Composite-coated positive electrode active material, all-solid-state battery, and method for manufacturing the same

Abstract

The application provides a composite-coated positive electrode active material, a full-solid-state battery and a preparation method thereof. The composite-coated positive electrode active material comprises a positive electrode material inner core and, in sequence, an inorganic oxide layer, a network intermediate layer and a flexible polymer layer outside the positive electrode material inner core. The composite-coated positive electrode active material, the full-solid-state battery and the preparation method thereof provided by the application optimize the interface of the solid-state battery positive electrode material through a gradient composite-coating technology, and realize the synergistic optimization of ion transmission and mechanical buffering.

Description

Technical Field

[0001] This application belongs to the field of solid-state batteries, and particularly relates to composite coated positive electrode active materials, all-solid-state batteries and their preparation methods. Background Technology

[0002] Solid-state batteries, as a core technology for next-generation high-energy-density power batteries, rely heavily on the interfacial compatibility between the cathode active material and the solid electrolyte for their performance. Ternary layered cathode materials, such as high-nickel ternary cathode materials, have attracted much attention due to their high capacity, but the solid-solid interface presents challenges such as space charge layer formation, element interdiffusion, and mechanical stress concentration, leading to increased interfacial impedance and capacity decay.

[0003] CN115172727A discloses a method for coating cathode materials with supercritical fluid. This method employs a high-pressure reactor, using a supercritical fluid such as CO2 to carry a coating agent, such as an organoboroate or titanate, to surface-treat cathode particles under a pressure of 20-80 MPa, forming a single inorganic coating layer (such as Ti-O or BO-based). The aim is to improve coating uniformity and enhance interfacial stability. This technology achieves rolling coating of particles using a mesh roller, followed by annealing and curing of the coated material at 500-1000℃. Results show that it can improve cycle performance to a certain extent; for example, the cycle retention rate of coated lithium iron phosphate materials reaches over 90%. However, this method does not address the issues of flexible buffering and gradient transition, and high-temperature annealing can easily damage the material structure.

[0004] In conclusion, there is an urgent need to develop new solid-state battery materials to meet the practical application requirements of high-performance all-solid-state batteries. Summary of the Invention

[0005] To address the interfacial compatibility issues between cathode active materials and solid electrolytes in existing technologies, this application proposes a composite-coated cathode active material, an all-solid-state battery, and a method for preparing the same. The composite-coated cathode active material achieves synergistic optimization of ion transport and mechanical buffering through a gradient arrangement of an inorganic oxide layer, a network layer, and a flexible polymer layer.

[0006] To achieve this objective, the following technical solution is adopted in this application: In a first aspect, this application provides a composite-coated positive electrode active material, comprising a positive electrode material core and, sequentially located outside the positive electrode material core, an inorganic oxide layer, a network intermediate layer, and a flexible polymer layer. The network intermediate layer is an interwoven structure of inorganic oxide and organic polymer.

[0007] The composite-coated positive electrode active material provided in this application constructs a gradient structure of an inorganic oxide layer, a network intermediate layer, and a flexible polymer layer, which can effectively reduce interfacial impedance and improve cycle stability.

[0008] In some embodiments, the particle size of the composite-coated positive electrode active material is 3~8μm.

[0009] In some embodiments, the cathode material core includes a ternary cathode material core.

[0010] In some embodiments, the molecular formula of the ternary cathode material core is LiNixCoyMn1-x-yO2, where 0.5≤x≤0.95 and 0≤y≤0.2.

[0011] In some embodiments, the average size of the cathode material core is 3~7 μm.

[0012] In some embodiments, the thickness of the inorganic oxide layer is 5 to 50 nm.

[0013] In some embodiments, the inorganic oxide in the inorganic oxide layer includes any one or a combination of at least two of titanium oxide, silicon oxide, or boron oxide.

[0014] In some embodiments, the polymer monomers of the organic polymer in the network intermediate layer include any one or a combination of at least two of ethylene oxide, vinylpyrrolidone, hydroxyethyl acrylate, hydroxyethyl methacrylate, polyethylene glycol methyl ether acrylate, or vinyl ethylene carbonate.

[0015] In some implementations, the thickness of the network intermediate layer is 10~100nm.

[0016] In some embodiments, the polymer monomers of the flexible polymer layer are the same as those of the organic polymer.

[0017] In some embodiments, the thickness of the flexible polymer layer is 5-80 nm.

[0018] Secondly, this application provides a method for preparing the composite-coated positive electrode active material described in the first aspect, the method comprising the following steps: The first cathode material is obtained by mixing cathode material raw materials, inorganic precursors and carriers and then performing supercritical fluid permeation treatment.

[0019] The polymer monomers, initiator and first cathode material are mixed and subjected to in-situ polymerization, followed by heat treatment to obtain a composite coated cathode active material.

[0020] The method for preparing composite-coated positive electrode active materials provided in the second aspect of this application employs a process combining supercritical fluid infiltration treatment, in-situ polymerization, and heat treatment. This process enables the construction of a composite coating layer with distinct gradient characteristics on the surface of the positive electrode material raw material. Specifically, supercritical fluid infiltration treatment allows a supercritical fluid medium to penetrate into the surface of the positive electrode material raw material, making it particularly suitable for industrial mass production processes. The supercritical fluid can penetrate into the pores of the accumulated positive electrode material raw material, thereby improving the uniformity and reproducibility of the coating layer structure. The subsequent in-situ polymerization reaction forms an organic-inorganic interwoven network structure on the surface of the inorganic precursor, and a flexible polymer layer continues to form on the surface as the polymerization reaction proceeds. The subsequent heat treatment further stabilizes the composite coating layer structure. The inner layer consists of a dense inorganic phase composed of inorganic oxides converted from the inorganic precursor, the middle layer is an interpenetrating network structure of inorganic oxides and polymers, and the outer layer is a flexible polymer phase. The prepared composite-coated positive electrode active material exhibits good compatibility with sulfide, oxide, or polymer solid electrolytes.

[0021] In some embodiments, the particle size D50 of the cathode material raw material is 3~7μm.

[0022] In some embodiments, the moisture content of the cathode material raw material is less than 50 ppm.

[0023] In some embodiments, the inorganic precursor includes any one or a combination of at least two of titanium precursors, silicon precursors, or boron precursors.

[0024] In some embodiments, the titanium precursor includes any one or a combination of at least two of tetrabutyl titanate, isopropyl titanate, ethyl titanate, or titanium tetrachloride.

[0025] In some embodiments, the silicon precursor comprises any one or a combination of at least two of tetraethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, or tetrabutyl orthosilicate.

[0026] In some embodiments, the boron precursor includes any one or a combination of at least two of trimethyl borate, triethyl borate, triisopropyl borate, or tributyl borate.

[0027] In some embodiments, the carrier includes any one or a combination of at least two of sodium dodecyl sulfate, perfluorooctanoic acid, or ethylene glycol octylphenyl ether.

[0028] In some embodiments, the supercritical fluid medium in the supercritical fluid permeation treatment includes any one or a combination of at least two of carbon dioxide, carbon monoxide, or ammonia.

[0029] In some embodiments, the mass ratio of the inorganic precursor to the cathode material raw material is (0.01~0.05):1.

[0030] In some embodiments, the mass ratio of the carrier to the cathode material raw material is (0.005~0.015):1.

