Preparation Method of Electrolyte Separator for Semi-Solid Secondary Battery, Semi-Solid Secondary Battery, Energy Storage Device and Electrical Equipment

Abstract

This application relates to the field of energy storage technologies, and particularly to a preparation method of an electrolyte separator for a semi-solid secondary battery, a semi-solid secondary battery, an energy storage device, and an electrical equipment. Among them, the preparation method includes the following steps: coating a first solution on the surface of a base film, the first solution including a linear monomer, a first thermal initiator, and a first electrolyte solution, and performing a first curing to form a first intermediate layer on the surface of the base film; coating a second solution on the surface of the first intermediate layer, the second solution including a multi-branched monomer, a second thermal initiator, and a second electrolyte solution, and performing a second curing to form a second intermediate layer on the surface of the base film; coating a third solution on the surface of the second intermediate layer, the third solution including a nitrile group-containing monomer, a third thermal initiator, and a third electrolyte solution, and performing a third curing to obtain an electrolyte separator. This electrolyte separator has excellent flame retardancy, ionic conductivity, mechanical properties, and thermal stability, so that the semi-solid secondary battery can have excellent safety performance and electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage, and particularly to a preparation method of an electrolyte for a semi-solid secondary battery, a semi-solid secondary battery, an energy storage device, and an electrical equipment. Background Art

[0002] Lithium-ion batteries have high energy density and reliable power supply, and play a crucial role in fixed energy storage systems. With the growing demand for next-generation batteries with higher performance, efforts are needed to develop new electrode materials, electrolytes, and battery systems. An ideal electrolyte should be a good lithium-ion conductor, have high chemical stability, and not cause other parasitic reactions on the electrode surface except for the migration of lithium ions. Although traditional organic liquid electrolytes have high ionic conductivity, their inherent instabilities, such as volatility, flammability, and other unsafe disadvantages, pose great safety hazards to the batteries. Currently, the solutions to the safety problems of lithium batteries mainly include: all-solid-state lithium-ion battery solutions, adding flame retardants to the electrolytes, and semi-solid electrolyte solutions. Among them, semi-solid electrolytes are a new type of functional polymer material between all-solid polymer electrolytes and liquid electrolytes, with stable electrochemical performance, and can be applied to secondary batteries in the form of diaphragms and electrolyte materials.

[0003] There are still some deficiencies in the performance of current semi-solid electrolytes, which will make it difficult for secondary batteries to balance electrochemical performance and safety performance. Summary of the Invention

[0004] The present application provides a preparation method of an electrolyte diaphragm for a semi-solid secondary battery, a semi-solid secondary battery, an energy storage device, and an electrical equipment, aiming to solve the technical problems mentioned in the above background art.

[0005] In a first aspect, an embodiment of the present application provides a preparation method of an electrolyte diaphragm for a semi-solid secondary battery, and the preparation method includes the following steps:

[0006] Provide a base film, coat a first solution on the surface of the base film, the first solution includes a linear monomer, a first thermal initiator, and a first electrolyte, and perform a first curing to form a first intermediate layer on the surface of the base film;

[0007] Coat a second solution on the surface of the first intermediate layer, the second solution includes a multi-branched monomer, a second thermal initiator, and a second electrolyte, and perform a second curing to form a second intermediate layer on the surface of the base film;

[0008] Coat a third solution on the surface of the second intermediate layer, the third solution includes a nitrile group-containing monomer, a third thermal initiator, and a third electrolyte, and perform a third curing to form a gel-like functional layer on the surface of the base film, obtaining an electrolyte diaphragm;

[0009] Based on the total mass content of the first solution, the second solution and the third solution being 100%, the total mass content of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer is 3% to 8%, and the mass ratio of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer is (12 to 16):(3 to 6):1.

[0010] In some embodiments, the linear monomer includes at least one of triethylene glycol dimethacrylate, methyl methacrylate, vinyl acetate, trifluoroethyl methacrylate and ethylene glycol diacrylate.

[0011] In some embodiments, the multi-branched monomer includes at least one of trimethylolpropane trifluoracrylate, pentaerythritol tetraacrylate, trimethylolpropane, pentaerythritol, four-arm polyethylene glycol-tetraacrylate and hyperbranched polyester polyol.

[0012] In some embodiments, the nitrile group-containing monomer includes at least one of acrylonitrile and methacrylonitrile.

[0013] In some embodiments, the first electrolyte, the second electrolyte and the third electrolyte independently include a lithium salt, an electrolyte and a flame retardant, and the content of the flame retardant is 2% to 15%.

[0014] In some embodiments, the lithium salt includes one or more of LiPF6, LiFSI, LiBF4, LiBOB, LiDFOB and LiTFSI.

[0015] In some embodiments, the electrolyte includes one or more of EC, PC, BC, DEC, DMC, DME, EMC, TEP and FEC.

[0016] In some embodiments, the flame retardant includes at least one of a phosphorus-nitrogen composite flame retardant, a phosphorus-based flame retardant, a phosphorus-fluorine composite flame retardant, a phosphorus-nitrile flame retardant and a bromine-based flame retardant.

[0017] In some embodiments, the first thermal initiator, the second thermal initiator and the third thermal initiator independently include at least one of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, diisopropylbenzene peroxide and ammonium persulfate.

[0018] In some embodiments, the temperature of the first curing is 40°C to 60°C, the temperature of the second curing is 60°C to 80°C, and the temperature of the third curing is 50°C to 70°C.

[0019] In some embodiments, the first curing step includes: preheating the base film coated with the first solution at 40°C to 45°C for 5 min to 10 min, then raising the temperature to 55°C to 60°C and holding for 50 min to 70 min, with a heating rate ≤ 2°C / min, and then cooling to room temperature.

[0020] In some embodiments, the second curing step includes: preheating the composite structure of the base film coated with the second solution and the first intermediate layer at 60°C to 65°C for 5 min to 10 min, then raising the temperature to 75°C to 80°C and holding for 25 min to 35 min, with a heating rate ≤ 2°C / min, and then cooling to room temperature.

