Composite separator, energy storage battery and manufacturing method for energy storage battery

Abstract

A composite separator, an energy storage battery and a manufacturing method for the energy storage battery. The composite separator is applied to the energy storage battery. The energy storage battery comprises a positive electrode sheet and a negative electrode sheet. The composite separator comprises a base film and a functional coating, wherein the functional coating covers the base film and comprises a base coating and polymer particles embedded in the base coating, and at least some polymer particles protrude from the surface of the base coating. The polymer particles are formed from a copolymer of a first monomer and a second monomer, the glass transition temperature of a polymer of the first monomer being higher than 80°C, and the glass transition temperature of a polymer of the second monomer being lower than 50°C. The energy storage battery satisfies: 0.003≤γ*d / σ≤0.3, wherein the molar ratio of the first monomer to the second monomer is γ, the particle size D50 of the polymer particles is d μm, and the porosity of the positive electrode sheet is σ. In this way, the composite separator and the electrode sheets can be well bonded during the process of manufacturing the energy storage battery, thereby improving manufacturing yield, and further, the polymer particles can remain in a glassy state during subsequent use of the energy storage battery and provide support points at interfaces between the composite separator and the electrode sheets, so as to facilitate infiltration of an electrolyte into the electrode sheets, thus also improving the kinetic performance of the energy storage battery.

Description

Composite separator, energy storage battery, and preparation method of energy storage battery

[0001] This application claims priority to Chinese Patent Application No. 202510373216.0, filed with the Chinese Patent Office on March 26, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of energy storage battery technology, and in particular to a composite separator, an energy storage battery, and a method for preparing the energy storage battery. Background Technology

[0003] In recent years, against the backdrop of "carbon neutrality," the new energy vehicle market has experienced rapid development. Currently, the power batteries used in new energy vehicles mainly include pouch batteries, prismatic batteries, and cylindrical batteries. Among them, prismatic batteries are widely used due to their advantages in structural safety performance, shape and space utilization, and charge and discharge performance.

[0004] In the manufacturing process of square batteries, the stacking method for manufacturing the cell pack has a high space utilization rate inside the energy storage battery, and the electrodes are subjected to uniform stress during the energy storage battery cycle, thus having advantages in terms of energy density and cycle life.

[0005] For thermal lamination technology, the electrodes and separator are bonded together by heating before lamination. Currently, embedded large-particle adhesive is commonly used to bond the separator and electrodes. However, if the electrode and separator are bonded too tightly, the direct contact area between the electrode and the electrolyte is reduced, which is detrimental to the subsequent wetting of the electrode by the electrolyte and thus affects the dynamic performance of the energy storage battery. Conversely, if the electrode and separator are not bonded tightly, the electrode may fall off during subsequent lamination, especially the positive electrode, which is usually heavier and has a higher risk of falling off due to poor bonding, thereby reducing the manufacturing yield. Technical issues

[0006] The main technical problem solved by this application is to provide a composite separator, an energy storage battery, and a method for preparing the energy storage battery. This method enables the composite separator and electrode sheet to not only bond well during the preparation of the energy storage battery and improve the preparation yield, but also to keep the polymer particles in a glassy state during the subsequent use of the energy storage battery. It provides support points at the interface between the composite separator and the electrode sheet, which is beneficial for the electrolyte to wet the electrode sheet, and thus can also improve the dynamic performance of the energy storage battery. Technical solutions

[0007] To solve the above-mentioned technical problems, one technical solution adopted in this application is: providing a composite separator for use in an energy storage battery, the energy storage battery including a positive electrode and a negative electrode, the composite separator including a base film and a functional coating, the functional coating covering the base film and including a base coating and polymer particles embedded in the base coating, wherein at least some of the polymer particles protrude from the surface of the base coating; wherein the polymer particles are a copolymer of a first monomer and a second monomer, the glass transition temperature of the polymer of the first monomer is greater than 80°C, the glass transition temperature of the polymer of the second monomer is less than 50°C, and the energy storage battery satisfies: 0.003≤γ*d / σ≤0.3, wherein the molar ratio of the first monomer to the second monomer is γ, the particle size D50 of the polymer particles is d μm, and the porosity of the positive electrode is σ.

