Co-coated positive electrode material with SEI-like film coating layer and preparation method of co-coated positive electrode material

Abstract

The invention provides a co-coated positive electrode material with an SEI-like film coating layer and a preparation method of the co-coated positive electrode material. The preparation method mainly comprises the following steps: carrying out cleaning and drying pretreatment on a positive electrode active powder material; preparing a target material in a magnetron sputtering chamber, and vacuumizing; pre-sputtering a target material; co-sputtering coating and ultrasonic vibration are carried out; and low-temperature sintering. According to the invention, a composite coating layer with an embedded structure and a solid electrolyte interface (SEI) membrane function is formed on the surfaces of the positive electrode material particles by adopting a magnetron co-sputtering method, and the prepared co-coated positive electrode material has relatively good electrochemical performance and stability.

Description

Technical Field

[0001] This invention relates to a cathode material, and more particularly to a co-coated cathode material with an SEI-like film coating layer and its preparation method. Background Technology

[0002] In the field of lithium-ion battery cathode materials, surface coating is widely used in industry due to its low cost and good effect. However, traditional surface coating methods have limitations: although the solvothermal method can form a coating layer, the coating layer is mostly island-shaped and it is difficult to form a complete and continuous nanoscale film. Moreover, water or other solvent residues may be introduced during the coating process, which will impair the electrochemical performance. Physical dry or wet mixing methods rely on mechanical force or van der Waals force for adhesion. The resulting coating layer has weak bonding force with the substrate and may peel off during the stirring and coating process of electrode preparation. It is difficult to maintain stability during long-term charge and discharge volume changes.

[0003] For the coating material itself, a single inorganic oxide (such as...) , Although it has high chemical stability, its intrinsic ionic conductivity is low, which severely hinders lithium-ion transport at the interface, leading to decreased rate performance and increased polarization. While single conductive polymers (such as PEDOT:PSS) or carbon materials provide electron channels, their electrochemical windows and structural stability are limited, making them prone to decomposition at high voltages and unable to effectively prevent electrolyte erosion of the cathode material.

[0004] Therefore, the existing cathode material surface coating technology has three major defects: poor coating layer continuity, weak interfacial bonding force, and single function. Specifically: (1) it is difficult to achieve uniform coating with controllable thickness and complete coverage at the nanoscale; (2) the bonding strength between the coating layer and the cathode material matrix is ​​not good and cannot withstand the test of electrode processing and electrochemical cycling; (3) it cannot synergistically improve the ionic conductivity, electronic insulation (preventing side reactions) and mechanical toughness of the interface. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a co-coated cathode material with a SEI-like film coating layer. The preparation method forms a composite coating layer with an embedded structure that has a solid electrolyte interphase (SEI) film function on the surface of cathode material particles. The resulting co-coated cathode material has good electrochemical performance and stability.

[0006] To solve the above technical problems, the application provides a strategy of "in-situ construction of composite solid-state electrolyte interface" which overturns the traditional idea: using a magnetron co-sputtering method in the physical vapor deposition technology, two functionally complementary lithium-containing oxides, i.e., one crystalline (providing a skeleton and a high-speed ion channel) and one amorphous (providing adhesion and densification) are simultaneously deposited on the surface of the positive electrode material in the form of atoms / molecules, and then through a carefully designed low-temperature heat treatment process, the amorphous phase is induced to flow and fill the skeleton formed by the crystalline phase, and finally a complete SEI-like film with a micro-inlaid structure is formed by "sintering". The specific technical scheme is as follows: A preparation method of a co-coated positive electrode material with an SEI-like film coating layer, comprising the following steps: S1. The positive electrode active powder material is immersed in anhydrous ethanol and ultrasonically cleaned for 5-10 min, and then transferred to a forced air drying oven for drying for 60-180 min to obtain a pretreated positive electrode active powder material; S2. The pretreated positive electrode active powder material obtained in step S1 is placed on a conveyor belt in a magnetron sputtering chamber, a crystalline lithium-containing ternary oxide target is installed as a first sputtering source and an amorphous lithium-containing ternary oxide target is installed as a second sputtering source in the magnetron sputtering chamber, the magnetron sputtering chamber is closed and vacuumized to a base vacuum degree of less than 5.0*10 -3 Pa, and the vacuumization is stopped; S3. Argon-oxygen mixed gas is introduced into the magnetron sputtering chamber treated in step S2 as a sputtering working gas, and the sputtering working pressure is maintained at 0.5-2.0 Pa, and the first sputtering source and the second sputtering source are pre-sputtered for 10-30 min; S4. The pretreated positive electrode active powder material on the conveyor belt is transported to the target sputtering area, and an ultrasonic vibration device is started to co-sputter the pretreated positive electrode active powder material for 20-120 min to form a coating layer uniformly mixed with crystalline and amorphous states to obtain a co-sputtered positive electrode material; S5. The co-sputtered positive electrode material obtained in step S4 is sintered in an air or oxygen atmosphere, and after cooling to room temperature, a co-coated positive electrode material with an SEI-like film coating layer is obtained.

