Composite oxide-coated modified positive electrode material and method for preparing the same, secondary battery

Abstract

The application provides a composite oxide coated modified positive electrode material and a preparation method thereof, a secondary battery, and a preparation method of the composite oxide coated modified positive electrode material, which comprises the following steps: mixing a silicon source and a titanium source, and performing acid hydrolysis to prepare a composite sol; mixing positive electrode material particles and the composite sol, and allowing the composite sol to gel on the surface of the positive electrode material particles to prepare a gel layer on the surface of the positive electrode material particles; and performing heat treatment on the positive electrode material particles with the gel layer on the surface in an oxidizing atmosphere, so that the gel layer is converted into a composite oxide coating layer and coated on the surface of the positive electrode material particles. The preparation method provided by the application can allow the composite of the multi-element coated oxide to be carried out at the molecular level, and the composite oxide coating layer formed has a heterogeneous interface with chemical bonding between the two phases, which is beneficial to improving the structural integrity and long-term cycle stability of the coating layer.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to a composite oxide-coated modified cathode material and its preparation method, and a secondary battery. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density and long cycle life. Improving the specific capacity and operating voltage of the cathode material is key to enhancing battery performance, and high-nickel layered oxide cathode materials have attracted much attention due to their high theoretical specific capacity.

[0003] However, during high-voltage cycling, traditional high-nickel cathode materials are prone to side reactions with the electrolyte, leading to increased interfacial impedance. Moreover, these cathode materials are prone to surface structure reconstruction and lattice oxygen loss during repeated lithium insertion / extraction processes, resulting in capacity decay. Furthermore, during long-term cycling, the propagation of microcracks in these cathode materials continuously exposes fresh interfaces to the electrolyte, exacerbating side reactions and transition metal dissolution.

[0004] To overcome the aforementioned shortcomings, researchers have employed surface coating modification to improve the interfacial stability of cathode materials. For example, CN108878827A and CN108598447A involve mixing the cathode material and coating precursor in a solvent, followed by evaporation and heat treatment. However, the coating lacks chemical bonding with the substrate, resulting in weak adhesion and poor uniformity, easily leading to discontinuous coatings. Another example is CN116040693B, which introduces the coating during the precursor stage followed by high-temperature sintering. However, the high-temperature sintering process makes it difficult to independently control the structure and thickness of the coating layer, and the high temperature easily leads to lithium volatilization and substrate structural degradation, while also causing the coating to agglomerate. Traditional coating methods struggle to balance coating uniformity, thickness control, bonding strength, and process simplicity, especially in simultaneously satisfying interfacial protection and ion conduction. Therefore, there is an urgent need to develop a uniform and controllable surface coating modification method. Summary of the Invention

[0005] In view of this, this application provides a composite oxide-coated modified cathode material and its preparation method, as well as a secondary battery. The present application improves the preparation method of the composite oxide-coated modified cathode material by utilizing the simultaneous co-condensation of the multi-component coating solvent during the acidic hydrolysis stage and the in-situ transformation during the gelation stage, so that the composite of the multi-component coating oxides takes place at the molecular level, and the two phases in the formed composite oxide coating layer have a chemically bonded heterogeneous interface, which is beneficial to improving the structural integrity and long-term cycle stability of the coating layer.

[0006] To achieve the above objectives, in a first aspect, this application provides a method for preparing a composite oxide-coated modified cathode material, comprising the following steps: mixing a silicon source and a titanium source and performing acidic hydrolysis to prepare a composite sol; mixing cathode material particles with the composite sol to gel the composite sol on the surface of the cathode material particles, thereby preparing a gel layer on the surface of the cathode material particles; and heat-treating the cathode material particles with the gel layer on their surface under an oxidizing atmosphere to transform the gel layer into a composite oxide coating layer, which coats the surface of the cathode material particles, thereby preparing a composite oxide-coated modified cathode material.

[0007] Based on the first aspect, in some embodiments, the pH of the acidic hydrolysis is 1 to 6.

[0008] Based on the first aspect, in some embodiments, the temperature for acid hydrolysis is 20°C to 80°C.

[0009] Based on the first aspect, in some embodiments, the acid hydrolysis time is 0.5 h to 12 h.

[0010] Based on the first aspect, in some embodiments, the acidic hydrolysis is also carried out in a solvent, which includes one or more of ethanol, isopropanol, methanol, deionized water, ethylene glycol, and propylene glycol.

[0011] Based on the first aspect, in some embodiments, the acidic hydrolysis is also carried out in the presence of a catalyst, which includes one or more of hydrochloric acid, nitric acid, acetic acid, citric acid, and oxalic acid.

[0012] Based on the first aspect, in some embodiments, based on the composite sol, the total mass ratio of silicon source and titanium source is 0.1wt%~0.35wt%, the molar ratio of silicon in silicon source to titanium in titanium source is 1~2, and the solid-liquid ratio of cathode material particles to composite sol is 1 g : (2~100) mL.

[0013] Based on the first aspect, in some embodiments, the gelation temperature is 20°C to 90°C.

[0014] Based on the first aspect, in some embodiments, the gelation time is 1 h to 24 h.

[0015] Based on the first aspect, in some embodiments, the heat treatment temperature is 200°C to 600°C.

[0016] Based on the first aspect, in some embodiments, the heat treatment time is 1 h to 10 h.

[0017] Based on the first aspect, in some embodiments, the heating rate for heat treatment is 1°C / min to 10°C / min.

[0018] Based on the first aspect, in some embodiments, the oxidizing atmosphere includes oxygen and an inert gas, wherein the volume percentage of oxygen is 5% to 100%.

[0019] Based on the first aspect, in some embodiments, the silicon source includes one or more of tetraethyl orthosilicate, methyl orthosilicate, sodium silicate, methyltriethoxysilane, and aminopropyltriethoxysilane.

[0020] Based on the first aspect, in some embodiments, the titanium source includes one or more of tetrabutyl titanate, isopropyl titanate, titanium tetrachloride, titanium sulfate, and ethyl titanate.

[0021] Based on the first aspect, in some embodiments, before heat treatment, the preparation method further includes a step of drying the positive electrode material particles with a gel layer on the surface, wherein the drying temperature is 60°C to 150°C and the drying time is 4 h to 24 h.