[0021] In some embodiments, the third curing step includes: preheating the composite structure of the base film coated with the third solution and the second intermediate layer at 50°C to 55°C for 5 min to 10 min, then raising the temperature to 65°C to 75°C and holding for 110 min to 130 min, with a heating rate ≤ 2°C / min, and then cooling to room temperature.

[0022] In a second aspect, an embodiment of the present application further provides a semi-solid secondary battery, including a positive electrode sheet, an electrolyte separator, and a negative electrode sheet, wherein the electrolyte separator is prepared by the preparation method described in the first aspect.

[0023] In some embodiments, in the electrolyte separator, the base film has a first side facing the positive electrode sheet and a second side facing the negative electrode sheet, and the functional layer is disposed on at least one of the first side and the second side, and the thickness of the functional layer is 10μm to 30μm.

[0024] In a third aspect, an embodiment of the present application further provides an energy storage device, including the semi-solid secondary battery described in the second aspect.

[0025] In a fourth aspect, an embodiment of the present application further provides an electrical equipment, including the semi-solid secondary battery described in the third aspect.

[0026] Compared with the prior art, the present technical solution has at least the following technical effects:

[0027] The technical solution of this application uses gradient copolymerization technology to form a gel-like functional layer with a gradient-like structure on the surface of the base film. The electrolyte separator prepared thereby not only has excellent flame retardancy, but also has excellent ionic conductivity, mechanical properties and thermal stability, so that the prepared semi-solid secondary battery can have excellent rate performance, cycle performance and safety performance. Compared with the conventional copolymerization method, the gradient copolymerization method of this application helps to avoid stress concentration in the functional layer and improve the electrochemical stability of the electrolyte separator. During the preparation process of the electrolyte separator, a first solution containing a linear monomer is first coated on the surface of the base film and preliminarily polymerized to form a flexible first intermediate layer. Then, a second solution is coated on the surface of the first intermediate layer, and the multi-branched monomer in the second solution is further polymerized with the first polymerized layer to form a second intermediate layer. The second intermediate layer is a three-dimensional network skeleton structure, which can provide continuous ion transport channels and help improve the ion mobility (conductivity) of the electrolyte separator. In addition, this three-dimensional network skeleton structure can also provide good physical support, taking into account flexibility and material stability. These characteristics enable the finally prepared electrolyte separator to obtain relatively excellent rate performance and cycle performance; by coating a third solution on the surface of the second intermediate layer and further polymerizing the third solution, the polarity of the outermost surface of the finally prepared electrolyte separator is enhanced, thereby improving the interfacial compatibility between the electrolyte separator and the electrolyte, reducing the interfacial resistance, and further improving the rate performance and cycle performance of the prepared semi-solid secondary battery. Brief Description of the Drawings

[0028] The present invention will be further described below in conjunction with the drawings and embodiments.

[0029] Figure 1 It is a process flow chart of the preparation method of the electrolyte separator of the semi-solid secondary battery of this application. Detailed Embodiments

[0030] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0031] Unless otherwise specified, the meanings of the terms in this specification are the same as those generally understood by those skilled in the art. However, if there is a conflict, the definition in this specification shall prevail.

[0032] In this text, terms such as "include", "comprise", "contain", "have", or other variants are intended to cover non-closed inclusion, and no distinction is made among these terms. The term "comprise" means that other steps and components can be added without affecting the final result. The term "comprise" also includes the terms "consist of" and "consist essentially of". The compositions and methods / processes of the present invention comprise, consist of, and consist essentially of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein.

[0033] All numerical values or statements related to component amounts, process conditions, etc. used in the specification and claims should be understood to be modified by "about" in all cases. All ranges related to the same component or property include the endpoints, and these endpoints can be combined independently. Since these ranges are continuous, they include every numerical value between the minimum and maximum values. It should also be understood that any numerical range cited in this application is expected to include all sub-ranges within that range.

[0034] It should be understood that the term "and / or" used in the present invention is merely a correlative relationship describing related objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the character " / " in this text generally represents an "or" relationship between the related objects before and after.

[0035] Semi-solid electrolytes are a new type of functional polymer material between all-solid polymer electrolytes and liquid electrolytes. There are still some deficiencies in the performance of current semi-solid electrolytes, such as: low ionic conductivity, poor thermal stability, and poor interfacial compatibility with electrolytes. These deficiencies will make it difficult for secondary batteries to balance electrochemical performances such as safety performance, rate performance, and cycle performance.

[0036] Based on this, in a first aspect, an embodiment of the present application proposes a method for preparing an electrolyte diaphragm of a semi-solid secondary battery.

[0037] Please refer to Figure 1 , in the embodiment of the present application, the preparation method includes the following steps:

[0038] S100. Provide a base film, coat a first solution on the surface of the base film. The first solution includes a linear monomer, a first thermal initiator, and a first electrolyte, and perform a first curing to form a first intermediate layer on the surface of the base film;

[0039] S200. Coat a second solution on the surface of the first intermediate layer. The second solution includes a multi-branched monomer, a second thermal initiator, and a second electrolyte, and perform a second curing to form a second intermediate layer on the surface of the base film;

[0040] S300. Coat a third solution on the surface of the second intermediate layer. The third solution includes a nitrile group-containing monomer, a third thermal initiator, and a third electrolyte solution, and perform a third curing to form a gel-like functional layer on the surface of the base film, thereby obtaining an electrolyte separator.

[0041] Based on the total mass content of the first solution, the second solution, and the third solution being 100%, the total mass content of the linear monomer, the multi-branched monomer, and the nitrile group-containing monomer is 3% - 8%, and the mass ratio of the linear monomer, the multi-branched monomer, and the nitrile group-containing monomer is (12 - 16):(3 - 6):1.

[0042] It should be noted that in the embodiments of the present application, the first intermediate layer is a gel-like polymer layer formed after the first curing of the first solution, the second intermediate layer is a gel-like polymer layer jointly formed by the second solution and the first intermediate layer after the second curing, and the functional layer is a gel-like polymer layer jointly formed by the third solution and the second intermediate layer after the third curing.

