WO2024145893A1

WO2024145893A1 - Separator and preparation method therefor, battery, and electrical apparatus

Info

Publication number: WO2024145893A1
Application number: PCT/CN2023/070857
Authority: WO
Inventors: 吉星; 钟华; 李婷; 郭满毅; 胡海
Original assignee: 宁德时代新能源科技股份有限公司
Filing date: 2023-01-06
Publication date: 2024-07-11

Abstract

The present application discloses a separator and a preparation method therefor, a battery, and an electrical apparatus. The separator of the present application comprises a base film and a coating provided on at least one surface of the base film; the coating contains polymer particles, and the number of branched carbons of a polymer contained in the polymer particles is 1-10. According to the embodiments of the present application, the separator contains the coating, and therefore has good air permeability, thereby improving the air permeability and working stability of the separator; moreover, the separator has overheating melting properties, thereby improving the electrochemical performance and safety of batteries. The preparation method can ensure the performance stability of a separator structure and the like. A battery contains the separator of the present application.

Description

Diaphragm and preparation method thereof, battery and electrical device

Technical Field

The present application relates to the field of battery technology, and in particular to a diaphragm and a preparation method thereof, a battery and an electrical device.

Background technique

In the context of energy conservation and emission reduction, new energy technologies are developing rapidly, among which the research breakthroughs and applications of battery technology are the most significant, and lithium-ion batteries are the batteries with the most prominent development momentum.

As battery applications become more and more extensive, especially in recent years with the rapid development of electric vehicles, power batteries have developed rapidly and the demand has increased dramatically. However, the safety performance of batteries has also received more and more attention, and the safety performance of batteries has become one of the important factors restricting the expansion of battery applications.

Among the safety issues of batteries, the most prominent one is the runaway of the exothermic reaction inside the battery. Although the existing safety modified diaphragms can improve the safety of the diaphragm's response to thermal runaway to a certain extent, it also leads to the relatively poor pressure resistance of the safety modified diaphragm when it is subjected to external pressure during battery production or normal operation, which affects the permeability of the diaphragm, thereby reducing the permeability of the electrolyte, resulting in affecting the electrochemical performance of the battery during production and normal operation.

Summary of the invention

In view of the above problems, the embodiments of the present application provide a diaphragm and a preparation method and application thereof to solve the technical problem of poor pressure resistance of existing safety modified diaphragms.

In a first aspect, an embodiment of the present application provides a separator, which comprises a base film and a coating disposed on at least one surface of the base film, wherein the coating contains polymer particles, and the number of carbon atoms in the branched chain of the polymer contained in the polymer particles is 1 to 10.

The coating in the diaphragm of the embodiment of the present application contains polymer particles in the range of branched carbon numbers, which gives the coating higher mechanical properties such as compression resistance on the basis of good air permeability, and can maintain good air permeability of the diaphragm under pressure, thereby maintaining the permeability of the diaphragm to the electrolyte and the stability of operation, thereby ensuring the stable electrochemical performance of the battery. Moreover, when the battery is abnormally heated to its melting point, the polymer particles in the range of branched carbon numbers can melt, thereby closing the pores contained in the base film, preventing or reducing chemical reactions inside the battery, including positive and negative electrode crosstalk reactions, thereby reducing the risk of thermal runaway of the battery and improving the safety performance of the battery.

In some embodiments, the polymer satisfies at least one of the following conditions (1) to (3):

(1) The weight average molecular weight of the polymer is 1500 to 5000, and can be optionally 1500 to 2500.

(2) the polydispersity index (PDI) of the polymer is 3 to 11, and can be 3 to 6;

(3) The carbon number of the branched chain of the polymer is 1 to 5.

By further adjusting and selecting the polymer molecular weight, PDI, and branched carbon number, etc., the mechanical properties of the above-mentioned polymer particles, including compression resistance, can be further improved, and the mechanical properties of the coating, including compression resistance, can be improved, thereby improving the electrolyte permeability and working stability of the diaphragm when it is subjected to pressure during battery production and normal operation, and at the same time improving the hot melt response rate of the diaphragm when thermal anomalies occur in the battery.

In some embodiments, the polymer particles contain nonionic groups, and in the exemplary embodiments, the nonionic groups include at least one of ethoxy, hydroxyl, and carboxylate groups. The material of the polymer particles contains nonionic groups, specifically such types of nonionic groups, which can further improve the above-mentioned mechanical properties of the polymer particles such as compression resistance on the basis of improving the hydrophilicity and dispersibility of the polymer to improve the coating quality and mechanical properties such as compression resistance, thereby improving the air permeability and working stability of the diaphragm when under pressure.

In some embodiments, the content of the polymer particles in the coating is ≥22wt%, and can be 22wt% to 37wt%, based on the total dry weight of the coating as 100%. By controlling and adjusting the content of the polymer particles in the coating, the mechanical properties of the coating such as compression resistance can be improved, thereby improving the mechanical properties of the membrane such as compression resistance and the working stability, and at the same time, the melting response rate of the membrane when abnormally heated can be increased, and the effect of the molten polymer particles in sealing the pores of the base membrane can be improved.

In some embodiments, the polymer particles satisfy at least one of the following conditions (1) to (4):

(1) The volume distribution particle size D _v 50 of the polymer particles is 0.1 μm to 5 μm;

(2) The melting point of the polymer particles is 100°C to 110°C;

(3) The polymer particles are in at least one of the following shapes: chain, spherical, quasi-spherical, fibrous, tubular, rod-shaped, amorphous, and pyramidal;

(4) The polymer includes at least one of polystyrene, polyethylene, polyimide, melamine resin, phenol resin, cellulose, cellulose modifier, polypropylene, polyester, polyphenylene sulfide, polyaramid, polyamideimide, polyimide, and a copolymer of butyl acrylate and ethyl methacrylate.

The polymer particles have any of the above characteristics and can improve the mechanical properties of the coating, such as air permeability and compression resistance, thereby improving the air permeability and working stability of the diaphragm, while further reducing the risk of thermal runaway of the battery and improving the electrochemical properties and safety performance of the battery, such as capacity retention rate.

In some embodiments, the coating further comprises inorganic particle fillers. The presence of inorganic particle fillers can further improve the air permeability and mechanical properties such as pressure resistance of the coating, thereby improving the air permeability and working stability of the diaphragm.

In some embodiments, the inorganic particle filler satisfies at least one of the following conditions:

Based on the total dry weight of the coating as 100%, the content of the inorganic particle filler in the coating is 18wt% to 22wt%;

The volume distribution particle size D _v 50 of the inorganic particle filler is 1 to 1.5 μm;

The inorganic particle filler includes at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reaction.

The inorganic particle filler has any of the above characteristics, and can further improve the air permeability and mechanical properties such as pressure resistance of the coating, thereby improving the air permeability and working stability of the diaphragm.

In some embodiments, the coating layer further comprises a solidified aqueous binder. By adding an aqueous binder to the coating layer, the mechanical strength of the membrane can be improved, and the air permeability and working stability of the membrane can be adjusted.

In the embodiment, the aqueous binder satisfies at least one of the following conditions:

The cured aqueous binder has a dry weight content of 18 wt % to 27 wt % in the coating;

The thermal decomposition temperature of the aqueous binder is higher than 160°C.

The aqueous binder has any of the above characteristics, can enhance the mechanical strength of the diaphragm, and further adjust the working stability of the diaphragm.

In some embodiments, the coating has a thickness of 2 μm to 5 μm.

By controlling the coating thickness, the coating, that is, the membrane's mechanical properties such as air permeability and compressive resistance can be improved, thereby improving the battery's electrochemical performance and reducing or preventing the risk of thermal battery runaway.

In some embodiments, the base film satisfies at least one of the following conditions:

The thickness of the base film is 4 μm to 7 μm;

The air permeability of the separator is 180s/100cc to 240s/100cc.

The base film with these characteristics can fully exert the role of the battery separator and improve the mechanical properties such as compression resistance and working stability of the separator.

In a second aspect, an embodiment of the present application provides a method for preparing a diaphragm. The method for preparing a diaphragm in an embodiment of the present application comprises the following steps:

Providing a base film and a coating slurry containing polymer particles; the polymer particles contain a polymer having a branched carbon number of 1 to 10;

The coating slurry is coated on at least one surface of the base film, and dried to form a coating to obtain a separator.

The diaphragm prepared by the diaphragm preparation method of the embodiment of the present application has the mechanical properties such as high compressive resistance and good air permeability as the diaphragm of the embodiment of the text application above, and can effectively reduce the risk of thermal runaway of the battery and improve the electrochemical performance and safety of the battery.

In some embodiments, the coating slurry is formed by mixing polymer particles, inorganic particle fillers and aqueous binders in a solvent; wherein the mass ratio of the polymer particles, inorganic particle fillers and aqueous binders in the coating slurry is (22 to 37):18 to 22):(18 to 27).

In some embodiments, the solid content of the coating slurry is 30 wt % to 40 wt %.

In some embodiments, the coating slurry has a viscosity of 100 mPa·s to 1000 mPa·s at 25°C.

