Preparation method and application of bio-based negative electrode material

Abstract

The invention discloses a preparation method and application of a bio-based negative electrode material, and belongs to the technical field of battery materials. Comprising the following steps: S1, crushing biomass to particle size, soaking, performing ultrasonic treatment, washing and drying to obtain biomass coarse powder; carrying out acid pretreatment on the biomass coarse powder to obtain acid pretreated biomass; mixing the pretreated biomass with water, carrying out high-temperature reaction, cooling, filtering, and drying to obtain a porous hydrothermal carbon precursor; s2, immersing the hydrothermal carbon precursor into a urea solution, heating, stirring, filtering, and drying; carrying out pre-oxidation and acid pickling in an air atmosphere, then washing with water until the pH is neutral, and drying to obtain a doped precursor; s3, dispersing the doped precursor, strontium-phosphorus hybrid phenolic resin and graphene in absolute ethyl alcohol, performing ball milling, and stirring until ethyl alcohol is volatilized to obtain a composite solid mixture; under the protection of nitrogen, gradient heating curing is performed, then high-temperature carbonization is performed, washing and drying are performed after cooling, and the bio-based negative electrode material is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and specifically relates to a preparation method and application of a bio-based negative electrode material. Background Art

[0002] The development of bio-based anode materials stems from the limitations of traditional fossil-based materials and the need for sustainable development. Traditional graphite anodes have low theoretical capacity and rely on non-renewable resources, making it difficult to meet the needs of high-energy-density batteries. Although silicon-based materials have high capacity, they have volume expansion problems. At the same time, with the rise of sodium-ion batteries, sodium ions, due to their larger radius, need to adapt to anode materials with wider interlayer spacing. Biomass-based hard carbon has become an ideal choice due to its wide raw material sources, low cost, environmental friendliness, high porosity and short-range ordered structure. In addition, the carbonization process of bio-based materials can regulate the microstructure and further optimize the sodium / lithium storage performance, which is in line with the trend of green manufacturing.

[0003] In the field of bio-based negative electrode materials, for example, a patent application with publication number CN108634097A introduces a method for preparing a porous silicon / carbon composite material using rice husks. This material exhibits excellent electrochemical performance and cycle stability when used as a negative electrode for lithium-ion batteries. Its advantages are that the raw material sources are wide and the cost is low, but its limitations are that the production process is relatively complicated and the carbonization conditions need to be precisely controlled to ensure the material performance. Another patent application with publication number CN118083951A provides a high-performance biomass-based hard carbon negative electrode material and a preparation method thereof, which uses biomass resources to develop hard carbon materials with excellent electrochemical properties. The advantages of these bio-based negative electrode materials are that they are derived from renewable resources, are environmentally friendly and sustainable, and in some cases can provide energy density and cycle life that are superior to traditional graphite negative electrodes. However, the main limitations of the existing technology are the high complexity of the production process, the difficulty of cost control, and the consistency and stability of the materials, which limit the speed of its large-scale commercial application.

[0004] Despite significant progress in the research of bio-based anode materials, large-scale commercial application still faces numerous challenges, such as material consistency and stability, production process optimization, and cost control. Furthermore, further research is needed to improve the electrochemical performance of these materials to meet the growing demand for high energy density and long cycle life. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of a bio-based negative electrode material to improve the cycle performance and coulombic efficiency of the bio-based negative electrode material.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a bio-based negative electrode material comprises the following steps:

[0008] S1. Crush the biomass into particles, soak it in an anhydrous ethanol / deionized water mixed solution, ultrasonically treat it, wash it, and dry it to obtain a biomass coarse powder; mix the biomass coarse powder with a sulfuric acid solution, heat and stir it, filter it, and wash it to obtain an acid-pretreated biomass; mix the pretreated biomass with water, react it at a high temperature, cool it, filter it, and dry it to obtain a porous hydrothermal carbon precursor;

[0009] S2, immersing the hydrothermal carbon precursor in a urea solution, heating and stirring, filtering, and drying; pre-oxidizing in an air atmosphere, acid washing, and then washing with water until the pH is neutral, and drying to obtain a doping precursor;

[0010] S3. Disperse the doping precursor, strontium-phosphorus hybrid phenolic resin and graphene in anhydrous ethanol, ball-mill and stir until the ethanol evaporates to obtain a composite solid mixture; under nitrogen protection, perform gradient temperature curing, then perform high-temperature carbonization, cool, wash and dry to obtain a bio-based negative electrode material.

[0011] Furthermore, the biomass is one or a combination of wood and straw; and the crushed particle size is 1-5 mm.

[0012] Furthermore, the volume ratio of anhydrous ethanol / deionized water is 1:1; the ultrasonic treatment time is 2-10 hours; and the drying is performed at 60-80° C. for 8-12 hours.

