A secondary battery and a method of manufacturing the same

Abstract

The application discloses a secondary battery and a preparation method thereof. The secondary battery comprises a positive electrode sheet, a separator and a negative electrode sheet, the separator is arranged between the positive electrode sheet and the negative electrode sheet, a polymerizable interface layer is arranged on one side surface of the positive electrode sheet facing the separator, and a heat-induced acid-releasing layer is arranged on the inside of the separator or on one side surface of the separator facing the positive electrode sheet. In the abnormal temperature rising working condition, the heat-induced acid-releasing layer releases acidic active centers under heat, diffuses to the positive electrode side across the interface, and triggers the cationic polymerization and cross-linking gelation of the polymerizable monomers in the positive electrode interface coating, so that a gel barrier layer is formed in situ on the dangerous interface between the positive electrode and the separator, direct contact between the positive electrode and the negative electrode is blocked or delayed, local short circuit formation is inhibited, heat transfer and side reaction expansion are slowed down, and the thermal safety of the battery can be improved under the premise of guaranteeing the conventional performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries are widely used due to their advantages such as high energy density, high output pressure, and high output power. The separator, as a crucial component of lithium-ion batteries, ensures the safety of the battery during cycling under various conditions and maintains its ion transport performance. However, a drawback of the separator is that under excessively high battery temperatures, it can experience thermal shrinkage, melting, or localized failure, leading to a rapid increase in the risk of direct contact between the positive and negative electrodes. This can induce safety issues such as localized short circuits, heat accumulation, and thermal runaway. Existing methods for improving the safety of lithium-ion batteries mainly include enhancing the heat resistance of the separator itself, using flame-retardant electrolytes, and relying on external thermal management. While these methods can improve battery safety to some extent, they still have significant shortcomings. Summary of the Invention

[0003] In view of the problems existing in the prior art, this application provides a secondary battery and a method for preparing the same.

[0004] A first aspect of this application provides a secondary battery comprising a positive electrode, a separator, and a negative electrode, wherein the separator is disposed between the positive electrode and the negative electrode; a polymerizable interface layer is disposed on the surface of the positive electrode facing the separator, and a thermotropic acid-releasing layer is disposed inside the separator or a thermotropic acid-releasing layer is disposed on the surface of the separator facing the positive electrode.

[0005] In some embodiments, the dry film thickness of the polymerizable interface layer is optionally 0.1 μm to 10 μm, preferably 0.5 μm to 5 μm, and more preferably 1 μm to 3 μm.

[0006] In some embodiments, the dry film thickness of the thermo-acid-releasing layer is optionally 0.1 μm to 3 μm, preferably 1 μm to 3 μm.

[0007] In some embodiments, optionally, the polymerizable interface layer comprises polymerizable monomers; based on the total mass of the polymerizable interface layer, the mass fraction of the polymerizable monomers is 50% to 100%, preferably 50% to 90%.

[0008] In some embodiments, the polymerizable monomer may optionally be a vinyl ether monomer, including one or more of monofunctional vinyl ether monomers, difunctional vinyl ether monomers, and polyfunctional vinyl ether monomers.

[0009] In some embodiments, the monofunctional vinyl ether monomer may optionally include one or a combination of two or more of ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, and triethylene glycol monovinyl ether.

[0010] In some embodiments, the difunctional vinyl ether monomer may optionally include one or a combination of two or more of ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, neopentyl glycol divinyl ether, and cyclohexanediethanol divinyl ether.

[0011] In some embodiments, the polyfunctional vinyl ether monomers may optionally include one or a combination of two or more of the following: trimethylolpropane trivinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, polyether-type vinyl ether oligomers containing three or more vinyl ether end groups, polyester-type vinyl ether oligomers containing three or more vinyl ether end groups, and polyurethane-type vinyl ether oligomers containing three or more vinyl ether end groups.

[0012] In some embodiments, the polymerizable interface layer may optionally include one or more of the following: a polymer binder, an inorganic filler, a polymer matrix, a high-pressure stabilizing agent, an interface stabilizer, and an auxiliary film-forming agent.

[0013] In some embodiments, the polymer binder may optionally include one or more of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); the mass fraction of the polymer binder is 0% to 20% based on the total mass of the polymerizable interface layer, preferably 3% to 20%.

[0014] In some embodiments, the inorganic filler may optionally include one or more combinations of inorganic ceramic particles such as alumina (Al2O3), titanium dioxide (TiO2), and boehmite; the mass fraction of the inorganic filler is 0% to 30% based on the total mass of the polymerizable interface layer.

[0015] In some embodiments, the polymer matrix may optionally include one or more of polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyimide, polyacrylate polymers, and fluorinated acrylate polymers; the mass fraction of the polymer matrix is ​​0% to 30% based on the total mass of the polymerizable interface layer.

[0016] In some embodiments, the high-pressure stabilizing agent may optionally include one or more of lithium phosphate, lithium metaphosphate, lithium pyrophosphate, lithium fluorophosphate, lithium difluorophosphate, lithium borate, lithium difluorooxalate borate, lithium bis(oxalate borate), tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, fluorophosphate compounds, and borate ester compounds; the mass fraction of the high-pressure stabilizing agent is 0% to 10% based on the total mass of the polymerizable interface layer.

[0017] In some embodiments, the interface stabilizer may optionally include one or more of lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorophosphate, lithium fluorophosphate, lithium phosphate, lithium borate, lithium sulfate, alumina, titanium dioxide, zirconium oxide, aluminum phosphate, and lithium aluminum titanium phosphate; the mass fraction of the interface stabilizer is 0% to 10% based on the total mass of the polymerizable interface layer.

[0018] In some embodiments, the auxiliary film-forming agent may optionally include one or more of polyvinylpyrrolidone, polyvinyl butyral, fluoroacrylate resins, polycarbonate polymers, and polyethylene glycol oligomers; the mass fraction of the auxiliary film-forming agent is 0% to 10% based on the total mass of the polymerizable interface layer.

[0019] In some embodiments, the thermo-acid-releasing layer optionally contains an acidic active center protonic acid and / or Lewis acid, and the thermal activation temperature of the thermo-acid-releasing layer is 90°C to 100°C.

[0020] In some embodiments, the thermotropic acid-releasing layer may optionally comprise a chemical thermotropic acid-releasing agent, a thermotropic acid-releasing polymer, or a physical phase change acid-releasing carrier; based on the total mass of the thermotropic acid-releasing layer, the mass fraction of the chemical thermotropic acid-releasing agent, the thermotropic acid-releasing polymer, or the physical phase change acid-releasing carrier is 50% to 90%.

[0021] In some embodiments, the chemically-induced thermogenic acid-releasing agent may optionally include one or a combination of two or more of amine-blocked p-toluenesulfonic acid (PTSA), amine-blocked dinonylnaphthalene disulfonic acid (DNNDSA), diphenyliodonium hexafluorophosphate (DPI-PF6), and phenyl dimethyl sulfonium trifluoromethanesulfonate.

[0022] In some embodiments, the thermotropic acid-releasing polymer may optionally include polymers containing sulfonate structural units, sulfonate structural units, ammonium salt sulfonate structural units, or onium salt sulfonate structural units.

[0023] In some embodiments, the physical phase change type acid-releasing carrier may optionally be a dispersion, microcapsule, composite ceramic coating carrier, layered composite carrier, etc.

[0024] In some embodiments, the physical phase change acid-releasing carrier may optionally include physical phase change acid-releasing microcapsules, wherein the physical phase change acid-releasing microcapsules include an acid source core material and a thermosensitive wall material.

[0025] In some embodiments, the acid source core material may optionally comprise a Lewis acid complex or an organic solid acid. Preferably, the Lewis acid complex comprises one or more of boron trifluoride-ethylamine complex (BF3·EA), boron trifluoride-diethyl ether complex, and boron trifluoride-ethyl acetate complex; the organic solid acid comprises one or more of methanesulfonic acid and p-toluenesulfonic acid.

[0026] In some embodiments, the heat-sensitive wall material may optionally include a polymer phase change material, wherein the melting point or softening temperature of the polymer phase change material is 90°C to 100°C; preferably, the polymer phase change material includes modified polyethylene wax (PEWax), ethylene-vinyl acetate copolymer (EVA), or maleic anhydride grafted polyethylene (MAH-g-PE), etc.

[0027] In some embodiments, the thermotropic acid-releasing layer may optionally include one or more of a binder, heat-resistant particles, and a pore structure modifier.

