A composite-coated ternary cathode material, its preparation method and application

Abstract

This invention provides a composite-coated ternary cathode material, its preparation method, and its application. The composite-coated ternary cathode material includes a ternary cathode material matrix and a coating layer coated on the surface of the ternary cathode material matrix; the chemical formula of the ternary cathode material matrix is ​​LiNi. x Co y Mn z O2; the coating layer comprises LiAlO2 and LiZrO3; the molar ratio of LiAlO2 to LiZrO3 is 3-5:1. The composite-coated ternary cathode material provided by this invention uses LiAlO2 and LiZrO3 as the composite coating layer, enabling the cathode material to possess both excellent barrier properties and lithium-ion conductivity. The interface is tightly bonded and not easily detached, suppressing side reactions and cation mixing, thus achieving synergistic optimization of structural stability, cycle performance, and rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a composite-coated ternary cathode material, its preparation method, and its application. Background Technology

[0002] Ultra-high nickel ternary cathode materials (Ni molar number ≥ 0.9) have become core materials for lithium-ion power batteries and energy storage batteries due to their high specific capacity and high energy density, and represent the mainstream direction for high-energy-density battery research and development in the new energy field. However, the crystal structure of this type of material is layered α-NaFeO2, and the repeated insertion and extraction of lithium ions during charging and discharging can easily cause lattice distortion. At the same time, the surface lattice oxygen has high activity, which easily leads to side reactions with the electrolyte, causing the dissolution of transition metal ions and the decomposition of electrolyte to produce gas. This results in a decrease in the material's cycle stability and thermal safety. Surface coating modification is one of the common methods to improve the above problems.

[0003] Surface coating modification involves constructing a dense coating layer on the material surface to prevent direct contact between the material and the electrolyte, thus suppressing side reactions. Existing coating modification methods are mainly divided into two categories: high-temperature sintering coating and liquid-phase wet coating. In high-temperature sintering coating methods, oxides such as Al2O3 and ZrO2 are often used as coating sources. The coating source is mechanically mixed with ultra-high nickel ternary cathode material and then sintered at a high temperature of 600-750℃ for 2-6 hours, using the high temperature to form a coating layer on the material surface. While this technology can achieve surface coating and improve interface stability to some extent, high-temperature sintering easily leads to particle agglomeration, increasing microstructural defects. At the same time, high temperatures exacerbate Li / Ni mixing within the material, resulting in a loss of specific capacity. Furthermore, the difference in thermal expansion coefficients between the coating layer and the substrate makes it easy to generate interfacial stress during cooling after high-temperature sintering, causing the coating layer to crack and peel off, thus losing its surface protection function. In addition, the coating layer formed by this method has poor ion conductivity, which hinders the transport of lithium ions on the material surface and reduces the rate performance of the material. Therefore, it is impossible to simultaneously achieve both interface stability and electrochemical kinetic performance.

[0004] Therefore, there is an urgent need for an ultra-high nickel ternary cathode material that can balance structural stability, cycle performance, and rate performance. Summary of the Invention

[0005] This invention provides a composite-coated ternary cathode material, its preparation method, and its application, in order to solve the problem that existing ultra-high nickel ternary cathode materials cannot simultaneously achieve structural stability, cycle performance, and rate performance.

[0006] In a first aspect, the present invention provides a composite-coated ternary cathode material, comprising a ternary cathode material matrix and a coating layer coated on the surface of the ternary cathode material matrix; the chemical formula of the ternary cathode material matrix is ​​LiNi. x Co y Mn z O2, wherein x≥0.9, 0.02≤y≤0.06, 0.02≤z≤0.06, x+y+z=1; the coating layer includes LiAlO2 and LiZrO3; the molar ratio of LiAlO2 and LiZrO3 is 3-5:1.

[0007] In one alternative embodiment, the thickness of the coating layer is 10-50 nm.

[0008] In one optional embodiment, the particle size D of the ternary cathode material matrix is... v 50 is 13-17μm.