[0008] To solve the above-mentioned technical problems, one technical solution adopted in this application is to provide an energy storage battery, which includes a positive electrode, a negative electrode and a separator located between the positive electrode and the negative electrode, wherein the separator is a composite separator as described above.

[0009] To solve the above-mentioned technical problems, one technical solution adopted in this application is: to provide a method for preparing an energy storage battery, the method comprising: obtaining a positive electrode sheet, a negative electrode sheet and a separator; wherein the separator is a composite separator as described above; hot-pressing the positive electrode sheet, the negative electrode sheet and the separator to obtain a core assembly; assembling the core assembly to obtain a core pack, and post-processing the core pack to obtain an energy storage battery. Beneficial effects

[0010] The beneficial effects of this application are as follows: Unlike existing technologies, this application provides a composite separator, an energy storage battery, and a method for preparing the energy storage battery. The composite separator is used in an energy storage battery, which includes a positive electrode and a negative electrode. The composite separator includes a base film and a functional coating. The functional coating covers the base film and includes a basic coating and polymer particles embedded in the basic coating, wherein at least some of the polymer particles protrude from the surface of the basic coating. The polymer particles are copolymers of a first monomer and a second monomer, where the glass transition temperature of the first monomer is greater than 80°C, and the glass transition temperature of the second monomer is less than 50°C. The energy storage battery satisfies: 0.003 ≤ γ*d / σ ≤ 0.3, where the molar ratio of the first monomer to the second monomer is γ, the particle size D50 of the polymer particles is d μm, and the porosity of the positive electrode is σ. When the core of the energy storage battery is prepared using a thermal composite stacking process, the polymer particles become viscoelastic under heating conditions and enter the pores of the corresponding electrode sheets, achieving adhesion between the electrode sheets and the composite separator. Understandably, when the porosity of the electrode sheet is small, it is more difficult for the polymer to enter the pores. In this case, the polymer particles need to exhibit better fluidity in the viscoelastic state, and the molecular chains of the polymer particles should exhibit good flexibility. However, the improvement of the flexibility of the polymer particle molecular chains inevitably leads to a decrease in the glass transition temperature of the polymer particles. This application adjusts the rigidity of the molecular chains of the copolymer of the first and second monomers by adjusting the molar ratio of the first monomer to the second monomer, and further selects appropriate polymer particle size and molecular chain rigidity according to the porosity of the positive electrode sheet. This allows the composite separator and electrode sheet to not only bond well during the preparation of the energy storage battery, improving the preparation yield, but also to keep the polymer particles in the glassy state during the subsequent use of the energy storage battery (the charging and discharging of the energy storage battery will cause the energy storage battery to heat up). This provides support points at the interface between the composite separator and the electrode sheet, which is beneficial to the wetting of the electrode sheet by the electrolyte, and thus can also improve the dynamic performance of the energy storage battery. Attached Figure Description

[0011] Figure 1 is a schematic diagram of the preparation method of the energy storage battery of this application;

[0012] Figure 2 is a schematic diagram of the process for preparing the separator in the method for preparing the energy storage battery of this application;

[0013] Figure 3 is a schematic diagram of the process for preparing polymer particles in the preparation method of the energy storage battery of this application. Embodiments of the present invention

[0014] This application provides a composite separator that can be used in energy storage batteries. The energy storage battery includes a positive electrode and a negative electrode, and the composite separator can be disposed between the positive electrode and the negative electrode.

