to 6.5 MPa and at a reaction temperature of 86°C to 95°C.

[0033] In any embodiment, the initiator may be one or two selected from potassium persulfate and ammonium persulfate.

[0034] In either embodiment, the first emulsifier is an alkali metal perfluorooctanoic acid salt.

[0035] In any embodiment, the second emulsifier is polyoxyethylene-4- Phenyl ether ammonium sulfate, and nonylphenol polyoxyethylene ether ammonium sulfate.

[0036] A third aspect of the present application provides an emulsion type binder comprising the core-shell structured polymer according to the first aspect.

[0037] The emulsion type binder is a direct product of the method for preparing the core-shell structured polymer of the second embodiment, and can be used as it is as a binder for the aqueous undercoat slurry, which can reduce the production cost and improve the production rate.

[0038] A fourth aspect of the present application provides the use of the core-shell polymer according to the first aspect in a secondary battery.

[0039] A fifth aspect of the present application provides an aqueous undercoat slurry comprising a binder, a conductive agent and an aqueous medium, the binder comprising the core-shell structured polymer according to the first aspect.

[0040] Compared with non-core-shell structured polymers, core-shell structured polymers have improved stability and dispersibility, and can enhance the filterability and dispersibility of the aqueous undercoat slurry, and reduce the film resistance of the sheet.

[0041] In either embodiment, the core-shell structured polymer is added to the aqueous basecoat slurry as an emulsion containing the core-shell structured polymer.

[0042] The core-shell structure polymer prepared by the preparation method according to the second embodiment above exists as an emulsion and can be directly added to an aqueous undercoat slurry for use, thereby reducing production costs and improving productivity.

[0043] In any embodiment, the mass ratio of the conductive agent to the binder is 0.8:1 to 1:1.

[0044] By controlling the mass ratio of the conductive agent to the binder within an appropriate range, it is possible to achieve both the adhesive strength and the film resistance of the slurry sheet, and to comprehensively improve the adhesive performance and dynamic performance of the sheet.

[0045] In any embodiment, when the solid content of the aqueous undercoat slurry is 10% to 20%, the viscosity of the aqueous undercoat slurry is 300 mPa·s to 900 mPa·s.

[0046] By controlling the solid content of the water-based undercoat slurry within an appropriate range, it is possible to achieve a good balance between the viscosity of the slurry and the adhesive strength of the sheet, thereby improving the overall processing and use performance of the slurry.

[0047] The viscosity of the aqueous undercoat slurry with a solid content of 10% to 20% is 300 mPa·s to 900 mPa·s. Therefore, the aqueous undercoat slurry prepared from the core-shell structure polymer does not require the addition of a separate dispersant or thickener to improve the processing performance, which contributes to improving the productivity and optimizing the production process.

[0048] A sixth aspect of the present application is Coating the aqueous undercoat slurry according to the fifth embodiment onto a current collector surface using a gravure coater; drying to obtain an aqueous undercoat layer, the thickness of the aqueous undercoat layer being 1 um to 3 um; A method for preparing a water-based subbing layer is provided. The method for preparing the water-based undercoat layer disclosed in the present application can increase the adhesion of the sheet and reduce the film resistance of the sheet.

[0049] A seventh aspect of the present application provides a secondary battery comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet and / or the negative electrode sheet includes an aqueous undercoat layer prepared by the preparation method according to the sixth aspect of the present application. In any embodiment, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0050] An eighth aspect of the present application provides a battery module including the secondary battery of the seventh aspect of the present application.

[0051] A ninth aspect of the present application provides a battery pack including the secondary battery according to the seventh aspect of the present application or the battery module according to the eighth aspect of the present application.

[0052] A tenth aspect of the present application provides an electric device including at least one selected from the secondary battery according to the seventh aspect of the present application, the battery module according to the eighth aspect of the present application, or the battery pack according to the ninth aspect of the present application. [Brief description of the drawings]

[0053] [Figure 1] FIG. 1 is a schematic diagram of the structure of a core-shell structure polymer according to one embodiment of the present application. [Diagram 2] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Diagram 3] FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 2. [Figure 4] FIG. 1 is a schematic diagram of a battery module according to an embodiment of the present application. [Diagram 5] FIG. 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 6] FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to the embodiment of the present application. [Figure 7] 1 is a schematic diagram of an electrical device powered by a secondary battery according to an embodiment of the present application. [Explanation of symbols]

[0054] 1-battery pack, 2-upper housing, 3-lower housing, 4-battery module, 5-secondary battery, 51-case, 52-electrode assembly, 53-cover plate, 6-core-shell structured polymer, 61-core portion, 62-shell portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Hereinafter, the embodiments specifically disclosing the binder, preparation method, electrode, battery, and electric device according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed description may be omitted. For example, detailed description of already well-known matters or redundant description of substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0056] The "ranges" disclosed herein are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may or may not include the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any other upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, the ranges of 60-110 and 80-120 are also expected to be understood. Also, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4, and 5, then ranges such as 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all expected. In this specification, unless otherwise stated, the numerical range "a-b" represents an abbreviation for 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" are listed herein, and "0-5" is simply shorthand for combinations of these numbers. Also, when a parameter is expressed as an integer ≧2, this is equivalent to disclosing that the parameter is an integer, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] Unless otherwise specified, all the embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0058] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a novel technical solution.

[0059] Unless otherwise stated, all steps in this application may be performed in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method performs steps (a) and (b) in sequence, or performs steps (b) and (a) in sequence. For example, the method mentioned above may further include step (c), which means that step (c) may be added to the method in any order, for example, the method includes steps (a), (b) and (c), the method includes steps (a), (c) and (b), or the method includes steps (c), (a) and (b), etc.

[0060] Unless otherwise specified, "comprise" and "contain" as referred to herein mean to be open-ended and may be closed-ended. For example, "comprise" and "contain" mean that other components not listed may also be included or contained, and only the listed components may be included or contained.

[0061] Unless otherwise specified, in the present invention, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." Specifically, any of the following conditions also satisfies the condition "A or B": 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 A and B are true (or exist).

[0062] The conductivity of the electrode is one of the most important research topics of secondary batteries. In the process of preparing a secondary battery sheet, a primer layer is coated between the current collector and the active material layer to provide electrical conduction between the active material layer and the current collector, and further reduce the contact resistance between the active material layer and the current collector, so that the sheet has good electronic conductivity and ionic conductivity, and improves the dynamic performance of the battery. In the prior art, the preparation of the primer layer is usually carried out using a binder and a conductive agent. The traditional polyvinylidene fluoride binder increases the viscosity of the slurry, worsens the filterability, and makes it difficult to coat uniformly, so that in the process of preparing the slurry, a dispersant needs to be added to improve the processing performance of the slurry. Of course, this increases the processing difficulty of the slurry, affects the production rate, and leads to a decrease in the stability of the slurry between batches. In view of the above-mentioned problems, the present application has developed a binder that allows the aqueous primer slurry to have suitable viscosity and excellent filterability in order to improve the production rate and production quality of the primer layer.

[0063] [Core-shell structure polymer] In view of this, the present application provides a core-shell structure polymer comprising a core portion and a shell portion covering at least a part of the core portion, wherein the core portion comprises a structural unit derived from a monomer represented by formula I, and the shell portion comprises a structural unit derived from a monomer represented by formula I, a structural unit derived from a monomer represented by formula II, and a structural unit derived from a monomer represented by formula III. [ka] (where R 1 , R 2 , R 3 are each independently hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1~3 alkyl; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 each independently represents hydrogen, a substituted or unsubstituted C 1~5alkyl, and Ar is a substituted or unsubstituted aromatic group.

[0064] In this specification, the term "polymer" includes, on the one hand, a chemically homogeneous aggregate of large molecules prepared in a polymerization reaction, but differing in terms of degree of polymerization, molar mass and chain length, and, on the other hand, the term also includes derivatives of such macromolecular aggregates formed in a polymerization reaction, i.e. chemically homogeneous or chemically non-homogeneous products obtained by reactions, for example addition or substitution, of functional groups on said macromolecules.

[0065] As used herein, the term "trifluoromethyl" refers to -CF 3 means a group.