[0028] In some embodiments, the adhesive may optionally include one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyimide, polyacrylate polymers, and fluorinated acrylate polymers; the mass fraction of the adhesive is 1% to 20% based on the total mass of the thermotropic acid-releasing layer.

[0029] In some embodiments, the heat-resistant particles may optionally include one or more of alumina, boehmite, silica, titanium dioxide, zirconium oxide, barium sulfate, boron nitride, aluminum phosphate, and lithium titanium aluminum phosphate; the mass fraction of the heat-resistant particles is 0% to 40% based on the total mass of the thermotropic acid release layer.

[0030] In some embodiments, the pore structure modifier may optionally include one or more of the following: polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, polyvinyl butyral, polyacrylate polymers, cellulose derivatives, ammonium bicarbonate, ammonium carbonate, volatile organic small molecule porogens, and extractable polymer particles; the mass fraction of the pore structure modifier is 0% to 15% based on the total mass of the thermo-released acid layer.

[0031] A second aspect of this application provides a method for preparing the secondary battery, comprising the following steps: coating a polymerizable interface layer on the surface of the positive electrode facing the separator; coating a thermotropic acid-releasing layer on the surface of the separator facing the positive electrode or embedding a thermotropic acid-releasing layer inside the separator; assembling the treated positive electrode, separator, and negative electrode in sequence, injecting electrolyte, and encapsulating to obtain the secondary battery.

[0032] In some embodiments, the coating may optionally include slurry coating, printing coating, transfer coating, spraying, roller coating, dip coating, etc.

[0033] In some embodiments, the processed positive electrode, separator, and negative electrode are optionally assembled by stacking or winding.

[0034] In some embodiments, the positive electrode sheet is optionally prepared by coating a positive electrode current collector with a positive electrode active material.

[0035] In some embodiments, the positive current collector may optionally include aluminum foil, and the positive active material may include lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, or lithium manganese oxide, etc.

[0036] In some embodiments, the negative electrode sheet is optionally prepared by coating a negative electrode current collector with a negative electrode active material.

[0037] In some embodiments, the negative electrode current collector may optionally include copper foil, and the negative electrode active material may include lithium metal, carbon-based negative electrode, silicon-based negative electrode, or alloy-based negative electrode.

[0038] In some embodiments, the electrolyte may optionally comprise a non-aqueous lithium salt solution.

[0039] This invention addresses the safety issues of secondary batteries under abnormal operating conditions such as thermal abuse, localized overheating, and precursors to internal short circuits. These conditions lead to thermal shrinkage, melting, or partial failure of the separator, resulting in a rapid increase in the risk of direct contact between the positive and negative electrodes. This can induce localized short circuits, heat accumulation, and thermal runaway. The invention proposes a safe cell structure that can actively trigger at the hazardous interface, form a film in situ, and preferentially block contact between the positive and negative electrodes. This application does not simply improve the heat resistance of the separator itself, nor does it simply add flame retardants or thermally responsive additives to the electrolyte. Instead, it constructs an abnormal temperature-triggered cross-interfacial polymerization protection mechanism at the high-risk interface between the positive electrode and the separator, ensuring that the protective reaction occurs at the most critical location, minimizing the impact on the normal electrochemical system.

[0040] The secondary battery described in this application, by setting an interface coating containing polymerizable monomers on the side of the positive electrode facing the separator, and setting a thermotropic acid-releasing layer containing acidic active centers on the side of the separator facing the positive electrode, maintains spatial separation between the two at normal operating temperatures, preventing significant polymerization reactions and improving structural and electrochemical stability under normal operating conditions. When the cell temperature rises abnormally, the thermotropic acid-releasing layer releases acidic active centers, which diffuse across the interface towards the positive electrode side, triggering rapid cationic polymerization and cross-linking gelation of the polymerizable monomers in the positive electrode interface coating. This forms a gel barrier layer in situ at the dangerous interface between the positive electrode and the separator, blocking or delaying direct contact between the positive and negative electrodes. Through physical isolation and electronic contact suppression, it inhibits the formation of local short circuits, slows down heat transfer and the spread of side reactions, and improves the thermal safety of the cell while maintaining conventional performance. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the structure of the secondary battery described in this application.

[0043] Figure 2 This is a schematic diagram of the structure of a secondary battery based on related technologies.

[0044] Figure 3 This is a schematic diagram of the mechanism of the secondary battery described in this application under thermal runaway conditions. Under abnormally high temperature conditions, a gel coating is formed between the positive electrode and the separator, blocking the direct contact between the positive and negative electrode plates.

[0045] Figure 4 This is a schematic diagram of the mechanism of secondary batteries under thermal runaway conditions. Under abnormally high temperatures, the separator shrinks, causing the positive and negative electrode plates to come into direct contact. Detailed Implementation

[0046] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0048] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0049] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0053] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0055] Unless otherwise specified, in this application, the terms "multiple" or "a variety" refer to two or more kinds.

[0056] In related technologies, the main methods for improving the safety of lithium-ion batteries include improving the heat resistance of the separator, using flame-retardant electrolytes, and relying on external thermal management. While these methods can improve battery safety to some extent, they still have significant shortcomings: 1) Under conditions of thermal abuse, internal short circuits, or local overheating, the separator may still experience thermal shrinkage, melting, or damage. Once the separator fails, the physical isolation between the positive and negative electrodes is destroyed, which can easily induce local short circuits, exacerbate heat release, and lead to thermal runaway. 2) Existing solutions are more of a passive protection for the material itself or the overall system, lacking a mechanism that can quickly activate and actively respond in critical dangerous temperature zones before and after separator failure. 3) If thermally responsive polymers are directly added to the electrolyte, the monomers will coexist with the electrolyte phase for a long time, posing risks of stability under high pressure, self-polymerization during long-term cycling, and non-localized gelation within the bulk phase. This can easily disturb the wettability, ion transport, and overall electrochemical performance of the electrolyte.

[0057] A first aspect of this application provides a secondary battery, such as Figure 1 As shown, it includes a positive electrode 10, a separator 20 and a negative electrode 30, with the separator 20 disposed between the positive electrode 10 and the negative electrode 30; a polymerizable interface layer 40 is disposed on the surface of the positive electrode 10 facing the separator 20, and a thermotropic acid-releasing layer 50 is disposed on the surface of the separator 20 facing the positive electrode 10.

[0058] In some embodiments, the thermotropic acid release layer can be directly disposed on the surface of the separator 20, or disposed within the ceramic layer or adhesive layer of the separator 20, or disposed in an additional functional coating between the separator 20 and the positive electrode 10.

[0059] In some embodiments, the polymerizable interface layer 40 comprises a polymerizable monomer, and the thermotropic acid-releasing layer 50 contains an acidic active center protonic acid and / or Lewis acid.

[0060] This invention addresses the issue of thermal shrinkage, melting, or partial failure of the separator in secondary batteries under abnormal operating conditions such as thermal abuse, localized overheating, and precursors to internal short circuits (e.g., ...). Figure 4 As shown in the figure, the risk of direct contact between the positive and negative electrodes increases rapidly, leading to safety issues such as local short circuits, heat accumulation, and thermal runaway. This paper proposes a safe battery cell structure that can be actively triggered at the dangerous interface, form a film in situ, and preferentially block the contact between the positive and negative electrodes. This application does not simply improve the heat resistance of the separator itself, nor does it simply add flame retardants or thermally responsive additives to the electrolyte. Instead, it constructs an abnormal temperature-triggered cross-interfacial polymerization protection mechanism at the high-risk interface between the positive electrode and the separator, ensuring that the protection reaction occurs at the most needed location, reducing the impact on the normal electrochemical system.

[0061] The secondary battery described in this application, by providing an interfacial coating containing polymerizable monomers on the side of the positive electrode facing the separator, and a thermotropic acid-releasing layer containing acidic active centers on the side of the separator facing the positive electrode, maintains spatial separation between the two under normal operating temperatures, preventing significant polymerization reactions and improving structural and electrochemical stability under normal operating conditions; when the battery cell experiences abnormal temperature rise, such as Figure 3 As shown, the thermally released acidic acid layer releases acidic active centers upon heating, which diffuse across the interface toward the positive electrode side and trigger the rapid cationic polymerization and cross-linking gelation of polymerizable monomers in the positive electrode interface coating. This forms a gel barrier layer in situ at the dangerous interface between the positive electrode and the separator, thereby blocking or delaying direct contact between the positive and negative electrodes. Through physical isolation and electronic contact suppression, it inhibits the formation of local short circuits, slows down heat transfer and the spread of side reactions, and improves the thermal safety of the battery cell while maintaining conventional performance.