[0031] In some embodiments, the temperature of the supercritical fluid permeation treatment is 40~60°C.

[0032] In some embodiments, the pressure of the supercritical fluid permeation treatment is 10~20 MPa.

[0033] In some embodiments, the material is turned over during the supercritical fluid permeation process.

[0034] In some embodiments, the rotational speed is 20-30 r / min.

[0035] In some embodiments, the flipping is performed using a twin-ribbon agitator.

[0036] In some embodiments, the supercritical fluid permeation treatment time is 3 to 6 hours.

[0037] In some embodiments, the mixed polymer monomer, initiator, and first cathode material includes adding the polymer monomer and initiator to the system of the first cathode material.

[0038] In some embodiments, the mass ratio of the polymer monomer to the cathode material raw material is (0.02~0.05):1.

[0039] In some embodiments, the initiator includes any one or a combination of at least two of anionic ring-opening polymerization initiators, free radical initiators, or redox initiators.

[0040] In some embodiments, when the polymer monomer comprises ethylene oxide, the initiator comprises any one or a combination of at least two of potassium hydroxide, potassium tert-butoxide, sodium methoxide, or sodium ethoxide.

[0041] In some embodiments, when the polymer monomer comprises vinylpyrrolidone and / or hydroxyethyl acrylate, the initiator comprises any one or a combination of at least two of azobisisobutyronitrile, benzoyl peroxide, ammonium persulfate, or potassium persulfate.

[0042] In some embodiments, the mass ratio of the initiator to the polymer monomer is (0.01~0.04):1.

[0043] In some embodiments, the addition time of the polymer monomer and the initiator is 10 to 20 minutes.

[0044] In some embodiments, the pressure of the in-situ polymerization reaction is 12~12.5 MPa.

[0045] In some embodiments, the in-situ polymerization reaction employs segmented temperature control.

[0046] In some embodiments, the segmented temperature control includes: first reacting for a first duration at a first temperature, then raising the temperature to a second temperature and continuing the second reaction for a second duration.

[0047] In some embodiments, the first temperature ranges from 48 to 52°C.

[0048] In some implementations, the first duration is 80-100 minutes.

[0049] In some embodiments, the viscosity of the material after the first reaction is 570~590 mPa·s.

[0050] In some embodiments, the second temperature ranges from 68 to 72°C.

[0051] In some implementations, the second duration is 130 to 170 minutes.

[0052] In some embodiments, the viscosity of the material after the second reaction is 610~630 mPa·s.

[0053] In some embodiments, the heat treatment is performed in an argon atmosphere.

[0054] In some embodiments, the heating rate of the heat treatment is 2~4℃ / min.

[0055] In some embodiments, the final temperature of the heat treatment is 380~420°C.

[0056] In some embodiments, the heat treatment is held for 1 to 4 hours.

[0057] In some embodiments, the preparation method further includes washing and drying the heat-treated cathode material sequentially.

[0058] In some embodiments, the washing process uses ethanol.

[0059] In some embodiments, the washing is a countercurrent washing.

[0060] In some embodiments, the drying temperature is 70~90°C.

[0061] Thirdly, this application provides an all-solid-state battery, the all-solid-state battery comprising the composite-coated positive electrode active material described in the first aspect.

[0062] In some embodiments, the electrolyte in the all-solid-state battery includes a sulfide solid electrolyte and / or an oxide solid electrolyte.

[0063] Compared with the prior art, the beneficial effects of this application are as follows: (1) This application provides a composite coated positive electrode active material, which achieves synergistic optimization of ion transport and mechanical buffering through the gradient arrangement of inorganic oxide layer, network intermediate layer and flexible polymer layer.

[0064] (2) This application provides a method for preparing a composite coated positive electrode active material, which combines supercritical fluid infiltration with in-situ polymerization reaction to construct a functional gradient coating layer at the molecular level.

[0065] (3) This application provides an all-solid-state battery that optimizes the chemical compatibility and wettability with sulfide / oxide solid electrolytes through the synergistic design of inorganic oxides and polymer phases. Attached Figure Description

[0066] Figure 1 This is a schematic diagram of the structure of the composite-coated positive electrode active material.

[0067] In the figure: 1. Positive electrode material core; 2. Inorganic oxide layer; 3. Network intermediate layer; 4. Flexible polymer layer. Detailed Implementation

[0068] To facilitate understanding of this application, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of this application.

[0069] The technical solution of this application will be further described below with reference to specific implementation methods.

[0070] The coating structure formed by existing coating technologies is too simple. For example, the supercritical fluid coating method used in CN115172727A can only form a single inorganic material coating. This coating is difficult to meet the dual requirements of ion conduction and mechanical buffering at the same time. Its rigidity cannot effectively buffer the stress generated by the volume change of the positive electrode material during charging and discharging. Long-term cycling can easily cause the coating to crack or separate from the substrate, resulting in interface contact failure.

[0071] In terms of process conditions, existing technologies have significant limitations. Supercritical fluid coating requires high annealing temperatures (500-1000℃) to complete the coating curing. This high-temperature process can cause irreversible damage to the bulk structure of the cathode material, especially for heat-sensitive materials such as high-nickel ternary materials, which can exacerbate cation mixing and the formation of residual lithium compounds on the surface. At the same time, the high supercritical pressure conditions (20-80MPa) increase equipment costs and energy consumption, while dry coating technologies such as mechanical ball milling are difficult to achieve uniformity and density of the coating, and are prone to forming discontinuous coatings on the particle surface.

[0072] Significant shortcomings also exist in terms of interface compatibility. Existing coatings exhibit poor chemical compatibility with sulfide solid electrolytes, and a single inorganic coating cannot completely block element interdiffusion, especially under high-voltage conditions, where transition metal ion migration leads to a continuous increase in interfacial impedance. Furthermore, existing coatings have poor wettability with polymer electrolytes, making it difficult to establish continuous ion transport channels between cathode particles.

[0073] Furthermore, existing technologies suffer from insufficient functional integration and lack synergistic design for the multifunctionality of coatings. Supercritical fluid coating primarily focuses on the uniformity and density of the coating but fails to consider introducing conductive components to improve electron transport. While mechanical ball milling can achieve physical mixing, it cannot construct ordered functional structures at the molecular level. This single-function-oriented design approach struggles to meet the stringent requirements of all-solid-state batteries for comprehensive interfacial performance and cannot simultaneously address key issues such as interfacial ion transport, electron conduction, and stress buffering.

[0074] In summary, existing technologies have significant shortcomings in coating structure design, process condition optimization, interface compatibility improvement, and functional integration. These deficiencies severely restrict further improvement in the performance of all-solid-state batteries, and there is an urgent need to develop new coating strategies to meet the practical application requirements of high-performance all-solid-state batteries.

[0075] As one specific implementation of this application, such as Figure 1 As shown, a composite coated positive electrode active material is provided, comprising a positive electrode material core 1 and an inorganic oxide layer 2, a network intermediate layer 3, and a flexible polymer layer 4 sequentially located outside the positive electrode material core 1. The network intermediate layer 3 is an interwoven structure of inorganic oxide and organic polymer.