[0022] Based on the first aspect, in some embodiments, the cathode material includes a high-nickel layered oxide cathode material with the general formula LiNi. x M 1-x O2, where M is one or more of Co, Mn, Al, Mg, Ti, Zr, W, Mo, Nb, Ta, B, Sr and Y, and 0.6 ≤ x < 1.0.

[0023] Secondly, this application provides a composite oxide-coated modified cathode material, prepared according to the above-described preparation method; the composite oxide coating layer includes a SiO2 phase, a TiO2 phase, and a Si-O-Ti bonded structure located in the transition region between the SiO2 phase and the TiO2 phase.

[0024] Based on the second aspect, in some embodiments, the composite oxide coating layer of the cathode material modified by composite oxide coating has a mass percentage of 0.05wt% to 5.0wt%.

[0025] Based on the second aspect, in some embodiments, the molar ratio of SiO2 to TiO2 in the composite oxide coating layer is 1 to 2.

[0026] Based on the second aspect, in some embodiments, the thickness of the composite oxide coating layer is 1 nm to 100 nm.

[0027] Thirdly, this application provides a secondary battery comprising the aforementioned composite oxide-coated modified cathode material.

[0028] Compared with traditional technologies, the beneficial effects of this application are as follows:

[0029] The method for preparing composite oxide-coated modified cathode materials provided in this application involves mixing silicon and titanium sources and then acidically hydrolyzing them. This allows the silicon and titanium sources to be uniformly dispersed at the molecular scale and hydrolyzed simultaneously. The silanol groups (Si-OH) and titaniumol groups (Ti-OH) undergo co-condensation, initially forming a composite sol system containing a Si-O-Ti heterogeneous bonding network. This lays the molecular structural foundation for the subsequent formation of a chemically bonded heterogeneous interface between the SiO2 and TiO2 phases. After mixing the composite sol with cathode material particles, it adsorbs and deposits on the particle surface to form a complete coating morphology. The sol's own fluidity drives the uniform dispersion of silicon and titanium species, providing a structural template for subsequent uniform and continuous coating. Based on this, heat treatment drives the gel layer to transform in situ into a composite oxide coating layer, in which the SiO2 and TiO2 phases are uniformly distributed at the molecular level and chemically bonded through the Si-O-Ti bonding network established in the gel stage, forming a heterogeneous interface with a chemically bonded interface. Therefore, this chemically bonded heterogeneous interface is beneficial for improving the integrity of the internal structure of the coating layer and its resistance to mechanical stress. During long-term charge-discharge volume changes, the coating layer is less prone to delamination, peeling, or microcrack propagation, which helps maintain the structural stability and continuous protective effect of the coating layer. At the same time, this heterogeneous interface is conducive to forming a continuous active ion transport channel at the interface between the two phases, which helps reduce the risk of ion transport obstruction caused by interfacial lattice mismatch or structural discontinuity in the physically mixed coating layer. In addition, the coating layer acts as a physical barrier to isolate the electrolyte from the surface of the cathode material, reducing the risk of interfacial side reactions, thus achieving both interface protection and ion transport performance. Detailed Implementation

[0030] To facilitate understanding of the technical solutions of this application, a more comprehensive description of the technical solutions will be provided below. The technical solutions of this application can be implemented in many different forms and are not limited to the embodiments described herein. Rather, these embodiments are provided to make the disclosure of the technical solutions of this application more thorough and comprehensive.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] One embodiment of this application provides a method for preparing a composite oxide-coated modified cathode material, comprising the following steps:

[0033] Step 1: Mix silicon source and titanium source and perform acidic hydrolysis to prepare composite sol.

[0034] In the above steps, the silicon source and titanium source are mixed and acidically hydrolyzed to make the silicon source and titanium source uniformly dispersed at the molecular scale and hydrolyzed simultaneously. The silanol groups (Si-OH) and titanium ol groups (Ti-OH) undergo co-condensation to initially form a composite sol system containing a Si-O-Ti heterobonded network, which lays the molecular structural foundation for the subsequent formation of a chemically bonded heterogeneous interface between the SiO2 phase and the TiO2 phase.

[0035] It should be noted that if the silicon and titanium sources are hydrolyzed separately before mixing, the formation and condensation of silanol and titanium hydroxyl groups occur in separate independent systems. During mixing, the silicon and titanium species have already formed oligomers dominated by Si-O-Si and Ti-O-Ti segments, respectively. The probability of co-condensation to form Si-O-Ti bonds between them is significantly reduced. In the final product, the SiO2 and TiO2 phases are mainly connected by physical interfaces rather than chemical bonds, which may not lay the molecular foundation for the subsequent formation of heterostructures with chemically bonded interfaces. Furthermore, the method of hydrolyzing separately before mixing makes it difficult to achieve a uniform distribution of silicon and titanium species at the molecular scale. During subsequent heat treatment, they tend to nucleate and grow independently, leading to phase separation in the coating layer. This not only affects the structural integrity of the coating layer but also hinders the formation of continuous lithium-ion transport channels at the SiO2 / TiO2 interface.

[0036] In some embodiments, the pH of acidic hydrolysis is 1 to 6. For example, the pH of acidic hydrolysis can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or any value within the range of any two of the above values. Furthermore, controlling the pH of acidic hydrolysis within the above range helps to regulate the hydrolysis rate and sol stability, thereby also helping to maintain the stability of the composite sol system, providing suitable kinetic conditions for the co-condensation reaction of silanol and titanium hydroxyl groups, and further promoting the construction of the Si-O-Ti heterobonded network.

[0037] In some embodiments, the acid hydrolysis temperature is 20°C to 80°C. For example, the acid hydrolysis temperature can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or any value within the range of any two of the above values. Furthermore, controlling the acid hydrolysis temperature within the above range is beneficial for providing appropriate activation energy for the hydrolysis reaction, allowing the hydrolysis rate of the silicon source and the titanium source to match the condensation rate, thereby facilitating the formation of a uniform composite sol.

[0038] In some embodiments, the acid hydrolysis time is 0.5 h to 12 h. For example, the acid hydrolysis time can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or any value within the range of any two of the above values. Furthermore, controlling the acid hydrolysis time within the above range helps to ensure sufficient hydrolysis and appropriate condensation of the silicon and titanium sources, thereby facilitating the acquisition of a composite sol system with suitable crosslinking density and reactivity.