[0015] In one embodiment, the composite separator includes a base membrane and a functional coating. The base membrane can specifically be a polyolefin base membrane, such as a polyethylene (PE) or polypropylene (PP) microporous membrane. The functional coating can be applied to the base membrane and is used to select a suitable functional coating based on the functional requirements of the composite separator, such as flame retardancy and dimensional stability. In this embodiment, the functional coating may include a base coating and polymer particles embedded in the base coating, wherein at least some of the polymer particles protrude from the surface of the base coating.

[0016] The polymer particles are copolymers of a first monomer and a second monomer. The glass transition temperature (GTH) of the polymer of the first monomer is greater than 80°C, and the GTH of the polymer of the second monomer is less than 50°C. It should be noted that the polymers of the first and second monomers refer to the polymers obtained by polymerizing the corresponding monomers. For example, when the first monomer is styrene, the polymer of the first monomer is polystyrene. Specifically, the GTH of the polymer of the first monomer can be 81°C, 83°C, 86°C, 90°C, etc., and the GTH of the polymer of the second monomer can be 49°C, 47°C, 43°C, 39°C, etc., without specific limitations.

[0017] The energy storage battery satisfies the following conditions: 0.003≤γ*d / σ≤0.3, where the molar ratio of the first monomer to the second monomer is γ, the particle size D50 of the polymer particles is d μm, and the porosity of the positive electrode is σ.

[0018] Specifically, the porosity of the positive electrode sheet can refer to the porosity of the positive electrode material coating on the positive electrode current collector.

[0019] Specifically, thermal lamination technology involves bonding the electrodes and separator through heating before lamination. Related technologies often use embedded large-particle adhesive coatings to bond the separator and electrodes. However, if the electrode and separator are bonded too tightly, the direct contact area between the electrode and the electrolyte is reduced, hindering subsequent electrolyte wetting and thus affecting the battery's dynamic performance.

[0020] It should be noted that when using the thermal composite stacking process to fabricate the battery pack, polymer particles become viscoelastic under heating conditions, entering the pores of the corresponding electrode sheets to achieve adhesion between the electrode sheets and the composite separator. Understandably, when the electrode sheet porosity is low, it is more difficult for the polymer to enter the pores. In this case, the polymer particles need to exhibit better fluidity in the viscoelastic state, and the polymer molecular chains should exhibit good flexibility; however, improving the flexibility of the polymer molecular chains inevitably leads to a decrease in the glass transition temperature of the polymer particles. The composite separator embodiment of this application adjusts the molar ratio of the first monomer to the second monomer to regulate the rigidity of the copolymer molecular chain. Furthermore, it selects appropriate polymer particle size and molecular chain rigidity based on the porosity of the positive electrode sheet. This ensures that the composite separator and electrode sheet not only adhere well during the preparation of the energy storage battery, improving the preparation yield, but also allows the polymer particles to remain in a glassy state during subsequent use of the energy storage battery (the charging and discharging of the energy storage battery will cause the energy storage battery to heat up). This provides support points at the interface between the composite separator and the electrode sheet, which is beneficial for the electrolyte to wet the electrode sheet. Therefore, it can also improve the dynamic performance of the energy storage battery.

[0021] Furthermore, the energy storage battery in this application is manufactured using a stacking technology, supporting a multi-tab design. This allows for the uniform distribution of multiple tabs along the edges of the positive and negative electrodes, significantly shortening the current transmission path, reducing internal resistance, and improving rate performance and thermal management capabilities. Simultaneously, the multi-tab design makes the current distribution more uniform, reducing the risk of localized overheating and enhancing safety. The stacking technology can more efficiently utilize the internal space of the energy storage battery, increasing cell capacity and energy density, and adapting to the needs of large-size and high-capacity energy storage batteries. Moreover, the uniformity and stability of the stacked structure provide a more reliable basis for the design and installation of explosion-proof valves, enabling more precise control of internal pressure release, reducing the risk of thermal runaway and explosion, thereby comprehensively improving the safety and reliability of the energy storage battery.

[0022] In one embodiment, the molar ratio of the first monomer to the second monomer is 0.05-1, specifically such as 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1, etc. The particle size D50 of the polymer particles is 3 μm-8 μm, specifically such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc.