[0043] The technical solution of the present application uses a gradient copolymerization technique to form a gel-like functional layer with a quasi-gradient structure on the surface of the base film. The electrolyte separator prepared thereby not only has excellent flame retardant properties, but also has excellent ionic conductivity, mechanical properties, and stability, so that the prepared semi-solid secondary battery can have excellent rate performance, cycle performance, and safety performance. Compared with the conventional copolymerization method, the gradient copolymerization method of the present application helps to avoid stress concentration in the functional layer and helps to improve the electrochemical stability of the electrolyte separator. During the preparation process of the electrolyte separator, first coat a first solution containing a linear monomer on the surface of the base film and preliminarily polymerize to form a flexible first intermediate layer, then coat a second solution on the surface of the first intermediate layer, and make the multi-branched monomer in the second solution further polymerize with the first polymer layer to form a second intermediate layer. The second intermediate layer is a three-dimensional network skeleton structure, which can provide continuous ion transport channels and help to improve the ion mobility (conductivity) of the electrolyte separator. In addition, this three-dimensional network skeleton structure can also provide good physical support, taking into account flexibility and material stability. These characteristics enable the finally prepared electrolyte separator to obtain relatively excellent rate performance and cycle performance; by coating a third solution on the surface of the second intermediate layer and further polymerizing the third solution, the polarity of the outermost surface of the finally prepared electrolyte separator is enhanced, thereby improving the interfacial compatibility between the electrolyte separator and the electrolyte solution, reducing the interfacial resistance, and further improving the rate performance and cycle performance of the prepared semi-solid secondary battery.

[0044] The preparation method of the electrolyte separator of the present application will be described in more detail below.

[0045] In the embodiments of the present application, based on the total mass content of the first solution, the second solution and the third solution being 100%, the total mass content of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer is 3% to 8%, specifically, it can be 3%, 4%, 5%, 6%, 7%, 8% or any value therebetween. The mass ratio of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer is (12 to 16):(3 to 6):1. Among them, the mass ratio of the linear monomer to the nitrile group-containing monomer can specifically be 12:1, 13:1, 14:1, 15:1, 16:1 or any value therebetween, and the mass ratio of the multi-branched monomer to the nitrile group-containing monomer can specifically be 3:1, 4:1, 5:1, 6:1 or any ratio therebetween.

[0046] By controlling the mass content of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer within the above range, it is beneficial to regulate the final polymerization form of the functional layer into a jelly-like gel structure. In this form, the electrochemical performance and flame retardant performance of the electrolyte diaphragm are both excellent. When the mass content of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer is not within the above range, it will either cause the functional layer to become hard and brittle, resulting in a significant decrease in the cycle performance of the semi-solid secondary battery; or it will cause the first solution, the second solution and the third solution to fail to solidify from the liquid state into a gel state, or cause the solidification time of the first solution, the second solution and the third solution to be too long, affecting the preparation efficiency of the electrolyte diaphragm.

[0047] In the embodiments of the present application, the material of the base film can be polyethylene, polypropylene, etc. Of course, it can also be other base film materials commonly used for semi-solid electrolyte diaphragms. The embodiments of the present application do not make specific limitations in this regard.

[0048] In some embodiments, the linear monomer includes one or more of triethylene glycol dimethacrylate, methyl methacrylate, vinyl acetate, trifluoroethyl methacrylate and ethylene glycol diacrylate. Of course, those skilled in the art can also select other linear monomers according to the actual situation.

[0049] In the embodiments of the present application, the multi-branched monomer can be a fluorine-containing monomer or a non-fluorine-containing monomer. Preferably, the multi-branched monomer is a fluorine-containing monomer. The three-dimensional network structure formed by the polymerization of the fluorine-containing monomer is not only beneficial to further improving the ionic conductivity of the electrolyte diaphragm, but also beneficial to improving the flame retardant performance of the electrolyte diaphragm.

[0050] In some embodiments, the fluorine-containing monomer includes one or more of trimethylolpropane trifluoracrylate and trifluoroethyl methacrylate.

[0051] In some embodiments, the non-fluorine-containing monomer includes one or more of pentaerythritol tetraacrylate, trimethylolpropane, pentaerythritol, four-armed polyethylene glycol-tetraacrylate and hyperbranched polyester polyol.

[0052] In some embodiments, the nitrile group-containing monomer includes at least one of acrylonitrile and methacrylonitrile. Of course, those skilled in the art can also select other nitrile group-containing monomers according to the actual situation.

[0053] In some embodiments, the first thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, dicumyl peroxide, and ammonium persulfate.

[0054] In some embodiments, the second thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, dicumyl peroxide, and ammonium persulfate.

[0055] In some embodiments, the third thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, dicumyl peroxide, and ammonium persulfate.

[0056] In some embodiments, the mass content of the first thermal initiator in the first solution is 0.1% - 0.3%, specifically it can be 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3% or any value between them; the mass content of the second thermal initiator in the second solution is 0.1% - 0.3%, specifically it can be 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3% or any value between them; the mass content of the third thermal initiator in the third solution is 0.1% - 0.3%, specifically it can be 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3% or any value between them. By controlling the contents of the first thermal initiator, the second thermal initiator, and the third thermal initiator within the above ranges respectively, it is beneficial to control the first curing rate, the second curing rate, and the third curing rate, and avoid the occurrence of explosive polymerization or overly long polymerization time.

[0057] In some embodiments, the first electrolyte solution, the second electrolyte solution, and the third electrolyte solution independently include a lithium salt, an electrolyte, and a flame retardant; in the first electrolyte solution, the second electrolyte solution, or the third electrolyte solution, the content of the flame retardant is 2% - 15%, specifically it can be 2%, 4%, 6%, 8%, 10%, 12%, 15% or any value between them. By adding an appropriate amount of flame retardant to the first electrolyte solution, the second electrolyte solution, and the third electrolyte solution, the flame retardant performance of the electrolyte diaphragm can be effectively improved.

[0058] More specifically, in some embodiments, the lithium salt includes one or more of LiPF6, LiFSI (lithium bis(trifluoromethanesulfonyl)imide), LiBF4, LiBOB (lithium bis(oxalato)borate), LiDFOB (lithium difluoro(oxalato)borate), LiTFSI (lithium bis(trifluoromethylsulfonyl)imide). Of course, those skilled in the art can also select other commonly used lithium salts in the art according to the actual situation.