The coating slurry having the above characteristics can improve the film-forming quality, and improve the quality of the coating as well as the air permeability, pressure resistance and other properties.

In some embodiments, when the polymer particles are polymer particles containing nonionic groups, the polymer particles are prepared by a method comprising the following steps:

The polymer precursor particles, the ethoxy-containing polymer and the initiator are mixed and reacted to obtain polymer particles containing nonionic groups;

The polymer particles containing nonionic groups are emulsified with a nonionic surfactant to obtain a nonionic polymer emulsion.

By using ethoxylated polymers to carry out polymerization reactions with polymer precursor particles, the non-ionic groups contained in the polymer particles can be increased, especially the mechanical properties of the polymer particles such as compression resistance can be improved, while the dispersibility of the polymer particles in the coating slurry can be improved, thereby improving the film-forming quality and mechanical properties such as compression resistance of the coating slurry, thereby improving the mechanical properties of the diaphragm and the stability of its operation.

In some embodiments, the polymer precursor particles, the ethoxy-containing polymer, and the initiator are mixed in a ratio of (300 to 400):(90 to 125):(20 to 50).

In some embodiments, the material of the polymer precursor particles includes at least one of polystyrene, polyolefin, polyimide, melamine resin, phenol resin, cellulose, polyester, polyphenylene sulfide, polyaromatic amide, polyamideimide, and a copolymer of butyl acrylate and ethyl methacrylate.

In some embodiments, the ethoxy-containing polymer includes at least one of allyl polyethylene glycol and bisallyl polyether.

In some embodiments, the initiator includes at least one of di-tert-butyl peroxide and diisopropylbenzene peroxide.

In some embodiments, the reaction temperature is 130°C to 140°C.

In some embodiments, the polymer particles and the nonionic surfactant are emulsified in a mass ratio of (4 to 6):1.

The above-mentioned reactant types, mixing ratios and reaction conditions can increase the non-ionic group grafting rate and content of the polymer particles, improve the mechanical properties of the polymer particles such as compression resistance and the dispersibility in the coating slurry.

In the embodiment, the nonionic polymer emulsion satisfies at least any one of the following conditions (1) to (4):

(1) The viscosity of the nonionic polymer emulsion at 25° C. is 10 mPa·s to 100 mPa·s;

(2) The solid content of the nonionic polymer emulsion is 35wt% to 40wt%;

(3) The pH value of the nonionic polymer emulsion is 5 to 6;

(4) The nonionic surfactant includes a molecular structure of Wherein, _R1 is a carbon chain alkyl group, _R2 is a hydrophilic group, and n is a positive integer from 3 to 20.

In an exemplary embodiment, the carbon chain alkyl group is a long carbon chain alkyl group of C12 to C18.

In the exemplary embodiment, the R ₂ is at least one of a carboxyl group, an amine group, an aldehyde group, an alcohol group, an amino group, and an amide group.

In the exemplary embodiment, the nonionic surfactant includes at least one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, castor oil polyoxyethylene ether, fatty amine polyoxyethylene ether, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid ester.

By selecting the type of nonionic surfactant, the stability of the nonionic polymer emulsion can be improved, and its dispersibility in the coating slurry can be improved, thereby improving the dispersion uniformity and stability of the polymer particles.

In some embodiments, the aqueous binder is added in the form of an aqueous binder solution, and the aqueous binder solution has at least one of the following conditions:

The viscosity of the binder aqueous solution at 25° C. is 3000 mPa·s to 10000 mPa·s;

The solid content of the binder aqueous solution is 40 wt % to 50 wt %.

In some embodiments, the coating slurry is applied at a rate of 20 m/min to 100 m/min.

In some embodiments, the drying process is carried out at a temperature of 50°C to 70°C.

In some embodiments, the drying time is 1 min to 5 min.

By adjusting the coating process conditions, the film quality, thickness and air permeability can be adjusted and optimized.

In a third aspect, the present application provides a battery. The battery of the present application includes a positive electrode, a negative electrode, and a separator stacked between the positive electrode and the negative electrode, wherein the separator is the separator described in the present application or a separator prepared by the separator preparation method of the present application. Since the battery of the present application includes the separator of the present application, the battery has high safety and good electrochemical properties such as capacity retention rate.

In an embodiment, the coating is disposed on one surface of the separator, and the coating faces the negative electrode. By only combining the coating on one surface of the separator, the overall thickness of the separator can be effectively reduced, thereby increasing the energy density of the battery.

In a fourth aspect, the embodiment of the present application provides an electric device. The electric device of the embodiment of the present application includes a battery as in the embodiment of the present application, and the battery is used to provide electric energy. The safety of the electric device of the embodiment of the present application is significantly improved.

The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

FIG1 is a schematic flow chart of a method for preparing a diaphragm according to an embodiment of the present application;

FIG2 is a schematic structural diagram of an implementation of a secondary battery in an embodiment of the present application;

FIG3 is an exploded schematic diagram of the secondary battery shown in FIG2 ;

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

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

FIG6 is a schematic diagram of the exploded structure of the battery pack shown in FIG5 ;

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

The reference numerals in the specific implementation manner are as follows:

10. secondary battery cell, 11. housing, 12. electrode assembly, 13. cover plate;

20. Battery module;

30. battery pack, 31. box body, 32. lower box body.

Detailed ways

The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

In the description of the embodiments of the present application, the term "and/or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character "/" in this article generally indicates that the associated objects before and after are in an "or" relationship.

In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

In ion batteries such as lithium-ion batteries, the separator is one of the important components. It is set between the positive and negative pole pieces to separate the positive and negative electrodes of the battery, prevent the two poles from contacting and short-circuiting, and pass the function of Li ⁺ . Therefore, in addition to having good electrolyte wettability, liquid retention, and mechanical strength, the separator also needs to have more and more performance such as thermal stability, which has an important impact on battery safety, as more and more attention is paid to battery safety performance.

Currently, the method of improving the thermal stability and other properties of the diaphragm is to modify the diaphragm, such as doping or coating modifiers such as flame retardant additives, fiber-like materials, electrochemically inert ceramics, etc. during the preparation of the diaphragm, in order to achieve the purpose of improving the thermal stability and other properties of the diaphragm and thus improving battery safety.

Although current methods such as doping or coating can improve the thermal stability and other properties of the diaphragm to a certain extent, the inventors found in their research that when the exothermic reaction inside the battery accumulates to a certain extent, the modified diaphragm cannot block the continued reaction inside the battery in time, making it difficult to delay the exothermic reaction inside the battery and reduce the possibility of internal short circuit or even thermal runaway of the battery. Therefore, it is not ideal for improving the safety of battery thermal runaway.

In order to improve the role of the diaphragm in suppressing thermal runaway of the battery, the surface of the diaphragm is currently modified, such as adding a modified coating. However, the inventors found in their research that adding a modified coating to the diaphragm has an adverse effect on the air permeability of the diaphragm. Therefore, the inventors proposed a modified diaphragm, specifically adding a coating containing polymer particles to the base membrane of the modified diaphragm, which ensures good air permeability of the diaphragm, and has good air permeability during normal production and use of the battery; when overheating occurs inside the battery, the coating can also melt and close the pores of the base membrane in time to form a blocking barrier layer, reducing or completely blocking the reaction inside the battery, thereby reducing the risk of thermal runaway of the battery and improving the safety performance of the battery.

On this basis, the inventors further studied and found that if the polymer particles contained in the coating of the modified diaphragm are further selected or modified, the mechanical properties of the coating such as compression resistance can be further improved on the basis of ensuring that the modified diaphragm has good air permeability and effectively reduces the risk of thermal runaway of the battery. When the battery is under pressure during assembly and normal operation, the good air permeability of the diaphragm is still guaranteed to ensure the normal function of the diaphragm and give full play to the function of the diaphragm, thereby improving the electrochemical properties of the battery such as cycle performance. Therefore, based on the previous modified diaphragm scheme, the following diaphragm improvement scheme is further proposed.

Diaphragm

In a first aspect, an embodiment of the present application provides a diaphragm. The diaphragm of the embodiment of the present application comprises a base film and a coating disposed on at least one surface of the base film. The coating contains polymer particles, and the number of carbon atoms of the branched chain of the polymer contained in the polymer particles is 1 to 10.

In the diaphragm of the embodiment of the present application, the base film contained constitutes the matrix of the diaphragm of the embodiment of the present application, and plays the usual role of the diaphragm. The coating is arranged on the base film, which has a modifying effect on the base film, that is, the diaphragm matrix. The branch carbon number can indicate the "branching degree" of the polymer, which refers to the number of carbon atoms on the branch chain of the polymer. The branch carbon number can be tested using nuclear magnetic resonance. The smaller the branch carbon number data, the more linear the polymer molecular structure is and the fewer the branches are.

