Porous carbon negative electrode material for lithium ion battery and preparation method of porous carbon negative electrode material

Abstract

The invention belongs to the technical field of lithium battery materials, and particularly discloses a porous carbon negative electrode material for a lithium ion battery and a preparation method of the porous carbon negative electrode material. Firstly, a copolymer is prepared through staged polymerization of a functional monomer and a chain transfer agent; secondly, taking nano molybdenum trioxide and zinc acetate dihydrate as raw materials, and performing ball milling and roasting to form a core-shell template; then, mixing and sieving the copolymer, the core-shell template, sodium chloride and the polymethyl methacrylate microspheres to obtain a precursor; and finally, carrying out multi-stage heating carbonization and post-treatment on the precursor to obtain the porous carbon negative electrode material. The obtained negative electrode material has a hierarchical porous structure and a high specific surface area, synergistic doping of multiple elements such as nitrogen, phosphorus and molybdenum is realized, rapid transmission and efficient storage of lithium ions are effectively promoted, the rate capability and cycling stability of a battery are remarkably improved, polarization impedance is reduced, and meanwhile, the electronic conductivity and interface stability of the material are further optimized; excellent comprehensive electrochemical performance is shown in the application of a high-energy-density lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery materials, and more specifically, relates to a porous carbon negative electrode material for lithium ion batteries and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy industry, lithium-ion batteries have become the mainstream technology in the energy storage field due to their high energy density, long cycle life, and environmental friendliness. As a core component of lithium-ion batteries, the performance of anode materials directly affects the battery's energy density, rate capability, and cycle stability. Although traditional graphite anode materials have been commercialized, their theoretical specific capacity is relatively low, at only 372mAh / g. They are also prone to problems such as lithium dendrite growth and structural collapse under high-rate charge and discharge conditions, making them difficult to meet the development needs of high-energy-density batteries.

[0003] Porous carbon materials have shown significant advantages in the field of lithium storage due to their adjustable pore structure, rich surface chemical properties and good electrical conductivity. By constructing a hierarchical porous structure, the lithium ion diffusion distance can be effectively shortened, active sites can be increased and volume expansion can be buffered, while heteroatom doping can adjust the electronic structure of carbon materials, improve surface wettability and lithium storage activity. However, the porous carbon materials prepared by existing technologies still have key shortcomings. For example, the traditional template method is difficult to achieve precise control of multi-level pores, and the single pore structure leads to limited electrolyte wettability and ion transfer efficiency; the synergistic optimization effect of single element doping on electronic conductivity and lithium storage sites is limited, and there is a lack of synergistic effect between multiple elements; in addition, the interface stability between carbon materials and electrolytes is insufficient, which easily triggers the repeated generation of SEI films, resulting in increased polarization impedance and capacity attenuation. Therefore, the present invention provides a porous carbon negative electrode material for lithium-ion batteries and a preparation method thereof to solve the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a porous carbon negative electrode material for lithium-ion batteries and a preparation method thereof. The material obtained by this preparation method has a hierarchical porous structure and a high specific surface area, and realizes the synergistic doping of multiple elements such as nitrogen, phosphorus, and molybdenum, which effectively promotes the rapid transmission and efficient storage of lithium ions, significantly improves the battery rate performance and cycle stability, reduces polarization impedance, and further optimizes the electronic conductivity and interface stability of the material, thereby showing excellent comprehensive electrochemical performance in high-energy-density lithium-ion battery applications.

[0005] In a first aspect, the present invention provides a method for preparing a porous carbon negative electrode material for a lithium ion battery, which adopts the following technical solution:

[0006] A method for preparing a porous carbon negative electrode material for a lithium ion battery comprises the following steps:

[0007] S1. Dissolve the functional monomer and chain transfer agent in N,N-dimethylformamide, add acrylonitrile and ammonium persulfate, and react at 68-72°C under nitrogen for 3-5 hours. Then add acrylonitrile and azobisisobutyronitrile, raise the temperature to 83-87°C, and react for 5-7 hours. Add the reaction solution into 5-7 times the volume of deionized water for precipitation, crush the gel, extract with Soxhlet, and dry to obtain a copolymer;

[0008] S2, mixing nano-molybdenum trioxide and zinc acetate dihydrate by ball milling, calcining in air at 280-320° C. for 1-3 h, and then washing and filtering to obtain a core-shell template;

[0009] S3, taking the copolymer, core-shell template, sodium chloride and polymethyl methacrylate microspheres, ball milling and mixing them, and then passing them through a 150-200 mesh sieve to obtain a precursor;

