Surface-modified lithium-rich manganese-based positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, and discloses a surface-modified lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium ion battery. The surface-modified lithium-rich manganese-based positive electrode material provided by the invention comprises a lithium-rich manganese-based hard core layer, a LiaXOb transition layer and a PEO-LiTFSI gel outer layer which are arranged in sequence, x in the chemical general formula of the LiaXOb transition layer comprises at least one of Nb, Si, Ti, Ta and Zr, a is greater than or equal to 1 and less than or equal to 4, and b is greater than or equal to 1 and less than or equal to 12. The LiaXOb transition layer is used as an inorganic ion conductor transition layer and has certain elasticity and high lithium ion conductivity. And the PEO-LiTFSI gel outer layer is used as an organic ion elastic gel protective layer and is flexible solid electrolyte gel. The LiNbO3 coating layer and the PEO-LiTFSI coating layer are adopted at the same time, so that the synergistic interaction effect is achieved, the cycle performance is remarkably improved, and meanwhile the volume expansion rate after circulation is reduced.

Description

Surface-modified lithium-rich manganese-based cathode materials, their preparation methods, and lithium-ion batteries Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials, specifically to a surface-modified lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-rich manganese-based layered oxides (LRMOs) are widely considered core cathode materials for next-generation high-energy-density power batteries due to their high specific capacity (>250 mAh / g) and low cost. However, their industrialization still faces the following bottlenecks: Structural instability: During charging, especially when the voltage is higher than 4.5V, the large-scale extraction of lithium ions triggers interlayer slippage of the transition metal, leading to significant irreversible volume expansion of the material along the c-axis. In repeated charge-discharge cycles, this repeated expansion and contraction of the lattice accumulates lattice stress, ultimately causing the generation and propagation of microcracks between grains.

[0003] Interfacial side reactions: The generation of microcracks provides new channels for electrolyte penetration, which will continuously erode the fresh surface of the material, exacerbate side reactions such as transition metal dissolution and oxygen release, and lead to a sharp increase in the electrode-electrolyte interface impedance.

[0004] In existing technologies, a common modification method to suppress interfacial side reactions is to coat the material surface with a rigid oxide coating (such as Al2O3, ZrO2, etc.). However, such rigid coatings cannot adapt to the volume changes of the lithium-rich material core. Instead, they become stress concentration points during cycling, exacerbating the cracking of the coating itself and the delamination of the interface with the core material, and failing to fundamentally solve the structural damage problem.

[0005] In summary, the existing lithium-rich manganese-based materials have the following defects: (1) the layered structure expands in volume during charging and discharging, leading to the accumulation of grain boundary stress and the generation of microcracks; (2) the traditional inorganic oxide coating layer has high rigidity, which makes it unable to buffer deformation and causes interface peeling; (3) HF corrosion in the electrolyte leads to increased impedance and reduced cycle life. Summary of the Invention

[0006] This invention provides a surface-modified lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery, to improve cycle performance and reduce post-cycle volume expansion rate.

[0007] In a first aspect, the present invention provides a surface-modified lithium-rich manganese-based cathode material, comprising a lithium-rich manganese-based hard core layer and a Li-based cathode layer sequentially disposed thereon. a XO bTransition layer and outer layer of PEO-LiTFSI gel; the Li a XO b In the general chemical formula of the transition layer, X includes at least one of Nb, Si, Ti, Ta, and Zr, and 1≤a≤4, 1≤b≤12; in the outer layer of the PEO-LiTFSI gel, PEO represents polyethylene oxide and LiTFSI represents lithium bis(trifluoromethanesulfonyl)imide.

[0008] In one optional embodiment, the general chemical formula of the lithium-rich manganese-based hard core layer is xLi₂MnO₃·(1-x)LiMO₂, wherein M includes at least one of Mn, Co, and Ni, and 0≤x≤1; preferably, the general chemical formula of the lithium-rich manganese-based hard core layer includes Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2; Optionally, the particle size D50 of the lithium-rich manganese-based hard core layer is 4-10 μm.