Since the polymer particles contained in the coating of the diaphragm of the embodiment of the present application exist in a particle morphology, and the number of branched carbons of the polymer material is in the range of 1 to 10, the polymer particles are given both high compressive resistance and sensitive hot melt response performance. In this way, when the diaphragm is used in a battery, it can ensure that the battery has high compressive resistance when it is subjected to pressure during production and normal operation, maintain the good air permeability and working stability of the diaphragm, and give the battery good electrochemical properties. When the battery is abnormally heated to the melting point of the polymer particles, the polymer particles can melt to close the pores contained in the base film, and the diaphragm plays a barrier role, thereby effectively reducing or preventing the chemical reactions inside the battery, including the migration of metal ions in the electrolyte, and the crosstalk reaction between the positive and negative electrodes. Among them, the migration of the metal ions includes lithium ions and metal precipitation from active materials, etc., to prevent them from passing through the diaphragm and depositing or further forming dendrites on the surface of the electrode, especially the negative electrode. The positive-negative electrode crosstalk reaction refers to the release of oxygen when the positive electrode active material of the battery undergoes a phase change at high temperature. The oxygen can diffuse to the negative electrode through the diaphragm, and react with the negative electrode, etc., and release a large amount of heat; it also includes the hydrogen released from the negative electrode at high temperature, which diffuses to the positive electrode through the diaphragm, and reacts with the positive electrode, etc., and releases a large amount of heat.

Therefore, the presence of polymer particles in the coating contained in the diaphragm of the present application, and the number of side-chain carbon atoms of the polymer material of the polymer particles is controlled in the range of 1 to 10, on the one hand, gives the coating, that is, the diaphragm containing the coating, good air permeability, which can ensure the compressive resistance of the diaphragm in battery production and normal operation, thereby having good air permeability, ensuring and improving the migration efficiency of ions between the positive and negative electrodes, thereby ensuring the normal electrochemical performance of the battery. If the number of side-chain carbon atoms of the polymer is higher than 10, the mechanical properties of the polymer particles such as compressive resistance will decrease; at the same time, it will also cause the melting point of the polymer particles to increase, and the hot melt response rate will also decrease accordingly. This will increase the hot melt response temperature range of the diaphragm and relatively reduce the hot melt response rate of the diaphragm. If the temperature of the battery rises abnormally due to thermal abnormality, the melting rate of the polymer particles will decrease, reducing the rate of closing the pores of the base membrane, thereby reducing the response rate of the diaphragm to thermal runaway of the battery.

In some embodiments, the polymer of the polymer particles may further be selected to satisfy at least any one of the following characteristics (1) to (3):

(1) The weight average molecular weight of the polymer may be 1500 to 5000, and optionally 1500 to 2500;

(2) the polydispersity index (PDI) of the polymer may be 3 to 11, and optionally 3 to 6;

(3) The number of carbon atoms in the branched chain of the polymer is further 1 to 5.

Among them, polydispersity index PDI = weight average molecular weight / number average molecular weight, the lower the value, the narrower the molecular weight distribution. It can be tested by the usual method.

By further selecting the polymer molecular weight, polydispersity index PDI and branched carbon number, the mechanical properties of the above-mentioned polymer particles, including compression resistance, can be further improved, thereby further improving the mechanical properties of the coating, that is, the diaphragm, such as compression resistance in battery production and normal operation, and improving the air permeability and stability of the diaphragm in a normal working environment, thereby improving the stability of the electrochemical performance of the battery in normal operation. At the same time, the hot melt response rate of the diaphragm to thermal anomalies of the battery further reduces or avoids the risk of thermal runaway of the battery.

In some embodiments, the morphology of the polymer particles contained in the coating may include at least one of chain, spherical, quasi-spherical, fibrous, tubular, rod-shaped, amorphous, and pyramidal. Combined with the above-mentioned branched carbon number or further molecular weight of the polymer particles in the range of 1500 to 5000 and PDI of 3 to 11, the polymer particles of these morphologies have relatively high compressive resistance, which can improve the air permeability and working stability of the diaphragm during the production and normal operation of the battery, and improve the electrochemical performance of the battery; at the same time, the polymer particles of these morphologies can increase the melting rate to accelerate the closure of the pores of the base film. Therefore, the polymer particles of this morphology can further reduce the risk of thermal runaway of the battery and improve the safety performance of the battery.

In some embodiments, the volume distribution particle size D _v 50 of the polymer particles contained in the coating can be 0.1 μm to 5 μm, and can be 0.3 μm to 3 μm. In the exemplary embodiment, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc. Typical but non-limiting particle sizes. By controlling the particle size of the polymer particles, if it is controlled within this range, the uniformity of the distribution of the polymer particles in the coating and the mechanical properties such as compressive strength can be improved, the air permeability and stability of the diaphragm can be improved, and the hot melt response rate of the coating, that is, the diaphragm can also be improved. Wherein, unless otherwise specified, the volume distribution particle size D _v 50 of the polymer particles in the examples of the present application and the inorganic particles below is determined by a particle size analyzer-laser diffraction method. Specifically, reference can be made to the standard GB/T 19077-2016, and a laser diffraction scattering particle size analyzer (Mastersizer 3000 laser particle size analyzer) is used for measurement according to the manufacturer's instructions.

In some embodiments, the polymer of the polymer particles in the above embodiments contains non-ionic groups. In the exemplary embodiment, the non-ionic group may include at least one of ethoxy, hydroxyl, and carboxylate groups. The material of the polymer particles contains non-ionic groups, such as these types of non-ionic groups, which can further improve the above-mentioned effects of the polymer particles, especially improve the compressive performance of the polymer particles, thereby improving the compressive resistance and stability of the diaphragm during the battery production process and normal operation; and can also improve the uniformity of the dispersion of the polymer particles in the coating, thereby improving the air permeability and stability of the diaphragm. It is also possible to adjust the melting point range of the polymer particles and improve their hot melt response rate. In addition, the non-ionic group can be a grafted side chain of the polymer, or it can be connected to the main chain of the polymer.

In some embodiments, the polymer of the polymer particles in the above embodiments may include at least one of polystyrene, polyolefin, polyimide, melamine resin, phenol resin, cellulose, polyester, polyphenylene sulfide, polyaromatic amide, polyamide-imide, copolymer of butyl acrylate and ethyl methacrylate and their respective modified polymers. By selecting the polymer material of the polymer particles, such as selecting these polymers, on the basis of the above-mentioned branched carbon number range or further molecular weight of 1500 to 5000 and PDI of 3 to 11, the mechanical properties of the polymer particles such as compression resistance can be effectively improved to further improve the air permeability and working stability of the diaphragm and adjust its hot melt response rate, thereby improving the volatilization effect of the above-mentioned effect of the diaphragm of the present application embodiment.

In addition, the polymer particles in the above embodiments can be solid particles, and of course can also be hollow particles. In the embodiments of the present application, the solid particles have a relatively high compressive resistance compared to the hollow particles, thereby improving the mechanical ability and stability of the diaphragm such as compressive resistance during battery production and normal operation, such as the polymer particles will not be deformed due to the extrusion force during battery manufacturing or use, thereby causing the basement membrane to block holes. Therefore, in the embodiments of the present application, solid polymer particles are relatively preferred compared to hollow polymer particles.

It has been determined that the melting points of the polymer particles in the above examples are between 100 and 110°C.

In some embodiments, the total weight (dry weight) of the coating contained in the separator of the above embodiments is 100%, and the content of the polymer particles in the coating can be ≥22wt%, and further can be 22wt% to 37wt%. By controlling and adjusting the content of the polymer particles in the coating, if it is controlled within this range, the mechanical properties such as the compressive resistance of the coating can be improved to improve the air permeability and stability of the separator; and when the battery stability is abnormal, the effect of the molten polymer melting and sealing the pores of the base film is improved, and the barrier performance of the separator during thermal runaway is improved.

In some embodiments, the coating contained in the separator of each of the above embodiments further contains an inorganic particle filler. By adding the inorganic particle filler to the coating, on the one hand, the mechanical properties of the coating such as compression resistance can be improved, and the air permeability and stability of the separator in battery production and normal operation can be improved; on the other hand, it can play a synergistic role with the above polymer particles, improve the air permeability and liquid storage capacity of the separator, and mechanical properties such as heat shrinkage resistance, and improve the responsiveness of the separator to hot melt. In addition, the inorganic particle filler is ideally formed into a mixture with the above polymer particles in the coating.

In the embodiment, the content of the inorganic particle filler in the coating can be 18wt% to 22wt% based on the total weight (dry weight) of the coating as 100%. By controlling the content ratio of the inorganic particle filler and the polymer particles in the coating, the synergistic effect between the two can be improved on the basis of fully volatilizing the effects of the two as described above, further improving the permeability and mechanical properties of the diaphragm, and further improving the electrochemical properties and safety performance of the battery such as the capacity retention rate.

In the embodiment, the average particle size D _v 50 of the inorganic particle filler is 1 μm to 1.5 μm. By adjusting the inorganic particle filler, it is compounded with the polymer particle size, such as controlling the D _v 50 to be in the range of 1 μm to 1.5 μm, which can play the role of coating skeleton, improve the mechanical properties of the coating such as compression resistance, and work together with the organic particles in the above particle size range to improve the air permeability of the diaphragm. For example, after testing, the air permeability of the diaphragm can reach the air permeability and stability shown in Table 1 below. Moreover, when hot melting occurs, the inorganic particle filler in this particle range can give full play to the skeleton role, so that the polymer particles melt and close the pores of the base film, and play the role of isolating the positive and negative electrodes together with the base film, reducing the risk of short-circuit thermal runaway.