[0010] S4. Under argon protection, the precursor is heated to 580-620° C. at 4-6° C. / min and kept warm for 1.5-2 h, then switched to mixed gas, heated to 730-770° C. at 9-11° C. / min and kept warm for 0.8-1.2 h, then heated to 930-970° C. at 4-6° C. / min and kept warm for 1.5-2.5 h, treated with oxalic acid solution at 75-85° C. for 3.5-4.5 h, washed with boiling water at 90-100° C. for 6-8 h, and ball-milled through a 170-200 mesh sieve to obtain a porous carbon negative electrode material for lithium ion batteries;

[0011] Preferably, the preparation steps of the functional monomer in step S1 are:

[0012] A1. Dissolve 2-pyridinecarboxaldehyde and 4-aminopyridine in anhydrous ethanol, add lanthanum trifluoromethanesulfonate, and reflux at 68-72°C for 3-5 hours. After cooling, wash and filter the reaction solution to obtain an intermediate;

[0013] A2. Dissolve the intermediate in tetrahydrofuran, control the temperature at -12 to -8°C in an ice bath, add dropwise a tetrahydrofuran solution of phenylphosphonyl dichloride, maintain the temperature at -7 to -3°C, raise the temperature to 23-27°C after addition, and react for 11-13 hours. Adjust the pH of the reaction solution to 7-8 with saturated sodium bicarbonate solution, extract, dry, filter, distill under reduced pressure, wash, and finally dry in vacuo to obtain a functional monomer.

[0014] Preferably, the preparation step of the chain transfer agent in step S1 is: dissolving sodium lignin sulfonate and 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid in N,N-dimethylformamide, reacting at 78-82° C. under nitrogen protection for 5-7 hours, adding 4-6 times the volume of acetone to precipitate the reaction solution, filtering, washing and vacuum drying to obtain the chain transfer agent.

[0015] Preferably, in step S1, the components by weight include 24-28 parts of functional monomer, 5-8 parts of chain transfer agent, 80-100 parts of N,N-dimethylformamide, 64-70 parts of acrylonitrile, 0.4-0.6 parts of ammonium persulfate, and 0.08-0.12 parts of azobisisobutyronitrile.

[0016] Preferably, in step S2, 9-11 parts by weight of nano-molybdenum trioxide and 14-16 parts by weight of zinc acetate dihydrate are used.

[0017] Preferably, in step S3, the components by weight are 28-32 parts of copolymer, 14-16 parts of core-shell template, 19-23 parts of sodium chloride and 18-22 parts of polymethyl methacrylate microspheres, and in step S4, the mixed gas is composed of ammonia and argon in a volume ratio of 1:(6-8).

[0018] Preferably, in step A1, the components comprised by weight are 45-55 parts of 2-pyridinecarboxaldehyde, 22-28 parts of 4-aminopyridine, 90-100 parts of anhydrous ethanol, and 1-3 parts of lanthanum trifluoromethanesulfonate.

[0019] Preferably, in step A2, the components are 5-7 parts by weight of the intermediate, 35-40 parts by weight of tetrahydrofuran, and 18-22 parts by weight of a 30-35 wt% tetrahydrofuran solution of phenylphosphonic dichloride.

[0020] Preferably, in the chain transfer agent preparation step, the components include 18-22 parts by weight of sodium lignin sulfonate, 4-6 parts by weight of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid, and 90-100 parts by weight of N,N-dimethylformamide.

[0021] In a second aspect, the present invention further provides a porous carbon negative electrode material for a lithium ion battery, which adopts the following technical solution:

[0022] A porous carbon negative electrode material for lithium ion batteries is prepared by the above preparation method.

[0023] In summary, the present invention has the following beneficial effects:

[0024] 1. The present invention prepares a porous carbon anode material by polymerizing functional monomers and chain transfer agents in stages, combining them with a core-shell template formed by nano-molybdenum trioxide and zinc acetate dihydrate, sodium chloride, and polymethyl methacrylate microspheres for composite pore formation. This material undergoes gradient carbonization and post-treatment to produce a porous carbon anode material. In this material, the core-shell template pyrolyzes to form a mesoporous and macroporous framework, and its residual molybdenum species migrate to the carbon layer to achieve atomic-level doping. Sodium chloride melt etching creates a microporous network, which synergizes with the macropores formed by the thermal decomposition of polymethyl methacrylate to form hierarchical mass transfer channels, significantly improving specific surface area and electrolyte wettability. The nitrogen and phosphorus heterocyclic structures introduced by the functional monomers are converted into pyridinic nitrogen, graphitic nitrogen, and CP bond active sites during carbonization. These structures, in synergy with molybdenum doping, optimize the electron cloud distribution, reduce the lithium ion adsorption energy barrier, and promote surface capacitance-dominated rapid lithium storage behavior. The multi-level pores and rigid carbon framework jointly buffer volume strain, inhibit structural pulverization, and ensure long-term cycling stability.

