A lithium battery anode material and its preparation method

Abstract

This invention provides a lithium battery anode material and its preparation method, relating to the field of lithium battery technology. The specific preparation steps include: (1) adding fulvic acid to an alkaline solution for impregnation, filtering, and freeze-drying to obtain treated fulvic acid; (2) adding the treated fulvic acid and melamine to a buffer solution, shaking, plasma treatment, filtering, and gradient calcination under an inert atmosphere to obtain layered nitrogen / carbon nanosheets; (3) adding the layered nitrogen / carbon nanosheets and maleic anhydride to n-hexane for reaction to obtain anhydride-grafted layered nitrogen / carbon nanosheets; (4) adding cellulose nanocrystals, sodium citrate, and (3-aminopropyl)triethoxysilane to a buffer solution, microwave treatment, to obtain modified cellulose nanocrystals; (5) combining the anhydride-grafted layered nitrogen / carbon nanosheets and modified cellulose nanocrystals to obtain the lithium battery anode material. The anode material of this invention significantly increases lithium-ion diffusion efficiency, enhances lithium storage performance, and improves rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a lithium battery anode material and its preparation method. Background Technology

[0002] With the rapid development of the electric vehicle industry and renewable energy worldwide, large-scale energy storage technology has become a key factor restricting its sustainable development and a major way to resolve the contradiction between the discontinuity of renewable energy sources such as wind and solar power and the continuity of energy demand. Lithium-ion batteries, as an advanced energy storage device, have been widely used in portable electronic products, electric vehicles, and large-scale energy storage systems. They possess advantages such as high energy density, low self-discharge rate, and long cycle life, making them a leader in current energy storage technologies. With the increasing severity of the energy crisis and environmental pollution, the development of efficient and environmentally friendly lithium-ion battery technology is particularly important. As a key component of lithium-ion batteries, the performance of the anode material directly affects the overall performance of the battery. Anode materials need to possess good electronic conductivity, ion diffusion, and structural stability.

[0003] Currently, non-carbon anode materials for lithium-ion batteries exhibit high lithium storage capacity, but due to issues such as low conductivity, large volumetric variation, and easy pulverization, they have not yet achieved large-scale application, even in commercially viable lithium-ion batteries. Carbon-based materials, on the other hand, not only possess a lower sodium intercalation plateau, higher capacity, and better cycle stability, but also offer advantages such as abundant resources and simple preparation. Therefore, carbon materials are the most promising key anode materials for driving the industrialization of lithium-ion batteries. However, existing carbon materials still suffer from insufficient stability and relatively low specific capacity, which cannot meet the long-term use requirements of lithium-ion batteries.

[0004] Therefore, it is necessary to develop a lithium battery anode material with good stability, high specific capacity, and excellent electrochemical performance to meet the high-rate performance requirements of batteries, which is of practical significance. Summary of the Invention

[0005] Therefore, this invention proposes a lithium battery anode material and its preparation method.

[0006] The technical solution of this invention is implemented as follows:

[0007] A method for preparing a lithium battery anode material, the specific preparation steps of which include:

[0008] (1) Add fulvic acid to an alkaline solution for impregnation, filter, freeze dry to obtain treated fulvic acid;

[0009] (2) Add the treated fulvic acid and melamine to a buffer solution, shake, treat with plasma, filter, calcine in an inert atmosphere, and cool with the furnace to obtain layered nitrogen / carbon nanosheets.

[0010] (3) Layered nitrogen / carbon nanosheets and maleic anhydride were added to n-hexane in sequence to react and obtain anhydride-grafted layered nitrogen / carbon nanosheets.

[0011] (4) Add cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane to a buffer solution and microwave treat to obtain modified cellulose nanocrystals;

[0012] (5) Add the anhydride-grafted layered nitrogen / carbon nanosheets and modified cellulose nanocrystals to n-hexane, heat and stir, filter, wash and dry to obtain the target lithium battery anode material.

[0013] Furthermore, in step (1), the solid-liquid ratio of the fulvic acid to the alkaline solution is 1:10-15 g / mL; the alkaline solution is a 0.1-0.2 mol / L sodium hydroxide solution or potassium hydroxide solution; and the soaking time is 4-6 h.

