Diaphragm and preparation method thereof, battery and electric device

Abstract

The invention discloses a diaphragm and a preparation method thereof, a battery and an electric device. The diaphragm comprises a base membrane and a coating arranged on at least one surface of the base membrane, the coating contains polymer particles, the polymer particles comprise first polymer particles and second polymer particles mixed with the first polymer particles, and the particle size Dv50 of the first polymer particles is different from that of the second polymer particles. The diaphragm provided by the embodiment of the invention contains the coating, namely, the diaphragm has high mechanical properties such as compression resistance and hot melting responsiveness on the basis of good air permeability, the balance between the mechanical properties such as compression resistance and the hot melting responsiveness is good, and the barrier property on precipitated metal is good. The preparation method can ensure stable performance of the diaphragm structure and the like. The battery comprises the diaphragm.

Description

Diaphragm and preparation method thereof, battery and electrical device Technical Field

[0001] 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 Art

[0002] 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 battery with the most prominent development momentum.

[0003] As battery applications expand, especially in recent years with the rapid development of electric vehicles, power batteries have experienced rapid development and a sharp increase in demand. However, battery safety performance has also received increasing attention and has become one of the key factors restricting the expansion of battery applications.

[0004] Among battery safety issues, the most prominent is the runaway exothermic reaction within the battery. While existing safety-modified separators can improve their safety against thermal runaway to a certain extent, in practice, they suffer from an imbalance between their thermal melt response rate and their compressive strength. This results in either an unsatisfactory thermal melt response rate or unstable performance, such as air permeability, which in turn affects the battery's electrochemical performance.

[0005] Summary of the Invention

[0006] In view of the above problems, the embodiments of the present application provide a diaphragm and its preparation method and application to solve the technical problem of the imbalance between the hot melt response rate and the pressure resistance of the existing safety modified diaphragm.

[0007] 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, wherein the coating comprises polymer particles, wherein the polymer particles comprise first polymer particles and second polymer particles mixed with the first polymer particles, wherein the volume distribution particle size D of the first polymer particles and the second polymer particles is v 50 different.

[0008] The volume distribution particle size D contained in the coating of the diaphragm of the embodiment of the present application is v By compounding 50 different first and second polymer particles, a porous structure with rich pores is constructed in the coating, resulting in improved air permeability for the separator. Furthermore, the coating formed by this compounded polymer particle system imparts enhanced mechanical properties, such as compressive strength, while also exhibiting good thermal melt responsiveness. It also acts as a barrier to the migration of precipitated metals, further enhancing the electrochemical performance and safety of the battery.

[0009] In some embodiments, the volume distribution particle size D of the first polymer particles is v 50 is greater than the volume distribution particle size D of the second polymer particles v 50, and the volume distribution particle size D of the first polymer particles v 50 is 2 μm to 2.5 μm, and the volume distribution particle size D of the second polymer particles is v 50 is 0.3 μm to 0.6 μm. By controlling the particle sizes of the first polymer particles and the second polymer particles in this range, the particle sizes D v The first polymer particles and the second polymer particles of 50 can be compounded to play a synergistic role, further improving the air permeability of the coating, that is, the membrane, balancing the mechanical properties such as compressive resistance and thermal melting responsiveness of the coating, that is, the membrane, and further improving the performance of preventing metal precipitation.

[0010] In some embodiments, the mass ratio of the first polymer particles to the second polymer particles is (1 to 1.5): 1. This ratio of composite polymer particles can further enhance the synergistic effect of the two, thereby further improving the balance between the mechanical properties of the coating (i.e., the membrane) such as air permeability and compressive strength and thermal melt responsiveness, and further improving the performance of preventing metal precipitate permeability.

[0011] In some embodiments, the melting point of the first polymer particles is 115°C to 120°C, and the melting point of the second polymer particles is 90°C to 110°C. By controlling the melting points of the first and second polymer particles within this temperature range, a melting point gradient can be formed among the polymer particles, thereby further improving the balance between mechanical properties such as compressive strength and thermal melt responsiveness of the coating, i.e., the diaphragm.

[0012] In some embodiments, the polymer particles satisfy at least any one of the following conditions (1) to (3):

[0013] (1) The morphology of the first polymer particles and the second polymer particles independently includes at least one of chain, spherical, quasi-spherical, fibrous, tubular, rod-like, amorphous, and pyramidal;

[0014] (2) at least one of the first polymer particles and the second polymer particles contains a nonionic group;

[0015] (3) The weight average molecular weight of at least one of the first polymer particles and the second polymer particles is from 1,000 to 10,000, and optionally from 1,500 to 4,000.

[0016] In some embodiments, the material of the polymer particles includes at least one of polystyrene, polyolefin, polyimide, melamine resin, phenol resin, cellulose, polyester, polyphenylene sulfide, polyaramid, polyamideimide, copolymer of butyl acrylate and ethyl methacrylate, and modified polymers thereof.

[0017] The polymer particles have any of the above characteristics, which can further improve the balance of mechanical properties such as air permeability, compressive resistance and thermal melt responsiveness of the coating, that is, the diaphragm, while further reducing the permeability to precipitated metals, thereby improving the electrochemical properties and safety performance of the battery, such as the capacity retention rate.

[0018] In some embodiments, the nonionic groups include at least one of ethoxy, hydroxyl, and carboxylate groups. These nonionic groups can further enhance the aforementioned effects of the polymer particles, particularly improving the compressive strength of the polymer particles, thereby improving the compressive strength and stability of the coating, i.e., the separator, during battery production and normal operation.

[0019] In some embodiments, the content of the polymer particles in the coating is ≥ 28 wt%, and can be 28 wt% to 38 wt%, 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 balance between the coating's mechanical properties, such as compressive strength, and its thermal melt responsiveness can be further improved, further enhancing its barrier properties against precipitated metals.

[0020] In some embodiments, the coating further comprises an inorganic particle filler. The presence of the inorganic particle filler can further improve the mechanical properties and stability of the coating, i.e., the membrane, such as air permeability and compressive strength, and enhance the barrier property against precipitated metals.

[0021] In some embodiments, the inorganic particulate filler satisfies at least one of the following conditions:

[0022] The content of the inorganic particulate filler in the coating is 22 wt % to 30 wt % based on the total dry weight of the coating as 100%;

[0023] The volume distribution particle size D of the inorganic particle filler v 50 is 1μm to 1.5μm;

[0024] The inorganic particle filler includes at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0025] The inorganic particle filler has any of the above characteristics, and can further improve the mechanical properties such as air permeability and compressive strength of the coating, that is, the diaphragm, and enhance the barrier property against precipitated metals.

[0026] In some embodiments, the coating further comprises a cured binder. By adding a binder to the coating, the mechanical strength of the membrane can be improved, the membrane's mechanical properties such as air permeability and compressive strength can be adjusted, and the barrier effect of the coating on precipitated metals can be enhanced.

[0027] In the embodiment, based on the total dry weight of the coating being 100%, the content of the binder in the coating after curing is 20 wt % to 30 wt %.

[0028] The thermal decomposition temperature of the binder is ≥160°C, and can be selected from 160°C to 300°C.

[0029] The aqueous binder having the above characteristics can enhance the mechanical strength of the diaphragm, further adjust the mechanical properties of the diaphragm such as air permeability and pressure resistance, and improve the barrier effect on precipitated metals.

[0030] In some embodiments, the base film has a thickness of 4 μm to 7 μm; a base film of this thickness, together with the coating, can effectively reduce the thickness of the separator while meeting battery application requirements.

[0031] In some embodiments, the coating has a thickness of 2 μm to 5 μm.

[0032] In some embodiments, the surface density of the coating is 2 g / m 2 Up to 8g / m 2 .

[0033] By controlling characteristics such as coating thickness and area, the coating, i.e., the diaphragm, can be further improved in terms of mechanical properties including permeability and compressive strength to precipitated metals, as well as its hot melt responsiveness.

[0034] 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:

[0035] providing a base film and a coating slurry containing polymer particles;

[0036] Applying the coating slurry on at least one surface of the base film and drying it to form a coating to obtain a diaphragm;

[0037] The polymer particles include first polymer particles and second polymer particles mixed with the first polymer particles, and the first polymer particles and the second polymer particles have different particle size distribution ranges.

[0038] The diaphragm prepared by the diaphragm preparation method of the embodiment of the present application has higher air permeability than the diaphragm of the embodiment of the text application, and at the same time has higher mechanical properties such as compressive resistance and thermal melt responsiveness, and the mechanical properties such as compressive resistance and thermal melt responsiveness are relatively balanced, which can further block the migration of precipitated metals and improve the capacity retention rate and safety performance of the battery.

