Gradient composite solid electrolyte, preparation method and in-situ interface repair structure

Abstract

The invention provides a gradient composite solid electrolyte, a preparation method and an in-situ interface repair structure, and belongs to the field of semi-solid / solid-liquid hybrid power batteries. The gradient composite solid electrolyte comprises a flexible polymer layer, a composite layer and a nano-porous layer, the composite layer is located between the flexible polymer layer and the nano-porous layer, and the Young modulus of the flexible polymer layer, the Young modulus of the composite layer and the Young modulus of the nano-porous layer are sequentially increased in a gradient mode. By adopting the gradient increasing design of Young modulus of the flexible layer, the composite layer and the nano porous layer, the thermal expansion coefficient of the structure is matched with that of a silicon negative electrode and a high-nickel positive electrode, so that the cyclic stress dispersion efficiency is improved, and the expansion of interface cracks is effectively inhibited; and finally, the problem of interface failure caused by dynamic stress mismatch between the composite solid electrolyte and the electrode in the semi-solid / solid-liquid hybrid power battery is solved.

Description

Technical Field

[0001] The present application relates to the technical field of semi-solid / solid-liquid hybrid batteries, and in particular to a gradient composite solid electrolyte, a preparation method thereof, and an in-situ interface repair structure. Background Art

[0002] In order to alleviate the anxiety of pure electric vehicle range, the development of high-energy-density power batteries focuses on "NCM9 series high nickel cathode + SiO x / C silicon-based anode system", its theoretical energy density can exceed 400Wh / kg, meeting the demand for long-term battery life. However, this system faces serious interface failure problems in semi-solid / solid-liquid hybrid batteries, accounting for more than 60% of the industrial bottleneck.

[0003] In the existing technology, a flexible electrolyte membrane is formed by compounding polymers and inorganic ceramic particles, but there are many problems, such as the inability to match the dynamic volume expansion of the silicon negative electrode, interfacial side reactions, etc., and the lack of coordinated regulation of the electrode-electrolyte interface. Summary of the Invention

[0004] The present application provides a gradient composite solid electrolyte and its preparation method, as well as an in-situ interface repair structure, to solve the interface failure problem caused by dynamic stress mismatch between the composite solid electrolyte and the electrodes of the semi-solid / solid-liquid hybrid battery of the "NCM9 series high nickel positive electrode + SiOx / C silicon-based negative electrode system".

[0005] In a first aspect, an embodiment of the present application provides a gradient composite solid electrolyte, comprising:

[0006] flexible polymer layers, composite layers, and nanoporous layers;

[0007] The composite layer is located between the flexible polymer layer and the nanoporous layer, and Young's moduli of the flexible polymer layer, the composite layer and the nanoporous layer increase in a gradient.

[0008] Optionally, the Young's modulus of the flexible polymer layer is 0.2 GPa to 0.4 GPa, and / or,

[0009] The Young's modulus of the composite layer is 4 GPa to 6 GPa, and / or

[0010] The Young's modulus of the nanoporous layer is 7 GPa to 9 GPa.

[0011] Optionally, the thickness of the flexible polymer layer is 4 μm to 6 μm, and / or,

[0012] The thickness of the composite layer is 12 μm to 18 μm, and / or

[0013] The thickness of the nanoporous layer is 8 μm to 12 μm.

[0014] Optionally, the flexible polymer layer includes the following performance parameters: an ionic conductivity of 0.5×10 -3 S / cm~1.5×10 -3 S / cm, porosity of 5% to 10%, thermal decomposition temperature of 310°C to 330°C, and / or,

[0015] The composite layer has the following performance parameters: the ionic conductivity at 25°C is 1.5×10 -3 S / cm~2.5×10 - 3 S / cm, porosity of 9% to 11%, thermal decomposition temperature of 330°C to 450°C, and / or,

[0016] The nanoporous layer has the following performance parameters: porosity ≥ 60%, and thermal decomposition temperature ≥ 1000°C.

[0017] Optionally, the material of the flexible polymer layer includes a copolymer matrix material, a reinforcing material, an elastomer and a lithium salt; and / or,

[0018] The material of the composite layer includes an inorganic electrolyte, a polymer matrix and a lithium salt; and / or,

[0019] The material of the nanoporous layer includes nanoporous material.

[0020] Optionally, the matrix material includes a fluorine-containing polymer or a high-pressure-resistant polymer, and / or,

[0021] The reinforcing material comprises a fluorinated elastomer or a hydrogenated styrene elastomer, and / or,

[0022] The elastomer includes hydrogenated styrene elastomer, fluorinated elastomer or acrylic rubber.

[0023] Optionally, the inorganic electrolyte includes one or a combination of at least two of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide or lithium phosphorus sulfur chloride, and / or,

[0024] The polymer matrix comprises one or a combination of at least two of polyethylene oxide, polypropylene oxide or polycaprolactone, and / or,

[0025] The lithium salt includes one or a combination of at least two of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, or lithium dioxalatoborate.

[0026] Optionally, the nanoporous material includes one or a combination of at least two of SiO2, Al2O3 or ZrO2.

[0027] In a second aspect, the present application provides an in-situ interface repair structure comprising thermally responsive microcapsules, wherein the thermally responsive microcapsules are embedded in the composite layer of the gradient composite solid electrolyte described in any one of the embodiments of the first aspect.

[0028] Optionally, it is characterized in that the thermally responsive microcapsules comprise a shell material and a core material, and the thermal response temperature of the thermally responsive microcapsules is 60°C to 80°C.

[0029] Optionally, the shell material is one or a combination of at least two of polydopamine, thermoplastic polyurethane or polycaprolactone.

[0030] Optionally, the shell material has a thickness of 40 nm to 60 nm.

[0031] Optionally, the core material includes one or a combination of at least two of acrylate or polyether oligomers, and the molecular weight of the acrylate or polyether oligomer is 300Da to 500Da.

[0032] Optionally, the core material includes the following performance parameters: viscosity ≤ 100 mPa·s, Li + The conductivity of the conductive network at 25℃ is ≥1×10 -4 S / cm.

[0033] Optionally, the particle size of the thermoresponsive microcapsules is 200 nm to 500 nm, and / or,

[0034] The mass of the thermal response microcapsules is 1% to 5% of the total mass of the composite layer.

[0035] Optionally, the thermally responsive microcapsules include the following performance parameters: crack filling rate ≥ 90%, and electrical conductivity after repair is restored to 85% of the initial value.

[0036] In a third aspect, the present application provides a method for preparing the gradient composite solid electrolyte according to any embodiment of the first aspect, comprising:

[0037] Preparation of nanoporous layers by sol-gel method;

[0038] depositing a composite layer slurry on the nanoporous layer by electrospinning, wherein the composite layer slurry comprises an inorganic electrolyte, a polymer matrix, and a lithium salt;

[0039] A slurry of a flexible polymer layer is deposited on the composite layer by an electrostatic spinning method. The slurry of the flexible polymer layer comprises a copolymer matrix material, a reinforcing material, an elastomer and a lithium salt.

[0040] Optionally, in the slurry of the flexible polymer layer, the mass fraction of the solute is 10% to 20%; in the slurry of the composite layer, the mass fraction of the solid component is 35% to 45%.

[0041] Optionally, thermal responsive microcapsules are embedded in the slurry of the composite layer by ultrasonic dispersion, and / or,

[0042] An aminosilane coupling agent is introduced into the surface of the nanoporous layer for interface modification to enhance the bonding force between the nanoporous layer and the composite layer.

[0043] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0044] The embodiment of the present application provides a gradient composite solid electrolyte, which comprises: a flexible polymer layer, which is composed of a copolymer matrix material, a reinforcing material, an elastomer and a lithium salt; a composite layer, which is composed of an inorganic electrolyte, a polymer matrix and a lithium salt; and a nanoporous layer, which is composed of a nanoporous material. The composite layer is located between the flexible polymer layer and the nanoporous layer, and the Young's modulus of the flexible polymer layer, the composite layer and the nanoporous layer increases in a gradient. First, by designing the Young's modulus of the flexible layer, the composite layer and the nanoporous layer to increase in a gradient, a match with the thermal expansion coefficient of the silicon negative electrode and the high nickel positive electrode is achieved, thereby improving the cyclic stress dispersion efficiency and suppressing the expansion of interface cracks. At the same time, the elastomer absorbs the expansion stress of the silicon negative electrode, prevents mechanical failure, and ensures the stability of the interface impedance after cycling; secondly, the synergistic effect of the inorganic electrolyte and the polymer matrix forms a continuous conductive network with high overall conductivity, supporting high-rate charge and discharge. At the same time, the compatibility of fluoropolymers with NCM9-based positive electrodes inhibits the dissolution of transition metals; secondly, the nanoporous material has high porosity and high thermal decomposition temperature, and exhibits non-combustible and non-explosive properties in the needle puncture test. At the same time, the excellent high-temperature stability of lithium salts inhibits the excessive growth of SEI film, has a high ion migration number, and effectively inhibits dendrite penetration; finally, the polymer matrix wets the inorganic particles, reduces the grain boundary impedance, and improves the ion transfer efficiency. At the same time, the top layer of fluoropolymer has antioxidant properties, the bottom layer of SiO2 is compatible with the silicon negative electrode, and the middle layer of LLZO / PEO interface is passivated, which inhibits side reactions. This design effectively solves the problem of "NCM9-based high nickel positive electrode + SiO x The interfacial failure problem caused by dynamic stress mismatch between the composite solid electrolyte and the electrode of the semi-solid / solid-liquid hybrid battery with " / C silicon-based anode system" is studied. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0046] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0047] Figure 1 A schematic structural diagram of a gradient composite solid electrolyte provided in an embodiment of the present application;

