Composite cathode material, preparation method and all-solid-state battery

Abstract

This invention discloses a composite cathode material, its preparation method, and an all-solid-state battery. The composite cathode material includes cathode active material particles, on which a polymer electrolyte interlayer and an inorganic solid electrolyte nanofiber network epitaxial layer are sequentially disposed. The electrolyte interlayer comprises a polyacrylonitrile-polyethylene oxide block copolymer matrix material and a lithium salt. The composite cathode material of this application is a multi-level interface system with spatial gradient ion conductivity characteristics, which effectively alleviates the ion transport barrier caused by abrupt changes in conductivity and significantly enhances the stability of the interface structure, suppressing the contact degradation between the active particles and the electrolyte during cycling, thereby improving lithium-ion transport capacity.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and more specifically, to composite cathode materials, preparation methods, and all-solid-state batteries. Background Technology

[0002] All-solid-state lithium batteries are considered a key development direction for next-generation energy storage technology due to their high safety and high energy density. However, the core challenge to their commercialization lies in the solid-solid interface problem between the electrode and the solid electrolyte. In traditional solid-state batteries, poor interface contact leads to high ion transport resistance and low efficiency, severely restricting practical applications. The positive electrode interface is particularly critical, as its ion transport efficiency directly affects the overall battery performance. In existing technologies, single-component or simply mixed composite positive electrodes cannot simultaneously guarantee high ionic conductivity and tight, stable interface contact, limiting the battery's energy density, rate performance, and cycle life.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide composite cathode materials, preparation methods, and all-solid-state batteries, which are beneficial for solving the solid-solid interface problem between the electrode and the solid electrolyte and improving ion transport efficiency.

[0005] This invention is implemented as follows: In a first aspect, the present invention provides a composite cathode material, comprising: cathode active material particles, wherein the cathode active material particles are sequentially coated with a polymer electrolyte interlayer and an inorganic solid electrolyte nanofiber network epitaxial layer, wherein the electrolyte interlayer comprises a polyacrylonitrile-polyethylene oxide block copolymer matrix material and a lithium salt.

[0006] In an optional embodiment, the thickness of the polymer electrolyte interlayer is 50 nm-200 nm; And / or, the mass fraction of the polymer electrolyte interlayer is 20-25%; And / or, in the raw materials of the polymer electrolyte interlayer, the mass fraction of polyacrylonitrile is 60%-85%, and the mass fraction of polyethylene oxide is 15%-40%; And / or, the lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; And / or, the mass fraction of lithium salt in the polymer electrolyte interlayer is 15 wt%-30 wt%; And / or, in the polymer electrolyte interlayer, the cyano groups in the polyacrylonitrile-polyethylene oxide block copolymer matrix material are connected to the transition metal ions on the surface of the cathode particles through coordination bonds.

[0007] In an optional embodiment, the solid electrolyte in the inorganic solid electrolyte nanofiber network epitaxial layer includes at least one of lithium lanthanum titanium oxide and lithium lanthanum titanium zirconium oxide. And / or, the diameter of the inorganic solid electrolyte nanofibers in the inorganic solid electrolyte nanofiber network epitaxial layer is 50nm-200nm; And / or, the lithium lanthanum titanium zirconium oxide nanofiber network includes radially ordered lithium lanthanum titanium zirconium oxide nanofibers; And / or, in the composite cathode material, the mass fraction of the inorganic solid electrolyte nanofiber network epitaxial layer is 30-40%.

[0008] In an optional embodiment, the mass ratio of the solid electrolyte to the polyacrylonitrile-polyethylene oxide block copolymer in the inorganic solid electrolyte nanofiber network epitaxial layer is 1:(1.5-2.5).

[0009] Secondly, the present invention provides a method for preparing the composite cathode material according to any one of the foregoing embodiments, comprising: The positive electrode active material particles were immersed in a precursor solution containing a polyacrylonitrile-polyethylene oxide block copolymer matrix material, lithium salt, crosslinking agent and solvent, and the coated particles were obtained after solid-liquid separation. Inorganic solid electrolyte precursor fibers are formed on the outer surface of the coated particles by electrospinning, thus forming a composite cathode material precursor. The composite cathode material precursor is subjected to heat treatment to obtain the composite cathode material.

[0010] In an optional embodiment, the positive electrode active material is selected from at least one of lithium-rich manganese-based positive electrode active materials, high-nickel ternary materials, and lithium iron phosphate materials.

[0011] In an optional embodiment, the solvent in the precursor solution has a mass fraction of 30%-95%; And / or, the solvent in the precursor solution is selected from at least one of N,N-dimethylformamide and acetone.