[0062] Compared with existing technologies that uniformly introduce thermally responsive polymerizable monomers into the entire electrolyte, this application uses spatial separation to confine the polymerizable monomers to the positive electrode interface layer and the trigger source to the thermotropic acid release layer of the separator membrane. This allows the thermal response behavior to be more concentrated at the positive electrode-separator membrane interface, reducing the long-term free exposure of polymerizable monomers in the entire electrolyte and reducing direct disturbance to the electrolyte system under normal operating conditions. This also allows the thermally triggered gel to form more effectively on the critical contact path, rather than randomly gelling in the liquid phase.

[0063] In some embodiments, the dry film thickness of the polymerizable interface layer 40 is 0.1 μm to 10 μm, preferably 0.5 μm to 5 μm, and more preferably 1 μm to 3 μm; the dry film thickness of the thermotropic acid-releasing layer 50 is 0.1 μm to 3 μm, preferably 1 μm to 3 μm.

[0064] The thickness of the polymerizable interface layer 40 is set to 0.1 μm to 10 μm based on the dry film thickness. This thickness range ensures sufficient polymerizable monomer reserves on the positive electrode side facing the separator, allowing it to form a continuous or semi-continuous gel barrier layer at the positive electrode-separator interface after the release of acidic active centers from the thermo-release acid layer. This effectively blocks or delays direct contact between the positive and negative electrodes. If the polymerizable interface layer 40 is too thin, the polymerizable monomer reserves will be insufficient, making it difficult to form an effective gel barrier structure after thermal triggering. If the polymerizable interface layer 40 is too thick, it may increase the positive electrode interface transport resistance, affecting electrolyte wetting and lithium-ion transport, and leading to an increase in the initial impedance of the battery.

[0065] The thickness of the thermotropic acid layer 50, measured in dry film thickness, is set to 0.1 μm to 3 μm. When the thermotropic acid layer is disposed inside the separator, this thickness can be understood as its equivalent distribution thickness in the separator thickness direction. This thickness range ensures that the thermotropic acid component can release a sufficient amount of acidic active centers during abnormal temperature rise and trigger cationic polymerization and cross-linking gelation of polymerizable monomers on the positive electrode side across the interface. If the thickness of the thermotropic acid layer 50 is too thin, the release of acidic active centers will be insufficient, which may lead to inadequate interfacial polymerization triggering; if the thickness of the thermotropic acid layer 50 is too thick, it may block the pores of the separator, reduce the electrolyte retention capacity, and increase ion transport resistance, thereby affecting the conventional electrochemical performance of the battery.

[0066] [Aggregatable Interface Layer] The core function of the polymerizable interface layer 40 is to serve as a functional layer that rapidly forms a film after being triggered. Its core component is a polymerizable monomer, which can rapidly undergo cationic polymerization under the action of acidic active centers and crosslink while the chain grows, ultimately forming a gel-state or network-state polymer layer.

[0067] In some embodiments, the polymerizable monomer is a vinyl ether monomer, including one or more of monofunctional vinyl ether monomers, difunctional vinyl ether monomers, and polyfunctional vinyl ether monomers. This vinyl ether monomer can undergo rapid cationic polymerization under the action of acidic active centers, and due to its difunctional or polyfunctional structure, it can crosslink while the chain grows, ultimately forming a gel-like or network-like polymer layer.

[0068] In some embodiments, the monofunctional vinyl ether monomers include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, or triethylene glycol monovinyl ether, etc. Monofunctional vinyl ether monomers can be used to adjust the viscosity, flexibility, wettability, and polymerization rate of polymerizable interfacial layers, but their crosslinking ability is limited when used alone. Therefore, they are more preferably used in combination with difunctional or polyfunctional vinyl ether monomers.

[0069] In some embodiments, the difunctional vinyl ether monomers include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, neopentyl glycol divinyl ether, or cyclohexanediethanol divinyl ether, etc.

[0070] In some embodiments, the multifunctional vinyl ether monomers include trimethylolpropane trivinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, polyether-type vinyl ether oligomers containing three or more vinyl ether end groups, polyester-type vinyl ether oligomers containing three or more vinyl ether end groups, or polyurethane-type vinyl ether oligomers containing three or more vinyl ether end groups.

[0071] The aforementioned bifunctional or polyfunctional vinyl ether monomers, after being triggered by acidic active centers, are more conducive to the formation of cross-linked gel networks, thereby improving the continuity and mechanical support of the gel barrier layer at the positive electrode-separator interface.

[0072] As an example, the polymerizable monomer is triethylene glycol divinyl ether (TEGDVE), or a mixture of triethylene glycol divinyl ether and other crosslinking monomers.

[0073] In some embodiments, the content of the polymerizable monomer in the polymerizable interface layer 40 is 50% to 100% by mass fraction, preferably 50% to 90%. This high percentage of polymerizable monomer ensures the rapid formation of a sufficiently dense cross-linked gel network upon triggering by acidic active centers, resulting in a dense gel barrier layer. If the amount of polymerizable monomer in the polymerizable interface layer is too low, the amount of reactants that can participate in cationic polymerization and cross-linking gelation will be insufficient after the release of acidic active centers from the thermo-release acid layer. This may lead to discontinuous, insufficiently thick, or low-crosslinking density gel barrier layer formed at the positive electrode-separator interface, making it difficult to effectively block direct contact between the positive and negative electrode sheets when the separator experiences thermal shrinkage, melting, or localized failure. Simultaneously, when the amount of polymerizable monomer is too low, the relative proportions of binders, inorganic fillers, or other auxiliary components in the interface layer increase, potentially making the interface layer more like a common inert coating rather than an in-situ polymerized film layer triggered by abnormal temperatures, thereby reducing the response speed and film integrity of the cross-interface polymerization reaction.

[0074] As an example, the content of the polymerizable monomer in the polymerizable interface layer 40 is calculated by mass fraction as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, etc.

[0075] In some embodiments, the polymerizable interface layer 40 further comprises one or more of the following: a polymer binder, an inorganic filler, a polymer matrix, a high-pressure stabilizing agent, an interface stabilizer, and an auxiliary film-forming agent. The purpose of adding these auxiliary components is to fix or restrict the migration of polymerizable monomers at room temperature, reduce the disturbance of polymerizable monomers to the overall electrolyte system under normal operating conditions, provide a local enrichment environment for rapid polymerization under abnormal temperature conditions, and improve the adhesion and film uniformity of the polymerizable interface coating.

[0076] In some embodiments, the polymer binder includes polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), etc. By adding a polymer binder, liquid polymerizable monomers can be effectively controlled within the interfacial coating and firmly bonded to the surface of the positive electrode active material. This improves the adhesion and film integrity of the polymerizable interfacial layer on the positive electrode surface. Furthermore, at room temperature, it can fix and confine liquid or low-viscosity polymerizable monomers, reducing their free migration into the electrolyte liquid phase, thereby minimizing their disturbance to the electrolyte system and electrochemical interface under normal operating conditions. Simultaneously, an appropriate amount of polymer binder can improve the uniformity and mechanical stability of the coating, maintaining a locally enriched state of polymerizable monomers at the positive electrode-separator interface, providing conditions for rapid cationic polymerization and cross-linking gelation during abnormal temperature rises.

[0077] In some embodiments, the content of the polymer binder in the polymerizable interface layer 40 is 0% to 20% by mass fraction, preferably 3% to 20%. If the amount of polymer binder is too low, the adhesion and film-forming support of the polymerizable interface layer will be insufficient, which may lead to local discontinuity, powdering, cracking, or increased migration of polymerizable monomers in the coating, thereby affecting the formation position and integrity of the gel barrier layer after thermal triggering. If the amount of polymer binder is too high, it will reduce the effective content of polymerizable monomers in the interface layer, thereby reducing the amount of monomers that can participate in the polymerization reaction in the interface layer, which will affect the formation rate, continuity, and crosslinking density of the gel barrier layer during abnormal temperature rise. At the same time, an excessively high polymer binder content may also increase the positive electrode interface impedance, reduce electrolyte wettability and lithium-ion transport efficiency, and have an adverse effect on the conventional electrochemical performance of the battery.

[0078] As an example, the content of the polymer binder in the polymerizable interface layer 40 is calculated by mass fraction as 3%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%, etc.