[0023] The porosity of the positive electrode sheet is 30%-55%, specifically 30%, 35%, 40%, 45%, 50%, 55%, etc. It should be noted that the porosity of the positive electrode sheet is related to the type of positive electrode material and the compaction of the positive electrode sheet; the appropriate positive electrode sheet should be selected based on actual needs.

[0024] In one embodiment, the first monomer includes styrene, and the second monomer includes acrylate. Of course, the first monomer may also include other monomers whose glass transition temperature is greater than 80°C, and the second monomer may also include other monomers whose glass transition temperature is less than 50°C; no specific limitations are imposed here.

[0025] In one embodiment, the acrylate may be selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, etc.

[0026] In one embodiment, the base coating comprises inorganic particles and a binder. The inorganic particles are uniformly dispersed in the binder.

[0027] Specifically, the inorganic particles can be selected from one or more of alumina (Al2O3), boehmite (AlOOH), titanium dioxide (TiO2), and silicon dioxide (SiO2).

[0028] The adhesive may be selected from 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.

[0029] In one embodiment, the thickness of the base coating is 1 μm-5 μm, specifically 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, which can be determined according to actual needs and is not limited here.

[0030] In one embodiment, the mass ratio of inorganic particles, binder, and polymer particles in the base coating satisfies (80-90):(5-10):(5-10), specifically such as 80:5:5, 85:8:8, 90:10:10, 82:6:9, 88:9:6, etc., which are not limited here.

[0031] In one embodiment, the positive electrode material corresponding to the positive electrode sheet in the energy storage battery is selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, and ternary positive electrode materials.

[0032] This application also provides an energy storage battery. In one embodiment, the energy storage battery includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The separator and the positive electrode correspond to the composite separator and positive electrode in the composite separator embodiment, respectively. Accordingly, the structure, composition, and function of the composite separator and the positive electrode can be the same as or similar to those in the composite separator embodiment. For details, please refer to the composite separator embodiment of this application; further details will not be repeated here.

[0033] It should be noted that when using the thermal composite stacking process to fabricate the battery pack, polymer particles become viscoelastic under heating conditions, entering the pores of the corresponding electrode sheets to achieve adhesion between the electrode sheets and the composite separator. Understandably, when the electrode sheet porosity is low, it is more difficult for the polymer to enter the pores. In this case, the polymer particles need to exhibit better fluidity in the viscoelastic state, and the polymer molecular chains should exhibit good flexibility; however, improving the flexibility of the polymer molecular chains inevitably leads to a decrease in the glass transition temperature of the polymer particles. The energy storage battery implementation method of this application adjusts the molar ratio of the first monomer to the second monomer to regulate the rigidity of the copolymer molecular chain, and further selects appropriate polymer particle size and molecular chain rigidity according to the porosity of the positive electrode sheet. This ensures that the composite separator and electrode sheet not only adhere well during the preparation of the energy storage battery, improving the preparation yield, but also allows the polymer particles to remain in a glassy state during the subsequent use of the energy storage battery (the charging and discharging of the energy storage battery will cause the energy storage battery to heat up). This provides support points at the interface between the composite separator and the electrode sheet, which is beneficial for the electrolyte to wet the electrode sheet, and thus can also improve the dynamic performance of the energy storage battery.

[0034] This application also provides a method for preparing an energy storage battery. Referring to Figure 1, the preparation method includes:

[0035] Step S10: Obtain the positive electrode, negative electrode and separator.

[0036] In this context, the separator and positive electrode plate refer to the composite separator and positive electrode plate in the composite separator embodiment, respectively. Accordingly, the structure, composition, and function of the composite separator and positive electrode plate can be the same as or similar to those in the composite separator embodiment. For relevant details, please refer to the composite separator embodiment of this application, which will not be repeated here.

[0037] Specifically, the positive electrode, negative electrode, and separator in this embodiment can be obtained by self-preparation or purchase, as long as they meet the actual needs, and are not limited here.