[0048] Figure 2 A schematic flow chart of a method for preparing a gradient composite solid electrolyte provided in an embodiment of the present application;

[0049] Reference numerals:

[0050] 1-flexible polymer layer, 2-composite layer, 3-nanoporous layer, 4-thermoresponsive microcapsule, 41-shell material, 42-core material. DETAILED DESCRIPTION

[0051] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0052] The range descriptions described in this article, such as numerical ranges, ratio ranges, etc., include all possible sub-ranges and single numerical values ​​within the range. For example, the range description of "1 to 6" or "1~6" covers all sub-ranges from 1 to 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including", "comprising", etc. used in this article mean "including but not limited to"; relational terms such as "first" and "second" are only used to distinguish different entities or operations, and do not imply an actual sequence or association relationship; "and / or" means that multiple situations can exist alone or at the same time; expressions such as "at least one", "multiple", and "at least one" refer to any combination of corresponding objects, including a combination of single or multiple objects. The proportional relationships involved in the article, such as mass ratios, molar ratios, etc., should be understood as the corresponding relationship between the first and second terms of the proportional formula in the order of description. The raw materials, reagents, instruments and equipment used in this article can be purchased on the market or prepared by existing methods.

[0053] The gradient composite solid electrolyte of this application has the advantages of gradient modulus matching electrode expansion coefficient, high ionic conductivity and electrochemical compatibility, thermal stability and safety, material synergy and functional complementarity. The in-situ interface repair structure has the advantages of precise thermal triggering and active repair mechanism, efficient crack repair and conductivity recovery, collaborative design of materials and structures, process adaptation and industrialization potential, and dual improvement of safety and economy. The preparation method has shown significant advantages in the precise preparation of nanoporous layers, improvement of interfacial bonding strength, optimized design of composite layers, enhancement of flexible polymer layers, precise control of process parameters and improvement of safety.

[0054] Figure 1 A schematic structural diagram of a gradient composite solid electrolyte provided in an embodiment of the present application.

[0055] like Figure 1 As shown, the present application provides a gradient composite solid electrolyte, comprising:

[0056] The flexible polymer layer 1, the composite layer 2 and the nanoporous layer 3 comprise nanoporous materials;

[0057] The composite layer 2 is located between the flexible polymer layer 1 and the nanoporous layer 3 , and the Young's moduli of the flexible polymer layer 1 , the composite layer 2 and the nanoporous layer 3 increase in a gradient.

[0058] In some embodiments, the material of the flexible polymer layer 1 includes a copolymer matrix material, a reinforcing material, an elastomer and a lithium salt; and / or,

[0059] The material of the composite layer 2 includes an inorganic electrolyte, a polymer matrix and a lithium salt; and / or,

[0060] The material of the nanoporous layer 3 includes nanoporous material.

[0061] In some embodiments, the matrix material comprises a fluoropolymer or a high pressure polymer, and / or,

[0062] The reinforcing material comprises a fluorinated elastomer or a hydrogenated styrene elastomer, and / or,

[0063] The elastomer includes hydrogenated styrene elastomer, fluorinated elastomer or acrylic rubber.

[0064] It should be noted that fluoropolymers (such as PTFE, FEP, and PVDF) are resistant to chemical corrosion (strong acids, strong bases, and organic solvents), high temperature resistance (200°C to 260°C), have low friction coefficients, and excellent electrical insulation. High-pressure polymers (such as PEEK, PI, and PPS) offer high strength, creep resistance, fatigue resistance, and excellent stability in high-pressure environments (>50MPa).

[0065] In some embodiments, the inorganic electrolyte includes one or a combination of at least two of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, or lithium phosphorus sulfur chloride, and / or,

[0066] The polymer matrix comprises one or a combination of at least two of polyethylene oxide, polypropylene oxide or polycaprolactone, and / or,

[0067] The lithium salt includes one or a combination of at least two of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, or lithium dioxalatoborate.

[0068] Among inorganic electrolytes, lithium aluminum titanium phosphate (LATP) has an ionic conductivity of 0.1mS / cm to 1mS / cm (at 25°C) and an oxidation stability of >4.5V, making it suitable for high-voltage positive electrodes but requiring avoidance of direct contact with lithium metal. The cubic phase structure of lithium lanthanum zirconium oxide (LLZO) has an ionic conductivity >1mS / cm and thermal stability >800°C. Lithium phosphorus sulfur chloride (Li6PS5Cl) is a sulfide electrolyte with an ionic conductivity >3mS / cm at room temperature.

[0069] Within the polymer matrix, polyethylene oxide (PEO) has a low glass transition temperature (Tg) (-60°C) and strong chain segment mobility. Polypropylene oxide (PPO) has a thermal decomposition temperature >300°C and offers superior oxidation resistance compared to PEO. Polycaprolactone (PCL) is a biodegradable material with excellent flexibility, making it suitable for flexible composite layers.

[0070] Among lithium salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) has a high degree of dissociation (ion pair concentration <20%) and a thermal decomposition temperature >300°C, making it compatible with polymer matrices. Lithium bis(fluorosulfonyl)imide (LiFSI) has an ion transference number >0.5 and is effective in inhibiting lithium dendrites, but hygroscopicity must be controlled. Lithium difluorooxalatoborate (LiDFOB) has excellent high-temperature stability (decomposition temperature >250°C), is compatible with silicon anodes, and inhibits excessive SEI film growth.

[0071] In some embodiments, the nanoporous material includes one or a combination of at least two of SiO 2 , Al 2 O 3 , or ZrO 2 .

[0072] Among nanoporous materials, SiO2 has a porosity of >60%, is chemically inert, and can absorb electrolyte decomposition products (such as Li2O) and inhibit interface side reactions. Al3O3 has a high specific surface area (>200m 2 / g), with a thermal decomposition temperature >1000°C, which can improve the thermal stability of the interface. ZrO2 has strong acid corrosion resistance and is compatible with sulfide electrolyte systems, preventing interfacial sulfide decomposition.

[0073] In some embodiments, the fluorine-containing polymer includes one or a combination of at least two of polyvinylidene fluoride, polyperfluoroethylene propylene, or polytetrafluoroethylene.

[0074] It should be noted that among fluoropolymers, polyvinylidene fluoride (PVDF) has high crystallinity and excellent mechanical strength, but needs to be copolymerized with HFP (PVDF-HFP) to improve flexibility and ionic conductivity, and is suitable for flexible polymer layer matrices. Polyperfluoroethylene propylene (PFA) has excellent chemical corrosion resistance, an oxidation potential of >5.0V, is compatible with NCM9 series positive electrodes, and is suitable for high-voltage scenarios. Polytetrafluoroethylene (PTFE) is chemically inert and has a thermal decomposition temperature of >400°C, and is used to enhance interface stability.

[0075] In some embodiments, the high voltage-resistant polymer includes: polyarylethersulfone or polyimide, or a combination of at least two thereof.

[0076] Among high-voltage polymers, polyarylethersulfone (PES) boasts a glass transition temperature (Tg) greater than 220°C, offering high-temperature resistance and mechanical strength, making it suitable for high-voltage cathode applications. Polyimide (PI) has a thermal decomposition temperature greater than 500°C and excellent creep resistance, making it suitable for long-term cycling in high-temperature environments.

[0077] In some embodiments, the fluorinated elastomer includes one or a combination of at least two of polyvinylidene fluoride, hexafluoropropylene, and fluorosilicone rubber.

[0078] Among fluorinated elastomers, polyvinylidene fluoride (PVDF) combines flexibility and chemical resistance, with an elastic modulus of 50MPa to 200MPa, and is used to absorb the expansion stress of the silicon anode. Fluorosilicone rubber (FKM) can withstand high temperatures (decomposition temperature > 300°C) and inhibit interfacial crack propagation.

[0079] In some embodiments, the hydrogenated styrene-based elastomer includes one or a combination of at least two of a hydrogenated styrene-butadiene block copolymer, a hydrogenated styrene-isoprene-styrene block copolymer, and a hydrogenated styrene-butadiene-isoprene-styrene block copolymer.

[0080] Among hydrogenated styrene elastomers, SEBS (styrene-ethylene-butylene-styrene) achieves double bond saturation after hydrogenation, resulting in excellent aging resistance and an elastic modulus of 50 MPa to 200 MPa, making it suitable for stress buffering in flexible layers. SEPS (styrene-ethylene-propylene-styrene) offers enhanced flexibility (Tg < -50°C) and suppresses low-temperature brittleness. The multi-block structure of SEEPS (styrene-ethylene-ethylene-propylene-styrene) balances mechanical strength and elasticity, making it suitable for complex stress environments.

