Binder and method for preparing same, and battery

Abstract

A binder, a method for preparing the binder, and a battery are provided. The binder includes binder particles. The binder particles include a core and a shell. The core includes a crystalline polymer. The shell encases at least a portion of the outer surface of the core, and the shell includes an amorphous polymer.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims priority to and benefit of Chinese Patent Application No. 202211487963.X, filed November 24, 2022, and entitled "BINDER AND PREPARATION METHOD THEREFOR, BATTERY SEPARATOR, AND BATTERY," the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to the field of batteries, in particular to binders and methods for preparing same, and batteries. [Background technology]

[0003] Currently, the process of bonding a separator to an electrode sheet mainly involves the following steps: a binder-coated separator is stacked with an electrode sheet, and then an electrolyte is injected. The binder swells in the electrolyte to create adhesion and is used to bond the separator to the electrode sheet. However, in the existing bonding method, the binder swells greatly in the electrolyte and easily blocks the pores of the separator, blocking the movement of lithium ions between the positive and negative electrode sheets, resulting in poor cycle performance of the battery. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present disclosure provides a binder, a preparation method thereof, and a battery. When the binder is used in a battery, the battery components can be bonded together before the electrolyte is injected. In addition, since the core of the binder's binding material particles is a crystalline polymer, the degree of swelling in the electrolyte is very low, and the separator pores cannot be blocked, thereby improving the cycle performance of the battery.

[0005] A first aspect of the present disclosure provides a binder. The binder includes binder particles. The binder particles include a core and a shell, the shell enclosing at least a portion of the outer surface of the core. The core includes a crystalline polymer, and the shell includes an amorphous polymer.

[0006] A second aspect of the present disclosure provides a method for preparing a binder, the method comprising the steps of: mixing a crystalline polymer, a shell material, an emulsifier, and a solvent and stirring them uniformly to obtain a mixed solution; adding an initiator dropwise to the mixed solution to allow the shell material to polymerize on the outer surface of the crystalline polymer to form a shell containing an amorphous polymer; the shell enveloping at least a portion of the outer surface of the crystalline polymer.

[0007] According to the binder and method for preparing the binder provided in the present disclosure, the binder particles in the binder comprise a core and a shell. The core comprises a crystalline polymer, and the shell comprises an amorphous polymer. When the binder is used in a battery, the separator can be separately bonded to the positive and negative electrode sheets by heating the binder at a low temperature before the electrolyte is injected. In addition, because the core is a crystalline polymer and has a low degree of swelling in the battery's electrolyte, the binder particles are unlikely to be bonded together, and the pores of the battery separator cannot be blocked. This improves the battery's cycle performance by helping ions move through the pores between the battery's positive and negative electrode sheets.

[0008] A third aspect of the present disclosure provides a battery. The battery includes a positive electrode sheet, a negative electrode sheet, and a battery separator. The battery separator is disposed between the positive electrode sheet and the negative electrode sheet. The battery separator includes a base film and a bonding layer. The bonding layer is disposed on one side or both sides of the base film, and the bonding layer includes the binder described above.

[0009] A battery separator is disposed between the positive and negative electrode sheets of the battery provided herein. The battery separator includes a base film and a bonding layer disposed on at least one surface of the base film. The bonding layer includes a binder. The binder particles in the binder include a core and a shell. The core includes a crystalline polymer, and the shell includes an amorphous polymer. Before the electrolyte is injected, the battery separator is heated at a low temperature. Under low-temperature heating, the amorphous polymer in the shell melts, allowing the battery separator to be separately bonded to the positive and negative electrode sheets of the battery. In addition, because the core is a crystalline polymer and has a low degree of swelling in the battery electrolyte, the binder particles are unlikely to be bonded together, and the pores of the battery separator cannot be blocked. This improves the battery's cycling performance by helping ions move between the positive and negative electrode sheets of the battery.

[0010] In order to more clearly describe the technical solutions in the present disclosure, the accompanying drawings required to describe the implementation are briefly introduced below. Obviously, the accompanying drawings in the following description only show some implementations of the present disclosure, and those skilled in the art may still derive other drawings from the accompanying drawings without original efforts. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of the structure of a binding particle of a binder according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a flow chart of a method for preparing a binder according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a schematic diagram of a cross-sectional structure of a battery separator according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic diagram of a cross-sectional structure of a battery separator according to another embodiment of the present disclosure. [Figure 5] FIG. 5 is a schematic diagram of a cross-sectional structure of a battery according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a scanning electron microscope view of a bonding layer of a battery separator according to one embodiment of the present disclosure. [Figure 7] FIG. 7 is a scanning electron microscope view of a bonding layer of a battery separator according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the technical solutions in the embodiments of the present disclosure will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some of the embodiments of the present disclosure, rather than all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without original efforts fall within the protection scope of the present disclosure.

[0013] In describing the present disclosure, terms such as "first" and "second" are used to distinguish various items, rather than to describe a particular order. In addition, the orientation or positional relationship indicated by terms such as "top," "bottom," and "outer" is based on the orientation or positional relationship shown in the accompanying drawings and is used solely to facilitate the description of the present disclosure and for simplicity of description, and does not indicate or imply that the described devices or elements need to have a particular orientation or be constructed or operated in a particular orientation. Therefore, such terms should not be construed as limiting the present disclosure.

[0014] In the description of this disclosure, unless otherwise expressly specified or defined, terms such as "connected" should be understood in a broad sense. For example, a connection may be a fixed connection, a detachable connection, or an integral connection; or a connection may be a direct connection, an indirect connection through an intermediate medium, or an internal communication between two elements; or a communication connection; or an electrical connection. Those skilled in the art will be able to understand the specific meaning of the above terms in this disclosure according to the particular situation.

[0015] The figures provided in the embodiments of the present disclosure only roughly describe the basic concept of the present disclosure. These figures only show the components related to the present disclosure in place of the drawings according to the number, shape, and size of the components in actual implementation. The types, number, and ratios of the components in actual implementation can be randomly changed, and the arrangement of the components will be more complex.

[0016] The present disclosure provides a binder. The binder includes binder particles. FIG. 1 is a schematic diagram of the structure of a binder particle 100 in a binder according to an embodiment of the present disclosure. As shown in FIG. 1, the binder particle 100 includes a core 10 and a shell 20. The shell 20 surrounds at least a portion of the outer surface of the core 10. The core 10 includes a crystalline polymer, and the shell 20 includes an amorphous polymer.

[0017] The binder provided in this embodiment of the present disclosure includes binder particles 100. The binder particles 100 include a core 10 and a shell 20. When the binder is used in a battery, the binder is provided on the battery's separator. Because the shell 20 includes an amorphous polymer, the battery's core can be encapsulated by dry pressing and molding. Specifically, before the electrolyte is injected, the binder is heated at a low temperature to melt and soften the amorphous polymer of the shell 20, creating an adhesive force to separately bond the separator to the positive and negative electrode sheets. Compared to existing bonding methods in which a binder-coated separator is stacked with electrode sheets, then an electrolyte is injected, and the binder swells in the electrolyte to bond the separator to the electrode sheets, creating an adhesive force. The binder particles provided in this embodiment of the present disclosure can bond the separator to the electrode sheets before the electrolyte is injected, so that the separator and electrode sheets are fixed together, preventing the separator and positive and negative electrode sheets from being offset and misaligned before they are encapsulated in a hard shell, which could affect battery performance. Additionally, because the core 10 comprises a crystalline polymer, the swelling rate of the core 10 in the battery's electrolyte is very low, preventing the binder particles 100 from bonding together and preventing the pores of the battery's separator from being blocked. This improves the cycle performance of the battery by helping ions move through the pores between the positive and negative electrode sheets of the battery. In the process of dry pressing and molding, the core 10 can be softened and adhesively formed by raising the temperature to a temperature equal to or slightly higher than the melting start temperature of the core 10; furthermore, since the separator of the battery is bonded separately to the positive electrode sheet and the negative electrode sheet, the bonding strength between the separator and the positive electrode sheet and the negative electrode sheet can be improved.

[0018] The core 10 and shell 20 form a core-shell structure. As shown in Figure 1, the shell 20 can completely encase the core 10. In another embodiment, the shell 20 can encase only a portion of the outer surface of the core 10.

[0019] The amorphous polymer of the shell 20 has a glass transition temperature of 0°C or higher and 70°C or lower. The glass transition temperature of the amorphous polymer of the shell 20 may be, but is not limited to, 0°C, 10°C, 20°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, etc. In some embodiments, the amorphous polymer of the shell 20 has a glass transition temperature of 10°C or higher and 70°C or lower. In some embodiments, the amorphous polymer of the shell 20 has a glass transition temperature of 30°C or higher and 70°C or lower. The amorphous polymer of the shell 20 has a glass transition temperature of 30°C or higher. In other words, the amorphous polymer of the shell 20 is in a glassy state at room temperature. Therefore, after the binder is applied to the base film to form the battery separator, the separators are not bonded together. The amorphous polymer of the shell 20 has a glass transition temperature of 70°C or lower. This helps the binder to bond with the objects to be bonded. For example, when a binder is used in a battery, the amorphous polymer of the shell 20 has a low glass transition temperature. When the binder is applied to the base film, the binder is heated at a low temperature, which melts the amorphous polymer and creates adhesion, allowing the binder particles to bond on the base film to form a separator. In addition, the separator can be bonded to the electrode sheet by melting and heating the amorphous polymer on the separator at a low temperature, which helps bond the separator to the electrode sheet. In some embodiments, the shell 20 is formed from an amorphous polymer. The glass transition temperature of the amorphous polymer is the same as the glass transition temperature of the shell 20.