[0014] Fulvic acid is a component of humic substances. It is rich in oxygen-containing functional groups and aromatic structures, and can form porous nanosheets with adjustable interlayer spacing, high specific surface area, biodegradability, and sustainability.

[0015] Furthermore, in step (2), the mass ratio of the treated fulvic acid to melamine is 1:0.3-0.5; the solid-liquid ratio of the treated fulvic acid to the buffer solution is 1:6-10 g / mL; and the buffer solution is a phosphate buffer solution with a pH of 6.5-7.5.

[0016] Furthermore, in step (2), the oscillation is performed at 200-250 rpm for 40-60 min; the plasma treatment is performed in an oxygen atmosphere at 50-60 W and 25-35 kHz for 20-30 min; and the inert atmosphere is nitrogen or argon.

[0017] Furthermore, in step (2), the gradient calcination is first heated to 250-350℃ at a heating rate of 1-2℃ / min and held for 1-2h, and then heated to 450-550℃ at a heating rate of 3-5℃ / min and held for 40-60min.

[0018] Furthermore, in step (3), the mass ratio of the layered nitrogen / carbon nanosheets to maleic anhydride is 1:0.1-0.3; the solid-liquid ratio of the layered nitrogen / carbon nanosheets to n-hexane is 1:6-8 g / mL; and the reaction is carried out at 60-80℃ for 1-3 h.

[0019] Furthermore, in step (4), the mass ratio of the cellulose nanocrystals to sodium citrate and (3-aminopropyl)triethoxysilane is 1:0.25-0.35:0.15-0.20; the buffer solution is a phosphate buffer solution with a pH of 6.5-7.5; and the solid-liquid ratio of the cellulose nanocrystals to the buffer solution is 1:10-20 g / mL.

[0020] Cellulose nanocrystals are an emerging nanomaterial prepared from cellulose molecules through special processing. Cellulose is a major component of plant cell walls, including cellulose fibers and cellulose microcrystals. The characteristics of cellulose nanocrystals include: 1. Cellulose nanocrystals are typically in the nanometer scale, possessing high specific surface area and unique physicochemical properties. 2. Cellulose nanocrystals are based on natural cellulose, exhibiting good biodegradability and being environmentally friendly. 3. By modifying cellulose nanocrystals, their morphology, structure, and properties can be adjusted to meet the needs of different applications.

[0021] Furthermore, in step (4), the microwave treatment is performed at 300-400W and 50-60℃ for 1-2 hours.

[0022] Furthermore, in step (5), the mass ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to the modified cellulose nanocrystals is 1-3:1; the solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:10-20 g / mL; and the heating and stirring are carried out at 50-60℃ and 200-250 rpm for 1-3 hours.

[0023] A lithium battery anode material, obtained by any of the preparation methods described above.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. This invention uses fulvic acid as a carbon precursor, forms layered carbon nanosheets by controlling calcination conditions, introduces melamine rich in nitrogen, and performs plasma treatment to increase the activity of the reactants. At the same time, it avoids interlayer accumulation during high-temperature carbonization, achieving uniform nitrogen doping into the carbon framework, significantly improving the conductivity of the carbon material, providing abundant defects and active sites, and enhancing lithium-ion adsorption capacity. The formed layered nitrogen / carbon nanosheets have a large specific surface area, and the layered structure and abundant defect sites can significantly increase lithium-ion diffusion efficiency, enhance lithium storage performance, and improve rate performance.

[0026] 2. This invention introduces anhydride groups on the surface of layered nitrogen / carbon nanosheets, which can change the surface properties of the material. At the same time, it can undergo esterification reaction with the hydroxyl groups on the surface of cellulose nanocrystals, enhance the interfacial bonding force between the layered nitrogen / carbon nanosheets and cellulose nanocrystals, avoid delamination and shedding of the negative electrode material during charging and discharging, and improve the stability and cycle life of the battery.