[0039] In some embodiments, the acidic hydrolysis is also carried out in a solvent, which includes one or more of ethanol, isopropanol, methanol, deionized water, ethylene glycol, and propylene glycol. For example, the silicon source and the titanium source can be mixed in the above-mentioned solvent, thereby allowing the acidic hydrolysis to proceed in the above-mentioned solvent. Furthermore, controlling the acidic hydrolysis to proceed in the above-mentioned solvent helps to fully dissolve the silicon source and the titanium source and to uniformly disperse them at the molecular scale, thereby facilitating the uniform progress of the co-condensation reaction.

[0040] In some embodiments, the acidic hydrolysis is also carried out under a catalyst, which includes one or more of hydrochloric acid, nitric acid, acetic acid, citric acid, and oxalic acid. For example, a silicon source or a titanium source can be mixed with the above-mentioned catalyst, thereby allowing the acidic hydrolysis to proceed in the aforementioned solvent. Furthermore, controlling the acidic hydrolysis to proceed under a catalyst helps to provide a suitable proton environment for the hydrolysis reaction, promoting the hydrolytic substitution reaction of alkoxy groups in the silicon source and alkoxy groups in the titanium source, thereby facilitating the full formation of silanol and titaniumol groups and the co-condensation reaction.

[0041] In some embodiments, the silicon source includes one or more of tetraethyl orthosilicate, methyl orthosilicate, sodium silicate, methyltriethoxysilane, and aminopropyltriethoxysilane. In some embodiments, the titanium source includes one or more of tetrabutyl titanate, isopropyl titanate, titanium tetrachloride, titanium sulfate, and ethyl titanate. Furthermore, when the silicon and titanium sources are selected from the above-mentioned substances, both the silicon and titanium sources exhibit good hydrolytic reactivity and can achieve uniform mixing and simultaneous hydrolysis at the molecular scale in the solution system. This facilitates the full co-condensation reaction between silanol and titanium hydroxyl groups, providing a suitable raw material basis for the subsequent formation of a composite sol system containing a Si-O-Ti heterobonded network.

[0042] In some embodiments, the cathode material includes a high-nickel layered oxide cathode material with the general formula LiNi. x M 1-xO2, where M is one or more of Co, Mn, Al, Mg, Ti, Zr, W, Mo, Nb, Ta, B, Sr, and Y, and 0.6 ≤ x < 1.0. In related technologies, the aforementioned high-nickel layered oxide cathode materials typically exhibit unstable surface structures and are prone to side reactions with the electrolyte during charge and discharge processes, necessitating surface coating modification to stabilize their interfaces. Furthermore, the preparation method of this application can form a composite oxide coating layer with a chemically bonded heterogeneous interface on the surface of high-nickel cathode material particles. This coating layer effectively suppresses interfacial side reactions of the high-nickel cathode material during high-voltage cycling, slows down surface structure reconstruction and transition metal dissolution, thereby improving the structural and electrochemical stability of the high-nickel cathode material under high-voltage and long-cycle conditions.

[0043] Step 2: Mix the cathode material particles with the composite sol to allow the composite sol to gel on the surface of the cathode material particles, thus preparing a gel layer on the surface of the cathode material particles.

[0044] In the above steps, after the composite sol is mixed with the cathode material particles, it is adsorbed and deposited on the particle surface to form a complete coating morphology. The fluidity of the sol itself drives the uniform dispersion of silicon and titanium species, providing a structural template for subsequent uniform and continuous coating.

[0045] It should be noted that if silicon and titanium sources are directly mixed with cathode material particles in solution form (rather than in composite sol form), the solution lacks the suitable viscosity and flowability of a composite sol. During solvent evaporation, silicon and titanium species tend to precipitate sequentially due to differences in solubility, making it difficult to form a complete and uniform coating morphology on the surface of the cathode material particles. This easily leads to discontinuous dot-like or island-like depositions. Simultaneously, the Si-O-Ti bonding network initially established in step one in solution form lacks the opportunity to be fixed and further cross-linked on the surface of the cathode material particles, making it highly susceptible to damage during subsequent heat treatment due to component migration and phase separation. Therefore, the subsequent heat treatment process lacks a uniform structural template for guidance, making it difficult for the oxide transformation of silicon and titanium species to form a uniform composite oxide coating layer, and also preventing the achievement of a chemically bonded heterogeneous interface between the SiO2 and TiO2 phases connected by the Si-O-Ti bonding network.

[0046] In some embodiments, based on the composite sol, the total mass ratio of silicon source and titanium source is 0.1wt%~0.35wt%, the molar ratio of silicon in silicon source to titanium in titanium source is 1~2, and the solid-liquid ratio of cathode material particles to composite sol is 1 g : (2~100) mL. For example, the total mass ratio of silicon source to titanium source in the composite sol can be 0.1wt%, 0.11wt%, 0.15wt%, 0.18wt%, 0.22wt%, 0.25wt%, 0.29wt%, 0.31wt%, 0.32wt%, 0.35wt%, or any value within the range of any two of the above values; the molar ratio of silicon in the silicon source to titanium in the titanium source can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any value within the range of any two of the above values; when the cathode material particles are 1 g, the volume of the composite sol can be 2 mL, 5 mL, 10 mL, 20 mL, 30 mL, 40 mL, 50 mL, 60 mL, 70 mL, 80 mL, 90 mL, 100 mL, or any value within the range of any two of the above values. Furthermore, controlling the solid-liquid ratio of the cathode material particles to the composite sol within the above-mentioned range helps to provide a suitable coating environment for the adsorption and deposition of the sol on the surface of the cathode material particles, enabling the sol to form a complete coating morphology on the particle surface while maintaining its own fluidity, thereby facilitating the uniform dispersion of silicon and titanium species on the particle surface.

[0047] In some embodiments, the solid-liquid ratio of the cathode material particles to the composite sol is 1 g : (5~50) mL. For example, when the cathode material particles are 1 g, the volume of the composite sol can be 5 mL, 14 mL, 18 mL, 22 mL, 26 mL, 30 mL, 34 mL, 38 mL, 42 mL, 46 mL, 50 mL, or any value within the range of any two of the above values. Furthermore, by controlling the solid-liquid ratio of the cathode material particles to the composite sol within the above-mentioned preferred range, when the cathode material particles and the composite sol are mixed, the composite sol can be tightly adsorbed and deposited on the surface of the cathode material particles, thereby helping to construct a highly dense composite oxide coating layer and further improving the integrity of the internal structure of the coating layer.