[0007] Further, in step S1, the positive electrode active powder material is one of 、 or , wherein x>0.8, y>0, and x+y<1. Step S1 is a pretreatment basic step of the positive electrode active powder material, and the purpose is to obtain a clean and active surface to facilitate the subsequent deposition of a high-quality coating layer.

[0008] Further, in the step S1, the ultrasonic frequency during the ultrasonic cleaning is 60-100 Hz, and the drying temperature is 70-100℃. The purpose of the ultrasonic cleaning is to clean and remove the contaminants on the surface of the positive active powder material, and the purpose of the drying is to remove the adsorbed water and anhydrous ethanol on the surface of the positive active powder material.

[0009] Further, in the step S2, the crystalline lithium-containing ternary oxide target is at least one of a target, a target or a target, the amorphous lithium-containing ternary oxide target is at least one of a target or a target, and the molar ratio of Li in the crystalline lithium-containing ternary oxide target to the amorphous lithium-containing ternary oxide target is 1:(0.5-2). The base vacuum degree (lower than 5.0*10 -3 Pa) in the step S2 is crucial, which can minimize the interference of residual gas (such as water vapor, nitrogen) on the deposition process and the pollution of the film layer; the selection of the working gas pressure (0.5-2.0 Pa) can balance the sputtering rate and the quality of the coating layer: if the gas pressure is too low, the particle energy is too high, which may cause bombardment damage to the surface of the powder; if the gas pressure is too high, the gas scattering is serious, which results in slow deposition rate and loose coating layer.

[0010] Further, in the step S3, the volume flow ratio of argon to oxygen in the argon-oxygen mixed gas is (18-30):(1-5). The purpose of the pre-sputtering is to remove the oxide layer and contaminants on the surface of the first sputtering source and the second sputtering source, which is a necessary step to ensure the accuracy of the coating composition and the purity.

[0011] Further, in the step S3, the RF power of the first sputtering source is 85-95 W, the RF power of the second sputtering source is 75-85 W, and the difference between the RF powers of the first sputtering source and the second sputtering source is 10 W, which can realize the matching of the co-deposition rates of the two components.

[0012] Further, in the step S4, the vibration frequency of the ultrasonic vibration device is 20-40 kHz, and the thickness of the coating layer is 80-150 nm, which can be accurately controlled by controlling the time of the co-sputtering film deposition. The ultrasonic vibration is one of the core auxiliary means for realizing the uniform coating of the powder material, and the parameters (vibration frequency 20-40 kHz) need to be carefully selected: if the frequency is too low, the energy is insufficient to fully fluidize the powder; if the frequency is too high, the collision between the powder particles may be too violent and cause damage.

[0013] Further, in step S5, the sintering process is as follows: heating at a temperature increasing rate of 2-5℃ / min to 350-450℃, and then keeping the temperature for 10-20h. The sintering process is another core of the present application. The temperature increasing rate (2-5℃ / min) must be slow to avoid cracking of the coating layer due to thermal stress. The sintering temperature (350-450℃) is strictly designed: it must be higher than the softening point of the amorphous lithium-containing ternary oxide (melting point about 700℃, but the glass transition temperature is lower, above 300℃, it starts to significantly soften and flow), so that it has sufficient flowability, and it must be far lower than the sintering temperature of most crystalline lithium-containing ternary oxides (such as LiCoO2, melting point 1250℃) and the positive electrode material itself, to prevent excessive grain growth, phase transition or lithium evaporation.

[0014] Another technical problem to be solved by the present application is to provide a co-coated positive electrode material with a SEI-like film coating layer prepared by the above preparation method. The surface of the co-coated positive electrode material has a SEI-like film coating layer with an inlaid structure formed by sintering of the crystalline lithium-containing ternary oxide and the amorphous lithium-containing ternary oxide, and there is an element interdiffusion layer with a thickness of 5-20nm between the coating layer and the positive electrode material substrate.