In an embodiment, the above inorganic particle filler may include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

In an exemplary embodiment, the inorganic material of the inorganic particles having a dielectric constant of 5 or more includes at least one of boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium _titanate , Pb(Zr, _Ti ) _O3 , _Pb1 _- mLamZr1-nTinO3, Pb( _Mg3Nb2 _/ ₃ ) _O3 -PbTiO3, and modified inorganic particles thereof, 0＜m＜1, 0＜n＜1.

In the exemplary embodiments, the inorganic material of the inorganic particles having ion conductivity but not storing ions includes _Li3PO4 _, lithium titanium phosphate _Lix1Tiy1 ( _PO4 ) ₃ , lithium aluminum titanium _phosphate _Lix2Aly2Tiz1 ( _PO4 ₎ ₃ , (LiAlTiP) _x3Oy3 type glass, _lithium _lanthanum _titanate _Lix4Lay4TiO3 , _lithium _germanium _{thiophosphate} _{Lix5Gey5Pz2Sw} _, _lithium _nitride _Lix6Ny6 _, _SiS2 type glass _Lix7Siy7Sz3 _and _P2S5 type glass _Lix8Py8Sz _. At least one of _z4 , 0＜x1＜2, 0＜y1＜3, 0＜x2＜2, 0＜y2＜1, 0＜z1＜3, 0＜x3＜4, 0＜y3＜13, 0＜x4＜2, 0＜y4＜3, 0＜x5＜4, 0＜y5＜1, 0＜z2＜1, 0＜w＜5, 0＜x6＜4, 0＜y6＜2, 0＜x7＜3, 0＜y7＜2, 0＜z3＜4, 0＜x8＜3, 0＜y8＜3, 0＜z4＜7;

In an exemplary embodiment, the inorganic material of the electrochemically reactive inorganic particles includes at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

By selecting the material type of the inorganic particle filler, the above-mentioned effect of the inorganic particle filler is improved, and the synergistic effect between the inorganic particle filler and the polymer particles is further improved, the mechanical properties and stability of the coating of the embodiment of the present application, that is, the diaphragm, are improved, and the electrochemical properties and safety performance such as the capacity retention rate of the battery are improved. Among them, the inorganic particle filler of the above-mentioned inorganic material also has good liquid absorption and storage capacity, thereby improving the liquid absorption and storage capacity of the diaphragm.

Based on the above polymer particles and inorganic particle fillers, in the exemplary embodiment, the polymer contained in the polymer particles contained in the coating is low-density polyethylene, specifically low-density polyethylene particles, and further can be low-density polyethylene containing non-ionic groups. Among them, low-density polyethylene refers to high-pressure polyethylene (LDPE), specifically polyethylene with a molecular weight of less than 10,000.

The above-mentioned inorganic particles are compounded with the low-density polyethylene particles to enhance the above-mentioned synergistic effect between the polymer particles and the inorganic particle fillers, thereby improving the mechanical properties and working stability of the coating of the embodiment of the present application, that is, the diaphragm, and also improving the liquid storage capacity of the diaphragm.

In some embodiments, the coating contained in the diaphragm of the above embodiments also contains a solidified aqueous binder. By adding an aqueous binder to the coating, the bonding force between the polymer particles or the inorganic particle filler can be effectively enhanced, thereby improving the mechanical properties of the coating such as compression resistance, and enhancing the bonding force between the coating and the base film. At the same time, the aqueous binder can also play a synergistic role with the polymer particles or further with the inorganic particle filler, adjust the air permeability and working stability of the coating, that is, the diaphragm, and improve the thermal responsiveness of the polymer particles to close the pores of the base film, thereby improving the electrochemical properties and safety performance of the battery such as the capacity retention rate.

In the embodiment, the content of the aqueous binder in the coating can be 18wt% to 27wt% based on the total weight (dry weight) of the coating as 100%. By controlling the content of the aqueous binder in the coating, the mechanical properties of the coating and the bonding force with the base film can be further enhanced, so as to further adjust the air permeability and working stability of the coating, i.e., the diaphragm.

In the embodiment, the thermal decomposition temperature of the above-mentioned cured aqueous binder is higher than 160°C, and can be selected from 160°C to 300°C. By selecting the decomposition temperature characteristics of the aqueous binder, the mechanical properties of the coating and the bonding force between the coating and the base film are enhanced, and the compressive resistance and air permeability of the diaphragm and the working stability are improved. When the battery is abnormally thermal, the barrier effect of the diaphragm is improved and the risk of thermal runaway of the battery is reduced.

In an embodiment, the aqueous binder may be a water-soluble binder or an emulsion binder, etc. In a demonstration example, the aqueous binder may include polyvinyl alcohol, polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, polyether acrylate, polyurethane, polyacrylate, polycarbonate, polyethylene oxide, rubber, polyacrylic acid, polyacrylonitrile, gelatin, chitosan, sodium alginate, cyanoacrylate, polymerized cyclic ether derivatives, and at least one of hydroxyl derivatives of cyclodextrin. These aqueous binders can enhance the bonding force between polymer particles or further inorganic particle fillers, thereby improving the mechanical properties of the coating and enhancing the bonding force between the coating and the base film. The mechanical properties such as the compressive strength of the diaphragm and the stability of the work are further adjusted to improve the electrochemical properties and safety performance of the battery including the capacity retention rate.

In the embodiment, when the coating contains both the above inorganic particle filler and the aqueous binder, in the coating, the dry weight ratio of the above polymer particles, the inorganic particle filler and the aqueous binder can be (22 to 37): (18 to 22): (18 to 27). By controlling the content ratio of the three components in the coating, the above effects of each component and the synergistic effect between the three components are further improved, thereby further improving the mechanical properties of the diaphragm such as compression resistance, so as to improve the electrochemical properties and safety performance of the battery such as capacity retention rate.

Based on the coating schemes in the above embodiments, in some embodiments, the coating thickness can be 2μm to 5μm. In the exemplary examples, the coating thickness can be 2μm, 3μm, 4μm, 5μm, and other typical but non-limiting thicknesses. By controlling the coating thickness, the content of components such as polymer particles can be controlled, thereby adjusting and improving the polymer particles to play the role described above, improving the efficiency of melting and effectively sealing the pores of the base film when the battery is abnormally hot, reducing or preventing the risk of thermal runaway, and improving the mechanical properties such as the compressive strength of the coating, i.e., the diaphragm, and the stability of the work, thereby improving the electrochemical properties and safety performance of the battery such as the capacity retention rate.

In addition, the coating contained in the separator of each embodiment above can be arranged on one surface of the base film, and of course, it can also be arranged on two opposite surfaces of the base film. Considering the battery energy density and dendrite formation characteristics, in the embodiment, the coating is arranged on one surface of the base film, that is, the coating is not arranged on the other opposite surface of the base film.

The base film contained in the separator of each embodiment above can be selected from the organic separator of the battery. For example, in the embodiment, the conductive thickness of the base film can be 4μm to 7μm. In other embodiments, the air permeability of the base film can be 180s/100cc to 240s/100cc. In the exemplary embodiment, the material of the base film includes at least one of non-woven fabrics, polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalene. The base films of these characteristics and materials can be combined with the above coating and play a synergistic role on the basis of giving full play to the role of the battery separator, so that the separator has high mechanical properties such as high compressive resistance, good air permeability, and improves the electrochemical properties and safety performance of the battery such as the capacity retention rate.

In some embodiments, the above-mentioned base membrane can also be a modified base membrane, such as a base membrane modified with at least one modifier such as flame retardants, fiber-like materials, electrochemically inert ceramics, etc., to improve the thermal stability of the base membrane, so as to cooperate with the above-mentioned coating to further improve the mechanical properties and safety performance of the diaphragm of the embodiment of the present application.

Preparation method of diaphragm

In a second aspect, the present invention provides a method for preparing a diaphragm. The process flow of the method for preparing a diaphragm in the present invention is shown in FIG1 . The method for preparing a diaphragm in the present invention may include the following steps:

S01: providing a basement membrane;

S02: providing coating slurry;

S03: coating the coating slurry on at least one surface of the base film, and performing a drying process to form a coating to obtain a separator.

In the preparation method of the diaphragm of the embodiment of the present application, after the coating slurry forms a coating on the surface of the base film, the coating is bonded to the surface of the base film. Since the preparation method of the diaphragm according to the embodiment of the present application is to prepare the diaphragm of the embodiment of the present application, the formed coating contains polymer particles, and the number of branched carbon atoms of the polymer particles is 1 to 10.

The diaphragm preparation method of the embodiment of the present application directly forms a film of a slurry of polymer particles with a branched carbon number of 1 to 10 on a base film, so that the prepared diaphragm is combined with a coating on at least one surface to achieve the coating's modification effect on the base film. Then the coating is the coating contained in the diaphragm of the above text application embodiment. Therefore, the diaphragm prepared by the diaphragm preparation method of the embodiment of the present application has the mechanical properties such as compression resistance and working stability and hot melt responsiveness as the diaphragm of the above text application embodiment, and can also effectively further reduce the risk of thermal runaway of the battery, and improve the electrochemical properties and safety performance of the battery such as the capacity retention rate. In addition, the process parameters of the diaphragm preparation method of the embodiment of the present application are controllable, and the quality and electrochemical properties of the prepared diaphragm are stable.