[0039] In some embodiments, the coating slurry further comprises an inorganic particle filler and a binder; wherein the mass ratio of the organic polymer particles, the inorganic particle filler and the binder in the coating slurry is (28 to 38):(22 to 30):(20 to 30).

[0040] In some embodiments, the coating slurry has a solid content of 30 wt % to 40 wt %.

[0041] In some embodiments, the coating slurry has a viscosity of 100 mPa·s to 1000 mPa·s at 25°C.

[0042] The coating slurry with the above characteristics can improve the film-forming quality, improve the quality of the coating, and relatively balance the air permeability, pressure resistance and hot melt responsiveness, and improve the barrier to metal precipitation permeability.

[0043] In some embodiments, the binder is added in the form of a binder aqueous solution, and the binder aqueous solution has at least one of the following conditions:

[0044] The viscosity of the binder aqueous solution at 25° C. is 3000 mPa·s to 10000 mPa·s;

[0045] The solid content of the binder aqueous solution is 40 wt % to 50 wt %.

[0046] The coating slurry having the above characteristics can improve the film-forming quality, the coating quality, and the air permeability, pressure resistance, and barrier properties including the permeability of precipitated metals.

[0047] 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:

[0048] The polymer precursor particles, the ethoxy-containing polymer and the initiator are mixed and reacted to obtain polymer particles containing nonionic groups;

[0049] The polymer particles containing nonionic groups are emulsified with a nonionic surfactant to obtain a nonionic polymer emulsion.

[0050] By using ethoxylated polymers to carry out polymerization reactions with polymer precursor particles, the polymer particles can be enriched with nonionic groups, particularly improving mechanical properties such as compressive strength. Furthermore, the particle size range of the prepared polymer particles can be effectively controlled.

[0051] In some embodiments, the polymer precursor particles, the ethoxy-containing polymer, and the initiator are mixed in a ratio of (300-400): (90-125): (20-50).

[0052] 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, polyaramid, polyamideimide, and a copolymer of butyl acrylate and ethyl methacrylate.

[0053] In some embodiments, the ethoxy-containing polymer includes at least one of allyl polyethylene glycol and bisallyl polyether.

[0054] In some embodiments, the initiator includes at least one of di-tert-butyl peroxide and dicumyl peroxide.

[0055] In some embodiments, the reaction temperature is 130°C to 160°C.

[0056] In some embodiments, the polymer particles and the nonionic surfactant are emulsified in a mass ratio of (4 to 6):1.

[0057] The above-mentioned reactant types, mixing ratios and reaction conditions can increase the non-ionic group grafting rate and content of the polymer particles and adjust the particle size, thereby improving the air permeability of the polymer particle-formed coating, i.e., the membrane, and its own mechanical properties such as compressive strength, and can also improve the relative balance between the compressive strength and hot melt responsiveness of the coating, i.e., the membrane.

[0058] In the embodiment, the nonionic polymer emulsion satisfies at least any one of the following conditions (1) to (4):

[0059] (1) The viscosity of the nonionic polymer emulsion at 25° C. is 10 mPa·s to 100 mPa·s;

[0060] (2) the solid content of the nonionic polymer emulsion is 35 wt% to 40 wt%;

[0061] (3) the pH value of the nonionic polymer emulsion is 5 to 6;

[0062] (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.

[0063] In an exemplary embodiment, the carbon chain alkyl group is a long carbon chain alkyl group ranging from C12 to C18.

[0064] In an exemplary embodiment, 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.

[0065] In an 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.

[0066] By selecting the type of nonionic surfactant, the stability of the nonionic polymer emulsion can be improved, its dispersibility in the coating slurry can be improved, and thus the dispersion uniformity and stability of the polymer particles can be improved.

[0067] In some embodiments, the aqueous binder is added in the form of an aqueous binder aqueous solution, and the aqueous binder aqueous solution has at least one of the following conditions:

[0068] The aqueous binder solution has a viscosity of 3000 to 10000 mPa·s at 25° C.;

[0069] The solid content of the aqueous binder solution is 40 wt % to 50 wt %.

[0070] These aqueous binders can improve the stability of the coating slurry and the uniformity of component dispersion, and improve the mechanical properties and air permeability of the formed coating, so as to improve the relative balance between the compressive strength and hot melt responsiveness of the coating, that is, the diaphragm.

[0071] In some embodiments, the coating slurry is applied at a rate of 20 m / min to 100 m / min, and optionally 50 m / min to 100 m / min.

[0072] In some embodiments, the drying temperature is 50°C to 70°C, and optionally 60°C to 70°C.

[0073] In some embodiments, the drying time is 1 min to 5 min, and can be optionally 1 min to 3 min.

[0074] By adjusting the coating process conditions, the film quality, thickness and permeability can be adjusted and optimized.

[0075] In a third aspect, embodiments of the present application provide a battery. The battery of the present application includes a positive electrode, a negative electrode, and a separator laminated between the positive and negative electrodes. The separator is the separator described in the embodiments of the present application or a separator prepared by the separator preparation method of the embodiments of the present application. Because the battery of the present application includes the separator of the embodiments of the present application, it has high battery safety and good electrochemical properties such as capacity retention.

[0076] In an embodiment, the coating is provided on one surface of the separator, with the coating facing the negative electrode. By only applying the coating to one surface of the separator, the overall thickness of the separator can be effectively reduced, thereby increasing the energy density of the battery.

[0077] In a fourth aspect, an embodiment of the present application provides an electrical device, wherein the electrical device includes a battery according to an embodiment of the present application, and the battery is used to provide electrical energy. The safety of the electrical device according to the embodiment of the present application is significantly improved.

[0078] 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

[0079] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0080] FIG1 is a schematic flow chart of a method for preparing a diaphragm according to an embodiment of the present application;

[0081] FIG2 is a schematic structural diagram of an embodiment of a secondary battery according to an embodiment of the present application;

[0082] FIG3 is an exploded schematic diagram of the secondary battery shown in FIG2 ;

[0083] FIG4 is a schematic structural diagram of an embodiment of a battery module according to the present application;

[0084] FIG5 is a schematic structural diagram of an embodiment of a battery pack according to the present application;

[0085] FIG6 is a schematic diagram of the exploded structure of the battery pack shown in FIG5 ;

[0086] FIG7 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;

[0087] FIG8 is a scanning electron microscope (SEM) image of the separator in Example A1 of the present application after being heated at 130° C. for 15 minutes;

[0088] FIG9 is a scanning electron microscope (SEM) image of the separator in Comparative Example A1 of the present application after being heated at 130° C. for 15 minutes.

[0089] The accompanying drawings in the specific implementation manner are as follows:

[0090] 10. Secondary battery cell, 11. Housing, 12. Electrode assembly, 13. Cover plate;

[0091] 20. Battery module;

[0092] 30. Battery pack, 31. Box, 32. Lower box. DETAILED DESCRIPTION

[0093] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0094] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art 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" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0095] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0096] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0097] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0098] 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).

[0099] 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., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and 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 device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0100] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0101] 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 battery with the most prominent development momentum.

[0102] In ion batteries such as lithium-ion batteries, the diaphragm is one of the important components, which is set between the positive and negative pole pieces to separate the positive and negative poles of the battery, preventing the two poles from contacting and short-circuiting, and preventing the Li-ion battery from passing through the positive and negative poles. + Therefore, in addition to having good electrolyte wettability, liquid retention, and mechanical strength, the separator also needs to have properties such as thermal stability that have a significant impact on battery safety, as battery safety performance is increasingly valued.

[0103] 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 substances, electrochemically inert ceramics, etc. during the preparation process of the diaphragm, so as to achieve the purpose of improving the thermal stability and other properties of the diaphragm and thus improving battery safety.

[0104] While current methods like doping or coating can improve separator performance, such as thermal stability, to a certain extent, the inventors discovered that when exothermic reactions within the battery accumulate to a certain level, the modified separator is unable to promptly block the continued reaction. This makes it difficult to mitigate and suppress the exothermic reaction, and thus, it is difficult to reduce the possibility of internal short circuits or even thermal runaway. Therefore, this approach is not ideal for improving battery safety, such as thermal runaway.

[0105] In order to improve the role of the diaphragm in suppressing battery thermal runaway, 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 seal 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.

[0106] Based on the diaphragm developed in the early stage, the inventor conducted further research on the diaphragm and found that when the diaphragm coating is prepared, the particle size of the polymer particles has an important influence on the air permeability, hot melt response rate and pressure resistance of the coating, as well as the barrier to the migration of precipitated metals, thereby affecting the corresponding performance of the diaphragm. In particular, the hot melt response rate and pressure resistance of the coating are unbalanced, resulting in a phenomenon of losing one while taking care of the other in the hot melt response rate and air permeability of the coating, which is also the diaphragm, and it is difficult to take both into account. Therefore, the inventor further studied and found that if polymer particles of different particle sizes are compounded so that the polymer particles are a mixture of different particle sizes, and polymer particles of different particle sizes are distributed in the coating, and the coating formed by polymer particles of different particle sizes is combined with the base film to form a diaphragm, the hot melt response rate and pressure resistance of the diaphragm can be significantly improved, and the balance between the two regulating the hot melt response rate and pressure resistance.