[0076] This application forms an organic-inorganic interwoven network intermediate layer and a flexible polymer layer. The coating structure has mechanical buffering and continuous ion transport channels, which can not only suppress side reactions and element interdiffusion between the cathode material and the solid electrolyte, but also reduce interfacial impedance, thereby significantly improving cycle retention, rate performance, and thermal stability. Furthermore, in this application, the inorganic oxide layer, the network intermediate layer, and the flexible polymer layer are arranged sequentially, which can form a uniform, dense, and gradient-transition interlayer structure, and the bonding uniformity between layers is better, thereby improving battery cycle performance.

[0077] In some specific embodiments, the particle size of the composite-coated positive electrode active material is 3~8μm, for example, it can be 3μm, 3.6μm, 4.2μm, 4.7μm, 5.3μm, 5.8μm, 6.4μm, 6.9μm, 7.5μm or 8μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0078] In some specific embodiments, the cathode material core includes a ternary cathode material core.

[0079] In some specific embodiments, the molecular formula of the ternary cathode material core is LiNi. x Co y Mn 1-x-y O2, where 0.5 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2. Specifically, the range of values ​​for x can be, for example, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95, but is not limited to the listed values; other unlisted values ​​within this range also apply. The range of values ​​for y can be, for example, 0.01, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0080] In some specific embodiments, the average size of the cathode material core is 3~7μm, for example, it can be 3μm, 3.5μm, 3.9μm, 4.4μm, 4.8μm, 5.3μm, 5.7μm, 6.2μm, 6.6μm or 7μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0081] In some specific embodiments, the thickness of the inorganic oxide layer is 5~50nm, for example, it can be 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0082] In some specific embodiments, the inorganic oxide in the inorganic oxide layer includes any one or a combination of at least two of titanium oxide, silicon oxide, or boron oxide, wherein typical but non-limiting combinations are combinations of titanium oxide and silicon oxide, combinations of boron oxide and silicon oxide, and combinations of titanium oxide and boron oxide.

[0083] The inorganic oxides used in this application employ several of the above-mentioned types. On the one hand, their precursors have excellent compatibility with supercritical fluid systems and stronger surface permeability, which is beneficial to improving the uniformity of inorganic oxide distribution. On the other hand, the above-mentioned oxides have stronger ion transport capabilities, which improves the electrochemical performance of the positive electrode active material.

[0084] In some specific embodiments, the polymer monomers of the organic polymer in the network intermediate layer include any one or a combination of at least two of ethylene oxide, vinylpyrrolidone, hydroxyethyl acrylate, hydroxyethyl methacrylate, polyethylene glycol methyl ether acrylate, or vinyl ethylene carbonate. Typical but non-limiting combinations include combinations of ethylene oxide and vinylpyrrolidone, combinations of hydroxyethyl acrylate and vinylpyrrolidone, combinations of ethylene oxide and hydroxyethyl acrylate, combinations of hydroxyethyl acrylate and hydroxyethyl acrylate, and combinations of vinyl ethylene carbonate and hydroxyethyl acrylate.

[0085] The monomers used in this application are selected from the above-mentioned types, and the polar segments formed therefrom can coordinate well with lithium ions, thereby improving the wettability of the flexible polymer layer to the solid electrolyte and the ion transport promotion effect, and reducing the interfacial impedance.

[0086] In some specific embodiments, the thickness of the network intermediate layer is 10~100nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0087] In some specific embodiments, the polymer monomers of the flexible polymer layer are the same as those of the organic polymer.

[0088] In some specific embodiments, the thickness of the flexible polymer layer is 5~80nm, for example, it can be 5nm, 14nm, 22nm, 30nm, 39nm, 47nm, 55nm, 64nm, 72nm or 80nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0089] As another specific embodiment of this application, this application provides a method for preparing the composite-coated positive electrode active material described in the first aspect, the preparation method comprising the following steps: The first cathode material is obtained by mixing cathode material raw materials, inorganic precursors and carriers and then performing supercritical fluid permeation treatment.

[0090] The polymer monomers, initiator and first cathode material are mixed and subjected to in-situ polymerization, followed by heat treatment to obtain a composite coated cathode active material.

[0091] This application incorporates a carrier agent to enable the inorganic precursor to fully penetrate into the cathode gap and surface micropores under the synergistic effect of the supercritical fluid and the carrier agent. This significantly improves the distribution uniformity of the inorganic precursor, reduces the interfacial impedance of the cathode active material, and enhances electrochemical performance.

[0092] In some specific embodiments, the particle size D50 of the cathode material raw material is 3~7μm, for example, it can be 3μm, 3.5μm, 3.9μm, 4.4μm, 4.8μm, 5.3μm, 5.7μm, 6.2μm, 6.6μm or 7μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0093] In some specific embodiments, the water content of the cathode material raw material is less than 50 ppm, for example, it can be 1 ppm, 7 ppm, 12 ppm, 18 ppm, 23 ppm, 29 ppm, 34 ppm, 40 ppm, 45 ppm or 49 ppm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0094] In some specific embodiments, the inorganic precursor includes any one or a combination of at least two of titanium precursors, silicon precursors, or boron precursors, wherein typical but non-limiting combinations are combinations of titanium and silicon precursors, combinations of boron and silicon precursors, and combinations of titanium and boron precursors.

[0095] The inorganic precursors used in this application are of several types mentioned above, which have excellent compatibility with supercritical fluid systems and stronger surface penetration capabilities, thereby improving the uniformity of inorganic precursor distribution. On the other hand, the oxides formed after the conversion of the above-mentioned precursors have stronger ion transport capabilities, thereby improving the electrochemical performance of the positive electrode active material.

[0096] In some specific embodiments, the titanium precursor includes any one or a combination of at least two of tetrabutyl titanate, isopropyl titanate, ethyl titanate, or titanium tetrachloride, wherein typical but non-limiting combinations are combinations of tetrabutyl titanate and isopropyl titanate, combinations of titanium tetrachloride and isopropyl titanate, combinations of tetrabutyl titanate and titanium tetrachloride, and combinations of ethyl titanate and isopropyl titanate.

[0097] In some specific embodiments, the silicon precursor includes any one or a combination of at least two of tetraethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, or tetrabutyl orthosilicate, wherein typical but non-limiting combinations are combinations of tetraethyl orthosilicate and methyl orthosilicate, combinations of tetrabutyl orthosilicate and methyl orthosilicate, combinations of tetraethyl orthosilicate and tetrabutyl orthosilicate, and combinations of methyltriethoxysilane and methyl orthosilicate.

[0098] In some specific embodiments, the boron precursor includes any one or a combination of at least two of trimethyl borate, triethyl borate, triisopropyl borate, or tributyl borate, wherein typical but non-limiting combinations are combinations of trimethyl borate and triethyl borate, combinations of tributyl borate and triethyl borate, combinations of trimethyl borate and tributyl borate, and combinations of triisopropyl borate and triethyl borate.

[0099] In some specific embodiments, the carrier includes any one or a combination of at least two of sodium dodecyl sulfate, perfluorooctanoic acid, or ethylene glycol octylphenyl ether, wherein typical but non-limiting combinations are the combination of sodium dodecyl sulfate and perfluorooctanoic acid, the combination of ethylene glycol octylphenyl ether and perfluorooctanoic acid, and the combination of sodium dodecyl sulfate and ethylene glycol octylphenyl ether.

[0100] In some specific embodiments, the initiator includes azobisisobutyronitrile (AIBN).