[0059] In some embodiments, the electrolyte includes one or more of EC (ethylene carbonate), PC (propylene carbonate), BC (butyronitrile), DEC (diethyl carbonate), DMC (dimethyl carbonate), DME (dimethoxyethane), EMC (ethyl methyl carbonate), TEP (triethyl phosphate), FEC (fluoroethylene carbonate). Of course, those skilled in the art can also select other commonly used electrolytes in the art according to the actual situation.

[0060] In some embodiments, the flame retardant includes at least one of a phosphorus-nitrogen composite flame retardant, a phosphorus-based flame retardant, a phosphorus-fluorine composite flame retardant, a phosphazene flame retardant, a bromine-based flame retardant, or other common organic flame retardants.

[0061] In some embodiments, the flame retardant includes an organic flame retardant and an inorganic flame retardant. The organic flame retardant and the inorganic flame retardant can synergistically improve the flame retardancy of the electrolyte separator.

[0062] In some embodiments, the phosphorus-nitrogen composite flame retardant includes one or more of ammonium polyphosphate (APP), melamine polyphosphate (MPP), pentaerythritol phosphate-melamine complex, etc.; the phosphorus-based flame retardant includes one or more of triphenyl phosphate (TPP), tricresyl phosphate (TCP), bisphenol A bis(diphenyl phosphate) (BDP), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), etc.; the phosphorus-fluorine composite flame retardant includes one or more of tris(2,2,2-trifluoroethyl) phosphate, hexafluorocyclotriphosphazene, etc.; the phosphazene flame retardant includes one or more of hexaphenoxycyclotriphosphazene (HPCTP), hexakis(4-aminophenoxy)cyclotriphosphazene, hexachlorocyclotriphosphazene, etc.; the bromine-based flame retardant includes one or more of decabromodiphenyl ether (Deca-BDE), tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), brominated polystyrene (BPS), brominated epoxy resin (BER), etc.

[0063] In some embodiments, the temperatures of the first curing, the second curing, and the third curing are 40°C to 80°C. Specifically, the temperatures of the first curing, the second curing, and the third curing can independently be 40°C, 50°C, 60°C, 70°C, 80°C, or any value therebetween. By controlling the temperatures of the first curing, the second curing, and the third curing within the above ranges, it is beneficial to control the final curing state of the functional layer formed on the surface of the base film to a gel state and also beneficial to improving the preparation efficiency of the electrolyte separator.

[0064] In a preferred embodiment, the temperature of the first curing is 40°C to 60°C, specifically, it can be 40°C, 45°C, 50°C, 55°C, 60°C, or any value therebetween; the temperature of the second curing is 60°C to 80°C, specifically, it can be 60°C, 65°C, 70°C, 75°C, 80°C, or any value therebetween; the temperature of the third curing is 50°C to 70°C, specifically, it can be 50°C, 55°C, 60°C, 65°C, 70°C, or any value therebetween. Such settings are beneficial to controlling the degree of polymerization of the linear monomer, the multi-branched monomer, and the nitrile group-containing monomer, so that the prepared electrolyte separator obtains relatively excellent mechanical properties, electrochemical properties, and flame retardant properties, while also being beneficial to improving the preparation efficiency of the electrolyte separator.

[0065] In the above preferred embodiment, the duration of the first curing is 55 min to 70 min, specifically, it can be 55 min, 60 min, 65 min, 70 min, or any value therebetween; the duration of the second curing is 33 min to 42 min, specifically, it can be 33 min, 35 min, 37 min, 39 min, 42 min, or any value therebetween; the duration of the third curing is 105 min to 130 min, specifically, it can be 105 min, 110 min, 115 min, 120 min, 125 min, 130 min, or any value therebetween.

[0066] In the above preferred embodiment, the first curing, the second curing, and the third curing all include a preheating stage, a heating-up stage, and a heat preservation stage carried out successively. The step-by-step operation of preheating first, then heating up, and then heat preservation not only improves the safety of the reaction but also significantly enhances the controllability of the product quality.

[0067] In some embodiments, the temperature in the heat preservation stage of the first curing is T1, the temperature in the heat preservation stage of the second curing is T2, and the temperature in the heat preservation stage of the third curing is T3, where T2 > T1 and T2 < T3. By making T2 > T1, it is beneficial to ensure that after the first preliminary polymerization of the linear monomer, a sufficient amount of active groups are retained to further polymerize with the multi-branched monomer in the second curing stage to form a gel-like three-dimensional network structure; by making T2 < T3, it is beneficial to prevent the further polymerization of the aforementioned gel-like three-dimensional network structure to form a fully solid structure.

[0068] In some embodiments, the steps of the first curing include: preheating the base film coated with the first solution at 40°C to 45°C for 5 min to 10 min, then raising the temperature to 55°C to 65°C and keeping it warm for 50 min to 70 min, and then cooling to room temperature. In the preheating stage, the first thermal initiator is activated, and the linear monomer is pre-crosslinked to form a flexible network. In the heat preservation stage, the linear monomer further polymerizes into a jelly-like gel state.

[0069] In some embodiments, the steps of the second curing include: preheating the composite structure of the base film coated with the second solution and the first intermediate layer at 60°C to 65°C for 5 min to 10 min, then raising the temperature to 75°C to 85°C and keeping it warm for 25 min to 35 min, and then cooling to room temperature.

[0070] In some embodiments, the steps of the third curing include: preheating the composite structure of the base film coated with the third solution and the second intermediate layer at 50°C to 55°C for 5 min to 10 min, then raising the temperature to 65°C to 75°C and keeping it warm for 110 min to 130 min, and then cooling to room temperature.

[0071] In some embodiments, in the steps of the first curing, the second curing, or the third curing, the heating rate ≤ 2°C / min. By controlling the heating rate within this range, it is beneficial to enhance the quality controllability of the product.

[0072] In some embodiments, in the steps of the first curing, the second curing, or the third curing, the cooling rate is ≥ 1°C / min. After the heat preservation is completed, through rapid cooling treatment, it is beneficial to avoid the accumulation of thermal stress on the polymerization product.