[0107] At the same time, the positive electrode material will undergo a crystal phase transition at high voltage or high temperature, resulting in metal precipitation. The precipitated metals include transition metals, etc., and will migrate to the negative electrode through the diaphragm to deposit or further form dendrites, which may puncture the diaphragm and cause risks such as short circuits. The inventors found that a coating formed by a mixture of polymer particles of different particle sizes can also act as a barrier to precipitated metals. Therefore, based on the previous diaphragm solution, the following diaphragm improvement solution is further proposed.

[0108] diaphragm

[0109] 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 comprises polymer particles, the polymer particles comprising first polymer particles and second polymer particles mixed with the first polymer particles, the first polymer particles and the second polymer particles having a volume distribution particle size D v 50 different.

[0110] In the separators of the present invention, the base film comprises the substrate and performs the usual functions of a separator. The coating is disposed on the base film and modifies the base film, i.e., the separator matrix. For example, when the battery overheats, the first and second polymer particles can undergo a gradient melting process, promptly sealing the pores in the base film.

[0111] The particle size D contained in the coating of the diaphragm of the embodiment of the present application is v 50 different first polymer particles and second polymer particles are compounded to construct a porous structure with rich pores in the coating, so that the diaphragm has better air permeability in a normal working environment, and also gives the coating, that is, the diaphragm, a barrier property that can effectively reduce or even prevent the metals such as transition metals precipitated from the positive electrode active material, thereby reducing or preventing the precipitated metal from reaching the negative electrode through the diaphragm of the embodiment of the present application and depositing or forming dendrites. Since the diaphragm has a barrier property to the precipitated metal, it can alleviate or reduce the rate of metal precipitation of the positive electrode active material, thereby improving the stability and cycle performance of the positive electrode active material. Among them, the precipitated metal includes metal elements or metal ions.

[0112] At the same time, the coating formed by the compounded polymer particles also has higher mechanical properties such as compressive strength, thereby further improving the compressive strength of the coating, i.e., the diaphragm during battery production and normal operation, and improving the stability of the diaphragm's performance such as air permeability. Moreover, when the diaphragm is in a thermal abnormality, the relatively small particle size D v 50% of the polymer particles can melt in time and close the pores of the base film. As the temperature continues to rise, the larger the particle size D vThe polymer particles at 50% will also melt, further sealing the pores of the base film and improving the thermal melt response of the diaphragm coating, thereby reducing or preventing chemical reactions within the battery, including those in the electrolyte, the migration of metal ions, and crosstalk reactions between the positive and negative electrodes, alleviating or terminating thermal runaway of the battery, thereby improving the safety performance of the battery. Furthermore, the inventors have discovered that the composite polymer particles impart a balance between the mechanical properties such as compressive strength and the thermal melt response rate of the coating, i.e., the diaphragm of the present application, which simultaneously possesses good mechanical properties such as compressive strength and thermal melt response performance.

[0113] The migration of metal ions includes lithium ions and metal precipitation from active materials, etc., to prevent them from passing through the diaphragm and depositing on the surface of the electrodes, especially the negative electrode, or further forming dendrites. Positive-negative electrode crosstalk reaction refers to the release of oxygen when the positive electrode active material undergoes a phase change at high temperature. Oxygen can diffuse through the diaphragm to the negative electrode and react with other substances including the negative electrode, releasing a large amount of heat. It also includes hydrogen released from the negative electrode at high temperature, which diffuses through the diaphragm to the positive electrode and reacts with other substances including the positive electrode, releasing a large amount of heat.

[0114] It is precisely because the diaphragm of the embodiment of the present application has the above-mentioned good and relatively balanced mechanical properties such as compressive resistance and hot melt response, and also has a barrier property against precipitated metals. Therefore, in the embodiment, the diaphragm of the embodiment of the present application can be used in a battery with high-voltage lithium cobalt oxide as the positive electrode material. In this way, even when the battery voltage reaches about 4.5V, when the hexagonal phase of the lithium cobalt oxide material transforms to the monoclinic phase and causes the dissolution of cobalt metal, the diaphragm of the embodiment of the present application will more effectively reduce or prevent the precipitated cobalt metal from passing through, thereby further reducing the risk of deposition of negative electrode cobalt metal or further formation of dendrites, thereby further improving the capacity retention rate and safety performance of the battery.

[0115] In some embodiments, the particle size D of the first polymer particles is v 50 is greater than the particle size D of the second polymer particles v 50, and the volume distribution particle size D of the first polymer particles v 50 is 2 μm to 2.5 μm, and the volume distribution particle size D of the second polymer particles is v 50 is 0.3 μm to 0.6 μm. By controlling the particle sizes of the first polymer particles and the second polymer particles in this range, the particle sizes D v The compounding effect and synergistic effect between the first polymer particles and the second polymer particles of 50 further improve the mechanical properties such as air permeability, pressure resistance and thermal melt response of the coating, that is, the diaphragm, and further improve the mitigation or prevention of energy effects including the permeation of precipitated metals. In the exemplary embodiment, the particle size volume distribution D of the first polymer particles is v50 can be, but is not limited to, typical non-limiting particle sizes such as 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, and 2.5 μm, and can optionally be 2.2 μm to 2.4 μm; in the exemplary embodiment, the volume distribution particle size D of the second polymer particles is v The particle size 50 may be, but is not limited to, typical non-limiting particle sizes such as 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, and optionally 0.4 μm to 0.5 μm.

[0116] In some embodiments, the mass ratio of the first polymer particles to the second polymer particles can be 1:1 to 1.5:1, specifically, typical non-limiting ratios such as 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, and 1.5:1. Controlling the compounding ratio of the first polymer particles to the second polymer particles within this range can further enhance the compounding effect between the first and second polymer particles, further improving the synergistic effect between the two, thereby further improving the air permeability, mechanical properties such as compressive strength, and thermal melt responsiveness of the coating, i.e., the membrane, further improving the balance between mechanical properties such as compressive strength and thermal melt responsiveness, and preventing the permeability of metal precipitation.

[0117] Based on the particle size ranges of the first and second polymer particles, in one embodiment, the melting point of the first polymer particles is 115°C to 120°C, specifically 115°C, 116°C, 117°C, 118°C, 119°C, 120°C, and other typical, non-limiting temperatures. In another embodiment, the melting point of the second polymer particles is 90°C to 110°C, specifically 90°C, 92°C, 94°C, 96°C, 98°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, and other typical, non-limiting temperatures. By controlling the melting points of the first and second polymer particles within this temperature range, the coating can have a thermal melt gradient, thereby further improving the pore sealing effect of the coating, i.e., the separator, in abnormally high temperature environments, thereby further improving the barrier properties and barrier stability of the separator during abnormal thermal conditions, and further enhancing battery safety.

[0118] In some embodiments, the polymer particles contained in the coating in each of the above embodiments, including at least one of the first polymer particles and the second polymer particles, may have a morphology of at least one of chain, spherical, quasi-spherical, fibrous, tubular, rod-shaped, amorphous, and pyramidal. Polymer particles with these morphologies have high compressive strength and hot-melt responsiveness, and can form a porous structure with abundant pores, thereby improving the compressive and other mechanical properties of the coating, i.e., the diaphragm, as well as the hot-melt responsiveness and the balance between the two. Furthermore, the coating, i.e., the diaphragm, can improve its balanced air permeability and barrier properties to precipitated metals, such as transition metals.

[0119] In some embodiments, the organic material of at least one of the first and second polymer particles in the polymer particles described above contains non-ionic groups. In some embodiments, the molar percentage of the non-ionic groups in the organic material of the polymer particles is 0.1% to 5%, specifically, a molar percentage of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or the like. In exemplary embodiments, the non-ionic groups may include at least one of ethoxy, hydroxyl, and carboxylate groups. By adding non-ionic groups to the polymer particles and further controlling the content and type of the non-ionic groups in the polymer particles, the aforementioned effects of the polymer particles can be further enhanced, particularly the compressive resistance of the polymer particles, thereby improving the balance between the mechanical properties of the coating (i.e., the compressive resistance) and the thermal melt response of the membrane. Furthermore, the dispersion uniformity of the polymer particles in the coating and the film quality of the coating can be improved. The non-ionic groups may be grafted side chains of the polymers or attached to the polymer backbone.