[0066] As used herein, the term “C 1~5 The term "alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms having 1 to 5 carbon atoms and attached to the rest of the molecule by a single bond, and in which the radical has no unsaturated bonds. 1~3 "Alkyl" should be interpreted accordingly. 1~5 Examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), butyl, and benzyl. In some embodiments, C 1000 or C 11000 or C 12000 or C 13000 or C 14000 or C 15000 or C 16000 or C 17000 or C 18000 or C 19000 or C 20000 or C 210000 or C 220000 or C 230000 or C 240000 or C 250000 or C 260000 or C 270000 or C 280000 or C 290000 or C 300000 or C 310000 or C 320000 or C 330000 or C 340000 or 1~3 Alkyl is -CF 3 , -CH 3 CH 2 F or -CH 2 FCH 2 It's F.

[0067] As used herein, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is replaced with another type of chemical moiety or substituent, where each substituent is independently selected from the group consisting of hydroxy, mercapto, amino, cyano, nitro, aldehyde groups, halogen atoms, alkenyl, alkynyl, aryl, heteroaryl, C 1~6 Alkyl, C 1~6 Selected from alkoxy.

[0068] As used herein, the term "aromatic group" refers to a functional group or substituent derived from a simple aromatic ring, such as, for example, phenyl, o-tolyl, 1-naphthyl (or α-naphthyl), and the like.

[0069] In some embodiments, R 1 is fluorine, R 2 , R 3 are each independently one or more selected from hydrogen, fluorine, chlorine, and trifluoromethyl; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 each independently represents one or two selected from hydrogen and methyl.

[0070] In some embodiments, the monomer according to formula I is one or more selected from vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene.

[0071] In some embodiments, the monomer according to formula II is one or two selected from acrylic acid, methacrylic acid.

[0072] In some embodiments, the monomer shown in formula III is one or two selected from styrene, 4-methylstyrene.

[0073] 1 is a schematic diagram of the structure of a core-shell polymer in one embodiment of the present application, the core-shell polymer 6 includes a core portion 61 and a shell portion 62, the shell portion 62 covers the surface of the core portion 61, the core portion 61 includes a structural unit derived from a monomer shown in formula I, the core portion 61 includes a fluorine-containing structural unit, and can enhance the thermal stability of the structure, the shell portion includes a structural unit derived from a monomer shown in formula I, a structural unit derived from a monomer shown in formula II, and a structural unit derived from a monomer shown in formula III, and the shell portion includes a carboxyl group, and can enhance the adhesion performance of the structure. Compared with traditional polyvinylidene fluoride, the core-shell polymer has a fluorine-containing unit located in the core portion and a non-fluorine unit located in the shell portion, which reduces the contact area between the fluorine-containing structural unit and the solvent, reduces the slurry viscosity, stabilizes the slurry, and plays a role in alleviating slurry sedimentation, and effectively improves the filterability of the slurry.

[0074] The core-shell structure polymer provided in the present application can reduce the viscosity of the slurry, improve the filterability of the slurry, significantly expand the process window of the slurry, and improve the processability of the slurry, so as to meet the production needs of the water-based undercoat layer without adding a dispersant to the slurry, which contributes to optimizing the production process of the water-based undercoat layer and improving its production rate.

[0075] In this specification, the term "process window" refers to a process section in which product quality can be ensured, and includes, but is not limited to, a temperature section, a pressure section, a length of storage time, etc., and it can be understood that the wider the process window, the lower the requirement for process accuracy.

[0076] In some embodiments, the mass content of the core portion is 40% to 50% based on the mass of the core-shell polymer. In some embodiments, the mass content of the core portion is any one of 40%, 45%, and 50% based on the mass of the core-shell polymer.

[0077] By controlling the mass content of the core part within an appropriate range, the slurry can have an appropriate viscosity, on the one hand, the sheet can have good adhesive strength, and on the other hand, the subsequent coating processing and coating drying operations can be compatible, thereby comprehensively improving the processing performance and use performance of the slurry.

[0078] In some embodiments, the mass content of the structural unit derived from the monomer represented by formula II is 10% to 40% based on the mass of the core-shell polymer. In some embodiments, the mass content of the structural unit derived from the monomer represented by formula II is any one of 10%, 20%, 30%, and 40% based on the mass of the core-shell polymer.

[0079] By controlling the mass content of the structural unit derived from the monomer shown in formula II within a suitable range, the slurry can have a suitable viscosity, on the one hand, the sheet can have good adhesion, and on the other hand, the subsequent coating processing and coating drying operations can be compatible, and the processing performance and use performance of the slurry can be comprehensively improved.

[0080] In some embodiments, the mass content of the structural unit derived from the monomer represented by formula III is 10% to 40% based on the mass of the core-shell polymer. In some embodiments, the mass content of the structural unit derived from the monomer represented by formula III is any one of 10%, 20%, 30%, and 40% based on the mass of the core-shell polymer.

[0081] By controlling the mass content of the structural unit derived from the monomer shown in formula III within a suitable range, the slurry can have a suitable viscosity, on the one hand, the sheet can have good adhesion, and on the other hand, the subsequent coating processing and coating drying operations can be compatible, and the processing performance and use performance of the slurry can be comprehensively improved.

[0082] In some embodiments, the weight average molecular weight of the core-shell polymer is 300,000 to 500,000. In some embodiments, the weight average molecular weight of the core-shell polymer is any one of 300,000, 400,000, and 500,000.

[0083] In this specification, the term "weight average molecular weight" refers to the sum of the products of the weight fractions of molecules having different molecular weights in a polymer and the corresponding molecular weights.

[0084] In the present application, the weight average molecular weight of the polymer is measured by a method known in the art, for example, gel chromatography, for example, Waters 2695 Isocratic HPLC type gel chromatography (differential refractive index detector 2141). In some embodiments, the measurement method is a method using a polystyrene solution sample with a mass fraction of 3.0% as a reference and a matched chromatography column (oil-based: Styragel HT5DMF7.8 * Select a 300 mm+Styragel HT4). Prepare a 3.0% core-shell structure polymer colloidal solution using purified N-methylpyrrolidone (NMP) solvent, and leave the prepared solution to stand for one day. When measuring, first, inhale tetrahydrofuran into the syringe and rinse several times. Then, inhale 5 ml of the test solution, expel the air in the syringe, and dry the needle tip. Finally, gradually inject the sample solution into the sample injection port. After the displayed number stabilizes, obtain the data and read the weight average molecular weight.

[0085] By controlling the weight-average molecular weight of the core-shell structured polymer within an appropriate range, it is advantageous for the dispersion of the core-shell structured polymer in the aqueous undercoat slurry, and the core-shell structured polymer is less likely to aggregate with the conductive agent, thereby improving the dispersibility of the conductive agent and reducing the film resistance of the sheet. At the same time, the core-shell structured polymer with a weight-average molecular weight within an appropriate range can form a three-dimensional network bond structure and provide an effective bonding effect.

[0086] In this manner, by controlling the weight-average molecular weight of the core-shell polymer within an appropriate range, it is possible to achieve both the adhesiveness and film resistance of the sheet, and to comprehensively improve the adhesive performance and dynamic performance of the sheet.

[0087] In some embodiments, the core-shell polymer has a Dv50 particle size of 100 nm to 10 μm. In some embodiments, the core-shell polymer has a Dv50 particle size of any one of 100 nm to 1000 nm, 500 nm to 1000 nm, and 500 nm to 10 μm.

[0088] In this specification, the term "Dv50 particle size" refers to the particle size corresponding to the cumulative particle size distribution number of particles reaching 50% in a particle size distribution curve, and in its physical meaning, it means that 50% of particles have a particle size smaller (or larger) than this value.

[0089] In one embodiment of the present application, there is provided a method for preparing a core-shell structured polymer, comprising the steps of: preparing a core portion of the core-shell structured polymer by polymerizing a monomer represented by formula I under a polymerizable condition; and preparing a shell portion of the core-shell structured polymer that covers at least a part of the core portion by polymerizing a monomer represented by formula I, a monomer represented by formula II, and a monomer represented by formula III. [ka] (where R 1 , R 2 , R 3 are each independently hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1~3 alkyl; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 each independently represents hydrogen, a substituted or unsubstituted C 1~5 alkyl, and Ar is a substituted or unsubstituted aromatic group.

[0090] As used herein, the term "polymerization conditions" refers to conditions, including temperature, pressure, reactant concentrations, optional solvents / diluents, reactant mixing / addition parameters, and other conditions selected by one of skill in the art that are conducive to the reaction of one or more monomers in at least one polymerization reactor.