[0073] In a second aspect, an embodiment of the present application further provides a semi-solid secondary battery, including a positive electrode sheet, an electrolyte separator, and a negative electrode sheet, where the electrolyte separator is prepared by the preparation method described in the first aspect.

[0074] The semi-cured secondary battery of the present application uses an electrolyte separator prepared by the preparation method described in the first aspect, which enables the semi-cured secondary battery to not only have excellent safety performance but also have excellent electrochemical performance.

[0075] In the embodiments of the present application, in the electrolyte separator, the thickness of the functional layer on the surface of the base film is 10 to 30 μm. By controlling the thickness of the functional layer within this range, it is beneficial to balance the ion transport efficiency, mechanical strength, energy density, and safety of the electrolyte separator.

[0076] In the embodiments of the present application, in the electrolyte separator, the base film has a first side facing the positive electrode sheet and a second side facing the negative electrode sheet, and the functional layer is disposed on at least one of the first side and the second side.

[0077] In the embodiments of the present application, the positive electrode sheet, the electrolyte separator, and the negative electrode sheet can be assembled into a stacked structure or a wound structure, and the specific assembly method can be adjusted according to the specific type of the semi-cured secondary battery.

[0078] In the embodiments of the present application, exemplarily, the preparation method of the semi-cured secondary battery includes:

[0079] Prepare a positive electrode sheet, a negative electrode sheet, and an electrolyte separator;

[0080] Stack or wind and assemble the positive electrode sheet, the electrolyte separator, and the negative electrode sheet to obtain a pre-assembled component;

[0081] Assemble the pre-assembled component with the housing to obtain a semi-cured secondary battery.

[0082] In the above preparation method, when the semi-cured secondary battery is a soft-pack battery, the housing is a film structure such as an aluminum-plastic composite film, and the stacking assembly of the positive electrode sheet, the electrolyte separator, and the negative electrode sheet can be carried out on the film structure. When the semi-cured secondary battery is a hard-shell battery such as a square-shell battery, usually the positive electrode sheet, the electrolyte separator, and the negative electrode sheet are first assembled, and then the assembled structure is placed in the housing.

[0083] In a third aspect, the embodiments of the present application further provide an energy storage device, which includes at least one semi-solid secondary battery described in the second aspect. When the energy storage device contains multiple batteries, the multiple batteries can be connected by at least one of parallel connection and series connection.

[0084] In a fourth aspect, the embodiments of the present application further provide an electrical equipment, which includes the energy storage device described in the third aspect.

[0085] It can be understood that the electrical equipment further includes an electrical equipment body, and the energy storage device is used to supply power to the electrical equipment body.

[0086] In the embodiments of the present application, the electrical equipment may include, but is not limited to: containers, household energy storage systems, battery cars, electric vehicles, ships, spacecrafts, electric toys, electric tools, etc. Among them, the spacecrafts are, for example, airplanes, rockets, space shuttles, spaceships, etc.; the electric toys include, for example, stationary or mobile electric toys, specifically, for example, electric vehicle toys, electric ship toys, electric airplane toys, etc.; the electric tools include, for example, metal cutting electric tools, grinding electric tools, assembly electric tools, and electric tools for railways. Specifically, for example, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, and electric planers.

[0087] The present application will be further described below through specific embodiments and comparative examples, but the present application is not limited to this specific example.

[0088] Example 1

[0089] 1. Preparation of electrolyte diaphragm

[0090] (1) Raw materials: 3.29 wt% triethylene glycol dimethacrylate + 1.175 wt% trimethylolpropane trifluoracrylate + 0.235 wt% acrylonitrile + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 0.1 wt% benzoyl peroxide + 95 wt% liquid electrolyte (90 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0091] The liquid electrolyte is divided into three parts, namely the first electrolyte, the second electrolyte, and the third electrolyte, and the mass ratio of the first electrolyte, the second electrolyte, and the third electrolyte is 3.29:1.175:0.235.

[0092] Mix the triethylene glycol dimethacrylate, ammonium persulfate, and the first electrolyte in the raw materials to prepare a first solution;

[0093] Mix the trimethylolpropane trifluoracrylate, azobisisobutyronitrile, and the second electrolyte in the raw materials to prepare a second solution;

[0094] Mix acrylonitrile, benzoyl peroxide, and the third electrolyte in the raw materials to prepare a third solution.

[0095] (2) Preparation steps:

[0096] S100. Provide a base film (polypropylene film), uniformly coat the first solution on the surface of the base film, place it in a segmented oven, preheat at 40°C for 10 minutes first, then heat up to 60°C at a rate of ≤2°C / min, then keep it warm for 60 minutes, and then quickly cool it to room temperature to form a first intermediate layer on the surface of the base film.

[0097] S200. Coating the second solution evenly on the surface of the first intermediate layer, putting it into a segmented oven, preheating at 60 °C for 5 minutes first, then heating up to 80 °C at a rate of ≤2 °C / min, then keeping warm for 30 minutes, and then quickly cooling to room temperature to form the second intermediate layer on the surface of the base film.

[0098] S300. Coating the third solution evenly on the surface of the second intermediate layer, putting it into a segmented oven, preheating at 50 °C for 10 minutes first, then heating up to 70 °C at a rate of ≤2 °C / min, then keeping warm for 120 minutes, and then quickly cooling to room temperature to obtain the electrolyte diaphragm.

[0099] 2. Assembly of half-cell

[0100] Mix the cathode material (lithium iron phosphate), conductive agent Super and polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) according to the ratio of 90:5:5, coat the formed slurry on the aluminum foil, and dry it at 105 °C under vacuum for 10 h to obtain the cathode sheet, and the counter electrode is a lithium sheet.

[0101] Use a cutting machine to cut the cathode sheet and lithium sheet into small round pieces with a diameter of 13 mm, and assemble the cathode shell, shrapnel, gasket, cathode sheet, the above-prepared electrolyte diaphragm, lithium sheet, and anode shell into a button cell in a glove box filled with argon (Ar).

[0102] 3. Performance testing

[0103] (1) Conductivity testing before and after polymerization

[0104] At 25 °C, use a conductivity meter to test the conductivity of the functional layer material of the electrolyte diaphragm.

