Diaphragm and energy storage battery

Abstract

The invention provides a diaphragm and an energy storage battery. The diaphragm comprises a base membrane, and a first functional coating and a second functional coating which are formed on two opposite surfaces of the base membrane, wherein the first functional coating and the second functional coating respectively and independently comprise inorganic particles, an adhesive and composite unit particles; wherein the composite unit particles in the functional coating on at least one surface of the base film comprise first composite unit particles, each first composite unit particle comprises a glass microsphere core and a first polymer coating the outer surface of the glass microsphere core, and the glass-transition temperature of the polymer is less than 30 DEG C. The first composite unit particles have two functions, specifically, on one hand, the wettability of the electrolyte on the diaphragm is remarkably improved; and on the other hand, the bonding strength between the pole piece and the diaphragm is enhanced. Through the effects of the two aspects, the problems that the pole piece and the diaphragm are not tightly bonded, so that the pole piece falls off in the subsequent lamination process, and the infiltration effect of electrolyte on the pole piece is poor are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of diaphragms, and in particular to a diaphragm and an energy storage battery. Background Art

[0002] In recent years, the new energy vehicle market has experienced rapid growth. Currently, the power batteries used in new energy vehicles mainly include soft-pack batteries, prismatic batteries, and cylindrical batteries. Prismatic batteries are widely used due to their advantages in structural safety, shape and space utilization, and charge and discharge performance.

[0003] At present, the core pack of square batteries is usually produced by winding or lamination. Among them, laminated batteries have a higher utilization rate of the space inside the battery, and the pole pieces are more evenly stressed during the battery cycle, so they have more advantages in terms of energy density and cycle life. However, the traditional lamination process has lower production efficiency than the winding process. In order to improve the efficiency of the lamination process, thermal composite lamination technology has ushered in development. The thermal composite lamination technology first bonds the pole piece and the diaphragm by heating before lamination. Under current technology, embedded large-particle glue mixed with the diaphragm is often used to achieve the bonding of the diaphragm and the pole piece. However, when the pole piece and the diaphragm are bonded too tightly, the direct contact area between the pole piece and the electrolyte is reduced, which is not conducive to the subsequent infiltration of the electrolyte into the pole piece, thereby affecting the dynamic performance of the battery.

[0004] In addition, in the existing technology, there is often a situation where the electrode sheets fall off during the subsequent stacking process due to loose bonding between the electrode sheets and the diaphragm. In particular, the positive electrode sheets are usually heavier, and the risk of subsequent falling off due to loose bonding is higher. Therefore, the thermal composite stacking technology still needs to be improved. Summary of the Invention

[0005] The main purpose of this application is to provide a diaphragm and an energy storage battery to solve the problems in the prior art of loose bonding between the electrode and the diaphragm, which leads to falling off during the subsequent lamination process and poor wetting effect of the electrolyte on the electrode.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a diaphragm is provided, comprising a base film and a first functional coating and a second functional coating formed on two opposite surfaces of the base film, the first functional coating and the second functional coating each independently comprising: inorganic particles, an adhesive, and composite unit particles; wherein the composite unit particles in the functional coating on at least one surface of the base film comprise first composite unit particles, the first composite unit particles comprising a glass microsphere inner core and a first polymer coated on the outer surface of the glass microsphere inner core, and the glass transition temperature of the polymer is less than 30°C.

[0007] Furthermore, the composite unit particles further include second composite unit particles, the material of which is a second polymer having a glass transition temperature of less than 30°C; and / or the D50 particle sizes of the first composite unit particles and the second composite unit particles are each independently 3 to 10 μm.

[0008] Furthermore, the mass ratio of the glass microsphere core to the first polymer is 0.3 to 1:1.

[0009] Furthermore, the mass ratio of the first composite unit particles to the second composite unit particles is 1:0.5-1.

[0010] Furthermore, the first polymer and the second polymer are independently selected from any one or more of polymethyl acrylate, polyethyl acrylate and polybutyl acrylate.

[0011] Furthermore, the D50 particle size of the inner core of the glass microsphere is 1-6 μm, and / or the inner core of the glass microsphere is a hollow microsphere.

[0012] Furthermore, the mass ratio of the above-mentioned inorganic particles, binder and composite unit particles is (80-90): (5-10): (5-10); and / or the inorganic particles are selected from any one or more of alumina, boehmite, titanium dioxide and silicon dioxide; and / or the binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide and polyethylene oxide.

[0013] According to another aspect of the present invention, there is provided an energy storage battery comprising a positive electrode, the above-mentioned separator and a negative electrode arranged in sequence, wherein the first functional coating of the separator is arranged in contact with the negative electrode, and the second functional coating of the separator is arranged in contact with the positive electrode.