[0038] Step S20: The positive electrode, negative electrode and separator are hot-pressed to obtain the core assembly.

[0039] The hot-pressing temperature is 60℃-110℃, the hot-pressing pressure is 100 kg-500 kg, and the hot-pressing time is 0.5 min-5 min.

[0040] Specifically, the hot-pressing temperature can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, etc., the hot-pressing pressure can be 100 kg, 200 kg, 300 kg, 400 kg, 500 kg, etc., and the hot-pressing time can be 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min. The specific choice can be made according to actual needs.

[0041] Step S30: Assemble the core components to obtain a core pack, and perform post-processing on the core pack to obtain an energy storage battery.

[0042] It should be noted that when using the thermal composite stacking process to fabricate the battery pack, polymer particles become viscoelastic under heating conditions, entering the pores of the corresponding electrode sheets to achieve adhesion between the electrode sheets and the composite separator. Understandably, when the electrode sheet porosity is low, it is more difficult for the polymer to enter the pores. In this case, the polymer particles need to exhibit better fluidity in the viscoelastic state, and the polymer molecular chains should exhibit good flexibility; however, improving the flexibility of the polymer molecular chains inevitably leads to a decrease in the glass transition temperature of the polymer particles. The method for preparing the energy storage battery described in this application adjusts the molar ratio of the first monomer to the second monomer to regulate the rigidity of the copolymer molecular chain. Furthermore, it selects appropriate polymer particle size and molecular chain rigidity based on the porosity of the positive electrode sheet. This ensures that the composite separator and electrode sheet not only adhere well during the preparation of the energy storage battery, improving the preparation yield, but also allows the polymer particles to remain in a glassy state during subsequent use of the energy storage battery (the charging and discharging of the energy storage battery will cause the energy storage battery to heat up). This provides support points at the interface between the composite separator and the electrode sheet, which is beneficial for the electrolyte to wet the electrode sheet. Therefore, it can also improve the dynamic performance of the prepared energy storage battery.

[0043] In one embodiment, referring to Figure 2, the step of obtaining the diaphragm in step S10 includes:

[0044] Step S11: Provide a base film;

[0045] Step S12: Mix polymer particles, inorganic particles, binder and water to form a slurry;

[0046] Step S13: Deposit the slurry onto the surface of the base membrane to form a functional coating and obtain a diaphragm.

[0047] The types of base membrane, polymer particles, inorganic particles, binders, etc. that can be used here are the same as those in the composite diaphragm embodiments of this application. For related details, please refer to the composite diaphragm embodiments of this application, which will not be repeated here.

[0048] It should be noted that during the formation of the functional coating, the slurry can be deposited on the surface of the base film by means of coating, spraying, etc.

[0049] In one embodiment, the method for preparing polymer particles includes:

[0050] Step S21: Provide the first monomer and the second monomer;

[0051] Step S22: Copolymerize the first monomer and the second monomer to obtain polymer particles.

[0052] Polymer particles can be obtained by copolymerizing the first monomer and the second monomer under the action of an initiator.

[0053] Specifically, this step will be explained using polymer particles of acrylate and styrene as an example.

[0054] First, the cellulose dispersant is dissolved in deionized water to obtain a mixed solution; then, the initiator, styrene, and acrylate are dissolved in deionized water and mixed with the mixed solution to obtain a polymerization reaction solution; the polymerization reaction solution is reacted at a temperature of 50℃-100℃ for 5 h-15 h to obtain a styrene-acrylate copolymer.

[0055] The cellulose dispersant can be one or more of methylcellulose, ethylcellulose, and carboxymethylcellulose. The initiator can be one or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and dodecyl peroxide. The amount of deionized water is 8-10 times the total mass of styrene and acrylate, such as 8, 9, or 10 times. The amount of initiator is 0.3%-3% of the total mass of styrene and acrylate, such as 0.3%, 0.6%, 1%, 2%, or 3%. Specific amounts can be selected according to actual needs and are not limited here.