[0105] (2) Self-extinguishing time testing

[0106] Take a small amount of electrolyte and place it on the anode shell of the button cell. After igniting it with a lighter for 5 s, start timing and observe the self-extinguishing time.

[0107] (3) Electrochemical performance testing

[0108] In this paper, the LAND testing system is used to test the cycling performance and rate performance of the above-assembled button cell in a constant temperature test cabinet at 25 °C. The current density for the cycling performance test is 0.3 C for 5 cycles of activation and then cycling at a current density of 1 C, and the voltage range is 2 - 3.75 V. The specified current densities for the rate performance test are 10 mA·g -1 、30 mA·g -1 、50 mA·g -1 、70 mA·g -1 、100 mA·g -1 、10 mA·g -1At each current density, cycle 5 times.

[0109] Example 2

[0110] The difference from Example 1 is that trimethylolpropane triacrylate in the raw materials is replaced by pentaerythritol tetraacrylate.

[0111] Example 3

[0112] The difference from Example 1 is that:

[0113] (1) Raw materials: 2.4 wt% triethylene glycol dimethacrylate + 0.6 wt% trimethylolpropane triacrylate + 0.2 wt% acrylonitrile + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 0.1 wt% benzoyl peroxide + 96.5 wt% liquid electrolyte (91.7 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0114] The liquid electrolyte is divided into three parts, namely the first electrolyte, the second electrolyte and the third electrolyte, and the mass ratio of the first electrolyte, the second electrolyte and the third electrolyte is 2.4:0.6:0.2.

[0115] Example 4

[0116] The difference from Example 1 is that:

[0117] (1) Raw materials: 5.44 wt% triethylene glycol dimethacrylate + 2.04 wt% trimethylolpropane triacrylate + 0.34 wt% acrylonitrile + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 0.1 wt% benzoyl peroxide + 91.7 wt% liquid electrolyte (86.7 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0118] The liquid electrolyte is divided into three parts, namely the first electrolyte, the second electrolyte and the third electrolyte, and the mass ratio of the first electrolyte, the second electrolyte and the third electrolyte is 5.6:2.04:0.34.

[0119] Example 5

[0120] The difference from Example 1 is that:

[0121] (1) Mix trimethylolpropane triacrylate, benzoyl peroxide in the raw materials with the second electrolyte to prepare a second solution; mix acrylonitrile, azobisisobutyronitrile in the raw materials with the third electrolyte to prepare a third solution.

[0122] (2) S200. Uniformly coat the second solution on the surface of the first intermediate layer, place it in a segmented oven, preheat at 50 °C for 10 minutes first, then heat it up to 70 °C at a rate of ≤2 °C / min, then keep it warm for 120 minutes, and then quickly cool it to room temperature to form a second intermediate layer on the surface of the base film.

[0123] S300. Uniformly coat the third solution on the surface of the second intermediate layer, place it in a segmented oven, preheat at 60 °C for 5 minutes first, then heat it up to 80 °C at a rate of ≤2 °C / min, then keep it warm for 30 minutes, and then quickly cool it to room temperature to obtain an electrolyte diaphragm.

[0124] Example 6

[0125] The difference from Example 1 is as follows:

[0126] (1) Mix triethylene glycol dimethacrylate, azobisisobutyronitrile, and the first electrolyte in the raw materials to prepare a first solution; mix trimethylolpropane trifluoracrylate, benzoyl peroxide, and the second electrolyte in the raw materials to prepare a second solution; mix acrylonitrile, ammonium persulfate, and the third electrolyte to prepare a third solution.

[0127] (2) S100. Provide a base film (polypropylene film), uniformly coat the first solution on the surface of the base film, place it in a segmented oven, preheat at 60 °C for 5 minutes first, then heat it up to 80 °C at a rate of ≤2 °C / min, then keep it warm for 30 minutes, and then quickly cool it to room temperature to form a first intermediate layer on the surface of the base film.

[0128] S200. Uniformly coat the second solution on the surface of the first intermediate layer, place it in a segmented oven, preheat at 50 °C for 10 minutes first, then heat it up to 70 °C at a rate of ≤2 °C / min, then keep it warm for 120 minutes, and then quickly cool it to room temperature to form a second intermediate layer on the surface of the base film.

[0129] S300. Uniformly coat the third solution on the surface of the second intermediate layer, place it in a segmented oven, preheat at 40 °C for 10 minutes first, then heat it up to 60 °C at a rate of ≤2 °C / min, then keep it warm for 60 minutes, and then quickly cool it to room temperature to obtain an electrolyte diaphragm.

[0130] Comparative Example 1

[0131] Liquid electrolyte (1M LiPF6 EMC: DMC = 3:4:3 vol%).

[0132] Comparative Example 2

[0133] The difference from Example 1 is as follows:

[0134] 1. Prepare an electrolyte diaphragm

[0135] (1)Raw materials: 4.7 wt% triethylene glycol dimethacrylate + 0.3 wt% ammonium persulfate + 95 wt% liquid electrolyte (90 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0136] Mix the triethylene glycol dimethacrylate, ammonium persulfate and electrolyte in the raw materials to prepare a first solution.

[0137] (2)Preparation steps:

[0138] S100. Provide a base film (polypropylene film), uniformly coat the first solution on the surface of the base film, put it into a segmented oven, preheat at 40 °C for 10 minutes first, then heat up to 60 °C at a rate of ≤2 °C / min, then keep warm for 60 minutes, and then quickly cool to room temperature to obtain an electrolyte separator.

[0139] Comparative Example 3

[0140] The difference from Example 1 is as follows:

[0141] 1. Preparation of electrolyte separator

[0142] (1)Raw materials: 3.54 wt% triethylene glycol dimethacrylate + 1.26 wt% trimethylolpropane trifluoracrylate + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 95 wt% liquid electrolyte (85 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0143] Divide the liquid electrolyte into two parts, namely the first electrolyte and the second electrolyte, and the mass ratio of the first electrolyte to the second electrolyte is 3.54:1.26.