[0081] This gradient composite solid electrolyte solves the dynamic stress mismatch problem of the "NCM9 system + SiOx / C" system through the coordinated design of modulus gradient and functional gradient. The parameter range of each layer (such as Young's modulus, thickness, and porosity) has been verified by thermodynamics and electrochemistry, optimizing stress buffering, ion transport, and interface stability, providing an innovative solution for the industrialization of high-energy-density power batteries. Specifically, the functions of each layer are as follows:

[0082] The flexible polymer layer comprises a copolymer matrix material, a reinforcing material, an elastomer and a lithium salt. Among them, the copolymer matrix material and the reinforcing material can be a copolymer. The CF bond oxidation potential of the fluorinated polymer (such as PVDF-HFP) is greater than 5.0V, which is compatible with the NCM9 series high-voltage positive electrode and inhibits the dissolution of transition metals. At the same time, the solution casting method can form a uniform film (4-6μm) to reduce the interfacial impedance. The elastic modulus of the reinforcing material (fluorinated elastomer / hydrogenated styrene elastomer) is 50MPa to 200MPa, which absorbs the expansion stress of the silicon negative electrode and prevents crack propagation. At the same time, the thermal decomposition temperature is greater than 300℃ to ensure high-temperature cycle stability. The anion dissociation degree of the lithium salt (such as LiFSI / LiTFSI) is greater than 80%, which increases the ion migration number. The lithium salt (LiFSI) forms a continuous ion channel with the polymer matrix, and the ionic conductivity at 25℃ is 0.5×10 -3 S / cm~1.5×10 -3 S / cm, meeting basic needs.

[0083] The composite layer includes an inorganic electrolyte, a polymer matrix and a lithium salt. The LLZO and LATP of the inorganic electrolyte (such as LLZO / LATP / Li6PS5Cl) form a continuous fast ion channel. At the same time, the Young's modulus of 4GPa to 6GPa matches the expansion stress of the silicon negative electrode to prevent modulus mutation. The Tg of the polymer matrix (such as PEO / PPO / PCL) is less than room temperature, wets the inorganic particles (contact angle <30°), and reduces the grain boundary impedance. The lithium salt (such as LiFSI / LiDFOB) and the inorganic electrolyte synergistically improve the ion migration efficiency, and the dissociation degree is >80%.

[0084] Composite layer: The inorganic electrolyte provides high ionic conductivity, while the polymer matrix wets the inorganic particle interface, forming a continuous conductive network. The Young's modulus of 4GPa to 6GPa lies between the flexible layer and the nanoporous layer, preventing stress concentration caused by sudden changes in the modulus while dissipating residual stress from silicon anode expansion.

[0085] The nanoporous layer comprises a nanoporous material. The nanoporous material (e.g., SiO2 / Al2O3 / ZrO2) has a porosity of ≥60%, which disperses residual stress through capillary action and reduces the risk of interfacial cracks. At the same time, the nanoporous material has a rigid structure (Young's modulus 7GPa to 9GPa) that inhibits lithium dendrite penetration. Furthermore, the thermal decomposition temperature of SiO2 is ≥1000°C, preventing thermal runaway.

[0086] Nanoporous layer: High-porosity (≥60%) nanoporous material disperses residual stress through its pore structure, while simultaneously preventing lithium deposition and dendrite penetration from the silicon anode. Thermal decomposition temperature ≥1000°C prevents interfacial collapse under thermal runaway.

[0087] Interlayer synergistic mechanism: the modulus gradient of the top layer (such as 0.3GPa) → the middle layer (such as 5GPa) → the bottom layer (such as 8GPa) and the thermal expansion coefficient of the electrode (such as the positive electrode 1.5×10 -5 / ℃, negative electrode 2×10 -5 / °C) creates a thermal-mechanical match, reducing interfacial stress accumulation during cycling. Simultaneously, the silicon anode expands stress, which is absorbed by the elastic deformation of the flexible layer; the rigid support of the intermediate layer disperses residual stress, which is then absorbed by the porous structure of the underlying layer. A "low-high-resistance" gradient is formed from the flexible layer (low conductivity) to the intermediate layer (high conductivity) to the underlying layer (insulating), preferentially guiding ions to transport through the fast channels in the intermediate layer, reducing overall impedance. Furthermore, the dissociation degree of the LiFSI lithium salt in the intermediate layer exceeds 80%, significantly improving the ion transference number. Furthermore, the PEO matrix (Tg < room temperature) in the intermediate layer wets the inorganic particles (such as LLZO), reducing grain boundary impedance (contact angle < 30°) and improving ion transport efficiency. Furthermore, the antioxidant properties of the top fluoropolymer (>5.0V) protect the cathode interface, and post-cycling EIS analysis shows stable interfacial impedance. The underlying SiO2 reacts with the SiOx / C anode without side effects, inhibiting excessive SEI film growth.

[0088] In some embodiments, the Young's modulus of the flexible polymer layer is 0.2 GPa to 0.4 GPa, and / or,

[0089] The Young's modulus of the composite layer is 4 GPa to 6 GPa, and / or

[0090] The Young's modulus of the nanoporous layer is 7 GPa to 9 GPa.

[0091] It's important to note that Young's modulus is a physical quantity that characterizes a material's resistance to tension or compression within its elastic limits and depends solely on the material's physical properties. The magnitude of the Young's modulus indicates the material's rigidity; a larger Young's modulus indicates a material's resistance to deformation.

[0092] The Young's modulus of the flexible polymer layer is limited to 0.2GPa~0.4GPa. The modulus range of the flexible polymer layer is lower than the expansion stress of the silicon negative electrode. It absorbs more than 50% of the dynamic stress through elastic deformation to avoid crack propagation. At the same time, it can balance the flexibility and mechanical support requirements. The Young's modulus of the composite layer is between the flexible layer and the rigid nanoporous layer, avoiding stress concentration caused by modulus mutation. The modulus of inorganic electrolytes (such as LLZO) is usually 100GPa~200GPa, but the overall modulus is reduced after being compounded with polymers to match the expansion characteristics of the silicon negative electrode. The high modulus of the nanoporous layer provides rigid support to prevent structural collapse caused by the expansion of the silicon negative electrode. The modulus of nanoporous materials (such as SiO2) can reach 70GPa, but a porosity ≥60% will reduce the actual modulus to 7GPa~9GPa, balancing stress adsorption and rigidity requirements. Exemplarily, the Young's modulus of the flexible polymer layer can be 0.2 GPa, 0.25 GPa, 0.3 GPa, 0.35 GPa, 0.4 GPa, etc., the Young's modulus of the composite layer is 4 GPa, 4.5 GPa, 5 GPa, 5.5 GPa, 6 GPa, etc., and the Young's modulus of the nanoporous layer is 7 GPa, 7.5 GPa, 8 GPa, 8.5 GPa, 9 GPa, etc.

[0093] Thus, the flexible polymer layer absorbs the expansion stress of the silicon negative electrode, the composite layer disperses the residual stress, and the nanoporous layer rigidly supports the positive electrode (such as 1.5×10 -5 / ℃) and negative electrode (such as 2×10 -5 / ℃) thermal expansion coefficient matching.

[0094] In some embodiments, the thickness of the flexible polymer layer is 4 μm to 6 μm, and / or,

[0095] The thickness of the composite layer is 12 μm to 18 μm, and / or

[0096] The thickness of the nanoporous layer is 8 μm to 12 μm.

[0097] The thickness of the flexible polymer layer is limited to 4μm to 6μm. The thin layer reduces the length of the ion transmission path. The porosity is 5% to 10% to balance the ionic conductivity and mechanical strength. If the thickness of the flexible polymer layer is too thick (>6μm), the internal resistance will increase. If the thickness of the flexible polymer layer is too thin (<4μm), it is easy to break due to stress. Exemplarily, the thickness of the flexible polymer layer can be 4μm, 4.5μm, 5μm, 5.5μm, 6μm, etc., and the porosity can be 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0098] The thickness of the composite layer is limited to 12μm to 18μm. The thicker layer ensures high loading of the inorganic electrolyte and maintains high ionic conductivity. The porosity is limited to 9% to 11%, which can optimize the inorganic / polymer interface contact and reduce grain boundary impedance. Exemplarily, the thickness of the composite layer can be 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, etc., and the porosity can be 9%, 9.5%, 10%, 10.5%, 11%, etc.

[0099] The thickness of the nanoporous layer is limited to 8μm to 12μm, and the porosity is ≥60%. The high porosity absorbs residual stress through capillary action. For every 10% increase in porosity, the stress dispersion efficiency is improved by 15%. At the same time, the thickness design can reduce the volume share and avoid the ion transmission path being too long. For example, the thickness of the nanoporous layer can be 8μm, 9μm, 10μm, 11μm, 12μm, etc., and the porosity can be 60%, 61%, 62%, 63%, 64%, 65%, etc.

[0100] In some embodiments, the flexible polymer layer comprises the following performance parameters: an ionic conductivity of 0.5×10 -3 S / cm~1.5×10 -3 S / cm, porosity of 5% to 10%, thermal decomposition temperature of 310°C to 330°C, and / or,

[0101] The composite layer has the following performance parameters: the ionic conductivity at 25°C is 1.5×10 -3 S / cm~2.5×10 - 3 S / cm, porosity of 9% to 11%, thermal decomposition temperature of 330°C to 450°C, and / or,

[0102] The nanoporous layer has the following performance parameters: porosity ≥ 60%, and thermal decomposition temperature ≥ 1000°C.

[0103] It should be noted that ionic conductivity refers to the ability of a material to conduct ions under unit electric field strength, and is measured in Siemens per centimeter (S / cm). Its value depends on the concentration of mobile ions in the material, their migration rate, and the connectivity of the carrier migration path.

[0104] Porosity refers to the percentage of pore volume in a material to the total volume, reflecting the density or open structure of the material.

[0105] Thermal decomposition temperature is the temperature at which a material begins to irreversibly decompose due to breaking of chemical bonds during heating, and is usually determined by thermogravimetric analysis.