[0014] Furthermore, the mass of the first composite unit particles in the first functional coating accounts for a% of the total mass of the composite unit particles in the first functional coating, the mass of the first composite unit particles in the second functional coating accounts for b% of the total mass of the composite unit particles in the second functional coating, and a>b.

[0015] Furthermore, the value range of a is 50-100, and the value range of b is 0-30.

[0016] Applying the technical solution of the present invention, the diaphragm contains inorganic particles, a binder, and unique composite unit particles. The first composite unit particles are composed of a glass microsphere core and a first polymer with a low glass transition temperature (Tg). The first composite unit particles have two functions. Specifically, on the one hand, the wettability of the electrolyte to the diaphragm is significantly improved. The use of the glass microsphere core can protrude from the surface of the functional coating during the heating and compounding process, forming microchannels and protrusions, which greatly enhances the wetting effect of the electrolyte on the diaphragm. This structure not only increases the contact area between the electrolyte and the electrode, but also promotes the uniform distribution of the electrolyte, thereby optimizing the dynamic performance of the battery, including the charge and discharge rate and cycle efficiency. On the other hand, the bonding strength between the electrode and the diaphragm is enhanced. The low Tg polymer shell on the surface of the first composite unit particle has good fluidity and viscosity in the heated state. The highly elastic low Tg polymer can be embedded in the pores of the electrode to achieve bonding, thereby significantly improving the bonding strength between the electrode and the diaphragm. This bonding effect is particularly critical for positive electrode plates, which are prone to delamination during the lamination process due to their high weight. Low-Tg polymers can effectively prevent this problem. These two effects solve the problems of loose adhesion between the electrode and the separator, which leads to falling during subsequent lamination, and poor electrolyte wetting of the electrode. This further significantly enhances the thermal stability and mechanical strength of the separator, improving the electrical properties of the energy storage battery, such as energy density and cycle life, making it suitable for high-energy-density battery applications such as electric vehicles and energy storage systems. DETAILED DESCRIPTION

[0017] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0018] As analyzed in the background technology of this application, there are problems in the prior art such as loose bonding between the electrode and the diaphragm, which leads to falling off during the subsequent stacking process, and poor wetting effect of the electrolyte on the electrode. In order to solve the above problems, this application provides a diaphragm and an energy storage battery.

[0019] In a typical embodiment of the present application, a diaphragm is provided, comprising a base film and a first functional coating and a second functional coating formed on two opposite surfaces of the base film, wherein the first functional coating and the second functional coating independently comprise: inorganic particles, an adhesive, and composite unit particles; wherein the composite unit particles in the functional coating on at least one surface of the base film comprise first composite unit particles, the first composite unit particles comprising a glass microsphere inner core and a first polymer coated on the outer surface of the glass microsphere inner core, and the glass transition temperature of the polymer is less than 30°C.

[0020] The diaphragm contains inorganic particles, adhesives and unique composite unit particles. The first composite unit particles are composed of a glass microsphere core and a first polymer with a low glass transition temperature (Tg). The first composite unit particles have two functions. Specifically, on the one hand, the wettability of the electrolyte to the diaphragm is significantly improved. The use of the glass microsphere core can protrude from the surface of the functional coating during the heating and compounding process, forming tiny channels and protrusions, which greatly enhances the wetting effect of the electrolyte on the diaphragm. This structure not only increases the contact area between the electrolyte and the electrode, but also promotes the uniform distribution of the electrolyte, thereby optimizing the dynamic performance of the battery, including the charge and discharge rate and cycle efficiency. On the other hand, the bonding strength between the electrode and the diaphragm is enhanced. The low Tg polymer shell on the surface of the first composite unit particle has good fluidity and viscosity in the heated state. The highly elastic low Tg polymer can be embedded in the pores of the electrode to achieve bonding, thereby significantly improving the bonding strength between the electrode and the diaphragm. This bonding effect is particularly critical for positive electrode plates, which are prone to delamination during the lamination process due to their high weight. Low-Tg polymers can effectively prevent this problem. These two effects solve the problems of loose adhesion between the electrode and the separator, which leads to falling during subsequent lamination, and poor electrolyte wetting of the electrode. This further significantly enhances the thermal stability and mechanical strength of the separator, improving the electrical properties of the energy storage battery, such as energy density and cycle life, making it suitable for high-energy-density battery applications such as electric vehicles and energy storage systems.

[0021] In addition, the use of glass microsphere core to replace the high Tg polymer core, on the one hand, brings better electrode / diaphragm interface support effect and improves the wettability of the electrolyte to the electrode, and on the other hand, it also has a lower cost advantage than polymer core glass microspheres.