[0012] In an optional embodiment, the solvent comprises N,N-dimethylformamide and acetone, wherein the mass ratio of N,N-dimethylformamide to acetone is (5-7):4; And / or, the soaking temperature is 60℃-80℃, and the soaking time is 15min-25min; And / or, the crosslinking agent is selected from polycarbodiimide crosslinking agents, and in the precursor solution, the mass fraction of the crosslinking agent to the mass fraction of the lithium salt is (105-115)%:1; And / or, the soaking is carried out under stirring conditions at a stirring rate of 1500 rpm - 3000 rpm.

[0013] In an optional embodiment, the spinning solution for forming the inorganic solid electrolyte precursor fiber includes a solid electrolyte, a polyacrylonitrile-polyethylene oxide block copolymer, and a spinning solvent, wherein the mass ratio of the polyacrylonitrile-polyethylene oxide block copolymer to the spinning solvent is 1:(5-20). And / or, the parameters of electrospinning include a voltage of 10 kV-25 kV, a temperature of 20℃-30℃, and a receiving distance of 10cm-20cm; preferably, electrospinning includes: a central fiber formation stage, with a voltage of 24-26 kV and a time of 30-60 seconds; a radial fiber growth stage, with the voltage reduced to 14-16 kV, a scanning mode of radial outward, and a time of 2-5 min; and a structure stabilization stage, with a voltage of 10-15 kV and a time of 1-2 min; And / or, the heat treatment temperature is 80℃-90℃, the time is 110min-130min, and the atmosphere is an inert atmosphere.

[0014] Thirdly, the present invention provides an all-solid-state battery, comprising the composite cathode material described in any one of the foregoing embodiments or the composite cathode material prepared by the method described in any one of the foregoing embodiments.

[0015] The present invention has the following beneficial effects: The composite cathode material of this application is a multi-level interface system with gradient ion conductivity characteristics, which can effectively alleviate the ion transport barrier caused by the sudden change in conductivity, significantly enhance the stability of the interface structure, suppress the contact degradation between active particles and electrolyte during cycling, and thus improve the lithium-ion transport capacity. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic cross-sectional view of a solid-state battery with a cathode material coating structure. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] This invention provides a composite cathode material, comprising: cathode active material particles, wherein the cathode active material particles are sequentially coated with a polymer electrolyte interlayer and an inorganic solid electrolyte nanofiber network epitaxial layer, wherein the electrolyte interlayer comprises a polyacrylonitrile-polyethylene oxide block copolymer matrix material and a lithium salt.

[0020] In this application, the polymer electrolyte interlayer in the composite cathode material utilizes the coordination between the cyano groups at the end of the PAN-b-PEO molecular chain and transition metal ions in the cathode active material particles to drive self-assembly, achieving chemical anchoring of the polymer electrolyte interlayer on the surface of the active particles. Furthermore, an inorganic solid electrolyte nanofiber network epitaxial layer with a solid electrolyte is formed on the outer side of the polymer electrolyte interlayer. This gradually increases the ionic conductivity of the cathode active material particles, the polymer electrolyte interlayer, and the inorganic solid electrolyte nanofiber network epitaxial layer, constructing a multi-level interface system with gradient ionic conductivity. This effectively alleviates the ion transport barrier caused by abrupt changes in conductivity, significantly enhances the stability of the interface structure, and suppresses the contact degradation between the active particles and the electrolyte during cycling, thereby improving lithium-ion transport capacity.

[0021] In an optional embodiment, the thickness of the polymer electrolyte interlayer is 50 nm-200 nm, such as 50 nm, 67 nm, 83 nm, 100 nm, 117 nm, 133 nm, 150 nm, 167 nm, 183 nm, and 200 nm. This is beneficial for forming a continuous, complete coating layer with effective ion conduction capabilities, avoiding problems such as uneven coverage, exposed interfaces, and insufficient chemical anchoring density caused by an excessively thin polymer electrolyte interlayer. At the same time, it can suppress problems such as prolonged redundancy of electron / ion transport paths, increased impedance, and decreased mechanical flexibility caused by an excessively thick polymer electrolyte interlayer, thus balancing ion conduction efficiency and interface uniformity and stability.

[0022] In an optional embodiment, the mass fraction of the polymer electrolyte interlayer in the composite cathode material is 20-25%, for example, 20%, 20.6%, 21.1%, 21.7%, 22.2%, 22.8%, 23.3%, 23.9%, 24.4%, or 25%. The mass fraction of the polymer electrolyte interlayer is closely related to the thickness. If the proportion of the interlayer is too low, the thickness will be too thin; conversely, if the proportion of the interlayer is too high, the thickness will be too thick, both of which are detrimental to the improvement of the performance of the composite cathode material.