[0106] The thermal decomposition temperature of the flexible polymer layer is limited to 310℃~330℃, which can match the working temperature of the NCM9 series positive electrode and avoid high-temperature decomposition. The thermal stability of fluorinated polymers (such as PVDF-HFP) is higher than that of ordinary polymers (such as PEO). The thermal decomposition temperature of the composite layer is limited to >400℃, and the thermal stability of inorganic electrolytes (such as LLZO, LATP) is >800℃. After the composite, the overall temperature resistance is improved to prevent high-temperature interface failure. The thermal decomposition temperature of the nanoporous layer is limited to ≥1000℃. Materials such as SiO2 and Al2O3 have excellent high temperature resistance to prevent interface collapse under thermal runaway. For example, the thermal decomposition temperature of the flexible polymer layer can be 310°C, 315°C, 320°C, 325°C, 330°C, etc., the thermal decomposition temperature of the composite layer can be 330°C, 340°C, 350°C, 380°C, 400°C, 420°C, 450°C, etc., and the thermal decomposition temperature of the nanoporous layer can be 1000°C, 1020°C, 1050°C, 1080°C, 1100°C, 1150°C, etc.

[0107] The high dissociation degree of the composite layer LiFSI increases the ion migration number, and the nanoporous layer adsorbs byproducts to reduce interface side reactions, forming a "low-high-resistance" gradient conduction path. At the same time, the fluoropolymer in the flexible polymer layer is resistant to oxidation, the nanoporous layer SiO2 is compatible with the silicon negative electrode, and the composite layer LLZO / PEO wets the interface, forming a chemically stable closed loop. For example, the ionic conductivity of the flexible polymer layer at 25°C can be 0.5×10 -3 S / cm, 0.7×10 -3 S / cm, 0.9×10 -3 S / cm, 1.1×10 - 3 S / cm, 1.3×10 -3 S / cm, 1.5×10 -3 S / cm, the ionic conductivity of the composite layer at 25°C can be 1.5×10 -3 S / cm, 1.8×10 -3 S / cm, 2.0×10 -3 S / cm, 2.2×10 -3 S / cm, 2.4×10 -3 S / cm, 2.5×10 -3 S / cm, etc.

[0108] Therefore, the gradient composite solid electrolyte provided in the embodiments of the present application has the following advantages:

[0109] (1) Dynamic stress adaptation and interface stability: By increasing the Young's modulus of the flexible layer (such as 0.2GPa to 0.4GPa), the composite layer (such as 4GPa to 6GPa), and the nanoporous layer (such as 7GPa to 9GPa), the dynamic stress adaptation and interface stability of the silicon negative electrode (such as 2×10-5 / ℃) and high nickel positive electrode (such as 1.5×10 -5 / °C), improving cyclic stress dispersion efficiency by >70%, inhibiting interfacial crack propagation. Meanwhile, elastomers such as SEBS / FKM absorb the expansion stress of the silicon anode, preventing mechanical failure and stabilizing interfacial impedance after cycling.

[0110] (2) High ionic conductivity and electrochemical compatibility: The LLZO / LATP inorganic electrolyte (ionic conductivity > 1mS / cm) and the PEO matrix (Tg < room temperature) synergistically form a continuous conductive network with an overall conductivity of 1.5-2.5×10-3S / cm, supporting high-rate charge and discharge. At the same time, the fluorinated polymer (such as PVDF-HFP) has an oxidation potential > 5.0V, which is compatible with the NCM9 cathode and inhibits transition metal dissolution.

[0111] (3) Thermal stability and safety: SiO2 / Al2O3 porosity ≥ 60%, thermal decomposition temperature ≥ 1000°C, UL9540A certified, and no fire or explosion during the needle penetration test. LiDFOB also exhibits excellent high-temperature stability (decomposition temperature > 250°C), inhibiting excessive SEI film growth; and LiFSI ion migration number > 0.5, inhibiting dendrite penetration.

[0112] (4) Material synergy and functional complementarity: The PEO matrix wets the LLZO particles (contact angle <30°), reducing the grain boundary impedance to 0.25 eV and improving ion transmission efficiency. At the same time, the top layer of fluoropolymer is resistant to oxidation, the bottom layer of SiO2 is compatible with the silicon anode, and the middle layer of LLZO / PEO interface is passivated, inhibiting side reactions.

[0113] Based on a general inventive concept, the present application provides an in-situ interface repair structure, comprising thermally responsive microcapsules, wherein the thermally responsive microcapsules are embedded in the composite layer of the gradient composite solid electrolyte described in any one of the above embodiments.

[0114] It should be noted that the thermal responsive microcapsule is a core-shell structure material with a temperature-triggered release function, consisting of a shell material (Shell) and a core material (Core). Its core function is: when the internal temperature of the battery reaches a preset threshold, the shell ruptures to release the core material, and the liquid core fills the interface cracks and solidifies to form Li + Conductive network to achieve in-situ self-repair.

[0115] In some embodiments, it is characterized in that the thermally responsive microcapsules comprise a shell material and a core material, and the thermal response temperature of the thermally responsive microcapsules is 60°C to 80°C.

[0116] The thermal response temperature is limited to 60℃~80℃, which matches the temperature of early thermal runaway precursors of the battery (such as local overheating or micro-short circuit) and is earlier than the critical temperature of thermal runaway (>100℃) to achieve active repair. At the same time, it is higher than the normal operating temperature of the battery (<60℃) to prevent the microcapsules from rupturing prematurely during normal cycles. For example, the thermal response temperature of the thermally responsive microcapsules can be 60℃, 65℃, 70℃, 75℃, 80℃, etc.

[0117] In some embodiments, the shell material is one or a combination of at least two of polydopamine, thermoplastic polyurethane, or polycaprolactone.

[0118] In some embodiments, the shell material has a thickness of 40 nm to 60 nm.

[0119] The shell material is polydopamine / TPU / PCL. Polydopamine (PDA) has high chemical stability, TPU has an adjustable Tg (60°C to 80°C), and PCL (Tg≈60°C) provides a low-temperature response option. The thickness of the shell material is limited to 40nm to 60nm, which can provide mechanical protection. The thickness of 40nm to 60nm balances structural strength and thermal conductivity efficiency. For example, the thickness of the shell material can be 40nm, 45nm, 50nm, 55nm, 60nm, etc.

[0120] In some embodiments, the core material includes one or a combination of at least two of acrylate or polyether oligomers, and the molecular weight of the acrylate or polyether oligomer is 300Da to 500Da.

[0121] In some embodiments, the acrylates include: PEGDA or polyethylene glycol methyl ether acrylate, or a combination of at least two thereof, and the polyether oligomer is polyethylene glycol diglycidyl ether.

[0122] In some embodiments, the core material includes the following performance parameters: viscosity ≤ 100 mPa·s, Li + The conductivity of the conductive network at 25℃ is ≥1×10 -4 S / cm.

[0123] The molecular weight of acrylates (such as PEGDA) and polyether oligomers (such as PEGDGE) is controlled at 300-500Da, making their viscosity ≤100mPa·s, ensuring that the core material can flow quickly and fill the cracks after the microcapsules are broken. At the same time, acrylates form a three-dimensional cross-linked network under the initiation of free radicals, and polyethers are cured by ring-opening polymerization of epoxy groups. After doping with lithium salts (such as LiTFSI), Li +transmission channel, improving the conductivity at 25°C. In addition, acrylate and polyether materials have no side reactions with inorganic electrolytes (such as LLZO) and polymer matrices (PEO), and the network is insoluble in the electrolyte after curing, avoiding secondary decomposition.

[0124] The molecular weight of the core material is limited to 300Da~500Da, and the viscosity is ≤100mPa·s. Low molecular weight reduces viscosity to ensure crack filling speed. Acrylate (such as PEGDA) forms a cross-linked network after curing. + Conductivity ≥1×10 -4 S / cm (25°C), which is close to 6.7% of the initial value of the composite layer (1.5×10-3 S / cm). For example, the molecular weight of the core material can be 300Da, 350Da, 380Da, 400Da, 450Da, 480Da, 500Da, etc., and the viscosity can be 50mPa·s, 60mPa·s, 700mPa·s, 800mPa·s, 900mPa·s, 100mPa·s, etc.

[0125] In some embodiments, the particle size of the thermoresponsive microcapsules is 200 nm to 500 nm, and / or,

[0126] The mass of the thermal response microcapsules is 1% to 5% of the total mass of the composite layer.

[0127] The particle size of the microcapsules is limited to 200-500 nm to ensure that the microcapsules are evenly distributed in the composite layer. The mass of the thermally responsive microcapsules is limited to 1%-5% of the total mass of the composite layer to balance the repair needs and electrolyte performance. For example, the particle size of the thermally responsive microcapsules can be 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., and the mass of the thermally responsive microcapsules can be 1%, 2%, 3%, 4%, 5%, etc. of the total mass of the composite layer.

[0128] In some embodiments, the thermally responsive microcapsules include the following performance parameters: crack filling rate ≥ 90%, and electrical conductivity after repair is restored to 85% of the initial value.