[0056] The technical solutions of this application will be further illustrated below through specific embodiments. These embodiments are only for the purpose of understanding this application and should not be regarded as specific limitations on this application.

[0057] Example 1

[0058] A method for preparing an energy storage battery, the method comprising:

[0059] (1) Methylcellulose was dissolved in deionized water to obtain a mixed solution. Then, azobisisobutyronitrile, 1 mol styrene, and 20 mol acrylate were dissolved in deionized water and mixed with the obtained mixed solution to obtain a polymerization reaction solution. The polymerization reaction solution was reacted at 80°C for 12 h to obtain styrene-acrylate polymer particles. The amount of deionized water used was 8 times the total mass of styrene and acrylate; the amount of initiator used was 1% of the total mass of monomer styrene and acrylate.

[0060] (2) A composite membrane was prepared based on the obtained styrene and acrylate polymer particles.

[0061] (3) The positive electrode, negative electrode and the prepared composite separator are hot-pressed to obtain the core assembly. The hot-pressing temperature is 80℃, the hot-pressing pressure is 200 kg and the hot-pressing time is 3 min.

[0062] (4) The core components are stacked to obtain a core pack, and the core pack is post-processed to obtain an energy storage battery.

[0063] Example 2

[0064] A method for preparing an energy storage battery, the method comprising:

[0065] (1) Methylcellulose was dissolved in deionized water to obtain a mixed solution. Then, azobisisobutyronitrile, 1 mol styrene, and 1 mol acrylate were dissolved in deionized water and mixed with the obtained mixed solution to obtain a polymerization reaction solution. The polymerization reaction solution was reacted at 80°C for 12 h to obtain styrene-acrylate polymer particles. The amount of deionized water used was 8 times the total mass of styrene and acrylate; the amount of initiator used was 1% of the total mass of styrene and acrylate.

[0066] (2) A composite membrane was prepared based on the obtained styrene and acrylate polymer particles.

[0067] (3) The positive electrode, negative electrode and the prepared composite separator are hot-pressed to obtain the core assembly. The hot-pressing temperature is 80℃, the hot-pressing pressure is 200 kg and the hot-pressing time is 3 min.

[0068] (4) The core components are stacked to obtain a core pack, and the core pack is post-processed to obtain an energy storage battery.

[0069] Example 3

[0070] A method for preparing an energy storage battery, the method comprising:

[0071] (1) Methylcellulose was dissolved in deionized water to obtain a mixed solution. Then, azobisisobutyronitrile, 1 mol styrene, and 2 mol acrylate were dissolved in deionized water and mixed with the obtained mixed solution to obtain a polymerization reaction solution. The polymerization reaction solution was reacted at 80°C for 12 h to obtain styrene-acrylate polymer particles. The amount of deionized water used was 8 times the total mass of styrene and acrylate; the amount of initiator used was 1% of the total mass of styrene and acrylate.

[0072] (2) A composite membrane was prepared based on the obtained styrene and acrylate polymer particles.

[0073] (3) The positive electrode, negative electrode and the prepared composite separator are hot-pressed to obtain the core assembly. The hot-pressing temperature is 80℃, the hot-pressing pressure is 200 kg and the hot-pressing time is 3 min.

[0074] (4) The core components are stacked to obtain a core pack, and the core pack is post-processed to obtain an energy storage battery.

[0075] Comparative Example 1

[0076] A method for preparing an energy storage battery, the method comprising:

[0077] (1) Methylcellulose was dissolved in deionized water to obtain a mixed solution. Then, azobisisobutyronitrile (AIBN) and 1 mol of acrylate were dissolved in deionized water and mixed with the obtained mixed solution to obtain a polymerization reaction solution. The polymerization reaction solution was reacted at 80°C for 12 h to obtain styrene-acrylate polymer particles. The amount of deionized water used was 8 times the total mass of styrene and acrylate; the amount of initiator used was 1% of the total mass of styrene and acrylate.