[0009] In one alternative implementation, the Li a XO b The thickness of the transition layer is 1-20 nm; and / or, the thickness of the outer layer of the PEO-LiTFSI gel is 1-10 nm; and / or, the Li a XO b The general chemical formula of the transition layer includes at least one of LiNbO3 and Li2ZrO3.

[0010] Secondly, the present invention provides a method for preparing the surface-modified lithium-rich manganese-based cathode material, comprising the following steps: S1. Weighing lithium salt, nickel salt, cobalt salt, and manganese salt according to stoichiometric ratio and dissolving them in a first solvent to obtain a first mixed solution; adding a complexing agent to the first mixed solution to obtain a second mixed solution; stirring the second mixed solution in a water bath, followed by drying and pre-calcination to obtain a precursor powder; S2. Calcining the precursor powder in S2 and cooling it to obtain the lithium-rich manganese-based cathode material; S3. Dispersing the lithium-rich manganese-based cathode material in S3 on Li a XO b In the solution, the solvent was evaporated after stirring, followed by heat treatment to obtain Li. a XO b Coated cathode material powder; S4. Dissolve polyethylene oxide and lithium bis(trifluoromethanesulfonyl)imide in a second solvent, stir to obtain a gel, and then mix the gel with the Li in S3. a XO b The coated cathode material powder is mixed, coated into a film, and then dried to obtain the surface-modified lithium-rich manganese-based cathode material.

[0011] In an optional embodiment, S1 satisfies at least one of the following conditions: (1) the lithium salt is selected from one or more of lithium hydroxide, lithium acetate, lithium nitrate and lithium chloride; (2) the nickel salt is selected from one or more of nickel sulfate, nickel nitrate, nickel chloride and nickel acetate; (3) the cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride and cobalt acetate; (4) the manganese salt is selected from one or more of manganese nitrate, manganese acetate, manganese sulfate and manganese chloride.

[0012] In an optional embodiment, S1 satisfies at least one of the following conditions: (1) The components of the first solvent in S1 include deionized water and ethanol; the volume ratio of deionized water to ethanol is (6-8):(2-4); (2) The molar concentration of total metal ions in the first mixed solution in S1 is 0.5-1.5 mol / L; (3) The complexing agent in S1 includes one or more of citric acid, glycolic acid, triethanolamine, acrylic acid, fatty acids and oxalic acid; (4) The molar ratio of total metal ions to complexing agent in the second mixed solution in S1 is (0.5-1.5):(1-2); (5) The temperature of water bath stirring in S1 is 70-90℃, and the stirring time is 2-4h; (6) The drying temperature in S1 is 110-130℃; (7) The pre-calcination temperature in S1 is 400-600℃, the pre-calcination heating rate is 4-6℃ / min, and the pre-calcination time is 2-5h.

[0013] In one optional embodiment, the calcination temperature in S2 is 700-800℃, and the holding time for calcination is 9-11h; optionally, the calcination atmosphere is an oxygen atmosphere, and the oxygen flow rate of the oxygen atmosphere is 40-60mL / min.

[0014] In one optional embodiment, the mass of the lithium-rich manganese-based cathode material in S3 is related to the mass of Li. a XO b The volume ratio of the solution is (9-11) g : (90-110) mL; optionally, the Li a XO b The mass concentration of the solution is 0.1%-1%; and / or, the stirring time in S3 is 1-3 hours; and / or, the heat treatment temperature in S3 is 400-500℃, and the heat treatment time is 3-5 hours.

[0015] In an optional embodiment, the molar ratio of ethylene oxide structural units in polyethylene oxide to lithium bis(trifluoromethanesulfonyl)imide in S4 is (14-16):(0.5-1.5); and / or, the second solvent in S4 includes one or more of acetonitrile, N,N-dimethylformamide, and acetone; and / or, the volume of the gel in S4 is relative to the Li a XOb The mass ratio of the coated cathode material powder is (0.4-0.6) mL: (0.4-0.6) g; and / or, the drying process in S4 is vacuum drying, the drying temperature is 50-70℃, and the drying time is 11-13 h.

