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

Abstract

The invention discloses a composite diaphragm, an energy storage battery and a preparation method of the energy storage battery. The composite membrane is applied to the energy storage battery, the energy storage battery comprises a positive plate and a negative plate, and the composite membrane comprises a base membrane and a functional coating, the functional coating covers the base film and comprises a basic coating and polymer particles embedded in the basic coating, and at least part of the polymer particles protrude out of the surface of the basic coating. 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 DEG C, the glass-transition temperature of the polymer of the second monomer is less than 50 DEG C, the energy storage battery meets the condition that gamma * d / sigma is greater than or equal to 0.003 and less than or equal to 0.3, the molar ratio of the first monomer to the second monomer is gamma, the particle size D50 of the polymer particles is d [mu] m, and the particle size D50 of the polymer particles is greater than or equal to 0.5. The porosity of the positive plate is sigma. Through the mode, the composite diaphragm and the electrode plate can be well bonded in the process of preparing the energy storage battery, the preparation yield is improved, the polymer particles can be kept in a glassy state in the subsequent use process of the energy storage battery, a supporting point is provided for an interface between the composite diaphragm and the electrode plate, and the service life of the energy storage battery is prolonged. Therefore, the dynamic performance of the energy storage battery can also be improved.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage batteries, and particularly relates to a composite separator, an energy storage battery, and a method for manufacturing an energy storage battery. Background Art

[0002] Currently, the power batteries used in new energy vehicles mainly include soft-pack batteries, square batteries, and cylindrical batteries. Among them, square batteries are widely used due to their advantages in terms of structural safety performance, shape and space utilization, and charge and discharge performance.

[0003] During the manufacturing process of square batteries, the method of manufacturing the core package by laminating has a high space utilization rate inside the energy storage battery, and the electrode sheets are evenly stressed during the cycling process of the energy storage battery. Therefore, it has more advantages in terms of energy density and cycle life.

[0004] For the thermal composite lamination technology, the electrode sheet and the separator are bonded by heating before lamination, and then lamination is carried out. Currently, an embedded large-particle adhesive is often used to mix and coat the separator to achieve the bonding between the separator and the electrode sheet. However, when the bonding between the electrode sheet and the separator is too tight, the direct contact area between the electrode sheet and the electrolyte will be reduced, which is not conducive to the subsequent infiltration of the electrolyte into the electrode sheet, thus affecting the kinetic performance of the energy storage battery; when the bonding between the electrode sheet and the separator is not tight, the electrode sheet will fall off during the subsequent lamination process. Especially, the positive electrode sheet usually has a greater weight, and the risk of falling off due to insufficient bonding is higher, thus reducing the manufacturing yield. Summary of the Invention

[0005] The main technical problem to be solved by the present application is to provide a composite separator, an energy storage battery, and a method for manufacturing an energy storage battery, which can enable the composite separator and the electrode sheet to be well bonded not only during the manufacturing process of the energy storage battery, improving the manufacturing yield, but also enabling the polymer particles to remain in a glassy state during the subsequent use process of the energy storage battery, providing support points at the interface between the composite separator and the electrode sheet, being conducive to the infiltration of the electrolyte into the electrode sheet, and therefore can also improve the kinetic performance of the energy storage battery.

[0006] To solve the above technical problems, a technical solution adopted in this application is: to provide a composite separator applied to an energy storage battery, the energy storage battery includes a positive electrode sheet and a negative electrode sheet, the composite separator includes a base film and a functional coating, the functional coating covers the base film and includes a base coating and polymer particles embedded in the base coating, wherein at least part 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, where γ is the molar ratio of the first monomer to the second monomer, the particle size D50 of the polymer particles is d μm, and σ is the porosity of the positive electrode sheet.

[0007] Among them, 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 sheet is 30 - 55.

[0008] Among them, the first monomer includes styrene, and the second monomer includes acrylate.

[0009] Among them, the acrylate is selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, and methyl methacrylate.

[0010] Among them, the base coating includes inorganic particles and a binder; among them, the inorganic particles are selected from one or more of alumina, boehmite, titanium dioxide, and silicon dioxide; the binder 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.

[0011] Among them, the thickness of the base coating is 1 μm - 5 μm.

[0012] Among them, in the base coating, the mass ratio of the inorganic particles, the binder, and the polymer particles is (80 - 90):(5 - 10):(5 - 10).