[0025] 2. The functional monomer of the present invention is prepared by condensing 2-pyridinecarboxaldehyde and 4-aminopyridine through lanthanide catalysis and then reacting with phenylphosphonyl dichloride. Its rigid pyridine and imine skeletons maintain structural integrity during the carbonization process, and provide fixed-point doping sites of nitrogen and phosphorus elements for the copolymer as heteroatom doping precursors. The intermolecular forces of the copolymer are also enhanced through the conjugated structure, so that the carbon skeleton formed after carbonization has a more ordered graphitized structure tendency, thereby improving the electronic conductivity; the nitrogen atoms in the pyridine ring exist in the carbon matrix in three forms: pyrrole type, pyridine type and graphite type, respectively, by providing lone pairs of electrons, forming defect sites and enhancing structural stability, thereby synergistically improving the electron transmission efficiency and lithium storage capacity of the material; the phosphorus atoms in the phosphono group are embedded in the carbon network in the C3-P=O configuration, acting as Lewis acid sites to enhance the chemical adsorption of lithium ions, thereby achieving the dual effects of physical lithium storage and chemical lithium storage during the charge and discharge process.

[0026] 3. The chain transfer agent of the present invention is prepared by grafting sodium lignin sulfonate with a thiocarbonyl-containing compound. The molecular self-assembly effect induced by the sulfonic acid groups causes the copolymer to form a cross-linked network, which is then converted into a three-dimensional continuous conductive framework after carbonization. The controllable chain scission characteristics of the thiocarbonyl groups regulate the polymer molecular weight distribution and avoid pore closure caused by excessive graphitization of the carbon skeleton. The lignin-derived biomass carbon source provides intrinsic oxygen and sulfur doping sites. The sulfur atoms enhance the reaction activity of the carbon layer edge in the thiophene-S configuration, synergistically optimizing the SEI membrane components with nitrogen and phosphorus doping to form a Li3N-Li2S composite interface layer with high ionic conductivity. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used are purchased from conventional biochemical reagent stores unless otherwise specified. The quantitative experiments in the following examples were all repeated three times, and the data are the average or mean ± standard deviation of the three repeated experiments.

[0029] Nano-molybdenum trioxide was purchased from Zhejiang Yamei Nano Technology Co., Ltd., CAS No. 1313-27-5;

[0030] Zinc acetate dihydrate was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd., product number PA01180;

[0031] Polymethyl methacrylate microspheres were purchased from Wenzhou Pinzhuo Biotechnology Co., Ltd., CAS No. 25188-98-1.

[0032] Lanthanum trifluoromethanesulfonate was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number S47858;

[0033] Phenylphosphonic acid dichloride, purchased from Hubei Kewode Chemical Co., Ltd., CAS No. 824-72-6;

[0034] 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid was purchased from Beijing Bailingwei Technology Co., Ltd., product number 16-0415.

[0035] Example 1

[0036] A method for preparing a porous carbon negative electrode material for a lithium ion battery comprises the following steps:

[0037] S1. Dissolve 24 parts of functional monomer and 5 parts of chain transfer agent in 80 parts of N,N-dimethylformamide, add 32 parts of acrylonitrile and 0.4 parts of ammonium persulfate, and react at 68°C, 400 rpm and 32 parts of acrylonitrile under nitrogen protection for 5 hours. Then add 0.08 parts of azobisisobutyronitrile, raise the temperature to 83°C and react for 7 hours. After the reaction is completed, add the reaction solution into 5 times the volume of deionized water relative to the reaction solution for precipitation. After the gel is crushed, it is extracted with Soxhlet and dried to obtain a copolymer;

[0038] S2, placing 9 parts of nano-molybdenum trioxide and 14 parts of zinc acetate dihydrate in a ball mill, mixing at 300 r / min for 4 hours, transferring the mixture to a muffle furnace, calcining it in an air atmosphere at 280°C for 3 hours, cooling it naturally, washing it with deionized water, and filtering it to obtain a core-shell template;

[0039] S3, adding 28 parts of copolymer, 14 parts of core-shell template, 20 parts of sodium chloride and 18 parts of polymethyl methacrylate microspheres into a ball mill, mixing at 400 r / min for 4 h, and passing through a 150 mesh sieve to obtain a precursor;

[0040] S4. Place the precursor in a tubular furnace, and under argon protection, heat it to 580°C at a heating rate of 4°C / min and keep it warm for 2 hours. Switch to a mixture of ammonia and argon with a volume ratio of 1:6, heat it to 730°C at a heating rate of 9°C / min and keep it warm for 1.2 hours. Heat it again and heat it to 930°C at a heating rate of 4°C / min and keep it warm for 2.5 hours. After carbonization, wait for the product to cool to room temperature, take it out and add it to 0.1mol / L oxalic acid solution, treat it at 200rpm and 75°C for 4.5 hours. After treatment, filter it and wash it with 90°C boiling water for 8 hours. Change the water every 2 hours during the washing process. Finally, ball mill the product at 200rpm for 40 minutes and pass it through a 150-mesh sieve to obtain a porous carbon negative electrode material for lithium-ion batteries.