[0129] In the embodiment of the present application, the in-situ interface repair structure is precisely designed with parameters of thermally responsive microcapsules, and the thermal trigger mechanism at 60°C to 80°C is earlier than thermal runaway, without the need for external circuit control. At the same time, the low-viscosity core material quickly fills the cracks, and the conductivity recovers to 85% after curing, extending the battery life. In addition, the microcapsules work together with the gradient composite solid electrolyte (LLZO / PEO), and the interface impedance increase after repair is less than 10%. The microcapsules can be embedded in the composite layer through a solution mixing process and adapted to existing production lines. This design provides a material-level self-repair solution to the interface failure problem of high-nickel silicon-based batteries, which is both safe and economical.

[0130] Therefore, the in-situ interface repair structure provided by the embodiments of the present application has the following advantages:

[0131] (1) Precise thermal triggering and active repair mechanism: The thermal response temperature is set at 60℃~80℃, matching the early signs of thermal runaway of the battery (such as local overheating or micro-short circuit), and earlier than the critical temperature of thermal runaway (>100℃), to achieve active early warning and repair, avoiding the risk of explosion. The pure material response mechanism does not require external circuit control, reducing system complexity.

[0132] (2) High efficiency crack repair and conductivity recovery: core material viscosity ≤ 100mPa·s (such as PEGDA viscosity ≈ 50mPa·s), can fill 10μm cracks within 5 seconds. + Conductivity ≥1×10 -4 S / cm, and the overall conductivity of the composite layer recovered to 85% of the initial value.

[0133] (3) Co-design of materials and structures: Polydopamine (PDA) has high chemical stability and a thickness of 40-60 nm, balancing mechanical strength and thermal response efficiency. The Tg of TPU / PCL is adjustable (60-80°C), adapting to different thermal runaway scenarios. Acrylate / polyether oligomers have a molecular weight of 300-500 Da and low viscosity to ensure fluidity. After curing, they are compatible with LLZO / PEO electrolytes.

[0134] (4) Process adaptability and industrialization potential: The microcapsule particle size is 200-500 nm, accounting for 1%-5% by mass, ensuring uniform dispersion without blocking ion channels. It can be embedded in the composite layer through a solution mixing process and is compatible with the existing solid-state battery manufacturing process.

[0135] (5) Improved safety and economy: The interface impedance after repair increases by less than 10%, and the nanoporous layer with a thermal decomposition temperature of ≥1000°C provides secondary protection. Microcapsule materials (such as PEGDA and TPU) are low-cost, with an addition amount of only 1% to 5%, resulting in an overall cost increase of less than 3%.

[0136] Figure 2 A schematic flow chart of a method for preparing a gradient composite solid electrolyte provided in an embodiment of the present application.

[0137] like Figure 2 As shown, the present application provides a method for preparing the gradient composite solid electrolyte described in any one of the above embodiments, comprising:

[0138] S1, preparing the nanoporous layer by sol-gel method;

[0139] It should be noted that the sol-gel method is a technique for preparing nanoporous materials by hydrolyzing and condensing liquid precursors (such as metal alkoxides) to form a gel, which is then dried and sintered. Its advantage lies in the uniform and controllable composition, making it suitable for the preparation of oxide thin films and porous structures.

[0140] The sol-gel method used in this application's examples forms a three-dimensional network structure through hydrolysis and condensation reactions, ultimately producing a nanoporous layer. This layer has a high specific surface area and uniform pores, which can improve ion transport efficiency and provide structural support for subsequent layers.

[0141] Specifically, step S1 may include:

[0142] S101, using tetraethyl orthosilicate as a precursor, hydrolyzing under acidic conditions to generate silicate sol;

[0143] S102, coating the silicate sol on a substrate to form a wet gel film, aging the film at 60° C. for 12 to 24 hours to perform a polycondensation reaction, and then heat-treating the film at 120° C. to form a porous structure layer with a pore size of 10 nm to 20 nm;

[0144] S103, introducing an aminosilane coupling agent (KH-550) on the surface of the porous structure layer to form hydrogen bonds with the ether oxygen bonds of the composite layer to obtain a nanoporous layer.

[0145] It should be noted that the aminosilane coupling agent is a silane compound containing an amino group (such as KH550), which improves the interfacial bonding strength between inorganic materials and organic polymers through chemical bonding.

[0146] The precursor is hydrolyzed in an acidic environment, which can control the hydrolysis rate and generate a uniform silica sol, providing a basis for the subsequent polycondensation reaction; the aging treatment enhances the gel network strength, reduces the cracks caused by drying stress, and forms a nanoporous structure with uniform pore size distribution through self-assembly; the heat treatment temperature is 120°C, which can stabilize the pore size through dehydroxylation reaction (Si-OH→Si-O-Si), thereby improving the thermal stability and mechanical strength of the porous layer; the introduction of the coupling agent modifies the surface hydroxyl group (Si-OH) to amino group (—NH2) through chemical bonding, and the amino group forms hydrogen bonds with the intermediate layer (such as polymer P containing ether oxygen bonds), thereby improving the interfacial chemical compatibility.

[0147] S2. depositing a slurry of a composite layer on the nanoporous layer by electrospinning, wherein the slurry of the composite layer comprises an inorganic electrolyte, a polymer matrix, and a lithium salt;

[0148] It should be noted that electrospinning is a technique that uses a high-voltage electric field to stretch a polymer solution or melt into nanofibers. In electrolyte preparation, it can form a high-porosity fiber network, enhancing ion transport pathways and mechanical strength.

[0149] After electrospinning, the composite layer slurry is directly deposited on the surface of the modified nanoporous layer, and the molecular chains of the polymer matrix penetrate the pores of the nanoporous layer (SEM shows a seamless interface). The composite layer is deposited on the nanoporous layer through electrospinning. The composite layer combines the high ionic conductivity of the inorganic electrolyte with the flexibility of the polymer matrix to form an intermediate layer that combines ion transport and mechanical strength. The lithium salt further optimizes ion migration.

[0150] In some embodiments, the slurry of the composite layer further includes a solvent, and the solvent includes one or a combination of methanol or ethanol.

[0151] In some embodiments, after the electrospinning process, the composite layer slurry is vacuum-dried at 80°C for 12 hours to completely volatilize the low-boiling-point solvent and prevent contact with the silicon anode. Furthermore, the selected solvent has a potential higher than the working potential of the silicon anode and does not trigger a reduction reaction on the anode surface. Furthermore, the lithium salt is stable in alcoholic solvents, and after drying, the lithium salt forms a composite phase with the polymer matrix / inorganic electrolyte, without releasing free solvent molecules. This indicates that the solvent in the lithium salt solution of the composite layer does not affect the silicon anode.

[0152] S3. Depositing a slurry of a flexible polymer layer on the composite layer by electrospinning, wherein the slurry of the flexible polymer layer comprises a copolymer matrix material, a reinforcing material, an elastomer, and a lithium salt.

[0153] The flexible polymer layer, primarily composed of a copolymer matrix and an elastomer, is deposited via electrospinning to enhance the mechanical toughness and interfacial stability of the electrolyte, inhibiting lithium dendrite penetration. The reinforcement creates a porous structure, increasing the contact area between the electrolyte and the electrode.

[0154] In some embodiments, thermally responsive microcapsules are embedded in the slurry of the composite layer by ultrasonic dispersion, and / or,

[0155] An aminosilane coupling agent is introduced into the surface of the nanoporous layer for interface modification to enhance the bonding force between the nanoporous layer and the composite layer.

[0156] Thermally responsive microcapsules are embedded in the composite layer through ultrasonic dispersion. These microcapsules can release flame-retardant or self-healing substances when the temperature is abnormal, improving battery safety. Aminosilane coupling agents are introduced to the surface of the nanoporous layer to enhance interfacial adhesion through chemical bonding (such as the reaction of -NH2 with hydroxyl groups on the surface of the inorganic layer), reducing the risk of delamination.

[0157] In some embodiments, the mass fraction of the solute in the slurry of the flexible polymer layer is 10% to 20%; and the mass fraction of the solid component in the slurry of the composite layer is 35% to 45%.

[0158] Limiting the mass fraction of the solid components of the composite layer's slurry to 35% to 45% can ensure moderate viscosity of the spinning slurry, facilitate the formation of a continuous fiber structure, reduce drying shrinkage, and avoid cracking. Limiting the mass fraction of the solute in the flexible polymer layer's slurry to 10% to 20% is conducive to the formation of an ultrafine fiber network, reducing porosity and enhancing flexibility; while avoiding spinning blockages caused by high concentrations. For example, the mass fraction of the solute in the flexible polymer layer's slurry can be 10%, 12%, 15%, 17%, 19%, 20%, etc., and the mass fraction of the solid components of the composite layer's slurry can be 35%, 37%, 39%, 40%, 42%, 44%, 45%, etc.

[0159] In some embodiments, the parameters of the electrospinning method are: voltage 18 kV, receiving distance 10 cm, flow rate 0.8 mL / h, temperature 25° C., and humidity <30%.

[0160] The voltage of electrospinning is limited to 18kV. The high-voltage electric field drives the polymer jet to stretch and form nano-scale fibers. Too high a voltage may cause fiber breakage, while too low a voltage may result in uneven fiber diameters. The receiving distance is limited to 10cm, which can control the solvent volatilization and fiber stretching degree during the jet flight. Too short a distance can easily lead to fiber adhesion, while too long a distance reduces the deposition efficiency. The flow rate is limited to 0.8mL / h, which can ensure a stable supply of slurry, avoid droplet injection or fiber breakage, and match the electric field stretching rate. The temperature of electrospinning is limited to 25℃, the humidity is <30%, and the solvent volatilization rate is moderate at room temperature to avoid structural defects caused by too rapid drying of the fiber surface.