[0013] Among them, the positive electrode material corresponding to the positive electrode sheet is selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, and ternary positive electrode materials.

[0014] To solve the above technical problems, a technical solution adopted in this application is: to provide an energy storage battery, the energy storage battery includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the separator is the composite separator as described above.

[0015] To solve the above technical problems, a technical solution adopted in this application is: to provide a preparation method for an energy storage battery, the preparation method comprising: obtaining a positive electrode sheet, a negative electrode sheet and a separator; wherein, the separator is the composite separator as described above; performing hot pressing treatment on the positive electrode sheet, the negative electrode sheet and the separator to obtain a core assembly; assembling the core assembly to obtain a core package, and performing post-treatment on the core package to obtain an energy storage battery.

[0016] Wherein, the step of obtaining the separator comprises: providing a base film; mixing polymer particles, inorganic particles, an adhesive and water to form a slurry; and depositing the slurry on the surface of the base film to form a functional coating to obtain the separator.

[0017] Wherein, the preparation method of the polymer particles comprises: providing a first monomer and a second monomer; and copolymerizing the first monomer and the second monomer to obtain polymer particles.

[0018] Wherein, during the hot pressing treatment, the hot pressing temperature is 60°C - 110°C, the hot pressing pressure is 100 kg - 500 kg, and the hot pressing time is 0.5 min - 5 min.

[0019] The beneficial effects of the present application are as follows: Different from the prior art, the present application provides a composite separator, an energy storage battery, and a method for preparing an energy storage battery. Among them, the composite separator is applied to the energy storage battery, and the energy storage battery includes a positive electrode sheet and a negative electrode sheet. The composite separator includes: a base film and a functional coating; the functional coating covers the base film and includes a base coating and polymer particles embedded in the base coating, wherein at least part 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, and the glass transition temperature of the polymer of the second monomer is less than 50 °C; further, 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 sheet is σ. Since when using the thermal composite lamination process to prepare the core package of the energy storage battery, the polymer particles will become viscoelastic under heating conditions and enter the pores of the corresponding electrode sheet to achieve the bonding between the electrode sheet and the composite separator. It can be understood that when the porosity of the electrode sheet is small, it is more difficult for the polymer to enter the pores. At this time, the polymer particles should 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 molecular chains of the polymer particles will inevitably lead to a decrease in the glass transition temperature of the polymer particles. The present application adjusts the molar ratio of the first monomer to the second monomer, adjusts the rigidity of the molecular chains of the copolymer of the first monomer and the second monomer, and further selects appropriate polymer particle sizes and molecular chain rigidities according to the porosity of the positive electrode sheet, so that the composite separator and the electrode sheet can not only be well bonded when preparing the energy storage battery, improving the preparation yield, but also keep the polymer particles 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 temperature of the energy storage battery to rise), providing support points at the interface between the composite separator and the electrode sheet, which is beneficial to the infiltration of the electrolyte into the electrode sheet, and therefore can also improve the kinetic performance of the energy storage battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Among them:

[0021] Figure 1 is a schematic flowchart of the method for preparing the energy storage battery of the present application;

[0022] Figure 2 is a schematic flowchart of preparing the separator in the method for preparing the energy storage battery of the present application;

[0023] Figure 3It is a schematic flow chart for preparing polymer particles in the method for preparing an energy storage battery of the present application. Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

[0025] The present application provides a composite separator, which can be applied to an energy storage battery. The energy storage battery includes a positive electrode sheet and a negative electrode sheet, and the composite separator can be disposed between the positive electrode sheet and the negative electrode sheet.

[0026] In an embodiment, the composite separator includes a base film and a functional coating. The base film can specifically be a polyolefin base film, such as a polyethylene (PE), polypropylene (PP) microporous film, etc. The functional coating can cover the base film and is used to select a suitable functional coating according to the functional requirements of the composite separator, such as flame retardancy, dimensional stability, etc. In this embodiment, the functional coating can include a base coating and polymer particles embedded in the base coating, wherein at least part of the polymer particles protrude from the surface of the base coating.