[0079] In some embodiments, the inorganic filler includes inorganic ceramic particles such as alumina (Al2O3), titanium dioxide (TiO2), or boehmite. Adding inorganic fillers facilitates the formation of an organic-inorganic composite structure in the polymerizable interface layer. Under normal operating conditions, this provides microporous channels to maintain good liquid retention and ionic conductivity. Under abnormal operating conditions such as thermal abuse, it can form a composite barrier layer together with the in-situ generated cross-linked gel network, improving the high-temperature mechanical strength and physical puncture resistance of the gel barrier layer, including its heat resistance, dimensional stability, and anti-collapse ability. This helps to delay the direct contact between the positive and negative electrode sheets after the separator fails.

[0080] In some embodiments, the content of the inorganic filler in the polymerizable interface layer 40 is 0% to 30% by mass fraction. If the amount of inorganic filler is too low, its effect on enhancing the heat resistance, structural support, and preventing shrinkage and collapse of the gel barrier layer will be insignificant, and the interface barrier layer will mainly rely on the organic gel itself for support, which may result in insufficient mechanical stability at high temperatures. If the amount of inorganic filler is too high, it will reduce the effective content of polymerizable monomers in the interface layer, thereby reducing the monomer reserves that can participate in cationic polymerization and cross-linking gelation, which will affect the continuity and cross-linking density of the gel barrier layer. At the same time, an excessively high content of inorganic filler may also lead to increased coating brittleness, particle accumulation, pore blockage, or increased interfacial impedance, which will have an adverse effect on electrolyte wetting and lithium-ion transport.

[0081] As an example, the content of the inorganic filler in the polymerizable interface layer 40 is calculated by mass fraction as 1%, 2%, 3%, 5%, 8%, 10%, 15%, 20%, 25%, or 30%, etc.

[0082] In some embodiments, the polymer matrix includes polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyimide, polyacrylate polymers, or fluorinated acrylate polymers. Adding a polymer matrix helps to fix or confine liquid polymerizable monomers at room temperature, improving the integrity and adhesion stability of the coating and reducing the free migration of polymerizable monomers into the electrolytic liquid phase.

[0083] In some embodiments, the content of the polymer matrix in the polymerizable interface layer 40 is 0% to 30% by mass fraction. If the polymer matrix content is too low, the confinement and film-forming support of the polymerizable monomers will be insufficient; if the polymer matrix content is too high, it will reduce the effective proportion of the polymerizable monomers in the interface layer, affect the formation efficiency of the gel barrier layer during abnormal temperature rise, and may increase the interfacial impedance.

[0084] As an example, the content of the polymer matrix in the polymerizable interface layer 40 is calculated by mass fraction as 1%, 2%, 3%, 5%, 8%, 10%, 15%, 20%, 25%, or 30%, etc.

[0085] In some embodiments, the high-voltage stabilizing agent includes lithium phosphate, lithium metaphosphate, lithium pyrophosphate, lithium fluorophosphate, lithium difluorophosphate, lithium borate, lithium difluorooxalate borate, lithium bis(oxalate borate), tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, fluorophosphate compounds, or borate ester compounds. By adding a high-voltage stabilizing agent, a certain degree of interface stabilization, acidic byproduct buffering, or high-voltage side reaction suppression can be achieved at the high-potential interface of the positive electrode, which helps to reduce the adverse effects of the polymerizable interface layer on the electrochemical performance of the battery under normal operating voltage.

[0086] In some embodiments, the content of the high-pressure stabilizing agent in the polymerizable interface layer 40 is 0% to 10% by mass fraction. If the content of the high-pressure stabilizing agent is too low, the interface stabilizing effect will be insignificant; if the content of the high-pressure stabilizing agent is too high, it may occupy the proportion of polymerizable monomers, change the pore structure of the coating, or increase the interfacial transport resistance.

[0087] As an example, the content of the high-pressure resistant stabilizing agent in the polymerizable interface layer 40 is calculated by mass fraction as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc.

[0088] In some embodiments, the interface stabilizer includes lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorophosphate, lithium fluorophosphate, lithium phosphate, lithium borate, lithium sulfate, alumina, titanium dioxide, zirconium oxide, aluminum phosphate, or lithium aluminum titanium phosphate, etc. Adding an interface stabilizer helps improve the chemical and structural stability between the cathode surface and the polymerizable interface layer, reduces the risk of side reactions between the high-potential cathode surface and the electrolyte and polymerizable monomers, and also helps improve the bonding stability between the in-situ gel barrier layer and the cathode surface.

[0089] In some embodiments, the content of the interface stabilizer in the polymerizable interface layer 40 is 0% to 10% by mass fraction. If the content of the interface stabilizer is too high, it may reduce the proportion of polymerizable components in the interface layer and have an adverse effect on lithium-ion transport.

[0090] As an example, the content of the interface stabilizer in the polymerizable interface layer 40 is calculated by mass fraction as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc.

[0091] In some embodiments, the auxiliary film-forming agent includes polyvinylpyrrolidone, polyvinyl butyral, fluoroacrylate resins, polycarbonate polymers, or polyethylene glycol oligomers. Adding an auxiliary film-forming agent improves the leveling properties of the slurry, the continuity of the coating, and the integrity of the dry film during the coating process, enabling the polymerizable interface layer to form a more uniform thin-film structure on the positive electrode surface.

[0092] In some embodiments, the content of the auxiliary film-forming agent in the polymerizable interface layer 40 is 0% to 10% by mass fraction. If the content of the auxiliary film-forming agent is too low, its effect on improving film formation is limited; if the content of the auxiliary film-forming agent is too high, it will reduce the effective content of polymerizable monomers and increase the risk of coating liquid absorption swelling or increased interfacial resistance.

[0093] As an example, the content of the auxiliary film-forming agent in the polymerizable interface layer 40 is calculated by mass fraction as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc.

[0094] It should be noted that the aforementioned polymer matrix, high-pressure stabilizing agent, interface stabilizer, and film-forming aid are all optional auxiliary components. Their main function is to improve the film-forming stability, monomer confinement ability, high-potential interface stability of the polymerizable interface layer, and coating processing adaptability. In specific applications, they can be selectively added according to the cathode system, electrolyte system, coating thickness, and impedance requirements; they do not necessarily need to be added simultaneously. When the above components are used in combination, the mass fraction of polymerizable monomers in the polymerizable interface layer should be maintained within a range sufficient to form a gel barrier layer, preferably not less than 50%, to ensure sufficient cross-linking gel formation ability after abnormal temperature triggering.

[0095] [Thermotropic acid release layer] The core function of the thermo-release acid layer 50 is to act as an abnormal temperature trigger source. It introduces components that release acidic active centers upon heating. When the separator is heated on the side facing the positive electrode, these acidic active centers release and diffuse across the local interface region to the positive electrode interface coating, where they rapidly undergo cationic polymerization with polymerizable monomers. The acidic active centers can be protonic acids and / or Lewis acids.

[0096] The thermal activation window of the thermotropic acid release layer 50 is designed to be above the normal operating temperature and before or near the area of ​​significant risk of failure of the separator membrane. In some embodiments, the thermal activation temperature of the thermotropic acid release layer 50 is designed to be 90°C to 100°C, which enables the thermal triggering action to occur earlier than or simultaneously with the dangerous shrinkage stage of the separator membrane, thereby reserving a time window for in-situ film formation at the interface.

[0097] In some embodiments, the thermo-acid-releasing layer comprises a chemical thermo-acid-releasing agent, a thermo-acid-releasing polymer, or a physical phase change-type acid-releasing carrier.

[0098] In some embodiments, the thermo-acid-releasing layer comprises a chemical thermo-acid-releasing agent.

[0099] As an example, the chemically-based thermotropic acid-releasing agent includes amine-blocked p-toluenesulfonic acid (PTSA) or amine-blocked dinonylnaphthalenedisulfonic acid (DNNDSA) with a desealing temperature of 90°C to 100°C. For example, a complex salt is generated by reacting cyclohexylamine, diethanolamine, or a specific tertiary amine with p-toluenesulfonic acid or dinonylnaphthalenedisulfonic acid. This type of substance is neutral in the electrolyte at room temperature. When the battery is abnormally heated to the desealing temperature, its "amine-acid" bond breaks, releasing a highly reactive proton acid (H2O) in situ. + p-Toluenesulfonic acid or dinonylnaphthalenedisulfonic acid.

[0100] As an example, the chemically-induced thermogenic acid-releasing agents include diphenyliodonium hexafluorophosphate (DPI-PF6) or phenyl dimethylsulfonate trifluoromethanesulfonate. These substances decompose upon reaching a heating threshold, producing strong protic acids (H... +Hexafluorophosphate or trifluoromethanesulfonic acid can efficiently initiate the cationic polymerization reaction of the TEGDVE in the positive electrode interface coating.