[0016] Thirdly, the present invention provides a lithium-ion battery using the aforementioned cathode material or a surface-modified lithium-rich manganese-based cathode material prepared according to the aforementioned preparation method.

[0017] The technical solution of this invention has the following advantages: 1. The surface-modified lithium-rich manganese-based cathode material provided by this invention includes a lithium-rich manganese-based hard core layer and a Li-based cathode layer sequentially disposed thereon. a XO b Transition layer and outer layer of PEO-LiTFSI gel; the Li a XO b In the general chemical formula of the transition layer, X includes at least one of Nb, Si, Ti, Ta, and Zr, and 1≤a≤4, 1≤b≤12.

[0018] Lithium-rich manganese-based hard core layer: As an active material, it provides high capacity, but it will undergo significant volume expansion during charging and discharging, which is a source of stress.

[0019] Li a XO b The transition layer, as an inorganic ion conductor transition layer, possesses a certain degree of elasticity and high lithium-ion conductivity. When the core expands, this layer can undergo a certain degree of elastic deformation, effectively buffering stress and preventing stress from being directly transmitted to the outer layer, thus avoiding crack propagation, while ensuring the smooth passage of lithium ions.

[0020] The outer layer of the PEO-LiTFSI gel, serving as a protective layer for organic ionic elastic gels, is a flexible solid electrolyte gel. The outer layer can freely expand and contract with changes in the volume of the inner structure, achieving macroscopic stress self-adaptation. Simultaneously, its dense coverage of the surface effectively prevents the electrolyte from corroding the internal materials and suppresses side reactions. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] The raw materials used in the embodiments and comparative examples provided in this invention are sourced from: lithium acetate, 99.9%, Sinopharm Chemical Reagent Co., Ltd. (Shanghai); nickel acetate, 99.9%, Sinopharm Chemical Reagent Co., Ltd. (Shanghai); cobalt acetate, 99.9%, Sinopharm Chemical Reagent Co., Ltd. (Shanghai); manganese acetate, 99.9%, Sinopharm Chemical Reagent Co., Ltd. (Shanghai); LiNbO3, 99.9%, Sigma-Aldrich; PEO, 99.9%, Sigma-Aldrich; LiTFSI, 99.9%, Sigma-Aldrich; and Li2ZrO3, 99.9%, Sigma-Aldrich.

[0024] Example 1 This example provides a method for preparing a surface-modified lithium-rich manganese-based cathode material, comprising the following steps: S1. Weigh lithium acetate, nickel acetate, cobalt acetate, and manganese acetate in a molar ratio of 1.2:0.13:0.13:0.54 and dissolve them in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol is 7:3) to obtain a first mixed solution (total metal ion concentration in the first mixed solution is 1.0 mol / L). Add citric acid as a complexing agent to obtain a second mixed solution (molar ratio of metal ions to citric acid in the second mixed solution is 1:1.5). Stir the second mixed solution in a water bath at 80°C for 3 hours, then dry it at 120°C, and finally heat it to 500°C at a heating rate of 5°C / min and pre-calcine it in air for 5 hours. After cooling, grind it to obtain a grayish-white precursor powder.

[0025] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 50 mL / min), heated to 780℃, held at that temperature for 10 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0026] S3. Disperse 10g of the lithium-rich manganese-based cathode material obtained in S2 above in 100mL of LiNbO3 solution (containing 0.5g LiNbO3), stir for 2h, evaporate the solvent, and then heat treat at 450℃ for 4h in an argon atmosphere to form a cathode material powder coated with LiNbO3 with a thickness of 5nm.