[0027] Further, 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, and the glass transition temperature of the polymer of the second monomer is less than 50 °C. It should be noted that the polymer of the first monomer or the second monomer here refers to the polymer obtained by polymerizing the corresponding monomer. For example, when the first monomer is styrene, the polymer of the first monomer is polystyrene. Specifically, the glass transition temperature of the polymer of the first monomer can be 81 °C, 83 °C, 86 °C, 90 °C, etc., and the glass transition temperature of the polymer of the second monomer can be 49 °C, 47 °C, 43 °C, 39 °C, and no specific limitation is made here.

[0028] Further, 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 sheet is σ.

[0029] Among them, the porosity of the positive electrode sheet can specifically refer to the porosity of the positive electrode material coating on the positive electrode current collector.

[0030] Specifically, in the thermal composite lamination technology, the pole piece and the separator are bonded by heating before lamination, and then lamination is carried out. In the related art, an embedded large-particle adhesive is often used to mix and coat the separator to achieve the bonding between the separator and the electrode sheet. However, when the bonding between the electrode sheet and the separator is too tight, the direct contact area between the electrode sheet and the electrolyte will be reduced, which is not conducive to the subsequent infiltration of the electrolyte into the electrode sheet, thus affecting the kinetic performance of the energy storage battery.

[0031] Furthermore, it should be further explained that when preparing the core package of the energy storage battery using the thermal composite lamination process, the polymer particles will become viscoelastic under heating conditions and enter the pores of the corresponding electrode sheet to achieve the bonding between the electrode sheet and the composite separator. It can be understood that when the porosity of the electrode sheet is small, it is more difficult for the polymer to enter the pores. At this time, the polymer particles should 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 molecular chains of the polymer particles will inevitably lead to a decrease in the glass transition temperature of the polymer particles. In the above embodiments of the present application, by adjusting the molar ratio of the first monomer to the second monomer, the rigidity of the copolymer molecular chain is adjusted, and further, according to the porosity of the positive electrode sheet, the appropriate particle size and molecular chain rigidity of the polymer particles are selected, so that the composite separator and the electrode sheet can not only be well bonded during the preparation of the energy storage battery, improving the preparation yield, but also enable the polymer particles to remain in the glass 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), providing support points at the interface between the composite separator and the electrode sheet, which is conducive to the infiltration of the electrolyte into the electrode sheet, so the kinetic performance of the energy storage battery can also be improved.

[0032] In addition, the core package of the energy storage battery in the present application is prepared by using the lamination technology, which supports the multi-tab design. Multiple tabs can be evenly distributed on the edges of the positive electrode sheet and the negative electrode sheet, significantly shortening the current transmission path, reducing the internal resistance, improving the rate performance and thermal management ability. At the same time, the multi-tab design makes the current distribution more uniform, reducing the risk of local overheating and enhancing the safety; the lamination technology can more efficiently utilize the internal space of the energy storage battery, improve the cell capacity and energy density, and meet the requirements of large-size and high-capacity energy storage batteries; in addition, the uniformity and stability of the laminated structure can provide a more reliable basis for the design and installation of the explosion-proof valve, more precisely control the internal pressure release, reduce the risk of thermal runaway and explosion, thus comprehensively improving the safety and reliability of the energy storage battery.

[0033] 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.

[0034] The porosity of the positive electrode sheet is 30%-55%, specifically such as 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, and the appropriate positive electrode sheet can be specifically selected according to actual needs.

[0035] In one embodiment, the first monomer includes styrene, and the second monomer includes acrylate. Of course, the first monomer may also include other monomers with a glass transition temperature of the corresponding polymer greater than 80°C, and the second monomer may also include other monomers with a glass transition temperature of the corresponding polymer less than 50°C, which are not specifically limited here.

[0036] In one embodiment, the acrylate can be selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, etc.

[0037] In one embodiment, the base coating includes inorganic particles and a binder. Among them, the inorganic particles can be uniformly dispersed in the binder.

[0038] Specifically, the inorganic particles can be selected from one or more of aluminum oxide (Al2O3), boehmite (AlOOH), titanium dioxide (TiO2), silicon dioxide (SiO2), etc.

[0039] The binder can 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.

[0040] Further, in one embodiment, the thickness of the base coating is 1μm - 5μm, specifically such as 1μm, 2μm, 3μm, 4μm, 5μm, and can be specifically determined according to actual needs, which is not limited here.

[0041] In one embodiment, in the base coating, the mass ratio of the inorganic particles, the binder, and the polymer particles 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 is not limited here.

