Secondary modified positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a secondary modified positive electrode material and a preparation method and application thereof. The preparation method of the secondary modified positive electrode material provided by the invention comprises the following steps: 1) putting the positive electrode material into a mixed solution of cyclodextrin and potassium metasilicate, stirring, separating out a solid, and drying to obtain a primary modified positive electrode material; and 2) mixing the primary modified positive electrode material obtained in the step 1) with boric acid, and sintering to obtain the secondary modified positive electrode material. The specific preparation method provided by the invention is simplified in steps, the prepared secondary modified positive electrode material is high in specific discharge capacity, first efficiency and cycle performance, and the safety of the battery can be further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery materials, and in particular relates to a secondary modified positive electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development of China's economy, the demand for energy has also increased, and the new energy industry has developed rapidly. Lithium-ion batteries are widely used in various fields of the new energy industry due to their high energy density, no memory effect and environmental friendliness. x Co y Mn 1-x-y O2 (x ≥ 0.8) belongs to the category of lithium-ion battery positive electrodes. It is considered to be the most promising high-energy specific electrode material because of its high energy density and low metal element cost. High-nickel ternary positive electrode materials have great advantages in capacity and cost, but there are still many problems to be solved in their commercial application.

[0003] The lithium storage activity of high-nickel layered cathode materials is based on the redox reaction of Ni 2+ / Ni 3+ 、Ni 3+ / Ni 4+ and Co 3+ / Co 4 + The occurrence of H2-H3 phase transition in ternary positive electrode materials with Ni content higher than 80% increases with the increase of Ni content, the lattice structure parameters change greatly, the phase transition intensifies, and the anisotropic expansion of the material structure causes its surface structure to break and produce a large number of cracks. During the cyclic charge and discharge process, the reversibility of the lithium storage phase transition will gradually decrease, resulting in poor cycle performance of the high-nickel layered positive electrode material. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor cycle performance of existing high-nickel layered positive electrode materials for lithium ion batteries, thereby providing a secondary modified positive electrode material and a preparation method and application thereof.

[0005] The present invention provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0006] 1) placing the positive electrode material in a mixed solution of cyclodextrin and potassium metasilicate and stirring, separating the solid, and drying to obtain a primary modified positive electrode material;

[0007] 2) Mixing the primary modified positive electrode material obtained in step 1) with boric acid, and sintering the mixture to obtain the secondary modified positive electrode material.

[0008] Preferably, the cyclodextrin and potassium metasilicate mixed solution in step 1) is prepared by mixing cyclodextrin, potassium metasilicate and water and standing for 6-12 hours;

[0009] The total mass concentration of cyclodextrin and potassium metasilicate in the mixed solution of cyclodextrin and potassium metasilicate is 0.01-0.1wt%;

[0010] The mass ratio of cyclodextrin to potassium metasilicate in the cyclodextrin and potassium metasilicate mixed solution is (0.3-1.1):1.

[0011] Preferably, the stirring treatment temperature in step 1) is 15-60°C, the stirring treatment speed is 300-400r / min, and the stirring treatment time is 5-30min;

[0012] The ratio of the total volume of the mixed solution of cyclodextrin and potassium metasilicate to the mass of the positive electrode material in step 1) is (0.5-2):1, in units of mL:g.

[0013] The drying temperature in step 1) is 200-600° C. and the drying time is 6-24 hours.

[0014] The present invention does not impose any specific limitation on the separation of solids. For example, the solid material and water can be separated by suction filtration or pressure filtration.

[0015] Preferably, the mass ratio of the primary modified positive electrode material and boric acid in step 2) is 300:(1-5);

[0016] The sintering temperature in step 2) is 200-600°C and the sintering time is 6-24h;

[0017] The sintering process is performed in an oxygen-containing atmosphere.

[0018] Preferably, the chemical formula of the positive electrode material in step 1) is Li x Ni a Co 1-a-b Mn b O2, and 1.00≤x≤1.08, 0.7≤a≤0.95, 0.01≤b≤0.1.

[0019] Preferably, the preparation method of the positive electrode material comprises the following steps: weighing a precursor and a lithium source according to a stoichiometric ratio, mixing, and calcining to obtain the positive electrode material;

[0020] Optionally, the chemical formula of the precursor is Ni a Co 1-a-b Mn b (OH)2, and 0.7≤a≤0.95, 0.01≤b≤0.1;

[0021] The lithium source is selected from at least one of lithium hydroxide and lithium carbonate;

[0022] The calcination temperature is 700-900°C and the calcination time is 8-24h;

[0023] The calcination is performed in an oxygen-containing atmosphere.