[0023] And / or, in the raw materials of the polymer electrolyte interlayer, the mass fraction of polyacrylonitrile is 60%-85%, for example 60%, 63%, 66%, 69%, 72%, 75%, 78%, 81%, 84%, 85%, and the mass fraction of polyethylene oxide is 15%-40%, for example 15%, 18%, 21%, 24%, 27%, 30%, 33%, 36%, 39%, 40%; In an optional embodiment, the lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; both possess high dissociation, strong anion delocalization, and excellent electrochemical stability, which is beneficial for increasing the concentration and transport number of free lithium ions in the polyacrylonitrile-polyethylene oxide block copolymer matrix material. The bis(trifluoromethanesulfonyl)imide anion and the bis(fluorosulfonyl)imide anion can form intermolecular coordination interactions with the cyano groups of the PAN segment and the ethylene oxide groups of the PEO segment. This is beneficial for enhancing local ion transport kinetics while maintaining the mechanical integrity of the intermediate layer, and for suppressing interfacial segregation or decomposition of the lithium salt during cycling.

[0024] In an optional embodiment, the mass fraction of lithium salt in the polymer electrolyte interlayer is 15 wt%-30 wt%, for example, 15 wt%, 16.7 wt%, 18.3 wt%, 20 wt%, 21.7 wt%, 23.3 wt%, 25 wt%, 26.7 wt%, 28.3 wt%, or 30 wt%. This helps to ensure sufficient carrier concentration and ionic conductivity while avoiding problems such as phase separation and restricted chain movement caused by excessive lithium salt. At the same time, it can maintain the structural stability of the cyano group and transition metal ion coordination network in the PAN-b-PEO matrix and prevent the coordination balance from being disrupted under high salt concentration, thus reducing the anchoring effect.

[0025] In an optional embodiment, in the polymer electrolyte interlayer, the cyano groups in the polyacrylonitrile-polyethylene oxide block copolymer matrix material are connected to the transition metal ions on the surface of the cathode particles through coordination bonds. This facilitates the realization of an irreversible bonding mechanism between the interlayer and the cathode particles, providing an interfacial bonding strength far exceeding that of van der Waals forces or physical coatings. Furthermore, it extends the ion transport path from the "contact interface" to the "chemical bonding interface," fundamentally improving ion transport efficiency.

[0026] In an optional embodiment, the solid electrolyte in the inorganic solid electrolyte nanofiber network epitaxial layer includes at least one of lithium lanthanum titanium oxide and lithium lanthanum titanium zirconium oxide; both have high ionic conductivity and excellent oxidation stability and lithium-ion migration ability; wherein LLTZO is due to Zr 4+ Doping can further suppress Ti 4+The increase in electronic conductivity caused by valence change is more compatible with interfacial chemistry in oxygen-rich / high-voltage cathode environments, which is beneficial for the inorganic solid electrolyte nanofiber network epitaxial layer to have both high ion flux and low side reaction activity.

[0027] In an optional embodiment, the diameter of the inorganic solid electrolyte nanofibers in the inorganic solid electrolyte nanofiber network epitaxial layer is 50nm-200nm, for example 50 nm, 67 nm, 83 nm, 100 nm, 117 nm, 133 nm, 150 nm, 167 nm, 183 nm, and 200 nm. Under this condition, sufficient ion conduction channels can be built by relying on the large specific surface area, and the resistance to lithium ion movement can be reduced by relying on the nano-confining effect.

[0028] In an optional embodiment, the lithium lanthanum titanium zirconium oxide nanofiber network includes lithium lanthanum titanium zirconium oxide nanofibers arranged radially in an ordered manner. This orientation structure makes the long axis of the fiber perpendicular to the surface of the positive electrode particle, forming the shortest and most continuous lithium ion transport channel from the active center to the solid electrolyte side. This reduces the detours that ions take at the interface and allows the outer layer structure to better adapt to the expansion and contraction deformation in different directions during battery charging and discharging, which is beneficial for buffering the stress caused by volume changes.

[0029] In an optional embodiment, the mass fraction of the inorganic solid electrolyte nanofiber network epitaxial layer in the composite cathode material is 30-40%, for example, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40%. If the proportion of the epitaxial layer is too low, a smooth inorganic conductive pathway cannot be established, and the gradient conductivity cannot be achieved. If the proportion of the epitaxial layer is too high, it will cover the reaction sites of the active material, affecting electron transport and reducing the energy density of the battery.

[0030] In an optional embodiment, the mass ratio of the solid electrolyte to the polyacrylonitrile-polyethylene oxide block copolymer in the inorganic solid electrolyte nanofiber network epitaxial layer is 1:(1.5-2.5).

[0031] The present invention also provides a method for preparing the composite cathode material according to any one of the foregoing embodiments, comprising: The positive electrode active material particles were immersed in a precursor solution containing a polyacrylonitrile-polyethylene oxide block copolymer matrix material, lithium salt, crosslinking agent and solvent, and the coated particles were obtained after solid-liquid separation. Inorganic solid electrolyte precursor fibers are formed on the outer surface of the coated particles by electrospinning, thus forming a composite cathode material precursor. The composite cathode material precursor is subjected to heat treatment to obtain the composite cathode material.