[0091] The core-shell structure polymer prepared by this method can reduce the viscosity of the slurry, improve the filterability of the slurry, significantly expand the process window of the slurry, and improve the processability of the slurry, so as to meet the production needs of the water-based undercoat layer without adding a dispersant to the slurry, which contributes to optimizing the production process of the water-based undercoat layer and improving its productivity.

[0092] In some embodiments, R 1 is fluorine, R 2 , R 3 are each independently selected from hydrogen, fluorine, chlorine, or trifluoromethyl; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are each independently selected from hydrogen or methyl.

[0093] In some embodiments, the mass content of the core portion is 40% to 50% based on the mass of the core-shell polymer. In some embodiments, the mass content of the core portion is any one of 40%, 45%, and 50%.

[0094] In some embodiments, based on the total mass of the monomers shown in formula I, II, and III, the mass content of the monomers shown in formula II is 10% to 40%. In some embodiments, based on the total mass of the monomers shown in formula I, II, and III, the mass content of the monomers shown in formula II is optionally any one of 10%, 20%, 30%, and 40%.

[0095] In some embodiments, based on the total mass of the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III, the mass content of the monomer shown in formula III is optionally any one of 10%, 20%, 30%, and 40%.

[0096] In some embodiments, the preparation process comprises a first stage polymerization and a second stage polymerization. First stage polymerization: providing an initiator, a first emulsifier, at least one monomer of formula I, and an aqueous medium, conducting a first stage polymerization reaction to obtain a core portion, and continuously feeding the monomer of formula I during the first stage polymerization reaction. Second-stage polymerization: after reacting for a certain time, add an initiator, a second emulsifier, at least one monomer represented by formula II and monomer represented by formula III, and an aqueous medium into the reaction vessel to carry out a second-stage polymerization reaction to obtain a core-shell structure polymer, and continuously introduce the monomer represented by formula I during the second-stage polymerization reaction.

[0097] The method provided in the present application firstly comprises continuously feeding the monomer represented by formula I to form a fluorine-containing core portion, so that the core portion has high thermal stability, and then feeding the monomer represented by formula I, the monomer represented by formula II and the monomer represented by formula III to form a core-shell structure polymer. In the emulsion system, the hydrophobic monomer represented by formula I is first added to carry out the first-stage polymerization to form a core portion, and the monomer represented by formula II, the monomer represented by formula III and the monomer represented by formula I as hydrophilic monomers are added to carry out the second-stage polymerization to form a shell portion, and the resulting core-shell structure polymer exists as a core-shell structure in an aqueous medium, which significantly improves the stability and dispersibility of the core-shell structure polymer compared with the non-core-shell structure polymer prepared by simultaneously feeding all the monomers into a reaction vessel, thereby enhancing the filterability and dispersibility of the aqueous undercoat slurry, reducing the film resistance of the sheet, and further expanding the process window of the slurry, thereby contributing to improving the productivity of the aqueous undercoat layer. At the same time, since all the structural units derived from the monomer represented by formula II are distributed in the shell portion, the carboxyl group of the shell portion can improve the adhesion of the sheet. In addition, when the monomer represented by formula II and the monomer represented by formula III are fed into the reaction vessel to carry out the second stage polymerization, the compatibility between the core and shell parts is increased and the stability of the core-shell structured polymer is improved by subsequently feeding the monomer represented by formula I into the reaction vessel.

[0098] As used herein, the term "hydrophobicity" refers to the physical property of molecules repelling water and each other.

[0099] As used herein, the term "hydrophilic" refers to the physical property of a molecule being able to form temporary associations with water via hydrogen bonds.

[0100] In some embodiments, the mass of the monomer of formula I fed to the first stage polymerization is 70%-85% of the total mass of the monomer of formula I fed to the polymerization reaction, and the mass of the monomer of formula I fed to the second stage polymerization reaction is 15%-30% of the total mass of the monomer of formula I fed to the polymerization reaction.

[0101] In some embodiments, the second stage polymerization includes adding an initiator to a reaction vessel followed by further adding a premix including a second emulsifier, at least one monomer shown in Formula II and one monomer shown in Formula III, and an aqueous medium.

[0102] In some embodiments, the initiator provided in the first stage polymerization and the initiator provided in the second stage polymerization are persulfates, and the weight percentage of the initiator provided in the first stage polymerization is 0.05% to 0.075%, and the weight percentage of the initiator provided in the second stage polymerization is 0.05% to 0.075%, based on the total weight of the monomer represented by Formula I, the monomer represented by Formula II, and the monomer represented by Formula III.

[0103] In some embodiments, the mass percentage of the first emulsifier is 0.28% to 0.42%, based on the total mass of the monomer represented by Formula I, the monomer represented by Formula II, and the monomer represented by Formula III.

[0104] In some embodiments, the mass percentage of the second emulsifier is 0.8% to 1.2%, based on the total mass of the monomer shown in Formula I, the monomer shown in Formula II, and the monomer shown in Formula III.

[0105] In some embodiments, based on the total mass of the monomer represented by formula I, the monomer represented by formula II, and the monomer represented by formula III, the mass percentage of the aqueous medium provided to the first stage polymerization is 200% to 500%, and the mass percentage of the aqueous medium provided to the second stage polymerization is 100% to 200%.

[0106] In some embodiments, the aqueous medium provided in the first stage polymerization and the aqueous medium provided in the second stage polymerization is deionized water.

[0107] In some embodiments, the first stage polymerization has a reaction pressure of 5.5 MPa to 7.5 MPa and a reaction temperature of 75°C to 85°C.

[0108] In some embodiments, the second stage polymerization has a reaction pressure of 4.5 MPa to 6.5 MPa and a reaction temperature of 86°C to 95°C.

[0109] In some embodiments, the initiator may be one or more selected from potassium persulfate, ammonium persulfate.

[0110] Ammonium persulfate or potassium persulfate is suitable as an initiator for emulsion polymerization because it effectively decomposes at 60° C. or higher to generate radical ions or ion radicals.

[0111] In some embodiments, the first emulsifier is an alkali metal salt of perfluorooctanoic acid, and optionally a sodium salt of perfluorooctanoic acid.

[0112] Alkali metal salts of perfluorooctanoic acid are often used as emulsifiers or dispersants in the polymerization reaction of fluorine-containing monomers.

[0113] In some embodiments, the second emulsifier is polyoxyethylene-4- Phenyl ether ammonium sulfate, and nonylphenol polyoxyethylene ether ammonium sulfate.

[0114] Polyoxyethylene-4- Phenyl Both ammonium ether sulfate and nonylphenol polyoxyethylene ether sulfate are anionic-nonionic emulsifiers, and have both anionic and nonionic properties. Therefore, they can be used alone without needing to be used in combination with other emulsifiers during emulsion polymerization.

[0115] In one embodiment of the present application, there is provided an emulsion type binder comprising the core-shell structured polymer of any of the embodiments.

[0116] The emulsion-type binder is the direct product of the method for preparing the core-shell structured polymer in any embodiment, and can be used as it is as a binder for the aqueous undercoat slurry, which can reduce the production cost and improve the production rate.

[0117] In one embodiment of the present application, there is provided a use of the core-shell structured polymer of any of the embodiments in a secondary battery, optionally the secondary battery comprising at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0118] In some embodiments is the use of a core-shell structured polymer as a binder in a secondary battery.

[0119] In some embodiments is the use of a core-shell structured polymer as a binder in a water-based undercoat layer in a secondary battery.

[0120] [Water-based primer slurry] In one embodiment of the present application, there is provided an aqueous undercoat slurry comprising a binder including the core-shell structured polymer according to any of the aspects, a conductive agent, and an aqueous medium.

[0121] As used herein, the term "binder" refers to a chemical compound, polymer or mixture that forms a colloidal solution or dispersion in the dispersing medium.

[0122] In some embodiments, the dispersion medium for the binder is an aqueous medium, such as deionized water, i.e., the binder is soluble in the aqueous medium.

[0123] Compared to non-core-shell structured polymers, the core-shell structured polymers have improved stability and dispersibility, improve the filterability of the aqueous basecoat slurry, improve the dispersibility of the aqueous basecoat slurry, and reduce the film resistance of the sheet.

[0124] In some embodiments, the core-shell structured polymer is added to the aqueous basecoat slurry as an emulsion comprising the core-shell structured polymer.