[0027] S4. Weigh 1g PEO and 0.434g LiTFSI (molar ratio of ethylene oxide structural units in PEO to LiTFSI = 15:1), dissolve in 20mL acetonitrile, and stir until completely dissolved to form a transparent gel. Take 0.5g of the LiNbO3-coated cathode material powder obtained in S3 above and mix it evenly with 1mL of the gel. After coating into a film, dry in a vacuum oven at 60℃ for 12h to obtain the surface-modified lithium-rich manganese-based cathode material, wherein the thickness of the outer layer of the PEO-LiTFSI gel is 5nm.

[0028] Example 2 This example provides a method for preparing a surface-modified lithium-rich manganese-based cathode material, comprising the following steps: S1. Weigh lithium acetate, nickel acetate, cobalt acetate, and manganese acetate in a molar ratio of 1.2:0.13:0.13:0.54 and dissolve them in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol is 7:3) to obtain a first mixed solution (total metal ion concentration in the first mixed solution is 1.0 mol / L). Add citric acid as a complexing agent to obtain a second mixed solution (molar ratio of metal ions to citric acid in the second mixed solution is 1:1.5). Stir the second mixed solution in a water bath at 70°C for 4 hours, then dry it at 130°C, and finally heat it to 500°C at a heating rate of 5°C / min and pre-calcine it in air for 4 hours. After cooling, grind it to obtain a grayish-white precursor powder.

[0029] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 50 mL / min), heated to 780℃, held at that temperature for 10 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0030] S3. Disperse 10g of the lithium-rich manganese-based cathode material obtained in S2 above in 100mL of LiNbO3 solution (containing 0.1g LiNbO3), stir for 2h, evaporate the solvent, and then heat treat at 450℃ for 4h in an argon atmosphere to form a LiNbO3-coated cathode material powder with a thickness of 1nm.

[0031] S4. Weigh 1g PEO and 0.434g LiTFSI (molar ratio of ethylene oxide structural units in PEO to LiTFSI = 15:1), dissolve in 20mL acetonitrile, and stir until completely dissolved to form a transparent gel. Take 0.5g of the LiNbO3-coated cathode material powder obtained in S3 above and mix it evenly with 1mL of the gel. After coating into a film, dry in a vacuum oven at 60℃ for 12h to obtain the surface-modified lithium-rich manganese-based cathode material, wherein the thickness of the outer layer of the PEO-LiTFSI gel is 5nm.

[0032] Example 3 This example provides a method for preparing a surface-modified lithium-rich manganese-based cathode material, comprising the following steps: S1. Weigh lithium acetate, nickel acetate, cobalt acetate, and manganese acetate in a molar ratio of 1.2:0.13:0.13:0.54 and dissolve them in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol is 7:3) to obtain a first mixed solution (total metal ion concentration in the first mixed solution is 1.0 mol / L). Add citric acid as a complexing agent to obtain a second mixed solution (molar ratio of metal ions to citric acid in the second mixed solution is 1:1.5). Stir the second mixed solution in a water bath at 80°C for 3 hours, then dry it at 120°C, and finally heat it to 500°C at a heating rate of 5°C / min and pre-calcine it in air for 5 hours. After cooling, grind it to obtain a grayish-white precursor powder.

[0033] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 50 mL / min), heated to 780℃, held at that temperature for 10 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0034] S3. Disperse 10g of the lithium-rich manganese-based cathode material obtained in S2 above in 100mL of LiNbO3 solution (containing 1g LiNbO3), stir for 2h and evaporate the solvent, then heat treat at 450℃ for 4h in an argon atmosphere to form a cathode material powder coated with LiNbO3 with a thickness of 10nm.

[0035] S4. Weigh 1g PEO and 0.434g LiTFSI (molar ratio of ethylene oxide structural units in PEO to LiTFSI = 15:1), dissolve in 20mL acetonitrile, and stir until completely dissolved to form a transparent gel. Take 0.5g of the LiNbO3-coated cathode material powder obtained in S3 above and mix it evenly with 1mL of the gel. After coating into a film, dry in a vacuum oven at 60℃ for 12h to obtain the surface-modified lithium-rich manganese-based cathode material, wherein the thickness of the outer layer of the PEO-LiTFSI gel is 5nm.