[0161] The product prepared by the preparation method of the gradient composite solid electrolyte is the above-mentioned gradient composite solid electrolyte. The chemical composition and microstructure of the gradient composite solid electrolyte prepared by the preparation method of the gradient composite solid electrolyte can refer to the above-mentioned embodiment. Since the preparation method of the gradient composite solid electrolyte adopts part or all of the technical solutions of the gradient composite solid electrolyte embodiment, it has at least all the beneficial effects brought by the technical solutions of the gradient composite solid electrolyte embodiment, which will not be repeated here.

[0162] Therefore, the preparation method of a gradient composite solid electrolyte provided in the embodiment of the present application has the following advantages:

[0163] (1) Precise preparation of the nanoporous layer: The sol-gel method is used to form a three-dimensional network structure through hydrolysis and condensation reactions. The pore size (10nm to 20nm) and pore distribution of the nanoporous layer can be precisely controlled, thereby providing a high specific surface area and uniform ion transport channels. At the same time, the hydrolysis rate of the precursor in an acidic environment is controllable, which is conducive to the generation of a uniform silicate sol, laying the foundation for subsequent polycondensation reactions and self-assembly processes. In addition, the aging and heat treatment steps further enhance the strength of the gel network, reduce cracks caused by drying stress, stabilize the pore size, and improve the thermal stability and mechanical strength of the porous layer.

[0164] (2) Significant improvement in interfacial bonding: An aminosilane coupling agent (such as KH550) is introduced onto the surface of the nanoporous layer. The surface hydroxyl groups are modified to amino groups through chemical bonding, forming hydrogen bonds with the ether oxygen bonds of the composite layer, significantly improving the interfacial chemical compatibility and bonding strength. This interface modification not only strengthens the bonding between the nanoporous layer and the composite layer, but also reduces the risk of delamination, improving the stability and reliability of the overall structure.

[0165] (3) Optimized design of the composite layer: The composite layer slurry is deposited on the nanoporous layer by electrospinning to form a fiber network with high porosity, which enhances the ion transport path and mechanical strength. At the same time, the composite layer slurry contains an inorganic electrolyte, a polymer matrix, and a lithium salt, combining the high ionic conductivity of the inorganic electrolyte and the flexibility of the polymer matrix to form an intermediate layer with both ion transport and mechanical strength. In addition, the selection of solvents and the optimization of drying conditions ensure the compatibility of the composite layer with the silicon negative electrode, avoiding the influence of free solvent molecules on the negative electrode.

[0166] (4) Reinforcement of the flexible polymer layer: The flexible polymer layer, mainly composed of a copolymer matrix and an elastomer, is deposited by electrospinning, which significantly enhances the mechanical toughness and interfacial stability of the electrolyte and effectively inhibits the penetration of lithium dendrites. At the same time, the introduction of the reinforcing material constructs a porous architecture, increases the contact area between the electrolyte and the electrode, and further optimizes the ion transport performance.

[0167] (5) Precise control of process parameters: The parameters of the electrospinning process (voltage, receiving distance, flow rate, temperature) are precisely set to ensure the uniformity and continuity of the fibers and avoid the occurrence of structural defects. At the same time, the limited slurry concentration ensures the stability of the spinning process and the quality of the fibers, while optimizing the flexibility and mechanical properties of the electrolyte.

[0168] (6) Improved safety: By ultrasonically dispersing thermally responsive microcapsules embedded in the composite layer, the microcapsules can release flame retardant or self-healing substances when the temperature is abnormal, effectively improving the safety of the battery.

[0169] In summary, the preparation method of this gradient composite solid electrolyte shows significant advantages in the precise preparation of the nanoporous layer, the improvement of the interfacial bonding force, the optimized design of the composite layer, the reinforcement of the flexible polymer layer, the precise control of the process parameters and the improvement of safety, providing strong support for the research and development of high-performance solid-state batteries.

[0170] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are generally measured according to industry standards. If there are no corresponding industry standards, then the methods are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0171] Examples 1 to 8 provide gradient composite solid electrolytes with different parameters and compositions and their preparation methods, with the specific parameters and properties described below. Examples 6 and 7 also provide specific preparation methods for thermally responsive microcapsules.

[0172] Example 1

[0173] This embodiment provides a gradient composite solid electrolyte, comprising:

[0174] a flexible polymer layer comprising a copolymer matrix material, a reinforcement material, an elastomer, and a lithium salt;

[0175] The copolymer matrix material and the reinforcing material are copolymers, and the mass ratio of the copolymer matrix material and the reinforcing material, the elastomer and the lithium salt is 85:10:5;

[0176] Copolymer of copolymer matrix material and reinforcing material: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, CAS No. 9011-17-0, chemical formula (-CH2CF2-)x[-CF2CF(CF3)-] y ), elastomer: acrylic rubber (ACM, CAS No. 67254-76-6), lithium salt: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI);

[0177] Performance parameters: Young's modulus: 0.3GPa, thickness: 5μm, ionic conductivity (25℃): 1.2×10 -3 S / cm, porosity: 8%, thermal decomposition temperature: 320℃.

[0178] a composite layer comprising an inorganic electrolyte, a polymer matrix, and a lithium salt;

[0179] Among them, the mass ratio of inorganic electrolyte, polymer matrix and lithium salt is 85:10:5;

[0180] Inorganic electrolyte: lithium aluminum titanium phosphate (LATP), polymer matrix: polyethylene oxide (PEO, CAS No. 68441-17-8), lithium salt: LiTFSI;

[0181] Performance parameters: Young's modulus: 5GPa, thickness: 15μm, ionic conductivity (25℃): 2.0×10 -3 S / cm, porosity: 10%, thermal decomposition temperature: 380℃.

[0182] a nanoporous layer comprising a nanoporous material;

[0183] Wherein, the nanoporous material is silicon dioxide;

[0184] Performance parameters: Young's modulus: 8GPa, thickness: 10μm, porosity: 65%, thermal decomposition temperature: 1000℃.

[0185] The composite layer is located between the flexible polymer layer and the nanoporous layer.

[0186] Based on the above-mentioned gradient composite solid electrolyte, this embodiment also provides a method for preparing a gradient composite solid electrolyte, which may include the following steps:

[0187] S11, using tetraethyl orthosilicate as a precursor, hydrolyzing it under acidic conditions to generate a silicic acid sol; coating the silicic acid sol on a substrate to form a wet gel film, aging it at 60° C. for 12 hours to undergo a polycondensation reaction, and then heat-treating it at 120° C. to form a porous structure layer with a pore size of 10 nm to 20 nm; introducing an aminosilane coupling agent on the surface of the porous structure layer to form hydrogen bonds with the ether oxygen bonds of the composite layer to obtain a nanoporous layer;

[0188] S2. depositing a slurry of a composite layer on the nanoporous layer by electrospinning, wherein the slurry of the composite layer comprises an inorganic electrolyte, a polymer matrix, and a lithium salt;

[0189] Wherein, the solid content of the slurry of the composite layer is 40%.

[0190] S3. Depositing a slurry of a flexible polymer layer on the composite layer by electrospinning, wherein the slurry of the flexible polymer layer comprises a copolymer matrix material, a reinforcing material, an elastomer, and a lithium salt.

[0191] The concentration of the slurry of the flexible polymer layer is 15%.

[0192] The parameters of the electrospinning method are: voltage 18 kV, receiving distance 10 cm, flow rate 0.8 mL / h, temperature 25° C., and humidity <30%.

[0193] Example 2

[0194] Compared with Example 1, this embodiment has the following differences, and the rest are the same:

[0195] The mass ratio of inorganic electrolyte, polymer matrix and lithium salt in the composite layer is 90:5:5, and the conductivity is improved to 3×10 -3 S / cm(25℃).

[0196] The nanoporous layer had a porosity of 85% and a thickness of 8 μm.

[0197] Example 3

[0198] Compared with Example 1, this embodiment has the following differences, and the rest are the same:

[0199] Copolymer matrix material and reinforcing material: PVDF-HFP, elastomer: hydrogenated styrene-ethylene-propylene block copolymer (SEP), lithium salt: LiFSI;

[0200] Inorganic electrolyte: LLZO cubic phase, polymer matrix: polypropylene oxide PPO, lithium salt: LiDFOB;

[0201] The nanoporous material is silicon dioxide.

[0202] Example 4

[0203] Compared with Example 1, this embodiment has the following differences, and the rest are the same:

[0204] Copolymer matrix material and reinforcing material: poly (perfluoroethylene propylene) FEP, elastomer: fluorosilicone rubber FVMQ, lithium salt: LiBOB;

[0205] Inorganic electrolyte: argyrodite-type Li6PS5Cl, polymer matrix: polycaprolactone PCL, lithium salt: LiTFSI;

[0206] The nanoporous material is silicon dioxide.

[0207] Example 5

[0208] Compared with Example 1, this embodiment has the following differences, and the rest are the same:

[0209] Copolymer matrix material and reinforcing material: polyimide PI, elastomer: acrylic rubber ACM, lithium salt: LiTFSI;

[0210] Inorganic electrolyte: LATP, polymer matrix: PEO, lithium salt: LiFSI;

[0211] The nanoporous material is silicon dioxide.

[0212] Example 6

[0213] Compared with Example 1, this embodiment has the following differences, and the rest are the same:

[0214] Thermal responsive microcapsules were embedded in the composite layer of the gradient composite solid electrolyte described in Example 1. During the embedding, the microcapsules were mixed with the composite layer slurry and then subjected to ultrasonic dispersion (200 W, 40 kHz, 20 min).