[0015] By synchronously sputtering the two functionally complementary lithium-containing ternary oxides of crystalline and amorphous states, and combining with subsequent low-temperature solid-state sintering, the present application successfully forms a dense, uniform, strong bonding and unique micro-inlaid structure composite coating layer on the surface of the positive electrode particles. The composite coating layer can simultaneously act as an excellent ion conductor and an electronic insulator, effectively inhibiting electrolyte decomposition, transition metal dissolution and material micro-crack propagation, thereby synergistically improving the first efficiency, rate performance, cycle life and safety performance of the battery.

[0016] The key technical features of the present application include: (1) double-target co-sputtering: ensuring uniform mixing and synchronous deposition of the two different phases on a nanometer scale, which is the prerequisite for forming a composite structure. (2) precise power and atmosphere control: RF power determines the sputtering rate and coating layer quality, and argon-oxygen mixed gas provides plasma for sputtering and prevents excessive generation of oxygen vacancies in the target material and the deposited layer during impact. (3) ultrasonic-assisted fluidization: for powder materials, this step is crucial, as it breaks the static accumulation of the powder, allowing each surface of each particle to have an equal opportunity to be exposed to the sputtering particle flow, achieving uniform three-dimensional coating. (4) low-temperature solid-state sintering: this step is the key to realizing the "inlaid structure", and the selected sintering temperature is higher than the softening point of the amorphous phase or ​the amorphous phase occurs viscous flow, like "cement" seeps into and fills the gap between the crystalline "aggregate", forming a dense whole, and interfacial interdiffusion with the matrix, thus producing a very strong binding force.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1) The superiority of the "trinity" structure: ①Uniformity and density: the atomic level deposition uniformity given by magnetron sputtering, plus the flow filling of amorphous phase, completely eliminates the pores and discontinuous area of the coating layer, forming a perfect physical barrier that can effectively prevent the penetration of electrolyte and the dissolution of transition metal ions; ②Excellent bonding force: the initial high bonding energy brought by high-energy sputtering particles, plus the 5-20nm thick element interdiffusion layer formed during sintering, realizes the qualitative leap from "physical adhesion" to "metallurgical bonding" of the coating layer and the matrix, greatly inhibiting the peeling of the coating layer in the cycle; (3) Unique inlaid structure: this structure ingeniously combines the high-speed lithium ion transport capacity and high Young's modulus (resistance to volume change) of the crystalline phase (such as ), and the interface wetting and defect filling capacity of the amorphous phase (such as ), this structure provides a continuous, low-energy barrier transport channel for lithium ions, while its overall electronic insulation effectively inhibits the oxidative decomposition of electrolyte at high voltage.

[0018] 2) Comprehensive improvement of comprehensive electrochemical performance: the lithium-rich coating layer itself can serve as an additional lithium source to compensate for the irreversible lithium loss during the first charge and discharge process, improving the first coulombic efficiency, and the optimized ion path significantly reduces the interfacial impedance, thereby improving the rate performance of the battery.

[0019] 3) The capacity retention rate of the co-coated positive electrode material prepared by the present application is high under harsh high voltage (for NCM / LCO) or long-term cycling, which is due to the effective protection of the coating layer to the bulk structure of the positive electrode material, inhibiting the initiation and expansion of microcracks, as well as the continuous accumulation of byproduct. The dense coating layer reduces the direct contact area between the positive electrode material and the electrolyte, thereby inhibiting the intense interface exothermic reaction of the battery under abuse conditions (such as overheating), improving the thermal stability and safety of the battery. DETAILED DESCRIPTION

[0020] The present application will be described in detail below with specific examples, and the illustrative examples and descriptions of the present application are used to explain the present application, but not as a limitation of the present application.