[0020] The glass transition temperature of the shell 20 can be measured by differential scanning calorimetry (DSC). Specifically, about 20 mg of binder particles 100 was placed in a crucible, and the crucible was heated at a temperature increase rate of 5°C / min. The heat flow and temperature during the temperature increase process were recorded until the temperature reached 80°C to obtain a DSC curve, and the glass transition temperature of the shell 20 was determined based on the DSC curve.

[0021] In some embodiments, the binder is used in a battery. The swelling degree of the core 10 in the battery electrolyte is greater than 0 and less than or equal to 0.5. Specifically, the swelling degree of the core 10 in the battery electrolyte is so low that the binder particles 100 are unlikely to be bonded together after the electrolyte is injected. This helps ions in the electrolyte pass through the gaps between the binder particles 100 and migrate between the positive and negative electrode sheets of the battery. In addition, because the binder particles 100 are unlikely to be bonded together, the pores of the battery separator are prevented from being blocked, further helping ions in the electrolyte migrate between the positive and negative electrode sheets, thereby improving the battery's cycle performance. Furthermore, the swelling degree of the core 10 in the electrolyte is so low that the amount of electrolyte absorbed by the core 10 is so small that the problem of the battery's internal resistance increasing due to a small amount of electrolyte is avoided. The swelling degree of the core 10 with respect to the battery electrolyte may be, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, and the like.

[0022] The swelling degree of the binder particles 100 in the electrolyte ranges from 0 to 6. In some embodiments, the swelling degree ranges from 0 to 4. In some embodiments, the swelling degree ranges from 0 to 3. The swelling degree of the binder particles 100 in the electrolyte may be, but is not limited to, 1, 2, 3, 4, 5, 6, etc. Because the swelling degree of the binder particles 100 in the electrolyte is low, the binder particles 100 can be prevented from bonding together and the pores of the battery separator cannot be blocked. This improves the cycle performance of the battery by helping ions move through the pores between the positive and negative electrode sheets of the battery.

[0023] The specific process for measuring the swelling degree of the binder particles 100 in the electrolyte can be as follows: the binder particles 100 are placed in a Teflon model measuring 5cm*5cm*2cm, and the Teflon model is placed in a baking oven at a temperature of 250°C. The binder particles 100 melt during baking. After baking for 12 hours, the Teflon model is removed and allowed to cool. The baked binder particles 100 are pressed into an adhesive film with a thickness of 0.5cm; the adhesive film is cut into a test film with a length and width of 1cm and 1cm, respectively. The test film is weighed and the weight W1 is recorded. The test film is immersed in a container containing the electrolyte, the container is sealed, and the container is placed in an oven at a temperature of 60°C. After 72 hours, the test film is removed from the container, weighed, and the weight W2 is recorded. The swelling degree S1 of the binder particles 100 in the electrolyte is calculated as S1=W2 / W1.

[0024] In some embodiments, the swelling index of the core 10 in the battery electrolyte is greater than 0 and less than or equal to 0.3, which can further reduce swelling of the core 10 in the battery electrolyte. In some embodiments, the swelling index of the core 10 in the battery electrolyte is greater than 0 and less than or equal to 0.15, which can further reduce swelling of the core 10 in the battery electrolyte. This further helps to improve the cycle performance of the battery and reduce the internal resistance of the battery.

[0025] In some embodiments, the mass ratio of the core 10 to the shell 20 is (60-90):(10-40). When the mass ratio of the core 10 to the shell 20 is within this range, the binder has good bonding performance and the overall swelling degree of the binder particles 100 is low.

[0026] The volume of the outer surface of the core 10 that is covered by the shell 20 can be controlled by controlling the mass ratio of the core 10 to the shell 20 .

[0027] In some embodiments, the binder is used in a battery, and the swelling degree of the shell 20 in response to the battery's electrolyte is greater than 0 and less than 5. The swelling degree of the shell 20 is not high, allowing it to absorb a small amount of electrolyte. In addition, because the proportion of the shell 20 is small compared to the core 10, when the binder particles 100 are in the electrolyte, the overall swelling degree of the binder particles 100 is low, the amount of electrolyte absorbed is small, and the binder particles 100 are unlikely to be bonded together, which helps ions in the electrolyte to pass through the binder particles 100 and move between the positive and negative electrode sheets of the battery. Furthermore, because the binder particles 100 are unlikely to be bonded together, the pores of the battery separator can be prevented from being blocked, which further helps ions in the electrolyte to move between the positive and negative electrode sheets, improving the battery's cycling performance. In addition, the swelling degree of the shell 20 is not high, allowing it to absorb a small amount of electrolyte, which avoids the problem of the battery's internal resistance increasing due to excessive absorption of electrolyte.

[0028] In some embodiments, the swelling index of shell 20 with respect to the battery electrolyte is greater than 1 and less than or equal to 3. In some cases, the swelling index of shell 20 with respect to the battery electrolyte is greater than 1 and less than or equal to 2.5.

[0029] In some embodiments, the average particle size (D50) of the binder particles 100 is in the range of 0.2 μm to 15 μm, which can take into consideration both the energy density and bonding performance of the battery. The average particle size of the binder particles 100 can be measured using a particle size analyzer. D50 refers to the particle size corresponding to the cumulative particle size distribution percentage in a sample reaching 50%. In other words, in a large number of binder particles 100, the amount of binder particles 100 with a particle size larger than D50 accounts for 50% of the total, and the amount of binder particles 100 with a particle size smaller than D50 accounts for 50% of the total.

[0030] The average particle size of the core 10 is in the range of 0.1 μm to 10 μm, and the average thickness of the shell 20 is in the range of 0.1 μm to 5 μm.

[0031] When the particle size of the binder particles 100 is in the range of 0.2 μm to 15 μm, a small amount of electrolyte can be absorbed by the shell 20, preventing the binder particles 100 from being bonded together and ensuring the bonding performance of the binder particles 100. The average particle size of the core 10 is not limited to, but may be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. The average thickness of the shell 20 is not limited to, but may be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0032] In some embodiments, the average particle size of the binder particles 100 is in the range of 0.5 μm to 10 μm, so that the bonding performance and energy density of the battery can be better considered. In some embodiments, the average particle size of the binder particles 100 is in the range of 0.5 μm to 5 μm, so that the bonding performance of the binder particles 100 and the energy density of the battery can be further considered.

[0033] In some embodiments, the average particle size of the core 10 is in the range of 0.4 μm to 6 μm, so that the bonding performance and energy density of the battery can be better considered. In some cases, the average particle size of the core 10 is in the range of 0.4 μm to 4 μm, so that the bonding performance of the binder particles 100 and the energy density of the battery can be further considered.

[0034] In some embodiments, the average thickness of shell 20 is in the range of 0.1 μm to 3 μm, so that the amount of electrolyte absorbed by shell 20 can be reduced and the energy density of the battery can be further considered. In some embodiments, the average thickness of shell 20 is in the range of 0.1 μm to 1.5 μm, so that the amount of electrolyte absorbed by shell 20 can be further reduced and the energy density of the battery can be further considered.

[0035] In some embodiments, the average thickness of the shell 20 is less than the average particle size of the core 10, so that the amount of electrolyte absorbed by the binder particles 100 per unit particle size can be reduced.

[0036] In some embodiments, the crystallinity of the crystalline polymer of core 10 ranges from 50% to 95%. In some embodiments, core 10 is formed of a crystalline polymer, and the crystallinity of the crystalline polymer is the crystallinity of core 10. The crystallinity of the crystalline polymer of core 10 may be, but is not limited to, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.

[0037] The crystallinity of the core 10 can be measured by differential scanning calorimetry (DSC). Specifically, approximately 20 mg of binder particles 100 were placed in a crucible, and the crucible was heated at a temperature increase rate of 5°C / min. The heat flow and temperature during the temperature increase process were recorded until the temperature reached 250°C, thereby obtaining a DSC curve. The enthalpy per unit mass of the core 10 was determined based on the DSC curve, and then the theoretical enthalpy of the material at 100% crystallinity was obtained based on querying the material of the core 10. The crystallinity of the core 10 is equal to the ratio of the enthalpy per unit mass of the core 10 to the theoretical enthalpy.

[0038] When the crystallinity of the crystalline polymer is within this range, the proportion of crystalline regions in the crystalline polymer is high and the crystalline regions do not swell in the electrolyte, so the swelling degree of the core 10 in the electrolyte is very low and the binder particles 100 are unlikely to be bonded in the electrolyte. In addition, when the electrolyte is injected, the crystalline regions of the crystalline polymer do not swell and, because the crystalline polymer has a high degree of crystallinity, the crystalline regions can play a role in supporting the framework, resulting in gaps between the separator and electrode sheets (positive electrode sheet / negative electrode sheet) of the battery, and the electrolyte can sufficiently wet the separator and electrode sheets through the gaps, thereby improving the wetting effect of the electrolyte, reducing the internal resistance of the battery, and improving the cycle performance of the battery.

[0039] In some embodiments, the core 10 comprises a polyolefin-based resin, ie, the crystalline polymer comprises a polyolefin-based resin.

[0040] In some embodiments, the polyolefin resin may include, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, poly-1-butene, and poly-4-methyl-1-pentene. All of the above polyolefin resins are crystalline polymers and contain crystalline regions. The polyethylene may include at least one of low-density polyethylene, high-density polyethylene, and linear low-density polyethylene.