[0215] The thermally responsive microcapsules comprise a shell material and a core material, and the thermal response temperature of the thermally responsive microcapsules is 60-70°C.

[0216] The shell material is polydopamine.

[0217] The average thickness of the shell material is 50 nm.

[0218] The core material is polyethylene glycol diacrylate (CAS No. 26570-48-9).

[0219] The core material has the following performance parameters: viscosity is 80mPa·s, and the Li formed after solidification is + The conductivity of the conductive network at 25°C is 1.05×10 -4 S / cm.

[0220] The average particle size of the thermally responsive microcapsules is 300 nm, and / or,

[0221] The mass of the thermally responsive microcapsules is 3% of the total mass of the composite layer.

[0222] This embodiment also provides a specific preparation method of thermal responsive microcapsules, which includes the following steps:

[0223] Polyethylene glycol diacrylate (PEGDA), 2-hydroxy-2-methylpropiophenone (HMPP, 1 wt%), and deionized water were mixed in proportion, ultrasonically dispersed until completely dissolved, and the concentration was adjusted to 20% (w / v) to obtain a core material solution; dopamine was dissolved in Tris buffer to a final concentration of 2 mg / mL to obtain a core material solution;

[0224] Using a microfluidic chip, the core material solution (PEGDA) was encapsulated by the shell precursor solution (dopamine), forming double-emulsion droplets (W / O / W structure), which were ultimately dispersed in the oil phase. By adjusting the flow rate ratio (core material:shell:oil phase = 1:4:20), the average droplet size was controlled to 300 nm, resulting in an emulsion.

[0225] The emulsion was transferred to a thermostatic reactor (25°C) and stirred continuously (200 rpm) for 12 h to allow dopamine to oxidatively self-polymerize at the droplet interface to form a homogeneous shell with an average thickness of nm.

[0226] The emulsion was exposed to a UV light source (wavelength 365 nm, intensity 10 mW / cm 2 ) for 15 minutes to initiate cross-linking and curing of PEGDA. Add n-hexane (twice the volume of the oil phase) and separate the microcapsules by centrifugation (5000 rpm, 10 minutes). Wash the microcapsules three times alternately with ethanol and deionized water to remove residual oil phase and unreacted monomers. Freeze-dry (-50°C, 24 hours) to obtain dry microcapsule powder.

[0227] Example 7

[0228] Compared with Example 6, this embodiment has the following differences, and the rest are the same:

[0229] The shell material is thermoplastic polyurethane (CAS No. 1211-14-9).

[0230] The core material is polyethylene glycol methyl ether acrylate (CAS No. 32171-39-4), and after curing, the electrical conductivity is increased to 1.2×10-4 S / cm (25°C).

[0231] The microcapsule thermal response temperature is adjusted to 70-80°C

[0232] Example 8

[0233] Compared with Example 6, this embodiment has the following differences, and the rest are the same:

[0234] The particle size of the thermoresponsive microcapsules is 450 nm.

[0235] The mass of the thermally responsive microcapsules is 5% of the total mass of the composite layer.

[0236] Comparative Examples 1 to Comparative Examples 4 are adjustments to Example 1, lacking the flexible polymer layer, the composite layer, the nanoporous layer, or adopting a non-gradient structure. Their performance is reduced compared with that of the example, as shown in the following specific data.

[0237] Comparative Example 1

[0238] This comparative example is based on the comparative test of Example 1, with the following specific adjustments:

[0239] The gradient composite solid electrolyte comprises: a composite layer and a nanoporous layer. The positive electrode interface lacks a flexible polymer layer. The composite layer and the nanoporous layer are stacked. The thickness of the composite layer is 15 μm, and the thickness of the nanoporous layer is 10 μm.

[0240] Comparative Example 2

[0241] This comparative example is based on the comparative test of Example 1, with the following specific adjustments:

[0242] A gradient composite solid electrolyte comprises: a flexible polymer layer and a nanoporous layer, but lacks a composite layer. The flexible polymer layer and the nanoporous layer are stacked, the thickness of the flexible polymer layer is 5 μm, and the thickness of the nanoporous layer is 10 μm.

[0243] Comparative Example 3

[0244] This comparative example is based on the comparative test of Example 1, with the following specific adjustments:

[0245] A gradient composite solid electrolyte comprises: a flexible polymer layer and a composite layer, lacking a nanoporous layer. The composite layer is directly deposited on the surface of the negative electrode. The composite layer and the flexible polymer layer are stacked. The thickness of the composite layer is 15 μm, and the thickness of the flexible polymer layer is 5 μm.

[0246] Comparative Example 4

[0247] This comparative example is based on the comparative test of Example 1, with the following specific adjustments:

[0248] The components of the flexible polymer layer, the components of the composite layer, and the components of the nanoporous layer are directly mixed to form a single layer with a non-gradient structure and a thickness of 30 μm.

[0249] The composite solid electrolytes obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were subjected to performance tests. The results are shown in Table 1. The specific test method is as follows:

[0250] The ionic conductivity is measured using the electrochemical impedance spectroscopy (EIS) method: the solid electrolyte sample is sandwiched between stainless steel (ion-blocking electrodes) to form a sandwich structure. An AC signal with a frequency range of 10 mHz to 1 MHz is applied, and the bulk resistance (R) is obtained through the high-frequency intercept of the impedance spectrum. The conductivity is calculated based on the sample thickness (L) and area (S).

[0251] The interface contact resistance is determined using the four-probe method: a constant current is applied at the interface between the solid electrolyte and the electrode, the voltage drop is measured, and the contact resistance is directly calculated.

[0252] The cycle life (weeks, capacity retention) is measured using the full-battery cycle test method: a full-battery with positive electrode (NCM9) / SE / Li metal is assembled and cycled hundreds of times under constant current charge and discharge conditions (e.g., 0.5C), and the capacity decay rate is recorded.

[0253] The thermal runaway trigger temperature was determined by differential scanning calorimetry (DSC): the sample was scanned at a heating rate of 10°C / min, and the thermal runaway trigger point was determined by the starting temperature of the exothermic peak.

[0254] The crack repair rate is tested using mechanical property recovery: after applying external force to the electrolyte to form a crack, the elastic modulus recovery rate after repair is measured by dynamic mechanical analysis (DMA).

[0255] Table 1 Properties of composite solid electrolytes of Examples 1 to 8 and Comparative Examples 1 to 4

[0256]

[0257]

[0258] Based on the data in Table 1, the factors affecting the performance of composite solid electrolytes are mainly reflected in the following aspects:

[0259] 1. Ionic conductivity

[0260] Effect of gradient structure: The gradient structure of Examples 1 and 2 improves ionic conductivity, which is mainly because the composite layer (LATP / PEO) exerts an inorganic-organic synergistic effect. Among them, LATP (lithium aluminum titanium phosphate) is used as an inorganic filler, and LATP forms a rigid skeleton, shortening the lithium ion migration path and reducing the resistance to ion migration. PEO (polyethylene oxide) is an organic polymer that dissociates from the lithium salt (LiTFSI) through an ether oxygen bond. The gradient structure ensures that PEO is concentrated in the middle layer, avoiding side reactions caused by direct contact with the electrode, further optimizing the ion transmission path, and making the transmission of lithium ions in the composite solid electrolyte smoother and more efficient, thereby improving the overall ionic conductivity.

[0261] Defects of non-gradient structure: In comparative example 4, there is no gradient structure, and the inorganic filler (LATP) and polymer (PEO) are disorderly distributed in the mixed layer, resulting in the breakage of ion channels. Lithium ions are more hindered during transmission, causing the conductivity to drop to 1.5×10-3S / cm, which is much lower than that of Examples 1 and 2.

[0262] 2. Interface contact resistance

[0263] The flexible polymer layer and the nanoporous layer work together: the interface contact resistance of Example 1 is 18Ω, which is significantly lower than the 45Ω of Comparative Example 1. This is because the flexible polymer layer (PVDF-HFP / ACM) has good elastic buffering properties, which can effectively reduce the interface stress and reduce problems such as poor mechanical contact at the interface. At the same time, the nanoporous layer (SiO2) bottom layer SiO2 and SiO x The Si-O-Si covalent bond is formed on the Si / C negative electrode, which enhances the interaction between the interfaces, further reduces the interfacial contact resistance, and makes the transmission of lithium ions at the interface smoother.

[0264] Impact of the Lack of a Flexible or Composite Layer: In Comparative Example 2, the composite layer is missing, and the direct contact between the flexible layer and the porous layer fails, with the interface resistance surging to 80Ω. This indicates that the composite layer plays a critical intermediate role in interfacial stability; its absence severely impacts ion transport at the interface, increasing interfacial contact resistance.

[0265] 3. Cycle life

[0266] Contribution of self-repair function: Examples 6 and 7 achieve self-repair function by embedding thermal responsive microcapsules in the composite layer, which significantly improves the cycle life. The microcapsules are triggered at 60-80°C, and the core material (PEGDA or PEGMEA) solidifies to form a conductive network after release, which can effectively inhibit crack propagation and repair ion channels, thereby maintaining the integrity of the internal structure of the electrolyte, reducing problems such as ion transmission obstruction caused by cracks during the cycle, and thus extending the cycle life of the battery. For example, the cycle life of Example 6 reaches 1800 weeks, and the capacity retention rate is 92%, which is significantly better than the 1300 weeks and 88% of Example 1.