[0041] The preparation steps of the functional monomer in step S1 are as follows:

[0042] A1. Add 45 parts of 2-pyridinecarboxaldehyde, 22 parts of 4-aminopyridine, 90 parts of anhydrous ethanol and 1 part of lanthanum trifluoromethanesulfonate to a three-necked flask, and reflux at 68° C. for 5 h. During the reaction, use a condensing reflux apparatus to maintain a nitrogen atmosphere. After the reaction, the reaction solution is cooled to room temperature, then washed with deionized water and filtered to obtain an intermediate;

[0043] A2. Dissolve 7 parts of the intermediate in 35 parts of tetrahydrofuran, control the temperature at -8°C in an ice bath, and add 18 parts of a 30wt% tetrahydrofuran solution of phenylphosphonic dichloride dropwise at a rate of 2 mL / min, maintaining the temperature at -3°C during the addition process. After the addition is completed, raise the temperature to 23°C and continue the reaction for 13 hours. After the reaction is completed, adjust the pH to 7 with a saturated sodium bicarbonate solution, extract, dry the organic phase with anhydrous sodium sulfate, filter, distill and wash under reduced pressure, and finally dry in vacuo to obtain the functional monomer.

[0044] Wherein, the step of chain transfer agent in step S1 is:

[0045] 22 parts of sodium lignin sulfonate, 6 parts of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid and 90 parts of N,N-dimethylformamide were added to a three-necked flask, and the reaction was carried out at 78° C. under nitrogen protection for 7 hours. After the reaction was completed, the reaction solution was added to acetone with a volume 5 times that of the reaction solution for precipitation, and the chain transfer agent was obtained by filtering, washing and vacuum drying.

[0046] Example 2

[0047] A method for preparing a porous carbon negative electrode material for a lithium ion battery comprises the following steps:

[0048] S1. Dissolve 25 parts of functional monomer and 6 parts of chain transfer agent in 85 parts of N,N-dimethylformamide, add 33 parts of acrylonitrile and 0.5 parts of ammonium persulfate, and react at 69°C and 410 rpm under nitrogen protection for 4.5 hours. Then add 33 parts of acrylonitrile and 0.09 parts of azobisisobutyronitrile, raise the temperature to 84°C, keep the nitrogen flow rate and stirring speed unchanged, and continue to react for 6.8 hours. After the reaction is completed, add the reaction solution to deionized water with a volume 6 times that of the reaction solution for precipitation. After the gel is crushed, it is extracted with Soxhlet and dried to obtain a copolymer;

[0049] S2. Place 10 parts of nano-molybdenum trioxide and 15 parts of zinc acetate dihydrate in a ball mill and mix them at 310 r / min for 3.8 hours. Transfer the mixture to a muffle furnace and calcine it in an air atmosphere at 290° C. for 2.8 hours. After natural cooling, wash it with deionized water and filter it to obtain a core-shell template.

[0050] S3, adding 29 parts of copolymer, 15 parts of core-shell template, 21 parts of sodium chloride and 19 parts of polymethyl methacrylate microspheres into a ball mill, mixing at 410 r / min for 3.8 h, and passing through a 150 mesh sieve to obtain a precursor;

[0051] S4. Place the precursor in a tubular furnace, and under argon protection, heat it to 590°C at a heating rate of 5°C / min and keep it warm for 1.9 hours. Switch to a mixture of ammonia and argon with a volume ratio of 1:7, heat it to 740°C at a heating rate of 10°C / min and keep it warm for 1.1 hours. Heat it again and heat it to 940°C at a heating rate of 5°C / min and keep it warm for 2.4 hours. After the carbonization is completed, wait for the product to cool to room temperature, take it out and add it to 0.2mol / L oxalic acid solution, treat it at 220rpm and 78°C for 4.2 hours. After the treatment is completed, filter it and wash it with 93°C boiling water for 7.6 hours. Change the water every 2 hours during the washing process. Finally, ball mill the product at 220rpm for 36 minutes and pass it through a 170-mesh sieve to obtain a porous carbon negative electrode material for lithium-ion batteries.

[0052] The preparation steps of the functional monomer in step S1 are as follows:

[0053] A1. Add 47 parts of 2-pyridinecarboxaldehyde, 24 parts of 4-aminopyridine, 95 parts of anhydrous ethanol and 2 parts of lanthanum trifluoromethanesulfonate to a three-necked flask, and reflux at 69° C. for 4.8 hours. During the reaction, use a condensing reflux apparatus to maintain a nitrogen atmosphere. After the reaction, the reaction solution is cooled to room temperature, then washed with deionized water and filtered to obtain an intermediate;

[0054] A2. Dissolve 6 parts of the intermediate in 36 parts of tetrahydrofuran, control the temperature at -10°C in an ice bath, and add 19 parts of a 31wt% tetrahydrofuran solution of phenylphosphonic dichloride dropwise at a rate of 3 mL / min, maintaining the temperature at -4°C during the addition process. After the addition is completed, the temperature is raised to 24°C and the reaction is continued for 12 hours. After the reaction is completed, the pH is adjusted to 7.5 with a saturated sodium bicarbonate solution, and then extracted. The organic phase is dried over anhydrous sodium sulfate, filtered, distilled under reduced pressure, washed, and finally dried in vacuo to obtain a functional monomer.