[0042] In one embodiment, in the energy storage battery, the positive electrode material corresponding to the positive electrode sheet is selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, and ternary positive electrode materials.

[0043] Furthermore, the present application also provides an energy storage battery. In one embodiment, the energy storage battery includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. Among them, the separator and the positive electrode sheet respectively correspond to the composite separator and the positive electrode sheet in the above composite separator embodiment. Correspondingly, the structures, compositions, functions, etc. of the composite separator and the positive electrode sheet can be the same as or similar to those in the above composite separator embodiment. For detailed information, please refer to the above embodiment and will not be elaborated here.

[0044] It should be noted that when using the thermal composite lamination process to prepare the core package of the energy storage battery, the polymer particles will become viscoelastic under heating conditions and enter the pores of the corresponding electrode sheet to achieve the bonding between the electrode sheet and the composite separator. It can be understood that when the porosity of the electrode sheet is small, it is more difficult for the polymer to enter the pores. At this time, the polymer particles should 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 molecular chains of the polymer particles will inevitably lead to a decrease in the glass transition temperature of the polymer particles. In the above embodiment of the present application, by adjusting the molar ratio of the first monomer to the second monomer, the rigidity of the copolymer molecular chain is adjusted, and further, according to the porosity of the positive electrode sheet, the appropriate particle size and molecular chain rigidity of the polymer particles are selected, so that the composite separator and the electrode sheet can not only be well bonded during the preparation of the energy storage battery, improving the preparation yield, but also 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 temperature of the energy storage battery to rise), providing support points at the interface between the composite separator and the electrode sheet, which is beneficial to the infiltration of the electrolyte into the electrode sheet. Therefore, the kinetic performance of the energy storage battery can also be improved.

[0045] The present application also provides a method for preparing an energy storage battery. Please refer to Figure 1 , and this preparation method includes:

[0046] Step S10: Obtain a positive electrode sheet, a negative electrode sheet, and a separator.

[0047] Among them, the separator and the positive electrode sheet here respectively correspond to the composite separator and the positive electrode sheet in the above composite separator embodiment. Correspondingly, the structures, compositions, functions, etc. of the composite separator and the positive electrode sheet can be the same as or similar to those in the above composite separator embodiment. For detailed information, please refer to the above embodiment and will not be elaborated here.

[0048] Specifically, the positive electrode sheet, negative electrode sheet, and separator in this embodiment can be obtained by self-preparation or purchase, etc., as long as the above requirements can be met, and no limitation is made here.

[0049] Step S20: Perform hot pressing treatment on the positive electrode sheet, negative electrode sheet, and separator to obtain a core assembly.

[0050] Among them, the hot pressing temperature is 60°C - 110°C, the hot pressing pressure is 100 kg - 500 kg, and the hot pressing time is 0.5 min - 5 min.

[0051] Specifically, the hot pressing temperature can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 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. Specifically, it can be selected according to actual needs.

[0052] Step S30: Assemble the core components to obtain a core package, and perform post-treatment on the core package to obtain a energy storage battery.

[0053] It should be noted that when using the hot composite laminate process to prepare the core package of the energy storage battery, the polymer particles will become viscoelastic under heating conditions and enter the pores of the corresponding electrode sheet to achieve the bonding between the electrode sheet and the composite separator. It can be understood that when the porosity of the electrode sheet is small, it is more difficult for the polymer to enter the pores. At this time, the polymer particles need to show better fluidity in the viscoelastic state, and the molecular chains of the polymer particles should show good flexibility; however, the improvement of the flexibility of the molecular chains of the polymer particles will inevitably lead to a decrease in the glass transition temperature of the polymer particles. In the above embodiments of the present application, by adjusting the molar ratio of the first monomer to the second monomer, the rigidity of the copolymer molecular chain is adjusted, and further, according to the porosity of the positive electrode sheet, the appropriate particle size and molecular chain rigidity of the polymer particles are selected, so that the composite separator and the electrode sheet can not only be well bonded during the preparation of the energy storage battery, improving the preparation yield, but also enable the polymer particles to remain 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), providing support points at the interface between the composite separator and the electrode sheet, which is beneficial to the infiltration of the electrolyte into the electrode sheet. Therefore, it can also improve the kinetic performance of the prepared energy storage battery.