[0101] In some specific embodiments, the supercritical fluid medium in the supercritical fluid permeation treatment includes any one or a combination of at least two of carbon dioxide, carbon monoxide, or ammonia, wherein typical but non-limiting combinations are combinations of carbon dioxide and carbon monoxide, combinations of ammonia and carbon monoxide, and combinations of carbon dioxide and ammonia.

[0102] In some specific embodiments, the mass ratio of the inorganic precursor to the cathode material raw material is (0.01~0.05):1, for example, it can be 0.01:1, 0.015:1, 0.019:1, 0.024:1, 0.028:1, 0.033:1, 0.037:1, 0.042:1, 0.046:1 or 0.05:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0103] This application controls the mass ratio of inorganic precursor to cathode material raw material within a reasonable range. On the one hand, it can have an isolation effect, but on the other hand, it can also avoid the situation where the surface inorganic oxide layer is too thick, which would increase the lithium-ion cross-interface transport path and interfacial polarization, and reduce local agglomeration.

[0104] In some specific embodiments, the mass ratio of the carrier to the cathode material raw material is (0.005~0.015):1, for example, it can be 0.005:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.011:1, 0.012:1, 0.013:1, 0.014:1 or 0.015:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0105] In some specific embodiments, the temperature of the supercritical fluid permeation treatment is 40~60℃, for example, it can be 40℃, 43℃, 45℃, 47℃, 49℃, 52℃, 54℃, 56℃, 58℃ or 60℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0106] In some specific embodiments, the pressure of the supercritical fluid permeation treatment is 10~20MPa, for example, it can be 10MPa, 12MPa, 13MPa, 14MPa, 15MPa, 16MPa, 17MPa, 18MPa, 19MPa or 20MPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0107] In some specific embodiments, the material is turned over during the supercritical fluid permeation process.

[0108] In some specific embodiments, the rotation speed is 20~30 r / min, for example, it can be 20 r / min, 22 r / min, 23 r / min, 24 r / min, 25 r / min, 26 r / min, 27 r / min, 28 r / min, 29 r / min or 30 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0109] In some specific embodiments, the flipping is performed using a dual-ribbon agitator.

[0110] In some specific embodiments, the supercritical fluid permeation treatment time is 3 to 6 hours, for example, it can be 3 hours, 3.4 hours, 3.7 hours, 4 hours, 4.4 hours, 4.7 hours, 5 hours, 5.4 hours, 5.7 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0111] In some specific embodiments, the mixed polymer monomer, initiator and first cathode material includes adding polymer monomer and initiator to the system of the first cathode material.

[0112] In some specific embodiments, the mass ratio of the polymer monomer to the cathode material raw material is (0.02~0.05):1, for example, it can be 0.02:1, 0.024:1, 0.027:1, 0.03:1, 0.034:1, 0.037:1, 0.04:1, 0.044:1, 0.047:1 or 0.05:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0113] This application controls the mass ratio of polymer monomers to cathode material raw materials within a reasonable range. On the one hand, it can play a certain role in isolation. On the other hand, it can reduce the situation where excessively thick polymer coating layer leads to reduced electron contact between cathode particles and increased mass transfer resistance. It can also avoid the situation where excessive polymer residue affects the interface stability after heat treatment.

[0114] In some specific embodiments, the mass ratio of the initiator to the polymer monomer is (0.01~0.04):1, for example, it can be 0.01:1, 0.014:1, 0.017:1, 0.02:1, 0.024:1, 0.027:1, 0.03:1, 0.034:1, 0.037:1 or 0.04:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0115] In some specific embodiments, the initiator includes any one or a combination of at least two of anionic ring-opening polymerization initiators, free radical initiators, or redox initiators, wherein typical but non-limiting combinations are combinations of anionic ring-opening polymerization initiators and free radical initiators, combinations of redox initiators and free radical initiators, and combinations of anionic ring-opening polymerization initiators and redox initiators.

[0116] In some specific embodiments, when the polymer monomer comprises ethylene oxide, the initiator comprises any one or a combination of at least two of potassium hydroxide, potassium tert-butoxide, sodium methoxide, or sodium ethoxide, wherein typical but non-limiting combinations are combinations of potassium hydroxide and potassium tert-butoxide, combinations of sodium methoxide and potassium tert-butoxide, combinations of potassium hydroxide and sodium methoxide, and combinations of sodium ethoxide and potassium tert-butoxide.

[0117] In some specific embodiments, when the polymer monomer comprises vinylpyrrolidone and / or hydroxyethyl acrylate, the initiator comprises any one or a combination of at least two of azobisisobutyronitrile, benzoyl peroxide, ammonium persulfate, or potassium persulfate, wherein typical but non-limiting combinations are a combination of azobisisobutyronitrile and benzoyl peroxide, a combination of ammonium persulfate and benzoyl peroxide, a combination of azobisisobutyronitrile and ammonium persulfate, or a combination of potassium persulfate and ammonium persulfate.

[0118] In some specific embodiments, the addition time of the polymer monomer and the initiator is 10 to 20 minutes, for example, it can be 10 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0119] In some specific embodiments, the pressure of the in-situ polymerization reaction is 12~12.5 MPa, for example, it can be 12.0 MPa, 12.06 MPa, 12.12 MPa, 12.17 MPa, 12.23 MPa, 12.28 MPa, 12.34 MPa, 12.39 MPa, 12.45 MPa or 12.5 MPa, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0120] In some specific embodiments, the in-situ polymerization reaction employs segmented temperature control.

[0121] In some specific embodiments, the segmented temperature control includes: first reacting for a first duration at a first temperature, and then raising the temperature to a second temperature to continue the second reaction for a second duration.

[0122] In some specific embodiments, the first temperature range is 48~52℃, for example, it can be 48℃, 48.5℃, 48.9℃, 49.4℃, 49.8℃, 50.3℃, 50.7℃, 51.2℃, 51.6℃ or 52℃, but is not limited to the listed values, other unlisted values ​​in this range are also applicable.

[0123] In some specific embodiments, the first duration is 80 to 100 minutes, for example, it can be 80 minutes, 83 minutes, 85 minutes, 87 minutes, 89 minutes, 92 minutes, 94 minutes, 96 minutes, 98 minutes or 100 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0124] In some specific embodiments, the viscosity of the material after the first reaction is 570~590 mPa·s, for example, it can be 570 mPa·s, 573 mPa·s, 575 mPa·s, 577 mPa·s, 579 mPa·s, 582 mPa·s, 584 mPa·s, 586 mPa·s, 588 mPa·s or 590 mPa·s, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0125] In some specific embodiments, the range of the second temperature is 68~72℃, for example, it can be 68℃, 68.5℃, 68.9℃, 69.4℃, 69.8℃, 70.3℃, 70.7℃, 71.2℃, 71.6℃ or 72℃, but is not limited to the listed values, other unlisted values ​​in this range are also applicable.

[0126] In some specific embodiments, the second duration is 130 to 170 minutes, for example, it can be 130 minutes, 135 minutes, 139 minutes, 144 minutes, 148 minutes, 153 minutes, 157 minutes, 162 minutes, 166 minutes or 170 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0127] In some specific embodiments, the viscosity of the material after the second reaction is 610~630 mPa·s, for example, it can be 610 mPa·s, 613 mPa·s, 615 mPa·s, 617 mPa·s, 619 mPa·s, 622 mPa·s, 624 mPa·s, 626 mPa·s, 628 mPa·s or 630 mPa·s, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0128] In some specific embodiments, the heat treatment is performed in an argon atmosphere.