[0013] Furthermore, the mass ratio of the biomass coarse powder to the sulfuric acid solution is 1:(8-12); the concentration of the sulfuric acid solution is 2-3 mol / L; and the stirring in S1 is at 60-80° C. for 4-6 hours.

[0014] Furthermore, the mass ratio of the pretreated biomass to water is 1:(15-20); and the high temperature reaction in S1 is carried out at 180-200° C. for 12-14 hours.

[0015] Furthermore, the mass concentration of the urea solution is 10% to 30%.

[0016] Furthermore, the heating and stirring in S2 is stirring at 100-120° C. for 6-8 hours; and the drying in S2 is drying at 95-105° C. for 18-24 hours.

[0017] Furthermore, the pre-oxidation is carried out at 220-250° C. for 4-6 hours; and the pickling is carried out at 60-80° C. for 2-3 hours using 0.5-1 mol / L hydrochloric acid.

[0018] Furthermore, the mass ratio of the doping precursor, strontium-phosphorus hybrid phenolic resin, graphene and anhydrous ethanol is 10:(1-3):(0.5-1.5):(80-120).

[0019] Furthermore, the ball milling time is 2-3 hours; and the temperature during stirring until ethanol volatilizes is 80-85°C.

[0020] Furthermore, the gradient temperature increase is firstly increasing the temperature to 120-130°C and then keeping the temperature for 1-1.5 hours, and then increasing the temperature to 180-200°C and keeping the temperature for 2-3 hours, with a heating rate of 5-10°C / min.

[0021] Furthermore, the high temperature carbonization is to increase the temperature to 900-1000° C. at a rate of 5-10° C. / min and carbonize for 2-3 hours under an inert gas atmosphere.

[0022] Furthermore, the strontium-phosphorus hybrid phenolic resin is prepared by the following steps:

[0023] Step 1: Dissolve strontium chloride in ethanol, add triethylamine and mix well to obtain solution A; mix triethylamine and phosphoric acid in ethanol to form solution B; slowly add solution B dropwise to solution A, stir for 20-25 hours, and then centrifuge and wash to obtain gel A;

[0024] Step 2: Dissolve 3-carboxyphenylboronic acid in methanol to obtain solution C; add the ethanol solution of gel A dropwise to solution C, stir for 12-16 hours, and then centrifuge to obtain modified gel A;

[0025] The third step is to dissolve the phenolic resin in ethanol to obtain a phenolic resin ethanol solution; add the modified gel A ethanol solution dropwise to the phenolic resin ethanol solution, stir at 60-80° C. for 6-8 hours, centrifuge, wash and dry to obtain a strontium-phosphorus hybrid phenolic resin.

[0026] Furthermore, the usage ratio of strontium chloride, ethanol and triethylamine in the solution A is (8-12) g: (450-550) mL: (40-50) mL.

[0027] Furthermore, the usage ratio of phosphoric acid, triethylamine and ethanol in the solution B is (8-10) mL: (20-40) mL: (200-250) mL.

[0028] Furthermore, the ratio of 3-carboxyphenylboric acid to methanol in the solution C is (3-8) g: (250-350) mL; and the ratio of gel A to ethanol in the ethanol solution of gel A is (5-15) g: (150-250) mL.

[0029] Furthermore, the ratio of phenolic resin to ethanol in the phenolic resin ethanol solution is (15-25) g: (350-450) mL; the ratio of modified gel A to ethanol in the modified gel A ethanol solution is (2-8) g: (80-120) mL.

[0030] A bio-based negative electrode material is prepared by the above-mentioned method for preparing the bio-based negative electrode material.

[0031] Application of a bio-based negative electrode material in lithium batteries.

[0032] Beneficial effects of the present invention:

[0033] (1) The doping precursor used in the present invention is a hydrothermal carbon precursor that is impregnated with urea. During the high-temperature pre-oxidation and carbonization process, urea decomposes to generate NH3, and nitrogen atoms are embedded in the carbon skeleton to form pyridinic nitrogen (N-6) and pyrrolic nitrogen (N-5) active sites; this can significantly enhance the surface polarity of the material, improve the lithium ion adsorption capacity, and thus improve the specific capacity.

[0034] (2) The strontium-phosphorus hybrid phenolic resin used in the present invention forms a covalently crosslinked network through the condensation of phenolic hydroxyl groups; gel A forms a continuous inorganic network through ionic crosslinking of strontium ions and phosphate groups. Through the covalent-ionic synergistic effect of the modified gel A and the phenolic resin, a uniform and stable organic-inorganic bicontinuous network structure is constructed. After carbonization, a rigid skeleton is formed, which effectively suppresses the volume expansion during the insertion / extraction of lithium ions. The three-dimensional crosslinked network generated by the carbonization of the phenolic resin further provides mechanical support, reduces electrode pulverization, and improves the cycle life of the negative electrode material.