[0036] Example 4 This example provides a method for preparing a surface-modified lithium-rich manganese-based cathode material, comprising the following steps: S1. Weigh lithium acetate, nickel acetate, cobalt acetate, and manganese acetate in a molar ratio of 1.2:0.13:0.13:0.54 and dissolve them in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol is 7:3) to obtain a first mixed solution (total metal ion concentration in the first mixed solution is 1.5 mol / L). Add citric acid as a complexing agent to obtain a second mixed solution (molar ratio of metal ions to citric acid in the second mixed solution is 1:1.5). Stir the second mixed solution in a water bath at 75°C for 3 hours, then dry it at 120°C, and finally heat it to 500°C at a heating rate of 5°C / min and pre-calcine it in air for 5 hours. After cooling, grind it to obtain a grayish-white precursor powder.

[0037] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 60 mL / min), heated to 800℃, held at that temperature for 9 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0038] S3. Disperse 10g of the lithium-rich manganese-based cathode material obtained in S2 above in 100mL of LiNbO3 solution (containing 0.5g LiNbO3), stir for 2h, evaporate the solvent, and then heat treat at 450℃ for 4h in an argon atmosphere to form a cathode material powder coated with LiNbO3 with a thickness of 5nm.

[0039] S4. Weigh 1g PEO and 0.434g LiTFSI (molar ratio of ethylene oxide structural units in PEO to LiTFSI = 15:1), dissolve in 20mL acetonitrile, and stir until completely dissolved to form a transparent gel. Take 0.5g of the LiNbO3-coated cathode material powder obtained in S3 above and mix it evenly with 0.5mL of the gel. After coating into a film, dry in a vacuum oven at 60℃ for 12h to obtain the surface-modified lithium-rich manganese-based cathode material, wherein the thickness of the outer layer of the PEO-LiTFSI gel is 1nm.

[0040] Example 5 This example provides a method for preparing a surface-modified lithium-rich manganese-based cathode material, comprising the following steps: S1. Weigh lithium acetate, nickel acetate, cobalt acetate, and manganese acetate in a molar ratio of 1.2:0.13:0.13:0.54 and dissolve them in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol is 7:3) to obtain a first mixed solution (the total metal ion concentration in the first mixed solution is 0.5 mol / L). Add citric acid as a complexing agent to obtain a second mixed solution (the molar ratio of metal ions to citric acid in the second mixed solution is 1:1.5). Stir the second mixed solution in a water bath at 90°C for 2 hours, then dry it at 110°C, and finally raise the temperature to 600°C at a heating rate of 4°C / min and pre-calcine it in air for 2 hours. After cooling, grind it to obtain a grayish-white precursor powder.

[0041] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 40 mL / min), heated to 800℃, held at that temperature for 9 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0042] S3. Disperse 10g of the lithium-rich manganese-based cathode material obtained in S2 above in 100mL of LiNbO3 solution (containing 0.5g LiNbO3), stir for 3h, evaporate the solvent, and then heat treat at 400℃ for 5h in an argon atmosphere to form a cathode material powder coated with LiNbO3 with a thickness of 5nm.

[0043] S4. Weigh 1g PEO and 0.434g LiTFSI (molar ratio of ethylene oxide structural units in PEO to LiTFSI = 15:1), dissolve in 20mL acetonitrile, and stir until completely dissolved to form a transparent gel. Take 0.5g of the LiNbO3-coated cathode material powder obtained in S3 above and mix it evenly with 2mL of the gel. After coating into a film, dry in a vacuum oven at 60℃ for 12h to obtain the surface-modified lithium-rich manganese-based cathode material, wherein the thickness of the outer layer of the PEO-LiTFSI gel is 10nm.