[0129] In some specific embodiments, the heating rate of the heat treatment is 2~4℃ / min, for example, it can be 2℃ / min, 2.3℃ / min, 2.5℃ / min, 2.7℃ / min, 2.9℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min or 4℃ / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0130] In some specific embodiments, the final temperature of the heat treatment is 380~420℃, for example, it can be 380℃, 385℃, 389℃, 394℃, 398℃, 403℃, 407℃, 412℃, 416℃ or 420℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0131] In some specific embodiments, the heat treatment holding time is 1 to 4 hours, for example, it can be 1 hour, 1.4 hours, 1.7 hours, 2 hours, 2.4 hours, 2.7 hours, 3 hours, 3.4 hours, 3.7 hours or 4 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0132] In some specific embodiments, the preparation method further includes: sequentially washing and drying the heat-treated cathode material.

[0133] In some specific embodiments, the washing process uses ethanol.

[0134] In some specific embodiments, the washing is countercurrent washing.

[0135] In some specific embodiments, the drying temperature is 70~90℃, for example, it can be 70℃, 73℃, 75℃, 77℃, 79℃, 82℃, 84℃, 86℃, 88℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0136] In some specific embodiments, the drying time is 6 to 15 hours, for example, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0137] As a technical solution of certain specific embodiments of this application, the preparation method includes the following steps: S1. The cathode material raw material is dried to obtain a cathode material raw material with a particle size D50 of 3~7μm and a water content of <50ppm; S2. Mix the cathode material raw material, inorganic precursor and carrier, with the mass ratio of inorganic precursor to cathode material raw material being (0.01~0.05):1 and the mass ratio of carrier to cathode material raw material being (0.005~0.015):1. Use a supercritical fluid medium of any one or at least two combinations of carbon dioxide, carbon monoxide or ammonia to perform supercritical fluid permeation treatment at a temperature of 40~60℃, a pressure of 10~20MPa and a time of 3~6h to obtain the first cathode material. The inorganic precursor comprises any one or a combination of at least two of titanium precursors, silicon precursors, or boron precursors; the titanium precursor comprises any one or a combination of at least two of tetrabutyl titanate, isopropyl titanate, ethyl titanate, or titanium tetrachloride; the silicon precursor comprises any one or a combination of at least two of ethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, or tetrabutyl silicate; the boron precursor comprises any one or a combination of at least two of trimethyl borate, triethyl borate, triisopropyl borate, or tributyl borate; and the carrier comprises any one or a combination of at least two of sodium dodecyl sulfate, perfluorooctanoic acid, or ethylene glycol octylphenyl ether. S3. Add a mixture of polymer monomers and initiator to the system of the first cathode material. The mass ratio of polymer monomers to cathode material raw materials is (0.02~0.05):1, and the mass ratio of initiator to polymer monomers is (0.01~0.04):1. Carry out an in-situ polymerization reaction under a pressure of 12~12.5MPa. The in-situ polymerization reaction adopts segmented temperature control. The segmented temperature control includes: firstly, the first reaction is carried out at 48~52℃ for 80~100min until the viscosity of the material after the first reaction is 570~590mPa·s, and then the temperature is raised to 68~72℃ to continue the second reaction for 130~170min until the viscosity of the material after the second reaction is 610~630mPa·s. S4. Transfer the material after polymerization reaction into a heat treatment device and heat it to 380-420℃ at a rate of 2-4℃ / min for 1-4 hours to obtain the heat-treated cathode material. S5. The heat-treated cathode material is sequentially washed with ethanol in countercurrent and dried at 70~90℃ for 6~15h to obtain the composite coated cathode active material.

[0138] As another specific embodiment of this application, this application provides an all-solid-state battery, which includes the composite coated positive electrode active material described in the first aspect.

[0139] The following detailed description uses specific examples.

[0140] It should be understood that in the description of this application, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0141] It should be noted that, in the description of this application, unless otherwise expressly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0142] Those skilled in the art should understand that this application necessarily includes the necessary pipelines, conventional valves and general pump equipment for achieving process integrity, but the above content is not the main inventive point of this application. Those skilled in the art can add layouts based on the process flow and equipment structure selection. This application does not make any special requirements or specific limitations in this regard.

[0143] Example 1 This embodiment provides a composite-coated positive electrode active material, which includes a positive electrode material core and, sequentially located outside the positive electrode material core, an inorganic oxide layer, a network intermediate layer, and a flexible polymer layer; the network intermediate layer is an interwoven structure of inorganic oxide and organic polymer. The average particle size of the composite-coated positive electrode active material is 4.6 μm.

[0144] The cathode material core includes a ternary cathode material core with the molecular formula LiNi. 0.8 Co 0.1 Mn 0.1 O2; the average size of the cathode material core is 4.5 μm.

[0145] The inorganic oxide layer has a thickness of 20 nm; the inorganic oxide in the inorganic oxide layer is titanium oxide.

[0146] The polymer monomer of the organic polymer in the network intermediate layer is ethylene oxide, that is, the organic polymer is polyethylene oxide; the thickness of the network intermediate layer is 50 nm.

[0147] The polymer monomer of the flexible polymer layer is the same as that of the organic polymer, that is, the flexible polymer layer is polyethylene oxide; the thickness of the flexible polymer layer is 30 nm.

[0148] This embodiment also provides a method for preparing the above-mentioned composite-coated positive electrode active material, the preparation method comprising the following steps: S1, for 20 kg of cathode material raw material (LiNi) 0.8 Co 0.1 Mn 0.1The cathode material raw material was obtained by drying with O2 to obtain a particle size D50 of 4.5 μm and a water content of <50 ppm. S2. Mix the cathode material raw materials, inorganic precursor, and carrier. The mass ratio of the inorganic precursor (tetrabutyl titanate) to the cathode material raw materials is 0.02:1, and the mass ratio of the carrier (sodium dodecyl sulfate) to the cathode material raw materials is 0.012:1. First, add the above mixture to the high-pressure reactor, then purge with nitrogen three times, and then pump carbon dioxide to a pressure of 12 MPa for supercritical fluid permeation treatment at a temperature of 45°C. While using a double ribbon stirrer to slowly turn the material at a speed of 25 rpm, the supercritical fluid permeation treatment lasts for 4 hours to obtain the first cathode material.

[0149] S3. Within 15 minutes, a mixture of polymer monomer (ethylene oxide) and initiator (potassium tert-butoxide) is added to the system of the first cathode material. The mass ratio of polymer monomer to cathode material raw material is 0.03:1, and the mass ratio of initiator to polymer monomer is 0.012:1. In-situ polymerization is carried out under a pressure of 12~12.5MPa. The in-situ polymerization reaction adopts segmented temperature control. The segmented temperature control includes: first, the first reaction is carried out at 50℃ for 90 minutes until the viscosity of the material after the first reaction is 580mPa·s (the initial viscosity is 125 mPa·s), and then the temperature is raised to 70℃ to continue the second reaction for 150 minutes until the viscosity of the material after the second reaction is 620mPa·s.

[0150] S4. The material after polymerization reaction is transferred to a heat treatment device and heated to 400℃ at 2.5℃ / min for 2 hours to obtain the heat-treated cathode material.