[0144] Mix the triethylene glycol dimethacrylate, ammonium persulfate and the first electrolyte in the raw materials to prepare a first solution;

[0145] Mix the trimethylolpropane trifluoracrylate, azobisisobutyronitrile and the second electrolyte in the raw materials to prepare a second solution.

[0146] (2)Preparation steps:

[0147] S100. Provide a base film (polypropylene film), uniformly coat the first solution on the surface of the base film, put it into a segmented oven, preheat at 40 °C for 10 minutes first, then heat up to 60 °C at a rate of ≤2 °C / min, then keep warm for 60 minutes, and then quickly cool to room temperature to form a first intermediate layer on the surface of the base film.

[0148] S200. Coat the second solution evenly on the surface of the first intermediate layer, place it in a segmented oven, preheat at 60 °C for 5 minutes first, then heat it up to 80 °C at a rate of ≤2 °C / min, then keep it warm for 30 minutes, and then quickly cool it to room temperature to obtain an electrolyte diaphragm.

[0149] Comparative Example 4

[0150] The difference from Example 1 is that:

[0151] (1) Raw materials: 1.19 wt% triethylene glycol dimethacrylate + 0.425 wt% trimethylolpropane trifluoracrylate + 0.085 wt% acrylonitrile + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 0.1 wt% benzoyl peroxide + 98 wt% liquid electrolyte (93 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0152] Divide the liquid electrolyte into three parts, namely the first electrolyte, the second electrolyte and the third electrolyte, and the mass ratio of the first electrolyte, the second electrolyte and the third electrolyte is 1.19:0.425:0.085.

[0153] Comparative Example 5

[0154] The difference from Example 1 is that:

[0155] (1) Raw materials: 6.09 wt% triethylene glycol dimethacrylate + 2.175 wt% trimethylolpropane trifluoracrylate + 0.435 wt% acrylonitrile + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 0.1 wt% benzoyl peroxide + 91 wt% liquid electrolyte (86 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0156] Comparative Example 6

[0157] The difference from Example 1 is that:

[0158] (1) Raw materials: 2.35 wt% triethylene glycol dimethacrylate + 1.645 wt% trimethylolpropane trifluoracrylate + 0.705 wt% acrylonitrile + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 0.1 wt% benzoyl peroxide + 95 wt% liquid electrolyte (90 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0159] The liquid electrolyte is divided into three parts, namely the first electrolyte, the second electrolyte, and the third electrolyte, and the mass ratio of the first electrolyte, the second electrolyte, and the third electrolyte is 2.35:1.645:0.705.

[0160] Comparative Example 7

[0161] The difference from Example 1 is as follows:

[0162] (1) Raw materials: 3.995 wt% triethylene glycol dimethacrylate + 0.611 wt% trimethylolpropane trifluoracrylate + 0.094 wt% acrylonitrile + 0.1 wt% ammonium persulfate + 0.1 wt% azobisisobutyronitrile + 0.1 wt% benzoyl peroxide + 95 wt% liquid electrolyte (90 wt% (1M LiPF6 EC:EMC:DMC = 3:4:3 vol%) + 5 wt% hexaphenoxycyclotriphosphazene).

[0163] The liquid electrolyte is divided into three parts, namely the first electrolyte, the second electrolyte, and the third electrolyte, and the mass ratio of the first electrolyte, the second electrolyte, and the third electrolyte is 3.995:0.611:0.094.

[0164] Comparative Example 8

[0165] The difference from Example 1 is as follows:

[0166] Preparation steps:

[0167] (2) S100. Provide a base film (polypropylene film), uniformly mix the first solution and the second solution and then uniformly coat them on the surface of the base film, place it in a segmented oven, preheat at 60°C for 10 minutes first, then heat up to 80°C at a rate of ≤2°C / min, then keep it warm for 60 minutes, and then quickly cool it to room temperature to form an intermediate layer on the surface of the base film.

[0168] S200. Uniformly coat the third solution on the surface of the first intermediate layer, place it in a segmented oven, preheat at 50°C for 10 minutes first, then heat up to 70°C at a rate of ≤2°C / min, then keep it warm for 120 minutes, and then quickly cool it to room temperature to obtain an electrolyte separator.

[0169] Comparative Example 9

[0170] The difference from Example 1 is as follows:

[0171] Preparation steps:

[0172] S100. Provide a base film (polypropylene film), uniformly coat the first solution on the surface of the base film, place it in a segmented oven, preheat at 40°C for 10 minutes first, then heat up to 60°C at a rate of ≤2°C / min, then keep it warm for 60 minutes, and then quickly cool it to room temperature to form an intermediate layer on the surface of the base film.

[0173] S200. After uniformly mixing the second solution and the third solution, coat them uniformly on the first intermediate layer, put them into a segmented oven, preheat at 60°C for 5 minutes first, then heat up to 80°C at a rate of ≤2°C / min, then keep warm for 30 minutes, and then quickly cool to room temperature to obtain an electrolyte separator.

[0174] Test results:

[0175] Table 1. Test results of conductivity and flame retardancy performance of each example and comparative example

[0176]

[0177] Table 2. Test results of cycle performance of each example and comparative example

[0178]

[0179] Table 3. Test results of rate performance of each example and comparative example

[0180]

[0181] It can be proved by the test results of Examples 1-6 and Comparative Examples 1-9 that the electrolyte separator prepared by using the gradient copolymerization technology described in the present application not only has excellent flame retardancy performance, but also has excellent ionic conductivity and material stability. The semi-solid secondary battery prepared therefrom has electrochemical performances such as rate performance and cycle performance similar to those of liquid electrolytes on the premise that the safety performance is significantly improved. Among them,

[0182] By comparing Examples 1-6 with Comparative Example 1, it can be proved that the semi-solid electrolyte (separator) of the present application has better flame retardancy performance than the common existing liquid electrolytes.

[0183] By comparing Example 1 with Comparative Examples 2 and 3, it can be proved that by adding multi-branched monomers to polymerize to form a three-dimensional network structure, the conductivity of the electrolyte separator can be improved, the stability of the electrode material is ensured, and it is beneficial to the improvement of the cycle performance of the semi-solid secondary battery.