[0120] In some embodiments, the polymer of the polymer particles can be a polymer with a weight average molecular weight of 1000 to 10000, and further can be a polymer with a weight average molecular weight of 1500 to 4000. Wherein, the molecular weight can be tested by gel permeation chromatography (GPC) and with reference to GBT27843-2011 chemical polymer low molecular weight component content detection method. In the exemplary embodiment, the material of the polymer particles can include at least one of a copolymer of polystyrene, polyolefin, polyimide, melamine resin, phenolic resin, cellulose, polyester, polyphenylene sulfide, polyaramid, polyamide-imide, butyl acrylate and ethyl methacrylate and their respective modified polymers. By selecting the polymer material of the polymer particles, such as selecting these polymers, the mechanical properties such as the first polymer particles and the second polymer particles compression resistance and the heat-melt responsiveness and the balance of mechanical properties such as compression resistance and the heat-melt responsiveness in the above-mentioned embodiments can be effectively improved.

[0121] In addition, the polymer particles in the above embodiments can be solid particles, and of course they can also be hollow particles. In the embodiments of the present application, solid particles can improve the compressive resistance of the polymer particles compared to hollow particles, thereby improving the stability of the coating, that is, the diaphragm, during battery production and normal operation. For example, the polymer particles will not be deformed due to the squeezing force during battery production or normal operation, thereby causing the base membrane to block pores. Therefore, in the embodiments of the present application, solid polymer particles are relatively preferred compared to hollow polymer particles.

[0122] In some embodiments, in each of the above embodiments, the total weight of the polymer particles, such as the first polymer particles and the second polymer particles, in the coating can be ≥28 wt%, and further can be 28 wt% to 38 wt%, based on the total dry weight of the coating as 100%. By controlling and adjusting the content of the polymer particles in the coating, if controlled within this range, the mechanical properties such as compressive strength and thermal melt responsiveness of the coating, i.e., the diaphragm, as well as the balance between these two properties, can be further improved. The polymer particles can also be enhanced to melt and seal pores in the base film during thermal anomalies, thereby improving the barrier properties of the coating, i.e., the diaphragm, during thermal runaway.

[0123] In some embodiments, the coatings included in the separators of the aforementioned embodiments further contain inorganic particulate fillers. Adding the inorganic particulate fillers to the coatings can, on the one hand, improve the coating's mechanical properties, such as compressive strength, and enhance the separator's stability during battery production and normal operation. Furthermore, they can synergize with the aforementioned polymer particles, further improving the coating's pore structure to enhance the coating's (i.e., the separator's) air permeability, mechanical properties such as compressive strength, and thermal shrinkage resistance, enhancing its barrier properties against precipitated metals and improving the coating's (i.e., the separator's) liquid storage capacity. Furthermore, the inorganic particulate fillers ideally form a mixture with the aforementioned polymer particles in the coating.

[0124] In an embodiment, the content of the inorganic particle filler in the coating layer may be 22 wt % to 30 wt %. By controlling the content ratio of the inorganic particle filler and the composite polymer particles in the coating layer, the respective effects of the inorganic particle filler and the composite polymer particles can be fully volatilized, and the synergistic effect between the two can be enhanced. This further improves the balance between mechanical properties such as compressive strength and thermal shrinkage resistance, while ensuring that the membrane has good air permeability, mechanical properties such as compressive strength and heat shrinkage resistance, liquid storage capacity, and metal barrier properties, including precipitated metals.

[0125] In the embodiment, the volume distribution particle size D of the inorganic particle filler is v 50 is 1 μm to 1.5 μm. By adjusting the inorganic particle filler, it is compounded with the polymer particles containing the first polymer particles and the second polymer particles. v 50 is 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 at the same time, work together with the first polymer particles and the second polymer particles in the above-mentioned particle size range to improve the air permeability, mechanical properties and liquid storage capacity of the diaphragm, as well as the performance including the barrier effect on metal precipitation.

[0126] In an embodiment, the inorganic particle filler may include at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0127] In an exemplary embodiment, the inorganic material of the inorganic particles having a dielectric constant of 5 or more includes 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, Pb 1-m La m Zr 1-n TinO3、Pb(Mg3Nb 2 / 3 )O3-PbTiO3, and at least one of their respective modified inorganic particles, 0<m<1, 0<n<1.

[0128] In an exemplary embodiment, the inorganic material of the inorganic particles having ion conductivity but not storing ions includes Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum lithium titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 、SiS2 type glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4 At least one of , 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;

[0129] 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.

[0130] By selecting the type of material for the inorganic particle filler, the aforementioned effects of the inorganic particle filler are enhanced, and the synergistic effect between the inorganic particle filler and the polymer particles is further enhanced. This improves the balance between the mechanical properties of the coating, i.e., the compressive strength, and the thermal melt responsiveness of the membrane, the coating of the present application, and the membrane, thereby further enhancing the barrier effect against precipitated metals and improving the electrochemical performance and safety performance of the battery, such as the capacity retention rate. Among them, the inorganic particle fillers of some of the aforementioned inorganic materials also have good liquid absorption and storage capabilities, thereby improving the liquid absorption and storage capabilities of the membrane.

[0131] Based on the polymer particles and inorganic particulate fillers described above, in this exemplary embodiment, the polymer particles contained in the coating are low-density polyethylene, specifically low-density polyethylene particles, and further, low-density polyethylene containing non-ionic groups. The low-density polyethylene refers to high-pressure polyethylene (LDPE), specifically polyethylene with a molecular weight of less than 10,000.

[0132] The above-mentioned inorganic particles are compounded with the low-density polyethylene particles to enhance the above-mentioned synergistic effect between the above-mentioned composite polymer particles and the inorganic particle filler, thereby improving the balance between the thermal melt responsiveness, mechanical properties, compressive strength and other mechanical properties of the coating of the embodiment of the present application, that is, the diaphragm and the thermal melt responsiveness, as well as the stability of properties including air permeability, and further enhancing the barrier effect on precipitated metals and the liquid absorption and storage capacity, thereby improving the electrochemical properties and safety performance of the battery, such as the capacity retention rate.

[0133] In some embodiments, the coating contained in the diaphragm of each of the above embodiments further contains a cured binder. By adding a 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 and enhancing the bonding force between the coating and the base film. At the same time, the binder can also play a synergistic role with the polymer particles or further with the inorganic particle filler, adjusting the balance between the mechanical properties of the coating, that is, the diaphragm, mechanical properties such as compressive strength and hot melt responsiveness, improving stability including air permeability and barrier effect including metal precipitation, so as to improve the electrochemical properties and safety performance of the battery such as capacity retention rate.

[0134] In an embodiment, the binder content in the coating can be 20 wt % to 30 wt % based on the total dry weight of the coating as 100%. By controlling the binder content in the coating, the mechanical properties of the coating and the adhesion to the base film can be further enhanced, thereby further adjusting the balance between the mechanical properties such as compressive strength and the thermal melt response of the coating (i.e., the separator), improving the barrier effect against precipitated metals, and improving the electrochemical performance and safety performance of the battery, such as the capacity retention rate.

[0135] In an embodiment, the thermal decomposition temperature of the cured binder is higher than 160°C, and can be selected from 160°C to 300°C. By selecting the decomposition temperature characteristic of the binder, the mechanical properties of the coating and the bonding strength between the coating and the base film are enhanced, and the balance between the mechanical properties such as compressive strength and thermal melt responsiveness of the separator is improved, as well as the stability of properties such as the barrier to metal precipitation.

[0136] In an embodiment, the binder can be a water-based binder. The water-based binder can be a water-soluble binder or an emulsion binder. In an exemplary embodiment, the binder can 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 hydroxyl derivative of cyclodextrin. These 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 balance between the mechanical properties such as compressive strength of the diaphragm and the hot melt responsiveness and the barrier effect of the coating on precipitated metals can be further adjusted to improve the electrochemical properties and safety performance of the battery, such as the capacity retention rate.

[0137] In an embodiment, when the coating contains both the above-mentioned inorganic particle filler and the binder, the dry basis mass ratio of the above-mentioned polymer particles, inorganic particle filler, and binder in the coating can be (25 to 35): (55 to 65): (25 to 35). By controlling the content ratio of the three components in the coating, the above-mentioned effects of each component and the synergistic effect between the three components are further improved, thereby further improving the balance between the mechanical properties such as compressive strength and the hot melt responsiveness of the coating, i.e., the separator, and the barrier effect on precipitated metals, thereby improving the capacity retention rate and safety performance of the battery.