[0041] In some embodiments, the melting point of the crystalline polymer of core 10 is 90°C or more and 200°C or less, ie, the melting point of core 10 is 90°C or more and 200°C or less.

[0042] The melting point of the core 10 can be measured by differential scanning calorimetry (DSC). Specifically, about 20 mg of binder particles 100 was placed in a crucible, and the crucible was heated at a temperature increase rate of 5°C / min. The heat flow rate and temperature during the temperature increase process were recorded until the temperature reached 250°C to obtain a DSC curve, and the melting point of the core 10 was determined based on the DSC curve.

[0043] In some embodiments, when a binder is used in a battery, the binder can be placed on both sides of the base film, and the binder can be heated at a low temperature to melt and soften the shell 20, bonding it to both sides of the base film and forming a separator. Then, positive and negative electrode sheets are placed on both sides of the separator, and the separator is bonded to the positive and negative electrode sheets by hot pressing. During hot pressing, the temperature can be increased to above the melting temperature of the core 10 but below its melting point. When the core 10 is placed in an environment where the temperature is equal to the melting temperature of the core 10, the core 10 begins to melt and develop a certain adhesive force, allowing the separator to be bonded to the positive or negative electrode sheet. After cooling, the separator, positive and negative electrode sheets are fixed together. In addition, during hot pressing, the amorphous polymer also melts, developing adhesive force and cooperating with the crystalline polymer to bond the separator to the positive and negative electrode sheets. The temperature during hot pressing may be lower than the melting point of the core 10, so that the core 10 is completely melted into a liquid, preventing the binder particles 100 from bonding together.

[0044] The melting peak of the core 10 can be obtained by using a differential scanning calorimetry (DSC) device, and the melting onset temperature of the core 10 is determined based on the obtained melting peak.

[0045] When a hot box test is performed on a battery containing a binder, the core 10 has a high melting point, so the core 10 can absorb part of the heat generated by the battery during the heating process, thereby improving the success rate of the hot box test on the battery.

[0046] In some embodiments, the melting point of the crystalline polymer of core 10 is 90° C. or higher and 160° C. or lower. In some cases, the melting point of core 10 is 90° C. or higher and 140° C. or lower, thereby further reducing the temperature at which core 10 begins to melt, thereby further reducing the temperature during hot pressing.

[0047] In some embodiments, the amorphous polymer of shell 20 is formed by polymerizing at least a first monomer, the first monomer being a monomer containing an allyl group. The amorphous polymer shell 20 can be obtained by polymerizing a monomer containing an allyl group.

[0048] In some embodiments, the allyl group-containing monomer includes, but is not limited to, at least one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and acrylonitrile. The glass transition temperature of the shell 20 formed by using at least one of the allyl group-containing monomers described above may be in the range of 0°C to 70°C, and the swelling index may be in the range of 0 to 5. The acrylonitrile includes, but is not limited to, methacrylonitrile.

[0049] In some embodiments, shell 20 comprises a polymer obtained by polymerizing a first monomer and a second monomer, where the second monomer is a monomer that includes an acid group.

[0050] The shell 20 can be made more easily wet by the electrolyte by adding a monomer containing an acid group.

[0051] In some embodiments, the monomer containing an acid group includes at least one of a compound containing a carboxyl group, a compound containing a sulfonic acid group, and a compound containing a phosphonic acid group. The compound containing a carboxyl group can include a monocarboxylic acid and / or a dicarboxylic acid. The monocarboxylic acid includes at least one of acrylic acid, methacrylic acid, and crotonic acid. The dicarboxylic acid includes at least one of maleic acid, fumaric acid, and itaconic acid. The compound containing a sulfonic acid group can include at least one of vinyl sulfonic acid, methyl vinyl sulfonic acid, (methyl)allyl sulfonic acid, (methyl)acrylate-2-ethyl sulfonate, 2-acrylamido-2-methylpropane sulfonic acid, and 3-allyloxy-2-hydroxypropane sulfonic acid. The compound containing a phosphonic acid group can include at least one of 2-(meth)acryloyloxyethyl phosphate, 2-(meth)acryloyloxyethyl methyl phosphate, and ethyl (meth)acryloyloxyethyl phosphate.

[0052] In some embodiments, the mass ratio of the first monomer to the second monomer in the shell polymer is (50-99.9):(0.1-50). When the mass ratio of the first monomer to the second monomer is within the above range, the resulting shell 20 has good bonding performance and wettability. The first monomer is a structural unit formed by polymerizing the first monomer, and the second monomer is a structural unit formed by polymerizing the second monomer.

[0053] The binder further includes a solvent, and the binder particles 100 are dispersed in the solvent. The solvent may be water or a mixture of water and an organic solvent. The organic solvent may be any one or more of alicyclic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone; nitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; and alcohols such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether.

[0054] 2 is a flowchart of a method for preparing a binder according to an embodiment of the present disclosure. The method for preparing a binder can be configured to prepare the binder provided in any one of the above-described embodiments. As shown in FIG. 2, the method for preparing a binder includes the following steps:

[0055] S10: The crystalline polymer, the shell material, the emulsifier, and the solvent are mixed and stirred uniformly to obtain a mixed solution.

[0056] S20: An initiator is added dropwise to the mixed solution to allow the shell material to polymerize on the outer surface of the crystalline polymer to form a shell 20 comprising the amorphous polymer, which shell 20 encases at least a portion of the outer surface of the crystalline polymer.

[0057] The crystalline polymer surrounded by the shell 20 forms the aforementioned core 10, and the shell 20 and the crystalline polymer form the aforementioned binder particles 100. The binder particles 100 are dispersed in a solvent to obtain a binder.

[0058] According to the method for preparing a binder provided in the present disclosure, the prepared binder includes binder particles 100. The binder particles 100 include a core 10 and a shell 20. When the binder is used in a battery, the binder is provided on the battery separator. Because the formed shell 20 is an amorphous polymer, the battery core can be encapsulated by dry pressing and molding. Specifically, before the electrolyte is injected, the binder is heated at a low temperature to melt and soften the amorphous polymer of the shell 20, creating an adhesive force that bonds the separator to the positive and negative electrode sheets separately. Compared to existing bonding methods in which a binder-coated separator is stacked with an electrode sheet, then an electrolyte is injected, and a binder is used to swell in the electrolyte and bond the separator to the electrode sheet, the binder particles in the binder provided in this embodiment of the present disclosure can bond the separator to the electrode sheet before the electrolyte is injected, thereby fixing the separator and electrode sheet together and preventing the separator and the positive and negative electrode sheets from being offset and misaligned before the separator and positive electrode sheet are encapsulated in a hard shell with the negative electrode sheet, which would affect battery performance. In addition, because the swelling rate of crystalline polymers in battery electrolytes is very low, the binder particles 100 can be prevented from bonding together, and the pores of the battery separator cannot be blocked. This helps ions move through the pores between the positive and negative electrode sheets of the battery, improving the battery's cycling performance. In the dry pressing and molding process, the crystalline polymer can be softened by raising the temperature to a temperature equal to or slightly higher than the melting point of the crystalline polymer, thereby generating adhesive strength. Furthermore, since the separator of the battery is bonded separately to the positive electrode sheet and the negative electrode sheet, the bonding strength between the separator and the positive electrode sheet and the negative electrode sheet can be improved.

[0059] The glass transition temperature of the formed shell 20 is 0°C or higher and 70°C or lower.

[0060] The crystalline polymer, shell material, emulsifier, and solvent were added to a reaction tank and stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated, raising the temperature of the mixed solution to 60-80°C. While the mixed solution was being stirred at a rotation speed of 500 rpm, the initiator was slowly added dropwise to the mixed solution while stirring. After the initiator was added dropwise, the temperature of the mixed solution was maintained at 80°C and the mixed solution was continuously stirred at 500 rpm for 2-8 hours, resulting in the formation of binder particles 100 and the production of a binder.

[0061] The dropwise addition rate of the initiator is in the range of 1 mL / min to 5 mL / min. If the dropwise addition rate of the initiator is greater than 5 mL / min, the initiator is added dropwise too quickly, resulting in the shell material not being polymerized and accumulating on the outer surface of the crystalline polymer, causing the formed shell 20 to contain unpolymerized monomer impurities and affecting the bonding performance of the binder particles 100. If the dropwise addition rate of the initiator is less than 1 mL / min, the initiator is added dropwise too slowly, resulting in an impact on the efficiency of binder preparation.

[0062] The emulsifier may include at least one of sodium dodecylbenzenesulfonate and octadecylamine acetate, or the emulsifier may be another type of emulsifier.

[0063] The initiator can include at least one of tert-butyl 2-ethylperoxyacetate, potassium persulfate, and cumene hydroperoxide, or the initiator can be another type of initiator.

[0064] The solvent may be water. In other embodiments, other types of solvents may be selected based on requirements.

[0065] The crystalline polymer may be polyolefin resin particles, and may further be at least one of polyethylene particles, polypropylene particles, polyvinylidene fluoride particles, poly-1-butene particles, and poly-4-methyl-1-pentene particles. The polyethylene particles may include at least one of low-density polyethylene particles, high-density polyethylene particles, and linear low-density polyethylene particles.

[0066] The crystallinity of the crystalline polymer ranges from 50% to 95%.

[0067] The crystallinity of the crystalline polymer in step S10 can be measured using differential scanning calorimetry (DSC). Specifically, approximately 20 mg of crystalline polymer was placed in a crucible, which was heated at a temperature increase rate of 5°C / min. The heat flow and temperature during the temperature increase process were recorded until the temperature reached 250°C, resulting in a DSC curve. The enthalpy per unit mass of the crystalline polymer was determined based on the DSC curve, and then the theoretical enthalpy of a crystalline polymer with 100% crystallinity was obtained based on the crystalline polymer query. The crystallinity of a crystalline polymer is equal to the ratio of the enthalpy per unit mass of the crystalline polymer to the theoretical enthalpy.