[0054] In one embodiment, please refer to Figure 2 , the steps of obtaining the separator in step S10 include:

[0055] Step S11: Provide a base film;

[0056] Step S12: Mix polymer particles, inorganic particles, binder and water to form a slurry;

[0057] Step S13: Deposit the slurry on the surface of the base film to form a functional coating and obtain the separator.

[0058] The types of the base film, polymer particles, inorganic particles, binder, etc. that can be selected here are the same as those in the above embodiments of the composite separator of the present application. For the relevant detailed content, please refer to the above embodiments and will not be elaborated here.

[0059] It should be noted that in the process of forming the functional coating, the slurry can be deposited on the surface of the base film by means such as coating and spraying.

[0060] In one embodiment, the preparation method of the polymer particles includes:

[0061] Step S21: Provide a first monomer and a second monomer;

[0062] Step S22: Copolymerize the first monomer and the second monomer to obtain polymer particles.

[0063] Among them, the polymer particles can be obtained by copolymerizing the first monomer and the second monomer under the action of an initiator.

[0064] Specifically, taking the polymer particles of acrylate and styrene as an example, this step will be described.

[0065] First, dissolve the cellulose dispersant in deionized water to obtain a mixed solution; then dissolve the initiator, styrene, and acrylate in deionized water, and mix with the above mixed solution to obtain a polymerization reaction solution; react the polymerization reaction solution at a temperature of 50°C - 100°C for 5h - 15h to obtain a copolymer of styrene and acrylate.

[0066] Among them, the cellulose dispersant can be one or more of methyl cellulose, ethyl cellulose, and carboxymethyl cellulose. The initiator can be one or more of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, and lauroyl peroxide. The amount of deionized water used is 8 - 10 times the total mass of styrene and acrylate, such as 8 times, 9 times, 10 times, etc. The amount of initiator used is 0.3% - 3% of the total mass of styrene and acrylate, such as 0.3%, 0.6%, 1%, 2%, 3%, etc. It can be specifically selected according to actual needs and is not limited here.

[0067] The technical solution of the present application will be further described below through specific examples. The examples are only for helping to understand the present application and should not be regarded as specific limitations of the present application.

[0068] Example 1

[0069] A preparation method of an energy storage battery, the preparation method includes:

[0070] (1) Dissolve methylcellulose in deionized water to obtain a mixed solution. Then dissolve azobisisobutyronitrile, 1 mol of styrene, and 20 mol of acrylate in deionized water, and mix it with the above mixed solution to obtain a polymerization reaction solution. React the polymerization reaction solution at 80 °C for 12 h to obtain styrene and acrylate polymer particles. Among them, the amount of deionized water used is 8 times the total mass of styrene and acrylate; the amount of initiator used is 1% of the total mass of monomer styrene and acrylate.

[0071] (2) Prepare a composite separator based on the obtained styrene and acrylate polymer particles.

[0072] (3) Perform hot pressing treatment on the positive electrode sheet, negative electrode sheet, and the above-obtained composite separator to obtain a core component. Among them, the hot pressing temperature is 80 °C, the hot pressing pressure is 200 kg, and the hot pressing time is 3 min.

[0073] (4) Perform lamination treatment on the core component to obtain a core package, and perform post-treatment on the core package to obtain a energy storage battery.

[0074] Example 2

[0075] A method for preparing an energy storage battery, the preparation method comprising:

[0076] (1) Dissolve methylcellulose in deionized water to obtain a mixed solution. Then dissolve azobisisobutyronitrile, 1 mol of styrene, and 1 mol of acrylate in deionized water, and mix it with the above mixed solution to obtain a polymerization reaction solution. React the polymerization reaction solution at 80 °C for 12 h to obtain styrene and acrylate polymer particles. Among them, the amount of deionized water used is 8 times the total mass of styrene and acrylate; the amount of initiator used is 1% of the total mass of styrene and acrylate.

[0077] (2) Prepare a composite separator based on the obtained styrene and acrylate polymer particles.

[0078] (3) Perform hot pressing treatment on the positive electrode sheet, negative electrode sheet, and the above-obtained composite separator to obtain a core component. Among them, the hot pressing temperature is 80 °C, the hot pressing pressure is 200 kg, and the hot pressing time is 3 min.

[0079] (4) Perform lamination treatment on the core component to obtain a core package, and perform post-treatment on the core package to obtain a energy storage battery.