[0009] In one optional embodiment, the particle size D of the composite-coated ternary cathode material is... v 50 represents 12-20 μm.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned composite-coated ternary cathode material, comprising the following steps: Step S1: The aluminum source, zirconium source and solvent are mixed in the first mixture to obtain a precursor solution. A complexing agent is added to the precursor solution to carry out the first reaction to obtain a precursor sol. Step S2: The lithium source and the precursor sol undergo a second reaction to obtain a composite coated sol; Step S2: The ternary cathode material matrix and the composite coating sol are mixed for the second time, and then dried and heat-treated to obtain the composite coated ternary cathode material.

[0011] In one optional embodiment, the molar ratio of aluminum in the aluminum source to zirconium in the zirconium source is 3-5:1.

[0012] In one optional embodiment, the ratio of the total number of moles of aluminum and zirconium in the aluminum source and zirconium source to the number of moles of lithium in the lithium source is 1:1.05-1.1.

[0013] In one optional embodiment, the ratio of the total molar number of aluminum and zirconium elements in the aluminum source and zirconium source to the molar number of the complexing agent is 1:1-1.5.

[0014] In one optional embodiment, the total metal ion concentration in the precursor solution is 0.2-0.3 mol / L.

[0015] In one optional embodiment, the mass ratio of the ternary cathode material matrix to the composite coated sol is 1:0.05-0.2.

[0016] In one optional embodiment, the aluminum source includes at least one of aluminum nitrate, aluminum nitrate hydrate, and aluminum chloride; preferably aluminum nitrate nonahydrate.

[0017] In one optional embodiment, the zirconium source includes at least one of zirconium nitrate, zirconium nitrate hydrate, and zirconium chloride; preferably aluminum nitrate pentahydrate.

[0018] In one alternative embodiment, the solvent comprises water and / or an alcohol compound; preferably a mixture of water and ethanol.

[0019] In one alternative embodiment, the volume ratio of water to ethanol is 1:2-3.

[0020] In one alternative embodiment, the complexing agent comprises citric acid and / or tartaric acid.

[0021] In one optional embodiment, the lithium source includes lithium acetate and / or lithium nitrate; preferably lithium acetate.

[0022] In one alternative embodiment, the first mixing speed is 200-400 rpm and the time is 20-40 min.

[0023] In one optional embodiment, the temperature of the first reaction is 60-70°C, the time is 30-40 min, and the rotation speed is 200-400 rpm.

[0024] In one optional embodiment, the temperature of the second reaction is 60-70°C, the time is 1-2 hours, and the rotation speed is 200-400 rpm.

[0025] In one optional embodiment, the second mixing speed is 300-500 rpm, and the time is 20-30 min. By using a specific mass ratio and mixing conditions between the composite coating sol and the ternary cathode material matrix, a uniform coating layer without any gaps in the coating can be ensured.

[0026] In one alternative embodiment, the second mixing process further includes a step of sonicating at a frequency of 70-90 kHz for 20-40 minutes.

[0027] The drying temperature is 80-100℃, the time is 6-8h, and the vacuum degree is -0.095~-0.085MPa.

[0028] In one alternative embodiment, the heat treatment is performed by raising the temperature from room temperature to 250-350°C at a rate of 1-2°C / min in an air atmosphere and holding the temperature for 3-5 hours.

[0029] In one optional embodiment, the gas flow rate of the air atmosphere is 50-100 mL / min.

[0030] Thirdly, the present invention provides a positive electrode sheet, comprising: Positive current collector, and A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the above-mentioned composite-coated ternary positive electrode material or the composite-coated ternary positive electrode material prepared by the above-mentioned preparation method.

[0031] Fourthly, the present invention provides a secondary battery comprising the aforementioned positive electrode sheet.

[0032] In one optional embodiment, the positive electrode sheet comprises a positive electrode active material layer, a conductive agent, and a binder, wherein the mass ratio of the positive electrode active material layer, the conductive agent, and the binder is 92-96:2-4:2-4; the conductive agent comprises carbon black and / or carbon nanotubes; preferably a mixture of carbon black and carbon nanotubes; wherein the mass ratio of carbon black and carbon nanotubes is (3-4):1; and the binder is polyvinylidene fluoride.

[0033] Fifthly, the present invention provides an electrical device comprising the aforementioned secondary battery.

[0034] In one alternative implementation, the secondary battery may be used for power batteries and / or energy storage batteries.