[0101] In some embodiments, the thermo-acid-releasing layer comprises a thermo-acid-releasing polymer.

[0102] As an example, the thermotropic acid-releasing polymer includes polymers containing sulfonate structural units, sulfonate structural units, ammonium salt type sulfonate structural units, or onium salt type sulfonate structural units. These substances decompose upon reaching a heating threshold, producing strong protic acids (H+). + Sulfonic acid initiates a cationic polymerization reaction of the TEGDVE in the positive electrode interface coating.

[0103] In some embodiments, the thermotropic acid-releasing layer comprises a physical phase change acid-releasing carrier. The physical phase change acid-releasing carrier may be in the form of a dispersion, microcapsule, composite ceramic coating carrier, layered composite carrier, or other carrier forms.

[0104] As an example, the physical phase change acid-releasing carrier employs physical phase change acid-releasing microcapsules, which include an acid source core material and a thermosensitive wall material. The thermosensitive wall material comprises a polymeric phase change material with a melting point or softening temperature between 90°C and 100°C. When the battery abnormally heats up to its melting point or softening temperature, it undergoes a phase change and releases the internal acid source core material. The acid source core material comprises a Lewis acid complex or an organic solid acid. After the thermosensitive wall material undergoes a phase change, it can rapidly release active acid ions (H+). + ).

[0105] As an example, the polymer phase change material includes modified polyethylene wax (PE Wax), ethylene-vinyl acetate copolymer (EVA), or maleic anhydride grafted polyethylene (MAH-g-PE) with a melting point or softening temperature between 90°C and 100°C.

[0106] The modified polyethylene wax refers to polyethylene wax whose melting point or softening temperature falls between 90℃ and 100℃ through grafting modification, oxidation modification, introduction of polar groups, molecular weight control, crystallinity control, or blending modification, thereby improving its film-forming properties as a release film coating and its coating stability on acid source core materials. Examples include maleic anhydride-grafted polyethylene wax, oxidized polyethylene wax, carboxylated polyethylene wax, or EVA blended modified polyethylene wax.

[0107] The ethylene-vinyl acetate copolymer can have its melting point or DSC melting peak temperature in the range of 90°C to 100°C by adjusting the content of its vinyl acetate structural unit (VA), for example, by controlling the VA content to 9wt% to 12wt%.

[0108] As an example, the acid source core material is a Lewis acid complex, such as boron trifluoride-ethylamine complex (BF3·EA), boron trifluoride-ethyl ether complex, boron trifluoride-ethyl acetate complex, etc.

[0109] As an example, the acid source core material is an organic solid acid, such as methanesulfonic acid, p-toluenesulfonic acid, etc.

[0110] In some embodiments, the mass fraction of the chemically-based thermogenic acid-releasing agent or the physically-based phase-change acid-releasing carrier is 50% to 90% based on the total mass of the thermogenic acid-releasing layer.

[0111] In some embodiments, the thermotropic acid-releasing layer further comprises one or more of a binder, heat-resistant particles, and a pore structure modifier.

[0112] In some embodiments, the binder includes polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyimide, polyacrylate polymers, or fluorinated acrylate polymers. Adding a binder helps to stably fix chemically-induced thermotropic acid-releasing agents or physically-phase-change-type acid-releasing carriers on the positive electrode side of the separator, reducing the risk of acid-releasing components detaching, migrating, or prematurely releasing under normal operating conditions.

[0113] In some embodiments, the content of the binder in the thermotropic acid-releasing layer 50 is 1% to 20% by mass fraction. If the content of the binder is too low, the adhesion between the thermotropic acid-releasing layer and the separator will be insufficient, and the coating will easily shed powder or become discontinuous in some areas; if the content of the binder is too high, it may coat or block the acid-releasing components, reduce the release efficiency of acidic active centers during abnormal temperature rise, and may block the pores of the separator and increase the resistance to ion transport.

[0114] As an example, the content of the adhesive in the thermotropic acid-releasing layer 50 is calculated by mass fraction as 1%, 2%, 3%, 5%, 8%, 10%, 15%, 18%, or 20%, etc.

[0115] In some embodiments, the heat-resistant particles include alumina, boehmite, silica, titanium dioxide, zirconium oxide, barium sulfate, boron nitride, aluminum phosphate, or lithium titanium aluminum phosphate. Adding heat-resistant particles helps improve the dimensional stability and support of the thermotropic acid release layer during abnormal temperature rise, reduces the risk of overall shrinkage, collapse, or flow of the functional layer on the surface of the separator when heated, and helps maintain a certain porosity structure.

[0116] In some embodiments, the content of the heat-resistant particles in the thermo-acid-releasing layer 50 is 0% to 40% by mass fraction. If the content of the heat-resistant particles is too low, the heat-resistant support effect on the thermo-acid-releasing layer will be limited; if the content of the heat-resistant particles is too high, it may reduce the effective content of the acid-releasing component, weaken the ability to trigger the polymerization of polymerizable monomers on the positive electrode side, and increase the brittleness of the coating and the interfacial resistance.

[0117] As an example, the content of the heat-resistant particles in the thermotropic acid-releasing layer 50 is calculated by mass fraction as 1%, 2%, 3%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%, etc.

[0118] In some embodiments, the pore structure modifier includes polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, polyvinyl butyral, polyacrylate polymers, cellulose derivatives, ammonium bicarbonate, ammonium carbonate, volatile organic small molecule porogens, or extractable polymer particles. By adding the pore structure modifier, the porosity and pore connectivity of the thermo-released acid layer can be adjusted, allowing the electrolyte to effectively wet the separator and maintain lithium-ion transport channels, while also providing a pathway for the diffusion of acidic active centers to the positive electrode side during abnormal temperature rises.

[0119] In some embodiments, the content of the pore structure modifier in the thermo-acid-releasing layer 50 is 0% to 15% by mass fraction. If the content of the pore structure modifier is too low, its effect on improving the pore structure of the coating is limited; if the content of the pore structure modifier is too high, it may lead to excessively large pores or decreased structural strength in the thermo-acid-releasing layer, affecting the fixation stability of the acid-releasing components and the integrity of the coating.

[0120] As an example, the content of the pore structure modifier in the thermo-induced acid release layer 50 is calculated by mass fraction as 1%, 2%, 3%, 5%, 8%, 10%, 12%, or 15%, etc.

[0121] It should be noted that the aforementioned binder, heat-resistant particles, and pore structure modifier are all optional auxiliary components. Their main function is to improve the adhesion stability, heat-resistant structural stability, and pore connectivity of the thermotropic acid-releasing layer 50 on the surface of the separator membrane, without changing the core function of the thermotropic acid-releasing layer 50 as an abnormal temperature triggering source. When the above components are used in combination, the mass fraction of the thermotropic acid-releasing component should not be less than 50% to ensure that a sufficient amount of acidic active centers can be released during abnormal temperature rise to trigger cationic polymerization and cross-linking gelation of the polymerizable interfacial layer on the positive electrode side.

[0122] A second aspect of this application provides a method for preparing the secondary battery, comprising the following steps: coating a polymerizable interface layer 40 on the surface of the positive electrode 10 facing the separator 20; coating a thermotropic acid-releasing layer 50 on the surface of the separator 20 facing the positive electrode 10 or embedding a thermotropic acid-releasing layer inside the separator 20; assembling the treated positive electrode 10, separator 20 and negative electrode 30 in sequence, injecting electrolyte, and encapsulating to obtain the secondary battery.

[0123] In some embodiments, the coating includes coating processes such as slurry coating, printing coating, transfer coating, spraying, roller coating, and dip coating.

[0124] In some embodiments, the processed positive electrode, separator and negative electrode are assembled by stacking or winding.

[0125] The preparation method provided in this application, by setting a polymerizable interface layer on the side of the positive electrode sheet facing the separator, and setting a thermotropic acid-releasing layer on the side of the separator facing the positive electrode sheet or inside the separator, enables the polymerizable monomers and thermotropic acid-releasing components to remain spatially separated under normal operating conditions. This reduces the risk of premature contact and unexpected polymerization or acid-releasing side reactions between the two during battery preparation, electrolyte injection, formation, storage, and routine cycling. At the same time, setting the polymerizable interface layer and the thermotropic acid-releasing layer opposite each other during battery assembly facilitates the diffusion of acidic active centers released by the thermotropic acid-releasing layer across the interface along the positive electrode direction during abnormal temperature rise. This preferentially triggers cationic polymerization and cross-linking gelation of monomers in the polymerizable interface layer on the positive electrode side, so that the gel barrier layer is formed at the high-risk contact interface of the positive electrode and the separator, rather than randomly gelling in the electrolyte liquid phase. Therefore, the preparation method of this application is beneficial to improve the directionality of the functional layer arrangement and the accuracy of the response position. While minimizing the disturbance of normal electrochemical performance, it enhances the interface barrier capability and thermal safety response capability of the battery under abnormal operating conditions such as thermal abuse, local overheating or thermal shrinkage of the separator.