[0027] 3. The cellulose nanocrystals of the present invention are a renewable, environmentally friendly, and biodegradable material with good biocompatibility. When applied to lithium battery anode materials, they can alleviate the volume expansion of carbon materials during charging and discharging, extend cycle life, and the flexible network of cellulose nanocrystals can effectively inhibit interlayer delamination of carbon nanosheets and improve cycle stability. Detailed Implementation

[0028] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0029] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0030] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0031] The alkaline solution of the present invention is a 0.1-0.2 mol / L sodium hydroxide solution or potassium hydroxide solution.

[0032] The buffer solution of the present invention is a phosphate buffer solution with a pH value of 6.5-7.5.

[0033] The inert atmosphere of this invention is nitrogen or argon.

[0034] Example 1

[0035] A method for preparing a lithium battery anode material, the specific preparation steps of which include:

[0036] (1) Add fulvic acid to an alkaline solution and soak for 5 hours according to a solid-liquid ratio of 1:13 g / mL. After the soaking is completed, filter the solution and freeze-dry the product to obtain the treated fulvic acid.

[0037] (2) The treated fulvic acid and melamine with a mass ratio of 1:0.4 were added to the buffer solution in sequence. The solid-liquid ratio of the treated fulvic acid to the buffer solution was 1:8 g / mL. The mixture was shaken repeatedly at 225 rpm for 50 min. Then, it was plasma treated at 55 W and 30 kHz for 25 min under an oxygen atmosphere. After the treatment was completed, the mixture was filtered. The product was then subjected to gradient calcination under an inert atmosphere. First, the temperature was increased to 300℃ at a heating rate of 1℃ / min and held for 1.5 h. Then, the temperature was increased to 500℃ at a heating rate of 4℃ / min and held for 50 min. The product was then cooled with the furnace to obtain layered nitrogen / carbon nanosheets.

[0038] (3) Layered nitrogen / carbon nanosheets with a mass ratio of 1:0.2 and maleic anhydride were added to n-hexane in sequence. The solid-liquid ratio of layered nitrogen / carbon nanosheets to n-hexane was 1:7 g / mL. The reaction was carried out at 70℃ for 2 h. After filtration, washing, and drying, anhydride-grafted layered nitrogen / carbon nanosheets were obtained.

[0039] (4) Cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane in a mass ratio of 1:0.3:0.18 were added to a buffer solution in sequence. The solid-liquid ratio of cellulose nanocrystals to buffer solution was 1:15 g / mL. The solution was microwaved at 350 W and 55 °C for 1.5 h to obtain modified cellulose nanocrystals.

[0040] (5) Add anhydride-grafted layered nitrogen / carbon nanosheets and modified cellulose nanocrystals in a mass ratio of 2:1 to n-hexane. The solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:15 g / mL. Stir at 55℃ and 225 rpm for 2 h, filter, wash, and dry to obtain the target lithium battery anode material.

[0041] Example 2

[0042] A method for preparing a lithium battery anode material, the specific preparation steps of which include:

[0043] (1) Add fulvic acid to an alkaline solution and soak for 4 hours according to a solid-liquid ratio of 1:10 g / mL. After the soaking is completed, filter the solution and freeze-dry the product to obtain the treated fulvic acid.

[0044] (2) The treated fulvic acid and melamine with a mass ratio of 1:0.3 were added to the buffer solution in sequence. The solid-liquid ratio of the treated fulvic acid to the buffer solution was 1:6 g / mL. The mixture was shaken repeatedly at 200 rpm for 40 min. Then, it was plasma treated at 50 W and 25 kHz for 20 min under an oxygen atmosphere. After filtration, the product was subjected to gradient calcination under an inert atmosphere. First, the temperature was raised to 250 °C at a heating rate of 1 °C / min and held for 1 h. Then, the temperature was raised to 450 °C at a heating rate of 3 °C / min and held for 40 min. The product was cooled with the furnace to obtain layered nitrogen / carbon nanosheets.

[0045] (3) Layered nitrogen / carbon nanosheets with a mass ratio of 1:0.1 and maleic anhydride were added to n-hexane in sequence. The solid-liquid ratio of layered nitrogen / carbon nanosheets to n-hexane was 1:6 g / mL. The reaction was carried out at 60℃ for 1 h. After filtration, washing, and drying, anhydride-grafted layered nitrogen / carbon nanosheets were obtained.