[0022] In one embodiment of the present application, the above-mentioned composite unit particles further include second composite unit particles, the material of the second composite unit particles is a second polymer with a glass transition temperature less than 30°C; and / or the D50 particle size of the first composite unit particles and the second composite unit particles are each independently 3 to 10 μm.

[0023] The second composite unit particles select a second polymer with a glass transition temperature of less than 30°C, which helps to achieve a synergistic effect between it and the first composite unit particles, so that the diaphragm has excellent flexibility, elasticity and mechanical strength. Controlling the D50 particle size of the first composite unit particles and the second composite unit particles in the range of 3 to 10 μm helps to achieve a more balanced force distribution during the thermal composite process. Smaller particle sizes help to form denser point contacts at the contact surface between the pole piece and the diaphragm, increase the number of contact points, and thus improve the stability of the composite. At the same time, the appropriate range of particle size ensures the uniform distribution of the composite unit particles in the functional coating, avoiding the problems of uneven coating and reduced internal battery space utilization due to excessively large particles, as well as the risk of reduced electrolyte wetting performance due to increased coating density due to excessively small particles.

[0024] In one embodiment of the present application, the mass ratio of the glass microsphere core to the first polymer is 0.3 to 1:1.

[0025] During the thermal lamination process, the glass microsphere core provides a certain degree of rigidity, helping to form microprotrusions when the electrode contacts the separator. This increases the contact points between the electrode and the functional coating, thereby enhancing the lamination effect and promoting the formation of microporous structures between the electrode and the separator. These microporous structures facilitate rapid electrolyte infiltration. The first polymer shell, with its low Tg value, maintains appropriate flexibility during thermal lamination, allowing the composite particles to adapt and closely adhere to even minor surface irregularities on the electrode, forming a stable and uniform composite interface that facilitates electrolyte penetration. Controlling the mass ratio of the glass microsphere core to the first polymer within the above range not only enhances the formation of a stable core-shell structure between the glass microsphere core and the first polymer, but also ensures that the amount of the first polymer is sufficient to form a continuous and uniform shell on the microsphere surface. If the mass ratio of the glass microsphere core to the first polymer is less than 0.3:1, the first polymer is relatively excessive, resulting in an excessively thick shell, which increases the elasticity of the composite particles, impairs electrolyte infiltration, and may also increase material cost. On the other hand, if the mass ratio of the glass microsphere core to the first polymer is higher than 1:1, the amount of the first polymer is insufficient to fully coat the glass microsphere core, resulting in an unstable particle structure of the first composite unit and a decrease in the bonding effect during thermal composite, thus affecting the electrochemical performance of the battery. This achieves an effective balance between cost and performance.

[0026] In one embodiment of the present application, the mass ratio of the first composite unit particles to the second composite unit particles is 1:0.5-1.

[0027] The first composite unit particles, due to their glass microsphere core and low-Tg first polymer shell, provide a composite material that is both elastic and maintains a certain degree of rigidity. During the thermal composite process, the first composite unit particles can achieve tight adhesion to the electrode under relatively low pressure. The second composite unit particles are composed of a low-Tg second polymer. Although they lack a core, their softness ensures good adaptability during the thermal composite process. By controlling the mass ratio of the first composite unit particles to the second composite unit particles, differentiated designs of the functional coatings of the positive and negative electrode separators of the battery can be achieved. An appropriate mass ratio of the first composite unit particles to the second composite unit particles further helps ensure that the functional coatings of the separator and the electrode after thermal composite neither affect electrolyte infiltration due to over-tight composite nor reduce the effective contact area between the electrode and the electrolyte due to loose composite. This balance ensures good dynamic performance and cycle stability of the battery during charge and discharge, while taking into account production cost and efficiency.

[0028] In one embodiment of the present application, the first polymer and the second polymer are independently selected from any one or more of polymethyl acrylate, polyethyl acrylate and polybutyl acrylate.

[0029] On the one hand, selecting a polymer with a Tg of less than 30°C as the shell material of the first composite unit particles, or as the main component of the second composite unit particles, can ensure that the separator has sufficient flexibility during the thermal composite process, facilitating good contact and adhesion with the electrode surface, while also reducing the risk of the separator being too hard and reducing the direct contact area with the electrolyte. On the other hand, the above polymers all have good adhesion and can effectively bond to the base film and inorganic particles to form a stable functional coating. Polyacrylate polymers contain carboxyl groups (-COOH) or ester groups (-COO-). These chemical groups can react with hydroxyl groups (-OH) on the surface of inorganic particles under certain conditions to form chemical bonds, thereby strengthening the bonding force between the various components of the separator and improving the mechanical strength and stability of the separator. Therefore, the selected polymer has good chemical stability and compatibility with the electrolyte, can remain stable under the battery's operating environment, and reduce the risk of side reactions with the electrolyte, thereby helping to optimize the battery's structural safety, energy density, and cycle life, while reducing production costs and achieving a balance between performance and cost.