[0080] Example 3

[0081] A method for preparing an energy storage battery, the preparation method comprising:

[0082] (1) Dissolve methylcellulose in deionized water to obtain a mixed solution. Then dissolve azobisisobutyronitrile, 1 mol of styrene, and 2 mol of acrylate in deionized water, and mix with the above mixed solution to obtain a polymerization reaction solution. React the polymerization reaction solution at 80 °C for 12 h to obtain styrene and acrylate polymer particles. Among them, the amount of deionized water used is 8 times the total mass of styrene and acrylate; the amount of initiator used is 1% of the total mass of styrene and acrylate.

[0083] (2) Prepare a composite separator based on the obtained styrene and acrylate polymer particles.

[0084] (3) Perform hot pressing treatment on the positive electrode sheet, negative electrode sheet, and the obtained composite separator to obtain a core assembly. Among them, the hot pressing temperature is 80 °C, the hot pressing pressure is 200 kg, and the hot pressing time is 3 min.

[0085] (4) Perform lamination treatment on the core assembly to obtain a core package, and perform post-treatment on the core package to obtain an energy storage battery.

[0086] Comparative Example 1

[0087] A method for preparing an energy storage battery, the preparation method comprising:

[0088] (1) Dissolve methylcellulose in deionized water to obtain a mixed solution. Then dissolve azobisisobutyronitrile and 1 mol of acrylate in deionized water, and mix with the above mixed solution to obtain a polymerization reaction solution. React the polymerization reaction solution at 80 °C for 12 h to obtain styrene and acrylate polymer particles. Among them, the amount of deionized water used is 8 times the total mass of styrene and acrylate; the amount of initiator used is 1% of the total mass of styrene and acrylate.

[0089] (2) Prepare a composite separator based on the obtained styrene and acrylate polymer particles.

[0090] (3) Perform hot pressing treatment on the positive electrode sheet, negative electrode sheet, and the obtained composite separator to obtain a core assembly. Among them, the hot pressing temperature is 80 °C, the hot pressing pressure is 200 kg, and the hot pressing time is 3 min.

[0091] (4) Perform lamination treatment on the core assembly to obtain a core package, and perform post-treatment on the core package to obtain an energy storage battery.

[0092] Comparative Example 2

[0093] A method for preparing an energy storage battery, the preparation method comprising:

[0094] (1) Dissolve methylcellulose in deionized water to obtain a mixed solution. Then dissolve azobisisobutyronitrile, 1 mol of styrene, and 0.67 mol of acrylate in deionized water, and mix it with the above mixed solution to obtain a polymerization reaction solution. React the polymerization reaction solution at 80 °C for 12 h to obtain styrene and acrylate polymer particles. Among them, the amount of deionized water used is 8 times the total mass of styrene and acrylate; the amount of initiator used is 1% of the total mass of styrene and acrylate.

[0095] (2) Prepare a composite separator based on the obtained styrene and acrylate polymer particles.

[0096] (3) Perform hot pressing treatment on the positive electrode sheet, negative electrode sheet, and the obtained composite separator to obtain a core assembly. Among them, the hot pressing temperature is 80 °C, the hot pressing pressure is 200 kg, and the hot pressing time is 3 min.

[0097] (4) Perform lamination treatment on the core assembly to obtain a core pack, and perform post-treatment on the core pack to obtain an energy storage battery.

[0098] In the above examples and comparative examples, the molar ratio of styrene to acrylate γ , the particle size D50d of the styrene and acrylate copolymer particles, and the porosity σ of the positive electrode sheet are specifically shown in the following table:

[0099] Table 1 Related parameters of Examples 1-3 and Comparative Examples 1-2

[0100] Example γ d σ Example 1 0.05 3 55％ Example 2 1 8 30％ Example 3 0.5 5 35％ Comparative Example 1 0 5 30％ Comparative Example 2 1.5 10 30％

[0101] Testing method:

[0102] Lamination yield testing method: Statistically analyze the yield of the lamination process section during continuous production. The yield is the number of good products / the number of inputs.

[0103] The DCR testing method is as follows: Fully charge the energy storage battery at 25 °C, let it stand for 0.5 h, then fully discharge the energy storage battery, and record the discharge capacity Q. Recharge the energy storage battery fully, let it stand for 0.5 h, then discharge it at 0.1C for 0.5Q, let it stand for 1 h, record the voltage V0 at this time, and then discharge it at 1C for 30 s, record the voltage V1 and current I at the end of discharge, then DCR = (V0 - V1) / I, and the unit conversion is mΩ.