[0024] Optionally, after the calcination step, a crushing step is also included.

[0025] The present invention provides a secondary modified positive electrode material, which is prepared by the above-mentioned method for preparing the secondary modified positive electrode material.

[0026] The present invention provides an application of the above-mentioned secondary modified positive electrode material in a lithium ion battery.

[0027] The technical solution of the present invention has the following advantages:

[0028] The preparation method of the secondary modified positive electrode material provided by the present invention comprises: 1) placing the positive electrode material in a mixed solution of cyclodextrin and potassium metasilicate, stirring and treating, separating the solid, and drying to obtain a primary modified positive electrode material; 2) mixing the primary modified positive electrode material obtained in step 1) with boric acid, and sintering to obtain the secondary modified positive electrode material. Cyclodextrin is a renewable and environmentally friendly biopolymer with a special slightly conical annular structure. It is a polysaccharide composed of glucose units. The precursor containing glucose units can be converted into carbon with a relatively high degree of graphitization at a relatively low temperature carbonization temperature, which will give the carbon high conductivity and chemical stability. In addition, it can strongly bind to alkali metal cations to form an extended structure. The mixed solution of the ligand formed by cyclodextrin and potassium metasilicate is tightly adsorbed on the surface of the ternary precursor. Compared with the single cyclodextrin or potassium metasilicate coating modification, the potassium metasilicate in the cyclodextrin-potassium metasilicate ligand is evenly distributed on the surface of the special structure of cyclodextrin, and then sintered at high temperature to form an organic carbon / potassium metasilicate organic interwoven composite layer, which can achieve uniform coating modification on the surface of the positive electrode material. Among them, cyclodextrin is a good binder because of its own characteristics. It can fix the primary particles, control their morphology and size, delay the evolution of cracks caused by cycling, and improve its cycle performance. The cyclodextrin and potassium metasilicate ligand are sintered to form a tightly adherent organic carbon / potassium metasilicate film, which improves the pore structure of the coating layer, alleviates the internal strain from the anisotropic volume change, increases the lattice stability of the high-nickel material, and further prevents the penetration of the electrolyte, inhibits surface side reactions, and achieves the purpose of improving the discharge specific capacity, first effect and cycle performance of the material and improving the electrochemical performance of the battery. The preparation method of the present invention uses the mixed solution as the washing solution, simplifying the washing step. The specific preparation method of the present invention has simplified steps, and the prepared secondary modified positive electrode material has high discharge specific capacity, first efficiency and cycle performance, which can further improve battery safety. DETAILED DESCRIPTION

[0029] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0030] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be purchased commercially.

[0031] Example 1

[0032] This embodiment provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0033] 1) Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 730°C in an oxygen atmosphere for 10 h and crushed to obtain the positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2; β-cyclodextrin, potassium metasilicate and water were mixed and allowed to stand for 6 hours to prepare a β-cyclodextrin and potassium metasilicate mixed solution; the total mass concentration of β-cyclodextrin and potassium metasilicate in the prepared β-cyclodextrin and potassium metasilicate mixed solution was 0.02wt%; the mass ratio of β-cyclodextrin and potassium metasilicate in the β-cyclodextrin and potassium metasilicate mixed solution was 0.8:1; 500g of the above-mentioned positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of the above-mentioned β-cyclodextrin and potassium metasilicate mixed solution and stirred at a temperature of 30°C, a stirring speed of 400 r / min, and a stirring time of 10 min. The solid material and water were separated by suction filtration; the separated solid material was dried at 120°C for 10 h to obtain a primary modified positive electrode material;

[0034] 2) 300 g of the primary modified positive electrode material obtained in step 1) and 1.72 g of boric acid were mixed, and sintered at 250° C. for 6 h to obtain the secondary modified positive electrode material.

[0035] Example 2

[0036] This embodiment provides a method for secondary modification of positive electrode materials, which is different from Embodiment 1 only in that the total mass concentration of β-cyclodextrin and potassium metasilicate in the mixed solution of β-cyclodextrin and potassium metasilicate in step 1) is 0.04 wt%.

[0037] Example 3

[0038] This embodiment provides a method for secondary modification of positive electrode materials, which is different from Embodiment 1 only in that the total mass concentration of β-cyclodextrin and potassium metasilicate in the mixed solution of β-cyclodextrin and potassium metasilicate in step 1) is 0.06 wt %.