[0048] In some embodiments, the gelation temperature is 20°C to 90°C. For example, the gelation temperature can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any value within the range of any two of the above values. Furthermore, controlling the gelation temperature within the above range helps to provide suitable energy for the condensation reaction during the gelation process, allowing the sol precursor to crosslink at an appropriate rate on the surface of the cathode material particles to form a three-dimensional network structure, thereby facilitating the formation of a structurally complete and uniform gel layer.

[0049] In some embodiments, the gelation temperature is 40°C to 80°C. For example, the gelation temperature can be 40°C, 44°C, 48°C, 52°C, 56°C, 60°C, 64°C, 68°C, 72°C, 76°C, 80°C, or any value within the range of any two of the above values. Furthermore, controlling the gelation temperature within the above-mentioned preferred range is also beneficial for further driving additional condensation of the composite sol in the current step, thereby further promoting the generation of more Si-O-Ti heterobonding on the basis of acidic hydrolysis, strengthening the heterobonding network structure, and helping to further improve the mechanical stress resistance of the resulting composite oxide coating layer.

[0050] In some embodiments, the gelation time is 1 h to 24 h. For example, the gelation time is 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or any value within the range of any two of the above values. Furthermore, controlling the gelation time within the above range helps ensure that the sol precursor is fully cross-linked on the surface of the cathode material particles, allowing the Si-O-Ti bonding network in the gel layer to develop sufficiently, thereby providing a good structural basis for the formation of a composite oxide coating layer with a chemically bonded interface after subsequent heat treatment.

[0051] Step 3: Heat-treat the cathode material particles with a gel layer on the surface under an oxidizing atmosphere to transform the gel layer into a composite oxide coating layer, which coats the surface of the cathode material particles, thus preparing a composite oxide-coated modified cathode material.

[0052] Building upon steps one and two, in the aforementioned steps, heat treatment drives the in-situ transformation of the gel layer into a composite oxide coating layer. The SiO2 and TiO2 phases are uniformly distributed at the molecular level and chemically bonded through the Si-O-Ti bonding network established during the gelation stage, forming a heterogeneous interface with chemical bonding. This chemically bonded heterogeneous interface enhances the integrity of the coating layer's internal structure and its resistance to mechanical stress. During long-term charge-discharge volume changes, the coating layer is less prone to delamination, peeling, or microcrack propagation, thus maintaining its structural stability and continuous protective effect. Simultaneously, this heterogeneous interface facilitates the formation of continuous active ion transport channels at the two-phase interface, reducing the risk of ion transport obstruction due to interfacial lattice mismatch or structural discontinuities in the physically mixed coating layer. Furthermore, the coating layer acts as a physical barrier, isolating the electrolyte from the cathode material surface and reducing the risk of interfacial side reactions, thereby balancing interfacial protection and ion transport performance.

[0053] It should be noted that without heat treatment to drive in-situ transformation of the gel layer, the organic components and residual solvents in the gel layer cannot be fully removed, and the crosslinking density and structural stability of the Si-O-Ti bonding network are insufficient to meet the requirements for a stable coating layer, thus failing to form a composite oxide coating layer with sufficient chemical stability and mechanical strength. If a direct high-temperature sintering method is used (i.e., directly mixing the silicon and titanium sources with the cathode material and then treating them at high temperatures without sol-gel in-situ coating), SiO2 and TiO2 will nucleate and grow independently, failing to achieve chemical bonding through the Si-O-Ti bonding network established in the gel stage. The coating layer lacks a chemical bonding interface, and the cathode material matrix is ​​prone to lithium volatilization and structural degradation at high temperatures. Therefore, heat treatment to drive in-situ transformation of the gel layer is beneficial for maintaining and strengthening the Si-O-Ti bonding structure established in the gel stage, while also preventing damage to the cathode material matrix from high temperatures.

[0054] In some embodiments, the heat treatment temperature is 200°C to 600°C. For example, the heat treatment temperature can be 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, or any value within the range of any two of the above values. Furthermore, controlling the heat treatment temperature within the above range helps to promote the full transformation of the amorphous gel into the oxide crystalline phase. During this process, the Si-O-Ti bonding network established in the gel stage is maintained and strengthened, thereby facilitating the formation of a composite oxide coating layer with a chemically bonded interface between the SiO2 and TiO2 phases. It should be noted that when the heat treatment temperature is high, some Si and Ti will exist in a doped form. Controlling the heat treatment temperature within the above range helps to reduce the doped Si and Ti, allowing more Si and Ti to exist in the form of a composite oxide coating layer.

[0055] In some embodiments, the heat treatment temperature is 350°C to 550°C. For example, the heat treatment temperature can be 350°C, 370°C, 390°C, 410°C, 430°C, 450°C, 470°C, 490°C, 510°C, 530°C, 550°C, or any value within the range of any two of the above values. Furthermore, controlling the heat treatment temperature within the above-mentioned preferred range helps to drive the full decomposition of organic residues in the gel layer. Simultaneously, controlling the heat treatment temperature below 600°C also helps to reduce the risk of lithium loss or structural degradation on the surface of the high-nickel cathode material at high temperatures.

[0056] In some embodiments, the heat treatment time is 1 h to 10 h. For example, the heat treatment time can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or any value within the range of any two of the above values. Furthermore, controlling the heat treatment time within the above range helps to ensure that the transformation of the gel layer into the oxide coating layer proceeds sufficiently, and makes the crystallization degree of the SiO2 phase and TiO2 phase in the composite oxide coating layer tend to be stable, thereby facilitating the acquisition of a structurally stable composite oxide coating layer.

[0057] In some embodiments, the heating rate for heat treatment is 1°C / min to 10°C / min. For example, the heating rate for heat treatment can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 10°C / min, or any value within the range of any two of the above values. Furthermore, controlling the heating rate within the above range helps to ensure uniform heating of the gel layer during heat treatment, reducing the risk of local overheating and damage to the gel layer structure when the temperature rises too quickly, thereby helping to maintain the integrity and uniformity of the coating layer.