Step S01:

The base film in step S01 may be the base film contained in the diaphragm of the above text application embodiment, and therefore, the base film may be the base film contained in the diaphragm of the above text application embodiment. As in the embodiment, the thickness of the provided base film may be 4 μm to 7 μm, and its air permeability may be 180 s/100 cc to 240 s/100 cc, and its material may include at least one of non-woven fabric, polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalene.

Step S02:

Since the coating slurry in step S02 is the slurry for forming the coating contained in the diaphragm of the above text application embodiment, the slurry must contain polymer particles and solvents. In the embodiment, it may further contain inorganic particle fillers and aqueous binders. Therefore, the material types and content ratios of the polymer particles contained in the coating slurry, or the inorganic particle fillers and aqueous binders further contained therein, are the same as the types and content ratios of the polymer particles, inorganic particle fillers and aqueous binders contained in the coating of the diaphragm of the above text application embodiment, such as the number of branched carbons of the polymer is 1 to 10, and optionally 1 to 5; further, the weight average molecular weight of the polymer particles is 1500 to 5000, and the polydispersity index PDI is 3 to 11. Therefore, in order to save space, the types, content ratios, etc. of polymer particles, inorganic particle fillers and aqueous binders will not be described here.

In order to improve the film-forming quality of the coating slurry, improve the quality of the coating as well as the properties such as air permeability and compressive resistance, in one embodiment, the solid content of the coating slurry can be 30wt% to 40wt%; in other embodiments, the viscosity of the coating slurry at 25°C is 500mPa·s to 800mPa·s.

In some embodiments, when the coating slurry in step S02 is formed by mixing polymer particles, inorganic particle fillers and aqueous binders in a solvent; then the mass ratio of polymer particles, inorganic particle fillers, aqueous binders and water in the coating slurry can be (22 to 37): (18 to 22): (18 to 27): (22 to 32). This ratio refers to the mixing ratio of aqueous binder to polymer particles and inorganic particle fillers before curing. By adjusting the ratio of the three, the film-forming quality of the coating slurry is improved, and the compressive resistance and other properties of the formed coating are enhanced, thereby further improving the electrochemical performance of the battery and reducing the risk of thermal runaway of the battery.

Among them, the aqueous binder should be an aqueous binder before curing, such as the aqueous binder before curing as described above. In the exemplary embodiment, it can be an aqueous binder before curing including at least one of polyvinyl alcohol, polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, polyether acrylate, polyurethane, polyacrylate, polycarbonate, polyethylene oxide, rubber, polyacrylic acid, polyacrylonitrile, gelatin, chitosan, sodium alginate, cyanoacrylate, polymerized cyclic ether derivatives, and hydroxyl derivatives of cyclodextrin.

For example, in the embodiment, the aqueous binder is added in the form of an aqueous binder aqueous solution to effectively adjust the viscosity of the coating slurry, improve the dispersion uniformity and stability of the coating slurry components, and improve the film-forming quality of the coating slurry. When the aqueous binder is added in the form of an aqueous binder solution, in the embodiment, the viscosity of the aqueous binder aqueous solution at 25°C can be 3000mPa·s to 10000mPa·s; in other embodiments, the solid content of the aqueous binder aqueous solution is 40wt% to 50wt%. By controlling and adjusting the viscosity of the aqueous binder aqueous solution or the solid content at the same time, the positive effect of the aqueous binder on the coating slurry can be further improved, including the slurry stability and dispersibility.

In the embodiment, when the polymer particles contained in the coating slurry are polymer particles containing non-ionic groups, the polymer particles can be prepared according to a method comprising the following steps:

Step S021: mixing and reacting the polymer precursor particles, the ethoxy-containing polymer and the initiator to obtain polymer particles containing nonionic groups;

Step S022: emulsifying the polymer particles containing nonionic groups with a nonionic surfactant to obtain a nonionic polymer emulsion.

In the reaction process of step S021, the polymer precursor particles and the ethoxy-containing polymer undergo a polymerization reaction under the action of an initiator, so that the ethoxy-containing group is grafted onto the polymer particles.

In the embodiment, the polymer precursor particles, the ethoxy-containing polymer and the initiator are mixed in a mass ratio of (300 to 400):(90 to 125):(20 to 50).

In the embodiment, the reaction temperature in step S021 can be 130° C. to 140° C., and the reaction time should be sufficient, such as 2.5 h to 4 h at 130° C. to 140° C. Meanwhile, during the reaction, the molten reactants are stirred to improve the efficiency and uniformity of the reaction.

By controlling and adjusting the mixing ratio of the reactants in step S021, or further controlling the reaction conditions, the polymer reaction efficiency can be improved, and the number of branched carbon atoms in the polymer particles can be increased from 1 to 10 or further increased to 1-5. At the same time, the content of grafted non-ionic groups such as ethoxy groups can be increased, thereby further improving the non-ionic group modification effect of the polymer particles, thereby further improving the above effects of the polymer particles, especially improving the mechanical properties of the polymer particles such as compressive strength.

In an exemplary embodiment, the material of the polymer precursor particles may include at least one of polystyrene, polyolefin, polyimide, melamine resin, phenol resin, cellulose, polyester, polyphenylene sulfide, polyaromatic amide, polyamideimide, and a copolymer of butyl acrylate and ethyl methacrylate.

The ethoxy-containing polymer may include at least one of allyl polyethylene glycol and bisallyl polyether.

The initiator may include at least one of di-tert-butyl peroxide and dicumyl peroxide.

The polymer precursor particles, ethoxylated polymer and initiator can undergo a polymer reaction in step S021 to improve the efficiency of grafting modification. The ethoxylated polymer can effectively provide ethoxylated nonionic groups to achieve grafting modification of the ethoxylated nonionic groups of the polymer precursor particles.

In step S022, during the emulsification process, the nonionic surfactant and the polymer particles containing nonionic groups form an emulsion in a solvent. In an embodiment, the mass ratio of the polymer particles containing nonionic groups to the nonionic surfactant can be (4 to 6): 1 for emulsification. The solvent should be water.

In addition, the mixing ratio of the nonionic surfactant and the polymer particles containing nonionic groups, as well as the amount of added water solvent, can be controlled to adjust and control the relevant properties of the nonionic polymer emulsion, such as viscosity, solid content, pH value, etc., so as to improve the dispersion uniformity and stability of the polymer particles in the coating slurry, thereby improving the above-mentioned effect of forming the coating and improving the electrochemical performance and safety performance of the prepared diaphragm. For example, in the embodiment, by controlling and conditioning the conditions of the emulsification treatment in step S022, the nonionic polymer emulsion has at least one of the following properties:

(2) the solid content of the nonionic polymer emulsion is 35 wt % to 40 wt %;

(3) The pH value of the nonionic polymer emulsion is 5 to 6;

In the embodiments, the above mixing ratio of the nonionic surfactant and the polymer particles can effectively adjust the viscosity and solid content of the nonionic polymer emulsion, thereby improving the dispersibility of the polymer particles and improving the uniformity and stability of the coating slurry.

In some embodiments, the nonionic surfactant may include a molecular structure of

Wherein, _R1 is a carbon chain alkyl group. In the exemplary embodiment, when it is a carbon chain alkyl group, _R1 is a long carbon chain alkyl group of C12 to C18.

R ₂ is a hydrophilic group. In the exemplary embodiment, R ₂ is at least one of a carboxyl group, an amine group, an aldehyde group, an alcohol group, an amino group, and an amide group.

n is a positive integer from 3 to 20. In the examples, n can be a typical but non-limiting positive integer such as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc.

In addition, there is no chronological order between step S01 and step S02 above, and the order can be adjusted according to actual production, or they can be performed simultaneously.

Step S03:

The purpose of coating the coating slurry on the base film in step S02 is to form a wet film on the base film, that is, the above coating before drying. The coating method may be unlimited, and any method that can form a film of the coating slurry on the base film is within the scope disclosed in the embodiments of the present application, such as but not limited to brushing, roller coating, spraying, etc. In addition, the coating process conditions may be further adjusted to adjust and optimize the film quality, thickness, air permeability, etc.

For example, in the embodiment, the coating slurry in step S02 may be coated at a rate of 20 m/min to 100 m/min, and further may be 20 m/min to 50 m/min. In the exemplary embodiment, the coating slurry may be coated at a rate of 20 m/min, 30 m/min, 40 m/min, 50 m/min, 60 m/min, 70 m/min, 80 m/min, 90 m/min, 100 m/min, etc. Typical but non-limiting rates may be used. The coating rate may improve the quality of the coating, adjust the air permeability and thickness, etc.