[0030] In one embodiment of the present application, the D50 particle size of the inner core of the glass microsphere is 1-6 μm, and / or the inner core of the glass microsphere is a hollow microsphere.

[0031] Glass microsphere cores with a D50 particle size of 1-6μm provide an appropriate degree of protrusion during the thermal lamination process, enhancing point contact between the electrode and the functional coating, thereby improving the lamination effect. Furthermore, glass microspheres within this particle size range do not significantly increase the thickness of the separator, maintaining good internal battery space utilization and avoiding a negative impact on the battery's energy density. Using hollow glass microspheres as the core increases the buoyancy of the first composite unit particles, making them more likely to protrude from the surface of the functional coating during the thermal lamination process and form close contact with the electrode. The hollow structure reduces the microsphere density, meaning they are lighter for the same volume. This reduces stress on the electrode during the lamination process, preventing excessive compression or deformation. This is particularly true for the positive electrode, ensuring its flatness and designed thickness after lamination, which helps maintain the battery's structural integrity. Furthermore, the pores of the hollow microspheres serve as microchannels for electrolyte infiltration, facilitating rapid electrolyte penetration between the composite particles and the electrode, increasing the contact area between the electrolyte and the electrode, and thus optimizing the battery's dynamic performance. Hollow microspheres have cost advantages over solid microspheres in terms of raw materials

[0032] In one embodiment of the present application, the mass ratio of the above-mentioned inorganic particles, binder and composite unit particles is (80-90): (5-10): (5-10); and / or the inorganic particles are selected from any one or more of alumina, boehmite, titanium dioxide and silicon dioxide; and / or the binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide and polyethylene oxide.

[0033] The above mass ratio improves the synergistic effect of inorganic particles, adhesives and composite unit particles. The inorganic particles mainly provide the heat resistance and mechanical stability of the diaphragm, while reducing the shrinkage rate of the diaphragm and ensuring the dimensional stability of the diaphragm during the battery charging and discharging process. The adhesive acts as a bridge between the inorganic particles and the base film, as well as between the first composite unit particles and the coating, ensuring the uniformity of the coating and the close bonding between the components. The composite unit particles provide additional bonding enhancement and electrolyte infiltration paths, especially through the polymer shell layer on their surface to form a good interface bond with the pole piece. The selection of inorganic particles such as alumina, boehmite, titanium dioxide and silicon dioxide based on chemical stability and high heat resistance will not react with the electrolyte in the battery, while maintaining structural stability at high temperatures, which helps to extend the battery life. The choice of adhesive enhances the bonding force between the inorganic particles and the composite unit particles.

[0034] In another typical embodiment of the present application, an energy storage battery is provided, comprising a positive electrode, the above-mentioned diaphragm and a negative electrode arranged in sequence, wherein the first functional coating of the diaphragm is arranged in contact with the negative electrode, and the second functional coating of the diaphragm is arranged in contact with the positive electrode.

[0035] The diaphragm contains inorganic particles, adhesives and unique composite unit particles. The first composite unit particles are composed of a glass microsphere core and a first polymer with a low glass transition temperature (Tg). The first composite unit particles have two functions. Specifically, on the one hand, the wettability of the electrolyte to the diaphragm is significantly improved. The use of the glass microsphere core can protrude from the surface of the functional coating during the heating and compounding process, forming tiny channels and protrusions, which greatly enhances the wetting effect of the electrolyte on the diaphragm. This structure not only increases the contact area between the electrolyte and the electrode, but also promotes the uniform distribution of the electrolyte, thereby optimizing the dynamic performance of the battery, including the charge and discharge rate and cycle efficiency. On the other hand, the bonding strength between the electrode and the diaphragm is enhanced. The low Tg polymer shell on the surface of the first composite unit particle has good fluidity and viscosity in the heated state. The highly elastic low Tg polymer can be embedded in the pores of the electrode to achieve bonding, thereby significantly improving the bonding strength between the electrode and the diaphragm. This bonding effect is particularly critical for positive electrode plates, which are prone to delamination during the lamination process due to their high weight. Low-Tg polymers can effectively prevent this problem. These two effects solve the problems of loose adhesion between the electrode and the separator, which leads to falling during subsequent lamination, and poor electrolyte wetting of the electrode. This further significantly enhances the thermal stability and mechanical strength of the separator, improving the electrical properties of the energy storage battery, such as energy density and cycle life, making it suitable for high-energy-density battery applications such as electric vehicles and energy storage systems.

[0036] In one embodiment of the present application, the mass of the first composite unit particles in the first functional coating accounts for a% of the total mass of the composite unit particles in the first functional coating, the mass of the first composite unit particles in the second functional coating accounts for b% of the total mass of the composite unit particles in the second functional coating, and a>b.