[0032] In the preparation of the composite cathode material in this application, a polyacrylonitrile-polyethylene oxide (PAN-b-PEO) block copolymer is used as the matrix to form a polymer interface layer on the surface of the cathode active particles, which combines ion conductivity (PEO segments) and mechanical / electrochemical stability (PAN segments). A lithium salt provides an in-situ lithium source, and a crosslinking agent enhances the structural integrity and thermal stability of the polymer layer, achieving chemical passivation and interfacial stress buffering of the cathode active material particles, suppressing side reactions and microcrack propagation during cycling. Inorganic solid electrolyte precursor fibers are constructed on the outer surface of the particles coated with the polymer electrolyte interlayer, forming a directional, continuous, high specific surface area three-dimensional lithium-conducting network. The morphology of the nanofiber network avoids the problems of poor interfacial contact and agglomeration caused by traditional powder mixing, which is beneficial to improving the efficiency of lithium-ion cross-interfacial transport. Heat treatment maintains the core-shell-fiber three-level structure of the coated particles without destroying the microphase separation characteristics of the PEO flexible segments and the PAN rigid segments, ultimately improving the interfacial stability, lithium-ion transport kinetics, and structural durability of the composite cathode material.

[0033] In an optional embodiment, the positive electrode active material is selected from at least one of lithium-rich manganese-based positive electrode active materials, high-nickel ternary materials, and lithium iron phosphate materials. It has universal applicability to positive electrode active materials with different surface chemical properties and structural stability, especially covering two typical challenging materials: high reactivity (lithium-rich, high-nickel) and low conductivity (LFP).

[0034] In an optional embodiment, the mass fraction of the solvent in the precursor solution is 30%-95%, for example 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95%. In an optional embodiment, the solvent in the precursor solution is selected from at least one of N,N-dimethylformamide and acetone.

[0035] In an optional embodiment, the solvent comprises N,N-dimethylformamide and acetone, wherein the mass ratio of N,N-dimethylformamide to acetone is (5-7):4, for example 5:4, 5.2:4, 5.4:4, 5.6:4, 5.8:4, 6:4, 6.2:4, 6.4:4, 6.6:4, 6.8:4, or 7:4.

[0036] The aforementioned precursor solution can balance the solubility of PAN-PEO copolymer and the dispersibility of lithium salt, resulting in a uniform and stable precursor solution.

[0037] In an optional embodiment, the soaking temperature is 60℃-80℃, for example 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, and the soaking time is 15min-25min, for example 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min; In an optional embodiment, the soaking is carried out under stirring conditions at a stirring rate of 1500 rpm to 3000 rpm, such as 1500 rpm, 1667 rpm, 1833 rpm, 2000 rpm, 2167 rpm, 2333 rpm, 2500 rpm, 2667 rpm, 2833 rpm, or 3000 rpm.

[0038] Immersion at 60–80℃ allows for moderate stretching and uniform adsorption of polymer chains. Stirring at 1500–3000 rpm enhances solution penetration and interfacial wetting, which helps ensure uniform coating thickness and particle surface coverage.

[0039] In an optional embodiment, the crosslinking agent is selected from polycarbodiimide crosslinking agents, and the mass fraction of the crosslinking agent to the mass fraction of the lithium salt in the precursor solution is (105-115)%:1, for example 105%:1, 106%:1, 107%:1, 108%:1, 109%:1, 110%:1, 111%:1, 112%:1, 113%:1, 114%:1, 115%:1; without causing premature gelation or local precipitation of the polymer, a loose but coherent network structure is formed through the slow reaction of isocyanate groups with the polymer terminal hydroxyl / amino groups, which maintains the lithium ion migration channels of the PEO segments and imparts the necessary mechanical cohesion to the coating layer.

[0040] In an optional embodiment, the spinning solution forming the inorganic solid electrolyte precursor fiber includes a solid electrolyte, a polyacrylonitrile-polyethylene oxide block copolymer, and a spinning solvent, wherein the mass ratio of the polyacrylonitrile-polyethylene oxide block copolymer to the spinning solvent is 1:(5-20), for example, 1:5, 1:8, 1:11, 1:14, 1:17, or 1:20.

[0041] In optional embodiments, the parameters of electrospinning include a voltage of 10 kV-25 kV, such as 10 kV, 12 kV, 13 kV, 15 kV, 17 kV, 18 kV, 20 kV, 22 kV, 23 kV, and 25 kV; a temperature of 20℃-30℃, such as 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, and 30℃; and a receiving distance of 10 cm-20 cm, such as 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, and 20 cm. Preferably, electrospinning includes: a central fiber formation stage, with a voltage of 24-26 kV and a time of 30-60 seconds, aiming to form an initiation point at the center of the particle; and a radial fiber growth stage, with the voltage reduced to 14-16 kV. The scanning mode is radial outward at kV for 2-5 minutes, aiming to form a radial structure. During the structure stabilization stage, the voltage is 10-15 kV for 1-2 minutes, aiming to solidify the fiber structure. By driving fiber growth radially outward from the particle center through gradient electric field design, combined with precise process parameter control and real-time monitoring and adjustment, a high-quality, highly consistent radial fiber structure is achieved.