[0151] S5. The heat-treated cathode material is sequentially washed with anhydrous ethanol in countercurrent and dried at 80°C for 8 hours to obtain the composite coated cathode active material.

[0152] Example 2 This embodiment provides a composite-coated positive electrode active material, which includes a positive electrode material core and, sequentially located outside the positive electrode material core, an inorganic oxide layer, a network intermediate layer, and a flexible polymer layer; the network intermediate layer is an interwoven structure of inorganic oxide and organic polymer. The average particle size of the composite-coated positive electrode active material is 5.3 μm.

[0153] The cathode material core includes a ternary cathode material core with the molecular formula LiNi. 0.9 Co 0.05 Mn 0.05 O2; the average size of the cathode material core is 5.2 μm.

[0154] The inorganic oxide layer has a thickness of 15 nm; the inorganic oxide in the inorganic oxide layer is silicon oxide.

[0155] The polymer monomer of the organic polymer in the network intermediate layer is vinylpyrrolidone, that is, the organic polymer is polyvinylpyrrolidone; the thickness of the network intermediate layer is 40 nm.

[0156] The polymer monomer of the flexible polymer layer is the same as that of the organic polymer, that is, the flexible polymer layer is polyvinylpyrrolidone; the thickness of the flexible polymer layer is 25 nm.

[0157] This embodiment also provides a method for preparing the above-mentioned composite-coated positive electrode active material, the preparation method comprising the following steps: S1, for 25 kg of cathode material raw material (LiNi) 0.9 Co 0.05 Mn 0.05 The cathode material raw material was obtained by drying with O2 to obtain a particle size D50 of 5.2 μm and a water content of <50 ppm.

[0158] S2. Mix the cathode material raw materials, inorganic precursor, and carrier. The mass ratio of the inorganic precursor (tetraethyl orthosilicate) to the cathode material raw materials is 0.01:1, and the mass ratio of the carrier (perfluorooctanoic acid) to the cathode material raw materials is 0.005:1. First, add the above mixture to the high-pressure reactor, then purge with nitrogen three times, and then pump carbon dioxide to a pressure of 10 MPa for supercritical fluid permeation treatment at a temperature of 60°C. While using a double ribbon stirrer to slowly turn the material at a speed of 30 rpm, the supercritical fluid permeation treatment lasts for 6 hours to obtain the first cathode material.

[0159] S3. Within 20 minutes, a mixture of polymer monomer (vinylpyrrolidone) and initiator (azobisisobutyronitrile) is added to the system of the first cathode material. The mass ratio of polymer monomer to cathode material raw material is 0.02:1, and the mass ratio of initiator to polymer monomer is 0.01:1. In-situ polymerization reaction is carried out under a pressure of 12~12.5MPa. The in-situ polymerization reaction adopts segmented temperature control. The segmented temperature control includes: firstly, the first reaction is carried out at 52℃ for 80 minutes until the viscosity of the material after the first reaction is 590mPa·s (the initial viscosity is 115mPa·s), and then the temperature is raised to 68℃ to continue the second reaction for 170 minutes until the viscosity of the material after the second reaction is 630mPa·s.

[0160] S4. The material after polymerization reaction is transferred to a heat treatment device and heated to 420℃ at 4℃ / min for 1.5h to obtain the heat-treated cathode material.

[0161] S5. The heat-treated cathode material is sequentially washed with anhydrous ethanol in countercurrent and dried at 70°C for 15 hours to obtain the composite coated cathode active material.

[0162] Example 3 This embodiment provides a composite-coated positive electrode active material, which includes a positive electrode material core and an inorganic oxide layer, a network intermediate layer, and a flexible polymer layer sequentially located outside the positive electrode material core; the network intermediate layer is an interwoven structure of inorganic oxide and organic polymer. The average particle size of the composite-coated positive electrode active material is 3.8 μm.

[0163] The cathode material core includes a ternary cathode material core with the molecular formula LiNi. 0.8 Co 0.1 Mn 0.1 O2; the average size of the cathode material core is 3.7 μm.

[0164] The inorganic oxide layer has a thickness of 30 nm; the inorganic oxide in the inorganic oxide layer is boron oxide.

[0165] The polymer monomer of the organic polymer in the network intermediate layer is hydroxyethyl acrylate, that is, the organic polymer is polyhydroxyethyl acrylate; the thickness of the network intermediate layer is 60 nm.

[0166] The polymer monomer of the flexible polymer layer is the same as that of the organic polymer, that is, the flexible polymer layer is hydroxyethyl polyacrylate; the thickness of the flexible polymer layer is 40 nm.

[0167] This embodiment also provides a method for preparing the above-mentioned composite-coated positive electrode active material, the preparation method comprising the following steps: S1, for 25 kg of cathode material raw material (LiNi) 0.8 Co 0.1 Mn 0.1 The cathode material raw material was obtained by drying with O2 to obtain a particle size D50 of 3.7 μm and a water content of <50 ppm.

[0168] S2. Mix the cathode material raw materials, inorganic precursor, and carrier. The mass ratio of the inorganic precursor (trimethyl borate) to the cathode material raw materials is 0.05:1, and the mass ratio of the carrier (ethylene glycol octylphenyl ether) to the cathode material raw materials is 0.015:1. First, add the above mixture to the high-pressure reactor, then purge with nitrogen three times, and then pump carbon dioxide to a pressure of 18 MPa for supercritical fluid permeation treatment at a temperature of 40°C. While using a double ribbon stirrer to slowly turn the material at a speed of 20 rpm, the supercritical fluid permeation treatment lasts for 3 hours to obtain the first cathode material.

[0169] S3. Within 10 minutes, a mixture of polymer monomer (hydroxyethyl acrylate) and initiator (azobisisobutyronitrile) is added to the system of the first positive electrode material. The mass ratio of polymer monomer to positive electrode material raw material is 0.05:1, and the mass ratio of initiator to polymer monomer is 0.04:1. In-situ polymerization reaction is carried out under a pressure of 12~12.3MPa. The in-situ polymerization reaction adopts segmented temperature control. The segmented temperature control includes: firstly, the first reaction is carried out at 48℃ for 100 minutes until the viscosity of the material after the first reaction is 570mPa·s (the initial viscosity is 123mPa·s), and then the temperature is raised to 72℃ to continue the second reaction for 130 minutes until the viscosity of the material after the second reaction is 610mPa·s.

[0170] S4. Transfer the material after polymerization reaction into a heat treatment device and heat it to 380℃ at a rate of 2℃ / min for 3 hours to obtain the heat-treated cathode material.

[0171] S5. The heat-treated cathode material is sequentially washed with anhydrous ethanol in countercurrent and dried at 90°C for 6 hours to obtain the composite-coated cathode active material.

[0172] Example 4 This embodiment provides a composite coated positive electrode active material. Except for the absence of sodium dodecyl sulfate as a carrier, the composite coated positive electrode active material is the same as that in Example 1, and will not be described again here.

[0173] Because no carrier was added, the dispersion and carrying capacity of tetrabutyl titanate in supercritical carbon dioxide decreased, making it difficult for the inorganic precursor to fully penetrate the interparticle gaps and surface micropores of the cathode material, resulting in reduced continuity and uniformity of the titanium oxide layer. Compared with Example 1, the interfacial impedance increased in this example, and the 1C cycle retention rate, 5C capacity retention rate, and initial thermal runaway temperature all decreased.