[0126] In some embodiments, the positive electrode sheet is prepared by coating a positive electrode active material 12 onto a positive electrode current collector 11.

[0127] As an example, the positive electrode current collector is aluminum foil, and the positive electrode active material may include any positive electrode active material that can be used in lithium batteries, including but not limited to layered lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate with olivine structure, and lithium manganese oxide with spinel structure.

[0128] In some embodiments, the negative electrode sheet is prepared by coating a negative electrode active material 32 onto a negative electrode current collector 31.

[0129] As an example, the negative electrode current collector is copper foil, and the negative electrode active material may include any negative electrode active material that can be used in lithium batteries, including but not limited to lithium metal, carbon-based negative electrode, silicon-based negative electrode or alloy negative electrode, etc.

[0130] In some embodiments, the electrolyte is a non-aqueous lithium salt solution.

[0131] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0132] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0133] Example 1 This embodiment provides a secondary battery, such as Figure 1 As shown, it includes a positive electrode 10, a separator 20 and a negative electrode 30, with the separator 20 disposed between the positive electrode 10 and the negative electrode 30; a polymerizable interface layer 40 is disposed on the surface of the positive electrode 10 facing the separator 20, and a thermotropic acid-releasing layer 50 is disposed on the surface of the separator 20 facing the positive electrode 10.

[0134] Positive electrode 10: Lithium nickel cobalt manganese oxide positive electrode active material (high nickel ternary positive electrode material LiNi) 0.8 Co 0.1 Mn 0.1 O2 (i.e., NCM811) and conductive agent, polyvinylidene fluoride are added to N-methylpyrrolidone in a mass ratio of 96:2:2 and mixed evenly to prepare a positive electrode slurry. The positive electrode slurry is then coated onto the positive electrode current collector aluminum foil 11 to form a 70μm thick positive electrode active material layer 12. After drying, cold pressing and slitting, the positive electrode sheet 10 is obtained.

[0135] Separator 20: A 20μm thick polyethylene porous membrane is selected as the separator 20. It should be noted that the separator 20 can be a polyethylene porous membrane, a polypropylene porous membrane, a polyethylene / polypropylene composite porous membrane, or a ceramic-coated separator.

[0136] Negative electrode sheet 30: Graphite negative electrode material, silicon-carbon negative electrode material, conductive agent, sodium carboxymethyl cellulose, and styrene-butadiene rubber are added to deionized water in a mass ratio of 90:5:1:1.5:2.5 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector copper foil 31 to form a 40μm thick negative electrode active material layer 32. After drying, cold pressing, and slitting, the negative electrode sheet 30 is obtained. It should be noted that the ratio of graphite negative electrode material to silicon-carbon negative electrode material can be adjusted according to the battery energy density, expansion control, and cycle performance requirements.

[0137] Polymerizable interface layer 40: Triethylene glycol divinyl ether (TEGDVE) is used as a polymerizable monomer and coated on one side surface of the positive electrode 10. The coating thickness is 2 μm based on the dry film thickness, forming a polymerizable interface layer 40.

[0138] Thermotropic acid-releasing layer 50: Modified polyethylene wax (PE Wax) with a melting point of 90℃~100℃ is used as the polymer phase change wall material, and boron trifluoride-ethylamine complex (BF3·EA) is used as the core material for the internal nucleic acid source. Thermotropic acid-releasing microcapsules are prepared by melt dispersion-cooling solidification method. Specifically, the wall material PE Wax is heated to 110~120℃ (10~20℃ higher than its melting point) to completely melt it, and the core material: wall material mass ratio is 1:3~1:5. BF3·EA core material was added and dispersed at high speed of 800~1200 rpm for 10~30 min under an inert atmosphere (N2) to form a uniform oil phase dispersion. The hot dispersion was then quickly poured into a cold medium at 5~10℃ and stirred continuously to allow the molten wall material to cool and solidify rapidly on the surface of the core material droplets into a shell. After filtration, washing and drying, core-shell type thermotropic acid-releasing microcapsules were obtained. The prepared thermotropic acid-releasing microcapsules were coated on one side of the isolation membrane 20 with a coating thickness of 1 μm based on the dry film thickness to form a thermotropic acid-releasing layer 50 with a thermal trigger temperature of 90℃.

[0139] Electrolyte: prepared by dissolving lithium hexafluorophosphate in ethylene carbonate, with a lithium hexafluorophosphate concentration of 1 mol / L.

[0140] The positive electrode 10 coated with a polymerizable interface layer 40, the separator 20 coated with a thermotropic acid-releasing layer 50, and the negative electrode 30 are stacked and assembled in the order of "positive electrode - separator - negative electrode", with the polymerizable interface layer 40 facing the separator 20 and the thermotropic acid-releasing layer 50 facing the positive electrode 10. Then, electrolyte is injected and the battery is encapsulated to obtain the secondary battery.

[0141] Example 2 This embodiment provides a secondary battery. Unlike embodiment 1, the polymerizable interface layer 40 is composed of triethylene glycol divinyl ether (TEGDVE, polymerizable monomer) and alumina (Al2O3, inorganic filler) in a mass ratio of 90:10. The remaining raw materials and preparation methods are the same as in embodiment 1.

[0142] Polymerizable interface layer 40: Triethylene glycol divinyl ether and alumina are mixed evenly in a mass ratio of 90:10 to form a polymerizable monomer slurry, which is then coated on one side surface of the positive electrode 10. The coating thickness is 2 μm based on the dry film thickness, forming a polymerizable interface layer 40.

[0143] Example 3 This embodiment provides a secondary battery. Unlike embodiment 1, the polymerizable interface layer 40 is composed of triethylene glycol divinyl ether (TEGDVE, polymerizable monomer), polyvinylidene fluoride (PVDF, polymer binder), and alumina (Al2O3, inorganic filler) in a mass ratio of 80:10:10. The remaining raw materials and preparation methods are the same as in embodiment 1.

[0144] Polymerizable interface layer 40: Triethylene glycol divinyl ether, polyvinylidene fluoride, and alumina are mixed evenly in a mass ratio of 80:10:10 to form a polymerizable monomer slurry, which is coated on one side surface of the positive electrode 10. The coating thickness is 2 μm based on the dry film thickness, thus forming a polymerizable interface layer 40.

[0145] Example 4 This embodiment provides a secondary battery. Unlike Embodiment 1, the polymerizable interface layer 40 is composed of triethylene glycol divinyl ether (TEGDVE, polymerizable monomer), polyvinylidene fluoride (PVDF, polymer binder), alumina (Al2O3, inorganic filler), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, polymer matrix), lithium difluorophosphate (high voltage stabilizing agent), lithium phosphate (interface stabilizer), and polyvinylpyrrolidone (film-forming aid) in a mass ratio of 70:8:10:6:2:2:2. The remaining raw materials and preparation methods are the same as in Embodiment 1.

[0146] Polymerizable interface layer 40: Triethylene glycol divinyl ether, polyvinylidene fluoride, alumina, polyvinylidene fluoride-hexafluoropropylene copolymer, lithium difluorophosphate, lithium phosphate and polyvinylpyrrolidone are mixed evenly in a mass ratio of 70:8:10:6:2:2:2 to form a polymerizable monomer slurry, which is coated on one side surface of the positive electrode 10. The coating thickness is 2 μm based on the dry film thickness, thus forming the polymerizable interface layer 40.

[0147] Example 5 This embodiment provides a secondary battery. Unlike embodiment 1, the thermally released acid layer 50 uses amine-blocked p-toluenesulfonic acid (PTSA) as the thermally released acid agent. The other raw materials and preparation methods are the same as in embodiment 1.

[0148] Thermotropic acid-releasing layer 50: Cyclohexylamine and p-toluenesulfonic acid undergo an acid-base complexation reaction to generate an amine-blocked p-toluenesulfonic acid complex salt as a thermotropic acid-releasing agent, which is coated on one side surface of the separator 20. The coating thickness is 1 μm based on the dry film thickness, forming the thermotropic acid-releasing layer 50.