[0055] Wherein, the step of chain transfer agent in step S1 is:

[0056] 19 parts of sodium lignin sulfonate, 5 parts of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid and 95 parts of N,N-dimethylformamide were added to a three-necked flask, and the reaction was carried out at 79° C. under nitrogen protection for 6.8 hours. After the reaction was completed, the reaction solution was added to acetone with a volume 6 times that of the reaction solution for precipitation, and the chain transfer agent was obtained by filtering, washing and vacuum drying.

[0057] Example 3

[0058] A method for preparing a porous carbon negative electrode material for a lithium ion battery comprises the following steps:

[0059] S1. Dissolve 28 parts of functional monomer and 8 parts of chain transfer agent in 100 parts of N,N-dimethylformamide, add 35 parts of acrylonitrile and 0.6 parts of ammonium persulfate, react at 72°C, under nitrogen protection and stirring at 450 rpm for 3 hours, then add 35 parts of acrylonitrile and 0.12 parts of azobisisobutyronitrile, raise the temperature to 87°C, keep the nitrogen flow rate and stirring speed unchanged, and continue to react for 5 hours. After the reaction is completed, add the reaction solution into deionized water with a volume 7 times that of the reaction solution for precipitation, crush the gel, extract it with Soxhlet, and dry it to obtain a copolymer;

[0060] S2. Place 11 parts of nano-molybdenum trioxide and 16 parts of zinc acetate dihydrate in a ball mill and mix them at 340 r / min for 2 h. Transfer the mixture to a muffle furnace and calcine it at 320° C. in air atmosphere for 1 h. After natural cooling, wash it with deionized water and filter it to obtain a core-shell template.

[0061] S3, adding 32 parts of copolymer, 16 parts of core-shell template, 23 parts of sodium chloride and 22 parts of polymethyl methacrylate microspheres into a ball mill, mixing at 440 r / min for 4 h, and passing through a 200 mesh sieve to obtain a precursor;

[0062] S4. Place the precursor in a tubular furnace, and under argon protection, heat it to 620°C at a heating rate of 6°C / min and keep it warm for 1.5 hours. Switch to a mixture of ammonia and argon with a volume ratio of 1:8, heat it to 770°C at a heating rate of 11°C / min and keep it warm for 0.8 hours. Heat it again and heat it to 970°C at a heating rate of 6°C / min and keep it warm for 1.5 hours. After carbonization, wait for the product to cool to room temperature, take it out and add it to 0.3 mol / L oxalic acid solution, treat it at 300 rpm and 85°C for 3.5 hours. After treatment, filter it and wash it with 100°C boiling water for 6 hours. Change the water every 2 hours during the washing process. Finally, ball mill the product at 260 rpm for 30 minutes and pass it through a 200 mesh sieve to obtain a porous carbon negative electrode material for lithium-ion batteries.

[0063] The preparation steps of the functional monomer in step S1 are as follows:

[0064] A1. Add 55 parts of 2-pyridinecarboxaldehyde, 28 parts of 4-aminopyridine, 100 parts of anhydrous ethanol and 3 parts of lanthanum trifluoromethanesulfonate to a three-necked flask, and reflux at 72° C. for 3 h. During the reaction, use a condensing reflux apparatus to maintain a nitrogen atmosphere. After the reaction, the reaction solution is cooled to room temperature, then washed with deionized water and filtered to obtain an intermediate;

[0065] A2. Dissolve 7 parts of the intermediate in 40 parts of tetrahydrofuran, control the temperature at -12 in an ice bath, and add 22 parts of a 35wt% tetrahydrofuran solution of phenylphosphonic dichloride dropwise at a rate of 2 mL / min, maintaining the temperature at -7°C during the addition process. After the addition is completed, raise the temperature to 27°C and continue the reaction for 11 hours. After the reaction is completed, adjust the pH to 8 with a saturated sodium bicarbonate solution, extract, dry the organic phase with anhydrous sodium sulfate, filter, distill and wash under reduced pressure, and finally vacuum dry to obtain a functional monomer.

[0066] Wherein, the step of chain transfer agent in step S1 is:

[0067] 22 parts of sodium lignin sulfonate, 6 parts of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid and 100 parts of N,N-dimethylformamide were added to a three-necked flask, and the mixture was reacted at 82° C. under nitrogen protection for 5 hours. After the reaction was completed, the reaction solution was added to acetone with a volume 7 times that of the reaction solution for precipitation, and the chain transfer agent was obtained by filtering, washing and vacuum drying.