[0035] (3) The Sr-P inorganic phase contained in the modified gel A used in the present invention can inhibit the oxidative decomposition of the carbon matrix at high temperature, thereby improving the thermal stability of the material; the surface of the Sr-P inorganic phase modified with 3-carboxyphenylboronic acid contains boric acid groups, which form a boron-doped conductive carbon layer after carbonization with phenolic resin, thereby improving electronic conductivity; and local defects are formed on the surface of the strontium phosphate nanoparticles, which promote the diffusion of lithium / sodium ions and improve the rate performance; the nitrogen doping in the doping precursor and the Sr-P inorganic phase in the strontium-phosphorus hybridized phenolic resin synergistically produce more active sites, further improving the electrode conductivity and specific capacity. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0037] Example 1

[0038] This embodiment provides a bio-based negative electrode material, which is prepared by the following steps:

[0039] S1. Dissolve 10 g of strontium chloride in 500 mL of ethanol, add 40 mL of triethylamine and mix well to obtain solution A; mix 30 mL of triethylamine and 10 mL of phosphoric acid in 200 mL of ethanol to form solution B; slowly add solution B dropwise to solution A, stir for 24 hours, and then centrifuge and wash to obtain gel A;

[0040] 5 g of 3-carboxyphenylboronic acid was dissolved in 300 mL of methanol to obtain solution C; 200 mL of an ethanol solution of gel A (containing 10 g of gel A) was added dropwise to solution C, stirred for 12 hours, and then centrifuged to obtain modified gel A;

[0041] 20 g of phenolic resin was dissolved in 400 mL of ethanol to obtain a phenolic resin ethanol solution; 100 mL of modified gel A ethanol solution (containing 5 g of modified gel A) was added dropwise to the phenolic resin ethanol solution, stirred at 80° C. for 6 hours, centrifuged, washed, and dried to obtain a strontium-phosphorus hybrid phenolic resin;

[0042] S2. The biomass (straw) was crushed to a particle size of 3 mm, immersed in a mixed solution of anhydrous ethanol / deionized water (volume ratio of 1:1), ultrasonically treated for 6 hours to remove lipids and impurities, washed with deionized water until neutral, and dried at 80°C for 12 hours to obtain biomass coarse powder; the biomass coarse powder was mixed with 3 mol / L sulfuric acid solution at a solid-liquid ratio of 1:10, stirred at 80°C for 4 hours to promote lignin degradation, filtered and washed with water until neutral to obtain acid-pretreated biomass; the pretreated biomass was mixed with water at a ratio of 1:15, placed in a hydrothermal kettle, reacted at 200°C for 12 hours, filtered and dried after cooling to obtain a porous hydrothermal carbon precursor;

[0043] S3, immersing the hydrothermal carbon precursor in a urea solution (mass concentration 20%), stirring at 120°C for 6 hours, filtering, drying at 105°C for 24 hours, pre-oxidizing at 250°C for 4 hours in an air atmosphere, acid washing with 1 mol / L hydrochloric acid at 80°C for 2 hours to remove unreacted salts, washing with water to pH = 7, and drying to obtain a doping precursor;

[0044] S4. Disperse 10 parts by weight of doping precursor, 2 parts by weight of strontium-phosphorus hybrid phenolic resin, and 1 part by weight of graphene in 100 parts by weight of ethanol, ball mill for 2 hours to form a homogeneous slurry, stir at 80°C until the ethanol evaporates to obtain a composite solid mixture, and solidify it by gradient heating under nitrogen protection (first heating to 120°C and then keeping it warm for 1 hour, then heating to 200°C and keeping it warm for 2 hours, with a heating rate of 5-10°C / min). Then, heat it to 1000°C at 5°C / min in a tubular furnace, carbonize it under Ar atmosphere for 2 hours, cool it naturally, wash it with 1 mol / L HCl to remove inorganic residues, and obtain a bio-based negative electrode material after drying.

[0045] Example 2

[0046] Compared with Example 1, this embodiment differs in that the ratio of the doping precursor and the strontium-phosphorus hybridized phenolic resin is increased, and the specific implementation steps of S4 are:

[0047] S4. Disperse 10 parts by weight of doping precursor, 1 part by weight of strontium-phosphorus hybrid phenolic resin, and 1.5 parts by weight of graphene in 100 parts by weight of ethanol, ball mill for 2 hours to form a homogeneous slurry, stir at 80°C until the ethanol evaporates to obtain a composite solid mixture, and solidify it by gradient heating under nitrogen protection (first heating to 120°C and then keeping it warm for 1 hour, then heating to 200°C and keeping it warm for 2 hours, with a heating rate of 5-10°C / min). Then, heat it to 1000°C at 5°C / min in a tubular furnace, carbonize it under Ar atmosphere for 2 hours, cool it naturally, wash it with 1 mol / L HCl to remove inorganic residues, and obtain a bio-based negative electrode material after drying.

[0048] The remaining raw materials and preparation process remain the same as in Example 1.