[0044] Example 6S1. Lithium acetate, nickel acetate, cobalt acetate, and manganese acetate were weighed and dissolved in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol was 7:3) at a molar ratio of 1.2:0.13:0.13:0.54 to obtain a first mixed solution (total metal ion concentration in the first mixed solution was 1.0 mol / L). Citric acid was added as a complexing agent to obtain a second mixed solution (molar ratio of metal ions to citric acid in the second mixed solution was 1:1.5). The second mixed solution was stirred in a water bath at 80°C for 3 hours, then dried at 120°C, and finally heated to 500°C at a heating rate of 5°C / min and pre-calcined in air for 5 hours. After cooling, it was ground to obtain a grayish-white precursor powder.

[0045] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 50 mL / min), heated to 780℃, held at that temperature for 10 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0046] S3. Disperse 10g of the lithium-rich manganese-based cathode material obtained in S2 above in 100mL of Li2ZrO3 solution (containing 0.5g Li2ZrO3), stir for 2h, evaporate the solvent, and then heat treat at 450℃ for 4h in an argon atmosphere to form a Li2ZrO3-coated cathode material powder with a thickness of 5nm.

[0047] S4. Weigh 1g PEO and 0.434g LiTFSI (molar ratio of ethylene oxide structural units in PEO to LiTFSI = 15:1), dissolve in 20mL acetonitrile, and stir until completely dissolved to form a transparent gel. Take 0.5g of the LiNbO3-coated cathode material powder obtained in S3 above and mix it evenly with 1mL of the gel. After coating into a film, dry in a vacuum oven at 60℃ for 12h to obtain the surface-modified lithium-rich manganese-based cathode material, wherein the thickness of the outer layer of the PEO-LiTFSI gel is 5nm.

[0048] Comparative Example 1: This comparative example provides a method for preparing a lithium-rich manganese-based cathode material, comprising the following steps: S1. Lithium acetate, nickel acetate, cobalt acetate, and manganese acetate are weighed in a molar ratio of 1.2:0.13:0.13:0.54 and dissolved in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol is 7:3) to obtain a first mixed solution (the total metal ion concentration in the first mixed solution is 1.0 mol / L). Citric acid is added as a complexing agent to obtain a second mixed solution (the molar ratio of metal ions to citric acid in the second mixed solution is 1:1.5). The second mixed solution is stirred in a water bath at 80°C for 3 hours, then dried at 120°C, and finally heated to 500°C at a heating rate of 5°C / min, pre-calcined in air for 5 hours, cooled, and ground to obtain a grayish-white precursor powder.

[0049] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 50 mL / min), heated to 780℃, held at that temperature for 10 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0050] Comparative Example 2: This comparative example provides a method for preparing a surface-modified lithium-rich manganese-based cathode material, comprising the following steps: S1. Lithium acetate, nickel acetate, cobalt acetate, and manganese acetate are weighed in a molar ratio of 1.2:0.13:0.13:0.54 and dissolved in a mixed solvent of deionized water and ethanol (volume ratio of deionized water to ethanol is 7:3) to obtain a first mixed solution (the total metal ion concentration in the first mixed solution is 1.0 mol / L). Citric acid is added as a complexing agent to obtain a second mixed solution (the molar ratio of metal ions to citric acid in the second mixed solution is 1:1.5). The second mixed solution is stirred in a water bath at 80°C for 3 hours, then dried at 120°C, and finally heated to 500°C at a heating rate of 5°C / min, pre-calcined in air for 5 hours, cooled, and ground to obtain a grayish-white precursor powder.

[0051] S2. The precursor powder obtained in S1 is placed in an oxygen atmosphere (oxygen flow rate 50 mL / min), heated to 780℃, held at that temperature for 10 h, and then cooled to obtain lithium-rich manganese-based cathode material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, with a particle size D50 of 8 μm.