[0078] (2) A composite membrane was prepared based on the obtained styrene and acrylate polymer particles.

[0079] (3) The positive electrode, negative electrode and the composite separator obtained above are subjected to hot pressing to obtain the core assembly. The hot pressing temperature is 80℃, the hot pressing pressure is 200 kg and the hot pressing time is 3 min.

[0080] (4) The core components are stacked to obtain a core pack, and the core pack is post-processed to obtain an energy storage battery.

[0081] Comparative Example 2

[0082] A method for preparing an energy storage battery, the method comprising:

[0083] (1) Methylcellulose was dissolved in deionized water to obtain a mixed solution. Then, azobisisobutyronitrile, 1 mol styrene, and 0.67 mol acrylate were dissolved in deionized water and mixed with the above mixed solution to obtain a polymerization reaction solution. The polymerization reaction solution was reacted at 80°C for 12 h to obtain styrene-acrylate polymer particles. The amount of deionized water used was 8 times the total mass of styrene and acrylate; the amount of initiator used was 1% of the total mass of styrene and acrylate.

[0084] (2) A composite membrane was prepared based on the obtained styrene and acrylate polymer particles.

[0085] (3) The positive electrode, negative electrode and the composite separator obtained above are subjected to hot pressing to obtain the core assembly. The hot pressing temperature is 80℃, the hot pressing pressure is 200 kg and the hot pressing time is 3 min.

[0086] (4) The core components are stacked to obtain a core pack, and the core pack is post-processed to obtain an energy storage battery.

[0087] In the above embodiments and comparative examples, the molar ratio γ of styrene to acrylate, the particle size D50 d of the styrene-acrylate copolymer particles, and the porosity σ of the positive electrode are specifically shown in the following table:

[0088] Table 1. Relevant parameters of Examples 1-3 and Comparative Examples 1-2

[0089] Example γdσ Example 1 0.05 355% Example 2 18 30% Example 3 0.55 35% Comparative Example 1 05 30% Comparative Example 2 1.5 10 30%

[0090] Test method:

[0091] Stacking yield testing method: The yield of the stacking process in continuous production is statistically analyzed, and the yield rate is the number of good products / the number of products put into production.

[0092] The DCR test method is as follows: At 25℃, fully charge the energy storage battery, let it rest for 0.5 hours, then fully discharge it and record the discharge capacity Q. Recharge the energy storage battery fully, let it rest for 0.5 hours, then discharge it at 0.1C to 0.5Q, let it rest for 1 hour, and record the voltage V0 at this point. Then discharge it at 1C for 30 seconds, and record the voltage V1 and current I at the end of the discharge. The DCR is then calculated as (V0 - V1) / I, converted to mΩ.

[0093] Cyclic performance test method: The energy storage battery is subjected to full charge and discharge cycles at 25℃, and the capacity retention rate is recorded at 500, 1000 and 3000 cycles.

[0094] In the above tests, the full charge conditions were: at a temperature of 25℃, charging at a constant current of 0.33C to the cutoff voltage (the cutoff voltage for energy storage batteries with lithium iron phosphate as the positive electrode active material is 3.65V, and the cutoff voltage for energy storage batteries with lithium manganese iron phosphate as the positive electrode active material is 4.2V for LMFP), and then switching to constant voltage charging with a cutoff current of 0.05C. The full discharge conditions were: at a temperature of 25℃, discharging at 1C to 2.5V.

[0095] Based on the above testing methods, the stacking yield, DCR, and cycle performance of the energy storage batteries in Examples 1-3 and Comparative Examples 1-2 were tested. The test results are shown in the table below:

[0096] Table 2 Test results of the energy storage batteries prepared in Examples 1-3 and Comparative Examples 1-2

[0097] Example 1: Stacking Yield, DCR, Capacity Retention after 500 Turns; Example 2: 99.78%, 0.89%, 796.57%; Example 3: 99.59%, 0.84%, 795.98%; Comparative Example 4: 99.87%, 0.97%, 893.01%; Comparative Example 5: 97.21%, 0.81%, 496.46%.