[0039] Example 4

[0040] This embodiment provides a method for secondary modification of positive electrode materials, which is different from Embodiment 1 only in that the total mass concentration of β-cyclodextrin and potassium metasilicate in the mixed solution of β-cyclodextrin and potassium metasilicate in step 1) is 0.08 wt %.

[0041] Example 5

[0042] This embodiment provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0043] 1) Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 700°C in an oxygen atmosphere for 24 hours and crushed to obtain the positive electrode material Li 1.01 Ni 0.88 Co 0.04 Mn 0.08 O2; β-cyclodextrin, potassium metasilicate and water were mixed and allowed to stand for 12 hours to prepare a β-cyclodextrin and potassium metasilicate mixed solution; the total mass concentration of β-cyclodextrin and potassium metasilicate in the prepared β-cyclodextrin and potassium metasilicate mixed solution was 0.02wt%; the mass ratio of β-cyclodextrin and potassium metasilicate in the β-cyclodextrin and potassium metasilicate mixed solution was 0.5:1; 500g of the above-mentioned positive electrode material Li 1.01 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of the above-mentioned mixed solution of β-cyclodextrin and potassium metasilicate and stirred at a temperature of 30°C, a stirring speed of 300 r / min, and a stirring time of 25 min. The solid material and water were separated by suction filtration; the separated solid material was dried at 100°C for 20 h to obtain a primary modified positive electrode material;

[0044] 2) 300 g of the primary modified positive electrode material obtained in step 1) and 1.72 g of boric acid were mixed, and sintered at 250° C. for 6 h to obtain the secondary modified positive electrode material.

[0045] Example 6

[0046] This embodiment provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0047] 1) Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 900°C in an oxygen atmosphere for 8 hours and crushed to obtain the positive electrode material Li 1.08 Ni 0.88 Co 0.04 Mn 0.08O2; β-cyclodextrin, potassium metasilicate and water were mixed and allowed to stand for 6 hours to prepare a β-cyclodextrin and potassium metasilicate mixed solution; the total mass concentration of β-cyclodextrin and potassium metasilicate in the prepared β-cyclodextrin and potassium metasilicate mixed solution was 0.1wt%; the mass ratio of β-cyclodextrin and potassium metasilicate in the β-cyclodextrin and potassium metasilicate mixed solution was 1.1:1; 500g of the above-mentioned positive electrode material Li 1.08 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of the above-mentioned mixed solution of β-cyclodextrin and potassium metasilicate and stirred at a temperature of 20°C, a stirring speed of 400 r / min, and a stirring time of 30 min. The solid material and water were separated by suction filtration; the separated solid material was dried at 140°C for 6 h to obtain a primary modified positive electrode material;

[0048] 2) 300 g of the primary modified positive electrode material obtained in step 1) and 1.72 g of boric acid were mixed, and sintered at 200° C. for 20 h to obtain the secondary modified positive electrode material.

[0049] Comparative Example 1

[0050] This comparative example provides a method for preparing a modified positive electrode material, comprising the following steps:

[0051] Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 730°C in an oxygen atmosphere for 10 h and crushed to obtain the positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2; 500g of the above positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of deionized water and stirred at a temperature of 30°C, a speed of 400 r / min, and a time of 10 min. The solid material and water were separated by filtration. The separated solid material was dried at 120°C for 10 h to obtain a modified positive electrode material.

[0052] Comparative Example 2

[0053] This comparative example provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0054] 1) Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 730°C in an oxygen atmosphere for 10 h and crushed to obtain the positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2; 500g of the above positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of deionized water and stirred at a temperature of 30°C, a speed of 400 r / min, and a time of 10 min. The solid material and water were separated by suction filtration. The separated solid material was dried at 120°C for 10 h to obtain a primary modified positive electrode material.

[0055] 2) 300 g of the primary modified positive electrode material obtained in step 1) and 1.72 g of boric acid were mixed, and sintered at 250° C. for 6 h to obtain the secondary modified positive electrode material.