[0046] (4) Cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane in a mass ratio of 1:0.25:0.15 were added to a buffer solution in sequence. The solid-liquid ratio of cellulose nanocrystals to buffer solution was 1:10 g / mL. The solution was microwaved at 300 W and 50 °C for 1 h to obtain modified cellulose nanocrystals.

[0047] (5) Add anhydride-grafted layered nitrogen / carbon nanosheets and modified cellulose nanocrystals in a mass ratio of 1-3:1 to n-hexane. The solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:10 g / mL. Stir at 50℃ and 200 rpm for 1 h, filter, wash, and dry to obtain the target lithium battery anode material.

[0048] Example 3

[0049] A method for preparing a lithium battery anode material, the specific preparation steps of which include:

[0050] (1) Add fulvic acid to an alkaline solution and soak for 6 hours according to a solid-liquid ratio of 1:15 g / mL. After the soaking is completed, filter the solution and freeze-dry the product to obtain the treated fulvic acid.

[0051] (2) The treated fulvic acid and melamine with a mass ratio of 1:0.5 were added to the buffer solution in sequence. The solid-liquid ratio of the treated fulvic acid to the buffer solution was 1:10 g / mL. The mixture was shaken repeatedly at 250 rpm for 60 min. Then, it was plasma treated at 60 W and 35 kHz for 30 min under an oxygen atmosphere. After the treatment was completed, the mixture was filtered. The product was then subjected to gradient calcination under an inert atmosphere. First, the temperature was increased to 350 °C at a heating rate of 2 °C / min and held for 2 h. Then, the temperature was increased to 550 °C at a heating rate of 5 °C / min and held for 60 min. The product was then cooled with the furnace to obtain layered nitrogen / carbon nanosheets.

[0052] (3) Layered nitrogen / carbon nanosheets with a mass ratio of 1:0.3 and maleic anhydride were added to n-hexane in sequence. The solid-liquid ratio of layered nitrogen / carbon nanosheets to n-hexane was 1:8 g / mL. The reaction was carried out at 80℃ for 3 h. After filtration, washing and drying, anhydride-grafted layered nitrogen / carbon nanosheets were obtained.

[0053] (4) Cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane in a mass ratio of 1:0.35:0.20 were added to a buffer solution in sequence. The solid-liquid ratio of cellulose nanocrystals to buffer solution was 1:20 g / mL. The solution was microwaved at 400 W and 60 °C for 2 h to obtain modified cellulose nanocrystals.

[0054] (5) Add anhydride-grafted layered nitrogen / carbon nanosheets and modified cellulose nanocrystals in a mass ratio of 3:1 to n-hexane. The solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:20 g / mL. Stir at 60℃ and 250 rpm for 3 h, filter, wash, and dry to obtain the target lithium battery anode material.

[0055] Comparative Example 1

[0056] The difference from Example 1 is that melamine is not added in step (2), but otherwise it is the same as Example 1.

[0057] This comparative example describes a method for preparing a lithium-ion battery anode material, and the specific preparation steps include:

[0058] (1) Add fulvic acid to an alkaline solution and soak for 5 hours according to a solid-liquid ratio of 1:13 g / mL. After the soaking is completed, filter the solution and freeze-dry the product to obtain the treated fulvic acid.

[0059] (2) The treated fulvic acid was added to the buffer solution at a solid-liquid ratio of 1:8 g / mL and shaken repeatedly at 225 rpm for 50 min. Then, it was plasma treated at 55 W and 30 kHz for 25 min under an oxygen atmosphere. After filtration, the product was subjected to gradient calcination under an inert atmosphere. First, the temperature was raised to 300℃ at a heating rate of 1℃ / min and held for 1.5 h. Then, the temperature was raised to 500℃ at a heating rate of 4℃ / min and held for 50 min. The product was then cooled with the furnace to obtain layered carbon nanosheets.

[0060] (3) Layered carbon nanosheets with a mass ratio of 1:0.2 and maleic anhydride were added to n-hexane in sequence. The solid-liquid ratio of layered carbon nanosheets to n-hexane was 1:7 g / mL. The reaction was carried out at 70℃ for 2 h. After filtration, washing, and drying, anhydride-grafted layered carbon nanosheets were obtained.