[0035] Compared with the prior art, the present invention has the following beneficial effects: 1. The composite-coated ternary cathode material provided by this invention achieves synergistic optimization of multi-dimensional performance by constructing a specific LiAlO2 and LiZrO3 composite coating layer on the substrate surface. Firstly, LiAlO2 possesses excellent structural density, effectively blocking direct contact between the ternary cathode material and the electrolyte, suppressing side reactions such as transition metal ion dissolution and electrolyte decomposition, and significantly improving interface stability. LiZrO3 exhibits excellent lithium-ion conductivity, ensuring rapid lithium-ion transport on the material surface. Furthermore, the composite coating layer of LiAlO2 and LiZrO3 effectively suppresses oxygen release and structural collapse during high-temperature delithiation, enhancing battery safety. Therefore, the cathode material provided by this invention combines excellent barrier properties with lithium-ion conductivity, exhibiting tight interfacial bonding that is not easily detached, suppressing side reactions and cation mixing, and achieving synergistic optimization of structural stability, cycle performance, and rate performance.

[0036] 2. The preparation method of the above-mentioned composite-coated ternary cathode material provided by the present invention, by preparing a composite-coated sol, allows the raw material components to be uniformly dispersed in the liquid phase, forming a continuous and uniform coating layer on the surface of the ternary cathode material. This ensures the consistency of the electrochemical performance of the prepared material and avoids the problems of material particle agglomeration and Li / Ni mixing caused by high temperature, effectively preserving the original crystal structure and high specific capacity characteristics of the material. In addition, this preparation method not only does not generate obvious interfacial stress between the coating layer and the material matrix, but also makes the coating layer and the matrix tightly bonded, not easy to crack or fall off, greatly improving the stability and service life of the coating layer. The process is simple, convenient to operate, requires no special production equipment, has good compatibility with existing production processes, and is suitable for large-scale industrial applications. Detailed Implementation

[0037] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0038] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0039] The particle size Dv50 test method in this invention is as follows: wet particle size analysis is performed using a laser particle size analyzer (Malvern Mastersizer 3000), with deionized water as the dispersion medium. After ultrasonic dispersion for 3 minutes, the particle size Dv50 is recorded.

[0040] The method for determining the coating thickness in this invention is as follows: the cross-section of the material is observed using a transmission electron microscope (TEM, FEI Tecnai G2F20), high-resolution images are captured under an accelerating voltage of 200kV, the coating thickness measurements at different locations are randomly selected, and the arithmetic mean is taken as the coating thickness.

[0041] Example 1 This embodiment provides a composite-coated ternary cathode material, including a ternary cathode material matrix (chemical formula LiNi). 0.92 Co 0.04 Mn 0.04O2 (particle size Dv50 = 15 μm), and a coating layer on the surface of the ternary cathode material substrate; the coating layer includes LiAlO2 and LiZrO3; the molar ratio of LiAlO2 to LiZrO3 is 4:1; the thickness of the coating layer is 25 nm; the particle size Dv50 of the composite coated ternary cathode material is 15.1 μm.

[0042] This embodiment also provides a method for preparing the above-mentioned composite-coated ternary cathode material, including the following steps: (1) Take 0.04 mol Al(NO3)3•9H2O and 0.01 mol Zr(NO3)4•5H2O, add 200 mL of solvent obtained by mixing deionized water and anhydrous ethanol (wherein the volume ratio of deionized water and anhydrous ethanol is 1:2.5), and then stir at 300 rpm for 30 min to obtain a precursor solution; add 0.075 mol citric acid to the precursor solution, and stir at 300 rpm for 35 min under 65℃ water bath conditions to achieve full complexation of metal ions; then add 0.0575 mol CH3COOLi according to the ratio of the total number of aluminum and zirconium elements in the aluminum source and zirconium source to the number of lithium elements in the lithium source of 1:1.05, maintain a 65℃ water bath and a stirring rate of 300 rpm, and continue stirring for 1.5 h to obtain a transparent and uniform LiAlO2-LiZrO3 composite coated sol; (2) Take 100g LiNi 0.92 Co 0.04 Mn 0.04 O2 matrix and 12g of the above composite coating sol were placed in a planetary ball mill and dispersed at 300rpm for 25min to allow the sol to be uniformly adsorbed on the matrix surface, resulting in a viscous coating slurry. Subsequently, the slurry was sonicated at 80kHz for 30min to further eliminate slurry agglomeration and ensure coating uniformity. (3) The coating slurry was transferred to a vacuum drying oven, the temperature was set to 90℃ and the vacuum degree to -0.09MPa, and after drying for 7h, the dried coating material was obtained. The composite coating layer was initially attached to the substrate surface. The dried coating material was placed in an alumina crucible and placed in a muffle furnace. An air atmosphere was introduced (the gas flow rate was 80mL / min), and the temperature was raised from room temperature to 300℃ at a rate of 1.5℃ / min. The temperature was kept for 4h to achieve the curing of the coating layer. The coating material was cooled to room temperature with the furnace and ground through a 200-mesh sieve to obtain a composite coated ternary cathode material.