[0058] In some embodiments, the oxidizing atmosphere includes oxygen and an inert gas, wherein the volume percentage of oxygen is 5% to 100%. For example, the volume percentage of oxygen can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any value within the range of any two of the above values. Furthermore, controlling the volume percentage of oxygen in the oxidizing atmosphere containing oxygen and an inert gas within the above range helps to provide a sufficient oxygen source for the oxidative decomposition of organic residues in the gel layer, and also helps to maintain the transition metal ions in the cathode material matrix at a higher valence state, thereby helping to maintain the intrinsic electrochemical activity of the cathode material.

[0059] In some embodiments, before heat treatment, the preparation method further includes a step of drying the positive electrode material particles with a gel layer on their surface. The drying temperature is 60°C to 150°C, and the drying time is 4 h to 24 h. For example, the drying temperature can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or any value within the range of any two of the above values, and the drying time can be 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or any value within the range of any two of the above values. Furthermore, drying the cathode material particles with a gel layer on their surface before heat treatment, and controlling the drying conditions within the aforementioned range, helps to remove the solvent from the gel layer before heat treatment, allowing the silicon and titanium species in the gel layer to be arranged in a more dense manner, which is beneficial for achieving more complete in-situ conversion during subsequent heat treatment. At the same time, drying before heat treatment also helps to keep the Si-O-Ti bonding network in the gel layer in a relatively stable structural state before the heat treatment temperature rise, which is beneficial for better maintaining the structural integrity of the coating layer during subsequent heat treatment.

[0060] An embodiment of this application also provides a composite oxide-coated modified cathode material, prepared according to the above-described preparation method; the composite oxide coating layer includes a SiO2 phase, a TiO2 phase, and a Si-O-Ti bonded structure located in the transition region between the SiO2 phase and the TiO2 phase.

[0061] The composite oxide-coated modified cathode material provided in this application is prepared by the above method. In its composite oxide coating layer, the SiO2 and TiO2 phases are uniformly distributed at the molecular level, and the two phases are chemically bonded together via a Si-O-Ti bonding structure, forming a heterogeneous structure with a chemically bonded interface. SiO2 exhibits good chemical stability, which is beneficial as a protective layer to reduce the risk of direct contact between the electrolyte and the cathode material surface. The TiO2 phase has good structural stability and adaptability to active ion conduction, which is beneficial to improving the ion transport characteristics of the coating layer. The Si-O-Ti bonding structure located between the SiO2 and TiO2 phases forms a chemically bonded interface, which is beneficial to improving the integrity of the internal structure of the coating layer and its resistance to mechanical stress. Through the synergistic effect of these three structural features, a good balance is achieved between interface protection and ion conduction, thereby contributing to improving the electrochemical stability of the cathode material under high-voltage, long-cycle conditions.

[0062] In some embodiments, the composite oxide coating layer of the cathode material modified with composite oxide coating has a mass percentage of 0.05 wt% to 5.0 wt%. For example, the mass percentage of the composite oxide coating layer can be 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5.0 wt%, or any value within the range of any two of the above values. Furthermore, controlling the mass percentage of the composite oxide coating layer within the above range is beneficial for forming a continuous and complete protective layer on the surface of the cathode material with an appropriate coating amount, thereby achieving effective interface protection while avoiding adverse effects on ion conduction due to excessive coating thickness.

[0063] In some embodiments, the molar ratio of SiO2 to TiO2 in the composite oxide coating layer is 1 to 2. For example, the molar ratio of SiO2 to TiO2 can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any value within the range of any two of the above values. Furthermore, controlling the molar ratio of SiO2 to TiO2 in the composite oxide coating layer within the above range is beneficial for achieving a synergistic match between the chemical stabilizing and protective effects of SiO2 and the ion conduction regulating effects of TiO2, thereby balancing the interfacial protection effect of the coating layer with the transport capacity of active ions (such as lithium ions).

[0064] In some embodiments, the thickness of the composite oxide coating layer is 1 nm to 100 nm. For example, the thickness of the composite oxide coating layer can be 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any value within the range of any two of the above values. Furthermore, controlling the thickness of the composite oxide coating layer within the above range is beneficial for forming a coating layer with a complete structure and appropriate thickness on the surface of the cathode material, thereby facilitating effective interface protection while maintaining a good lithium-ion conduction path.

[0065] One embodiment of this application also provides a secondary battery, comprising the above-described composite oxide-coated modified cathode material.

[0066] The secondary battery provided in this application comprises the aforementioned composite oxide-coated modified cathode material. In the composite oxide coating layer on the surface of this cathode material, the SiO2 and TiO2 phases are chemically bonded together through a Si-O-Ti bonding structure, which is beneficial for maintaining the structural integrity and continuous protective effect of the coating layer during long-term charge-discharge processes. Simultaneously, this coating layer helps reduce the risk of interfacial side reactions between the cathode material and the electrolyte and helps maintain a good lithium-ion transport path. Therefore, it is beneficial for the secondary battery to achieve better cycle stability and rate performance under high-voltage operating conditions.

[0067] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0068] Example 1:

[0069] A composite oxide-coated modified cathode material is prepared by the following method:

[0070] Step 1: Add 0.05 g of tetraethyl orthosilicate and 0.08 g of tetrabutyl titanate to 50 mL of anhydrous ethanol, then add 2 mL of deionized water and 0.2 mL of glacial acetic acid. Glacial acetic acid is used as an acidic hydrolysis catalyst and pH adjuster to adjust the pH to 4. Stir at 50 °C for 2 h to obtain a composite sol.

[0071] The second step is to weigh 10 g of LiNi. 0.9 Co 0.05 Mn 0.05 Using O2 cathode material as the matrix material, the matrix material was added to 50 mL of composite sol and stirred continuously at 70℃ for 6 h to allow the composite sol to be uniformly deposited and gelled on the surface of the cathode material particles.

[0072] Step 3: After the reaction is completed, the product is separated by centrifugation, washed twice with ethanol, and dried under vacuum at 100°C for 12 h. Then the dried product is placed in a tube furnace and heated to 450°C at 3°C / min under an oxygen atmosphere and held for 4 h.