[0125] The core-shell structure polymer prepared by using any of the preparation methods in the above-mentioned embodiments exists as an emulsion product, and can be directly added to the undercoat slurry for use, thereby reducing production costs and improving production rate.

[0126] In some embodiments, 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.

[0127] In some embodiments, the aqueous medium is deionized water.

[0128] In some embodiments, the mass ratio of the conductive agent to the binder is 0.8:1 to 1:1.

[0129] By controlling the mass ratio of the conductive agent to the binder within an appropriate range, it is possible to achieve both the adhesive strength and the film resistance of the slurry sheet, and to comprehensively improve the adhesive performance and dynamic performance of the sheet.

[0130] In some embodiments, when the solids content of the aqueous basecoat slurry is 10% to 20%, the viscosity of the aqueous basecoat slurry is 300 mPa·s to 900 mPa·s.

[0131] In some embodiments, the solids content of the aqueous basecoat slurry is optionally any one of 10%, 15%, 18%, 20%.

[0132] In some embodiments, the viscosity of the aqueous basecoat slurry is optionally any one of 350 mPa·s to 900 mPa·s, 350 mPa·s to 800 mPa·s, 380 mPa·s to 800 mPa·s, 400 mPa·s to 800 mPa·s, 350 mPa·s to 700 mPa·s, and 400 mPa·s to 700 mPa·s.

[0133] By controlling the solid content of the water-based undercoat slurry within an appropriate range, the sheet can have good adhesion, and at the same time the slurry can have an appropriate viscosity, which allows the subsequent coating processing and coating drying operations to be compatible, thereby comprehensively improving the processing performance and use performance of the slurry.

[0134] The aqueous basecoat slurry with a solid content of 10%-20% has a viscosity of 300 mPa·s-900 mPa·s. Therefore, the aqueous basecoat slurry prepared using the core-shell structure binder does not require the addition of a separate dispersant or thickener to improve processing performance, which contributes to increasing productivity and optimizing the production process.

[0135] [Water-based undercoat layer] One embodiment of the present application is Coating the undercoat slurry according to the fourth embodiment onto a surface of a current collector using a gravure coater; drying to obtain an aqueous undercoat layer, the thickness of the aqueous undercoat layer being 1 um to 3 um; A method for preparing a water-based subbing layer is provided.

[0136] The method for preparing the water-based undercoat layer disclosed in the present application can increase the adhesion of the sheet and reduce the film resistance of the sheet.

[0137] In one embodiment of the present application, a secondary battery is provided that includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet and / or the negative electrode sheet includes an aqueous undercoat layer according to any of the embodiments. In some embodiments, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery. During the charge and discharge process of the battery, active ions are repeatedly inserted and removed between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and serves mainly to prevent short-circuiting between the positive electrode and the negative electrode, while allowing the passage of ions.

[0138] [Positive electrode sheet] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer and an aqueous undercoat layer provided on at least one surface of the positive electrode current collector.

[0139] For example, the positive electrode current collector has two opposing faces through its thickness, and the positive electrode film layer and the aqueous undercoat layer are provided on either or both of the two opposing surfaces of the positive electrode current collector.

[0140] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) in a polymer material. Base Layer (For example, it may be formed on a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0141] In some embodiments, the positive electrode active material may be a battery positive electrode active material known in the art. For example, the positive electrode active material may include at least one of lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials used as battery positive electrode active materials may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, an example of a lithium transition metal oxide is lithium cobalt oxide (e.g., LiCoO 2 ), lithium nickel oxide (e.g., LiNiO 2 ), lithium manganese vapor (e.g., LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM 333 (also abbreviated as LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM 523 (also abbreviated as LiNi 0.5 Co 0.25 Mn 0.25 O 2 (NCM 211 (also abbreviated as LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622 (also abbreviated as LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811 Lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O 2) and modified compounds thereof. Examples of lithium-containing phosphates having an olivine structure include, but are not limited to, lithium iron phosphate (e.g., LiFePO 4 (also abbreviated as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (e.g., LiMnPO 4 ), a composite of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite of lithium iron manganese phosphate and carbon.

[0142] In some embodiments, the positive electrode membrane layer further includes an optional binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0143] In some embodiments, the positive electrode membrane layer further optionally includes a conductive agent. For 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.

[0144] In some embodiments, the positive electrode sheet can be manufactured in the following manner: In any embodiment, the components for preparing the aqueous undercoat layer, such as an emulsion of a core-shell structured polymer and a conductive agent, are dispersed in a solvent (e.g., deionized water) to form an aqueous undercoat slurry, and the aqueous undercoat slurry is coated on an aluminum foil current collector using a gravure coater and dried to form an aqueous undercoat layer, i.e., an aqueous undercoated current collector, and the components for preparing the above-mentioned positive electrode membrane layer, such as a positive electrode active material, a conductive agent, a binder, and other optional components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on the aqueous undercoated current collector, followed by drying, cold rolling, and other processes to obtain a positive electrode sheet.

[0145] [Negative electrode sheet] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector.

[0146] For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0147] In some embodiments, the negative electrode current collector can be a metal foil sheet or a composite current collector. For example, a copper foil can be used as the metal foil sheet. The composite current collector can be a polymer base layer and a polymer material. Base Layer The composite current collector may include a metal layer formed on at least one surface of the polymer material. Base Layer (For example, it may be formed on a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0148] In some embodiments, the negative electrode active material may be a negative electrode active material used in batteries known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may be at least one selected from elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other traditional materials used as negative electrode active materials in batteries may be used. The negative electrode active material may be used alone or in combination of two or more types.

[0149] In some embodiments, the negative electrode membrane layer optionally includes a binder, which may be one or more selected from styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and chitosan methyl carboxylate (CMCS). In some embodiments, the negative electrode membrane layer optionally includes a conductive agent, which may be one or more selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0150] In some embodiments, the negative electrode membrane layer optionally includes other auxiliary agents, such as, for example, a thickening agent (eg, sodium carboxymethylcellulose (CMC-Na)).

[0151] In some embodiments, the negative electrode sheet can be manufactured in the following manner: The components for manufacturing the negative electrode sheet described above, for example, the negative electrode active material, the conductive agent, the binder, and other optional components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, and the negative electrode slurry is coated on a negative electrode current collector, and the negative electrode sheet can be obtained through processes such as drying and cold rolling.

[0152] [Electrolyte] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. In the present application, the type of electrolyte is not specifically limited and can be selected as necessary. For example, the electrolyte may be liquid, gel, or all solid.

[0153] In some embodiments, the electrolyte is an electrolytic solution that includes an electrolyte salt and a solvent.

[0154] In some embodiments, the electrolyte salt may be at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0155] In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0156] In some embodiments, the electrolyte may further include an optional additive, for example, an additive that can improve certain battery performance, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature and low-temperature performance of the battery, or an additive that can improve certain battery performance, such as an additive that can improve the overcharge performance of the battery, or an additive that can improve the high-temperature and low-temperature performance of the battery.

[0157] [Separator] In some embodiments, the secondary battery further includes a separator. In the present application, the type of the separator is not particularly limited, and any known separator having a porous structure and excellent chemical and mechanical stability can be selected and used.

[0158] In some embodiments, the separator may be made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and is not particularly limited.

[0159] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0160] In some embodiments, the secondary battery may include an exterior case that is used to seal the electrode assembly and electrolyte.

[0161] In some embodiments, the exterior of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft bag such as a pouch-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0162] In the present application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular or any other shape. For example, FIG. 2 shows a secondary battery 5 having a rectangular structure as an example.

[0163] In some embodiments, referring to FIG. 3, the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate may be surrounded to form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening so as to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and can be selected by those skilled in the art according to specific practical needs.

[0164] In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0165]

[0166] Fig. 4 shows an example of a battery module 4. Referring to Fig. 4, in the battery module 4, the multiple secondary batteries 5 may be arranged in order along the length direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by a fastener.

[0167] Optionally, the battery module 4 may further include a housing having an accommodation space for accommodating a plurality of secondary batteries 5 .

[0168] In some embodiments, the battery module may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0169] 5 and 6 show an example battery pack 1. Referring to FIG. 5 and FIG. 6, the battery pack 1 may include a battery housing and a plurality of battery modules 4 provided in the battery housing. The battery housing includes an upper housing 2 and a lower housing 3, and the upper housing 2 can be fitted over the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in any manner within the battery housing.