[0049] Example 3

[0050] Compared with Example 1, this embodiment differs in that the ratio of the doping precursor and the strontium-phosphorus hybridized phenolic resin is reduced, and the specific implementation steps of S4 are:

[0051] S4. Disperse 10 parts by weight of doping precursor, 3 parts by weight of strontium-phosphorus hybrid phenolic resin, and 0.5 parts by weight of graphene in 100 parts by weight of ethanol, ball mill for 2 hours to form a homogeneous slurry, stir at 80°C until the ethanol evaporates to obtain a composite solid mixture, and solidify it by gradient heating under nitrogen protection (first heating to 120°C and then keeping it warm for 1 hour, then heating to 200°C and keeping it warm for 2 hours, with a heating rate of 5-10°C / min). Then, heat it to 1000°C at 5°C / min in a tubular furnace, carbonize it under Ar atmosphere for 2 hours, cool it naturally, wash it with 1 mol / L HCl to remove inorganic residues, and obtain a bio-based negative electrode material after drying.

[0052] The remaining raw materials and preparation process remain the same as in Example 1.

[0053] Example 4

[0054] Compared with Example 1, this embodiment differs in that the mass concentration of the urea solution is increased, and the specific implementation steps of S3 are:

[0055] S3, immersing the hydrothermal carbon precursor in a urea solution (mass concentration 30%), stirring at 120°C for 6 hours, filtering, drying at 105°C for 24 hours, pre-oxidizing at 250°C for 4 hours in an air atmosphere, acid washing with 1 mol / L hydrochloric acid at 80°C for 2 hours to remove unreacted salts, washing with water to pH = 7, and drying to obtain a doping precursor;

[0056] The remaining raw materials and preparation process remain the same as in Example 1.

[0057] Example 5

[0058] Compared with Example 1, this embodiment differs in that the mass concentration of the urea solution is reduced, and the specific implementation steps of S3 are:

[0059] S3, immersing the hydrothermal carbon precursor in a urea solution (mass concentration 10%), stirring at 120°C for 6 hours, filtering, drying at 105°C for 24 hours, pre-oxidizing at 250°C for 4 hours in an air atmosphere, acid washing with 1 mol / L hydrochloric acid at 80°C for 2 hours to remove unreacted salts, washing with water to pH = 7, and drying to obtain a doping precursor;

[0060] The remaining raw materials and preparation process remain the same as in Example 1.

[0061] Example 6

[0062] Compared with Example 1, this embodiment differs in that the content of the components in solution A, solution B, and solution C are adjusted. The specific implementation steps of S1 are as follows:

[0063] S1. Dissolve 12 g of strontium chloride in 550 mL of ethanol, add 50 mL of triethylamine and mix well to obtain solution A; mix 30 mL of triethylamine and 10 mL of phosphoric acid in 200 mL of ethanol to form solution B; slowly add solution B dropwise to solution A, stir for 24 hours, and then centrifuge and wash to obtain gel A;

[0064] 3 g of 3-carboxyphenylboronic acid was dissolved in 250 mL of methanol to obtain solution C; 200 mL of an ethanol solution of gel A (containing 10 g of gel A) was added dropwise to solution C, stirred for 12 hours, and then centrifuged to obtain modified gel A;

[0065] 20 g of phenolic resin was dissolved in 400 mL of ethanol to obtain a phenolic resin ethanol solution; 100 mL of modified gel A ethanol solution (containing 5 g of modified gel A) was added dropwise to the phenolic resin ethanol solution, stirred at 80° C. for 6 hours, centrifuged, washed, and dried to obtain a strontium-phosphorus hybrid phenolic resin;

[0066] The remaining raw materials and preparation process remain the same as in Example 1.

[0067] Example 7

[0068] Compared with Example 1, this embodiment differs in that the content of the components in solution A, solution B, and solution C are adjusted. The specific implementation steps of S1 are as follows:

[0069] S1. Dissolve 8 g of strontium chloride in 500 mL of ethanol, add 50 mL of triethylamine and mix well to obtain solution A; mix 30 mL of triethylamine and 10 mL of phosphoric acid in 200 mL of ethanol to form solution B; slowly add solution B dropwise to solution A, stir for 24 hours, and then centrifuge and wash to obtain gel A;

[0070] 8 g of 3-carboxyphenylboronic acid was dissolved in 350 mL of methanol to obtain solution C; 200 mL of an ethanol solution of gel A (containing 10 g of gel A) was added dropwise to solution C, stirred for 12 hours, and then centrifuged to obtain modified gel A;

[0071] 20 g of phenolic resin was dissolved in 400 mL of ethanol to obtain a phenolic resin ethanol solution; 100 mL of modified gel A ethanol solution (containing 5 g of modified gel A) was added dropwise to the phenolic resin ethanol solution, stirred at 80° C. for 6 hours, centrifuged, washed, and dried to obtain a strontium-phosphorus hybrid phenolic resin;

[0072] The remaining raw materials and preparation process remain the same as in Example 1.