[0042] The combination of the above spinning solution and electrospinning parameters helps to ensure that the inorganic solid electrolyte precursor fiber has a continuous morphology, appropriate diameter and good adhesion, so that it can be anchored to the polymer electrolyte intermediate layer during heat treatment to form a stable spatial support skeleton, rather than relying on high-temperature sintering to achieve bonding.

[0043] In an optional embodiment, the heat treatment temperature is 80℃-90℃, for example 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, or 90℃, and the time is 110min-130min, for example 110 min, 112 min, 114 min, 116 min, 118 min, 120 min, 122 min, 124 min, 126 min, 128 min, or 130 min, in an inert atmosphere. During the heat treatment process, solvent removal, polymer chain rearrangement, and low-temperature cross-linking and shaping are achieved, physically anchoring the polymer electrolyte interlayer and the inorganic solid electrolyte nanofiber network epitaxial layer.

[0044] The present invention also provides an all-solid-state battery, comprising the composite cathode material described in any one of the foregoing embodiments or the composite cathode material prepared by the method described in any one of the foregoing embodiments.

[0045] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0046] Example 1 This embodiment provides a method for preparing a composite cathode material, specifically including the following steps: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 10mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone solvent (mass ratio 6:4, solvent to LiTFSI ratio 100ml:1g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the mass fraction of the lithium salt was 110%:1, forming a homogeneous precursor solution. 15g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70℃, a stirring rate of 1800rpm, and a soaking time of 20min. Then, they were placed in an oven at 60℃ for vacuum drying for 4h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 100nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 25 kV, time: 45 seconds); a radial fiber growth stage (voltage reduced to 15 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 15 cm. This process allows the LLTO nanofiber precursor to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat-treated in an inert atmosphere at a temperature of 85℃ for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity; wherein the mass fraction of the intermediate layer is 23%, the mass fraction of the epitaxial layer is 35%, and the average diameter of the inorganic solid electrolyte nanofibers in the epitaxial layer is 100nm. Example 2 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that increasing the concentration of the precursor solution increases the mass fraction of the intermediate layer, resulting in a thickness of 150 nm. The method specifically includes the following steps: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 10mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone (mass ratio 6:4) solvent (solvent to LiTFSI ratio 65 ml: 1 g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the lithium salt was 110%:1, forming a homogeneous precursor solution. 15 g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70 °C, a stirring rate of 1800 rpm, and a soaking time of 20 min. Then, they were placed in an oven at 60 °C for vacuum drying for 4 h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 150 nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8 wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 25 kV, time: 45 seconds); a radial fiber growth stage (voltage reduced to 15 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 15 cm. This allows the LLTO nanofiber precursor (105-115)%:1 to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity. Example 3 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that the concentration of the precursor solution is reduced, resulting in a lower mass fraction of the intermediate layer with a thickness of 70 nm. The specific steps include: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 10mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone (mass ratio 6:4) solvent (solvent to LiTFSI ratio 125 ml: 1 g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the lithium salt was 110%:1, forming a homogeneous precursor solution. 15 g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70°C, a stirring rate of 1800 rpm, and a soaking time of 20 min. Then, they were placed in an oven at 60°C for vacuum drying for 4 h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 70 nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8 wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 25 kV, time: 45 seconds); a radial fiber growth stage (voltage reduced to 15 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 15 cm. This allows the LLTO nanofiber precursor (105-115)%:1 to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity. Example 4 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that the concentration of the LLTO precursor solution is increased, resulting in a high mass fraction of the epitaxial layer, which is 45 wt%. The method specifically includes the following steps: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 8mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone solvent (mass ratio 6:4, solvent to LiTFSI ratio 100ml:1g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the mass fraction of the lithium salt was 110%:1, forming a homogeneous precursor solution. 15g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70℃, a stirring rate of 1800rpm, and a soaking time of 20min. Then, they were placed in an oven at 60℃ for vacuum drying for 4h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 100nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 25 kV, time: 45 seconds); a radial fiber growth stage (voltage reduced to 15 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 15 cm. This allows the LLTO nanofiber precursor (105-115)%:1 to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity. Example 5 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that the concentration of the LLTO precursor solution is reduced to make the mass fraction of the epitaxial layer too small, at 20 wt%. The specific steps include: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 13mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone solvent (mass ratio 6:4, solvent to LiTFSI ratio 100ml:1g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the mass fraction of the lithium salt was 110%:1, forming a homogeneous precursor solution. 15g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70℃, a stirring rate of 1800rpm, and a soaking time of 20min. Then, they were placed in an oven at 60℃ for vacuum drying for 4h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 100nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 25 kV, time: 45 seconds); a radial fiber growth stage (voltage reduced to 15 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 15 cm. This allows the LLTO nanofiber precursor (105-115)%:1 to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity.