[0138] Based on the coating schemes in the above embodiments, in some embodiments, the coating thickness can be 2μm to 5μm. In exemplary embodiments, 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 fully play the role described above, improving the electrochemical stability of the battery during production and normal operation and the barrier to precipitated metals, avoiding migration and deposition to the negative electrode and the possible formation of dendrites; when the battery experiences thermal anomalies, the polymer particles in the diaphragm coating can melt in time and effectively seal the pores of the base membrane, reducing or preventing the risk of thermal runaway, thereby improving the battery's electrochemical performance and safety performance, such as capacity retention.

[0139] After testing, the surface density of the coating contained in the above-mentioned embodiments can be controlled at 2g / m2 Up to 8g / m 2 By controlling and optimizing these properties of the coating, the membrane's air permeability, mechanical properties such as compressive strength, the balance between mechanical properties such as compressive strength and thermal melt responsiveness, and its ability to prevent the migration of precipitated metals can be further improved, thereby further enhancing the battery's electrochemical performance and safety.

[0140] Furthermore, the coating included in the separators of the above embodiments may be disposed on one surface of the base membrane, or alternatively, on two opposing surfaces of the base membrane. Based on considerations such as battery energy density and the direction of metal precipitation and migration, in the embodiments, the coating may be disposed on one surface of the base membrane, i.e., the opposing surface of the base membrane may not be coated.

[0141] The base film contained in the separators of the above embodiments can be an organic battery separator. For example, in the embodiments, 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 embodiments, the base film material includes at least one of non-woven fabric, polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. Base films with these characteristics and materials, while fully utilizing the functions of battery separators, can be combined with the above coatings to enhance their synergy, resulting in a separator with high mechanical properties such as compressive strength, a balance between mechanical properties such as compressive strength and thermal melt responsiveness, good air permeability, and excellent barrier properties, including those against precipitated metals. This can effectively reduce the risk of thermal runaway of the battery and improve the electrochemical properties and safety performance of the battery, such as capacity retention.

[0142] 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 substances, electrochemically inert ceramics, etc., to improve the thermal stability of the base membrane, to cooperate with the above-mentioned coating, and further improve the mechanical properties and safety performance of the diaphragm of the embodiment of the present application.

[0143] Method for preparing diaphragm

[0144] In a second aspect, the present invention provides a method for preparing a diaphragm. The process flow of the method for preparing a diaphragm according to the present invention is shown in FIG1 . The method for preparing a diaphragm according to the present invention may include the following steps:

[0145] S01: providing a basement membrane;

[0146] S02: providing coating slurry;

[0147] S03: coating the coating slurry on at least one surface of the base film, performing a drying process to form a coating layer, and obtaining a separator.

[0148] In the method for preparing the diaphragm of the embodiment of the present application, after the coating slurry is formed into a coating on the surface of the base film, the coating is bonded to the surface of the base film. Since the method for preparing the diaphragm of 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 polymer particles are the polymer particles contained in the coating of the diaphragm of the embodiment of the present application, which include first polymer particles and second polymer particles mixed with the first polymer particles, and the cumulative distribution particle size D of the first polymer particles and the second polymer particles is v 50 different.

[0149] The diaphragm preparation method of the present application embodiment is to set the particle size D v 50 Different first polymer particles and second polymer particles are formulated into a coating slurry, and are directly treated to form a film on the base membrane, so that the prepared membrane is combined with the coating on at least one surface to achieve the coating's modification effect on the base membrane.

[0150] Then the coating is the coating contained in the diaphragm of the embodiment of the above text application. Therefore, the diaphragm prepared by the diaphragm preparation method of the embodiment of the present application has better mechanical properties such as compressive strength, and a relative balance between mechanical properties such as compressive strength and hot melt responsiveness as the diaphragm of the embodiment of the above text application. While having good air permeability, the barrier effect on precipitated metals can also be further improved, which can effectively further improve the electrochemical performance 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 performance of the prepared diaphragm are stable.

[0151] Step S01:

[0152] The base film in step S01 can be the base film included in the separator of the embodiment of the above-mentioned application. Therefore, the base film can be the base film included in the separator of the embodiment of the above-mentioned application. As shown in the embodiment, the thickness of the provided base film can be 4 μm to 7 μm, and its air permeability can be 180 s / 100 cc to 240 s / 100 cc. Its material can include at least one of non-woven fabric, polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene.

[0153] Step S02:

[0154] Since the coating slurry in step S02 is a slurry for forming the coating contained in the above text application embodiment diaphragm, the slurry must contain polymer particles and a solvent. In the embodiment, it may further contain an inorganic particle filler and a binder. Therefore, the polymer particles contained in the coating slurry, or the material types and content ratios of the inorganic particle fillers and binders further contained therein are the same as the types and content ratios of the polymer particles, inorganic particle fillers and binders contained in the coating of the above text application embodiment diaphragm. Therefore, in order to save space, the types, content ratios, etc. of polymer particles, inorganic particle fillers and binders will not be described in detail here.

[0155] In order to further improve the film-forming quality of the coating slurry, improve the quality of the coating as well as the air permeability, pressure resistance and barrier properties including metal precipitation, 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 100mPa·s 1000mPa·s.

[0156] In some embodiments, when the coating slurry in step S02 is formed by mixing polymer particles, inorganic particle fillers and binders in a solvent; then the mass ratio of polymer particles, inorganic particle fillers, binders and water in the coating slurry can be (28 to 38): (22 to 30): (20 to 30): (25 to 35). This ratio refers to the mixing ratio of the binder to the 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 at the same time, the relative balance of mechanical properties such as air permeability, mechanical properties, compressive strength and hot melt responsiveness of the formed coating, that is, the diaphragm, and the barrier properties including metal precipitation are enhanced, thereby improving the electrochemical performance of the battery and reducing the risk of thermal runaway of the battery.

[0157] The binder may be a pre-cured binder, such as the pre-cured aqueous binder described above. In an exemplary embodiment, the binder may be a pre-cured binder comprising 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.

[0158] For example, in the embodiments, the binder is added in the form of an aqueous binder 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 binder is added in the form of an aqueous binder solution, in the embodiments, the viscosity of the aqueous binder solution at 25°C can be 3000mPa·s to 10000mPa·s; in other embodiments, the solid content of the aqueous binder solution is 40wt% to 50wt%. By controlling and adjusting the viscosity of the aqueous binder solution or the solid content at the same time, the positive effect of the binder on the coating slurry can be further enhanced, further improving the slurry stability and dispersibility.

[0159] In the embodiment, when the polymer particles contained in the coating slurry are polymer particles containing nonionic groups, the polymer particles can be prepared according to a method comprising the following steps:

[0160] Step S021: mixing and reacting polymer precursor particles, an ethoxy-containing polymer, and an initiator to obtain polymer particles containing nonionic groups;

[0161] Step S022: emulsifying the polymer particles containing nonionic groups with a nonionic surfactant to obtain a nonionic polymer emulsion.

[0162] During 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.

[0163] 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).

[0164] In an 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 to 4 hours at 130° C. to 140° C. At the same time, during the reaction process, the molten reactants are stirred to improve the efficiency and uniformity of the reaction.

[0165] By controlling and adjusting the mixing ratio of the reactants in step S021, or further controlling the reaction conditions, the polymer reaction efficiency is improved and the particle size of the polymer particles is within the range of D above. v On the basis of the range of 50 being 2μm to 2.5μm and 0.3μm to 0.6μm, the content of ethoxy nonionic groups grafted onto the polymer particles is increased, thereby improving the nonionic group modification effect of the polymer particles, thereby improving the above effects of the polymer particles, especially improving the mechanical properties such as compressive strength of the polymer particles and the relative balance between mechanical properties such as compressive strength and hot melt responsiveness.

[0166] 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, polyaramid, polyamideimide, and a copolymer of butyl acrylate and ethyl methacrylate.

[0167] The ethoxy-containing polymer may include at least one of allyl polyethylene glycol and bisallyl polyether.

[0168] The initiator may include at least one of di-tert-butyl peroxide and dicumyl peroxide.

[0169] The polymer precursor particles, ethoxylated polymer, and initiator can undergo a polymerization reaction in step S021 to improve the efficiency of graft modification. The ethoxylated polymer can effectively provide ethoxylated nonionic groups to achieve graft modification of the ethoxylated nonionic groups of the polymer precursor particles.

[0170] In step S022, during the emulsification process, a nonionic surfactant and nonionic group-containing polymer particles are combined in a solvent to form an emulsion. In embodiments, the mass ratio of the nonionic group-containing polymer particles to the nonionic surfactant can be (4 to 6):1, and in an exemplary embodiment, 4.5:1. The solvent can be water.