[0056] Comparative Example 3

[0057] This comparative example provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0058] 1) Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 730°C in an oxygen atmosphere for 10 h and crushed to obtain the positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2; β-cyclodextrin, aluminum hydroxide and water were mixed and allowed to stand for 6 hours to prepare a β-cyclodextrin and aluminum hydroxide mixed solution; the total mass concentration of β-cyclodextrin and aluminum hydroxide in the prepared β-cyclodextrin and aluminum hydroxide mixed solution was 0.02wt%; the mass ratio of β-cyclodextrin and aluminum hydroxide in the β-cyclodextrin and aluminum hydroxide mixed solution was 0.8:1; 500g of the above-mentioned positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of the above-mentioned mixed solution of β-cyclodextrin and aluminum hydroxide and stirred at a temperature of 30°C, a stirring speed of 400 r / min, and a stirring time of 10 min. The solid material and water were separated by suction filtration; the separated solid material was dried at 120°C for 10 h to obtain a primary modified positive electrode material;

[0059] 2) 300 g of the primary modified positive electrode material obtained in step 1) and 1.72 g of boric acid were mixed, and sintered at 250° C. for 6 h to obtain the secondary modified positive electrode material.

[0060] Comparative Example 4

[0061] This comparative example provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0062] 1) Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 730°C in an oxygen atmosphere for 10 h and crushed to obtain the positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2; potassium metasilicate and water were mixed and allowed to stand for 6 hours to prepare a potassium metasilicate solution; the mass concentration of potassium metasilicate in the prepared potassium metasilicate solution was 0.02wt%; 500g of the above-mentioned positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of the above potassium metasilicate solution and stirred at a temperature of 30°C, a speed of 400 r / min, and a time of 10 min. The solid material and water were separated by suction filtration. The separated solid material was dried at 120°C for 10 h to obtain a primary modified positive electrode material.

[0063] 2) 300 g of the primary modified positive electrode material obtained in step 1) and 1.72 g of boric acid were mixed, and sintered at 250° C. for 6 h to obtain the secondary modified positive electrode material.

[0064] Comparative Example 5

[0065] This comparative example provides a method for preparing a secondary modified positive electrode material, comprising the following steps:

[0066] 1) Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 730°C in an oxygen atmosphere for 10 h and crushed to obtain the positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08O2; β-cyclodextrin and water were mixed and allowed to stand for 6 hours to prepare a β-cyclodextrin solution; the total mass concentration of β-cyclodextrin in the prepared β-cyclodextrin solution was 0.02wt%; 500g of the above-mentioned positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2 was placed in 500 mL of the above β-cyclodextrin solution and stirred at a temperature of 30°C, a speed of 400 r / min, and a time of 10 min. The solid material and water were separated by suction filtration. The separated solid material was dried at 120°C for 10 h to obtain a primary modified positive electrode material.

[0067] 2) 300 g of the primary modified positive electrode material obtained in step 1) and 1.72 g of boric acid were mixed, and sintered at 250° C. for 6 h to obtain the secondary modified positive electrode material.

[0068] Comparative Example 6

[0069] This comparative example provides a method for preparing a positive electrode material, comprising the following steps:

[0070] Weigh an appropriate amount of Ni according to the stoichiometric ratio 0.88 Co 0.04 Mn 0.08 (OH)2 and lithium hydroxide were mixed in a high-speed mixer, and then calcined at 730°C in an oxygen atmosphere for 10 h and crushed to obtain the positive electrode material Li 1.03 Ni 0.88 Co 0.04 Mn 0.08 O2.

[0071] Test Case

[0072] The secondary modified positive electrode materials of Examples 1-6, the modified positive electrode materials of Comparative Example 1, the secondary modified positive electrode materials in Comparative Examples 2-5 and the positive electrode materials of Comparative Example 6 were respectively used as main materials, and the mass ratio of main material: polyvinylidene fluoride (PVDF): conductive carbon black (SP): N-methylpyrrolidone as a dispersant was 97.2:1.3:1.5:100 for homogenization, and then coated on aluminum foil, and finally placed in an 80°C forced air drying oven for drying for 2 hours, and the positive electrode sheet coating surface density was 17 mg / cm 2 Using metallic lithium as the negative electrode, glass fiber as the separator, and 1 mol / L LiPF6 ethylene carbonate (EC) / dimethyl carbonate (DMC) solution as the electrolyte (the volume ratio of EC and DMC is 1:1), in an argon atmosphere of a glove box, the positive electrode, negative electrode, separator, electrolyte, gasket and spring are placed in a button cell to assemble a CR2032 button cell.

[0073] The battery is placed in the blue power test system for electrical performance testing. The electrical performance test parameters are set as follows: voltage range 2.5V-4.25V, first charge and discharge at 0.2C / 0.2C rate, test the first charge specific capacity and first discharge specific capacity, and calculate the first efficiency, first efficiency = and first discharge specific capacity / first charge specific capacity * 100%, then charge and discharge for one cycle at 0.2C / 1C rate, charge and discharge for one cycle at 0.2C / 1C rate, and finally charge and discharge for 50 cycles at 0.5C / 0.1C rate, and test the discharge specific capacity retention rate after 50 cycles of charge and discharge at 0.5C / 0.1C rate. The test results are shown in Table 1.