[0068] Example 4

[0069] A method for preparing a porous carbon negative electrode material for a lithium ion battery comprises the following steps:

[0070] S1. Dissolve 28 parts of functional monomer and 8 parts of chain transfer agent in 100 parts of N,N-dimethylformamide, add 34 parts of acrylonitrile and 0.5 parts of ammonium persulfate, react at 72°C, under nitrogen protection and stirring at 450 rpm for 3.5 hours, then add 34 parts of acrylonitrile and 0.1 parts of azobisisobutyronitrile, raise the temperature to 85°C, keep the nitrogen flow rate and stirring speed unchanged, and continue to react for 5 hours. After the reaction is completed, add the reaction solution into deionized water with a volume 7 times that of the reaction solution for precipitation, crush the gel, extract it with Soxhlet, and dry it to obtain a copolymer;

[0071] S2. Place 10 parts of nano-molybdenum trioxide and 15 parts of zinc acetate dihydrate in a ball mill and mix them at 340 r / min for 2.5 hours. Transfer the mixture to a muffle furnace and calcine it at 320°C in air atmosphere for 1 hour. After natural cooling, wash it with deionized water and filter it to obtain a core-shell template.

[0072] S3, adding 32 parts of copolymer, 15 parts of core-shell template, 22 parts of sodium chloride and 20 parts of polymethyl methacrylate microspheres into a ball mill, ball milling at 440 r / min for 3 h, and passing through a 170 mesh sieve to obtain a precursor;

[0073] S4. Place the precursor in a tubular furnace, and under argon protection, heat it to 600°C at a heating rate of 5°C / min and keep it warm for 1.6 hours. Switch to a mixture of ammonia and argon with a volume ratio of 1:8, heat it to 760°C at a heating rate of 10°C / min and keep it warm for 1 hour. Heat it again and heat it to 960°C at a heating rate of 5°C / min and keep it warm for 2 hours. After carbonization, wait for the product to cool to room temperature, take it out and add it to 0.3 mol / L oxalic acid solution, treat it at 300 rpm and 85°C for 4 hours. After treatment, filter it and wash it with 100°C boiling water for 6 hours. Change the water every 2 hours during the washing process. Finally, ball mill the product at 260 rpm for 32 minutes and pass it through a 200 mesh sieve to obtain a porous carbon negative electrode material for lithium-ion batteries.

[0074] The preparation steps of the functional monomer in step S1 are as follows:

[0075] A1. Add 55 parts of 2-pyridinecarboxaldehyde, 28 parts of 4-aminopyridine, 100 parts of anhydrous ethanol and 2 parts of lanthanum trifluoromethanesulfonate to a three-necked flask, and reflux at 72° C. for 3.4 hours. During the reaction, a condensing reflux apparatus is used to maintain a nitrogen atmosphere. After the reaction is completed, the reaction solution is cooled to room temperature, then washed with deionized water and filtered to obtain an intermediate;

[0076] A2. Dissolve 6 parts of the intermediate in 40 parts of tetrahydrofuran, control the temperature at -10°C in an ice bath, and add 21 parts of a 32wt% tetrahydrofuran solution of phenylphosphonic dichloride dropwise at a rate of 2 mL / min, maintaining the temperature at -6°C during the addition process. After the addition is completed, raise the temperature to 26°C and continue the reaction for 11. After the reaction is completed, adjust the pH to 7 with a saturated sodium bicarbonate solution, extract, and dry the organic phase over anhydrous sodium sulfate, filter, distill and wash under reduced pressure, and finally dry in vacuo to obtain a functional monomer.

[0077] Wherein, the step of chain transfer agent in step S1 is:

[0078] 22 parts of sodium lignin sulfonate, 5 parts of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid and 100 parts of N,N-dimethylformamide were added to a three-necked flask and reacted at 80°C under nitrogen protection for 6 hours. After the reaction, the reaction solution was added to acetone with a volume 7 times that of the reaction solution for precipitation, and the chain transfer agent was obtained by filtering, washing and vacuum drying.

[0079] Comparative Example 1

[0080] A method for preparing a porous carbon anode material for lithium-ion batteries differs from Example 4 in that the functional monomer synthesis step is omitted, and pyridine monomers are directly involved in the polymerization reaction. Specifically, in step S1, 28 parts of 4-vinylpyridine are directly substituted for the functional monomer. The remaining chain transfer agent, reaction solvent, and polymerization conditions are the same as in Example 4.