[0267] Other factors: In addition to the self-healing function, the gradient structure also has a positive impact on cycle life. For example, Example 4 has high ionic conductivity (3.2×10-3 S / cm) and low interface contact resistance (14Ω), and its cycle life reaches 1900 cycles with a capacity retention rate of 91%. This shows that good ion transport performance and interface stability are important foundations for achieving long cycle life.

[0268] 4. Thermal runaway trigger temperature

[0269] Synergistic Effect of the Nanoporous Layer and Microcapsule Shell: The thermal runaway trigger temperatures of Examples 6 and 7 are higher than those of the other examples, primarily due to the "thermal barrier" effect of the nanoporous layer (SiO2, melting point >1000°C), which effectively blocks heat transfer and prevents rapid heat accumulation and diffusion within the electrolyte. Furthermore, the microcapsule shell (polydopamine or polyurethane) has a suppressive effect on local hot spots. When the local temperature rises, the microcapsule shell can absorb some of the heat or mitigate the local thermal effect through structural changes, thereby improving the thermal stability of the entire composite solid-state electrolyte and increasing the thermal runaway trigger temperature.

[0270] Negative impact of the lack of a flexible layer or gradient structure: Comparative Example 1 lacks a flexible layer, and the stress concentration at the lithium metal negative electrode interface increases the risk of dendrite penetration, shortens the cycle life to 600 weeks, and the capacity retention rate is only 75%. Moreover, since the composite layer (380°C) is directly exposed and there is no buffering and protection of the flexible layer, the thermal runaway temperature is reduced to 190°C. In Comparative Example 4, there is no gradient structure, and the inorganic filler and polymer are disorderly distributed in the mixed layer, which not only leads to the rupture of the ion channel, but also deteriorates the thermal stability, and the thermal runaway temperature is only 170°C.

[0271] 5. Crack repair rate

[0272] The role of thermoresponsive microcapsules: Examples 6 and 7 achieved high crack repair rates of 92% and 95%, respectively, attributed to the thermoresponsive microcapsules embedded in the composite layer. Triggered at a specific temperature, the microcapsules release the core material and solidify to form a conductive network. This effectively repairs cracks caused by mechanical stress and other factors, restoring the integrity of ion channels and thus ensuring the performance stability of the electrolyte. This self-healing function is crucial for improving battery safety and service life, particularly by effectively addressing potential structural damage during long-term battery operation.

[0273] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0274] In the examples of this application, a gradient-increased Young's modulus design for the flexible layer, composite layer, and nanoporous layer matches the thermal expansion coefficients of the silicon anode and high-nickel cathode, improving cyclic stress dispersion efficiency and suppressing interfacial crack propagation. Simultaneously, the elastomer absorbs the silicon anode's expansion stress, preventing mechanical failure and stabilizing interfacial impedance after cycling.

[0275] In the examples of this application, the inorganic electrolyte and polymer matrix synergistically form a continuous conductive network, resulting in high overall conductivity and support for high-rate charge and discharge. Furthermore, the fluoropolymer is compatible with the NCM9-based cathode, inhibiting transition metal dissolution.

[0276] In the examples of this application, the nanoporous material exhibits high porosity and a high thermal decomposition temperature, passing UL9540A certification and refractory to fire or explosion during a needle penetration test. Furthermore, the lithium salt exhibits excellent high-temperature stability, inhibiting excessive SEI film growth, and a high ion mobility, inhibiting dendrite penetration.

[0277] In this embodiment, the polymer matrix wets the inorganic particles, reducing grain boundary resistance and improving ion transport efficiency. Furthermore, the top layer of fluoropolymer provides antioxidant properties, the bottom layer of SiO2 is compatible with the silicon anode, and the middle layer of LLZO / PEO provides passivation at the interface, inhibiting side reactions.

[0278] In the embodiment of the present application, the thermal responsive microcapsules are embedded in the composite layer. When the internal temperature of the battery reaches a preset threshold, the shell layer ruptures to release the core material, and the liquid core material fills the interface cracks and solidifies to form Li + The conductive network enables in-situ self-repair. After the core material solidifies, the conductivity recovers to 85% of the initial value, and the crack filling rate is greater than 90%.

[0279] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A gradient composite solid electrolyte comprising: flexible polymer layers, composite layers, and nanoporous layers; The composite layer is located between the flexible polymer layer and the nanoporous layer, and Young's moduli of the flexible polymer layer, the composite layer and the nanoporous layer increase in a gradient.

2. The gradient composite solid electrolyte according to claim 1, characterized in that The Young's modulus of the flexible polymer layer is 0.2 GPa to 0.4 GPa, and / or The Young's modulus of the composite layer is 4 GPa to 6 GPa, and / or The Young's modulus of the nanoporous layer is 7 GPa to 9 GPa.

3. The gradient composite solid electrolyte according to claim 1, characterized in that The thickness of the flexible polymer layer is 4 μm to 6 μm, and / or The thickness of the composite layer is 12 μm to 18 μm, and / or The thickness of the nanoporous layer is 8 μm to 12 μm.

4. The gradient composite solid electrolyte according to claim 1, characterized in that The flexible polymer layer has the following performance parameters: ionic conductivity at 25°C is 0.5×10 -3 S / cm~1.5×10 -3 S / cm, porosity of 5% to 10%, thermal decomposition temperature of 310°C to 330°C, and / or, The composite layer has the following performance parameters: the ionic conductivity at 25°C is 1.5×10 -3 S / cm~2.5×10 -3 S / cm, porosity of 9% to 11%, thermal decomposition temperature of 330°C to 450°C, and / or, The nanoporous layer has the following performance parameters: porosity ≥ 60%, and thermal decomposition temperature ≥ 1000°C.

5. The gradient composite solid electrolyte according to claim 1, characterized in that The material of the flexible polymer layer includes a copolymer matrix material, a reinforcing material, an elastomer and a lithium salt; and / or, The material of the composite layer includes an inorganic electrolyte, a polymer matrix and a lithium salt; and / or, The material of the nanoporous layer includes nanoporous material.

6. The gradient composite solid electrolyte according to claim 5, characterized in that The matrix material includes a fluorine-containing polymer or a high-pressure-resistant polymer, the reinforcing material includes a fluorinated elastomer or a hydrogenated styrene elastomer, and the elastomer includes a hydrogenated styrene elastomer, a fluorinated elastomer or an acrylic rubber.

7. The gradient composite solid electrolyte according to claim 5, characterized in that The inorganic electrolyte includes one or a combination of at least two of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide or lithium phosphorus sulfur chloride, the polymer matrix includes one or a combination of at least two of polyethylene oxide, polypropylene oxide or polycaprolactone, and the lithium salt includes one or a combination of at least two of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate or lithium dioxalatoborate.

8. The gradient composite solid electrolyte according to claim 5, characterized in that The nanoporous material includes one or a combination of at least two of SiO2, Al2O3 or ZrO2.

9. An in-situ interface repair structure, comprising thermally responsive microcapsules embedded in the composite layer of the gradient composite solid electrolyte according to any one of claims 1 to 7.

10. The in-situ interface repair structure according to claim 9, characterized in that: The thermally responsive microcapsules comprise a shell material and a core material, and the thermal response temperature of the thermally responsive microcapsules is 60° C. to 80° C.

11. The in-situ interface repair structure according to claim 10, characterized in that: The shell material is one of polydopamine, thermoplastic polyurethane or polycaprolactone, or a combination of at least two of them.

12. The in-situ interface repair structure according to claim 10 or 11, characterized in that: The thickness of the shell material is 40nm to 60nm.

13. The in-situ interface repair structure according to claim 10, characterized in that: The core material includes one or a combination of at least two of acrylate or polyether oligomers, and the molecular weight of the acrylate or polyether oligomer is 300Da to 500Da.

14. The in-situ interface repair structure according to claim 10 or 13, characterized in that: The core material has the following performance parameters: viscosity ≤ 100 mPa·s, conductivity of the Li+ conductive network formed after curing at 25°C ≥ 1×10 -4 S / cm.

15. The in-situ interface repair structure according to claim 9, characterized in that: The particle size of the thermally responsive microcapsules is 200 nm to 500 nm, and / or, The mass of the thermal response microcapsules is 1% to 5% of the total mass of the composite layer.

16. The in-situ interface repair structure according to claim 9, characterized in that: The thermally responsive microcapsules include the following performance parameters: crack filling rate ≥ 90%, and electrical conductivity after repair is restored to 85% of the initial value.

17. A method for preparing the gradient composite solid electrolyte according to any one of claims 1 to 8, comprising: Preparation of nanoporous layers by sol-gel method; depositing a composite layer slurry on the nanoporous layer by electrospinning, wherein the composite layer slurry comprises an inorganic electrolyte, a polymer matrix, and a lithium salt; A slurry of a flexible polymer layer is deposited on the composite layer by electrospinning.

18. The preparation method according to claim 17, characterized in that: The mass fraction of the solute in the slurry of the flexible polymer layer is 10% to 20%; the mass fraction of the solid component in the slurry of the composite layer is 35% to 45%.

19. The preparation method according to claim 17, characterized in that The method further comprises: embedding thermal responsive microcapsules in the slurry of the composite layer by ultrasonic dispersion, and / or, An aminosilane coupling agent is introduced into the surface of the nanoporous layer for interface modification to enhance the bonding force between the nanoporous layer and the composite layer.

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