[0170] The present application further provides an electric device. The electric device includes at least one of the secondary batteries, battery modules, or battery packs provided in the present application. The secondary batteries, battery modules, or battery packs may be used as a power source for the electric device, or may be used as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., electric cars, hybrid electric cars, plug-in hybrid electric cars, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, satellites, energy storage systems, etc.

[0171] The electric device can be selected as a secondary battery, a battery module or a battery pack according to the needs of its use.

[0172] 7 shows an example of an electric device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack or a battery module can be adopted to meet the high power and high energy density needs of the secondary battery of the electric device.

[0173] Another example of the device may be a mobile phone, a tablet, a laptop, etc. Such devices are usually required to be thin and can use secondary batteries as a power source. EXAMPLES

[0174] The following is a description of the examples of the present application. The examples described below are illustrative and are used only to explain the present application, and should not be interpreted as limitations of the present application. If no specific techniques or conditions are shown in the examples, they are carried out according to the techniques or conditions described in the literature of the field or according to the product's instruction manual. If no manufacturer is specified, the reagents or equipment used are all conventional products available from the market.

[0175] 1. Preparation method Example 1 1) Preparation of core-shell structured polymers First-stage polymerization: 21 kg of deionized water having an electric conductivity of 2 μs / cm or less, 21 g of sodium perfluorooctanoate, and 71.4 g of a 5% potassium persulfate solution were added in that order to a reaction kettle, and the reaction kettle was closed. The kettle was repeatedly evacuated and refilled with nitrogen gas until the oxygen gas concentration in the reaction kettle became less than 100 ppm. Vinylidene fluoride monomer was fed into the reaction kettle so that the pressure in the kettle became 7.0 MPa, and the temperature in the kettle was raised to 80° C. to start the reaction. During the reaction process, vinylidene fluoride monomer was continuously fed so that the reaction pressure in the kettle was kept constant. Second-stage polymerization: 9 kg of the remaining deionized water (electrical conductivity of deionized water: 2 μs / cm or less), polyoxyethylene-4- Phenyl 60 g of ammonium ether sulfate, 1.5 kg of styrene monomer and 1.5 kg of acrylic acid monomer were placed in a stirring tank and stirred uniformly to obtain a preliminary mixed liquid. When the total amount of vinylidene fluoride monomer supplied reached 2.4 kg, the remaining 30.6 g of 5% potassium persulfate solution and 48.0 g of 5% ammonium persulfate solution were added, the reaction pressure was adjusted to 5.5 MPa, the temperature was raised to 90°C, and the preliminary mixed liquid was gradually added to the reaction kettle. The total addition time of the preliminary mixed liquid was 1.5 hours, and at the same time, the remaining 0.6 kg of vinylidene fluoride monomer was gradually supplied. The reaction was terminated when the pressure in the kettle dropped to 0.2 MPa. The mixture was cooled to room temperature and filtered to obtain an emulsion of vinylidene fluoride-acrylic acid-styrene copolymer with a core-shell structure having a Dv50 particle size of 400 nm.

[0176] 2) Preparation of water-based undercoat slurry An emulsion of a core-shell structured vinylidene fluoride-acrylic acid-styrene copolymer was prepared to a solid content of 25%. 2.25 kg of conductive carbon black powder was weighed out, and this and 9 kg of the emulsion of a core-shell structured vinylidene fluoride-acrylic acid-styrene copolymer were added in that order to a stirring tank. The stirring speed was set at 300 revolutions per minute and the stirring time was set at 10 minutes. The stirring speed was set at 2000 revolutions per minute and the stirring time was set at 120 minutes. 25.5 kg of deionized water was weighed out and added to the stirring tank, and the stirring speed was set to 2000 rpm and the stirring time to 120 minutes. The slurry was filtered through a 300 mesh filter to obtain an aqueous basecoat slurry.

[0177] 3) Preparation of the Water-Based Undercoat Layer The aqueous undercoat slurry was coated onto the surface of an aluminum foil current collector substrate using a gravure coater, and then dried to obtain an aqueous undercoat layer with a thickness of 2 um, that is, an aqueous undercoated current collector was obtained.

[0178] 4) Seat manufacturing The components for preparing the positive electrode film layer, lithium nickel cobalt manganese (NCM) material, conductive carbon black, polyvinylidene fluoride binder, and N-methylpyrrolidone (NMP) were uniformly stirred and mixed in a weight ratio of 96.9:2.1:1:21 to obtain a positive electrode slurry, the solid content of which was 73%. The positive electrode slurry was then uniformly coated on the aqueous undercoated current collector, and the positive electrode sheet was obtained after drying, cold rolling, and slitting.

[0179] 5) Manufacturing of negative electrode sheets The active material, artificial graphite, the conductive agent, carbon black, the binder, styrene butadiene rubber (SBR), and the thickener, sodium carboxymethyl cellulose (CMC), were dissolved in deionized water as a solvent in a weight ratio of 96.2:0.8:0.8:1.2 and mixed uniformly to prepare anode slurry. The anode slurry was then uniformly coated once or multiple times on the anode current collector, copper foil, and the anode sheet was obtained after drying, cold rolling, and slitting.

[0180] 6) Separator A polypropylene film was used as the separator.

[0181] 7) Preparation of electrolyte Argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1 ppm), the organic solvents ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3 / 7, and 12.5% ​​LiPF 6The lithium salt was added to and dissolved in the organic solvent, and the mixture was stirred uniformly to obtain the electrolyte solution of Example 1.

[0182] 8) Battery manufacturing The positive electrode sheet, separator, and negative electrode sheet were stacked in order so that the separator was positioned between the positive electrode sheet and the negative electrode sheet to play the role of isolation, and then wound to obtain a bare cell, a tab was welded to the obtained bare cell, the bare cell was placed in an aluminum case, baked at 80°C to remove moisture, an electrolyte was poured in, and the case was sealed to obtain an uncharged battery. Next, the uncharged battery was left to stand, hot and cold rolled, chemically formed, shaped, capacity measured, etc., to obtain the lithium ion battery product of Example 1.

[0183] Examples 2 to 9 The preparation method was almost the same as that of Example 1, except that the mass contents of the core and shell parts and the ratio of each monomer in the synthesis of the core-shell structure polymer were adjusted. The specific parameters are shown in Tables 1 and 2.

[0184] Examples 10 to 13 The preparation method was almost the same as that in Example 1, but the difference was that the core-shell structure polymer had different weight average molecular weights by adjusting the initiator mass and reaction temperature in the synthesis of the core-shell structure polymer, and the specific parameters are shown in Tables 1 and 2.

[0185] Example 10 The preparation method was almost the same as that of Example 1, except that the amount of potassium persulfate solution with a concentration of 5% in the first stage polymerization was adjusted to 85.32g. The specific parameters are shown in Tables 1 and 2.

[0186] Example 11 The preparation method was almost the same as that of Example 1, except that the amount of potassium persulfate solution with a concentration of 5% in the first stage polymerization was adjusted to 78.54g. The specific parameters are shown in Tables 1 and 2.

[0187] Example 12 The preparation method was almost the same as that of Example 1, except that the amount of potassium persulfate solution with a concentration of 5% in the first-stage polymerization was adjusted to 64.26g, and the reaction temperature in the first-stage polymerization was adjusted to 75°C. The specific parameters are shown in Tables 1 and 2.

[0188] Example 13 The preparation method was almost the same as that of Example 1, except that the amount of potassium persulfate solution with a concentration of 5% in the first-stage polymerization was adjusted to 60g, and the reaction temperature in the first-stage polymerization was adjusted to 75°C. The specific parameters are shown in Tables 1 and 2.

[0189] Examples 14 to 17 The preparation method was almost the same as that of Example 1, except that the mass ratio of the conductive agent and the binder in the aqueous undercoat slurry was adjusted. The specific parameters are shown in Tables 1 and 2.

[0190] Examples 18 to 21 The preparation method was almost the same as that of Example 1, except that the solid content of the aqueous undercoat slurry was adjusted. The specific parameters are shown in Tables 1 and 2.

[0191] Example 22 to Example 23 The preparation method was almost the same as that of Example 1, except that the thickness of the aqueous undercoat layer was adjusted. The specific parameters are shown in Tables 1 and 2.