[0068] The melting point of the crystalline polymer in step S10 is in the range of 90°C to 200°C. In some cases, the melting point of the crystalline polymer is in the range of 90°C to 180°C. In some cases, the melting point of the crystalline polymer is in the range of 90°C to 165°C.

[0069] The melting point of the crystalline polymer in step S10 can be measured using differential scanning calorimetry (DSC). Specifically, about 20 mg of the crystalline polymer was placed in a crucible, and the crucible was heated at a temperature increase rate of 5°C / min. The heat flow and temperature during the temperature increase process were recorded until the temperature reached 250°C to obtain a DSC curve, and the melting point of the crystalline polymer was determined based on the DSC curve.

[0070] The crystalline polymer in step S10 may be spherical, ellipsoidal, or the like.

[0071] The extent to which the shell 20 encases the outer surface of the crystalline polymer, specifically, the extent to which it encases only a portion or all of the outer surface of the crystalline polymer, can be controlled by controlling the mass ratio of crystalline polymer to shell material.

[0072] The mass ratio of the crystalline polymer, shell material, emulsifier, and initiator is (60-90):(10-40):(0.1-2):(0.1-2), so that the mass ratio of core 10 to shell 20 in the resulting binder particle 100 is (60-90):(10-40).

[0073] In some embodiments, the crystalline polymer in step S10 is in the form of particles, and the average particle size (D50) of the crystalline polymer in the form of particles is in the range of 0.1 μm to 10 μm. The average thickness of the shell 20 formed by polymerization is in the range of 0.1 μm to 5 μm, so that the average particle size of the binder particles 100 formed is in the range of 0.2 μm to 15 μm. The average particle size of the crystalline polymer in the form of particles can be measured using a particle size analyzer. D50 refers to the particle size corresponding to the cumulative particle size distribution percentage in a sample reaching 50%. In other words, in a large number of crystalline polymers in the form of particles, the amount of crystalline polymer in the form of particles with a particle size greater than D50 accounts for 50% of the total, and the amount of crystalline polymer in the form of particles with a particle size less than D50 accounts for 50% of the total.

[0074] In some cases, the average particle size of the core 10 is in the range of 0.4 μm to 7 μm. In some cases, the average particle size of the core 10 is in the range of 0.4 μm to 4 μm.

[0075] In some cases, the average thickness of the formed shell 20 is in the range of 0.1 μm to 3 μm. In some cases, the average thickness of the formed shell 20 is in the range of 0.5 μm to 1 μm.

[0076] In some cases, the average particle size of the formed binder particles 100 is in the range of 0.5 μm to 10 μm. In some cases, the average particle size of the formed binder particles 100 is in the range of 0.9 μm to 5 μm.

[0077] The average particle size of the crystalline polymer in the form of particles can be measured by using a particle size analyzer. After the binder particles are obtained, the average particle size of the binder particles can be measured by using a particle size analyzer to calculate the average thickness of the shell 20. The average thickness of the shell 20 is equal to the difference between the average particle size of the binder particles and the average particle size of the crystalline polymer in the form of particles.

[0078] In some embodiments, the crystalline polymer in step S10 is polyolefin-based resin particles. In step S10, mixing and uniformly stirring the crystalline polymer, shell material, emulsifier, and solvent to obtain a mixed solution includes the following: mixing and uniformly stirring the polyolefin-based resin particles, shell material, emulsifier, and solvent to obtain a mixed solution. The mass ratio of the polyolefin-based resin particles, shell material, emulsifier, and initiator is (60-90):(10-40):(0.1-2):(0.1-2), so that the mass ratio of core 10 to shell 20 in the resulting binder particles 100 is (60-90):(10-40).

[0079] In some embodiments, the crystalline polymer in step S10 may be polyethylene particles in a wax microemulsion. In step S10, mixing and uniformly stirring the crystalline polymer, shell material, emulsifier, and solvent to obtain a mixed solution includes the following: mixing and uniformly stirring the wax microemulsion, shell material, emulsifier, and solvent to obtain a mixed solution. The wax microemulsion includes polyethylene particles, a polyethylene emulsifier, and water. The polyethylene particles are dispersed in water under the action of the polyethylene emulsifier, thereby reducing the sedimentation of the polyethylene particles. The particle size of the polyethylene particles ranges from 0.3 μm to 2 μm. The polyethylene particles in the wax microemulsion may be spherical, ellipsoidal, etc.

[0080] The mass ratio of the polyethylene particles, shell material, emulsifier, and initiator in the wax microemulsion is (60-90):(10-40):(0.1-2):(0.1-2). The mass ratio of the wax microemulsion to the shell material can be determined according to the mass ratio of the polyethylene particles to the shell material and the solid content of the polyethylene particles in the wax microemulsion.

[0081] In some embodiments, the binder is used in a battery, and the swelling index of the crystalline polymer in step S10 with respect to the battery electrolyte is greater than 0 and less than or equal to 0.5. In some embodiments, the swelling index of the crystalline polymer with respect to the battery electrolyte is greater than 0 and less than or equal to 0.3. In some embodiments, the swelling index of the crystalline polymer with respect to the battery electrolyte is greater than 0 and less than or equal to 0.15.

[0082] The process of measuring the swelling degree of the crystalline polymer in step S10 in the electrolyte solution includes the following: the crystalline polymer is dissolved in NMP (N-methylpyrrolidone) to prepare a 15 wt% core material solution; the core material solution is dropped into a Teflon mold, and the Teflon mold is placed in an oven at an oven temperature of 80°C and baked for 12 hours to form an adhesive film with a thickness of 0.5 cm; the adhesive film is cut to obtain a test film with a length and width of 1 cm and 1 cm, respectively, and the test film is weighed and the weight W3 is recorded; the test film is immersed in a container containing the electrolyte solution, the container is sealed, and the container is placed in an oven at an oven temperature of 60°C; after 72 hours, the test film is removed from the container, weighed, and the weight W4 is recorded; the swelling degree S2 of the crystalline polymer in the electrolyte solution is calculated as S2 = W4 / W3.

[0083] The swelling degree S2 of the crystalline polymer in the electrolyte is the swelling degree of the core 10 in the electrolyte.

[0084] In some embodiments, the shell material comprises a first monomer, and adding an initiator dropwise to the mixed solution to allow the shell material to polymerize on the outer surface of the crystalline polymer to form a shell 20 comprising an amorphous polymer comprises: adding an initiator dropwise to the mixed solution to allow the first monomer to polymerize on the outer surface of the crystalline polymer to form a shell 20 comprising an amorphous polymer.

[0085] The extent to which the formed shell 20 encases the exterior surface of the crystalline polymer can be controlled by controlling the weight ratio of the crystalline polymer to the first monomer.

[0086] In some embodiments, the shell material comprises a first monomer and a second monomer. Before the crystalline polymer, shell material, emulsifier, and solvent are mixed, the method for preparing the binder further includes: uniformly mixing the first monomer and the second monomer to obtain the shell material. The first monomer and the second monomer are uniformly mixed in advance. This is beneficial for the subsequent polymerization of the first monomer and the second monomer to form the shell 20.

[0087] In some embodiments, the first monomer and the second monomer in a mass ratio of (50-99.9):(0.1-50) may be added to a stirred tank and stirred at a rotation speed of 500 rpm for 1 h to obtain a shell material.

[0088] When the shell material comprises a first monomer and a second monomer, adding an initiator dropwise to the mixed solution to allow the shell material to polymerize on the outer surface of the crystalline polymer to form a shell 20 comprising an amorphous polymer includes: adding an initiator dropwise to the mixed solution to allow the first monomer and the second monomer to polymerize on the outer surface of the crystalline polymer to form a shell 20 comprising an amorphous polymer.

[0089] The first and second monomers are polymerized on the exterior surface of the crystalline polymer to obtain a polymer formed by polymerization of the first monomer itself or a polymer formed by polymerization of the first and second monomers.

[0090] The extent to which the formed shell 20 encases the exterior surface of the crystalline polymer can be controlled by controlling the mass ratio of the crystalline polymer, the first monomer, and the second monomer.

[0091] The addition of the second monomer can improve the surface wettability of the formed shell 20. When the binder is used in a battery, the addition of the second monomer allows the battery electrolyte to have a good wetting effect on the surface of the shell 20.

[0092] The first monomer is a monomer containing an allyl group, and the allyl group-containing monomer includes at least one of methacrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and acrylonitrile. The second monomer is a monomer containing an acid group, and the acid group-containing monomer includes at least one of a compound containing a carboxyl group, a compound containing a sulfonic acid group, and a compound containing a phosphonic acid group.

[0093] The glass transition temperature of the shell 20 formed by polymerizing the first monomer or the shell 20 formed by polymerizing the first monomer and the second monomer is in the range of 10°C to 70°C or 30°C to 70°C by selecting appropriate first monomer and second monomer.

[0094] In some embodiments, the binder is used in a battery. The shell material can be selected, specifically, the first monomer, or the first monomer and the second monomer, to obtain a shell 20 having a swelling index in the electrolyte of greater than 0 and less than or equal to 5, or a shell 20 having a swelling index of greater than 1 and less than or equal to 3, or a shell 20 having a swelling index of greater than 1 and less than or equal to 2.5.