[0073] Comparative Example 1

[0074] Compared with Example 1, this comparative example is different in that nitrogen doping is not performed. The specific implementation steps are as follows:

[0075] S1. Dissolve 10 g of strontium chloride in 500 mL of ethanol, add 40 mL of triethylamine and mix well to obtain solution A; mix 30 mL of triethylamine and 10 mL of phosphoric acid in 200 mL of ethanol to form solution B; slowly add solution B dropwise to solution A, stir for 24 hours, and then centrifuge and wash to obtain gel A;

[0076] 5 g of 3-carboxyphenylboronic acid was dissolved in 300 mL of methanol to obtain solution C; 200 mL of an ethanol solution of gel A (containing 10 g of gel A) was added dropwise to solution C, stirred for 12 hours, and then centrifuged to obtain modified gel A;

[0077] 20 g of phenolic resin was dissolved in 400 mL of ethanol to obtain a phenolic resin ethanol solution; 100 mL of modified gel A ethanol solution (containing 5 g of modified gel A) was added dropwise to the phenolic resin ethanol solution, stirred at 80° C. for 6 hours, centrifuged, washed, and dried to obtain a strontium-phosphorus hybrid phenolic resin;

[0078] S2. The biomass (straw) was crushed to a particle size of 3 mm, immersed in a mixed solution of anhydrous ethanol / deionized water (volume ratio of 1:1), ultrasonically treated for 6 hours to remove lipids and impurities, washed with deionized water until neutral, and dried at 80°C for 12 hours to obtain biomass coarse powder; the biomass coarse powder was mixed with 3 mol / L sulfuric acid solution at a solid-liquid ratio of 1:10, stirred at 80°C for 4 hours to promote lignin degradation, filtered and washed with water until neutral to obtain acid-pretreated biomass; the pretreated biomass was mixed with water at a ratio of 1:15, placed in a hydrothermal kettle, reacted at 200°C for 12 hours, filtered and dried after cooling to obtain a porous hydrothermal carbon precursor;

[0079] S3, pre-oxidizing the hydrothermal carbon precursor in air at 250°C for 4 hours, acid-washing with 1 mol / L hydrochloric acid at 80°C for 2 hours to remove unreacted salts, washing with water to pH = 7, and drying to obtain a doping precursor;

[0080] S4. Disperse 10 parts by weight of doping precursor, 2 parts by weight of strontium-phosphorus hybrid phenolic resin, and 1 part by weight of graphene in 100 parts by weight of ethanol, ball mill for 2 hours to form a homogeneous slurry, stir at 80°C until the ethanol evaporates to obtain a composite solid mixture, and solidify it by gradient heating under nitrogen protection (first heating to 120°C and then keeping it warm for 1 hour, then heating to 200°C and keeping it warm for 2 hours, with a heating rate of 5-10°C / min). Then, heat it to 1000°C at 5°C / min in a tubular furnace, carbonize it under Ar atmosphere for 2 hours, cool it naturally, wash it with 1 mol / L HCl to remove inorganic residues, and obtain a bio-based negative electrode material after drying.

[0081] The remaining raw materials and preparation process remain the same as in Example 1.

[0082] Comparative Example 2

[0083] This comparative example differs from Example 1 in that no strontium doping is performed. The specific implementation steps are as follows:

[0084] S1. Mix 30 mL of triethylamine and 10 mL of phosphoric acid in 200 mL of ethanol to form solution B; dissolve 5 g of 3-carboxyphenylboronic acid in 300 mL of methanol to obtain solution C; add solution B dropwise to solution C, stir for 12 hours, and then centrifuge to obtain modified gel A;

[0085] 20 g of phenolic resin was dissolved in 400 mL of ethanol to obtain a phenolic resin ethanol solution; 100 mL of modified gel A ethanol solution (containing 5 g of modified gel A) was added dropwise to the phenolic resin ethanol solution, stirred at 80° C. for 6 hours, centrifuged, washed, and dried to obtain a strontium-phosphorus hybrid phenolic resin;

[0086] S2. The biomass (straw) was crushed to a particle size of 3 mm, immersed in a mixed solution of anhydrous ethanol / deionized water (volume ratio of 1:1), ultrasonically treated for 6 hours to remove lipids and impurities, washed with deionized water until neutral, and dried at 80°C for 12 hours to obtain biomass coarse powder; the biomass coarse powder was mixed with 3 mol / L sulfuric acid solution at a solid-liquid ratio of 1:10, stirred at 80°C for 4 hours to promote lignin degradation, filtered and washed with water until neutral to obtain acid-pretreated biomass; the pretreated biomass was mixed with water at a ratio of 1:15, placed in a hydrothermal kettle, reacted at 200°C for 12 hours, filtered and dried after cooling to obtain a porous hydrothermal carbon precursor;