[0171] In addition, the mixing ratio of the nonionic surfactant and the polymer particles containing nonionic groups, as well as the amount of added aqueous solvent, can be controlled to adjust and control the relevant properties of the nonionic polymer emulsion, such as viscosity, solid content, pH value, etc., thereby improving 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 separator. For example, by controlling and adjusting the conditions of the emulsification treatment in step S022, the nonionic polymer emulsion has at least one of the following properties:

[0172] (1) The viscosity of the nonionic polymer emulsion is 10 mPa·s to 100 mPa·s;

[0173] (2) the solid content of the nonionic polymer emulsion is 35 wt % to 40 wt %;

[0174] (3) The pH value of the nonionic polymer emulsion is 5 to 6.

[0175] Among them, the 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.

[0176] In some embodiments, the nonionic surfactant may include a molecular structure of

[0177] Wherein, R1 is a carbon chain alkyl group. In an exemplary embodiment, when it is a carbon chain alkyl group, R1 is a long carbon chain alkyl group of C12 to C18.

[0178] R2 is a hydrophilic group. In an exemplary embodiment, 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.

[0179] 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.

[0180] In an 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.

[0181] By selecting the type of nonionic surfactant, the stability of the nonionic polymer emulsion can be improved, its dispersibility in the coating slurry can be improved, and thus the dispersion uniformity and stability of the polymer particles can be improved.

[0182] In addition, there is no specific order between step S01 and step S02 above. The order can be adjusted according to actual production, or they can be performed simultaneously.

[0183] Step S03:

[0184] The coating slurry is applied to the base film in step S02 to form a wet film, i.e., the coating layer before drying. The coating method is not limited to any method capable of forming a film of the coating slurry on the base film, and is within the scope of the embodiments disclosed herein. Examples include, but are not limited to, brushing, roller coating, and spraying. Furthermore, the coating process conditions can be further adjusted to optimize the film quality, thickness, and air permeability.

[0185] In the embodiment, the coating slurry in step S02 is applied at a rate of 20 m / min to 100 m / min, or 50 m / min to 100 m / min. This coating rate can improve the quality of the coating, adjust the air permeability and thickness, and adjust the mechanical properties to adjust the relative balance between mechanical properties such as compressive strength and hot melt responsiveness.

[0186] The drying process is primarily intended to remove solvent from the wet film. Based on the melting temperature range of the organic particles contained in the coating slurry, the drying process should be performed at a temperature below the melting temperature of the organic particles and should ensure coating quality and stability. For example, in the embodiment, the drying process temperature can be 50°C to 70°C, optionally 60°C to 70°C. In exemplary embodiments, typical but non-limiting temperatures such as, but not limited to, 50°C, 52°C, 55°C, 58°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, and 70°C can be used. Within this drying process temperature range, the drying time should be sufficient, for example, the drying process time can be 1 to 5 minutes, optionally 1 to 3 minutes.

[0187] Battery

[0188] In a third aspect, an embodiment of the present application provides a battery comprising 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 embodiment of the present application.

[0189] In the examples, the separator is coated only on one surface, with the coated surface facing the negative electrode. By orienting the coating toward the negative electrode, the separator fully utilizes the functions described in the examples above, improving the electrochemical performance and safety of the battery. Furthermore, by only coating the separator on one surface, the overall thickness of the separator can be effectively reduced, thereby increasing the battery's energy density.

[0190] In some embodiments, 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. Specifically, the negative electrode of the secondary battery is the negative electrode of the embodiment described above, and the negative electrode contains the modified artificial graphite of the embodiment described above.

[0191] In this way, the battery of the embodiment of the present application, specifically the secondary battery, has high energy density, high rate capability and good cycle stability.

[0192] In an embodiment, the secondary battery of the present application may include any one of a battery cell, a battery module, and a battery pack.

[0193] A battery cell is a structure that includes a battery housing and a cell encapsulated within the housing. The shape of a battery cell is not particularly limited and can be cylindrical, square, or any other shape. A square-shaped battery cell 10 is shown in FIG2 .

[0194] In some embodiments, as shown in Figure 3, 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, diaphragm and negative electrode contained in the secondary battery of the embodiment of the present application can be formed into 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 can be one or more, which can be adjusted according to actual needs.

[0195] The preparation method of the battery cell 10 is well known. In some embodiments, the positive electrode, separator, negative electrode, and electrolyte can be assembled to form the battery cell 10. As an example, the positive electrode, separator, and negative electrode can be wound or laminated to form the electrode assembly 12. The electrode assembly 12 is placed in an outer package, dried, and then injected with electrolyte. The battery cell 10 is then vacuum packaged, allowed to stand, formed, and shaped.

[0196] A battery module is assembled from the battery cells 10 , that is, it may contain a plurality of battery cells 10 , and the specific number can be adjusted according to the application and capacity of the battery module.

[0197] In some embodiments, FIG4 is a schematic diagram of an exemplary battery module 20. As shown in FIG4 , in the battery module 20, multiple battery cells 10 may be arranged sequentially along the length of the battery module 20. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 10 may be secured together using fasteners.

[0198] 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.

[0199] A battery pack is assembled from the battery cells 10 described above, and may contain multiple battery cells 10, wherein multiple battery cells 10 may be assembled into the battery module 20 described above. The specific number of battery cells 10 or battery modules 20 contained in a battery pack may be adjusted according to the application and capacity of the battery pack.

[0200] In the embodiment, Figures 5 and 6 are schematic diagrams of an exemplary battery pack 30. The battery pack 30 may include a battery box and multiple battery modules 20 disposed within the battery box. The battery box includes an upper box body 31 and a lower box body 32. The upper box body 31 covers the lower box body 32 and forms an enclosed space for accommodating the battery modules 20. The multiple battery modules 20 may be arranged in any manner within the battery box.

[0201] Electrical devices

[0202] Fourthly, embodiments of the present application further provide an electrical device comprising the battery of the aforementioned embodiments, which may further comprise a secondary battery. The battery can serve as both a power source and an energy storage unit for the electrical device. Consequently, the electrical device of the embodiments of the present application has a long standby or battery life.

[0203] Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc. These electrical devices may use secondary batteries, battery modules, or battery packs based on their usage requirements.

[0204] Figure 7 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0205] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0206] Example

[0207] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0208] 1. Diaphragm and its preparation method embodiment

[0209] Example A1

[0210] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment comprises 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 2 μm. The coating contains copolymerized polypropylene wax particles of two particle sizes: one of which is a particle size D v 50 is 2 μm (recorded as the first polymer particle), and the other is the particle size D v 50 is 0.3 μm (denoted as the second polymer particles), and the mass ratio of the first polymer particles to the second polymer particles is 1:1; specific parameters such as the melting point and particle size of the polymer particles are shown in Table 1 below.

[0211] The diaphragm preparation method of this embodiment includes the following steps:

[0212] S1. Preparation of coating slurry:

[0213] S11. Preparation of polymer particles

[0214] a. According to the copolymerized polypropylene wax: allyl polyethylene glycol: initiator = 300:100:20 ratio, the copolymerized polypropylene wax, allyl polyethylene glycol, di-tert-butyl peroxide were mixed and heated to melt and stirred uniformly, and the intermediate product was obtained after a constant temperature of 160 ℃ and 3h;

[0215] b. Preparation of polymer particles of different particle sizes

[0216] Large particle size D v 50 first polymer particles:

[0217] The intermediate product and nonionic emulsifier (fatty alcohol polyoxyethylene ether OS-10) were mixed in a ratio of 4.5:1, heated to 75°C, stirred to form a uniform emulsion, and water was added to adjust the viscosity to an appropriate range of 10mPa·s to 100mPa·s (25°C, the same below), and the solid content to 35wt% to 40wt% to obtain a nonionic copolymerized polypropylene wax emulsion with a particle size of D v 50 is 2 μm;

[0218] Small particle size D v 50 second polymer particles:

[0219] The intermediate product and nonionic emulsifier (fatty alcohol polyoxyethylene ether OS-10) were mixed in a ratio of 4.5:20, heated to 90°C, stirred to form a uniform emulsion, and water was added to adjust the viscosity to an appropriate range of 10mPa·s to 100mPa·s and the solid content to 35wt% to 40wt%. A nonionic copolymerized polypropylene wax emulsion with a particle size of D v 50 is 0.3 μm;

[0220] S12. Prepare coating slurry:

[0221] Copolymerized polypropylene wax emulsion, polyacrylonitrile, boehmite, and water were mixed in a ratio of 12.5%: 12.5%: 25%: 20%: 30% of first polymer particles: second polymer particles: polyacrylonitrile: boehmite: water. All materials were added to a double planetary stirring tank, and the mixture was stirred at 30 rpm and 2000 rpm for 3 hours, with vacuum defoaming applied throughout the process. The viscosity of the coating slurry was controlled between 500 mPa·s and 800 mPa·s.