[0047] Example 6 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that the electrospinning voltage is maintained at 12KV so that the LLTO nanofiber precursor in the epitaxial layer is not deposited radially ordered on the outside of the intermediate layer, but rather randomly deposited. The specific steps include: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 10mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone solvent (mass ratio 6:4, solvent to LiTFSI ratio 100ml:1g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the mass fraction of the lithium salt was 110%:1, forming a homogeneous precursor solution. 15g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70℃, a stirring rate of 1800rpm, and a soaking time of 20min. Then, they were placed in an oven at 60℃ for vacuum drying for 4h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 100nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 12 kV, time: 45 seconds); a radial fiber growth stage (voltage maintained at 12 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 15 cm. This allows the LLTO nanofiber precursor (105-115)%:1 to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity. Example 7 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that shortening the electrospinning acceptance distance results in a larger diameter of the LLTO nanofiber precursor in the epitaxial layer, which is 150 nm. The specific steps include: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 10mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone solvent (mass ratio 6:4, solvent to LiTFSI ratio 100ml:1g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the mass fraction of the lithium salt was 110%:1, forming a homogeneous precursor solution. 15g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70℃, a stirring rate of 1800rpm, and a soaking time of 20min. Then, they were placed in an oven at 60℃ for vacuum drying for 4h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 100nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 25 kV, time: 45 seconds); a radial fiber growth stage (voltage reduced to 15 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 12 cm. This process allows the LLTO nanofiber precursor (105-115)%:1 to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity. Example 8 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that the electrospinning acceptance distance is extended, resulting in a larger diameter of the LLTO nanofiber precursor in the epitaxial layer, which is 75 nm. The specific steps include: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, PAN-b-PEO and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 10mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone solvent (mass ratio 6:4, solvent to LiTFSI ratio 100ml:1g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the mass fraction of the lithium salt was 110%:1, forming a homogeneous precursor solution. 15g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70℃, a stirring rate of 1800rpm, and a soaking time of 20min. Then, they were placed in an oven at 60℃ for vacuum drying for 4h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 100nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8wt%, resulting in coated particles. 3. Epitaxial Layer Deposition: Using coated particles as the collecting substrate, the LLTO precursor solution is spun onto its surface using electrospinning technology. The electrospinning process includes: a central fiber formation stage (voltage: 25 kV, time: 45 seconds); a radial fiber growth stage (voltage reduced to 15 kV, scanning mode: radial outward, time: 3.5 min); and a structure stabilization stage (voltage: 12 kV, time: 1.5 min); a temperature of 25℃; and a receiving distance of 18 cm. This allows the LLTO nanofiber precursor (105-115)%:1 to be deposited radially ordered on the outer side of the intermediate layer, forming a porous network structure epitaxial layer, thus obtaining the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity. Example 9 This embodiment provides a method for preparing a composite cathode material. The main difference from Embodiment 1 is that electrospinning is replaced by direct wetting with an LLTO precursor solution followed by drying. This results in the LLTO nanofiber precursor in the epitaxial layer not forming fibers, but being directly deposited on the outer side of the intermediate layer. The specific steps include: 1. Raw material preparation: Prepare lithium-rich manganese-based positive electrode active material particles (LRMO, D50 of 1.5μm), PAN-b-PEO copolymer (PAN to PEO block ratio of 2:1, molecular weight of 40000), LiTFSI lithium salt, and LLTO precursor solution (composition includes: N,N-dimethylformamide DMF, polyacrylonitrile PAN and lithium lanthanum titanium oxide LLTO particles, and the ratio of the three is 10mL:0.65g:0.35g). 2. Intermediate Layer Construction: PAN-b-PEO and LiTFSI were dissolved in a DMF / acetone solvent (mass ratio 6:4, solvent to LiTFSI ratio 100ml:1g) at a mass ratio of 3:2, and a polycarbodiimide crosslinking agent was added to the solvent. The mass fraction of the crosslinking agent to the mass fraction of the lithium salt was 110%:1, forming a homogeneous precursor solution. 15g of positive electrode active particles were immersed in this precursor solution at a controlled temperature of 70℃, a stirring rate of 1800rpm, and a soaking time of 20min. Then, they were placed in an oven at 60℃ for vacuum drying for 4h, allowing PAN-b-PEO molecules to coordinate with transition metal ions on the particle surface through cyano groups. Simultaneously, in-situ crosslinking was achieved under the action of the crosslinking agent, forming a homogeneous polymer electrolyte intermediate layer with an average thickness of approximately 100nm. The LiTFSI content in the polymer electrolyte intermediate layer was 27.8wt%, resulting in coated particles. 3. Epitaxial layer deposition: The coated particles are immersed in an LLTO precursor solution and then dried at 85°C for 2 hours in an inert atmosphere to obtain the composite cathode material precursor. 4. Heat treatment: The composite cathode material precursor is heat treated in an inert atmosphere at a temperature of 85°C for 2 hours to crystallize LLTO nanofibers and remove residual solvent, finally obtaining a composite cathode material with gradient ion conductivity; wherein the mass fraction of the intermediate layer is 23% and the mass fraction of the epitaxial layer is 35%. Comparative Example 1 This comparative example provides a method for preparing a composite cathode material. The main difference from Example 1 is that steps 3 and 4 are omitted, and the coated particles prepared in step 2 are directly subjected to heat treatment to obtain the composite cathode material.