[0043] Example 2 This embodiment provides a composite-coated ternary cathode material, including a ternary cathode material matrix (chemical formula LiNi). 0.9 Co 0.05 Mn 0.05O2 (particle size Dv50 = 13 μm), and a coating layer on the surface of the ternary cathode material substrate; the coating layer includes LiAlO2 and LiZrO3; the molar ratio of LiAlO2 to LiZrO3 is 3:1; the thickness of the coating layer is 15 nm; the particle size Dv50 of the composite coated ternary cathode material is 13.1 μm.

[0044] This embodiment also provides a method for preparing the above-mentioned composite-coated ternary cathode material, including the following steps: (1) Take 0.03 mol Al(NO3)3•9H2O and 0.01 mol Zr(NO3)4•5H2O, add 200 mL of deionized water and anhydrous ethanol (the volume ratio of deionized water and anhydrous ethanol is 1:2), and stir at 400 rpm for 20 min to obtain a precursor solution; add 0.04 mol citric acid to the precursor solution, and stir at 400 rpm for 30 min under 60℃ water bath conditions to achieve full complexation of metal ions; then add 0.0432 mol CH3COOLi according to the ratio of the total number of aluminum and zirconium elements in the aluminum source and zirconium source to the number of lithium elements in the lithium source of 1:1.08, maintain a 60℃ water bath and a stirring rate of 400 rpm, and continue stirring for 1 h to obtain a transparent and uniform LiAlO2-LiZrO3 composite coated sol; (2) Take 100g LiNi 0.9 Co 0.05 Mn 0.05 O2 matrix and 5g of the above composite coating sol were placed in a planetary ball mill and dispersed at 500rpm for 20min to allow the sol to be uniformly adsorbed on the matrix surface, resulting in a viscous coating slurry; then, it was sonicated at 90kHz for 20min to further eliminate slurry agglomeration and ensure coating uniformity. (3) The coating slurry was transferred to a vacuum drying oven, the temperature was set to 80℃ and the vacuum degree to -0.085MPa, and dried for 8 hours to obtain the dried coating material. The composite coating layer was initially attached to the substrate surface. The dried coating material was placed in an alumina crucible and placed in a muffle furnace. An air atmosphere was introduced (the gas flow rate was 50mL / min), and the temperature was raised from room temperature to 250℃ at a rate of 1℃ / min. The temperature was kept for 5 hours to achieve the curing of the coating layer. The coating material was cooled to room temperature with the furnace and ground through a 200-mesh sieve to obtain the composite coated ternary cathode material.

[0045] Example 3 This embodiment provides a composite-coated ternary cathode material, including a ternary cathode material matrix (chemical formula LiNi). 0.95 Co 0.03 Mn 0.03O2 (particle size Dv50 = 17 μm), and a coating layer on the surface of the ternary cathode material substrate; the coating layer includes LiAlO2 and LiZrO3; the molar ratio of LiAlO2 to LiZrO3 is 5:1; the thickness of the coating layer is 40 nm; the particle size Dv50 of the composite coated ternary cathode material is 17.1 μm.