[0037] Since the composite of the positive electrode and the diaphragm is often more difficult during thermal composite, a higher pressure is often used to composite the positive electrode and the diaphragm in the process. However, excessive pressure will cause the elongation of the positive electrode to deviate from the design value, which may lead to problems such as low capacity of the battery. By controlling the mass ratio of the first composite unit particles to the second composite unit particles in the first functional coating and the second functional coating, a differentiated design of the functional coatings of the positive and negative electrode diaphragms of the battery can be achieved. Specifically, the present invention improves the composite performance and reduces the pressure requirements of the composite process by selecting composite particles with good flexibility on the positive electrode side, while selecting composite particles with high rigidity on the negative electrode side to ensure the infiltration of the electrolyte into the electrode sheet.

[0038] In one embodiment of the present application, the value range of a is 50-100, and the value range of b is 0-30.

[0039] By controlling the values of a and b, the balance between electrolyte wetting and electrode sheet composite can be optimized, which has a direct impact on the battery's kinetic performance. The bonding effect of the positive electrode sheet and the electrolyte wettability of the negative electrode sheet are important factors determining the battery's charge and discharge rate and cycle stability. The range of a and b ensures optimization of both aspects. Specifically, on the negative electrode side, due to the higher a value, it means more first composite unit particles, providing more micro-convex structures, thereby significantly enhancing the electrolyte wetting effect on the negative electrode, which is crucial for improving the battery's electrochemical performance, especially the charge and discharge efficiency and cycle life. The positive electrode sheet is generally heavier and requires higher pressure to achieve bonding with the separator during the thermal composite process. By reducing the b value and reducing the proportion of first composite unit particles in the functional coating on the positive electrode side, the reduction in electrolyte contact area caused by over-tight composite can be avoided, while retaining sufficient adhesive and inorganic particles to ensure stable composite between the positive electrode sheet and the separator, reduce damage to the positive electrode sheet, and optimize the structural safety of the battery. The lower proportion of first composite unit particles on the positive electrode side reduces the pressure required during the composite process, making the process operation gentler, reducing equipment wear and improving production efficiency.

[0040] In addition, the present application provides a method for preparing the first composite unit particles. Specifically, glass microspheres with a core-shell structure @ polymethyl acrylate are used as an example. The preparation methods of the first composite unit particles with other polymers as the coating layer can also refer to the following preparation method:

[0041] 1. 100 g of glass microspheres (HM10, D50 = 5 μm, purchased from Zhengzhou Shenglait Hollow Microsphere New Materials Co., Ltd.) were mixed with 1000 mL of a 0.5 mol / L sodium hydroxide aqueous solution, heated under reflux at 80-100° C. for 3-5 h, filtered, washed to neutrality (washing water, pH = about 7), and dried at 80-100° C. for 8-12 h to obtain surface hydroxylated glass microspheres;

[0042] 2. Take 100g of surface hydroxylated glass microspheres and 100mL of dioxane and add them to a 250mL three-necked flask. Ultrasonicate for 20min to disperse them evenly. Add 2g of γ-aminopropyltriethoxysilane (silane coupling agent KH-550) and react at 80℃ for 1h under nitrogen protection. Use the condensation reaction between the silane group and the surface hydroxyl group of the glass microspheres to introduce amino groups on the surface of the glass microspheres.

[0043] 3. After the reaction is completed, transfer the three-necked flask to an ice bath environment, add 1g of S-ethyl-S'-(α,α'-dimethyl-α"-acetoxy) trithiocarbonate (EDMAT, a chain transfer agent for RAFT polymerization), 0.1g of 4-dimethylaminopyridine (DMAP, a catalyst), and 0.5g of dicyclohexylcarbodiimide (DCC, a water absorbent) to the three-necked flask, protect with nitrogen, and react at 5°C for 8h; the RAFT agent is attached to the surface of the glass microspheres.

[0044] 4. Finally, add 10 g of methyl acrylate and 0.1 g of azobisisobutyronitrile (AIBN, initiator) into a three-necked flask, protect with nitrogen, and react at 70 ° C for 6 h. After the reaction is completed, filter and rinse with excess ethanol to remove the residual reactants to obtain glass microspheres with a core-shell structure @ polymethyl acrylate.