[0104] Cycling performance testing method: Perform full charge and full discharge cycling on the energy storage battery at 25 °C, and record the capacity retention rate at 500 cycles, 1000 cycles, and 3000 cycles.

[0105] In the above tests, the full charge conditions were as follows: at a temperature of 25°C, constant current charging was carried out at 0.33C until the cut-off voltage (the cut-off voltage of the energy storage battery with lithium iron phosphate as the positive active material was 3.65V, and the cut-off voltage of the energy storage battery with lithium manganese iron phosphate as the positive active material was 4.2V for LMFP), and then it was changed to constant voltage charging with a cut-off current of 0.05C. The full discharge conditions were: at 25°C, discharging at 1C until 2.5V.

[0106] Based on the above test methods, the lamination 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 following table:

[0107] Table 2 Test results of the energy storage batteries prepared in Examples 1-3 and Comparative Examples 1-2

[0108] Example Lamination yield DCR Retention rate of capacity after 500 cycles Example 1 99.78 0.897 96.57 Example 2 99.23 0.839 96.19 Example 3 99.59 0.847 95.98 Comparative Example 1 99.87 0.978 93.01 Comparative Example 2 97.21 0.814 96.46

[0109] Combined with the preparation methods in the above Examples 1-3 and Comparative Examples 1-2 and the above test results, it can be concluded that in Comparative Example 1, due to the small rigidity of the polymer, the polymer was in a viscoelastic state during the operation of the energy storage battery and had no supporting effect, resulting in poor wettability of the electrolyte on the electrode sheet. Therefore, although its lamination yield was acceptable, its DC resistance was large and its cycle performance was poor. In Comparative Example 2, due to the large rigidity and size of the polymer, the thermal composite effect was poor and the lamination yield was low. In contrast, the energy storage battery obtained based on the implementation mode provided in this application has a good lamination yield, low DC internal resistance, and good cycle performance.

[0110] The above is only the implementation mode of this application, and it does not limit the patent scope of this application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of this application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of this application.

Claims

1. A composite diaphragm, applied to an energy storage battery, wherein the energy storage battery comprises a positive electrode sheet and a negative electrode sheet, characterized in that: The composite diaphragm comprises: basement membrane; and a functional coating covering the base film and comprising a base coating and polymer particles embedded in the base coating, wherein at least part of the polymer particles protrude from the surface of the base coating; Among them, 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, 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 dμm, and the porosity of the positive electrode sheet is σ.

2. The composite diaphragm according to claim 1, characterized in that: 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 sheet is 30-55.

3. The composite diaphragm according to claim 1, characterized in that: The first monomer includes styrene, and the second monomer includes acrylate.

4. The composite diaphragm according to claim 3, characterized in that: 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, characterized in that: The base coating includes inorganic particles and a binder; Wherein, 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, characterized in that: The base coating has a thickness of 1 μm to 5 μm.

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

8. The composite diaphragm according to claim 1, characterized in that: The positive electrode material corresponding to the positive electrode sheet is selected from one or more of lithium iron phosphate, lithium iron manganese phosphate, and ternary positive electrode materials.

9. An energy storage battery, characterized in that: The energy storage battery comprises a positive electrode sheet, a negative electrode sheet and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the separator is a composite separator as claimed in any one of claims 1 to 8.

10. A method for preparing an energy storage battery, characterized in that: The preparation method comprises: Obtain a positive electrode sheet, a negative electrode sheet and a separator; wherein the separator is a composite separator as described in any one of claims 1 to 8; Performing hot pressing on the positive electrode sheet, the negative electrode sheet and the separator to obtain a 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, characterized in that: Obtaining the diaphragm, comprising: providing a basement membrane; mixing polymer particles, inorganic particles, a binder and water to form a slurry; and The slurry is deposited on the surface of the base film to form a functional coating to obtain the separator.

12. The preparation method according to claim 11, characterized in that: The preparation method of the polymer particles comprises: providing 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, characterized in that: During the hot pressing process, the hot pressing temperature is 60° C.-110° C., the hot pressing pressure is 100 kg-500 kg, and the hot pressing time is 0.5 min-5 min.

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