[0222] S2. Film formation treatment of coating slurry on the surface of base film:

[0223] The coating slurry in step S1 was coated on one side of a 7 μm PE base film to form a wet film, and then dried to form a 2 μm coating on one side of the PE base film; wherein the coating slurry coating speed was 80 m / min, the oven temperature was 65° C., and the total drying time was 2 min.

[0224] Example A2

[0225] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of embodiment A1 except for the different particle sizes of the polymer particles contained in the coating. The first polymer particle D v 50 is 2.5 μm, the second polymer particle D v 50 is 0.6μm.

[0226] Specifically, in step b of step S11, the first polymer particles were mixed at a ratio of 10:1 of the intermediate product and the nonionic emulsifier (fatty alcohol polyoxyethylene ether OS-10), and heated to 70° C. The second polymer particles were mixed at a ratio of 4.5:15 of the intermediate product and the nonionic emulsifier (fatty alcohol polyoxyethylene ether OS-10), and heated to 85° C.

[0227] Example A3

[0228] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of Example A1, except for a different coating formulation. Specifically, the coating slurry components are mixed in a ratio of 15%: 10%: 25%: 20%: 30% for first polymer particles, 2% for second polymer particles, 3% for polyacrylonitrile, 4% for boehmite, and 5% for water.

[0229] Example A4

[0230] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of Example A1 except for the polymer particles. Specifically, the polymer particles of this embodiment are directly made of copolymerized polypropylene wax (i.e., not copolymerized with allyl polyethylene glycol), and step S11 is omitted.

[0231] Example A5

[0232] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of Example A1 except for the polymer particles. Specifically, the polymer particles of this embodiment are directly made of low-melting-point polyamide (i.e., not copolymerized with allyl polyethylene glycol).

[0233] Example A6

[0234] This embodiment provides a separator and a method for preparing the same. The separator in this embodiment is identical to the separator in Example A1, except that the coating contains no inorganic particles. The coating slurry components are mixed in a ratio of 22.5% first polymer particles: 22.5% second polymer particles: polyacrylonitrile: boehmite: water: 0%: 30%.

[0235] Example A7

[0236] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of Example A1, except for the coating formulation. Specifically, the coating slurry components are mixed in a ratio of 16.7% for first polymer particles: 8.3% for second polymer particles: 25% for polyacrylonitrile: 20% for boehmite: 30% for water.

[0237] Example A8

[0238] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of Example A1, except for the coating formulation. Specifically, the coating slurry components are mixed in a ratio of 8.3% first polymer particles: 16.7% second polymer particles: polyacrylonitrile: boehmite: water: 25%: 20%: 30%.

[0239] Comparative Example A1

[0240] 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 remaining features are identical.

[0241] The diaphragm preparation method of this comparative example refers to the diaphragm preparation method of Example A1. The difference from the preparation method of Example A1 is that when preparing the coating slurry, the coating slurry components are mixed in a ratio of first polymer particles: second polymer particles: polyacrylonitrile: boehmite: water = 0%: 0%: 25%: 45%: 30%. The steps and process conditions are the same.

[0242] Comparative Example A2

[0243] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of embodiment A1 except for the different particle sizes of the polymer particles contained in the coating. The first polymer particle D v 50 is 2 μm, the second polymer particle D v 50 is 0.2μm.

[0244] Specifically, the second polymer particles in step b of step S11 are mixed in a ratio of intermediate product to nonionic emulsifier (fatty alcohol polyoxyethylene ether OS-10) = 4.5:25 and heated to 95°C.

[0245] Comparative Example A3

[0246] This embodiment provides a diaphragm and a method for preparing the same. The diaphragm of this embodiment is identical to the diaphragm of embodiment A1 except for the different particle sizes of the polymer particles contained in the coating. The first polymer particle D v 50 is 3 μm, the second polymer particle D v 50 is 0.6μm.

[0247] Specifically, in step b of step S11, the first polymer particles were mixed at a ratio of intermediate product to nonionic emulsifier (fatty alcohol polyoxyethylene ether OS-10) of 20:1 and heated to 70° C. The second polymer particles were mixed at a ratio of intermediate product to nonionic emulsifier (fatty alcohol polyoxyethylene ether OS-10) of 4.5:15 and heated to 85° C.

[0248] Comparative Example A4

[0249] 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 for the different polymer particles. Specifically, the polymer particles in this embodiment are copolymerized polypropylene wax, and step S11 is not performed. The particle size D v 50 is 2.5μm.

[0250] Comparative Example A5

[0251] 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 for the different polymer particles. Specifically, the polymer particles in this embodiment are copolymerized polypropylene wax, and step S11 is not performed. The particle size D v 50 is 0.3μm.

[0252] 2. Secondary Battery Cell Example

[0253] Example B1 to Example B8 and Comparative Examples B1 to Comparative Examples B5;

[0254] Embodiments B1 to B8 and Comparative Examples B1 to B5 each provide a secondary battery cell, each comprising a positive electrode, a separator, and a negative electrode, and an electrolyte. The separators provided in Embodiments A1 to A8 and Comparative Examples A1 to A5 are the separators of secondary battery embodiments B1 to B8 and Comparative Examples B1 to B5, respectively. The separator in Embodiment A1 serves as the separator in the battery cell of secondary battery embodiment B1, the separator in Embodiment A2 serves as the separator in the battery cell of secondary battery embodiment B2, and so on. The separator in Comparative Example A5 serves as the separator in the battery cell of Comparative Example B5.

[0255] The positive electrode was prepared as follows:

[0256] Using methyl pyrrolidone (NMP) as solvent, LiNi 0.8 Co 0.1 Mn 0.1 O2, carbon nanotubes (CNT), and binder (PVDF) are mixed in a mass ratio of 97:2:1 to prepare a cathode slurry with a solid content of 85%. The cathode slurry is evenly coated on aluminum foil on both sides, with an area density of 0.131g / 1540.25m 2 After being fully dried, cold pressed and cut, the positive electrode sheet is obtained as the positive electrode.

[0257] Negative electrode: Using water as solvent, artificial graphite, conductive agent SP, dispersant (CMC), and binder (SBR) were mixed at a mass ratio of 96:1:1:2 to prepare a negative electrode slurry with a solid content of 58%. The positive electrode slurry was evenly coated on aluminum foil, with a double-sided coating, where the surface density of each single side was 0.065g / 1540.25m 2 After being fully dried, cold pressed and cut, the negative electrode sheet is obtained as the negative electrode.

[0258] Electrolyte: Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1 at room temperature, and LiPF6 was added to the mixed solution to obtain a solution with a concentration of 1 mol / L as the electrolyte;

[0259] Secondary battery assembly: In a low-humidity constant temperature room, the positive and negative electrode sheets prepared as above are stacked and wound in the order of "positive electrode-separator-negative electrode" to form a bare cell, which is then filled with electrolyte to assemble into a lithium-ion secondary battery.

[0260] Performance tests of diaphragms and secondary battery cells

[0261] The separators and secondary battery cells provided in the above embodiments and comparative examples were tested respectively.

[0262] 1. Diaphragm performance test:

[0263] 1.1 The membranes in the above-mentioned Examples A1 to A8 and Comparative Examples A1 to A5 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 carried out according to the industry standard method). The measured results are shown in Table 1 below. For example, the air permeability is tested using a membrane air permeability tester in accordance with the reference standard GB / T36363-2018; the melting point can be obtained by testing using a universal differential scanning calorimeter (DSC) method with reference to the standard ISO 11357-3-2018; unless otherwise specified, the volume distribution particle size Dv50 of the organic particles in the embodiments of the present application is determined by a particle size analyzer-laser diffraction method. Specifically, the standard GB / T 19077-2016 can be referred to, and the laser diffraction scattering particle size analyzer (Mastersizer3000 laser particle size analyzer) can be used for measurement according to the manufacturer's instructions.

[0264] Table 1

[0265]

[0266]

[0267] Table 1 shows that the air permeability of Comparative Example A1 at room temperature and after heating at 120°C for 15 minutes is essentially equivalent to that of Examples A1 to A8. This indicates that the separators of the present invention have good air permeability when the ambient temperature is below the melting point of the polymer particles contained in the coating. When the ambient temperature is above the melting point of the polymer particles contained in the coating, the polymer particles contained in the separator coating melt and seal the pores in the base membrane, causing the separator to lose its air permeability, thereby effectively preventing metal ion migration or positive-negative electrode crosstalk reactions within the battery.

[0268] Compared with Example A1, the air permeability of Example A6 at room temperature is poor. It can be seen that it is preferred to add inorganic particle fillers to increase the porosity of the coating and improve the air permeability.

[0269] Compared with Example A1, the room temperature air permeability of Example A7 and Example A8 is poor. It can be seen that the matching ratio of the first polymer and the second polymer needs to be optimized. If there are too few small-size particles as in Example A7 or too many small-size particles as in Example A8, it will affect the air permeability of the diaphragm during normal use.