[0061] (4) Cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane in a mass ratio of 1:0.3:0.18 were added to a buffer solution in sequence. The solid-liquid ratio of cellulose nanocrystals to buffer solution was 1:15 g / mL. The solution was microwaved at 350 W and 55 °C for 1.5 h to obtain modified cellulose nanocrystals.

[0062] (5) Add anhydride-grafted layered carbon nanosheets and modified cellulose nanocrystals in a mass ratio of 2:1 to n-hexane. The solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:15 g / mL. Stir at 55℃ and 225 rpm for 2 h, filter, wash, and dry to obtain lithium battery anode material.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that step (2) does not involve plasma treatment, but otherwise it is the same as Example 1.

[0065] This comparative example describes a method for preparing a lithium-ion battery anode material, and the specific preparation steps include:

[0066] (1) Add fulvic acid to an alkaline solution and soak for 5 hours according to a solid-liquid ratio of 1:13 g / mL. After the soaking is completed, filter the solution and freeze-dry the product to obtain the treated fulvic acid.

[0067] (2) The treated fulvic acid and melamine with a mass ratio of 1:0.4 were added to the buffer solution in sequence. The solid-liquid ratio of the treated fulvic acid to the buffer solution was 1:8 g / mL. The mixture was shaken repeatedly at 225 rpm for 50 min. After filtration, the product was subjected to gradient calcination under an inert atmosphere. First, the temperature was raised to 300℃ at a heating rate of 1℃ / min and held for 1.5 h. Then, the temperature was raised to 500℃ at a heating rate of 4℃ / min and held for 50 min. The product was then cooled with the furnace to obtain layered nitrogen / carbon nanosheets.

[0068] (3) Layered nitrogen / carbon nanosheets with a mass ratio of 1:0.2 and maleic anhydride were added to n-hexane in sequence. The solid-liquid ratio of layered nitrogen / carbon nanosheets to n-hexane was 1:7 g / mL. The reaction was carried out at 70℃ for 2 h. After filtration, washing, and drying, anhydride-grafted layered nitrogen / carbon nanosheets were obtained.

[0069] (4) Cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane in a mass ratio of 1:0.3:0.18 were added to a buffer solution in sequence. The solid-liquid ratio of cellulose nanocrystals to buffer solution was 1:15 g / mL. The solution was microwaved at 350 W and 55 °C for 1.5 h to obtain modified cellulose nanocrystals.

[0070] (5) Add anhydride-grafted layered nitrogen / carbon nanosheets and modified cellulose nanocrystals in a mass ratio of 2:1 to n-hexane. The solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:15 g / mL. Stir at 55℃ and 225 rpm for 2 h, filter, wash, and dry to obtain lithium battery anode material.

[0071] Comparative Example 3

[0072] The difference from Example 1 is that in step (2), the calcination is directly raised to 500°C at a heating rate of 5°C / min and held for 2 hours. The rest is the same as in Example 1.

[0073] This comparative example describes a method for preparing a lithium-ion battery anode material, and the specific preparation steps include:

[0074] (1) Add fulvic acid to an alkaline solution and soak for 5 hours according to a solid-liquid ratio of 1:13 g / mL. After the soaking is completed, filter the solution and freeze-dry the product to obtain the treated fulvic acid.

[0075] (2) The treated fulvic acid and melamine with a mass ratio of 1:0.4 were added to the buffer solution in sequence. The solid-liquid ratio of the treated fulvic acid to the buffer solution was 1:8 g / mL. The mixture was shaken repeatedly at 225 rpm for 50 min. Then, it was plasma treated at 55 W and 30 kHz for 25 min under an oxygen atmosphere. After the treatment, the mixture was filtered. The product was calcined under an inert atmosphere and heated to 500 °C at a heating rate of 5 °C / min and held for 2 h. The product was then cooled with the furnace to obtain nitrogen / carbon nanosheets.

[0076] (3) Nitrogen / carbon nanosheets with a mass ratio of 1:0.2 and maleic anhydride were added to n-hexane in sequence. The solid-liquid ratio of nitrogen / carbon nanosheets to n-hexane was 1:7 g / mL. The reaction was carried out at 70°C for 2 h. After filtration, washing, and drying, anhydride-grafted nitrogen / carbon nanosheets were obtained.