[0046] This embodiment also provides a method for preparing the above-mentioned composite-coated ternary cathode material, including the following steps: (1) Take 0.05 mol Al(NO3)3•9H2O and 0.01 mol Zr(NO3)4•5H2O, add 200 mL of solvent obtained by mixing deionized water and anhydrous ethanol (wherein the volume ratio of deionized water and anhydrous ethanol is 1:3), and then stir at 200 rpm for 40 min to obtain a precursor solution; add 0.09 mol citric acid to the precursor solution, and stir at 200 rpm for 40 min under 70℃ water bath conditions to achieve full complexation of metal ions; then add 0.066 mol CH3COOLi according to the ratio of the total number of aluminum and zirconium elements in the aluminum source and zirconium source to the number of lithium elements in the lithium source of 1:1.1, maintain a 70℃ water bath and a stirring rate of 200 rpm, and continue stirring for 2 h to obtain a transparent and uniform LiAlO2-LiZrO3 composite coated sol; (2) Take 100g LiNi 0.95 Co 0.03 Mn 0.03 O2 matrix and 20g of the above composite coating sol were placed in a planetary ball mill and dispersed at 400rpm for 30min to allow the sol to be uniformly adsorbed on the matrix surface, resulting in a viscous coating slurry. Subsequently, the slurry was sonicated at 70kHz for 40min to further eliminate slurry agglomeration and ensure coating uniformity. (3) The coating slurry was transferred to a vacuum drying oven, the temperature was set to 100℃ and the vacuum degree to -0.095MPa, and dried for 6 hours to obtain the dried coating material. The composite coating layer was initially attached to the substrate surface. The dried coating material was placed in an alumina crucible and placed in a muffle furnace. An air atmosphere was introduced (the gas flow rate was 100mL / min), and the temperature was raised from room temperature to 350℃ at a rate of 2℃ / min. The temperature was kept for 3 hours to achieve the curing of the coating layer. The coating material was cooled to room temperature with the furnace and ground through a 200-mesh sieve to obtain the composite coated ternary cathode material.

[0047] Comparative Example 1 This comparative example provides an alumina-coated ternary cathode material, the preparation method of which is basically the same as that of Example 1, except that the composite coating sol is replaced with an equal mass of alumina slurry. The alumina slurry is prepared by mixing alumina powder and anhydrous ethanol at a mass ratio of 1:20 and ball milling and dispersing at 300 rpm for 1 hour.

[0048] Comparative Example 2 This comparative example provides a LiZrO3-coated ternary cathode material, the preparation method of which is basically the same as that of Example 1, the only difference being that steps (1) and (2) are different. In step (1) of this comparative example, Al(NO3)3•9H2O is omitted, and the amount of Zr(NO3)4•5H2O is adjusted to 0.05mol. Then, 0.0575mol of CH3COOLi is added according to the ratio of the number of moles of zirconium element in the zirconium source to the number of moles of lithium element in the lithium source of 1:1.05. The remaining process conditions are the same as those of Example 1, and LiZrO3 sol is obtained. In step (2), the composite coating gel is replaced with an equal mass of LiZrO3 sol, and the remaining process conditions are the same as those of Example 1.

[0049] Comparative Example 3 This comparative example provides a LiAlO2-coated ternary cathode material, the preparation method of which is basically the same as that of Example 1, the only difference being that steps (1) and (2) are different. In step (1) of this comparative example, Zr(NO3)4•5H2O is omitted, and the amount of Al(NO3)3•9H2O is adjusted to 0.05mol. Then, 0.0575mol of CH3COOLi is added according to the ratio of the number of moles of aluminum in the aluminum source to the number of moles of lithium in the lithium source of 1:1.05. The remaining process conditions are the same as those of Example 1, and LiAlO2 sol is obtained. In step (2), the composite coating gel is replaced with an equal mass of LiAlO2 sol, and the remaining process conditions are the same as those of Example 1.

[0050] Comparative Example 4 This comparative example provides a ternary cathode material, namely the ternary cathode material matrix used in Example 1 (chemical formula LiNi). 0.92 Co 0.04 Mn 0.04 O2, particle size Dv50=15μm).

[0051] Experimental Example 1 1. The positive electrode materials obtained in each embodiment and comparative example are assembled into coin cells. The preparation method of the coin cells is as follows: (1) Preparation of positive electrode sheet: The positive electrode material, conductive agent (including conductive carbon black and carbon nanotubes with a mass ratio of 3.5:1) and binder polyvinylidene fluoride obtained in each example and comparative example are mixed in a mass ratio of 94:3:3. N-methylpyrrolidone is added and mixed into a uniform slurry. The slurry is coated on aluminum foil, vacuum dried at 120°C for 12 hours, and then rolled to obtain the positive electrode sheet.