[0045] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0046] Diaphragm Examples and Comparative Examples

[0047] Example 1

[0048] 1. 100 g of glass microspheres (HM10, D50 = 5 μm, purchased from Zhengzhou Shenglait Hollow Microsphere New Materials Co., Ltd.) were mixed with 1000 mL of a 0.5 mol / L sodium hydroxide aqueous solution, heated under reflux at 100° C. for 5 h, filtered, washed to neutrality (washed water, pH = about 7), and dried at 100° C. for 12 h to obtain surface hydroxylated glass microspheres;

[0049] 2. Take 100g of surface hydroxylated glass microspheres and 100mL of dioxane and add them to a 250mL three-necked flask. Ultrasonicate for 20min to disperse them evenly. Add 2g of γ-aminopropyltriethoxysilane (silane coupling agent KH-550) and react at 80℃ for 1h under nitrogen protection. Use the condensation reaction between the silane group and the surface hydroxyl group of the glass microspheres to introduce amino groups on the surface of the glass microspheres.

[0050] 3. After the reaction is completed, transfer the three-necked flask to an ice bath environment, add 1g of S-ethyl-S'-(α,α'-dimethyl-α"-acetoxy) trithiocarbonate (EDMAT, a chain transfer agent for RAFT polymerization), 0.1g of 4-dimethylaminopyridine (DMAP, a catalyst), and 0.5g of dicyclohexylcarbodiimide (DCC, a water absorbent) to the three-necked flask, protect with nitrogen, and react at 5°C for 8h; the RAFT agent is attached to the surface of the glass microspheres.

[0051] 4. Finally, 10 g of methyl acrylate and 0.1 g of azobisisobutyronitrile (AIBN, initiator) were added to a three-necked flask, protected by nitrogen, and reacted at 70 ° C for 6 h. After the reaction was completed, the residual reactants were removed by filtration and rinsed with excess ethanol to obtain glass microspheres with a core-shell structure @ polymethyl acrylate, wherein the mass ratio of glass microspheres to polymethyl acrylate was 0.5:1.

[0052] The second composite unit particles are polyethyl acrylate, and the D50 particle size thereof is independently 8 μm.

[0053] Alumina, polyvinylidene fluoride, and composite unit particles are mixed in a mass ratio of 85:7.5:7.5 to obtain a first mixture and a second mixture. In the first mixture, the mass ratio of glass microspheres @ polymethyl acrylate and polyethyl acrylate is 1:0.5, and in the second mixture, the mass ratio of glass microspheres @ polymethyl acrylate and polyethyl acrylate is 1:1.

[0054] The first mixed material and the second mixed material are respectively coated on two opposite surfaces of the base film to form a diaphragm including a first functional coating layer and a second functional coating layer.

[0055] Example 2

[0056] The difference from Example 1 is that the mass ratio of glass microspheres to polymethyl acrylate is 0.3:1, and a diaphragm is finally obtained.

[0057] Example 3

[0058] The difference from Example 1 is that the mass ratio of glass microspheres to polymethyl acrylate is 1:1, and a diaphragm is finally obtained.

[0059] Example 4

[0060] The difference from Example 1 is that the mass ratio of glass microspheres to polymethyl acrylate is 1.2:1, and a diaphragm is finally obtained.

[0061] Example 5

[0062] The difference from Example 1 is that in the first mixture, the mass ratio of glass microspheres @ polymethyl acrylate to polyethyl acrylate is 1:0.8, and in the second mixture, the mass ratio of glass microspheres @ polymethyl acrylate to polyethyl acrylate is 1:0.5, and finally a diaphragm is obtained.

[0063] Example 6

[0064] The difference from Example 1 is that in the first mixture, the mass ratio of glass microspheres @ polymethyl acrylate to polyethyl acrylate is 1:1, and in the second mixture, the mass ratio of glass microspheres @ polymethyl acrylate to polyethyl acrylate is 1:0.8, and finally a diaphragm is obtained.

[0065] Example 7

[0066] The difference from Example 1 is that in the first mixture, the mass ratio of glass microspheres @ polymethyl acrylate to polyethyl acrylate is 1:0.4, and in the second mixture, the mass ratio of glass microspheres @ polymethyl acrylate to polyethyl acrylate is 1:1.1, and finally a diaphragm is obtained.

[0067] Example 8

[0068] The difference from Example 1 is that the mass ratio of aluminum oxide, polyvinylidene fluoride, and composite unit particles is 90:5:5, and the diaphragm is finally obtained.

[0069] Example 9

[0070] The difference from Example 1 is that the mass ratio of aluminum oxide, polyvinylidene fluoride, and composite unit particles is 92:4:4, and the diaphragm is finally obtained.

[0071] Comparative Example 1

[0072] The difference from Example 1 is that 10 g of polymethyl methacrylate and 0.1 g of azobisisobutyronitrile (AIBN, initiator) were added to a three-necked flask, the reaction was carried out at 70° C. for 6 h under nitrogen protection, and after the reaction was completed, the residual reactants were removed by suction filtration and rinsed with excess ethanol to obtain glass microspheres @ polymethyl methacrylate with a core-shell structure, wherein the mass ratio of the glass microspheres to the polymethyl methacrylate was 0.5:1, and finally a diaphragm was obtained.