[0077] (4) Cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane in a mass ratio of 1:0.3:0.18 were added to a buffer solution in sequence. The solid-liquid ratio of cellulose nanocrystals to buffer solution was 1:15 g / mL. The solution was microwaved at 350 W and 55 °C for 1.5 h to obtain modified cellulose nanocrystals.

[0078] (5) Add anhydride-grafted nitrogen / carbon nanosheets and modified cellulose nanocrystals in a mass ratio of 2:1 to n-hexane. The solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:15 g / mL. Stir at 55℃ and 225 rpm for 2 h, filter, wash, and dry to obtain lithium battery anode material.

[0079] Comparative Example 4

[0080] The difference from Example 1 is that the negative electrode material is a layered nitrogen / carbon nanosheet, while the rest is the same as in Example 1.

[0081] This comparative example describes a method for preparing a lithium-ion battery anode material, and the specific preparation steps include:

[0082] (1) Add fulvic acid to an alkaline solution and soak for 5 hours according to a solid-liquid ratio of 1:13 g / mL. After the soaking is completed, filter the solution and freeze-dry the product to obtain the treated fulvic acid.

[0083] (2) The treated fulvic acid and melamine with a mass ratio of 1:0.4 were added to the buffer solution in sequence. The solid-liquid ratio of the treated fulvic acid to the buffer solution was 1:8 g / mL. The mixture was shaken repeatedly at 225 rpm for 50 min. Then, it was plasma treated at 55 W and 30 kHz in an oxygen atmosphere for 25 min. After filtration, the product was subjected to gradient calcination in an inert atmosphere. First, the temperature was raised to 300℃ at a heating rate of 1℃ / min and held for 1.5 h. Then, the temperature was raised to 500℃ at a heating rate of 4℃ / min and held for 50 min. The product was cooled with the furnace to obtain layered nitrogen / carbon nanosheets, which are lithium battery anode materials.

[0084] Test case

[0085] The negative electrode materials, binders, and conductive agents prepared in Examples 1-3 and Comparative Examples 1-4 were mixed in a mass ratio of 8:1:1, and then stirred. The mixture was then prepared into a slurry using N-methylpyrrolidone. The slurry was coated onto a current collector (using copper foil as the current collector), with a coating areal density of 8 mg / cm³. 2 After rolling, a negative electrode sheet is obtained. The negative electrode sheet, separator, and positive electrode sheet (using lithium nickel cobalt manganese oxide as the positive electrode material) are stacked sequentially and wound to obtain a bare cell. The tabs are welded, and the bare cell is placed in a soft-pack aluminum-plastic film, top-side sealed, and injected with electrolyte (1 mol / L LiPF6 ethyl carbonate + dimethyl carbonate (volume ratio 1:1)). After top sealing, formation, volume adjustment, and venting and sealing are performed to obtain a secondary battery, which is then subjected to performance testing. Test indicators: first discharge specific capacity; first efficiency; capacity retention rate after 100 cycles; full charge expansion rate.

[0086] First-cycle efficiency refers to the ratio of the first discharge capacity to the first charge capacity, reflecting the reversibility of the material during the first cycle, i.e., the coulombic efficiency of the material during the first charge and discharge; First-cycle efficiency (%) = charge capacity / discharge capacity × 100%.

[0087] The test method for battery cycle capacity retention rate is as follows: charge with a current of 0.5 times the battery capacity and discharge with a current of 1 times the battery capacity, cycle for 100 times, and calculate the capacity retention rate on the 100th cycle. The capacity retention rate is calculated by the following formula: Capacity retention rate on the 100th cycle (%) = Discharge capacity on the 100th cycle / Discharge capacity on the first cycle × 100%.

[0088] The test method for the full charge expansion rate of a battery is as follows: Fully charge the battery with a current of 0.5 times its capacity, disassemble it, measure the thickness of the negative electrode after full charge, compare it with the thickness after rolling, and calculate the full charge expansion rate. The full charge expansion rate is calculated by the following formula: Full charge expansion rate (%) = (Thickness of negative electrode after full charge - Thickness of negative electrode after rolling) / Thickness of negative electrode after rolling × 100%.