[0095] According to a method for measuring the swelling degree of the shell 20 in the electrolyte, a shell material corresponding to a swelling degree greater than 0 and less than or equal to 5 can be selected for preparing the shell 20, or a shell material corresponding to a swelling degree greater than 1 and less than or equal to 3 can be selected for preparing the shell 20, or a shell material corresponding to a swelling degree greater than 1 and less than or equal to 2.5 can be selected for preparing the shell 20.

[0096] In some embodiments, the shell material configured to form shell 20 can be determined by performing a swelling test on the polymer formed after the shell material is directly polymerized. Specifically, the first monomer was polymerized, or the first monomer and the second monomer were polymerized to obtain a polymer; the polymer was placed in a Teflon board model measuring 5 cm * 5 cm * 2 cm, and the Teflon model was placed in an oven for baking, where the oven temperature was 100 ° C. The polymer was melted during baking. After baking for 12 hours, the Teflon model was removed, allowed to cool, and pressed to obtain an adhesive film with a thickness of 0.5 cm; the adhesive film was cut into test films with a length and width of 1 cm, respectively, and the test film was weighed and the weight W5 was recorded; the test film was immersed in a container containing an electrolyte, the container was sealed, and the container was placed in an oven at an oven temperature of 60 ° C.; After 72 hours, the test film was removed from the container, weighed, and the weight W6 was recorded; and the swelling degree S3 of the shell material in the electrolyte was calculated, S3 = W6 / W5.

[0097] The swelling degree S3 of the shell material in the electrolyte is the swelling degree of the shell 20 in the electrolyte.

[0098] A shell material corresponding to a swelling index greater than 0 and less than or equal to 5 is selected for preparing shell 20, or a shell material corresponding to a swelling index greater than 1 and less than or equal to 3 is selected for preparing shell 20, or a shell material corresponding to a swelling index greater than 1 and less than or equal to 2.5 is selected for preparing shell 20.

[0099] In the above-described embodiments, the description of each embodiment has different focuses, and for parts not described in detail in one embodiment, reference can be made to the related descriptions of other embodiments.

[0100] The method for preparing the binder corresponds to the above-mentioned binder. Reference can be made to the contents of the above-mentioned binder embodiments for more detailed descriptions, and the method for preparing the binder and the contents of the above-mentioned binder can also be cross-referenced.

[0101] 3 is a schematic diagram of a cross-sectional structure of a battery separator 200 according to an embodiment of the present disclosure. As shown in FIG. 3, the battery separator 200 includes a base film 30 and a bonding layer 40. The bonding layer 40 is disposed on one side of the base film 30. The bonding layer 40 includes a binder according to any one of the above-described embodiments. The bonding layer 40 is configured to be bonded to a positive electrode sheet or a negative electrode sheet.

[0102] 4 is a schematic diagram of a cross-sectional structure of a battery separator 200 according to another embodiment of the present disclosure. As shown in FIG. 4, the bonding layer 40 includes a first bonding layer 41 and a second bonding layer 42. The first bonding layer 41 and the second bonding layer 42 are disposed on opposite sides of the base film 30, one layer each. The first bonding layer 41 and the second bonding layer 42 both include binder particles 100 in a binder according to any one of the above-described embodiments. The first bonding layer 41 and the second bonding layer 42 are configured to be bonded to the positive electrode sheet and the negative electrode sheet, respectively.

[0103] The base film 30 may have a porous structure, and ions in the electrolyte can pass through the pores of the base film 30 and move between the positive electrode sheet and the negative electrode sheet.

[0104] The material of the base film 30 may be a polyolefin resin, such as polyethylene or polypropylene.

[0105] In some embodiments, the bonding layer 40 further comprises a filler material, wherein the filler material comprises a heat resistant material.

[0106] The heat-resistant material includes at least one of aluminum oxide, silicon dioxide, boehmite, magnesium hydroxide, calcium oxide, and titanium oxide. The primary component of boehmite is hydrated aluminum oxide.

[0107] The filler may be a powdered refractory material, such as powdered aluminum oxide or powdered silicon dioxide.

[0108] The heat resistance performance of the bonding layer 40 can be improved by adding a heat-resistant material, so that the heat resistance performance of the battery separator 200 during hot pressing and high-temperature use can be improved, and the heat resistance and safety of the battery can be improved. In addition, the addition of a heat-resistant material can improve the surface wettability of the battery separator 200, so that the electrolyte can spread more easily on the battery separator 200.

[0109] Some embodiments of the present disclosure further provide a method for preparing a battery separator, which includes: coating the binder prepared in any one of the above-described embodiments onto at least a base film 30; drying the base film 30 to remove the solvent from the binder coated on the base film 30 and form a bonding layer 40 located on the base film 30, thereby preparing a battery separator 200.

[0110] In some embodiments, a binder may be coated onto one side of the base film 30 and the solvent in the binder is removed to form the tie layer 40 .

[0111] In some other embodiments, the binder may be coated on both sides of the base film 30 and the solvent in the binder is removed to form the first tie layer 41 and the second tie layer 42 .

[0112] The binder can be coated onto the base film 30 by using one or more of the following coating methods: microgravure roll coating, dot coating, rotary atomization, and extrusion coating.

[0113] The base film 30 can be dried by an air drying method such as warm air, hot air, or low humidity air. Alternatively, the base film 30 can be dried by energy ray irradiation such as infrared rays, far infrared rays, or electron beams. The specific drying method can be selected depending on the type of solvent in the binder.

[0114] The battery separator 200 prepared by forming the bonding layer 40 on the base film 30 can be separately bonded to the positive electrode sheet and the negative electrode sheet by using the bonding layer 40, in other words, the battery separator 200 is fixed to the positive electrode sheet and the negative electrode sheet. Therefore, offset and misalignment between the battery separator 200 and the positive electrode sheet and the negative electrode sheet during encapsulation can be avoided, and direct contact and short circuit between the positive electrode sheet and the negative electrode sheet can be avoided, thereby improving battery performance.

[0115] In some embodiments, coating the binder prepared in any one of the above embodiments onto at least the base film 30 includes: uniformly mixing the binder prepared in any one of the above embodiments and the filler to obtain a slurry, wherein the filler comprises a heat-resistant material; and coating the slurry onto the base film 30.

[0116] The slurry can be coated onto one or both sides of the base film 30 .

[0117] The method for preparing the battery separator corresponds to the above-mentioned battery separator 200. For more detailed descriptions, reference may be made to the contents of the above-mentioned embodiment of the battery separator 200, and cross-reference may also be made to the method for preparing the battery separator and the contents of the above-mentioned battery separator 200.

[0118] 5 is a schematic diagram of a cross-sectional structure of a battery 300 according to one embodiment of the present disclosure. As shown in FIG. 5, the battery 300 includes a positive electrode sheet 50, a battery separator 200, and a negative electrode sheet 60. The battery separator 200 is disposed between the positive electrode sheet 50 and the negative electrode sheet 60. The battery separator 200 includes the bonding layer 40 described above. The bonding layer 40 is configured to bond the positive electrode sheet 50 to the negative electrode sheet 60. The bonding layer 40 includes binder particles 100 in a binder provided in any one of the above-described embodiments.

[0119] In some embodiments, the battery separator 200 further includes a base film 30, as described above. As shown in FIG. 5 , the tie layer 40 includes a first tie layer 41 and a second tie layer 42 disposed on opposite sides of the base film 30. A positive electrode sheet 50 is disposed on one side of the first tie layer 41 away from the base film 30. A negative electrode sheet 60 is disposed on one side of the second tie layer 42 away from the base film 30. In other words, the positive electrode sheet, the first tie layer, the base film, the second tie layer, and the negative electrode sheet are stacked in succession. The first tie layer 41 is configured to bond the positive electrode sheet 50 to the base film 30, and the second tie layer 42 is configured to bond the negative electrode sheet 60 to the base film 30, thereby bonding the positive electrode sheet 50 to the negative electrode sheet 60.

[0120] In some other embodiments, the battery separator 200 includes only the bonding layer 40; in other words, the battery 300 includes a sequentially stacked positive electrode sheet 50, bonding layer 40, and negative electrode sheet 60. The binder can be coated directly onto the positive electrode sheet 50 or the negative electrode sheet 60 and dried. The binder-coated positive electrode sheet 50 is then bonded to the negative electrode sheet 60, or the binder-coated negative electrode sheet 60 is then bonded to the positive electrode sheet 50.

[0121] In some embodiments, the battery 300 further comprises an electrolyte, the electrolyte comprising a carbonate compound and a lithium-containing compound.

[0122] In some embodiments, the battery 300 includes a housing. At least one storage cavity is formed in the interior space of the housing. The storage cavity is configured to accommodate an electrode core set. The electrode core set includes at least one electrode core. Each electrode core includes an electrode core body, a positive electrode tab, and a negative electrode tab. The electrode core body includes a positive electrode sheet 50, a battery separator 200, and a negative electrode sheet 60 stacked in series. The positive electrode tab is connected to the positive electrode sheet 50, and the negative electrode tab is connected to the negative electrode sheet 60. The positive electrode sheet 50, the battery separator 200, and the negative electrode sheet 60 can be assembled into the electrode core body by, but not limited to, a winding method, a stacking method, or a heating and bonding method.

[0123] The battery 300 includes an electrolyte fill port configured to inject electrolyte into the receiving cavity, the electrolyte configured to wet the electrode core body.

[0124] In some embodiments, the electrolyte in each containment cavity can only flow within the containment cavity under the restriction of the divider.