[0081] Comparative Example 2

[0082] A method for preparing a porous carbon negative electrode material for a lithium-ion battery differs from Example 4 in that the phenylphosphonyl dichloride reaction is omitted from the preparation of the functional monomer. Specifically, in the synthesis of the functional monomer, only the reflux reaction of 2-pyridinecarboxaldehyde and 4-aminopyridine is performed to produce the intermediate, and the subsequent reaction step of the intermediate with phenylphosphonyl dichloride is omitted, i.e., the introduction path for phosphorus doping is omitted. The unmodified intermediate is subsequently used to replace the fully synthesized functional monomer in the preparation of the copolymer. The remaining chain transfer agent, polymerization reaction, and post-treatment conditions are the same as those in Example 4.

[0083] Comparative Example 3

[0084] A method for preparing a porous carbon anode material for lithium-ion batteries differs from Example 4 in that, in the preparation of the core-shell template, the ball milling and calcination process of nano-molybdenum trioxide and zinc acetate dihydrate is abandoned, and instead, equal parts by weight of zinc oxide powder are used as a single template. Specifically, in step S2, the core-shell template is directly replaced with 15 parts of zinc oxide powder, without ball milling and high-temperature calcination. Subsequently, the single template is mixed with other components to prepare a precursor, which is then carbonized. The remaining conditions for copolymer synthesis, pore-forming agent addition, and carbonization post-treatment are the same as those in Example 4.

[0085] Comparative Example 4

[0086] A method for preparing a porous carbon negative electrode material for lithium-ion batteries differs from Example 4 in that, during the chain transfer agent preparation process, unmodified sodium lignin sulfonate is used directly in the polymerization reaction, eliminating the grafting reaction step with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid. Specifically, in step S1, 8 parts of unmodified sodium lignin sulfonate are directly used in place of the modified chain transfer agent and added to the polymerization system to participate in the reaction. The remaining functional monomers, polymerization reaction conditions, and post-processing steps are the same as those in Example 4.

[0087] Comparative Example 5

[0088] A method for preparing a porous carbon anode material for lithium-ion batteries differs from Example 4 in that polymethyl methacrylate microspheres are not added during precursor preparation in step S3. Specifically, sodium chloride is used as the sole pore-forming agent for ball milling with the copolymer and core-shell template, without the addition of polymethyl methacrylate microspheres. The remaining conditions for copolymer synthesis, core-shell template preparation, and carbonization post-treatment are the same as those in Example 4.

[0089] Comparative Example 6

[0090] A method for preparing a porous carbon negative electrode material for a lithium-ion battery differs from Example 4 in that nano-molybdenum trioxide is not used in step S2. Specifically, 15 parts of zinc acetate dihydrate are ball-milled and calcined at high temperature, without adding nano-molybdenum trioxide. The molybdenum-free template is then mixed with other components to prepare a precursor and carbonized. The remaining copolymer synthesis, pore-forming agent addition, and carbonization post-treatment conditions are the same as those in Example 4.

[0091] The porous carbon negative electrode materials for lithium ion batteries prepared in Examples 1-4 and Comparative Examples 1-6 were tested for pore structure performance. The test results are shown in Table 1.

[0092] The porous carbon negative electrode materials for lithium-ion batteries prepared in Examples 1-4 and Comparative Examples 1-6 were mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was prepared using N-methylpyrrolidone as a solvent to form a slurry. The slurry was then coated onto copper foil and, after drying, cut into electrode sheets. CR2032 button cells were assembled in a glove box using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and a 1 mol / L, 1:1, volume ratio of LiPF6-EC / DEC as the electrolyte. The electrochemical performance of the assembled lithium-ion batteries was tested. The test results are shown in Table 2.

[0093] Table 1

[0094] Test items <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Micropore volume (cm 3 / g)]]> <![CDATA[Mesopore volume (cm 3 / g)]]> <![CDATA[Total pore volume (cm 3 / g)]]> Conductivity (S / cm) Example 1 2585 0.77 1.22 2.02 8.83 Example 2 2693 0.78 1.25 2.05 9.54 Example 3 2829 0.81 1.28 2.25 9.96 Example 4 2952 0.83 1.30 2.28 11.05 Comparative Example 1 2311 0.75 1.18 2.01 6.82 Comparative Example 2 2451 0.77 1.21 2.07 7.53 Comparative Example 3 2127 0.73 1.12 1.95 6.35 Comparative Example 4 2414 0.76 1.16 1.99 5.97 Comparative Example 5 2517 0.79 1.14 1.81 8.14 Comparative Example 6 2363 0.74 1.19 2.04 7.12

[0095] Table 2

[0096] Test items First discharge capacity (mAh / g) 1C cycle 100 times capacity retention rate (%) 5C rate capacity (mAh / g) Charge transfer resistance (Ω) Example 1 685 92.55 518 18.26 Example 2 705 93.86 538 16.55 Example 3 728 95.27 562 14.34 Example 4 782 97.68 605 11.73 Comparative Example 1 645 87.49 450 27.63 Comparative Example 2 655 88.77 465 26.88 Comparative Example 3 595 82.22 405 36.22 Comparative Example 4 632 86.55 438 29.49 Comparative Example 5 668 89.16 480 20.37 Comparative Example 6 610 85.31 420 32.50