[0052] (2) Assembly of button cell: In an argon-protected glove box, using a positive electrode sheet (punched into a 12mm diameter disc) as the positive electrode, a lithium metal sheet as the negative electrode, Celgard 2400 as the separator, and 1mol / L LiPF6 as the electrolyte (the solvent is ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1), the negative electrode shell, negative electrode sheet, electrolyte, separator, positive electrode sheet, electrolyte, positive electrode shell, and electrolyte are placed in sequence, and the positive electrode shell is covered. The sealing machine is used to press and seal the battery to assemble a CR2032 type button cell.

[0053] 2. Perform performance tests on the button cells prepared above. (1) Charge and discharge test: At 25℃, charge to 4.3V at a rate of 0.2C and then discharge to 3.0V at a rate of 0.2C. Record the first charge specific capacity and the first discharge specific capacity, and calculate the first coulombic efficiency according to (first discharge capacity / first charge capacity) × 100%.

[0054] (2) Cyclic performance test: At 25℃, the button cell is first activated at 0.2C for two cycles (i.e., charge and discharge for two cycles), and then charged and discharged at 1C rate for 500 cycles, with a voltage range of 3.0V-4.3V; the capacity retention rate after 500 cycles at 1C = (discharge specific capacity at 500 cycles at 1C / discharge specific capacity at 1C in the first cycle at 1C) × 100%.

[0055] (3) Rate performance test: At 25℃, the button cell was charged and discharged 5 times at 0.2C and 5C respectively, with a voltage range of 3.0-4.3V. The discharge specific capacity was recorded. The 5C rate was calculated based on the 5C discharge specific capacity / 0.2C discharge specific capacity.

[0056] (4) Thermal runaway temperature test: Charged at a rate of 0.2C to 4.3V, and after reaching the cutoff voltage, charged at a constant voltage until the current drops to 0.01C to obtain the delithiated cathode material. The battery was disassembled in an argon glove box, the cathode sheet was removed, washed three times with dimethyl carbonate (DMC), vacuum dried, and the cathode material powder was scraped off. 5mg of sample was weighed and sealed in an aluminum crucible, and tested using a differential scanning calorimeter (DSC, TA Q2000). Under an argon atmosphere, the temperature was heated from room temperature to 400℃ at a heating rate of 5℃ / min, and the extrapolated temperature of the exothermic peak was recorded as the thermal runaway initiation temperature.

[0057] 3. Test Results Table 1 Performance Test Results

[0058] As shown in Table 1, the initial coulombic efficiency of the composite-coated ternary cathode materials prepared in Examples 1-3 of this invention is significantly higher than that of Comparative Examples 1-4, indicating that the composite coating layer of LiAlO2 and LiZrO3 effectively suppresses interfacial side reactions during the initial charge-discharge process and reduces irreversible capacity loss. Regarding cycle performance, the capacity retention rate of the composite-coated ternary cathode materials prepared in Examples 1-3 after 500 cycles at 1C is much higher than that of Comparative Examples 1-4, indicating that the composite coating layer combines the dense barrier properties of LiAlO2 with the high ion conductivity of LiZrO3, synergistically suppressing interfacial side reactions and structural degradation during long-term cycling. Regarding rate performance, the 5C / 0.2C capacity retention rate of the composite-coated ternary cathode materials prepared in Examples 1-3 is significantly better than that of Comparative Examples 1-4, indicating that the composite coating layer of LiAlO2 and LiZrO3 effectively improves the lithium-ion conductivity of the material and enhances its high-rate charge-discharge performance. Regarding thermal stability, the thermal runaway initiation temperatures of the composite-coated ternary cathode materials prepared in Examples 1-3 were all higher than those in Comparative Examples 1-4, indicating that the composite coating effectively suppressed oxygen release and structural collapse of the material under high-temperature delithiation conditions, thereby improving battery safety.

[0059] In summary, the composite-coated ternary cathode material provided by this invention achieves a comprehensive improvement in interface stability, cycle performance, rate performance, and thermal safety through the synergistic effect of two lithium-ion conductor coating layers, LiAlO2 and LiZrO3.