[0125] The carbonate compound includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate. The lithium-containing compound includes at least one of LiPF, LiAsF, LiBF, LiSbF, LiAlCl, LiClO, CFSOLi, CFSOLi, CFCoLi, (CFCO)NLi, (CFSO)NLi, and (CFSO)NLi.

[0126] The swelling degree of the core 10 in the electrolyte is greater than 0 and less than 0.5, and the swelling degree of the shell 20 in the electrolyte is greater than 0 and less than 5.

[0127] The present disclosure will be described in more detail below in combination with specific embodiments. The following embodiments are only used to describe and explain the present disclosure, and do not limit the present disclosure.

[0128] Embodiment 1 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres, and the crystallinity of the high-density polyethylene microspheres is 90%. The swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, and the concentration of LiPF6 is 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 0.7 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0129] The first and second monomers were prepared. The first monomer was methyl methacrylate, and the second monomer was methacrylic acid. The methyl methacrylate and methacrylic acid were added to a stirring tank in a mass ratio of 98:2 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0130] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 87:12.7:0.3. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While the mixed solution was being stirred at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The methyl methacrylate and methacrylic acid, as well as the methyl methacrylate itself, were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0131] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 0.3 μm, and the swelling degree of the formed shell 20 in the electrolyte is 2.5. The average particle size of the formed binder particles 100 is 1.0 μm, and the swelling degree of the formed binder particles 100 is 0.5.

[0132] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0133] Embodiment 2 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres. The crystallinity of the high-density polyethylene microspheres is 90%, and the swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 5.2 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0134] The first and second monomers were prepared. The first monomer was methyl methacrylate, and the second monomer was methacrylic acid. The methyl methacrylate and methacrylic acid were added to a stirring tank in a mass ratio of 98:2 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0135] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 78:21.5:0.5. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While the mixed solution was being stirred at a rotation speed of 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The methyl methacrylate and methacrylic acid, as well as the methyl methacrylate itself, were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0136] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 0.3 μm, and the swelling index of the formed shell 20 in an electrolyte solution is 2.5. The average particle size of the formed binder particles 100 is 5.5 μm, and the swelling index of the formed binder particles 100 is 0.55.

[0137] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0138] Embodiment 3 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres. The crystallinity of the high-density polyethylene microspheres is 90%, and the swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 8.7 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0139] The first and second monomers were prepared. The first monomer was methyl methacrylate, and the second monomer was methacrylic acid. The methyl methacrylate and methacrylic acid were added to a stirring tank in a mass ratio of 98:2 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0140] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 70:29:1.0. The mixture was stirred for 1 hour to obtain a mixed solution, and then the reaction tank was heated to raise the temperature of the mixed solution to 60-80°C. While the mixed solution was being stirred at a rotation speed of 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. Methyl methacrylate, methacrylic acid, and the methyl methacrylate itself were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binder particles 100 were dispersed in water to form a binder.

[0141] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 0.3 μm, and the swelling index of the formed shell 20 in an electrolyte solution is 2.5. The average particle size of the formed binder particles 100 is 9.0 μm, and the swelling index of the formed binder particles 100 is 0.57.

[0142] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0143] Embodiment 4 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres. The crystallinity of the high-density polyethylene microspheres is 90%, and the swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 19.7 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0144] The first and second monomers were prepared. The first monomer was methyl methacrylate, and the second monomer was methacrylic acid. The methyl methacrylate and methacrylic acid were added to a stirring tank in a mass ratio of 98:2 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0145] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 67:32:1.5. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While the mixed solution was being stirred at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. Methyl methacrylate, methacrylic acid, and the methyl methacrylate itself were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binder particles 100 were dispersed in water to form a binder.

[0146] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 0.3 μm, and the swelling index of the formed shell 20 in an electrolyte solution is 2.5. The average particle size of the formed binder particles 100 is 20.0 μm, and the swelling index of the formed binder particles 100 is 0.52.

[0147] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0148] Embodiment 5 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres, and the crystallinity of the high-density polyethylene microspheres is 90%. The swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, and the concentration of LiPF6 is 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 0.7 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0149] The first and second monomers were prepared. The first monomer was methyl methacrylate, and the second monomer was methacrylic acid. The methyl methacrylate and methacrylic acid were added to a stirring tank in a mass ratio of 98:2 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0150] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 34.5:62:3.5. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring the mixed solution at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The methyl methacrylate and methacrylic acid, as well as the methyl methacrylate itself, were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0151] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 6.5 μm, and the swelling index of the formed shell 20 in an electrolyte solution is 2.5. The average particle size of the formed binder particles 100 is 7.2 μm, and the swelling index of the formed binder particles 100 is 3.2.

[0152] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0153] Embodiment 6 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres, and the crystallinity of the high-density polyethylene microspheres is 90%. The swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, and the concentration of LiPF6 is 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 0.7 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0154] The first and second monomers were prepared. The first monomer was methyl methacrylate, and the second monomer was methacrylic acid. The methyl methacrylate and methacrylic acid were added to a stirring tank in a mass ratio of 98:2 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0155] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 90.0:8.0:2.0. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring the mixed solution at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The methyl methacrylate and methacrylic acid, as well as the methyl methacrylate itself, were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0156] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 0.3 μm, and the swelling degree of the formed shell 20 in the electrolyte is 2.5. The average particle size of the formed binder particles 100 is 1.0 μm, and the swelling degree of the formed binder particles 100 is 0.2.

[0157] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0158] Embodiment 7 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres, and the crystallinity of the high-density polyethylene microspheres is 90%. The swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, and the concentration of LiPF6 is 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 0.7 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0159] The first and second monomers, methyl methacrylate and methacrylic acid, were prepared. The first and second monomers were added to a stirring tank in a mass ratio of 42:58 and stirred at 500 rpm for 1 h to obtain the shell material.

[0160] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 87.0:12.7:0.3. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring the mixed solution at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The methyl methacrylate and methacrylic acid, as well as the methyl methacrylate itself, were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0161] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 0.3 μm, and the swelling degree of the formed shell 20 in the electrolyte is 2.5. The average particle size of the formed binder particles 100 is 1.0 μm, and the swelling degree of the formed binder particles 100 is 0.6.

[0162] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0163] Embodiment 8 A crystalline polymer was prepared. The crystalline polymer was a trimonomer graft of polyethylene (PE), glycidyl methacrylate (Gma), styrene (St), and butyl acrylate (BA), or simply PE-g-(Gma+St+BA) trimonomer graft. The crystallinity of the crystalline polymer was 44%, and the swelling index of the crystalline polymer in the electrolyte was 0.27. The electrolyte was a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester was a mixture of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the crystalline polymer was 0.7 μm, and the melting point of the crystalline polymer was 120.5°C.

[0164] The first and second monomers were prepared. The first monomer was methyl methacrylate, and the second monomer was methacrylic acid. The methyl methacrylate and methacrylic acid were added to a stirring tank in a mass ratio of 98:2 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0165] PE-g-(Gma+St+BA) trimonomer graft, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 87.0:12.7:0.3 (high-density polyethylene microspheres, shell material, and sodium dodecylbenzenesulfonate). The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The methyl methacrylate and methacrylic acid, as well as the methyl methacrylate itself, were polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0166] The glass transition temperature of the formed shell 20 is 60°C, the average thickness of the formed shell 20 is 0.3 μm, and the swelling index of the formed shell 20 in an electrolyte solution is 2.5. The average particle size of the formed binder particles 100 is 1.0 μm, and the swelling index of the formed binder particles 100 is 1.2.

[0167] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0168] Embodiment 9 A crystalline polymer is prepared. The crystalline polymer is polypropylene microspheres, and the crystallinity of the polypropylene microspheres is 93%. The swelling index of the polypropylene microspheres in the electrolyte is 0.01. The electrolyte is a carbonate solution of LiPF6, and the LiPF6 concentration is 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the polypropylene microspheres is 3.5 μm, and the melting point of the polypropylene microspheres is 160°C.

[0169] The first and second monomers were prepared. The first monomer was ethyl methacrylate, and the second monomer was a compound containing sulfonic acid groups. The ethyl methacrylate and the compound containing sulfonic acid groups were added to a stirring tank in a mass ratio of 97:3 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0170] Polypropylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 59.2:39.0:1.8. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The ethyl methacrylate and sulfonic acid group-containing compounds, as well as the ethyl methacrylate itself, were polymerized on the polypropylene microspheres to form a shell 20 that completely enveloped the polypropylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0171] The glass transition temperature of the formed shell 20 is 70°C, the average thickness of the formed shell 20 is 1.5 μm, and the swelling degree of the formed shell 20 in an electrolyte solution is 2. The average particle size of the formed binder particles 100 is 5 μm.

[0172] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0173] Embodiment 10 A crystalline polymer is prepared. The crystalline polymer is low-density polyethylene microspheres. The crystallinity of the low-density polyethylene microspheres is 52%, and the swelling index of the low-density polyethylene microspheres in the electrolyte is 0.11. The electrolyte is a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the low-density polyethylene microspheres is 1.2 μm, and the melting point of the low-density polyethylene microspheres is 90°C.

[0174] A first monomer and a second monomer were prepared. The first monomer contained ethyl methacrylate and acrylonitrile, and the second monomer was a carboxylic acid monomer. The first monomer and the second monomer were added to a stirred tank in a mass ratio of 96:4 and stirred at a rotation speed of 500 rpm for 1 hour to obtain a shell material.