[0192] Example 24 The preparation method was almost the same as that of Example 1, except that the acrylic acid monomer was replaced with methacrylic acid monomer. The specific parameters are shown in Tables 1 and 2.

[0193] Example 25 The procedure was almost the same as in Example 1, except that the aqueous undercoat layer was prepared in the following manner. The aqueous undercoat slurry was coated onto the surface of the aluminum foil current collector substrate by using doctor blade technology, and after drying, an aqueous undercoat layer with a thickness of 2 microns was formed to obtain an aqueous undercoated current collector, the specific parameters of which are shown in Tables 1 and 2.

[0194] Examples 26-27 Examples 26 to 27 were almost the same as Example 1, except that the thickness of the water-based undercoat layer was adjusted. The specific parameters are shown in Tables 1 and 2.

[0195] Comparative Example 1 The preparation method was almost the same as that of Example 1, but was different in that the binder in the conductive slurry was polyvinylidene fluoride having a weight average molecular weight of 400,000.

[0196] Comparative Example 2 The preparation method was almost the same as that of Example 1, except that the amount of styrene monomer in the second stage polymerization was adjusted from 1.5 kg to 3 kg.

[0197] Comparative Example 3 The preparation method was almost the same as that of Example 1, except that in the second stage polymerization, 1.5 kg of styrene monomer and 1.5 kg of acrylic acid monomer were used to prepare 3 kg of acrylic acid monomer.

[0198] Comparative Example 4 The preparation method was almost the same as in Example 1. ,Ko The difference was that the ashel structure vinylidene fluoride-acrylic acid-styrene copolymer emulsion was replaced with the vinylidene fluoride-acrylic acid-styrene copolymer emulsion prepared by the traditional method. The synthesis method was as follows: 30 kg of deionized water (electrical conductivity: 2 μs / cm or less), 21 g of sodium perfluorooctanoate, and 150 g of 5% potassium persulfate solution were placed in the reaction kettle in that order, and the reaction kettle was closed. The kettle is evacuated and filled with nitrogen gas, and the oxygen gas concentration in the reaction kettle is repeatedly reduced to less than 100 ppm. Vinylidene fluoride monomer, 1.5 kg of styrene monomer, and 1.5 kg of acrylic acid monomer were fed into the reaction kettle so that the pressure in the kettle became 7.5 MPa. The temperature in the kettle is raised to 85°C to start the reaction. During the reaction, vinylidene fluoride monomer is continuously fed to maintain the reaction pressure in the kettle constant. The total mass of vinylidene fluoride monomer fed is 3 kg. The pressure in the kettle at the end of the reaction was reduced to 0.2 MPa, and the unreacted vinylidene fluoride monomer was recovered, cooled to room temperature, and filtered to obtain an emulsion, that is, a vinylidene fluoride-acrylic acid-styrene copolymer emulsion.

[0199] 2.Measurement method 1. Core-shell structure polymer weight average molecular weight The emulsion containing the core-shell polymer was vacuum dried at 120° C. for 180 minutes to obtain a core-shell polymer powder. A Waters 2695 Isocratic HPLC type gel chromatography (differential refractive index detector 2141) was employed. A styrene solution sample with a mass fraction of 3.0% was used as a reference, and a matching chromatography column (oil-based: Styragel HT5DMF7.8×300 mm+Styragel HT4) was selected. A 3.0% core-shell structure polymer solution was formulated using purified N-methylpyrrolidone (NMP) solvent, and the formulated solution was left to stand for one day to prepare. During the measurement, first, tetrahydrofuran was aspirated into the syringe and rinsed multiple times. Then, 5 ml of the sample solution was aspirated, the air in the syringe was expelled, and the needle tip was dried. Finally, the sample solution was gradually injected into the sample injection port. After the display number stabilized, the data was acquired and the weight average molecular weight was read.

[0200] 2. Dv50 particle size measurement of core-shell structure polymer Refer to GB / T 19077-2016 Particle size distribution laser diffraction method, weigh 0.1g-0.13g of core-shell structure polymer emulsion into a 50ml beaker, and weigh 5g of deionized water and add it to the beaker containing the core-shell structure polymer emulsion, put in a stirrer with a length of about 2.5mm, and seal with plastic wrap. The sample was put into an ultrasonic machine and ultrasonicated for 5 minutes, then transferred to a magnetic stirrer and stirred at a speed of 500 rpm for more than 20 minutes, and two samples were selected for each batch of products to be measured. Measured with a laser particle size analyzer, for example, Mastersizer 2000 E type laser particle size analyzer from Marvin Instruments Co., Ltd. in the UK.

[0201] 3. Viscosity measurement of water-based undercoat slurry The viscosity of the water-based undercoat slurry was measured with a rotational viscometer. Select a suitable rotor, fix the rotor of the viscometer, and place the water-based undercoat slurry under the viscometer rotor so that the slurry just submerges the scale line. The instrument number is Shanghai Fangrui NDJ-5S, rotor: 62#, rotational viscosity: 30 rpm, measurable viscosity range of the slurry: 0~1000mPa·s, rotor: 63#, rotation speed: 30 rpm, measurable viscosity range of the slurry: 0~2000mPa·s, measurement temperature: 25℃, measurement time: 5 minutes, and read the data after the display number stabilizes.

[0202] 4. Water-based undercoat slurry filtration performance test Put a 500ml beaker on the bottom of the 200 mesh filter bracket, take 500ml of water-based undercoat slurry, put it into the filter and filter, record the time when the volume of the slurry in the beaker reaches 300ml, this time is used to judge the filtration performance of the slurry, if the filtration time is less than 10s, it indicates that the filtration performance of the slurry is good, it is judged as "YES" and recorded as "Y", if the filtration time of the slurry is more than 10s or it cannot pass through the filter, it indicates that the filtration performance of the slurry is poor, it is judged as "NG" and recorded as "N".

[0203] 5. Difference in solid content of water-based undercoat slurry after standing for 24 hours A small sheet was taken and weighed in the weight loss meter, recorded as M0, and reset to zero. The upper layer aqueous undercoat slurry was taken and a small amount was coated on a sheet, and then the coating was placed in a weight loss measuring device to measure the weight, which was designated as M1. The equipment was closed and drying commenced. Upon completion, the nominal weight data was recorded and recorded as M2, and the solids content was calculated, which was (M2-M0) / (M1-M0). The solids content of the lower layer water-based undercoat slurry was measured using the same method, and the solids content of the upper layer water-based undercoat slurry was subtracted from the solids content of the lower layer water-based undercoat slurry to obtain the difference in solids content of the water-based undercoat slurry after being allowed to stand for 24 hours.

[0204] 6. Adhesive strength of the sheet The adhesive strength measurement process of the present embodiment and comparative examples was as follows, referring to GB-T2790-1995 Chinese national standard "Test method for 180° peel strength of adhesive". That is, a blade was used to cut out a sample with a width of 30 mm and a length of 100 to 160 mm, and a special double-sided tape was attached to a steel plate, with the tape width being 20 mm and the length being 90 to 150 mm. The positive electrode membrane layer surface of the cut-out sheet sample was attached to the double-sided tape, and then rolled three times in the same direction with a 2 kg press roller. A tape with the same width as the sheet and a length of 250 mm was fixed to the sheet current collector, and was fixed with crepe tape. The power supply (sensitivity: 1N) of the Sansi take-off machine was turned on, the lamp was turned on, the stopper was adjusted to an appropriate position, and the end of the steel plate on which the sheet was not attached was fixed with the lower jig. The paper tape was folded up and fixed with the upper jig, and the position of the upper jig was adjusted with the "up" and "down" buttons of the manual operation device attached to the take-off machine. The force when the sheet was in balance was divided by the width of the tape to obtain the adhesive force per unit length of the sheet, which represented the adhesive strength between the material layer on the current collector and the current collector.

[0205] 7. Sheet resistance After drying, the positive electrode sheet was cut into the left, center, and right of the sheet, and cut into a round sheet with a diameter of 10 mm. Turn on the Yuan Neng Technology film resistance meter, place the film resistance meter probe in the appropriate position, click the "Start" button, and read out after the displayed number stabilizes. Two points were measured for each round sheet, and the average of the last six measured values ​​was calculated to obtain the film layer resistance of the sheet.