[0052] S3. Disperse 10g of the lithium-rich manganese-based cathode material obtained in S2 above in 100mL of LiNbO3 solution (containing 0.5g LiNbO3), stir for 2h, evaporate the solvent, and then heat treat at 450℃ for 4h in an argon atmosphere to form a lithium-rich manganese-based cathode material powder coated with LiNbO3 with a thickness of 5nm.

[0053] Test Example 1: The materials prepared in Examples 1-5 or Comparative Examples 1-2 were used as positive electrode active materials and homogenized with polyvinylidene fluoride (PVDF) and acetylene black in a mass ratio of 80:10:10. The coating surface density was controlled at 4 g / cm³. 2 According to the electrode compaction density of 2g / cm³ 3 Electrodes were fabricated, with lithium metal sheets as the counter electrode, glass fiber as the separator, and a 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC volume ratio of 1:1) as the electrolyte. The cells were assembled into CR2032 coin cells in an argon-filled glove box. Finally, the cells were placed in the Blue Electric Test System for electrical performance testing.

[0054] The electrical performance test conditions are as follows: the charge / discharge voltage range for cyclic testing is 2.0V-4.8V, the test temperature is 25℃, and after the open-circuit voltage stabilizes, the battery's initial charge / discharge performance is tested by cycling at 0.1C / 0.1C for one week; the initial charge capacity is defined as the capacity when the battery is charged at a constant current of 0.1C until the voltage reaches 4.8V, and the initial discharge capacity is defined as the capacity when the battery is discharged at a constant current of 0.1C until the cutoff voltage reaches 2.0V. The initial coulombic efficiency is then calculated. The battery is charged at a constant current of 1C until 4.8V, and then discharged at a constant current of 1C until the cutoff voltage reaches 2.0V. This cycle is repeated 50 times, and the cycle capacity retention rate of the battery after 50 cycles is calculated. The cycle capacity retention rate (%) = discharge capacity of the 50th cycle / discharge capacity of the 1st cycle × 100%.

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

[0056] As shown in Table 1, Examples 1-6 and Comparative Examples 1-2 exhibit larger initial discharge capacity, higher initial coulombic efficiency, higher cycle capacity retention, and smaller post-cycle volume expansion rate compared to Comparative Examples 1-2. This indicates that the coated cathode material possesses excellent kinetic performance, resulting in high capacity retention and good cycle performance when applied to lithium-ion batteries. Furthermore, the embodiments of this invention employ both LiNbO3 and PEO-LiTFSI coating layers. Compared to Comparative Example 1, which did not surface-coat the lithium-rich manganese-based cathode material, and Comparative Example 2, which only used one type of LiNbO3 coating layer, this method demonstrates a synergistic effect, significantly improving cycle performance while reducing post-cycle volume expansion rate.

[0057] 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 surface-modified lithium-rich manganese-based cathode material, characterized in that, Including a lithium-rich manganese-based hard core layer, Li a XO b Transition layer and outer layer of PEO-LiTFSI gel; the Li a XO b In the general chemical formula of the transition layer, X includes at least one of Nb, Si, Ti, Ta, and Zr, and 1≤a≤4, 1≤b≤12.

2. The surface-modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, The general chemical formula of the lithium-rich manganese-based hard core layer is xLi₂MnO₃·(1-x)LiMO₂, where M includes at least one of Mn, Co, and Ni, and 0≤x≤1; preferably, the general chemical formula of the lithium-rich manganese-based hard core layer includes Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2; Optionally, the particle size D50 of the lithium-rich manganese-based hard core layer is 4-10 μm.

3. The surface-modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, The Li a XO b The thickness of the transition layer is 1-20 nm; and / or, the thickness of the outer layer of the PEO-LiTFSI gel is 1-10 nm; and / or, the Li a XO b The general chemical formula of the transition layer includes at least one of LiNbO3 and Li2ZrO3.