[0021] Example 1 The co-coated positive electrode material with SEI film coating layer was prepared according to the following steps: S1. The positive electrode active powder material LiNi 0.9 Co 0.05 Mn 0.05 O2 was immersed in anhydrous ethanol and ultrasonically cleaned at an ultrasonic frequency of 80 Hz for 10 min. Then it was transferred to a forced-air drying oven and dried at 80 ℃ for 60 min to obtain pretreated positive electrode active powder material. S2. Place the pretreated positive electrode active powder material obtained in step S1 onto the conveyor belt of the magnetron sputtering chamber, and install it in the magnetron sputtering chamber. The target material serves as the primary sputtering source. The target material serves as the second sputtering source, and Target and In the target material The molar ratio is 1:1. The magnetron sputtering chamber is shut down and evacuated to a background vacuum of 5.0 × 10⁻⁶. -3 Pa; S3. Introduce an argon-oxygen mixture into the magnetron sputtering chamber after step S2 as the sputtering working gas, wherein the volumetric flow rate of argon is 24 cm³. 3 / min, oxygen volumetric flow rate is 3cm 3 / min, and maintain the sputtering working pressure at 1.0Pa, pre-sputter the first sputtering source and the second sputtering source for 20min, the RF power of the first sputtering source is 90W, and the RF power of the second sputtering source is 80W; S4. Transport the pretreated positive electrode active powder material on the conveyor belt to the target sputtering area, start the ultrasonic vibration device, and perform co-sputtering coating on the pretreated positive electrode active powder material for 30 minutes to form a coating layer and obtain the co-sputtered positive electrode material. The vibration frequency of the ultrasonic vibration device is 30kHz, and the thickness of the coating layer is 80nm. S5. The co-sputtered cathode material obtained in step S4 is sintered in air atmosphere and cooled to room temperature to obtain a co-coated cathode material with an SEI-like film coating layer. The sintering process is as follows: the temperature is increased to 350°C at a heating rate of 2°C / min, and then held for 20 hours.

[0022] Example 2 The co-coated cathode material with an SEI-like film coating layer was prepared according to the following steps: S1. The positive electrode active powder material LiCoO2 was immersed in anhydrous ethanol, ultrasonically cleaned at a frequency of 60Hz for 8 minutes, and then dried in a forced-air drying oven at 100℃ for 120 minutes to obtain the pretreated positive electrode active powder material. S2. Place the pretreated positive electrode active powder material obtained in step S1 onto the conveyor belt of the magnetron sputtering chamber, and install it in the magnetron sputtering chamber. The target material serves as the first sputtering source, and the Li3BO3 target material serves as the second sputtering source. Target and The molar ratio of Li in the target material is 1:0.5, the magnetron sputtering chamber is closed and vacuumed to a base vacuum of 4.9x10 -3 Pa; S3. Argon-oxygen mixed gas is introduced into the magnetron sputtering chamber treated in step S2 as sputtering working gas, wherein the volume flow rate of argon is 18cm 3 / min, the volume flow rate of oxygen is 1cm 3 / min, and the sputtering working pressure is maintained at 1.0Pa, the first sputtering source and the second sputtering source are pre-sputtered for 10min, the RF power of the first sputtering source is 95W, and the RF power of the second sputtering source is 85W; S4. The pretreated positive active powder material on the conveying belt is transported to the target sputtering area, the ultrasonic vibration device is started, and the pretreated positive active powder material is co-sputtered and plated for 20min to form a coating layer to obtain a co-sputtered positive material, the vibration frequency of the ultrasonic vibration device is 40kHz, and the thickness of the coating layer is 100nm; S5. The co-sputtered positive material obtained in step S4 is sintered in an oxygen atmosphere, and after cooling to room temperature, a co-coated positive material with a SEI film-like coating layer is obtained, and the sintering process is as follows: heating to 400℃ at a heating rate of 4℃ / min, and then maintaining for 12h.

[0023] Example 3 A co-coated positive material with a SEI film-like coating layer is prepared according to the following steps: S1. The positive active powder material LiFePO4 is immersed in anhydrous ethanol, ultrasonically cleaned at a frequency of 100Hz for 5min, and then transferred to a forced air drying oven for drying at 70℃ for 180min to obtain a pretreated positive active powder material; S2. The pretreated positive active powder material obtained in step S1 is placed on the conveying belt in the magnetron sputtering chamber, Li2TiO3 target material is installed as the first sputtering source and Li2SiO3 target material is installed as the second sputtering source in the magnetron sputtering chamber, and the molar ratio of Li in the Li2TiO3 target material and the Li2SiO3 target material is 1:2, the magnetron sputtering chamber is closed and vacuumed to a base vacuum of 5.0x10 -3 Pa; S3. Argon-oxygen mixed gas is introduced into the magnetron sputtering chamber treated in step S2 as sputtering working gas, wherein the volume flow rate of argon is 30cm 3 / min, the volume flow rate of oxygen is 5cm 3 / min, and the sputtering working pressure is maintained at 2.0Pa, the first sputtering source and the second sputtering source are pre-sputtered for 30min, the RF power of the first sputtering source is 85W, and the RF power of the second sputtering source is 75W; S4. The pretreated positive electrode active powder material on the conveyor belt is transported to the target sputtering area, the ultrasonic vibration device is started, and the pretreated positive electrode active powder material is co-sputtered for 120 min to form a coating layer to obtain a co-sputtered positive electrode material. The vibration frequency of the ultrasonic vibration device is 20 kHz, and the thickness of the coating layer is 150 nm. S5. The co-sputtered positive electrode material obtained in step S4 is sintered in an air atmosphere, and after cooling to room temperature, a co-coated positive electrode material with a SEI film-like coating layer is obtained. The sintering process is as follows: heating at a rate of 5°C / min to 450°C, and then holding for 10 h.