[0087] S3, immersing the hydrothermal carbon precursor in a urea solution (mass concentration 20%), stirring at 120°C for 6 hours, filtering, drying at 105°C for 24 hours, pre-oxidizing at 250°C for 4 hours in an air atmosphere, acid washing with 1 mol / L hydrochloric acid at 80°C for 2 hours to remove unreacted salts, washing with water to pH = 7, and drying to obtain a doping precursor;

[0088] S4. Disperse 10 parts by weight of doping precursor, 2 parts by weight of strontium-phosphorus hybrid phenolic resin, and 1 part by weight of graphene in 100 parts by weight of ethanol, ball mill for 2 hours to form a homogeneous slurry, stir at 80°C until the ethanol evaporates to obtain a composite solid mixture, and solidify it by gradient heating under nitrogen protection (first heating to 120°C and then keeping it warm for 1 hour, then heating to 200°C and keeping it warm for 2 hours, with a heating rate of 5-10°C / min). Then, heat it to 1000°C at 5°C / min in a tubular furnace, carbonize it under Ar atmosphere for 2 hours, cool it naturally, wash it with 1 mol / L HCl to remove inorganic residues, and obtain a bio-based negative electrode material after drying.

[0089] The remaining raw materials and preparation process remain the same as in Example 1.

[0090] Comparative Example 3

[0091] This comparative example differs from Example 1 in that strontium-phosphorus hybridization is not performed. The specific implementation steps are as follows:

[0092] S1, 5g of 3-carboxyphenylboronic acid was dissolved in 300mL of methanol to obtain solution C; 20g of phenolic resin was dissolved in 400mL of ethanol to obtain a phenolic resin ethanol solution; solution C was added dropwise to the phenolic resin ethanol solution, stirred at 80°C for 6 hours, and centrifuged, washed, and dried to obtain a hybrid phenolic resin;

[0093] S2. The biomass (straw) was crushed to a particle size of 3 mm, immersed in a mixed solution of anhydrous ethanol / deionized water (volume ratio of 1:1), ultrasonically treated for 6 hours to remove lipids and impurities, washed with deionized water until neutral, and dried at 80°C for 12 hours to obtain biomass coarse powder; the biomass coarse powder was mixed with 3 mol / L sulfuric acid solution at a solid-liquid ratio of 1:10, stirred at 80°C for 4 hours to promote lignin degradation, filtered and washed with water until neutral to obtain acid-pretreated biomass; the pretreated biomass was mixed with water at a ratio of 1:15, placed in a hydrothermal kettle, reacted at 200°C for 12 hours, filtered and dried after cooling to obtain a porous hydrothermal carbon precursor;

[0094] S3, immersing the hydrothermal carbon precursor in a urea solution (mass concentration 20%), stirring at 120°C for 6 hours, filtering, drying at 105°C for 24 hours, pre-oxidizing at 250°C for 4 hours in an air atmosphere, acid washing with 1 mol / L hydrochloric acid at 80°C for 2 hours to remove unreacted salts, washing with water to pH = 7, and drying to obtain a doping precursor;

[0095] S4. Disperse 10 parts by weight of doping precursor, 2 parts by weight of hybrid phenolic resin, and 1 part by weight of graphene in 100 parts by weight of ethanol, ball mill for 2 hours to form a homogeneous slurry, stir at 80°C until the ethanol evaporates to obtain a composite solid mixture, and solidify it by gradient heating under nitrogen protection (first heating to 120°C and then keeping warm for 1 hour, then heating to 200°C and keeping warm for 2 hours, with a heating rate of 5-10°C / min). Then, heat it to 1000°C at 5°C / min in a tubular furnace, carbonize it under Ar atmosphere for 2 hours, cool it naturally, wash it with 1 mol / LHCl to remove inorganic residues, and obtain a bio-based negative electrode material after drying.

[0096] The remaining raw materials and preparation process remain the same as in Example 1.

[0097] Comparative Example 4

[0098] Compared with Example 1, this comparative example differs in that 3-carboxyphenylboronic acid is not added for modification. The specific implementation steps are as follows:

[0099] S1. Dissolve 10 g of strontium chloride in 500 mL of ethanol, add 40 mL of triethylamine and mix well to obtain solution A; mix 30 mL of triethylamine and 10 mL of phosphoric acid in 200 mL of ethanol to form solution B; slowly add solution B dropwise to solution A, stir for 24 hours, and then centrifuge and wash to obtain gel A;

[0100] 20 g of phenolic resin was dissolved in 400 mL of ethanol to obtain a phenolic resin ethanol solution; 100 mL of gel A ethanol solution (containing 5 g of gel A) was added dropwise to the phenolic resin ethanol solution, stirred at 80° C. for 6 hours, and centrifuged, washed, and dried to obtain a strontium-phosphorus hybrid phenolic resin;