[0149] Preparation of amine-blocked p-toluenesulfonic acid complex salt: Anhydrous p-toluenesulfonic acid was dissolved in anhydrous ethanol to form a p-toluenesulfonic acid solution; cyclohexylamine was dissolved in anhydrous ethanol to form a cyclohexylamine solution; the cyclohexylamine solution was slowly added dropwise to the p-toluenesulfonic acid solution under ice bath conditions, with a molar ratio of sulfonic acid groups to cyclohexylamine of 1:1.05, and the reaction was stirred for 6 h. Then the solvent was removed, and the solution was vacuum dried at 40℃~60℃ for 12 h to obtain the amine-blocked p-toluenesulfonic acid complex salt, whose thermal deblocking temperature was 90℃~100℃.

[0150] Example 6 This embodiment provides a secondary battery. Unlike embodiment 1, the thermotropic acid-releasing layer 50 uses diphenyliodonium hexafluorophosphate (DPI-PF6) as the thermotropic acid-releasing agent. The other raw materials and preparation methods are the same as in embodiment 1.

[0151] Thermotropic acid-releasing layer 50: Diphenyliodonium hexafluorophosphate is used as a thermotropic acid-releasing agent and coated on one side surface of the separator 20. The coating thickness is 1 μm based on the dry film thickness, forming the thermotropic acid-releasing layer 50.

[0152] Example 7 This embodiment provides a secondary battery. Unlike Embodiment 1, the thermotropic acid-releasing layer 50 is composed of thermotropic acid-releasing microcapsules, polyvinylidene fluoride-hexafluoropropylene copolymer (binder), alumina (heat-resistant particles), and polyvinylpyrrolidone (pore structure regulator) in a mass ratio of 70:8:18:4. The thermotropic acid-releasing microcapsules are prepared according to the preparation method of Embodiment 1, and the other raw materials and preparation methods are the same as those in Embodiment 1.

[0153] Thermotropic acid-releasing layer 50: Thermotropic acid-releasing microcapsules, polyvinylidene fluoride-hexafluoropropylene copolymer, alumina and polyvinylpyrrolidone are mixed evenly in a mass ratio of 70:8:18:4 to form a thermotropic acid-releasing slurry, which is then coated on one side of the separating membrane 20. The coating thickness is 1 μm based on the dry film thickness, thus forming the thermotropic acid-releasing layer 50.

[0154] Example 8 This embodiment provides a secondary battery. Unlike Embodiment 1, the polymerizable interface layer 40 uses tetraethylene glycol divinyl ether as a polymerizable monomer, and the thermo-acid-releasing layer 50 uses a thermo-acid-releasing polymer (thermal trigger temperature of 100°C) containing p-toluenesulfonate structural units as a thermo-acid-releasing agent. The remaining raw materials and preparation methods are the same as in Embodiment 1.

[0155] Comparative Example 1 This comparative example provides a conventional secondary battery, such as Figure 2 As shown, it includes a positive electrode 10, a separator 20 and a negative electrode 30, with the separator 20 disposed between the positive electrode 10 and the negative electrode 30.

[0156] Positive electrode 10: Lithium nickel cobalt manganese oxide positive electrode active material (high nickel ternary positive electrode material LiNi) 0.8 Co 0.1 Mn 0.1 O2 (i.e., NCM811) and conductive agent, polyvinylidene fluoride are added to N-methylpyrrolidone in a mass ratio of 96:2:2 and mixed evenly to prepare a positive electrode slurry. The positive electrode slurry is then coated onto the positive electrode current collector aluminum foil 11 to form a 70μm thick positive electrode active material layer 12. After drying, cold pressing and slitting, the positive electrode sheet 10 is obtained.

[0157] Separator 20: A 20μm thick polyethylene porous membrane is selected as the separator 20.

[0158] Negative electrode sheet 30: Graphite negative electrode material, silicon carbon negative electrode material, conductive agent, sodium carboxymethyl cellulose and styrene-butadiene rubber are added to deionized water in a mass ratio of 90:5:1:1.5:2.5 and mixed evenly to prepare a negative electrode slurry; then the negative electrode slurry is coated on the negative electrode current collector copper foil 31 to form a 40μm thick negative electrode active material layer 32, which is dried, cold pressed and slit to obtain the negative electrode sheet 30.

[0159] Electrolyte: prepared by dissolving lithium hexafluorophosphate in ethylene carbonate, with a lithium hexafluorophosphate concentration of 1 mol / L.

[0160] The positive electrode 10, the separator 20, and the negative electrode 30 are stacked and assembled in the order of "positive electrode - separator - negative electrode", then the electrolyte is injected and the battery is encapsulated to obtain the secondary battery.

[0161] Comparative Example 2 This comparative example provides a secondary battery. Unlike Comparative Example 1, the positive electrode 10 has a polymerizable interface layer 40 on the side facing the separator 20. The other raw materials and preparation methods are the same as those in Comparative Example 1.

[0162] Polymerizable interface layer 40: Triethylene glycol divinyl ether (TEGDVE) is used as a polymerizable monomer and coated on one side surface of the positive electrode 10. The coating thickness is 2 μm based on the dry film thickness, forming a polymerizable interface layer 40.

[0163] The positive electrode 10, separator 20 and negative electrode 30 coated with polymerizable interface layer 40 are stacked and assembled in the order of "positive electrode - separator - negative electrode", with the polymerizable interface layer 40 facing the separator 20. Then, electrolyte is injected and the battery is encapsulated to obtain the secondary battery.

[0164] Comparative Example 3 This comparative example provides a secondary battery. Unlike Comparative Example 1, the separator 20 has a thermotropic acid release layer 50 on the surface facing the positive electrode 10. The other raw materials and preparation methods are the same as those in Comparative Example 1.

[0165] Thermotropic acid-releasing layer 50: Modified polyethylene wax (PE Wax) with a melting point of 90℃~100℃ is used as the polymer phase change wall material, and boron trifluoride-ethylamine complex (BF3·EA) is used as the inner nucleic acid source core material. Thermotropic acid-releasing microcapsules are prepared by melt dispersion-cooling solidification method. The prepared thermotropic acid-releasing microcapsules are coated on one side surface of the isolation membrane 20. The coating thickness is 1μm based on the dry film thickness to form thermotropic acid-releasing layer 50, and its thermal triggering temperature is 90℃.

[0166] The positive electrode 10, the separator 20 coated with the thermotropic acid layer 50, and the negative electrode 30 are stacked and assembled in the order of "positive electrode - separator - negative electrode", with the thermotropic acid layer 50 facing the positive electrode 10. Then, electrolyte is injected and the battery is encapsulated to obtain the secondary battery.

[0167] Comparative Example 4 This comparative example provides a secondary battery. Unlike Comparative Example 1, the electrolyte contains triethylene glycol divinyl ether (TEGDVE) and diphenyliodonium hexafluorophosphate (DPI-PF6). The other raw materials and preparation methods are the same as those in Comparative Example 1.

[0168] Electrolyte: prepared by dissolving lithium hexafluorophosphate, triethylene glycol divinyl ether and diphenyliodonium hexafluorophosphate in ethylene carbonate, wherein the concentration of lithium hexafluorophosphate is 1 mol / L, the mass concentration of triethylene glycol divinyl ether is 2%, and the mass concentration of diphenyliodonium hexafluorophosphate is 1%.

[0169] Test case The secondary batteries prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to performance tests, and the test results are shown in Table 1 below.

[0170] Initial Coulombic Efficiency Test: The secondary batteries prepared in each example and comparative example were subjected to formation testing after being left to stand at 25±2℃. They were charged at a constant current of 0.05C to the set upper limit voltage, then charged at a constant voltage until the cutoff current was 0.02C, and finally discharged at a constant current of 0.05C to 2.5V. The initial charge capacity and initial discharge capacity were recorded. The initial Coulombic efficiency was calculated using the following formula: Initial coulombic efficiency = Initial discharge capacity / Initial charge capacity × 100%.

[0171] EIS Initial Interface Impedance Test: After formation, the secondary battery was adjusted to 0% SOC and allowed to stand at 25±2℃ for 2 hours. Then, an AC impedance test was performed using an electrochemical workstation. The test frequency range was 100kHz ~ 0.01Hz, and the AC disturbance voltage was 5mV. Based on the obtained Nyquist plot, an equivalent circuit was fitted, and the impedance values ​​in the mid-to-high frequency region related to the interface film impedance and charge transfer impedance were used as the EIS initial interface impedance. The EIS initial interface impedance is used to evaluate the influence of the polymerizable interface layer, the thermotropic acid-releasing layer, and their combined structures on the initial interface transport resistance of the battery.