[0073] Lithium-ion battery examples and comparative examples

[0074] Battery Examples 1 to 9, Battery Comparative Example 1

[0075] A positive electrode (a positive electrode slurry obtained by mixing lithium iron phosphate: conductive carbon black: carbon nanotubes: polyvinylidene fluoride in a mass ratio of 97.4:0.5:0.4:1.7, coated on aluminum foil, dried, and baked to obtain a positive electrode), a separator (one of the separators described in Examples 1 to 9 and Comparative Example 1), and a negative electrode (a negative electrode slurry obtained by mixing graphite: conductive carbon black: carboxymethyl cellulose: styrene-butadiene rubber in a mass ratio of 96.7:0.6:1.2:1.5, coated on copper foil, dried, and baked to obtain a positive electrode) were stacked in sequence and then superimposed, with a first functional coating layer in contact with the negative electrode and a second functional coating layer in contact with the positive electrode. The mass of the glass microspheres @ polymethyl acrylate in the first functional coating layer accounted for 80% of the total mass of the composite unit particles in the first functional coating layer, and the mass of the glass microspheres @ polyethyl acrylate in the second functional coating layer accounted for 20% of the total mass of the composite unit particles in the second functional coating layer. After welding the tabs, they are placed in an outer packaging aluminum-plastic film and go through processes such as vacuum packaging, liquid injection, standing at room temperature for 24 hours, formation (charging at a constant current of 0.02C to 3.75V, then charging at a constant current of 0.1C to 4.3V), shaping, and capacity testing to obtain a soft-pack laminated lithium metal battery.

[0076] The positive and negative sides of the separator both include the first composite unit particles (the ratio can be adjusted according to the requirements, and multiple embodiments can be set to protect the endpoints, such as the positive electrode is a mixture of the first and second, the negative electrode is only the second; both the positive and negative electrodes are a mixture of the first and second, etc.)

[0077] Battery Example 10

[0078] The difference from Battery Example 1 is that the mass of the glass microspheres @ polymethyl acrylate in the first functional coating accounts for 100% of the total mass of the composite unit particles in the first functional coating, and the mass of the glass microspheres @ polyethyl acrylate in the second functional coating accounts for 0% of the total mass of the composite unit particles in the second functional coating, and finally a soft-pack laminated lithium metal battery is obtained.

[0079] Battery Example 11

[0080] The difference from Battery Example 1 is that the mass of the glass microspheres @ polymethyl acrylate in the first functional coating accounts for 50% of the total mass of the composite unit particles in the first functional coating, and the mass of the glass microspheres @ polyethyl acrylate in the second functional coating accounts for 30% of the total mass of the composite unit particles in the second functional coating, and finally a soft-pack laminated lithium metal battery is obtained.

[0081] Battery Comparison Example 1

[0082] The difference from Battery Example 1 is that the mass of the glass microspheres @ polymethyl acrylate in the first functional coating accounts for 5% of the total mass of the composite unit particles in the first functional coating, and the mass of the glass microspheres @ polyethyl acrylate in the second functional coating accounts for 30% of the total mass of the composite unit particles in the second functional coating, and finally a soft-pack laminated lithium metal battery is obtained.

[0083] Battery Comparison Example 2

[0084] The difference from Battery Example 1 is that the mass of the glass microspheres @ polymethyl acrylate in the first functional coating accounts for 0% of the total mass of the composite unit particles in the first functional coating, that is, the first functional coating only includes polymethyl acrylate, and the mass of the glass microspheres @ polyethyl acrylate in the second functional coating accounts for 0% of the total mass of the composite unit particles in the second functional coating, that is, the second functional coating only includes polymethyl acrylate, and finally a soft-pack laminated lithium metal battery is obtained.

[0085] Battery Comparison Example 3

[0086] The difference from Battery Example 1 is that the first functional coating and the second functional coating of the separator only include glass microbeads, and a soft-pack laminated lithium metal battery is finally obtained.

[0087] Performance testing:

[0088] The soft-pack laminated lithium metal batteries obtained from battery examples 1 to 11 and battery comparison examples 1 to 3 were cycled on a charge and discharge device, charged to 4.3V at a charge rate of 0.3C, and then discharged to 3V at a discharge rate of 1C, thereby performing a cycle.

[0089] DCIR test method: Fully charge the battery at 25°C, let it sit for 0.5h, then fully discharge it, recording the discharge capacity (Q). Fully charge the battery again, let it sit for 0.5h, then discharge it at 0.1C for 0.5Q. Let it sit for 1h, recording the voltage at this point as V0. Then discharge it at 1C for 30s, recording the voltage (V1) and current (I) at the end of discharge. DCIR = (V0 - V1) / I, converted to mΩ. Full charge conditions: At 25°C, charge at a constant current of 0.33C to a cutoff voltage of 3.65V, then switch to constant voltage charging with a cutoff current of 0.05C. Full discharge conditions: At 25°C, discharge at a 1C rate to 2.5V.