4. A method for preparing a surface-modified lithium-rich manganese-based cathode material according to any one of claims 1-3, characterized in that, The process includes the following steps: S1. Weigh lithium salt, nickel salt, cobalt salt, and manganese salt according to stoichiometric ratio and dissolve them in a first solvent to obtain a first mixed solution. Add a complexing agent to the first mixed solution to obtain a second mixed solution. Stir the second mixed solution in a water bath, then dry and pre-calcine it to obtain a precursor powder; S2. Calcinate the precursor powder from S2 and cool it to obtain a lithium-rich manganese-based cathode material; S3. Disperse the lithium-rich manganese-based cathode material from S3 in Li... a XO b In the solution, the solvent was evaporated after stirring, followed by heat treatment to obtain Li. a XO b Coated cathode material powder; S4. Dissolve polyethylene oxide and lithium bis(trifluoromethanesulfonyl)imide in a second solvent, stir to obtain a gel, and then mix the gel with the Li in S3. a XO b The coated cathode material powder is mixed, coated into a film, and then dried to obtain the surface-modified lithium-rich manganese-based cathode material.

5. The method for preparing the surface-modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, The S1 satisfies at least one of the following conditions: (1) the lithium salt is selected from one or more of lithium hydroxide, lithium acetate, lithium nitrate and lithium chloride; (2) the nickel salt is selected from one or more of nickel sulfate, nickel nitrate, nickel chloride and nickel acetate; (3) the cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride and cobalt acetate; (4) the manganese salt is selected from one or more of manganese nitrate, manganese acetate, manganese sulfate and manganese chloride.

6. The method for preparing the surface-modified lithium-rich manganese-based cathode material according to claim 4 or 5, characterized in that, The S1 satisfies at least one of the following conditions: (1) The components of the first solvent in the S1 include deionized water and ethanol; the volume ratio of the deionized water to ethanol is (6-8):(2-4); (2) The molar concentration of the total metal ions in the first mixed solution in the S1 is 0.5-1.5 mol / L; (3) The complexing agent in the S1 includes one or more of citric acid, glycolic acid, triethanolamine, acrylic acid, fatty acids and oxalic acid; (4) The molar ratio of the total metal ions to the complexing agent in the second mixed solution in the S1 is (0.5-1.5):(1-2); (5) The temperature of the water bath stirring in the S1 is 70-90℃, and the stirring time is 2-4h; (6) The drying temperature in the S1 is 110-130℃; (7) The pre-calcination temperature in the S1 is 400-600℃, the pre-calcination heating rate is 4-6℃ / min, and the pre-calcination time is 2-5h.

7. The method for preparing the surface-modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, The calcination temperature in S2 is 700-800℃, and the holding time for calcination is 9-11h; optionally, the calcination atmosphere is an oxygen atmosphere, and the oxygen flow rate of the oxygen atmosphere is 40-60mL / min.

8. The method for preparing the surface-modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, The mass of the lithium-rich manganese-based cathode material in S3 and Li a XO b The volume ratio of the solution is (9-11) g : (90-110) mL; optionally, the Li a XO b The mass concentration of the solution is 0.1%-1%; and / or, the stirring time in S3 is 1-3 hours; and / or, the heat treatment temperature in S3 is 400-500℃, and the heat treatment time is 3-5 hours.

9. The method for preparing the surface-modified lithium-rich manganese-based cathode material according to claim 4, characterized in that, In S4, the molar ratio of ethylene oxide structural units in polyethylene oxide to lithium bis(trifluoromethanesulfonyl)imide is (14-16):(0.5-1.5); and / or, the second solvent in S4 includes one or more of acetonitrile, N,N-dimethylformamide, and acetone; and / or, the volume of the gel in S4 is related to the Li a XO b The mass ratio of the coated cathode material powder is (0.4-0.6) mL: (0.4-0.6) g; and / or, the drying process in S4 is vacuum drying, the drying temperature is 50-70℃, and the drying time is 11-13 h.

10. A lithium-ion battery, characterized in that, Surface-modified lithium-rich manganese-based cathode materials prepared using the cathode material according to any one of claims 1-3 or the preparation method according to any one of claims 4-9.

Images