[0074] Table 1

[0075]

[0076]

[0077] It can be seen from the table that the secondary modified positive electrode material prepared by the embodiment of the present invention has a significant first discharge specific capacity and a significantly higher first charge and discharge specific capacity than the comparative example. The organic carbon on the surface of the secondary modified positive electrode material prepared by the embodiment of the present invention can inhibit the precipitation of Li ions in the internal structure of the high-nickel positive electrode material during the drying and second calcination process, and play a role in delaying crack evolution. At the same time, the residual alkali content on the surface of the material synthesized by the present invention is not much different from the residual alkali content on the surface of the material synthesized by the conventional method.

[0078] Comparing the discharge capacity retention rate of the battery corresponding to the embodiment of the present invention and the comparative example after 50 cycles, the damage to the surface structure of the material is small, and the discharge capacity retention rate of the high-nickel layered positive electrode material of the lithium-ion battery can be significantly improved. It can be seen that in the specific preparation method of the present invention, the use of β-cyclodextrin / potassium metasilicate ligands to form an organic carbon / potassium metasilicate film through sintering can inhibit the side reactions on the surface of the positive electrode material and improve the battery capacity and cycle performance.

[0079] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing a secondary modified positive electrode material, characterized in that: The following steps are involved: 1) placing the positive electrode material in a mixed solution of cyclodextrin and potassium metasilicate and stirring, separating the solid, and drying to obtain a primary modified positive electrode material; 2) Mixing the primary modified positive electrode material obtained in step 1) with boric acid, and sintering the mixture to obtain the secondary modified positive electrode material.

2. The method for preparing the secondary modified positive electrode material according to claim 1, characterized in that: The cyclodextrin and potassium metasilicate mixed solution in step 1) is prepared by mixing cyclodextrin, potassium metasilicate and water and standing for 6-12 hours; The total mass concentration of cyclodextrin and potassium metasilicate in the mixed solution of cyclodextrin and potassium metasilicate is 0.01-0.1wt%; The mass ratio of cyclodextrin to potassium metasilicate in the cyclodextrin and potassium metasilicate mixed solution is (0.3-1.1):

1.

3. The method for preparing the secondary modified positive electrode material according to claim 1 or 2, characterized in that: In step 1), the stirring treatment temperature is 15-60°C, the stirring treatment speed is 300-400r / min, and the stirring treatment time is 5-30min; The ratio of the total volume of the mixed solution of cyclodextrin and potassium metasilicate to the mass of the positive electrode material in step 1) is (0.5-2):1, in units of mL:g.

4. The method for preparing the secondary modified positive electrode material according to any one of claims 1 to 3, characterized in that: The drying temperature in step 1) is 100-140° C. and the drying time is 6-24 hours.

5. The method for preparing the secondary modified positive electrode material according to any one of claims 1 to 4, characterized in that: The mass ratio of the primary modified positive electrode material and boric acid in step 2) is 300:(1-5); The sintering temperature in step 2) is 200-600°C and the sintering time is 6-24h; The sintering process is performed in an oxygen-containing atmosphere.

6. The method for preparing the secondary modified positive electrode material according to any one of claims 1 to 5, characterized in that: The chemical formula of the positive electrode material in step 1) is Li x Ni a Co 1-a-b Mn b O2, and 1.00≤x≤1.08, 0.7≤a≤0.95, 0.01≤b≤0.

1.

7. The method for preparing the secondary modified positive electrode material according to claim 6, characterized in that: The preparation method of the positive electrode material comprises the following steps: weighing a precursor and a lithium source according to a stoichiometric ratio, mixing the mixture, and calcining to obtain the positive electrode material.

8. The method for preparing the modified positive electrode material according to claim 7, characterized in that: The chemical formula of the precursor is Ni a Co 1-a-b Mn b (OH)2, and 0.7≤a≤0.95, 0.01≤b≤0.1; The lithium source is selected from at least one of lithium hydroxide and lithium carbonate; The calcination temperature is 700-900°C and the calcination time is 8-24h; The calcination is performed in an oxygen-containing atmosphere.

9. A secondary modified positive electrode material, characterized in that: The secondary modified positive electrode material is prepared by the preparation method of any one of claims 1 to 8.

10. Use of the secondary modified positive electrode material according to claim 9 in lithium ion batteries.

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