[0073] Step 4: After natural cooling, a composite oxide-coated modified cathode material is obtained. In this modified cathode material, the mass percentage of the composite oxide coating layer is 0.5 wt%. The composite oxide coating layer contains SiO2 phase and TiO2 phase, and the molar ratio of SiO2 to TiO2 is approximately 1:1.

[0074] Example 2:

[0075] A composite oxide-coated modified cathode material is prepared by the following method:

[0076] Step 1: Add 0.010 g of tetraethyl orthosilicate and 0.0085 g of tetrabutyl titanate to 20 mL of anhydrous ethanol, then add 1 mL of deionized water and 0.05 mL of glacial acetic acid. Glacial acetic acid is used as an acidic hydrolysis catalyst and pH adjuster to adjust the pH to 1. Stir at 80 °C for 0.5 h to obtain a composite sol.

[0077] The second step is to weigh 10 g of LiNi. 0.8 Co 0.1 Mn 0.1 Using O2 cathode material as the matrix material, the matrix material was added to 20 mL of composite sol and stirred continuously at 90℃ for 1 h to allow the composite sol to be uniformly deposited and gelled on the surface of the cathode material particles.

[0078] Step 3: After the reaction is completed, the product is separated by centrifugation, washed twice with ethanol, and dried under vacuum at 60°C for 24 h. Then, the dried product is placed in a tube furnace and heated to 600°C at 10°C / min under an oxygen atmosphere and held for 1 h.

[0079] Step 4: After natural cooling, a composite oxide-coated modified cathode material is obtained. In this modified cathode material, the mass percentage of the composite oxide coating layer is 0.05 wt%. The composite oxide coating layer contains SiO2 phase and TiO2 phase, and the molar ratio of SiO2 to TiO2 is approximately 2:1.

[0080] Example 3:

[0081] A composite oxide-coated modified cathode material is prepared by the following method:

[0082] Step 1: Add 0.313 g of tetraethyl orthosilicate and 0.255 g of tetrabutyl titanate to 250 mL of anhydrous ethanol, then add 10 mL of deionized water and 0.5 mL of glacial acetic acid. Glacial acetic acid is used as an acidic hydrolysis catalyst and pH adjuster to adjust the pH to 1. Stir at 80 °C for 0.5 h to obtain a composite sol.

[0083] The second step is to weigh 10 g of LiNi. 0.8 Co 0.1 Mn 0.1 Using O2 cathode material as the matrix material, the matrix material was added to 250 mL of composite sol and stirred continuously at 80℃ for 2 h to allow the composite sol to be uniformly deposited and gelled on the surface of the cathode material particles.

[0084] Step 3: After the reaction is completed, the product is separated by centrifugation, washed twice with ethanol, and dried under vacuum at 60°C for 24 h. Then the dried product is placed in a tube furnace and heated to 550°C at 6°C / min under an oxygen atmosphere and held for 2 h.

[0085] Step 4: After natural cooling, a composite oxide-coated modified cathode material is obtained. In this modified cathode material, the mass ratio of the composite oxide coating layer is 1.5 wt%. The composite oxide coating layer contains SiO2 phase and TiO2 phase, and the molar ratio of SiO2 to TiO2 is about 2:1.

[0086] Example 4:

[0087] A composite oxide-coated modified cathode material is prepared by the following method:

[0088] Step 1: Weigh 1.25 g of sodium silicate nonahydrate (Na2SiO3·9H2O) and dissolve it in 100 mL of deionized water to obtain an aqueous sodium silicate solution. Separately, weigh 0.84 g of isopropyl titanate and add it to 900 mL of anhydrous ethanol. After stirring evenly, slowly add the above aqueous sodium silicate solution dropwise to the isopropyl titanate ethanol solution. Then, add about 0.6 mL of glacial acetic acid as an acidic hydrolysis catalyst and pH adjuster to adjust the pH of the system to 6. Stir at 20 °C for 12 h to allow the silicon source and titanium source to undergo a hydrolysis-condensation reaction, obtaining a composite sol.

[0089] Step 2: Weigh out 10 g of LiNi 0.6 Co 0.2 Mn 0.2 Using O2 cathode material as the matrix material, the matrix material was added to 1000 mL of composite sol and stirred continuously at 20℃ for 24 h to allow the composite sol to be uniformly deposited and gelled on the surface of the cathode material particles.

[0090] Step 3: After the reaction is completed, the product is centrifuged and washed twice with ethanol to remove free sodium salt, organic residues and unreacted precursors. It is then vacuum dried at 150°C for 4 h. The dried product is then placed in a tube furnace and heated to 200°C at 1°C / min under an oxygen atmosphere and held for 10 h.

[0091] Step 4: After natural cooling, the composite oxide-coated modified cathode material is obtained. In this modified cathode material, the composite oxide coating layer accounts for 5.0 wt% of the total mass and contains SiO2 and TiO2 phases, with a molar ratio of SiO2 to TiO2 of approximately 3:2.

[0092] Example 5:

[0093] A composite oxide-coated modified cathode material is prepared by the following method:

[0094] Step 1: Weigh 0.75 g of sodium silicate nonahydrate (Na2SiO3·9H2O) and dissolve it in 50 mL of deionized water to obtain an aqueous sodium silicate solution. Separately, weigh 0.50 g of isopropyl titanate and add it to 450 mL of anhydrous ethanol. After stirring evenly, slowly add the above aqueous sodium silicate solution dropwise to the isopropyl titanate ethanol solution. Then, add about 0.4 mL of glacial acetic acid as an acidic hydrolysis catalyst and pH adjuster to adjust the pH of the system to 6. Stir at 20 °C for 12 h to allow the silicon source and titanium source to undergo a hydrolysis-condensation reaction, obtaining a composite sol.

[0095] Step 2: Weigh out 10 g of LiNi 0.6 Co 0.2 Mn 0.2 Using O2 cathode material as the matrix material, the matrix material was added to 500 mL of composite sol and stirred continuously at 40℃ for 20 h to allow the composite sol to be uniformly deposited and gelled on the surface of the cathode material particles.

[0096] Step 3: After the reaction is completed, the product is centrifuged and washed twice with ethanol to remove free sodium salt, organic residues and unreacted precursors. It is then vacuum dried at 150°C for 4 h. The dried product is then placed in a tube furnace and heated to 350°C at 2°C / min under an oxygen atmosphere and held at that temperature for 9 h.