[0184] By comparing Example 1 with Comparative Example 3, it can be proved that by finally adding a cyano-containing monomer to improve the interfacial compatibility between the electrolyte separator and the electrolyte solution, the conductivity of the electrolyte separator can be increased, which is beneficial to the improvement of the rate performance of the semi-solid secondary battery.

[0185] By comparing Example 1 with Comparative Example 8 and Comparative Example 9, it can be demonstrated that, compared with the synchronous copolymerization method, in the present application, the linear monomer, the multi-branched monomer, and the cyano-containing monomer are sequentially added for gradient polymerization to form a layered structure, and the interaction between the layers enables the rate performance and cycle performance of the semi-cured secondary battery to be improved.

[0186] By comparing Example 1 with Comparative Examples 4-7, it can be demonstrated that when the total mass content of the linear monomer, the multi-branched monomer, and the nitrile group-containing monomer in the raw materials does not meet 3% - 8%, or the mass ratio of the linear monomer, the multi-branched monomer, and the nitrile group-containing monomer does not meet (12 - 16):(3 - 6):1, it results in severe electrolyte curing, inability to form a gel, or a poor gel state, thereby making the rate performance and cycle performance of the semi-cured secondary battery poor.

[0187] By comparing Example 1 with Example 2, it can be demonstrated that when the multi-branched monomer is a fluorine-containing monomer, it is more conducive to improving the conductivity of the electrolyte membrane, and thus more conducive to improving the flame retardancy and rate performance of the semi-cured secondary battery.

[0188] By comparing Example 1 with Example 5 and Example 6, it can be concluded that, compared with increasing or decreasing the temperatures of the first curing, the second curing, and the third curing (holding temperatures, the same below) in sequence, making the temperature of the second curing higher than that of the first curing and lower than that of the third curing is more conducive to enhancing the polymerization between the electrolyte layers, and thus more conducive to improving the rate performance and cycle performance of the semi-cured secondary battery.

[0189] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. 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 method for preparing an electrolyte separator of a semi-solid secondary battery, characterized in that, The preparation method includes the following steps: Provide a base film, coat a first solution on the surface of the base film, the first solution includes a linear monomer, a first thermal initiator and a first electrolyte, and perform a first curing to form a first intermediate layer on the surface of the base film. The linear monomer includes at least one of triethylene glycol dimethacrylate, methyl methacrylate, vinyl acetate, trifluoroethyl methacrylate and ethylene glycol diacrylate; Coat a second solution on the surface of the first intermediate layer, the second solution includes a multi-branched monomer, a second thermal initiator and a second electrolyte, and perform a second curing to form a second intermediate layer on the surface of the base film. The multi-branched monomer includes at least one of trimethylolpropane trifluoracrylate, pentaerythritol tetraacrylate and four-arm polyethylene glycol-tetraacrylate; Coat a third solution on the surface of the second intermediate layer, the third solution includes a nitrile group-containing monomer, a third thermal initiator and a third electrolyte, and perform a third curing to form a gel-like functional layer on the surface of the base film, obtaining an electrolyte separator; Based on the total mass content of the first solution, the second solution and the third solution being 100%, the total mass content of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer is 3% - 8%, and the mass ratio of the linear monomer, the multi-branched monomer and the nitrile group-containing monomer is (12 - 16):(3 - 6):

1.

2. The preparation method according to claim 1, characterized in that, The nitrile group-containing monomer includes at least one of acrylonitrile and methacrylonitrile.

3. The preparation method according to claim 1, characterized in that, The first electrolyte, the second electrolyte and the third electrolyte independently include a lithium salt, an electrolyte and a flame retardant, and the content of the flame retardant is 2% - 15%.

4. The preparation method according to claim 3, characterized in that, Includes at least one of the following features (1)-(3): (1) The lithium salt includes one or more of LiPF6, LiFSI, LiBF4, LiBOB, LiDFOB and LiTFSI; (2) The electrolyte includes one or more of EC, PC, BC, DEC, DMC, DME, EMC, TEP and FEC; (3) The flame retardant includes at least one of a phosphorus-nitrogen composite flame retardant, a phosphorus-based flame retardant, a phosphorus-fluorine composite flame retardant, a phosphonitrile flame retardant and a bromine-based flame retardant.

5. The preparation method according to claim 1, characterized in that, The first thermal initiator, the second thermal initiator and the third thermal initiator independently include at least one of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, dicumyl peroxide and ammonium persulfate.

6. The preparation method according to any one of claims 1-5, characterized in that, The temperature of the first curing is 40°C - 60°C, the temperature of the second curing is 60°C - 80°C, and the temperature of the third curing is 50°C - 70°C.

7. The preparation method according to claim 6, characterized in that, Includes at least one of the following features (1)-(3): (1) The step of the first curing includes: preheating the base film coated with the first solution at 40°C - 45°C for 5 min - 10 min, then raising the temperature to 55°C - 60°C and holding for 50 min - 70 min, with a heating rate ≤ 2°C / min, and then cooling to room temperature; (2) The steps of the second curing include: preheating the composite structure of the base film coated with the second solution and the first intermediate layer at 60°C to 65°C for 5 min to 10 min, then heating up to 75°C to 80°C and holding for 25 min to 35 min, with a heating rate ≤ 2°C / min, and then cooling to room temperature; (3) The steps of the third curing include: preheating the composite structure of the base film coated with the third solution and the second intermediate layer at 50°C to 55°C for 5 min to 10 min, then heating up to 65°C to 75°C and holding for 110 min to 130 min, with a heating rate ≤ 2°C / min, and then cooling to room temperature.

8. A semi-solid secondary battery, characterized in that, It includes a positive electrode sheet, an electrolyte separator, and a negative electrode sheet, and the electrolyte separator is prepared by the preparation method described in any one of claims 1-7.

9. The semi-solid secondary battery according to claim 8, wherein In the electrolyte separator, the base film has a first side facing the positive electrode sheet and a second side facing the negative electrode sheet, the functional layer is provided on at least one of the first side and the second side, and the thickness of the functional layer is 10μm to 30μm.

10. A energy storage device, characterized in that, It includes a semi-solid secondary battery as described in claim 9.

11. An electrical device, characterized in that, It includes a semi-solid secondary battery as described in claim 10.

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