[0175] Low-density polyethylene microspheres, shell material, octadecylamine acetate, and water were added to a reaction tank in a mass ratio of 84.2:15.0:0.8. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring the mixed solution at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the 2-ethylperoxytert-butyl acetate was added dropwise, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. Methyl methacrylate, acrylonitrile, and carboxylic acid monomers were polymerized on the low density polyethylene microspheres, and the methyl methacrylate and acrylonitrile were polymerized on the low density polyethylene microspheres to form a shell 20 that completely encases the low density polyethylene microspheres, thereby forming binder particles 100. The binder particles 100 were dispersed in water to form a binder.

[0176] The glass transition temperature of the formed shell 20 is 65°C, the average thickness of the formed shell 20 is 0.5 µm, and the swelling index of the formed shell 20 in an electrolyte is 1.1. The average particle size of the formed binder particles 100 is 1.7 µm.

[0177] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0178] Embodiment 11 A crystalline polymer is prepared. The crystalline polymer is polyvinylidene fluoride microspheres. The crystallinity of the polyvinylidene fluoride microspheres is 50%, and the swelling index of the polyvinylidene fluoride microspheres in the electrolyte is 0.15. The electrolyte is a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the polyvinylidene fluoride microspheres is 0.4 μm, and the melting point of the polyvinylidene fluoride microspheres is 152°C.

[0179] A first monomer, methacrylonitrile, and a second monomer, a sulfonic acid group-containing compound, were prepared. The first monomer was methacrylonitrile, and the second monomer was a sulfonic acid group-containing compound. The methacrylonitrile and the sulfonic acid group-containing compound were added to a stirring tank in a mass ratio of 99.7:0.3 and stirred at 500 rpm for 1 h to obtain the shell material.

[0180] Polyvinylidene fluoride microspheres, shell material, octadecylamine acetate, and water were added to a reaction tank in a mass ratio of 89.3:10.0:0.7. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring at 500 rpm, cumene hydroperoxide was slowly added to the mixed solution while stirring. After the dropwise addition of cumene hydroperoxide, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. Methacrylonitrile and sulfonic acid group-containing compounds, as well as methacrylonitrile itself, were polymerized on the polyvinylidene fluoride microspheres to form shells 20 that completely enveloped the polyvinylidene fluoride microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0181] The formed shell 20 has a glass transition temperature of 35°C, an average thickness of 0.1 µm, and a swelling index of 1.2 in an electrolyte solution. The formed binder particles 100 have an average particle size of 0.5 µm.

[0182] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0183] Embodiment 12 A crystalline polymer is prepared. The crystalline polymer is poly-1-butene microspheres, and the crystallinity of the poly-1-butene microspheres is 72%. The mass ratio of the poly-1-butene microspheres, shell material, and sodium dodecylbenzenesulfonate is 77.5:21.0:1.5. The swelling index of the poly-1-butene microspheres in the electrolyte is 0.08. The electrolyte is a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester is a mixture of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the poly-1-butene microspheres is 2.0 μm, and the melting point of the poly-1-butene microspheres is 110°C.

[0184] A first monomer and a second monomer were prepared. The first monomer was ethyl methacrylate, and the second monomer contained a compound containing a sulfonic acid group and a compound containing a carboxyl group. The first monomer and the second monomer were added to a stirring tank in a mass ratio of 95.2:4.8 and stirred at 500 rpm for 1 hour to obtain the shell material.

[0185] Poly-1-butene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank and stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While the mixed solution was being stirred at 500 rpm, cumene hydroperoxide was slowly added to the mixed solution while stirring. After the dropwise addition of cumene hydroperoxide, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. Ethyl methacrylate, a compound containing sulfonic acid groups, and a compound containing carboxyl groups were polymerized on the poly-1-butene microspheres, and the ethyl methacrylate itself was polymerized on the poly-1-butene microspheres to form a shell 20 that completely enveloped the poly-1-butene microspheres, thereby forming binder particles 100. The binder particles 100 were dispersed in water to form a binder.

[0186] The formed shell 20 has a glass transition temperature of 45°C, an average thickness of 1 µm, and a swelling index of 1.5 with respect to the electrolyte of the formed shell 20. The formed binder particles 100 have an average particle size of 3 µm.

[0187] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0188] Embodiment 13 A crystalline polymer is prepared. The crystalline polymer is linear low-density polyethylene microspheres. The crystallinity of the linear low-density polyethylene microspheres is 63%, and the swelling index of the linear low-density polyethylene microspheres in the electrolyte is 0.095. The electrolyte is a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the linear low-density polyethylene microspheres is 1.3 μm, and the melting point of the linear low-density polyethylene microspheres is 120°C.

[0189] The first monomer was ethyl acrylate, and the second monomer was a compound containing phosphonic acid groups. The ethyl acrylate and the compound containing phosphonic acid groups were added to a stirring tank in a mass ratio of 97.4:2.6 and stirred at 500 rpm for 1 h to obtain the shell material.

[0190] Linear low-density polyethylene microspheres, shell material, octadecylamine acetate, and water were added to a reaction tank in a mass ratio of 81.8:17.0:1.2. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring at 500 rpm, cumene hydroperoxide was slowly added to the mixed solution while stirring. After the dropwise addition of cumene hydroperoxide, the temperature of the mixed solution was maintained at 80°C and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. Ethyl acrylate and a compound containing phosphonic acid groups were polymerized on the linear low-density polyethylene microspheres, and the ethyl acrylate itself was polymerized on the linear low-density polyethylene microspheres to form a shell 20 that completely enveloped the linear low-density polyethylene microspheres, thereby forming binder particles 100. The binding material particles 100 were dispersed in water to form a binder.

[0191] The glass transition temperature of the formed shell 20 is 45°C, the average thickness of the formed shell 20 is 0.6 µm, and the swelling degree of the formed shell 20 in the electrolyte is 1.8. The average particle size of the formed binder particles 100 is 1.9 µm.

[0192] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0193] Embodiment 14 A crystalline polymer is prepared. The crystalline polymer is high-density polyethylene microspheres, and the crystallinity of the high-density polyethylene microspheres is 90%. The swelling index of the high-density polyethylene microspheres in the electrolyte is 0.02. The electrolyte is a carbonate solution of LiPF6, and the concentration of LiPF6 is 1 mol / L. The carbonate ester is a mixture formed by mixing dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the high-density polyethylene microspheres is 0.7 μm, and the melting point of the high-density polyethylene microspheres is 130°C.

[0194] A first monomer was prepared. The first monomer was methyl methacrylate. The methyl methacrylate was added to a stirring tank and stirred at a rotation speed of 500 rpm for 1 hour to obtain a shell material.

[0195] High-density polyethylene microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 87:12.7:0.3. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring at 500 rpm, 2-ethylperoxytert-butyl acetate was slowly added to the mixed solution while stirring. After the dropwise addition of 2-ethylperoxytert-butyl acetate, the temperature of the mixed solution was maintained at 80°C and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. The methyl methacrylate itself was polymerized on the high-density polyethylene microspheres to form a shell 20 that completely enveloped the high-density polyethylene microspheres, forming binder particles 100. The binder particles 100 were dispersed in water to form a binder.

[0196] The formed shell 20 has a glass transition temperature of 60°C, an average thickness of 0.3 μm, and a swelling index of 2.5 in an electrolyte solution. The formed binder particles 100 have an average particle size of 1 μm. The difference between embodiment 14 and embodiment 1 is that the shell material of embodiment 14 does not contain a second monomer.

[0197] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0198] Comparative Example 1 A crystalline polymer, poly(methyl methacrylate) microspheres, was prepared. The swelling ratio of the poly(methyl methacrylate) microspheres in the electrolyte was 2.5. The electrolyte was a carbonate solution of LiPF6, with a LiPF6 concentration of 1 mol / L. The carbonate ester was a mixture of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:2:1:2. The average particle size of the poly(methyl methacrylate) microspheres was 0.7 μm.

[0199] The first and second monomers were prepared. The first monomer was styrene sulfonic acid, and the second monomer was a carboxyl-containing monomer. The styrene sulfonic acid and the carboxyl-containing monomer were added to a stirring tank in a mass ratio of 96.2:3.8 and stirred at 500 rpm for 1 h to obtain the shell material.

[0200] Poly(methyl methacrylate) microspheres, shell material, sodium dodecylbenzenesulfonate, and water were added to a reaction tank in a mass ratio of 87:12.7:0.3. The mixture was stirred for 1 hour to obtain a mixed solution. The reaction tank was then heated to raise the temperature of the mixed solution to 60-80°C. While stirring the mixed solution at 500 rpm, tert-butyl 2-ethylperoxyacetate was slowly added to the mixed solution while stirring. After the dropwise addition of tert-butyl 2-ethylperoxyacetate, the temperature of the mixed solution was maintained at 80°C, and the mixed solution was continuously stirred at 500 rpm for 2-8 hours. Styrene sulfonic acid and carboxyl group-containing monomers, as well as styrene sulfonic acid itself, were polymerized onto poly(methyl methacrylate) microspheres to form binder particles by forming a shell that completely enveloped the poly(methyl methacrylate) microspheres.

[0201] The glass transition temperature of the formed shell is 80°C, the average thickness of the formed shell is 0.3 μm, the swelling index of the formed shell in the electrolyte is 3.8, and the average particle size of the formed binder particles is 1.0 μm.

[0202] According to the above-described method for preparing a battery separator, a battery separator is prepared by using the formed binder, and a battery is prepared by using the resulting battery separator, a positive electrode sheet, and a negative electrode sheet.

[0203] Comparative Example 2 A battery is prepared using a base film 30, a positive electrode sheet, and a negative electrode sheet. The base film 30 is a polyethylene film.