In the drying process, the main purpose is to remove the solvent in the wet film. Based on the melting temperature range characteristics of the organic particles contained in the coating slurry, the drying process should be lower than the melting temperature of the organic particles, and should ensure the quality and stability of the coating. For example, in the embodiment, the drying temperature can be 50°C to 70°C. In the exemplary embodiment, it can be but not limited to typical but non-limiting temperatures such as 50°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, and 70°C. In the drying temperature range, the drying time should be sufficient, such as the drying time of 1 min to 5 min.

Battery

In a third aspect, the present application provides a battery, which includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the separator of the above-mentioned application embodiment.

In the embodiment, the diaphragm is only combined with a coating on one surface, and the surface of the diaphragm containing the coating faces the negative electrode. By facing the coating toward the negative electrode, the diaphragm can fully play the role described in the diaphragm of the embodiment of the above application, which can further improve the electrochemical performance of the battery and reduce the risk of thermal runaway of the battery, thereby improving the safety of the battery. At the same time, only combining the coating on one surface of the diaphragm can effectively reduce the overall thickness of the diaphragm and improve the energy density of the battery.

In the exemplary embodiment, the battery of the present application can be a secondary battery. When the battery of the present application is a secondary battery, it includes a positive electrode, a separator and a negative electrode. That is, the negative electrode contained in the secondary battery is the negative electrode of the above-mentioned application embodiment, that is, the negative electrode contains the modified artificial graphite of the above-mentioned application embodiment.

In this way, the battery of the embodiment of the present application, such as a secondary battery, has a high energy density, a high rate capability and good cycle stability.

In an embodiment, the secondary battery of the embodiment of the present application may include any one of a battery cell, a battery module, and a battery pack.

The battery cell refers to a battery housing and a battery cell encapsulated in the battery housing. The shape of the battery cell is not particularly limited, and it can be cylindrical, square or any other shape. A square battery cell 10 is shown in FIG. 2 .

In some embodiments, as shown in FIG3 , the outer packaging of the battery cell 10 may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 is used to cover the opening to close the receiving cavity. The positive electrode, the separator and the negative electrode contained in the secondary battery of the embodiment of the present application can form an electrode assembly 12 through a winding process and/or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 10 may be one or more, which can be adjusted according to actual needs.

The preparation method of the battery cell 10 is well known. In some embodiments, the positive electrode, the separator, the negative electrode and the electrolyte can be assembled to form the battery cell 10. As an example, the positive electrode, the separator and the negative electrode can be formed into the electrode assembly 12 through a winding process or a lamination process, and the electrode assembly 12 is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, left to stand, formed, shaped and other processes are performed to obtain the battery cell 10.

The battery module is assembled from the battery cells 10 , that is, it may contain a plurality of the battery cells 10 , and the specific number can be adjusted according to the application and capacity of the battery module.

In some embodiments, FIG. 4 is a schematic diagram of a battery module 20 as an example. As shown in FIG. 4 , in the battery module 20, a plurality of battery cells 10 may be arranged in sequence along the length direction of the battery module 20. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 10 may be fixed by fasteners.

Optionally, the battery module 20 may further include a housing having an accommodation space, and the plurality of battery cells 10 may be accommodated in the accommodation space.

A battery pack is composed of the above-mentioned battery cells 10, that is, it may contain multiple battery cells 10, wherein multiple battery cells 10 may be assembled into the above-mentioned battery module 20. The specific number of battery cells 10 or battery modules 20 contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

As shown in the embodiment, FIG. 5 and FIG. 6 are schematic diagrams of a battery pack 30 as an example. The battery pack 30 may include a battery box and a plurality of battery modules 20 disposed in the battery box. The battery box includes an upper box body 31 and a lower box body 32, and the upper box body 31 is used to cover the lower box body 32 and form a closed space for accommodating the battery module 20. The plurality of battery modules 20 may be arranged in the battery box in any manner.

Electrical devices

In a fourth aspect, the present application also provides an electric device, which includes the battery of the above-mentioned embodiment of the present application, and further can be a secondary battery. The battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. Therefore, the electric device of the present application embodiment has a long standby or battery life.

The electrical device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc. The electrical device may select a secondary battery, a battery module or a battery pack according to its use requirements.

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

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

Example

Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.

1. Diaphragm and its preparation method embodiment

Example A1

This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment includes a PE base film and a coating bonded to one surface of the PE base film. The thickness of the PE base film is 7 μm; the thickness of the coating is 3 μm. The coating contains nonionic linear low-density polyethylene particles, and the polymer particles contain ethoxy groups. After testing, the parameters of the polymer such as molecular weight, PDI and branched carbon number are shown in Table 1 below.

The diaphragm preparation method of this embodiment includes the following steps:

S1. Preparation of coating slurry:

S11. Preparation of polymer particles:

a. Mix linear low-density polyethylene (LLDPE): allyl polyethylene glycol: di-tert-butyl peroxide in a ratio of 350:100:50, heat and melt, stir evenly, and keep the temperature at 140°C for 3h to obtain an intermediate product;

b. Mix the intermediate product and nonionic emulsifier (fatty alcohol polyoxyethylene ether AEO-3) in a ratio of 4.5:1, heat to melt, stir to form a uniform emulsion, add water to adjust to a suitable 50 mPa·s (25°C), and the solid content is 35% to obtain a modified LLDPE emulsion; wherein the weight average molecular weight of the polymer particle polymer is 1500, the PDI is 5, and the number of branched carbon atoms is 5 to 10;

S12. Preparation of coating slurry:

Nonionic polyethylene wax emulsion, polymethyl methacrylate, boehmite and water are mixed in a ratio of polymer particles: polymethyl methacrylate: boehmite: water = 25%: 19%: 26%: 30%, all materials are added into a double planetary stirring tank, and then the mixture is stirred for 3 hours at a revolution of 30 rpm and a rotation of 2000 rpm, and vacuum defoaming is performed throughout the process; the viscosity of the coating slurry is controlled at 700 mPa·s (25° C.).

S2. Film formation of coating slurry on the surface of base film:

The coating slurry in step S1 is coated on one side of a 7 μm PE base film to form a wet film, and then dried to form a 3 μm coating on one side of the PE base film; wherein the coating slurry coating speed is 60 m/min, the oven temperature is 60° C., and the total drying time is 5 min.

Example A2

This embodiment provides a diaphragm and a preparation method thereof. The diaphragm of this embodiment and the diaphragm in Example A1 are identical in all other features except that the modification conditions of the polymer particles contained in the coating are different. Specifically, in this embodiment, LLDPE: allyl polyethylene glycol: di-tert-butyl peroxide are mixed in a ratio of 400: 115: 20, heated to melt and stirred evenly, and the intermediate product is obtained after a constant temperature of 130°C for 3 hours. The modified LLDPE emulsion finally obtained has a weight-average molecular weight of 5000 in Table 1, a PDI of 6, and a branched carbon number of 5 to 10.

The preparation method of the diaphragm in this embodiment refers to the preparation method of the diaphragm in Example A1.

Example A3

This embodiment provides a diaphragm and a preparation method thereof. The diaphragm of this embodiment and the diaphragm in Example A1 are identical in all other features except that the modification conditions of the polymer particles contained in the coating are different. Specifically, in this embodiment, LLDPE: allyl polyethylene glycol: di-tert-butyl peroxide are mixed in a ratio of 300: 125: 40, heated to melt and stirred evenly, and the intermediate product is obtained after a constant temperature of 140°C for 2.5 hours. The modified LLDPE emulsion finally obtained has a weight-average molecular weight of 1500 in Table 1, a PDI of 11, and a branched carbon number of 5 to 10.

Example A4

This embodiment provides a diaphragm and a preparation method thereof. The diaphragm of this embodiment is identical to the diaphragm in Example A1 except that the modification conditions of the polymer particles contained in the coating are different. Specifically, in this embodiment, LLDPE: allyl polyethylene glycol: di-tert-butyl peroxide = 350:90:40 are mixed, heated, melted and stirred evenly, and the intermediate product is obtained after the temperature is kept at 140°C for 4 hours. The modified LLDPE emulsion finally obtained has a weight average molecular weight of 1500 in Table 1, a PDI of 5, and a branched carbon number of 1 to 5.

Example A5

This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm in Embodiment A1 except that the polymer particles contained in the coating are different. Specifically, in this embodiment, the modified polyester: allyl polyethylene glycol: di-tert-butyl peroxide are mixed in a ratio of 400:115:20, heated to melt and stirred evenly, and the intermediate product is obtained after the temperature is kept at 130°C for 2.5 hours. The modified polyester finally obtained has a weight-average molecular weight of 3000 in Table 1, a PDI of 5, and a branched carbon number of 5 to 10.

Example A6

This embodiment provides a diaphragm and a method for preparing the same. The diaphragm in this embodiment is identical to the diaphragm in embodiment A1 except that the polymer particles contained in the coating are different. Specifically, the material of the polymer particles in this embodiment is ordinary LLDPE, and the S12 coating slurry configuration is directly performed without the S11 modification step.

Example A7

This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm in embodiment A1 except that the coating does not contain inorganic particle fillers. The components of the coating slurry are mixed in a ratio of polymer particles: polymethyl methacrylate: boehmite: water = 51%: 19%: 0%: 30%.