[0097] Step 4: After natural cooling, the composite oxide-coated modified cathode material is obtained. In this modified cathode material, the composite oxide coating layer accounts for 3.0 wt% of the total mass, and the composite oxide coating layer contains SiO2 phase and TiO2 phase, with a molar ratio of SiO2 to TiO2 of approximately 3:2.

[0098] Please refer to Table 1 for a comparison of some preparation conditions in Examples 1-5 of this application.

[0099] Table 1. Some preparation conditions of Examples 1-5 of this application

[0100]

[0101] Comparative Example 1:

[0102] The difference from Example 1 is that the first step is adjusted as follows: 0.05 g of tetraethyl orthosilicate is added to 25 mL of anhydrous ethanol, along with 1 mL of deionized water and 0.1 mL of glacial acetic acid, and the pH is adjusted to 4. The mixture is stirred at 50°C for 2 h to obtain a silica sol. Separately, 0.08 g of tetrabutyl titanate is added to 25 mL of anhydrous ethanol, along with 1 mL of deionized water and 0.1 mL of glacial acetic acid, and the pH is adjusted to 4. The mixture is stirred at 50°C for 2 h to obtain a titanium sol. The silica sol and titanium sol are mixed and stirred at 50°C for another 0.5 h to obtain a mixed sol.

[0103] Comparative Example 2:

[0104] The difference from Example 1 is that the first step is adjusted as follows: 0.05 g of tetraethyl orthosilicate and 0.08 g of tetrabutyl titanate are added to 50 mL of anhydrous ethanol, along with 2 mL of deionized water and 0.2 mL of glacial acetic acid. The mixture is stirred at room temperature to obtain a mixed solution of silicon and titanium sources. This mixed solution is then used to mix with the matrix material.

[0105] Comparative Example 3:

[0106] A composite oxide-coated modified cathode material is prepared by the following method:

[0107] Step 1: Weigh 10 g of LiNi 0.9 Co 0.05 Mn 0.05 Using O2 cathode material as the matrix material, 0.05 g of tetraethyl orthosilicate and 0.08 g of tetrabutyl titanate were dissolved in 10 mL of anhydrous ethanol, directly mixed with the matrix material and ground evenly to obtain a mixture.

[0108] Step 2: Place the mixture in a tube furnace and heat it to 900°C at a rate of 5°C / min under an oxygen atmosphere, and hold it at that temperature for 9 hours.

[0109] Step 3: After natural cooling, the composite oxide-coated modified cathode material is obtained.

[0110] In this application, the composite oxide-coated modified cathode materials obtained in Examples 1-5 and Comparative Examples 1-3 were separately mixed with a conductive agent and a binder at a mass ratio of 90:5:5, and N-methylpyrrolidone was added to form a slurry. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to prepare a cathode sheet. A coin cell was assembled using a lithium metal sheet as the anode, a polypropylene membrane as the separator, and a carbonate solution containing LiPF6 as the electrolyte. Electrochemical performance tests, including cycle performance and rate performance, were then conducted in the voltage range of 2.5 V to 4.35 V, with 1 C = 185 mAh / g. The test results are shown in Table 2.

[0111] Table 2. Electrochemical performance test results of the coin cells obtained in Examples 1-5 and Comparative Examples 1-3 of this application.

[0112]

[0113] The composite oxide-coated modified cathode materials provided in Examples 1-5 of this application involve the preparation of silicon and titanium sources. During preparation, silicon and titanium sources are mixed and acidically hydrolyzed, resulting in uniform dispersion and simultaneous hydrolysis at the molecular scale. Si-OH and titanium-OH hydroxyl groups undergo co-condensation, initially forming a composite sol system containing a Si-O-Ti heterogeneous bonding network. This lays the molecular structural foundation for the subsequent formation of a chemically bonded heterogeneous interface between the SiO2 and TiO2 phases. After mixing the composite sol with cathode material particles, it adsorbs and deposits on the particle surface, forming a complete coating morphology. The sol's own fluidity drives the uniform dispersion of silicon and titanium species, providing a structural template for subsequent uniform and continuous coating. Based on this, heat treatment drives the in-situ transformation of the gel layer into a composite oxide coating layer, in which the SiO2 and TiO2 phases are uniformly distributed at the molecular level and chemically bonded through the Si-O-Ti bonding network established during the gelation stage, forming a heterogeneous interface with a chemically bonded interface. Therefore, this chemically bonded heterogeneous interface is beneficial for improving the integrity of the internal structure of the coating layer and its resistance to mechanical stress. During long-term charge-discharge volume changes, the coating layer is less prone to delamination, peeling, or microcrack propagation, which helps maintain the structural stability and continuous protective effect of the coating layer. At the same time, this heterogeneous interface is conducive to forming a continuous active ion transport channel at the interface between the two phases, which helps reduce the risk of ion transport obstruction caused by interfacial lattice mismatch or structural discontinuity in the physically mixed coating layer. In addition, the coating layer acts as a physical barrier to isolate the electrolyte from the surface of the cathode material, reducing the risk of interfacial side reactions, thus achieving both interface protection and ion transport performance.

[0114] Please refer to Table 2. The composite oxide-coated modified cathode materials obtained in Examples 1-5 of this application all exhibit good electrochemical performance, with initial coulombic efficiency of 89.9%~92.1%, capacity retention of 92.2%~99.0% after 100 cycles at 1C, and 5C rate specific capacity of 130.6~181.6 mAh / g. These results demonstrate that the preparation method of the composite oxide-coated modified cathode material provided in this application has good applicability and stability under different raw material ratios and process conditions, and can achieve effective coating modification of cathode materials within a wide parameter window.