[0090] Thermal composite stacking process yield: Statistics are collected on the yield of the stacking process in continuous production. The yield is the number of good products divided by the input quantity.

[0091] Cycle performance: The battery is fully charged and discharged at 25°C, and the capacity retention rate is recorded after 1000 cycles.

[0092] The above test data are listed in Table 1.

[0093] Table 1

[0094]

[0095]

[0096] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0097] The diaphragm contains inorganic particles, adhesives and unique composite unit particles. The first composite unit particles are composed of a glass microsphere core and a first polymer with a low glass transition temperature (Tg). The first composite unit particles have two functions. Specifically, on the one hand, the wettability of the electrolyte to the diaphragm is significantly improved. The use of the glass microsphere core can protrude from the surface of the functional coating during the heating and compounding process, forming tiny channels and protrusions, which greatly enhances the wetting effect of the electrolyte on the diaphragm. This structure not only increases the contact area between the electrolyte and the electrode, but also promotes the uniform distribution of the electrolyte, thereby optimizing the dynamic performance of the battery, including the charge and discharge rate and cycle efficiency. On the other hand, the bonding strength between the electrode and the diaphragm is enhanced. The low Tg polymer shell on the surface of the first composite unit particle has good fluidity and viscosity in the heated state. The highly elastic low Tg polymer can be embedded in the pores of the electrode to achieve bonding, thereby significantly improving the bonding strength between the electrode and the diaphragm. This bonding effect is particularly critical for positive electrode plates, which are prone to delamination during the lamination process due to their high weight. Low-Tg polymers can effectively prevent this problem. These two effects solve the problems of loose adhesion between the electrode and the separator, which leads to falling during subsequent lamination, and poor electrolyte wetting of the electrode. This further significantly enhances the thermal stability and mechanical strength of the separator, improving the electrical properties of the energy storage battery, such as energy density and cycle life, making it suitable for high-energy-density battery applications such as electric vehicles and energy storage systems.

[0098] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A diaphragm comprising a base film and a first functional coating and a second functional coating formed on two opposite surfaces of the base film, characterized in that: The first functional coating and the second functional coating each independently comprise: Inorganic particles; Adhesives; Composite unit particles; The composite unit particles in the functional coating on at least one surface of the base film include first composite unit particles, which include a glass microsphere core and a first polymer coated on the outer surface of the glass microsphere core, and the glass transition temperature of the polymer is less than 30°C.

2. The diaphragm according to claim 1, characterized in that The composite unit particles further include second composite unit particles, the material of the second composite unit particles is a second polymer with a glass transition temperature less than 30° C.; and / or the D50 particle size of the first composite unit particles and the second composite unit particles are each independently 3 to 10 μm.

3. The diaphragm according to claim 2, characterized in that The mass ratio of the glass microsphere core to the first polymer is 0.3 to 1:

1.

4. The diaphragm according to claim 2, characterized in that The mass ratio of the first composite unit particles to the second composite unit particles is 1:0.5-1.

5. The diaphragm according to any one of claims 2 to 4, characterized in that The first polymer and the second polymer are independently selected from any one or more of polymethyl acrylate, polyethyl acrylate and polybutyl acrylate.

6. The diaphragm according to any one of claims 1 to 5, characterized in that The D50 particle size of the inner core of the glass microsphere is 1-6 μm, and / or the inner core of the glass microsphere is a hollow microsphere.

7. The diaphragm according to any one of claims 1 to 6, characterized in that The mass ratio of the inorganic particles, the adhesive and the composite unit particles is (80-90): (5-10): (5-10); and / or the inorganic particles are selected from any one or more of alumina, boehmite, titanium dioxide and silicon dioxide; and / or the adhesive is selected from any one or more of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide and polyethylene oxide.

8. An energy storage battery comprising a positive electrode, a separator according to any one of claims 1 to 7, and a negative electrode arranged in sequence, characterized in that: The first functional coating of the separator is arranged in contact with the negative electrode, and the second functional coating of the separator is arranged in contact with the positive electrode.

9. The energy storage battery according to claim 8, characterized in that: The mass of the first composite unit particles in the first functional coating accounts for a% of the total mass of the composite unit particles in the first functional coating, the mass of the first composite unit particles in the second functional coating accounts for b% of the total mass of the composite unit particles in the second functional coating, and a>b.

10. The energy storage battery according to claim 9, characterized in that: The value range of a is 50-100, and the value range of b is 0-30.

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