[0206] 8, Battery DC blocking The measurement process of the battery DC resistance was as follows: The battery corresponding to Example 1 was cut to 1 / 3 at 25°C. * The battery was charged to 4.3 V at a constant current of 0.05 C, and then charged to a constant voltage of 4.3 V at a current of 0.05 C. After 5 minutes, the voltage V1 was recorded. Then, the battery was discharged at 1 / 3 C for 30 seconds, and the voltage V2 was recorded. * The internal resistance of the battery, DCR, was obtained as (V2-V1) / C.

[0207] 9. Thickness of water-based primer layer A sheet of aluminum foil was placed on a flat table so that its width exceeded the width of the table by 5 cm, and the aluminum foil on the table was pressed down to prevent the aluminum foil from moving. I opened the scale and reset the display to zero. Five points were selected at different locations on the aluminum foil, and the thickness of the aluminum foil was measured in sequence, and the average value was taken and recorded as L1. After using a gravure coater to coat one side of an aluminum foil with the aqueous undercoat slurry and drying, take the dried aluminum foil and place it on a flat table, so that the width of the aluminum foil is more than 5 cm than the table, and press the aluminum foil on the table to prevent the aluminum foil from moving. I opened the scale and reset the display to zero. Five points were selected at different locations on the aluminum foil, and the thickness of the aluminum foil was measured in sequence, and the average value was taken and recorded as L2. The water-based subbing layer thickness was (L2-L1).

[0208] 3. Analysis of Measurement Results of Examples and Comparative Examples According to the above-mentioned methods, the aqueous undercoat slurry, the aqueous undercoat layer and the positive electrode sheet of each of the examples and comparative examples were prepared, and each parameter was measured. The results are shown in Tables 1 and 2 below.

[0209] Table 1. Preparation parameters and results for the examples and comparative examples [Table 1-1] [Table 1-2] [Table 1-3] [Table 1-4] [Table 1-5]

[0210] Table 2. Preparation parameters and results for the examples and comparative examples [Table 2-1] [Table 2-2] [Table 2-3] [Table 2-4]

[0211] As can be seen from the results of Tables 1 and 2, the binders in the aqueous undercoat slurries of Examples 1 to 27 are all core-shell structure polymers including a core and a shell covering at least a part of the core, the core including a vinylidene fluoride-derived structural unit, and the shell including a vinylidene fluoride-derived structural unit, an acrylic acid or methacrylic acid-derived structural unit, and a styrene-derived structural unit. When the core-shell structure vinylidene fluoride-acrylic acid-styrene copolymer or the core-shell structure vinylidene fluoride-methacrylic acid-styrene copolymer is used as a binder, good effects are obtained in all cases. Compared with the traditional polyvinylidene fluoride binder of Comparative Example 1, the core-shell structure vinylidene fluoride-acrylic acid-styrene copolymer or the core-shell structure vinylidene fluoride-methacrylic acid-styrene copolymer binder provided in the present application can reduce the viscosity of the aqueous undercoat slurry, increase the filterability of the aqueous undercoat slurry, and improve the processability of the aqueous undercoat slurry.

[0212] The vinylidene fluoride-styrene copolymer and the vinylidene fluoride-acrylic acid copolymer of Example 1, Comparative Example 2, and Comparative Example 3 As can be seen from the comparison with The core-shell structured vinylidene fluoride-acrylic acid-styrene copolymer disclosed in the present application achieves both the settling resistance of the slurry and the adhesion of the sheet, thereby comprehensively improving the storage performance and usage performance of the water-based undercoat slurry.

[0213] As can be seen from the comparison between Example 1 and Comparative Example 4, compared with the non-core-shell structure polymer prepared by the traditional preparation method, the core-shell structure polymer disclosed in the present application can reduce the viscosity of the slurry, improve the filterability of the slurry, increase the adhesion of the sheet, and reduce the membrane resistance of the sheet, thereby comprehensively improving the processing performance and use performance of the water-based undercoat slurry.

[0214] As can be seen from the comparison between Examples 1 to 3 and Examples 4 to 5, when the mass content of the core portion is 40% to 50% based on the total mass of the core-shell structure polymer, the core-shell structure polymer can achieve both the viscosity of the slurry and the adhesiveness of the sheet, and can comprehensively improve the processing performance and usage performance of the aqueous undercoat slurry.

[0215] As can be seen from the comparison between Example 1, Examples 6-7 and Examples 8-9, when the mass content of the structural units derived from acrylic acid in the core-shell structure polymer is 10% to 40% based on the mass of the core-shell structure polymer, the core-shell structure polymer can achieve both the viscosity of the aqueous undercoat slurry and the adhesive strength of the sheet, and can comprehensively improve the processing performance and use performance of the aqueous undercoat slurry.

[0216] As can be seen from the comparison between Example 1, Examples 4-5 and Examples 6-7, when the mass content of the styrene-derived structural unit in the core-shell structure polymer is 10% to 40% based on the mass of the core-shell structure polymer, the core-shell structure polymerization can achieve both the adhesive strength and the film resistance of the sheet, and can comprehensively improve the adhesive performance and dynamic performance of the sheet.

[0217] As can be seen from the comparison of Examples 1, 11 and 12 with Examples 10 and 13, when the weight average molecular weight of the core-shell structure polymer is 300,000 to 500,000, the core-shell structure polymerization can achieve both the adhesive strength and the film resistance of the sheet, and can comprehensively improve the adhesive performance and dynamic performance of the sheet.

[0218] The aqueous undercoat slurries in Examples 1 to 27 all contained a core-shell structured polymer, a conductive agent, and water, and among them, the core-shell structured polymer was added to the aqueous coating layer slurry as an emulsion.

[0219] As can be seen from a comparison of Examples 1, 15 and 16 with Examples 14 and 17, when the mass ratio of the conductive agent to the core-shell structure binder in the aqueous undercoat slurry was 0.8:1 to 1:1, the adhesive strength and film resistance of the slurry sheet were both achieved, and the adhesive performance and dynamic performance of the sheet were comprehensively improved.

[0220] As can be seen from a comparison of Examples 1, 19 and 20 with Examples 18 and 21, when the solid content of the water-based undercoat slurry is 10% to 20%, the water-based undercoat slurry can achieve both the shipping viscosity and the adhesive strength of the sheet, and the processing performance and use performance of the slurry can be improved comprehensively.

[0221] As can be seen from Examples 1 to 17, Examples 19 to 20, and Examples 22 to 24, when the solid content of the aqueous undercoat slurry is 10% to 20%, the viscosity of the aqueous undercoat slurry is 300 mPa.s to 900 mPa.s, and the aqueous coating layer slurry prepared using the core-shell structure binder does not require the addition of a separate dispersant or thickener to improve processing performance, which contributes to improving productivity and optimizing the production process.

[0222] The preparation methods of the water-based undercoat layers in Examples 1 to 24 all included the following steps.

[0223] A step of coating the prepared undercoat slurry on the current collector surface using a gravure coater.

[0224] A step of drying to obtain an aqueous undercoat layer, the thickness of the aqueous undercoat layer being 1 um to 3 um.

[0225] As can be seen from a comparison between Example 1 and Example 25, when the aqueous undercoat layer prepared by the preparation method disclosed in the present application was used, the adhesive strength of the sheet was increased and the film resistance of the sheet was reduced.

[0226] As can be seen from the comparison between Examples 1, 22-23 and Examples 26-27, when the coating thickness of the aqueous undercoat layer is 1um-3um, the film resistance of the sheet is reduced, and the sheet has good adhesion, thereby improving the dynamic performance of the battery.

[0227] The present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is merely an example, and any embodiment having substantially the same configuration as the technical idea and having the same effect within the scope of the technical proposal of the present application is included in the technical scope of the present application. In addition, various modifications conceived by a person skilled in the art to the embodiment and other forms constructed by combining some of the components in the embodiment are also included in the scope of the present application, as long as they do not deviate from the gist of the present application.

Claims

1. A core-shell structure polymer having a core portion and a shell portion covering at least a part of the core portion, wherein the core portion contains structural units derived from a monomer shown in formula I, and the shell portion contains structural units derived from a monomer shown in formula I, structural units derived from a monomer shown in formula II, and structural units derived from a monomer shown in formula III, and the mass content of structural units derived from the monomer shown in formula II is 20% to 40% based on the mass of the core-shell structure polymer. 【Chemistry 1】 (Here, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C1-3 alkyl groups containing at least one fluorine atom; R4, R5, R6, R7, R8, and R9 are each independently selected from hydrogen, substituted or unsubstituted C1-5 alkyl groups; and Ar is a substituted or unsubstituted aromatic group.)