[0174] Example 5 This embodiment provides a composite coated positive electrode active material. Except for the replacement of tetrabutyl titanate with sodium aluminate, the composite coated positive electrode active material is the same as that in Example 1, and will not be described again here.

[0175] Sodium aluminate exhibits weaker compatibility and surface permeability with supercritical carbon dioxide than tetrabutyl titanate, and the alumina layer formed by aluminum source conversion has relatively weak ion transport capacity, easily leading to increased interfacial polarization. Compared to Example 1, the initial capacity and rate performance of this example are reduced, and the cycle retention rate is slightly decreased.

[0176] Example 6 This embodiment provides a composite coated positive electrode active material. Except for the polymer monomer being replaced by methyl methacrylate instead of ethylene oxide, the composite coated positive electrode active material is the same as that in Example 1, and will not be described again here.

[0177] The polymer segments formed from methyl methacrylate have weaker polarity and lithium-ion coordination ability than those formed from polyethylene oxide, resulting in insufficient wettability of the flexible polymer layer to the solid electrolyte and inadequate ion transport promotion. Compared to Example 1, the interfacial impedance in this example is significantly increased, and the cycle retention rate and rate performance are reduced.

[0178] Example 7 This embodiment provides a composite coated positive electrode active material. Except for the mass ratio of tetrabutyl titanate to the positive electrode material raw material being 0.06:1, the composite coated positive electrode active material is the same as that in Example 1, and will not be described again here.

[0179] When the amount of tetrabutyl titanate added is too high, the inorganic oxide layer on the surface becomes too thick, which increases the lithium-ion cross-interface transport path and interfacial polarization, and may lead to local agglomeration. Compared with Example 1, the interfacial impedance of this example is increased, and the initial capacity and rate performance are reduced.

[0180] Example 8 This embodiment provides a composite coated positive electrode active material. Except for the mass ratio of ethylene oxide to the positive electrode material raw material being 0.08:1, the composite coated positive electrode active material is the same as that in Example 1, and will not be described again here.

[0181] When the amount of ethylene oxide added is too high, the outer polymer coating layer becomes too thick, which can easily reduce the electron contact between cathode particles and increase mass transfer resistance. Some residual polymer can also affect the interface stability after heat treatment. Compared with Example 1, the initial capacity at 1C, cycle retention rate, and 5C capacity retention rate of this Example 1 all decreased.

[0182] Comparative Example 1 This comparative example provides a coated positive electrode active material. Except for step S2, in which tetrabutyl titanate is not added and only supercritical fluid permeation treatment is performed, the coated positive electrode active material is the same as in Example 1, and will not be described again here.

[0183] Without the addition of tetrabutyl titanate, supercritical fluid infiltration treatment cannot form an effective inorganic oxide isolation layer on the surface of the cathode material, making it difficult to suppress side reactions and elemental interdiffusion between the cathode material and the solid electrolyte. Compared with Example 1, the interfacial impedance of this comparative example is significantly increased, and the cycle retention rate, rate performance, and thermal stability are significantly reduced.

[0184] Comparative Example 2 This comparative example provides a coated positive electrode active material. Except for skipping step S3 and directly proceeding to steps S4 to S5, the coated positive electrode active material is the same as in Example 1, and will not be described again here.

[0185] Because the organic-inorganic interwoven network intermediate layer and flexible polymer layer are not formed, the coating structure lacks mechanical buffering and continuous ion transport channels, making the solid-solid interface contact more prone to degradation during long cycles. Compared with Example 1, the interface impedance of this comparative example is increased, and the cycle retention rate, rate performance, and thermal stability are decreased.

[0186] Comparative Example 3 This comparative example provides a composite coated positive electrode active material. Except for step S2, which is omitted and tetrabutyl titanate is added to step S3, the composite coated positive electrode active material is the same as that in Example 1, and will not be described again here.

[0187] When tetrabutyl titanate is added directly in step S3 without supercritical fluid permeation treatment, the inorganic precursor is mainly distributed on the outer surface of the particles, making it difficult to form a uniform, dense, and gradient-transition inner layer structure. Consequently, the bonding uniformity between the subsequent polymer layer and the inorganic layer is poor. Compared to Example 1, this comparative example shows increased interfacial impedance and a significant decrease in cycle stability and rate performance.

[0188] Comparative Example 4 This comparative example provides a composite coated positive electrode active material. Except for the absence of the heat treatment in step S4, the composite coated positive electrode active material is the same as that in Example 1, and will not be described again here.

[0189] Without the heat treatment in step S4, the conversion of the inorganic precursor to the inorganic oxide is insufficient, the network intermediate layer is not sufficiently cured, and the structural stability of the coating layer during cycling is poor. Compared with Example 1, the interfacial impedance of this comparative example is increased, and the cycle retention rate, rate performance, and initial thermal runaway temperature are all decreased.

[0190] Test method: Electrochemical impedance spectroscopy (EIS) was used to test the interfacial impedance of all-solid-state batteries assembled with composite-coated positive electrode active materials. The test conditions were: test after standing at 25℃ for 2 hours, frequency range of 100kHz~0.01Hz, AC disturbance voltage of 5mV, and the interfacial impedance was obtained by fitting the high-frequency / mid-frequency semicircles in the Nyquist plot.

[0191] Battery performance test: Preparation of all-solid-state battery: Under an Ar atmosphere, the positive electrode material, Li3InCl6 and SP of the all-solid-state battery described in the above examples and comparative examples are mixed in a mass ratio of 60:35:5 to obtain a mixed positive electrode powder. Then, the mixed positive electrode powder is placed at the bottom of an all-solid-state mold made of PTFE material with an inner diameter of 10 mm. Then, Li6PS5Cl powder is added on top of the mixed positive electrode powder. Then, the negative electrode material (the negative electrode material is a LiIn alloy film with an In molar ratio of 3:1) is evenly distributed on top of the Li6PS5Cl powder. Finally, a pressure of 3T is applied to the upper and lower ends of the all-solid-state mold and held to fix it, thereby assembling an all-solid-state battery.

[0192] The all-solid-state battery was tested for its capacity, rate performance, and cycle performance. The test conditions were as follows: after the battery was assembled and aged for 12 hours, charge-discharge tests were performed at different potentials. After activation at 3.5-4.8V and 0.1C rate for 3 cycles, it was then cycled 1000 times at 1C to obtain its capacity retention rate. The capacity retention rate at 5C was also tested.

[0193] Thermal runaway test: The initial thermal runaway temperature of the above-mentioned all-solid-state battery was tested using an adiabatic accelerated calorimeter (ARC). The test adopted the Heat-Wait-Search mode, with an initial temperature of 80℃, a heating step of 5℃, and a waiting time of 10min. The initial thermal runaway temperature was recorded when the self-heating rate reached 0.02℃ / min.

[0194] The test results of the above embodiments and comparative examples are shown in Table 1.

[0195] Table 1 Based on the data in Table 1, the following points can be observed: (1) As can be seen from Examples 1-3, this application utilizes a gradient composite coating technology, employing supercritical fluid infiltration, in-situ polymerization, and thermal treatment to synergistically construct an inorganic oxide layer, a network intermediate layer, and a flexible polymer layer. This results in the lowest interfacial impedance, optimal cycle retention, rate performance, and thermal stability, achieving significant results in optimizing the interface of solid-state battery cathode materials. Compared to existing technologies, the interfacial impedance of the cathode material prepared in this application is reduced to 48 Ω·cm. 2 Within this range, the lithium-ion transport efficiency is reduced by approximately 70-75% compared to uncoated materials, significantly improving lithium-ion transport efficiency. In terms of cycle performance, after 1000 cycles, the capacity retention rate reaches over 95.2%, and the 5C capacity retention rate is over 85.3%, with high thermal stability and an initial thermal runaway temperature above 285℃.