[0024] Comparative Example 1 The difference from Example 1 is that in step S2, only LiNbO3 single target is used for magnetron sputtering of LiNi 0.9 Co 0.05 Mn 0.05 O2 to form a LiNbO3 single coating layer with a thickness of about 80 nm, and step S5 is not included.

[0025] Comparative Example 2 The positive electrode material is prepared according to the following steps: (1) Dry mechanical mixing of crystalline LiTbO3 and amorphous Li3BO3 in a molar ratio of Tb to B of 1:1 to obtain a mixed coating agent; (2) Immersing the positive electrode active powder material LiCoO2 in anhydrous ethanol, ultrasonic treatment at 80 Hz for 10 min, and then drying at 70°C for 60 min to obtain pretreated LiCoO2; (3) Dry mechanical mixing of the mixed coating agent obtained in step (1) and the pretreated LiCoO2 obtained in step (2) to obtain a mixed material with a total coating layer thickness of about 100 nm; (4) Sintering the mixed material obtained in step (3) in an oxygen atmosphere at a heating rate of 4°C / min to 400°C, and holding for 12 h to obtain a positive electrode material.

[0026] Comparative Example 3 The positive electrode material is prepared according to the following steps: Immersing the positive electrode active powder material LiFePO4 in anhydrous ethanol, ultrasonic treatment at 70 Hz for 5 min to clean the surface, and then transferring to a forced air drying oven, drying at 80°C for 60 min to obtain an uncoated positive electrode material.

[0027] Experimental Example Preparation of positive electrode sheet: the prepared positive electrode material (Examples 1-3, Comparative Examples 1-3) was mixed with the conductive agent SP and the binder PVDF in a mass ratio of 80:10:10, and then NMP was added to adjust the solid content of the slurry to 20% to obtain a slurry. The slurry was coated on the surface of a 12 μm thick aluminum foil to obtain an electrode sheet, and the coating thickness was 150 μm. The coated electrode sheet was dried in a forced air drying oven at 90°C for 10 h, and then rolled and cut into a circular sheet with a diameter of 12 mm and a thickness of 0.1 mm to obtain a positive electrode sheet.

[0028] Assembly of battery: the positive electrode sheet prepared in the above step was used as the positive electrode, lithium metal was used as the negative electrode, porous polypropylene film (Celgard2325) was used as the separator, and 1 mol / L concentration LiPF6 solution (the solvent of the LiPF6 solution was composed of ethylene carbonate EC and dimethyl carbonate DMC in a volume ratio of 1:1) was used as the electrolyte. Circular port springs and gaskets were used to assemble the above materials in an argon-filled glove box, and the water and oxygen values in the glove box were controlled to be less than 0.01 ppm. A sealing machine was used to pressurize and seal the assembled battery to obtain a button cell.

[0029] Performance test: the assembled button cell was tested for electrochemical performance at 25°C. LiFePO4 positive electrode material (Example 3, Comparative Example 3) was tested according to GB / T42161-2022 (test method for first discharge specific capacity and first charge-discharge efficiency of lithium iron phosphate electrochemical performance test), and the test voltage interval was 2-4V. LiCoO2 positive electrode material (Example 2, Comparative Example 2) was tested according to GB / T 23365-2023 (test method for first discharge specific capacity and first charge-discharge efficiency of lithium cobalt oxide electrochemical performance test), and the test voltage interval was 3-4.5V. LiNi x Co y Mn 1xy O2 positive electrode material (Example 1, Comparative Example 1) was tested according to GB / T 37201-2018 (test method for first discharge specific capacity and first charge-discharge efficiency of lithium nickel cobalt manganese oxide electrochemical performance test), and the test voltage interval was 2.75-4.2V.