[0089] The test results are shown in Table 1.

[0090] Table 1

[0091]

[0092] As shown in Table 1, compared with the negative electrode materials of Comparative Examples 1-4, the negative electrode materials prepared in Examples 1-3 of the present invention have significantly higher initial discharge specific capacity and significantly lower full-charge expansion rate. It can be seen that the negative electrode material of the present invention can effectively buffer and suppress volume expansion, extend the cycle life of the battery, and after 100 cycles of charge and discharge, the assembled battery still maintains a high capacity retention rate with no obvious attenuation, and has good stability performance.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium battery anode material, characterized in that, The specific preparation steps include: (1) Add fulvic acid to an alkaline solution for impregnation, filter, freeze dry to obtain treated fulvic acid; (2) Add the treated fulvic acid and melamine in a mass ratio of 1:0.3-0.5 to a buffer solution, shake, treat with plasma, filter, calcine in an inert atmosphere, and cool with the furnace to obtain layered nitrogen / carbon nanosheets. The gradient calcination involves first raising the temperature to 250-350℃ at a heating rate of 1-2℃ / min and holding it for 1-2 hours, then raising the temperature to 450-550℃ at a heating rate of 3-5℃ / min and holding it for 40-60 minutes. (3) Layered nitrogen / carbon nanosheets with a mass ratio of 1:0.1-0.3 and maleic anhydride were added to n-hexane in sequence to react and obtain anhydride-grafted layered nitrogen / carbon nanosheets. (4) Add cellulose nanocrystals, sodium citrate and (3-aminopropyl)triethoxysilane in a mass ratio of 1:0.25-0.35:0.15-0.20 to a buffer solution and microwave treat to obtain modified cellulose nanocrystals; (5) Add anhydride-grafted layered nitrogen / carbon nanosheets and modified cellulose nanocrystals in a mass ratio of 1-3:1 to n-hexane, heat and stir, filter, wash and dry to obtain the target lithium battery anode material.

2. The method for preparing a lithium battery anode material as described in claim 1, characterized in that, In step (1), the solid-liquid ratio of fulvic acid to alkaline solution is 1:10-15 g / mL; the alkaline solution is a 0.1-0.2 mol / L sodium hydroxide solution or potassium hydroxide solution; and the soaking time is 4-6 h.

3. The method for preparing a lithium battery anode material as described in claim 1, characterized in that, In step (2), the solid-liquid ratio of the treated fulvic acid to the buffer solution is 1:6-10 g / mL; the buffer solution is a phosphate buffer solution with a pH of 6.5-7.

5.

4. The method for preparing a lithium battery anode material as described in claim 1, characterized in that, In step (2), the oscillation is performed at 200-250 rpm for 40-60 min; the plasma treatment is performed in an oxygen atmosphere at 50-60 W and 25-35 kHz for 20-30 min; and the inert atmosphere is nitrogen or argon.

5. The method for preparing a lithium battery anode material as described in claim 1, characterized in that, In step (3), the solid-liquid ratio of the layered nitrogen / carbon nanoparticles and n-hexane is 1:6-8 g / mL; the reaction is carried out at 60-80℃ for 1-3 h.

6. The method for preparing a lithium battery anode material as described in claim 1, characterized in that, In step (4), the buffer solution is a phosphate buffer solution with a pH of 6.5-7.5; the solid-liquid ratio of the cellulose nanocrystals to the buffer solution is 1:10-20 g / mL.

7. The method for preparing a lithium battery anode material as described in claim 1, characterized in that, In step (4), the microwave treatment is performed at 300-400W and 50-60℃ for 1-2 hours.

8. The method for preparing a lithium battery anode material as described in claim 1, characterized in that, In step (5), the solid-liquid ratio of the anhydride-grafted layered nitrogen / carbon nanosheets to n-hexane is 1:10-20 g / mL; the heating and stirring are carried out at 50-60℃ and 200-250 rpm for 1-3 hours.

9. A lithium battery anode material, characterized in that, It is obtained by the preparation method according to any one of claims 1-8.

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