[0060] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite-coated ternary cathode material, characterized in that, It includes a ternary cathode material matrix and a coating layer covering the surface of the ternary cathode material matrix; the chemical formula of the ternary cathode material matrix is ​​LiNi. x Co y Mn z O2, wherein x≥0.9, 0.02≤y≤0.06, 0.02≤z≤0.06, x+y+z=1; the coating layer includes LiAlO2 and LiZrO3; the molar ratio of LiAlO2 and LiZrO3 is 3-5:

1.

2. The composite-coated ternary cathode material according to claim 1, characterized in that, The thickness of the coating layer is 10-50 nm; And / or, the particle size D of the ternary cathode material matrix v 50 is 13-17μm; And / or, the particle size D of the composite-coated ternary cathode material v 50 represents 12-20 μm.

3. The method for preparing the composite-coated ternary cathode material according to claim 1 or 2, characterized in that, Includes the following steps: Step S1: The aluminum source, zirconium source and solvent are mixed in the first mixture to obtain a precursor solution. A complexing agent is added to the precursor solution to carry out the first reaction to obtain a precursor sol. Step S2: The lithium source and the precursor sol undergo a second reaction to obtain a composite coated sol; Step S3: The ternary cathode material matrix and the composite coating sol are mixed for the second time, and then dried and heat-treated to obtain the composite coated ternary cathode material.

4. The method for preparing the composite-coated ternary cathode material according to claim 3, characterized in that, The molar ratio of aluminum in the aluminum source to zirconium in the zirconium source is 3-5:1; And / or, the ratio of the total number of moles of aluminum and zirconium in the aluminum source and zirconium source to the number of moles of lithium in the lithium source is 1:1.05-1.1; And / or, the ratio of the total molar number of aluminum and zirconium elements in the aluminum source and zirconium source to the molar number of complexing agent is 1:1-1.5; And / or, the total metal ion concentration in the precursor solution is 0.2-0.3 mol / L; And / or, the mass ratio of the ternary cathode material matrix to the composite coated sol is 1:0.05-0.

2.

5. The method for preparing the composite-coated ternary cathode material according to claim 3, characterized in that, The aluminum source includes at least one of aluminum nitrate, aluminum nitrate hydrate, and aluminum chloride; preferably aluminum nitrate nonahydrate. And / or, the zirconium source includes at least one of zirconium nitrate, zirconium nitrate hydrate, and zirconium chloride; preferably zirconium nitrate pentahydrate; And / or, the solvent includes water and / or alcohol compounds; preferably a mixture of water and ethanol; Optionally, the volume ratio of water to ethanol is 1:2-3; And / or, the complexing agent includes citric acid and / or tartaric acid; And / or, the lithium source includes lithium acetate and / or lithium nitrate; preferably lithium acetate.

6. The method for preparing the composite-coated ternary cathode material according to claim 4, characterized in that, The first mixing speed is 200-400 rpm, and the time is 20-40 min; And / or, the temperature of the first reaction is 60-70℃, the time is 30-40 min, and the rotation speed is 200-400 rpm.

7. The method for preparing the composite-coated ternary cathode material according to claim 4, characterized in that, The second reaction is carried out at a temperature of 60-70℃ for 1-2 hours and at a rotation speed of 200-400 rpm. And / or, the second mixing speed is 300-500 rpm, and the time is 20-30 min; And / or, the second mixing process further includes a step of sonication at a frequency of 70-90 kHz for 20-40 minutes; And / or, the drying temperature is 80-100℃, the time is 6-8h, and the vacuum degree is -0.095~-0.085MPa; And / or, the heat treatment is performed by raising the temperature from room temperature to 250-350°C at a rate of 1-2°C / min in air atmosphere and holding it at that temperature for 3-5 hours; Optionally, the gas flow rate of the air atmosphere is 50-100 mL / min.

8. A positive electrode sheet, characterized in that, include: Positive current collector, and A positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises the composite-coated ternary positive electrode material as described in claim 1 or 2 or the composite-coated ternary positive electrode material prepared by the preparation method described in any one of claims 3-7.

9. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 8.

10. An electrical device, characterized in that, Includes the secondary battery as described in claim 9.

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