[0048] Comparative Example 2: This comparative example provides a method for preparing a composite cathode material. The main difference from Example 1 is that step 2 is omitted, and an epitaxial layer is directly deposited on lithium-rich manganese-based cathode active material particles to obtain the composite cathode material.

[0049] Comparative Example 3 This comparative example provides a method for preparing a composite cathode material. The main difference from Example 1 is that there is no gradient, and steps 2 and 3 are performed simultaneously. That is, the LLTO precursor solution in steps 2 and 3 is uniformly mixed and then coated onto lithium-rich manganese-based cathode active material particles, followed by heat treatment, and finally a composite cathode material without gradient ion conductivity is obtained. The heat treatment steps are the same as in Example 1. Comparative Example 4 This comparative example provides a method for preparing a composite cathode material. The main difference from Example 1 is that there is no radial fiber structure in the epitaxial layer. Specifically, step 3 includes: mixing the coated particles from step 2 with the LLTO precursor solution, and then drying them at 85°C for 2 hours under an inert atmosphere to obtain the composite cathode material precursor. Other steps are the same as in Example 1.

[0050] The composite positive electrode materials prepared in the above embodiments and comparative examples were used to prepare composite positive electrode sheets. Then, the composite positive electrode sheets and solid electrolyte sheets (sulfide electrolyte Li) were combined. 3.2 PS4I 0.2 The lithium metal negative electrode sheets are stacked in sequence, aligned, and placed into the lower casing of the battery. After placing the gaskets and spring contacts in sequence, the upper casing is snapped shut for encapsulation, thus producing the CR2032 type all-solid-state lithium metal coin cell battery. A schematic diagram is shown below. Figure 1 As shown. Electrochemical tests were performed on the assembled all-solid-state battery. The specific test methods and conditions are as follows: 1C discharge specific capacity: Charging conditions: CC-CV mode, termination current 0.05C; Discharge conditions: 1C constant current discharge to cutoff voltage (2.5V / cell); Capacity calculation: Discharge capacity (Ah) = Discharge current (A) × Discharge time (h).

[0051] Solid-state battery interface impedance: Electrochemical impedance spectroscopy (EIS) test, test frequency range: 100kHz-0.01Hz; AC amplitude: 5-10mV; environmental control: constant temperature 25℃±2℃, avoid electromagnetic interference.

[0052] LFP-1C & 200-cycle cycle retention: Tested using 1C charge-discharge cycles. Charging: 1C constant current charging to the cutoff voltage, then switching to constant voltage charging until the current drops to 0.05C; Discharging: 1C constant current discharging to the discharge cutoff voltage; Capacity data is recorded every 50 cycles.

[0053] Critical current density: bidirectional CCD test: symmetrical stepped constant current test.

[0054] Test procedure: Start with a low current density and gradually increase the current density, maintaining each current density for a certain period of time (usually 10-30 minutes). Monitor voltage changes and record the point when the voltage suddenly drops to zero. Define the lowest current density at which a short circuit occurs as the CCD.

[0055] The test results are shown in Table 1.

[0056] Table 1

[0057] As can be seen from Table 1, the embodiments show excellent performance in terms of 1C discharge specific capacity, solid-state battery interface impedance, 1C & 200-cycle cycle retention rate and critical current density, which are far superior to the comparative examples.

[0058] In summary, the composite cathode material in this application has the following technical advantages: 1. Gradient ionic conductivity: By combining the polymer electrolyte interlayer and the inorganic solid electrolyte nanofiber network epitaxial layer, a gradient change in ionic conductivity is achieved, which effectively reduces the interfacial impedance and promotes the rapid transport of lithium ions. 2. Stable interfacial contact: The cyano groups in the polymer electrolyte interlayer form coordination bonds with the transition metal ions on the surface of the positive electrode active particles, achieving strong chemical anchoring and avoiding interfacial degradation during cycling. 3. Ordered ion channels: The radially ordered inorganic solid electrolyte nanofiber network in the epitaxial layer forms a three-dimensional high-speed ion conduction pathway, which significantly improves the bulk ion conductivity of the composite cathode. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite cathode material, characterized in that, include: Positive electrode active material particles, wherein a polymer electrolyte interlayer and an inorganic solid electrolyte nanofiber network epitaxial layer are sequentially coated on the positive electrode active material particles, wherein the electrolyte interlayer comprises a polyacrylonitrile-polyethylene oxide block copolymer matrix material and a lithium salt.