[0101] S2. The biomass (straw) was crushed to a particle size of 3 mm, immersed in a mixed solution of anhydrous ethanol / deionized water (volume ratio of 1:1), ultrasonically treated for 6 hours to remove lipids and impurities, washed with deionized water until neutral, and dried at 80°C for 12 hours to obtain biomass coarse powder; the biomass coarse powder was mixed with 3 mol / L sulfuric acid solution at a solid-liquid ratio of 1:10, stirred at 80°C for 4 hours to promote lignin degradation, filtered and washed with water until neutral to obtain acid-pretreated biomass; the pretreated biomass was mixed with water at a ratio of 1:15, placed in a hydrothermal kettle, reacted at 200°C for 12 hours, filtered and dried after cooling to obtain a porous hydrothermal carbon precursor;

[0102] S3, immersing the hydrothermal carbon precursor in a urea solution (mass concentration 20%), stirring at 120°C for 6 hours, filtering, drying at 105°C for 24 hours, pre-oxidizing at 250°C for 4 hours in an air atmosphere, acid washing with 1 mol / L hydrochloric acid at 80°C for 2 hours to remove unreacted salts, washing with water to pH = 7, and drying to obtain a doping precursor;

[0103] S4. Disperse 10 parts by weight of doping precursor, 2 parts by weight of strontium-phosphorus hybrid phenolic resin, and 1 part by weight of graphene in 100 parts by weight of ethanol, ball mill for 2 hours to form a homogeneous slurry, stir at 80°C until the ethanol evaporates to obtain a composite solid mixture, and solidify it by gradient heating under nitrogen protection (first heating to 120°C and then keeping it warm for 1 hour, then heating to 200°C and keeping it warm for 2 hours, with a heating rate of 5-10°C / min). Then, heat it to 1000°C at 5°C / min in a tubular furnace, carbonize it under Ar atmosphere for 2 hours, cool it naturally, wash it with 1 mol / L HCl to remove inorganic residues, and obtain a bio-based negative electrode material after drying.

[0104] The remaining raw materials and preparation process remain the same as in Example 1.

[0105] Performance Testing

[0106] After grinding the bio-based negative electrode materials prepared in Examples 1-7 and Comparative Examples 1-4, 8 parts of the ground powder were mixed with 1 part of acetylene black as a conductive agent and 1 part of CMC as a binder. The mixture was stirred to form a uniform slurry, which was then coated on a copper foil current collector. After vacuum drying, the slurry was pressed into a negative electrode sheet. In an argon atmosphere glove box, the positive electrode (lithium sheet), separator, and electrolyte were assembled into a button cell. The electrolyte contained LiPF6 as the solute and ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1 as the solvent. The separator was Celgard 2400. The electrochemical performance of the first cycle and after 500 cycles was tested using a constant current charge and discharge mode. The results are shown in Table 1:

[0107] Table 1

[0108]

[0109] As can be seen from Table 1, compared with Example 1, after adjusting the ratio of the doping precursor and the strontium-phosphorus hybrid phenolic resin, the experimental results of Examples 2-3 are slightly lower than those of Example 1; compared with Example 1, it can be seen from the results that whether the amount of nitrogen doping is too high or too low, it will have a certain negative effect on the material; compared with Example 1, the content of the synthetic components of the strontium-phosphorus hybrid phenolic resin is adjusted in Examples 6-7, and the results are all slightly lower, but still have a great advantage over the comparative example.

[0110] Compared with Example 1, Comparative Example 1 shows that since nitrogen atoms are embedded in the carbon skeleton, carbon-nitrogen active sites are formed, which significantly enhances the surface polarity of the material and improves the lithium ion adsorption capacity, thereby increasing the specific capacity. Therefore, after nitrogen doping, the performance of Comparative Example 1 is reduced; Compared with Example 1, Comparative Examples 2-3 show a significant downward trend in both the first discharge capacity, the first coulombic efficiency and the capacity retention rate after 2000 cycles. This is because the ionic crosslinking of strontium ions and phosphate groups forms a continuous inorganic network; and the inorganic network can condense with the phenolic resin to form a covalent crosslinking network to produce covalent- The ions act synergistically to form an organic-inorganic bicontinuous network structure, which greatly improves the chemical stability. This organic-inorganic bicontinuous network structure can not only improve the cycle life of the negative electrode material, but also enhance the electronic conductivity and increase the specific capacity of the material. Compared with Example 1, in Comparative Example 4, since the surface of the Sr-P inorganic phase modified with 3-carboxyphenylboronic acid contains boric acid groups, a boron-doped conductive carbon layer is generated after carbonization with phenolic resin, which can improve electronic conductivity. Therefore, the electrochemical performance of the material in Comparative Example 4 without the addition of 3-carboxyphenylboronic acid modification shows a significant decline.