[0098] Based on the preparation methods in Examples 1-3 and Comparative Examples 1-2 and the test results described above, it can be concluded that in Comparative Example 1, due to the low rigidity of the polymer, the polymer is in a viscoelastic state during the operation of the energy storage battery, providing no support. This results in poor wettability of the electrolyte on the electrode sheets. Therefore, although its stacking yield is acceptable, its DC resistance is high and its cycle performance is poor. In Comparative Example 2, due to the rigidity and large size of the polymer, the thermal recombination effect is poor, resulting in a low stacking yield. In contrast, the energy storage battery obtained based on the embodiments provided in this application has good stacking yield, low DC internal resistance, and good cycle performance.

Claims

1. A composite separator for use in an energy storage battery, the energy storage battery comprising a positive electrode and a negative electrode, the composite separator comprising: Base film; and A functional coating is applied to the base film and includes a base coating and polymer particles embedded in the base coating, wherein at least some of the polymer particles protrude from the surface of the base coating. The polymer particles are copolymers of a first monomer and a second monomer. The glass transition temperature of the polymer of the first monomer is greater than 80°C, and the glass transition temperature of the polymer of the second monomer is less than 50°C. The energy storage battery satisfies the following: 0.003≤γ*d / σ≤0.3, where the molar ratio of the first monomer to the second monomer is γ, the particle size D50 of the polymer particles is d μm, and the porosity of the positive electrode is σ.

2. The composite diaphragm according to claim 1, wherein, The molar ratio of the first monomer to the second monomer is 0.05-1, the particle size D50 of the polymer particles is 3 μm-8 μm, and the porosity of the positive electrode is 30%-55%.

3. The composite diaphragm according to claim 1, wherein, The first monomer includes styrene, and the second monomer includes acrylate.

4. The composite diaphragm according to claim 3, wherein, The acrylate is selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, and methyl methacrylate.

5. The composite diaphragm according to claim 1, wherein, The base coating comprises inorganic particles and a binder; The inorganic particles are selected from one or more of alumina, boehmite, titanium dioxide, and silicon dioxide. The adhesive is selected from 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.

6. The composite diaphragm according to claim 1, wherein, The thickness of the base coating is 1 μm-5 μm.

7. The composite diaphragm according to claim 1, wherein, In the base coating, the mass ratio of the inorganic particles, binder, and polymer particles is (80-90):(5-10):(5-10).

8. The composite diaphragm according to claim 1, wherein, The cathode material corresponding to the cathode sheet is selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, and ternary cathode materials.

9. An energy storage battery, the energy storage battery comprising a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode, wherein, The diaphragm is a composite diaphragm as described in any one of claims 1-8.

10. A method for preparing an energy storage battery, the method comprising: Obtain a positive electrode, a negative electrode, and a separator; wherein the separator is a composite separator as described in any one of claims 1-8; The positive electrode, negative electrode, and separator are hot-pressed to obtain the core assembly; The core components are assembled to obtain a core pack, and the core pack is post-processed to obtain the energy storage battery.

11. The preparation method according to claim 10, wherein, Obtaining the diaphragm includes: Provide base film; Mixing polymer particles, inorganic particles, binders, and water to form a slurry; and The slurry is deposited on the surface of the base membrane to form a functional coating, thereby obtaining the diaphragm.

12. The preparation method according to claim 11, wherein, The method for preparing the polymer particles includes: Provide a first monomer and a second monomer; and The first monomer and the second monomer are copolymerized to obtain the polymer particles.

13. The preparation method according to claim 10, wherein, During the hot pressing process, the hot pressing temperature is 60℃-110℃, the hot pressing pressure is 100 kg-500 kg, and the hot pressing time is 0.5 min-5 min.

Images