[0030] Formation was carried out by charging and discharging at 0.1C rate for 2 cycles, first discharge specific capacity test was carried out at 1C rate, and capacity retention rate test was carried out by cycling 100 times at 1C rate. The test results are shown in Table 1.

[0031] Table 1

[0032] As can be seen from Table 1, the first cycle discharge specific capacity, discharge specific capacity after 100 cycles and capacity retention rate after 100 cycles of the co-coated electrode material prepared in Examples 1-3 are all superior to those of Comparative Examples 1-3, indicating that the co-coated electrode material prepared in the application can effectively improve the rate performance and stability of the battery.

[0033] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed in the present application should be covered by the claims of the present application.

Claims

1. A method for preparing a co-coated cathode material with an SEI-like film coating layer, characterized in that: Includes the following steps: S1. Immerse the positive electrode active powder material in anhydrous ethanol, ultrasonically clean for 5-10 minutes, and then transfer it to a forced-air drying oven to dry for 60-180 minutes to obtain the pretreated positive electrode active powder material. S2. Place the pretreated positive electrode active powder material obtained in step S1 onto the conveyor belt of the magnetron sputtering chamber. Install a crystalline lithium-containing ternary oxide target as the first sputtering source and an amorphous lithium-containing ternary oxide target as the second sputtering source in the magnetron sputtering chamber. Close the magnetron sputtering chamber and evacuate to a background vacuum level below 5.0 × 10⁻⁶. -3 Pa; S3. Introduce an argon-oxygen mixture into the magnetron sputtering chamber after step S2 as the sputtering working gas, and maintain the sputtering working gas pressure at 0.5-2.0 Pa, and pre-sputter the first sputtering source and the second sputtering source for 10-30 min; S4. Transport the pretreated positive electrode active powder material on the conveyor belt to the target sputtering area, start the ultrasonic vibration device, and perform co-sputtering coating on the pretreated positive electrode active powder material for 20-120 minutes to form a coating layer and obtain the co-sputtered positive electrode material. S5. The co-sputtered cathode material obtained in step S4 is sintered in an air or oxygen atmosphere and cooled to room temperature to obtain a co-coated cathode material with an SEI-like film coating layer.

2. The method for preparing a co-coated cathode material with an SEI-like film coating layer according to claim 1, characterized in that: In step S1, the positive electrode active powder material is... , or One of them, where x≥0.8, y>0, and x+y<1.

3. The method for preparing a co-coated cathode material with an SEI-like film coating layer according to claim 1, characterized in that: In step S1, the ultrasonic frequency during ultrasonic cleaning is 60-100Hz, and the drying temperature during drying is 70-100℃.

4. The method for preparing a co-coated cathode material with an SEI-like film coating layer according to claim 1, characterized in that: In step S2, the crystalline lithium-containing ternary oxide target material is... Target material Target material or At least one of the target materials, the amorphous lithium-containing ternary oxide target material is... Target material or At least one of the target materials, and the molar ratio of Li in the crystalline lithium-containing ternary oxide target material and the amorphous lithium-containing ternary oxide target material is 1:(0.5-2).

5. The method for preparing a co-coated cathode material with an SEI-like film coating layer according to claim 1, characterized in that: In step S3, the volume flow rate ratio of argon to oxygen in the argon-oxygen mixture is (18-30):(1-5).

6. The method for preparing a co-coated cathode material with an SEI-like film coating layer according to claim 1, characterized in that: In step S3, the RF power of the first sputtering source is 85-95W, the RF power of the second sputtering source is 75-85W, and the difference in RF power between the first sputtering source and the second sputtering source is 10W.

7. The method for preparing a co-coated cathode material with an SEI-like film coating layer according to claim 1, characterized in that: In step S4, the vibration frequency of the ultrasonic vibration device is 20-40kHz, and the thickness of the coating layer is 80-150nm.

8. The method for preparing a co-coated cathode material with an SEI-like film coating layer according to claim 1, characterized in that: In step S5, the sintering process is as follows: the temperature is increased to 350-450℃ at a heating rate of 2-5℃ / min, and then held at that temperature for 10-20 hours.

9. The co-coated cathode material with an SEI-like film coating layer prepared by the preparation method according to claims 1 to 8.

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