[0111] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a bio-based negative electrode material, characterized in that: The following steps are involved: S1. Crush the biomass into small particles, soak in an anhydrous ethanol / deionized water mixed solution, ultrasonically treat, wash and dry to obtain biomass coarse powder; mix the biomass coarse powder with a sulfuric acid solution, heat and stir, filter and wash to obtain acid-pretreated biomass; The pretreated biomass is mixed with water, reacted at high temperature, cooled, filtered, and dried to obtain a porous hydrothermal carbon precursor; S2, immersing the hydrothermal carbon precursor in a urea solution, heating and stirring, filtering, and drying; pre-oxidizing in an air atmosphere, acid washing, and then washing with water until the pH is neutral, and drying to obtain a doping precursor; S3. Disperse the doping precursor, strontium-phosphorus hybrid phenolic resin and graphene in anhydrous ethanol, ball-mill and stir until the ethanol evaporates to obtain a composite solid mixture; under nitrogen protection, perform gradient temperature curing, then perform high-temperature carbonization, cool, wash and dry to obtain a bio-based negative electrode material.

2. The method for preparing a bio-based negative electrode material according to claim 1, characterized in that: The biomass is one or a combination of wood and straw; the crushed particle size is 1-5 mm; the volume ratio of anhydrous ethanol / deionized water is 1:1; the ultrasonic treatment time is 2-10 hours; and the drying is performed at 60-80° C. for 8-12 hours.

3. The method for preparing a bio-based negative electrode material according to claim 1, characterized in that: The mass ratio of the biomass coarse powder to the sulfuric acid solution is 1:(8-12); the concentration of the sulfuric acid solution is 2-3 mol / L; the stirring in S1 is stirring at 60-80°C for 4-6 hours; the mass ratio of the pretreated biomass to water is 1:(15-20); and the high-temperature reaction in S1 is reacting at 180-200°C for 12-14 hours.

4. The method for preparing a bio-based negative electrode material according to claim 1, wherein: The mass concentration of the urea solution is 10% to 30%; the heating and stirring in S2 is stirring at 100-120°C for 6-8 hours; the drying in S2 is drying at 95-105°C for 18-24 hours; the pre-oxidation is pre-oxidation at 220-250°C for 4-6 hours; and the pickling is pickling with 0.5-1 mol / L hydrochloric acid at 60-80°C for 2-3 hours.

5. The method for preparing a bio-based negative electrode material according to claim 1, characterized in that: The mass ratio of the doping precursor, strontium-phosphorus hybrid phenolic resin, graphene and anhydrous ethanol is 10:(1-3):(0.5-1.5):(80-120); the ball milling time is 2-3 hours; and the temperature for stirring until ethanol volatilizes is 80-85°C.

6. The method for preparing a bio-based negative electrode material according to claim 1, characterized in that: The gradient heating is to first heat to 120-130°C and then keep it for 1-1.5 hours, then heat to 180-200°C and keep it for 2-3 hours, with a heating rate of 5-10°C / min; the high-temperature carbonization is to heat to 900-1000°C at 5-10°C / min and carbonize for 2-3 hours under an inert gas atmosphere.

7. The method for preparing a bio-based negative electrode material according to claim 1, characterized in that: The strontium-phosphorus hybrid phenolic resin is prepared by the following steps: Step 1: Dissolve strontium chloride in ethanol, add triethylamine and mix well to obtain solution A; mix triethylamine and phosphoric acid in ethanol to form solution B; slowly add solution B dropwise to solution A, stir for 20-25 hours, and then centrifuge and wash to obtain gel A; Step 2: Dissolve 3-carboxyphenylboronic acid in methanol to obtain solution C; add the ethanol solution of gel A dropwise to solution C, stir for 12-16 hours, and then centrifuge to obtain modified gel A; The third step is to dissolve the phenolic resin in ethanol to obtain a phenolic resin ethanol solution; add the modified gel A ethanol solution dropwise to the phenolic resin ethanol solution, stir at 60-80° C. for 6-8 hours, centrifuge, wash and dry to obtain a strontium-phosphorus hybrid phenolic resin.

8. The method for preparing a bio-based negative electrode material according to claim 7, characterized in that: The amount ratio of strontium chloride, ethanol and triethylamine in the solution A is (8-12) g: (450-550) mL: (40-50) mL; the amount ratio of phosphoric acid, triethylamine and ethanol in the solution B is (8-10) mL: (20-40) mL: (200-250) mL; the amount ratio of 3-carboxyphenylboric acid and methanol in the solution C is (3-8) g: (250-350) mL; the amount ratio of gel A to ethanol in the ethanol solution of gel A is (5-15) g: (150-250) mL; the amount ratio of phenolic resin to ethanol in the ethanol solution of phenolic resin is (15-25) g: (350-450) mL; and the amount ratio of modified gel A to ethanol in the ethanol solution of modified gel A is (2-8) g: (80-120) mL.

9. A bio-based negative electrode material, characterized in that: The bio-based negative electrode material is prepared by the preparation method of any one of claims 1 to 8.

10. Use of the bio-based negative electrode material according to claim 9 in a lithium battery.

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