Example A8

This embodiment provides a diaphragm and a preparation method thereof. Compared with the diaphragm in Example A1, the diaphragm in this comparative example has the same characteristics except that the molecular weight of the polymer particles contained in the coating is different. Specifically, in this comparative example, modified LLDPE: allyl polyethylene glycol: di-tert-butyl peroxide = 350:100:60 are mixed, heated, melted and stirred evenly, and the intermediate product is obtained after the temperature is kept at 150°C for 3h. The modified LLDPE emulsion finally obtained has a weight average molecular weight of 1200 in Table 1, a PDI of 5, and a branched carbon number of 5 to 10.

Embodiment A9

The diaphragm of this embodiment is completely identical to the diaphragm in Example A1 except that the polymer particles contained in the coating are different. Specifically, in this comparative example, LLDPE: allyl polyethylene glycol: di-tert-butyl peroxide = 400: 115: 5 are mixed, heated, melted and stirred evenly, and the intermediate product is obtained after being kept at a constant temperature of 120°C for 3 hours. The modified LLDPE emulsion finally obtained has a weight average molecular weight of 6000 in Table 1, a PDI of 5, and a branch carbon number of 5 to 10.

Comparative Example A1

This comparative example provides a separator, which is different from the separator in Example A1 in that the separator coating does not contain polymer particles. The other features are exactly the same.

The preparation method of the diaphragm in this comparative example refers to the preparation method of the diaphragm in Example A1, and the difference from the preparation method in Example A1 is that when preparing the coating slurry, the components of the coating slurry are mixed according to the mass ratio of polymer particles: polymethyl methacrylate: boehmite: water = 0%: 19%: 51%: 30%. The steps and process conditions are the same.

Comparative Example A2

This comparative example provides a diaphragm. The diaphragm in this comparative example is completely the same as the diaphragm in Example A1 except that the polymer particles contained in the coating are different and the degree of branching is different. Specifically, in this comparative example, low-density polyethylene LDPE: allyl polyethylene glycol: di-tert-butyl peroxide = 350:100:50 are mixed, heated, melted and stirred evenly, and the intermediate product is obtained after the temperature is kept at 140°C for 3 hours. The modified LDPE emulsion finally obtained has a weight-average molecular weight of 1500 in Table 1, a PDI of 5, and a branched carbon number of >11.

2. Secondary battery cell example

Example B1 to Example B9 and Comparative Example B1 to Comparative Example B2;

The present embodiment B1 to embodiment B9 and comparative examples B1 to comparative examples B2 respectively provide a secondary battery monomer, each of which includes a battery cell formed by a positive electrode, a separator and a negative electrode, and also includes an electrolyte. Among them, the separators provided in embodiments A1 to embodiment A9 and comparative examples A1 to comparative examples A2 are the separators of secondary battery embodiments B1 to embodiment B9 and comparative examples B1 to comparative examples B2, respectively. Among them, the separator in the above embodiment A1 is used as the separator in the battery cell of the secondary battery embodiment B1, the separator in the embodiment A2 is used as the separator in the battery cell of the secondary battery embodiment B2, and so on, and the separator in comparative example A2 is used as the separator in the battery cell of the battery comparative example B2.

The positive electrode was prepared as follows:

Using methyl pyrrolidone (NMP) as solvent, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , carbon nanotubes (CNT) and binder (PVDF) are mixed in a mass ratio of 97:2:1 to prepare a positive electrode slurry with a solid content of 80%. The positive electrode slurry is evenly coated on an aluminum foil for double-sided coating, wherein the surface density of each single side is 0.131 g/1540.25 mm ² . After being fully dried, cold pressed and cut, a positive electrode sheet is obtained as a positive electrode.

Negative electrode: Using water as solvent, artificial graphite, conductive agent SP, dispersant (CMC), and binder (SBR) are mixed in a mass ratio of 96:1:1:2 to prepare a negative electrode slurry with a solid content of 58%; the positive electrode slurry is evenly coated on aluminum foil for double-sided coating, wherein the surface density of each single side is 0.065g/ ^1540.25mm2 , and after sufficient drying, cold pressing, and slitting, a negative electrode sheet is obtained as the negative electrode.

Electrolyte: At room temperature, ethylene carbonate (EC)/diethyl carbonate (DEC) were mixed in a volume ratio of 1:1, and LiPF ₆ was added to the mixed solution to obtain a solution with a concentration of 1 mol/L as the electrolyte.

Secondary battery assembly: In a low-humidity constant temperature room, the positive and negative electrode plates prepared as above are stacked and wound in the order of "positive electrode-separator-negative electrode" to form a bare cell, and then filled with electrolyte to assemble into a lithium-ion secondary battery.

Related performance tests of diaphragms and secondary battery cells

The separators and secondary battery cells provided in the above embodiments and comparative examples were tested respectively.

1. Diaphragm performance test:

1.1 The membranes in the above-mentioned Examples A1 to A9 and Comparative Examples A1 to A2 were respectively subjected to the relevant performance tests in Table 1. Among them, all test methods are in accordance with the national standard (if there is no national standard, the test is conducted according to the industry standard method). For example, the molecular weight and PDI are tested by gel chromatography (GPC) and refer to the GBT27843-2011 chemical polymer low molecular weight component content detection method; the air permeability is tested using a membrane air permeability tester in accordance with the reference standard GB/T 36363-2018; the characterization method of the branched carbon number is as follows:

¹³ C NMR test was performed using a Bruker AVANCEⅢ 400 MHz NMR spectrometer with a resolution of 0.09 Hz. Deuterated o-dichlorobenzene was used as the solvent, and 250 mg of the polymer sample was placed in 2.5 ml of the deuterated reagent and melted in a 130°C oil bath to form a uniform solution. ¹³ C NMR test conditions were: 125°C, 20 Hz rotation speed, 90° pulse, Waltz16 continuous decoupling, spectral width 80 ppm, sampling time AQ 5 s, and delay time D1 10 s.

The measured results are shown in Table 1 below.

Table 1

It can be seen from the performance data of the diaphragm in Table 1 that the diaphragms in Examples A1 to A9 can close the pores of the base film after heating at 120°C for 15 minutes, thereby improving the safety performance of the battery. Among them, Example A8 has a relatively small molecular weight, although its hot melt response speed is fast, and the pores are basically completely closed after heating at 120°C for 15 minutes, but due to its relatively small molecular weight, its diaphragm stability is relatively weak during the charge and discharge process, such as relatively weak cycle performance. When ordinary LLDPE in Example A6 is used, the stability of the diaphragm is relatively weak, such as relatively weak cycle performance. Example A9 has a relatively large molecular weight and a slow hot melt response speed. After heating at 120°C for 15 minutes, there is still a certain amount of air permeability, that is, the base film pores are not completely closed, but the air permeability is also significantly reduced, such as 700s/100cc. Compared with Comparative Example A2, the diaphragm of the embodiment of the present application has higher thermal stability. For example, after injection aging and 1000 cycles, the air permeability of the diaphragm of the embodiment of the present application is significantly higher than that of Comparative Example A2.

The air permeability of the membranes in Examples A1 to A6 and A8 to A9 at room temperature is comparable to that of Comparative Example A1, indicating that such organic particles do not affect the air permeability of the membrane at room temperature. However, the air permeability of Example A7 at room temperature is poor, indicating that it is preferred to add inorganic particle fillers to increase the porosity of the coating and improve the air permeability.

Therefore, by controlling the number of branched carbons contained in the polymer particles contained in the coating of the diaphragm of the embodiment of the present application to 1 to 10, or further controlling the polymer molecular weight to be in the range of 1500 to 5000 and the PDI to be 3 to 11, the mechanical properties such as compression resistance of the coating of the embodiment of the present application can be further improved, thereby ensuring the high mechanical properties such as compression resistance of the diaphragm in battery production and normal operation, thereby further improving the stability of the air permeability of the diaphragm, thereby significantly improving the electrochemical performance of the battery. On this basis, the overheating responsiveness of the polymer particles can be improved. When the battery temperature rises to the melting point of the polymer particles, they can effectively melt and close the pores of the base film, causing the diaphragm to lose its air permeability, thereby effectively terminating the metal ion migration or positive and negative electrode crosstalk reactions in the battery, thereby improving the battery safety performance.

2. Secondary battery monomer performance test:

2.1 Secondary battery cell membrane air permeability test after liquid injection

After the secondary battery cells in the above-mentioned Examples B1 to B9 and Comparative Examples B1 to B2 were liquid-injected and formed under the same liquid-injection forming conditions, the batteries were disassembled to obtain each diaphragm, and the air permeability of each diaphragm was tested according to the diaphragm permeability method in Section 1.1 above. The measured results are shown in "After liquid injection aging" in Table 1.

2.2 Secondary battery cell membrane air permeability test after cycling

After the secondary battery cells in the above-mentioned Examples B1 to B9 and Comparative Examples B1 to B2 were cycled at 25°C and 1C/1C, the batteries were disassembled to obtain each diaphragm, and the air permeability of each diaphragm was tested according to the diaphragm permeability method in Section 1.1 above. The measured results are shown in "After 1000 cycles" in Table 1.