2. The composite cathode material of claim 1, wherein, The thickness of the polymer electrolyte interlayer is 50nm-200nm; And / or, the mass fraction of the polymer electrolyte interlayer is 20-25%; And / or, in the raw materials of the polymer electrolyte interlayer, the mass fraction of polyacrylonitrile is 60%-85%, and the mass fraction of polyethylene oxide is 15%-40%; And / or, the lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; And / or, the mass fraction of lithium salt in the polymer electrolyte interlayer is 15 wt%-30 wt%; And / or, in the polymer electrolyte interlayer, the cyano groups in the polyacrylonitrile-polyethylene oxide block copolymer matrix material are connected to the transition metal ions on the surface of the cathode particles through coordination bonds.

3. The composite cathode material of claim 1, wherein, The solid electrolyte in the inorganic solid electrolyte nanofiber network epitaxial layer includes at least one of lithium lanthanum titanium oxide and lithium lanthanum titanium zirconium oxide. And / or, the diameter of the inorganic solid electrolyte nanofibers in the inorganic solid electrolyte nanofiber network epitaxial layer is 50nm-200nm; And / or, the inorganic solid electrolyte nanofiber network epitaxial layer includes inorganic solid electrolyte nanofibers arranged radially in an ordered manner; And / or, in the composite cathode material, the mass fraction of the inorganic solid electrolyte nanofiber network epitaxial layer is 30-40%.

4. The composite cathode material of claim 3, wherein In the inorganic solid electrolyte nanofiber network epitaxial layer, the mass ratio of the solid electrolyte to the polyacrylonitrile-polyethylene oxide block copolymer is 1:(1.5-2.5).

5. A method for preparing the composite cathode material according to any one of claims 1 to 4, characterized in that, include: The positive electrode active material particles were immersed in a precursor solution containing a polyacrylonitrile-polyethylene oxide block copolymer matrix material, lithium salt, crosslinking agent and solvent, and the coated particles were obtained after solid-liquid separation. Inorganic solid electrolyte precursor fibers are formed on the outer surface of the coated particles by electrospinning, thus forming a composite cathode material precursor. The composite cathode material precursor is subjected to heat treatment to obtain the composite cathode material.

6. The method of claim 5, wherein the lithium transition metal composite cathode material is prepared by the following steps of: The positive electrode active material is selected from at least one of lithium-rich manganese-based positive electrode active materials, high-nickel ternary materials, and lithium iron phosphate materials. ​ 7. The method for preparing the composite cathode material according to claim 5, characterized in that, The mass fraction of the solvent in the precursor solution is 30%-95%; And / or, the solvent in the precursor solution is selected from at least one of N,N-dimethylformamide and acetone.

8. The method for preparing the composite cathode material according to claim 5, characterized in that, The solvent includes N,N-dimethylformamide and acetone, and the mass ratio of N,N-dimethylformamide to acetone is (5-7):4; And / or, the soaking temperature is 60℃-80℃, and the soaking time is 15min-25min; And / or, the crosslinking agent is selected from polycarbodiimide crosslinking agents, and in the precursor solution, the mass fraction of the crosslinking agent to the mass fraction of the lithium salt is (105-115)%:1; And / or, the soaking is carried out under stirring conditions at a stirring rate of 1500 rpm - 3000 rpm.

9. The method of claim 5, wherein the composite cathode material is prepared by the steps of: mixing a lithium metal oxide, a conductive material, and a binder to form a mixture; and coating the mixture on a current collector to form a cathode. The spinning solution for forming the inorganic solid electrolyte precursor fiber includes a solid electrolyte, a polyacrylonitrile-polyethylene oxide block copolymer, and a spinning solvent, wherein the mass ratio of the polyacrylonitrile-polyethylene oxide block copolymer to the spinning solvent is 1:(5-20). And / or, the parameters of electrospinning include a voltage of 10 kV-25 kV, a temperature of 20℃-30℃, and a receiving distance of 10cm-20cm; preferably, electrospinning includes: a central fiber formation stage, with a voltage of 24-26 kV and a time of 30-60 seconds; a radial fiber growth stage, with the voltage reduced to 14-16 kV, a scanning mode of radial outward, and a time of 2-5 min; and a structure stabilization stage, with a voltage of 10-15 kV and a time of 1-2 min; And / or, the heat treatment temperature is 80℃-90℃, the time is 110min-130min, and the atmosphere is an inert atmosphere.

10. An all-solid battery, characterized by, The composite cathode material includes the composite cathode material according to any one of claims 1-4 or the composite cathode material prepared by the method according to any one of claims 5-9.

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