2. The core-shell structure polymer according to claim 1, characterized in that R1 is fluorine, R2 and R3 are each independently selected from hydrogen, fluorine, chlorine, or trifluoromethyl, and R4, R5, R6, R7, R8, and R9 are each independently selected from hydrogen or methyl.

3. The core-shell structure polymer according to claim 1, characterized in that the mass content of the core portion is 40% to 50% based on the mass of the core-shell structure polymer.

4. The core-shell structure polymer according to claim 1, characterized in that, based on the mass of the core-shell structure polymer, the mass content of structural units derived from the monomer shown in formula II is 20% to 30%.

5. The core-shell structure polymer according to claim 1, characterized in that, based on the mass of the core-shell structure polymer, the mass content of structural units derived from the monomer shown in formula III is 10% to 40%.

6. The core-shell structure polymer according to claim 1, characterized in that the weight-average molecular weight of the core-shell structure polymer is 300,000 to 500,000.

7. The core-shell structure polymer according to claim 1, characterized in that the monomer shown in formula I is one or more selected from vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene.

8. The core-shell structure polymer according to claim 1, characterized in that the monomer shown in formula II is one or two selected from acrylic acid and methacrylic acid.

9. The core-shell structure polymer according to claim 1, characterized in that the monomer shown in formula III is one or two selected from styrene and 4-methylstyrene.

10. The core-shell structure polymer according to claim 1, characterized in that the Dv50 particle size is 100 nm to 10 μm.

11. A method for preparing a core-shell structure polymer, comprising the steps of: preparing a core portion of the core-shell structure polymer by polymerizing a monomer shown in formula I under polymerizable conditions; and preparing a shell portion of the core-shell structure polymer that covers at least a part of the core portion by polymerizing the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III. A method for preparing a core-shell structure polymer, characterized in that the mass content of the monomer shown in formula II is 20% to 40%, based on the total mass of the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III. 【Chemistry 2】 (Here, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, and one or more C1-3 alkyl groups containing at least one fluorine atom; R4, R5, R6, R7, R8, and R9 are each independently selected from hydrogen, substituted or unsubstituted C1-5 alkyl groups; and Ar is a substituted or unsubstituted aromatic group.)

12. The method for preparing a core-shell structure polymer according to claim 11, characterized in that R1 is fluorine, R2 and R3 are each independently selected from hydrogen, fluorine, chlorine, and trifluoromethyl, one or more of them, and R4, R5, R6, R7, R8, and R9 are each independently selected from hydrogen and methyl, one or two of them.

13. The method for preparing a core-shell structure polymer according to claim 11, characterized in that the mass content of the core portion is 40% to 50% based on the mass of the core-shell structure polymer.

14. A method for preparing a core-shell structure polymer according to claim 11, characterized in that the mass content of the monomer shown in formula II is 20% to 30%, based on the total mass of the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III.

15. A method for preparing a core-shell structure polymer according to claim 11, characterized in that the mass content of the monomer shown in formula III is 10% to 40%, based on the total mass of the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III.

16. The method for preparing a core-shell structure polymer according to claim 11, characterized in that the preparation method comprises a first step of polymerization and a second step of polymerization. Polymerization in the first stage: A polymerization is carried out by providing an initiator, a first emulsifier, at least one monomer represented by formula I, and an aqueous medium, and a first stage polymerization reaction is performed to obtain a core, and during the process of the first stage polymerization reaction, the monomer represented by formula I is continuously supplied. Second stage polymerization: After a certain period of time, an initiator, a second emulsifier, at least one monomer represented by formula II and a monomer represented by formula III, and an aqueous medium are added to the reaction vessel to carry out the second stage polymerization reaction to obtain a core-shell structure polymer, and during the process of the second stage polymerization reaction, monomers represented by formula I are continuously supplied.

17. The second step of polymerization involves adding an initiator to a reaction vessel, followed by the addition of a preliminary mixture containing a second emulsifier, at least one monomer represented by formula II, a monomer represented by formula III, and an aqueous medium. A method for preparing a core-shell structure polymer according to feature 16.

18. The method for preparing a core-shell structure polymer according to claim 16, characterized in that the mass of the monomer represented by formula I supplied to the first step of polymerization is 70% to 85% of the total mass of the monomer represented by formula I supplied to the polymerization reaction, and the mass of the monomer represented by formula I supplied to the second step of polymerization is 15% to 30% of the total mass of the monomer represented by formula I supplied to the polymerization reaction.

19. A method for preparing a core-shell structure polymer according to claim 16, characterized in that the initiator provided for the first step of polymerization and the initiator provided for the second step of polymerization are both persulfates, and based on the total mass of the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III, the mass percentage of the initiator provided for the first step of polymerization is 0.05% to 0.075%, and the mass percentage of the initiator provided for the second step of polymerization is 0.05% to 0.075%.

20. A method for preparing a core-shell structure polymer according to claim 16, characterized in that the mass percentage of the first emulsifier is 0.28% to 0.42% based on the total mass of the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III.

21. A method for preparing a core-shell structure polymer according to claim 16, characterized in that the mass percentage of the second emulsifier is 0.8% to 1.2% based on the total mass of the monomer shown in formula I, the monomer shown in formula II, and the monomer shown in formula III.

22. A method for preparing a core-shell structure polymer according to claim 16, characterized in that, based on the total mass of the monomers shown in formula I, formula II, and formula III, the mass percentage of the aqueous medium provided for the first step of polymerization is 200% to 500%, and the mass percentage of the aqueous medium provided for the second step of polymerization is 100% to 200%.

23. The method for preparing a core-shell structure polymer according to claim 16, characterized in that the polymerization in the first step is carried out at a reaction pressure of 5.5 MPa to 7.5 MPa and a reaction temperature of 75°C to 85°C.

24. The preparation method according to claim 16, characterized in that the polymerization in the second step is carried out at a reaction pressure of 4.5 MPa to 6.5 MPa and a reaction temperature of 86°C to 95°C.

25. The method for preparing a core-shell structure polymer according to claim 16, characterized in that the initiator is one or two selected from potassium persulfate and ammonium persulfate.

26. A method for preparing a core-shell structure polymer according to claim 16, characterized in that the first emulsifier is an alkali metal perfluorooctanoate.

27. The method for preparing a core-shell structure polymer according to claim 16, characterized in that the second emulsifier is one or two of polyoxyethylene-4-phenyl ether ammonium sulfate and nonylphenol polyoxyethylene ether ammonium sulfate.

28. A polymer emulsion characterized by containing the core-shell structure polymer described in claim 1.

29. Use of the core-shell structure polymer according to claim 1 in a secondary battery.

30. An aqueous primer slurry comprising a binder, a conductive agent, and an aqueous medium, wherein the binder comprises the core-shell structure polymer described in claim 1.

31. The aqueous primer slurry according to claim 30, characterized in that the core-shell structure polymer is added to the aqueous primer slurry as an emulsion containing the core-shell structure polymer.

32. The aqueous primer slurry according to claim 30 or 31, characterized in that the mass ratio of the conductive agent to the binder is 0.8:1 to 1:

1.

33. The aqueous primer slurry according to claim 30, characterized in that when the solid content of the aqueous primer slurry is 10% to 20%, the viscosity of the aqueous primer slurry is 300 mPa·s to 900 mPa·s.

34. The steps include coating the surface of the current collector with the aqueous primer slurry described in claim 30 using a gravure coater, A step of drying to obtain a water-based primer layer, wherein the thickness of the water-based primer layer is 1 μm to 3 μm, A method for preparing an aqueous primer layer, characterized by containing the following:

35. A secondary battery comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet and / or the negative electrode sheet include an aqueous primer layer prepared by the preparation method described in claim 34.

36. The secondary battery according to claim 35, characterized in that the secondary battery includes at least one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, and a potassium-ion battery.

37. A battery module characterized by including the secondary battery described in claim 35.

38. A battery pack characterized by including the secondary battery described in claim 35.

39. An electrical device comprising at least one selected from the secondary battery described in claim 35 or 36, the battery module described in claim 37, and the battery pack described in claim 38.

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