[0115] In Example 3, based on Example 2, a preferred solid-liquid ratio, gelation temperature, and heat treatment temperature were further adopted. In Example 5, based on Example 4, a preferred solid-liquid ratio, gelation temperature, and heat treatment temperature were further adopted. The preferred solid-liquid ratio allows the composite sol to be tightly adsorbed and deposited on the surface of the cathode material particles, thus helping to construct a dense composite oxide coating layer and further improving the integrity of the internal structure of the coating layer. The preferred gelation temperature facilitates further condensation of the composite sol during the gelation process, thereby promoting the generation of more Si-O-Ti heterobonding on the basis of acidic hydrolysis, strengthening the heterobonding network structure, and further improving the mechanical stress resistance of the obtained composite oxide coating layer. The preferred heat treatment temperature helps to fully decompose organic residues in the gel layer. Simultaneously, controlling the heat treatment temperature below 600°C also helps to reduce the risk of lithium loss or structural degradation on the surface of the high-nickel cathode material at high temperatures. Therefore, the composite oxide-coated modified cathode materials obtained in Examples 3 and 5 exhibit better electrochemical performance when used in batteries.

[0116] Compared to Example 1 of this application, Comparative Example 1 places the silicon source and titanium source in two separate systems for hydrolysis, forming silicon sol and titanium sol respectively, and then mixes them. The co-condensation reaction of silanol and titanium ol is difficult to occur effectively, and it is impossible to initially form a composite sol system containing a Si-O-Ti heterobonded network. As a result, the electrochemical performance of the obtained cathode material is not as good as that of the example of this application.

[0117] Compared to Example 1 of this application, in Comparative Example 2, the silicon source and titanium source were not fully hydrolyzed and condensed to form a composite sol, but were directly mixed with the cathode material particles in solution form. During the solvent evaporation process, the silicon species and titanium species in the solution tend to precipitate out one after the other, making it difficult to form a complete and uniform coating morphology on the particle surface. The Si-O-Ti bonding network that was initially established in step one also lacked the opportunity to be fixed on the cathode material particle surface and further crosslinked, resulting in the electrochemical performance of the cathode material obtained being inferior to that of the examples of this application.

[0118] Compared to Example 1 of this application, in the preparation process of Comparative Example 3, the sol-gel process was not carried out. Instead, the silicon source and titanium source were directly mixed with the cathode material matrix and then sintered at high temperature. SiO2 and TiO2 nucleated and grew independently at high temperature. The two phases coexisted mainly through physical mixing. They could not form a heterostructure with a chemical bonding interface through the Si-O-Ti bonding network established in the gel stage. At the same time, the cathode material matrix underwent long-term sintering at 900°C, which easily led to lithium volatilization and structural degradation, resulting in the electrochemical performance of the obtained cathode material being inferior to that of the examples of this application.

[0119] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0120] The embodiments described above are merely illustrative of several implementations of the technical solution of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the technical solution of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing a composite oxide-coated modified cathode material, characterized in that, Includes the following steps: A composite sol was prepared by mixing a silicon source and a titanium source and then subjecting them to acidic hydrolysis. The positive electrode material particles are mixed with the composite sol, and the composite sol is gelled on the surface of the positive electrode material particles to prepare a gel layer on the surface of the positive electrode material particles. The cathode material particles with the gel layer on their surface are heat-treated in an oxidizing atmosphere to transform the gel layer into a composite oxide coating layer, which coats the surface of the cathode material particles, thus preparing the composite oxide-coated modified cathode material.

2. The preparation method according to claim 1, characterized in that, The acidic hydrolysis satisfies at least one of the following conditions: (1) The pH of the acidic hydrolysis is 1 to 6; (2) The temperature of the acid hydrolysis is 20℃~80℃; (3) The acid hydrolysis time is 0.5 h to 12 h; (4) The acidic hydrolysis is also carried out in a solvent, which includes one or more of ethanol, isopropanol, methanol, deionized water, ethylene glycol and propylene glycol; (5) The acidic hydrolysis is also carried out under a catalyst, which includes one or more of hydrochloric acid, nitric acid, acetic acid, citric acid and oxalic acid.

3. The preparation method according to claim 1, characterized in that, The gelation satisfies at least one of the following conditions: (1) Based on the composite sol, the total mass ratio of the silicon source and the titanium source is 0.1wt%~0.35wt%, the molar ratio of silicon in the silicon source to titanium in the titanium source is 1~2, and the solid-liquid ratio of the cathode material particles to the composite sol is 1 g : (2~100) mL; (2) The gelation temperature is 20℃~90℃; (3) The gelation time is 1 h to 24 h.

4. The preparation method according to claim 1, characterized in that, The heat treatment satisfies at least one of the following conditions: (1) The temperature of the heat treatment is 200℃~600℃; (2) The heat treatment time is 1 h to 10 h; (3) The heating rate for the heat treatment is 1℃ / min to 10℃ / min; (4) The oxidizing atmosphere includes oxygen and inert gas, wherein the volume percentage of oxygen is 5% to 100%.

5. The preparation method according to claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The silicon source includes one or more of tetraethyl orthosilicate, methyl orthosilicate, sodium silicate, methyltriethoxysilane and aminopropyltriethoxysilane; (2) The titanium source includes one or more of tetrabutyl titanate, isopropyl titanate, titanium tetrachloride, titanium sulfate and ethyl titanate.

6. The preparation method according to any one of claims 1 to 5, characterized in that, Before the heat treatment, the preparation method further includes a step of drying the positive electrode material particles with the gel layer on their surface, wherein the drying temperature is 60℃~150℃ and the drying time is 4 h~24 h.

7. The preparation method according to any one of claims 1 to 5, characterized in that, The cathode material includes a high-nickel layered oxide cathode material with the general formula LiNi. x M 1-x O2, wherein M includes one or more of Co, Mn, Al, Mg, Ti, Zr, W, Mo, Nb, Ta, B, Sr and Y, and 0.6 ≤ x < 1.

0.

8. A composite oxide-coated modified cathode material, characterized in that, Prepared according to the preparation method according to any one of claims 1-7; The composite oxide coating layer includes a SiO2 phase, a TiO2 phase, and a Si-O-Ti bonded structure located in the transition region between the SiO2 phase and the TiO2 phase.

9. The composite oxide-coated modified cathode material as described in claim 8, characterized in that, It satisfies at least one of the following conditions: (1) In the cathode material modified by the composite oxide coating, the mass percentage of the composite oxide coating layer is 0.05wt%~5.0wt%; (2) In the composite oxide coating layer, the molar ratio of SiO2 to TiO2 is 1~2; (3) The thickness of the composite oxide coating layer is 1 nm to 100 nm.

10. A secondary battery, characterized in that, Including the composite oxide-coated modified cathode material as described in claim 8 or 9.

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