Controlled by the relevant data in Table 1, the air permeability of the diaphragm after liquid injection and circulation in Examples A1 to A5 is equivalent to that of Comparative Example A1. It can be seen that the pressure resistance of the polymer particles can be effectively improved by optimizing the modification (Comparative Example A6), molecular weight (Example A8) and degree of branching (Comparative Example A2), and the polymer particles can be prevented from being squeezed and deformed by the expansion force of the battery during normal use of the diaphragm, resulting in blockage of the diaphragm pores and affecting the air permeability.

2.3 Secondary battery cell cycle test

The secondary battery cells in the above-mentioned Examples B1 to B9 and Comparative Examples B1 to B2 were subjected to cycle tests at 25° C. and 1C/1C conditions, and the test results are shown in Table 2.

Table 2

实施例Example	首圈放电容量(％)First cycle discharge capacity (%)	循环100圈后容量保持率(％)Capacity retention after 100 cycles (%)
实施例B1Example B1	100100	8989
实施例B2Example B2	100100	8989
实施例B3Example B3	100100	8989
实施例B4Example B4	100100	9090
实施例B5Example B5	100100	8989
实施例B6Example B6	9595	8080
实施例B7Example B7	9898	8888
实施例B8Example B8	9797	8585
实施例B9Example B9	100100	9090
对比例B1Comparative Example B1	100100	9090
对比例B2Comparative Example B2	9595	7676

From Table 2, it can be seen that the battery, the secondary battery monomer of the embodiment of the present application contains the diaphragm of the embodiment of the present application, and the coating contained therein has high mechanical properties such as high pressure resistance. When the battery is formed, it can effectively maintain the good air permeability and structural stability of the diaphragm. For example, the capacity retention rate of Example B1 to Example B5 after 1000 cycles is equivalent to that of Comparative Example A1. It can be seen that the pressure resistance of the polymer particles can be effectively improved by optimizing the modification (Comparative Example B6), molecular weight (Example B8 and Example B9) and branching degree (Comparative Example B2), and the polymer particles can be prevented from being squeezed and deformed by the battery cycle expansion force, resulting in clogging of the diaphragm pores and affecting the cycle performance.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

A diaphragm, characterized in that it comprises a base film and a coating disposed on at least one surface of the base film, wherein the coating contains polymer particles, and the number of branched carbon atoms of the polymer contained in the polymer particles is 1 to 10.
The diaphragm according to claim 1, characterized in that the polymer satisfies at least any one of the following conditions (1) to (3):

(1) The weight average molecular weight of the polymer is 1500 to 5000, and can be 1500 to 2500;

(2) the polydispersity index (PDI) of the polymer is 3 to 11, and can be 3 to 6;

(3) The carbon number of the branched chain of the polymer is 1 to 5.
The diaphragm according to claim 1 or 2 is characterized in that the polymer particles contain non-ionic groups, and optionally, the non-ionic groups include at least one of ethoxy groups, hydroxyl groups, and carboxylate groups.
The diaphragm according to any one of claims 1 to 3 is characterized in that, based on the total dry weight of the coating being 100%, the content of the polymer particles in the coating is ≥ 22 wt%, and can be optionally 22 wt% to 37 wt%.
The separator according to any one of claims 1 to 4, characterized in that the polymer particles satisfy at least one of the following conditions (1) to (4):

(1) The volume distribution particle size D v 50 of the polymer particles is 0.1 μm to 5 μm;

(2) The melting point of the polymer particles is 100°C to 110°C;

(3) The polymer particles are in at least one of the following shapes: chain, spherical, quasi-spherical, fibrous, tubular, rod-shaped, amorphous, and pyramidal;

(4) The polymer includes at least one of polystyrene, polyethylene, polyimide, melamine resin, phenol resin, cellulose, cellulose modifier, polypropylene, polyester, polyphenylene sulfide, polyaramid, polyamideimide, polyimide, and a copolymer of butyl acrylate and ethyl methacrylate.
The diaphragm according to any one of claims 1 to 5, characterized in that the coating further comprises an inorganic particle filler.
The diaphragm according to claim 6, characterized in that the content of the inorganic particulate filler in the coating is 18wt% to 22wt% based on the total weight of the coating as 100%; and/or

The volume distribution particle size D v 50 of the inorganic particle filler is 1 μm to 1.5 μm; and/or

The inorganic particle filler includes at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reaction.
The diaphragm according to any one of claims 1 to 7, characterized in that the coating further comprises an aqueous binder.
The diaphragm according to claim 8, characterized in that the aqueous binder satisfies at least one of the following conditions:

The dry weight content of the aqueous binder in the coating is 18wt% to 27wt%; and/or

The thermal decomposition temperature of the aqueous binder is ≥160°C.
The diaphragm according to any one of claims 1 to 9, characterized in that

The thickness of the base film is 4 μm to 7 μm; and/or

The coating has a thickness of 2 μm to 5 μm; and/or

The air permeability of the separator is 180s/100cc to 240s/100cc.
A method for preparing a diaphragm, characterized in that it comprises the following steps:

Providing a base film and a coating slurry containing polymer particles; the polymer particles contain a polymer having a branched carbon number of 1 to 10;

The coating slurry is coated on at least one surface of the base film, and dried to form a coating to obtain a separator.
The preparation method according to claim 11 is characterized in that: the coating slurry further includes an inorganic particle filler and an aqueous binder; wherein the mass ratio of the polymer particles, the inorganic particle filler and the aqueous binder in the coating slurry is (22 to 37): (18 to 22): (18 to 27); and/or

The solid content of the coating slurry is 30wt% to 40wt%; and/or

The coating slurry has a viscosity of 100 mPa·s to 1000 mPa·s at 25°C.
The preparation method according to claim 11 or 12, characterized in that the polymer particles are prepared by a method comprising the following steps:

The polymer precursor particles, the ethoxy-containing polymer and the initiator are mixed and reacted to obtain polymer particles containing nonionic groups;

The polymer particles containing nonionic groups are emulsified with a nonionic surfactant to obtain a nonionic polymer emulsion.
The preparation method according to claim 13, characterized in that the polymer precursor particles, the ethoxy-containing polymer and the initiator are mixed in a ratio of (300 to 400): (90 to 125): (20 to 50); and/or

The material of the polymer precursor particles includes at least one of polystyrene, polyolefin, polyimide, melamine resin, phenol resin, cellulose, polyester, polyphenylene sulfide, polyaramid, polyamideimide, and copolymer of butyl acrylate and ethyl methacrylate; and/or

The ethoxy-containing polymer comprises at least one of allyl polyethylene glycol and bisallyl polyether; and/or

The initiator comprises at least one of di-tert-butyl peroxide and dicumyl peroxide; and/or

The reaction temperature is 130°C to 140°C; and/or

The polymer particles and the nonionic surfactant are emulsified in a mass ratio of (4 to 6):1.
The preparation method according to claim 13 or 14, characterized in that the non-ionic polymer emulsion satisfies at least any one of the following conditions (1) to (4):

The nonionic polymer emulsion satisfies at least one of the following conditions (1) to (5):

(1) The viscosity of the polymer particle nonionic emulsion at 25° C. is 10 mPa·s to 100 mPa·s;

(2) the solid content of the polymer particle nonionic emulsion is 35 wt % to 40 wt %;

(3) the pH value of the polymer particle nonionic emulsion is 5 to 6; and/or

(4) The nonionic surfactant includes a molecular structure of Wherein, R1 is a carbon chain alkyl group, R2 is a hydrophilic group, and n is a positive integer from 3 to 20.
The preparation method according to claim 15, characterized in that the carbon chain alkyl is a long carbon chain alkyl of C12 to C18; and/or

The R2 is at least one of a carboxyl group, an amine group, an aldehyde group, an alcohol group, an amino group, and an amide group.
The preparation method according to any one of claims 13 to 16, characterized in that the nonionic surfactant includes at least one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, castor oil polyoxyethylene ether, fatty amine polyoxyethylene ether, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid ester.
The preparation method according to any one of claims 12 to 17, characterized in that the aqueous binder is added in the form of an aqueous binder solution, and the aqueous binder solution has at least one of the following conditions:

The viscosity of the binder aqueous solution at 25° C. is 3000 mPa·s to 10000 mPa·s;

The solid content of the binder aqueous solution is 40 wt % to 50 wt %.
The preparation method according to any one of claims 11 to 18, characterized in that: the coating slurry is applied at a rate of 20 m/min to 100 m/min; and/or

The drying temperature is 50°C to 70°C; and/or

The drying time is 1 min to 5 min.
A battery, characterized in that it comprises a positive electrode, a negative electrode and a separator stacked between the positive electrode and the negative electrode, wherein the separator is the separator according to any one of claims 1 to 10 or a separator prepared by the preparation method according to any one of claims 11 to 19.
The battery according to claim 20 is characterized in that the coating is provided on one surface of the separator, and the coating faces the negative electrode.
An electrical device, characterized in that the electrical device comprises a battery as described in claim 20 or 21, and the battery is used to provide electrical energy.