[0270] Compared with Example A1, the air permeability of Comparative Example A2 at room temperature is poor, which shows that the D of the second polymer particles needs to be optimized. v 50. If it is too small, it will affect the air permeability of the diaphragm during normal use.

[0271] Compared with Example A2, the air permeability of Comparative Example A3 after heating at 120°C for 15 minutes is not large enough, which shows that the D of the first polymer particles needs to be optimized. v 50. If it is too large, it will affect the blocking response speed of the diaphragm at high temperature.

[0272] Compared with Example A2, the air permeability values ​​of Comparative Examples A4 and A5 after heating at 120°C for 15 minutes are not large enough. It can be seen that the large and small particle size matching scheme of the present invention is needed to improve the response speed of the diaphragm at high temperature.

[0273] 2. Secondary battery cell performance test:

[0274] 2.1 Secondary battery cell membrane air permeability after liquid injection

[0275] After the secondary battery cells in the above-mentioned Examples B1 to B8 and Comparative Examples B1 to B5 were injected and formed under the same injection and formation 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 injection and high-temperature (85°C) aging" in Table 1.

[0276] 2.2 Secondary battery cell cycle test

[0277] The secondary battery cells in the above-mentioned Examples B1 to B8 and Comparative Examples B1 to B5 were subjected to cycle tests at 25° C. and 1C / 1C conditions, and the test results are shown in Table 2.

[0278] Table 2

[0279]

[0280] As can be seen from Table 2, compared with Example A1, the capacity retention rate of Example A4 is lower. It can be seen that it is preferred to perform non-ionic group modification to improve the pressure resistance of the polymer particles, so that they will not deform and block the holes during the use of the battery, affecting the cycle performance. Among them, compared with other embodiments in Examples A1 to A8, the mass mixing ratio of the polymer particles in the coating of the diaphragm of the present application will affect the capacity retention rate of the battery. Relatively speaking, the mass ratio of the first polymer particles (large particle size) to the second polymer particles (small particle size) is 1:1 to 1.5:1, which is relatively preferred.

[0281] The relatively low capacity retention rates of Comparative Examples A2 and A5 indicate that the particle size and dosage of the small-particle polymer need to be limited, otherwise the normal battery capacity will be affected.

[0282] 2.3 Secondary battery cell air permeability test after cycling

[0283] After the secondary battery cells in the above-mentioned Examples B1 to B8 and Comparative Examples B1 to B5 were cycled at 25°C and 1C / 1C conditions, the batteries were disassembled to obtain the various diaphragms. 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.

[0284] Compared with Example B1, the air permeability of Example B4 after injection aging and circulation is poor. It can be seen that non-ionic group modification is preferred to help improve the pressure resistance of polymer particles during battery use.

[0285] 2.4 Test of metal deposition before and after cycling of secondary battery cells

[0286] The secondary battery cells in the above-mentioned Examples B1 to B8 and Comparative Examples B1 to B5 were respectively disassembled before and after cycling at 25°C and 1C / 1C conditions to obtain the negative electrode sheets. The metal element content on the negative electrode sheets was tested using ICP. The test results of the total metal content (excluding lithium) are shown in Table 3 below.

[0287] Table 3

[0288]

[0289]

[0290] As shown in Table 3, compared with Examples B1 to B8, Comparative Example B1 has a large amount of metal deposition (except lithium) on the negative electrode sheet after battery cycling, which may pierce the diaphragm and cause safety issues. It can be seen that using the solution of the present invention, the combination of large and small particle sizes can construct limited pores, preventing metal ions with larger ion radius from passing through the diaphragm. From Comparative Example B4, it can be seen that the diaphragm containing only large particle size materials does not have this effect. And from Comparative Example B5, it can be seen that if the diaphragm contains only small particle size to construct limited pores, it will affect the air permeability of the diaphragm during normal use.

[0291] 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions 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

1. A diaphragm, characterized in that: The invention comprises a base film and a coating layer disposed on at least one surface of the base film, wherein the coating layer contains polymer particles, wherein the polymer particles include first polymer particles and second polymer particles, and the volume distribution particle size D of the first polymer particles and the second polymer particles is v 50 different.

2. The diaphragm according to claim 1, characterized in that The volume distribution particle size D of the first polymer particles v 50 is greater than the volume distribution particle size D of the second polymer particles v 50, and the volume distribution particle size D of the first polymer particles v 50 is 2 μm to 2.5 μm, and the volume distribution particle size D of the second polymer particles is v 50 is 0.3μm to 0.6μm.

3. The diaphragm according to claim 2, characterized in that: The mass ratio of the first polymer particles to the second polymer particles is (1 to 1.5):1; and / or The first polymer particles have a melting point of 115°C to 120°C, and the second polymer particles have a melting point of 90°C to 110°C.

4. The diaphragm according to any one of claims 1 to 3, characterized in that: The polymer particles satisfy at least any one of the following conditions (1) to (3): (1) The morphology of the first polymer particles and the second polymer particles independently includes at least one of chain, spherical, quasi-spherical, fibrous, tubular, rod-shaped, amorphous, and pyramidal; (2) at least one of the first polymer particles and the second polymer particles contains a nonionic group; (3) The weight average molecular weight of at least one of the first polymer particles and the second polymer particles is from 1,000 to 10,000, and may be from 1,500 to 4,000.

5. The diaphragm according to any one of claims 1 to 4, characterized in that: The material of the polymer particles includes at least one of polystyrene, polyolefin, polyimide, melamine resin, phenol resin, cellulose, polyester, polyphenylene sulfide, polyaramid, polyamideimide, copolymer of butyl acrylate and ethyl methacrylate and their respective modified polymers; and / or The nonionic group includes at least one of an ethoxy group, a hydroxyl group, and a carboxylate group.

6. The diaphragm according to any one of claims 1 to 5, characterized in that: Based on the total dry weight of the coating as 100%, the content of the polymer particles in the coating is ≥ 28 wt%, optionally 28 wt% to 38 wt%; and / or The coating also contains an inorganic particulate filler.

7. The diaphragm according to claim 6, characterized in that The inorganic particle filler satisfies at least one of the following conditions: The content of the inorganic particle filler in the coating is 22 wt % to 30 wt % based on the total dry weight of the coating as 100 %; The volume distribution particle size D of the inorganic particle filler v 50: 1 μm 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.

8. The diaphragm according to any one of claims 1 to 7, characterized in that: The coating also includes a binder.

9. The diaphragm according to claim 8, characterized in that The content of the binder in the coating is 20wt% to 30wt% based on the total dry weight of the coating as 100%; and / or The thermal decomposition temperature of the binder is ≥160°C, and can be selected from 160°C to 300°C.

10. The diaphragm according to any one of claims 1 to 8, 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 surface density of the coating is 2 g / m 2 Up to 8g / m 2 .

11. A method for preparing a diaphragm, characterized in that: The steps include: providing a base film and a coating slurry containing polymer particles; Applying the coating slurry on at least one surface of the base film, and drying the base film to form a coating to obtain a separator; The polymer particles include first polymer particles and second polymer particles mixed with the first polymer particles, and the particle sizes D of the first polymer particles and the second polymer particles are v 50 different.

12. The preparation method according to claim 11, characterized in that: The coating slurry further comprises an inorganic particle filler and a binder; wherein the mass ratio of the organic polymer particles, the inorganic particle filler and the binder in the coating slurry is (28 to 38): (22 to 30): (20 to 30); and / or The solid content of the coating slurry is 30wt% to 40wt%; and / or The coating slurry has a viscosity of 100 to 1000 mPa·s at 25° C.

13. The preparation method according to claim 12, characterized in that: The binder is added in the form of a binder aqueous solution, and the binder aqueous 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 %.

14. The preparation method according to any one of claims 11 to 13, characterized in that: 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.

15. The preparation method according to claim 14, 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 160°C; and / or The polymer particles and the nonionic surfactant are emulsified in a mass ratio of (4 to 6):

1.

16. The preparation method according to claim 14 or 15, characterized in that: 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.

17. The preparation method according to claim 16, 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.

18. The preparation method according to any one of claims 14 to 17, 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.

19. 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 optionally 50 m / min to 100 m / min; and / or The drying temperature is 50°C to 70°C, and can be 60°C to 70°C; and / or The drying time is 1 min to 5 min, and can be optionally 1 min to 3 min.

20. A battery, characterized in that: The invention 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.

21. The battery according to claim 20, characterized in that The coating layer is disposed on one surface of the separator, and the coating layer faces the negative electrode.

22. An electrical device, characterized in that: The electrical device comprises the battery as claimed in claim 20 or 21, and the battery is used to provide electrical energy.

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