[0196] (2) Comparing Example 1 and Examples 4-8, it can be seen that the interface impedance of Example 1 is 35 Ω·cm. 2After 1000 cycles at 1C, the capacity retention was 97.8%, and at 5C, it was 87.9%. The initial thermal runaway temperature was 295℃, indicating that the gradient composite coating layer can balance interfacial stability, ion transport, and mechanical buffering. Although Examples 4-8 still possessed a composite coating structure, due to the absence of a carrier, changes in the type of inorganic oxide, or deviations in the amount of coating components from the specified range, the interfacial impedance increased to 58-72 Ω·cm. 2 As a result, the capacity retention and rate performance decrease. This indicates that there is a synergistic effect between the supercritical fluid infiltration, in-situ polymerization, and heat treatment steps in this application. By adding a carrier, selecting specific inorganic oxides, and adjusting the amount of coating components, this application can improve the cycle performance, rate performance, and thermal stability of the positive electrode active material, and reduce the interfacial impedance.

[0197] (3) In Comparative Examples 1 to 4, due to the lack of an inorganic oxide layer, a network intermediate layer, a supercritical infiltration process, or a heat treatment curing process, the interfacial impedance further increased to 78 to 116 Ω·cm. 2 The cycling and safety performance is significantly weaker than that of Example 1. This indicates that the present application, by employing supercritical fluid infiltration, in-situ polymerization, and heat treatment to synergistically construct a gradient-structured inorganic oxide layer, network interlayer, and flexible polymer layer, can reduce interfacial impedance and improve cycle retention, rate performance, and thermal stability.

[0198] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A composite-coated positive electrode active material, characterized in that, The composite coated positive electrode active material includes a positive electrode material core and an inorganic oxide layer, a network intermediate layer, and a flexible polymer layer located sequentially outside the positive electrode material core; The intermediate layer of the network is an interwoven structure of inorganic oxides and organic polymers.

2. The composite-coated positive electrode active material according to claim 1, characterized in that, The particle size of the composite-coated positive electrode active material is 3~8μm; And / or, the cathode material core includes a ternary cathode material core; And / or, the molecular formula of the ternary cathode material core is LiNi. x Co y Mn 1-x-y O2, where 0.5≤x≤0.95, 0≤y≤0.2; And / or, the average size of the cathode material core is 3~7μm.

3. The composite-coated positive electrode active material according to claim 1 or 2, characterized in that, The thickness of the inorganic oxide layer is 5~50 nm; And / or, the inorganic oxides in the inorganic oxide layer include any one or a combination of at least two of titanium oxide, silicon oxide, or boron oxide.

4. The composite-coated positive electrode active material according to any one of claims 1 to 3, characterized in that, The polymer monomers of the organic polymer in the intermediate layer of the network include any one or a combination of at least two of ethylene oxide, vinylpyrrolidone, hydroxyethyl acrylate, hydroxyethyl methacrylate, polyethylene glycol methyl ether acrylate, or vinyl ethylene carbonate. And / or, the thickness of the network intermediate layer is 10~100nm; And / or, the polymer monomers of the flexible polymer layer are the same as those of the organic polymer; And / or, the thickness of the flexible polymer layer is 5~80nm.

5. A method for preparing a composite-coated positive electrode active material as described in any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: The first cathode material is obtained by mixing cathode material raw materials, inorganic precursors and carriers and performing supercritical fluid permeation treatment. The polymer monomers, initiator and first cathode material are mixed and subjected to in-situ polymerization, followed by heat treatment to obtain a composite coated cathode active material.

6. The preparation method according to claim 5, characterized in that, The particle size D50 of the cathode material raw material is 3~7μm; And / or, the moisture content of the cathode material raw material is less than 50 ppm; And / or, the inorganic precursor includes any one or a combination of at least two of titanium precursors, silicon precursors or boron precursors; Wherein, the titanium precursor comprises any one or a combination of at least two of tetrabutyl titanate, isopropyl titanate, ethyl titanate, or titanium tetrachloride; and / or, the silicon precursor comprises any one or a combination of at least two of ethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, or tetrabutyl silicate; and / or, the boron precursor comprises any one or a combination of at least two of trimethyl borate, triethyl borate, triisopropyl borate, or tributyl borate. And / or, the carrier includes any one or a combination of at least two of sodium dodecyl sulfate, perfluorooctanoic acid, or ethylene glycol octylphenyl ether; And / or, the supercritical fluid medium in the supercritical fluid permeation treatment includes any one or a combination of at least two of carbon dioxide, carbon monoxide, or ammonia. And / or, the mass ratio of the inorganic precursor to the cathode material raw material is (0.01~0.05):1; And / or, the mass ratio of the carrier to the cathode material raw material is (0.005~0.015):

1.

7. The preparation method according to claim 5 or 6, characterized in that, The temperature for the supercritical fluid permeation treatment is 40~60℃; And / or, the pressure of the supercritical fluid permeation treatment is 10~20MPa; And / or, the supercritical fluid permeation treatment time is 3~6 hours.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The mass ratio of the polymer monomer to the cathode material raw material is (0.02~0.05):1; And / or, the initiator includes any one or a combination of at least two of anionic ring-opening polymerization initiators, free radical initiators, or redox initiators; And / or, when the polymer monomer comprises ethylene oxide, the initiator comprises any one or a combination of at least two of potassium hydroxide, potassium tert-butoxide, sodium methoxide or sodium ethoxide; And / or, when the polymer monomer comprises vinylpyrrolidone and / or hydroxyethyl acrylate, the initiator comprises any one or a combination of at least two of azobisisobutyronitrile, benzoyl peroxide, ammonium persulfate or potassium persulfate; And / or, the mass ratio of the initiator to the polymer monomer is (0.01~0.04):1; And / or, the pressure of the in-situ polymerization reaction is 12~12.5 MPa; And / or, the in-situ polymerization reaction employs segmented temperature control; wherein, the segmented temperature control includes: first reacting at a first temperature for a first duration, then raising the temperature to a second temperature and continuing the reaction for a second duration; wherein, the range of the first temperature is 48~52℃; and / or, the first duration is 80~100min; and / or, the viscosity of the material after the first reaction is 570~590mPa·s; and / or, the range of the second temperature is 68~72℃; and / or, the second duration is 130~170min; and / or, the viscosity of the material after the second reaction is 610~630mPa·s.

9. The preparation method according to any one of claims 5 to 8, characterized in that, The heat treatment was carried out in an argon atmosphere; And / or, the heating rate of the heat treatment is 2~4℃ / min; And / or, the final temperature of the heat treatment is 380~420℃; And / or, the heat treatment holding time is 1~4h.

10. An all-solid-state battery, characterized in that, The all-solid-state battery includes the composite-coated positive electrode active material as described in any one of claims 1 to 4; And / or, the electrolyte in the all-solid-state battery includes a sulfide solid electrolyte and / or an oxide solid electrolyte.

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