[0204] The battery capacity retention rate test is conducted on the batteries of Embodiments 1 to 14 and Comparative Examples 1 and 2. The test process is as follows: the battery is placed in a crystal oven at 25°C so that the battery is charged and discharged at a rate of 1C / 1C, and the cycle is performed 100 times to obtain the discharge capacity of the 100th cycle of the test. The capacity retention rate (%) of the battery is obtained by dividing the discharge capacity by the maximum discharge capacity. See Table 1 for the results.

[0205] [Table 1]

[0206] From Table 1, it can be seen that the capacity retention rates after 100 cycles of the batteries prepared in Examples 1 to 14 are higher than that of Comparative Example 1, which indicates that the batteries prepared by using the binder particles provided in the present disclosure have better cycle performance than the binder particles in which both the core and shell are amorphous polymers.

[0207] The capacity retention rates after 100 cycles of the batteries prepared in Examples 1 to 14 are higher than that of Comparative Example 2, indicating that the batteries prepared by using the binder particles provided in the present disclosure have better cycle performance than batteries prepared without a binder.

[0208] The capacity retention rates after 100 cycle tests of the batteries prepared in Examples 1 to 3 are higher than that of Example 4, indicating that the use of binder particles with cores having an average particle size in the range of 0.1 μm to 10 μm provides better cycle performance than the use of binder particles with cores having an average particle size outside the range of 0.1 μm to 10 μm.

[0209] The capacity retention rate after 100 cycles of the battery prepared in embodiment 1 is higher than that of embodiment 5, indicating that the use of binder particles with a shell having an average thickness in the range of 0.1 μm to 5 μm provides better cycle performance than the use of binder particles with a shell having an average thickness outside the range of 0.1 μm to 5 μm.

[0210] The capacity retention rate after 100 cycles of the battery prepared in embodiment 1 is higher than that of embodiment 6, indicating that binder particles having a mass ratio of crystalline polymer to shell material in the range of (60-90):(10-40) have better cycle performance than binder particles having a mass ratio of crystalline polymer to shell material outside the range of (60-90):(10-40).

[0211] The capacity retention rate after 100 cycles of the battery prepared in embodiment 1 is higher than that of embodiment 7, indicating that the binder particles having a mass ratio of the first monomer to the second monomer in the range of (50-99.9):(0.1-50) have better cycle performance than the binder particles having a mass ratio of the first monomer to the second monomer outside the range of (50-99.9):(0.1-50).

[0212] The capacity retention rate after 100 cycles of the battery prepared in embodiment 1 is higher than that of embodiment 8, indicating that the use of binder particles with a core having a crystallinity in the range of 50% to 95% provides better cycle performance than the use of binder particles with a core having a crystallinity outside the range of 50% to 95%.

[0213] The capacity retention rate after 100 cycles of the battery prepared in embodiment 1 is higher than that of embodiment 14, indicating that the binder particles having a shell polymerized with the first monomer and the second monomer have better cycle performance than the binder particles having a shell polymerized with only the first monomer.

[0214] Figure 6 is a scanning electron microscope image of a bonding layer 40 of a battery separator 200 according to one embodiment of the present disclosure. The bonding layer 40 shown in Figure 6 is formed by coating a base film 30 with the binder prepared in Example 1 above and drying the base film 30. The bonding layer 40 includes spherical binder particles 100 (indicated by arrows in Figure 6).

[0215] Figure 7 is a scanning electron microscope view of a bonding layer 40 of a battery separator 200 according to another embodiment of the present disclosure. The bonding layer 40 shown in Figure 7 is formed by mixing the binder prepared in Example 9 and aluminum oxide to obtain a slurry, where the weight of the binder particles in the binder is equal to 6% of the weight of the aluminum oxide, then coating the slurry onto a base film 30 and drying the base film 30. The bonding layer 40 includes spherical binder particles 100 (indicated by arrows in Figure 7).

[0216] In the above-described embodiments, the description of each embodiment has different focuses, and for parts not described in detail in one embodiment, reference can be made to the related descriptions of other embodiments.

[0217] The above description is some implementations of the present disclosure. It should be noted that those skilled in the art can make some improvements and modifications without departing from the principle of the present disclosure, and these improvements and modifications should fall within the protection scope of the present disclosure. [Explanation of symbols]

[0218] 10 cores 20 shells 30 base film 40 bonding layer 41 First bonding layer 42 Second bonding layer 50 positive electrode sheet 60 negative electrode sheet 100 binder particles 200 Battery Separator 300 battery

Claims

1. A binder comprising binder particles (100), the binder particles (100) comprising: a core (10) comprising a crystalline polymer; and A shell (20) enveloping at least a portion of the outer surface of the core (10) and comprising an amorphous polymer. A binder.

2. 2. The binder of claim 1, wherein the crystallinity of the crystalline polymer ranges from 50% to 95%.

3. 2. The binder according to claim 1, wherein the crystalline polymer is a polyolefin resin.

4. 4. The binder of claim 3, wherein the polyolefin resin comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, poly-1-butene, and poly-4-methyl-1-pentene.

5. 2. The binder according to claim 1, wherein the melting point of the crystalline polymer is 90°C or higher and 200°C or lower.

6. 2. The binder according to claim 1, wherein the amorphous polymer has a glass transition temperature of 0°C or higher and 70°C or lower.

7. 10. The binder of claim 1, wherein the amorphous polymer is formed by polymerizing at least a first monomer, the first monomer being a monomer comprising an allyl group.

8. 8. The binder of claim 7, wherein the monomer comprising an allyl group comprises at least one of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and acrylonitrile.

9. 8. The binder of claim 7, wherein the amorphous polymer is formed by polymerizing a first monomer and a second monomer, the second monomer being a monomer comprising an acid group.

10. 10. The binder of claim 9, wherein the monomer comprising an acid group comprises at least one of a compound comprising a carboxyl group, a compound comprising a sulfonic acid group, and a compound comprising a phosphonic acid group.

11. 10. The binder of claim 9, wherein the weight ratio of the first monomer to the second monomer in the amorphous polymer is (50-99.9):(0.1-50).

12. 2. The binder of claim 1, wherein the weight ratio of the core (10) to the shell (20) is (60-90):(10-40).

13. 2. The binder according to claim 1, wherein the average particle size of the binder particles (100) is in the range of 0.2 μm to 15 μm, the average particle size of the core (10) is in the range of 0.1 μm to 10 μm, and the average thickness of the shell (20) is in the range of 0.1 μm to 5 μm.

14. 1. A method for preparing a binder, comprising: Mixing the crystalline polymer, the shell material, the emulsifier, and the solvent and stirring to obtain a uniform mixed solution; and adding an initiator dropwise to the mixed solution to allow the shell material to polymerize on the outer surface of the crystalline polymer to form a shell (20) comprising an amorphous polymer; wherein a shell (20) encases at least a portion of the outer surface of the crystalline polymer, and the crystalline polymer encased by the shell (20) forms the core (10) of the binder particle.

15. the shell material comprises a first monomer, the first monomer being a monomer comprising an allyl group; and adding an initiator dropwise to the mixed solution to allow the shell material to polymerize on the outer surface of the crystalline polymer to form a shell (20) comprising an amorphous polymer; An initiator is added dropwise to the mixed solution to allow the first monomer to polymerize on the outer surface of the crystalline polymer to form a shell (20) comprising an amorphous polymer.

15. The method for preparing a binder according to claim 14, wherein the dropwise addition rate of the initiator is in the range of 1 mL / min to 5 mL / min.

16. The shell material may comprise a first monomer and a second monomer, the first monomer being a monomer having an allyl group and the second monomer being a monomer having an acid group, and prior to mixing the crystalline polymer, the shell material, the emulsifier, and the solvent, the method for preparing the binder may further comprise: Uniformly mixing the first monomer and the second monomer to obtain a shell material Provided with: Adding an initiator dropwise to the mixed solution allows the shell material to polymerize on the outer surface of the crystalline polymer to form a shell (20) comprising an amorphous polymer:

15. A method for preparing a binder according to claim 14, comprising: adding an initiator dropwise to the mixed solution to allow the first monomer and the second monomer to polymerize on the outer surface of the crystalline polymer to form a shell (20) comprising an amorphous polymer, wherein the dropwise addition rate of the initiator is in the range of 1 mL / min to 5 mL / min.

17. 15. The method for preparing a binder according to claim 14, wherein the weight ratio of the crystalline polymer to the shell material is (60-90):(10-40).

18. A battery (300) comprising a positive electrode sheet (50), a negative electrode sheet (60), and a battery separator (200), wherein the battery separator (200) is disposed between the positive electrode sheet (50) and the negative electrode sheet (60), the battery separator (200) comprising a base film (30) and a bonding layer (40), the bonding layer (40) being disposed on one side of the base film (30) or on both sides of the base film (30), and the bonding layer (40) comprising the binder according to any one of claims 1 to 13.

19. 20. The battery (300) of claim 18, wherein the bonding layer (40) further comprises a filler, the filler comprising a heat-resistant material, the heat-resistant material comprising at least one of aluminum oxide, silicon dioxide, boehmite, magnesium hydroxide, calcium oxide, and titanium oxide.

20. 20. The battery (300) of claim 19, further comprising an electrolyte, wherein the swelling index of the core (10) of the binder particles (100) in the binder with the electrolyte is greater than 0 and less than or equal to 0.5, and the swelling index of the shell (20) of the binder particles (100) in the binder with the battery electrolyte is greater than 0 and less than or equal to 5.

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