[0172] 135℃ Hot Chamber Test: The rechargeable battery, having completed formation and fully charged, is placed in a hot chamber at 135℃ for 1 hour. During the test, the battery surface temperature, voltage changes, and the battery's appearance are recorded. If the battery does not catch fire, explode, or exhibit significant thermal runaway during the test, it is considered a Pass; if it does, it is considered a Fail. The 135℃ hot chamber test is used to evaluate the safety response capability of rechargeable batteries under thermal abuse conditions.

[0173] Cell electrode surface analysis after 100℃ disassembly: The formed secondary battery was placed in a 100℃ environment for 1 hour to allow the thermo-induced acid release layer to reach the acid release trigger temperature window. Subsequently, the battery was cooled to room temperature and disassembled in a dry environment or under an inert atmosphere to observe the morphological changes of the positive electrode facing the separator, the separator facing the positive electrode, and the positive electrode-separator interface region.

[0174] Table 1

[0175] As can be seen from the above test results, the secondary batteries prepared in Examples 1-8 can form an in-situ gel barrier layer across the interface between the positive electrode and the separator, blocking direct contact between the positive and negative electrodes, avoiding battery short circuits, and without affecting the overall electrochemical performance of the battery. Examples 2 and 3, by adding inorganic fillers to polymerizable monomers, can generate organic-inorganic composite gels, thereby enhancing the mechanical barrier effect of the gel barrier layer. Example 4, by adding a polymer matrix, high-pressure stabilizing agent, interface stabilizer, and film-forming agent to polymerizable monomers, can form a composite gel barrier layer with good continuity, improving the stability of the interface layer's bonding with the positive electrode surface. Examples 5, 6, and 8, using chemically-based thermotropic acid-releasing agents and thermotropic acid-releasing polymers, can also produce good thermotropic acid-releasing effects. Example 7, by adding binders, heat-resistant particles, and pore structure modifiers to thermotropic acid-releasing microcapsules, can form a composite thermally responsive barrier layer with good support. As can be seen from the test results of Comparative Examples 2 and 3, neither a polymerizable interface layer nor a thermotropic acid-releasing layer alone can trigger film formation at abnormal temperatures and thus cannot prevent battery short circuits. As can be seen from the test results of Comparative Example 4, adding polymerizable monomers and active acid sources to the electrolyte produces adverse electrochemical side reactions, thereby affecting the overall electrochemical performance of the battery.

[0176] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, include: A positive electrode, a separator, and a negative electrode are provided, wherein the separator is disposed between the positive electrode and the negative electrode; a polymerizable interface layer is provided on the surface of the positive electrode facing the separator, and a thermotropic acid-releasing layer is provided inside the separator or on the surface of the separator facing the positive electrode.

2. The secondary battery according to claim 1, characterized in that: The dry film thickness of the polymerizable interface layer is 0.1 μm to 10 μm, and the dry film thickness of the thermotropic acid-releasing layer is 0.1 μm to 3 μm.

3. The secondary battery according to claim 1, characterized in that: The polymerizable interface layer comprises polymerizable monomers; the polymerizable monomers include one or more of monofunctional vinyl ether monomers, difunctional vinyl ether monomers, and polyfunctional vinyl ether monomers; based on the total mass of the polymerizable interface layer, the mass fraction of the polymerizable monomers is 50% to 100%.

4. The secondary battery according to claim 3, characterized in that: The polymerizable interface layer further comprises one or more of the following: polymer binder, inorganic filler, polymer matrix, high-pressure stabilizing agent, interface stabilizer, and film-forming agent.

5. The secondary battery according to claim 4, characterized in that: The polymer binder comprises one or more of polyvinylidene fluoride, polymethyl methacrylate, and polyvinylidene fluoride-hexafluoropropylene copolymer; the mass fraction of the polymer binder is 0% to 20% based on the total mass of the polymerizable interface layer. The inorganic filler comprises one or more of alumina, titanium dioxide, boehmite, and inorganic ceramic particles; based on the total mass of the polymerizable interface layer, the mass fraction of the inorganic filler is 0% to 30%. The polymer matrix comprises one or more of the following: polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyimide, polyacrylate polymers, and fluorinated acrylate polymers; based on the total mass of the polymerizable interface layer, the mass fraction of the polymer matrix is ​​0% to 30%. The high-pressure stabilizing agent comprises one or more of the following: lithium phosphate, lithium metaphosphate, lithium pyrophosphate, lithium fluorophosphate, lithium difluorophosphate, lithium borate, lithium difluorooxalate borate, lithium bis(oxalate borate), tris(trimethylsilyl)phosphate, tris(trimethylsilyl)boronic acid ester, fluorophosphate compounds, and borate ester compounds; based on the total mass of the polymerizable interface layer, the mass fraction of the high-pressure stabilizing agent is 0% to 10%. The interface stabilizer comprises one or more of lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorophosphate, lithium fluorophosphate, lithium phosphate, lithium borate, lithium sulfate, alumina, titanium dioxide, zirconium oxide, aluminum phosphate, and lithium aluminum titanium phosphate; based on the total mass of the polymerizable interface layer, the mass fraction of the interface stabilizer is 0% to 10%; The auxiliary film-forming agent includes one or more of polyvinylpyrrolidone, polyvinyl butyral, fluoroacrylate resins, polycarbonate polymers, and polyethylene glycol oligomers; the mass fraction of the auxiliary film-forming agent is 0% to 10% based on the total mass of the polymerizable interface layer.

6. The secondary battery according to claim 1, characterized in that: The thermally released acid layer contains acidic active centers of protic acids and / or Lewis acids; the thermal activation temperature of the thermally released acid layer is 90℃~100℃.

7. The secondary battery according to claim 6, characterized in that: The thermotropic acid-releasing layer comprises a chemical thermotropic acid-releasing agent, a thermotropic acid-releasing polymer, or a physical phase change type acid-releasing microcapsule; based on the total mass of the thermotropic acid-releasing layer, the mass fraction of the chemical thermotropic acid-releasing agent, the thermotropic acid-releasing polymer, or the physical phase change type acid-releasing microcapsule is 50% to 90%.

8. The secondary battery according to claim 7, characterized in that: The chemically-based thermotropic acid-releasing agent includes one or more of the following: amine-blocked p-toluenesulfonic acid, amine-blocked dinonylnaphthalene disulfonic acid, diphenyliodonium hexafluorophosphate, and phenyl dimethylsulfonate trifluoromethanesulfonate. The thermo-acid-releasing polymer includes polymers containing sulfonate structural units, sulfonate structural units, ammonium salt type sulfonate structural units, or onium salt type sulfonate structural units; The physical phase change type acid-releasing microcapsule includes an acid source core material and a thermosensitive wall material. The acid source core material includes Lewis acid complexes or organic solid acids. The thermosensitive wall material includes one or more of the following: modified polyethylene wax, ethylene-vinyl acetate copolymer, and maleic anhydride grafted polyethylene, with a melting point or softening temperature of 90℃~100℃.

9. The secondary battery according to claim 8, characterized in that: The thermo-acid-releasing layer also includes one or more of the following: binder, heat-resistant particles, and pore structure modifier. The adhesive comprises one or more of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyimide, polyacrylate polymers, and fluorinated acrylate polymers; based on the total mass of the thermotropic acid-releasing layer, the mass fraction of the adhesive is 1% to 20%. The heat-resistant particles comprise one or more of the following: alumina, boehmite, silica, titanium dioxide, zirconium oxide, barium sulfate, boron nitride, aluminum phosphate, and lithium titanium aluminum phosphate; based on the total mass of the thermally released acid layer, the mass fraction of the heat-resistant particles is 0% to 40%. The pore structure modifier includes one or more of the following: polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, polyvinyl butyral, polyacrylate polymers, cellulose derivatives, ammonium bicarbonate, ammonium carbonate, volatile organic small molecule porogens, and extractable polymer particles; the mass fraction of the pore structure modifier is 0% to 15% based on the total mass of the thermo-released acid layer.

10. A method for preparing the secondary battery according to any one of claims 1 to 9, characterized in that, The process includes the following steps: coating a polymerizable interface layer on the surface of the positive electrode facing the separator; coating a thermotropic acid-releasing layer on the surface of the separator facing the positive electrode or embedding a thermotropic acid-releasing layer inside the separator; assembling the treated positive electrode, separator, and negative electrode in sequence, injecting electrolyte, and encapsulating to obtain the secondary battery.

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