[0097] Judging from the test data in Tables 1 and 2, the synergistic optimization effect of material structure and performance is significant. Examples 1-4 exhibit excellent pore structure characteristics and electrochemical performance, with Example 4 being the best. Its high specific surface area of ​​2952m² / g, balanced micropore and mesopore volumes of 0.83cm³ / g and 1.30cm³ / g, and high total pore volume of 2.28cm³ / g indicate that the hierarchical pore channel is successfully constructed, which is due to the synergistic pore-forming effect of the core-shell template, sodium chloride, and polymethyl methacrylate microspheres. The core-shell template pyrolysis forms a mesoporous skeleton and residual molybdenum doping sites, sodium chloride melt etching produces a microporous network, and polymethyl methacrylate decomposition contributes to macroporous channels. The three together optimize the ion transport path and electrolyte wettability. At the same time, the high electronic conductivity of 11.05 S / cm and the low charge transfer resistance of 11.73Ω in Example 4 verify the synergistic effect of multi-element doping with nitrogen, phosphorus, and molybdenum, that is, the pyridinic nitrogen / graphitic nitrogen and CP bond active sites provided by the functional monomer optimize the electron cloud distribution, molybdenum doping improves the conductivity of the carbon layer, and sulfur doping derived from the chain transfer agent promotes the formation of a Li3N-Li2S composite interface layer with high ionic conductivity, which jointly reduce the lithium ion diffusion energy barrier.

[0098] In contrast, in Comparative Example 1, 4-vinylpyridine was directly used to replace the functional monomer, which lost the advantages of phosphorus doping and rigid skeleton, resulting in a 38% decrease in electronic conductivity and a 10% decrease in cycle retention rate, proving that the molecular design of the functional monomer is indispensable for the synergistic doping of multiple elements; in Comparative Example 2, the phenylphosphine dichloride modification step was omitted, and no phosphorus doping was introduced, and the charge transfer impedance increased by 129%, highlighting the key role of phosphorus atoms as Lewis acid sites for lithium ion chemical adsorption; in Comparative Example 3, single zinc oxide was used to replace the core-shell template, resulting in a 28% decrease in specific surface area and a 33% attenuation of 5C rate capacity, reflecting the core-shell structure. The double failure of mesopore construction and molybdenum doping; Comparative Example 4 uses unmodified sodium lignin sulfonate, and due to the lack of molecular weight regulation of thiocarbonyl and contribution of sulfur doping, the electronic conductivity decreases by 46% and the interface impedance increases by 151%; Comparative Example 5 does not add polymethyl methacrylate microspheres, the mesopore volume is reduced by 12% and the loss of macropores causes the total pore volume to decrease by 21%, confirming that the hierarchical channels require multi-template coordination; Comparative Example 6 omits nano-molybdenum trioxide, and due to the lack of molybdenum species doping and template skeleton support, the cycle retention rate decreases by 12%, revealing the necessity of molybdenum element to stabilize the carbon skeleton and improve interface stability.

[0099] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a porous carbon negative electrode material for a lithium ion battery, characterized in that: The following steps are involved: S1. Dissolving functional monomers and a chain transfer agent in N,N-dimethylformamide, adding acrylonitrile and ammonium persulfate, carrying out a first-stage polymerization reaction under nitrogen protection, then adding acrylonitrile and azobisisobutyronitrile to carry out a second-stage polymerization reaction at elevated temperature, precipitating the reaction solution in deionized water, crushing the gel, extracting with Soxhlet, and drying to obtain a copolymer; S2, mixing nano-molybdenum trioxide and zinc acetate dihydrate by ball milling, calcining, washing and filtering to obtain a core-shell template; S3, taking the copolymer, core-shell template, sodium chloride and polymethyl methacrylate microspheres, mixing them by ball milling and sieving to obtain a precursor; S4. Under an inert atmosphere, the precursor is first heated to a first carbonization temperature and kept warm, then switched to a mixed gas atmosphere and heated to a second carbonization temperature and kept warm, and then heated to a third carbonization temperature and kept warm. The product is treated with an oxalic acid solution, washed with boiling water, ball-milled and sieved to obtain a porous carbon negative electrode material for lithium-ion batteries.

2. The preparation method according to claim 1, characterized in that The functional monomer in step S1 is prepared by the following steps: A1. Dissolve 2-pyridinecarboxaldehyde and 4-aminopyridine in anhydrous ethanol, add lanthanum trifluoromethanesulfonate and reflux. After cooling, wash and filter the reaction solution to obtain an intermediate; A2. The intermediate is dissolved in tetrahydrofuran, and a tetrahydrofuran solution of phenylphosphonyl dichloride is added dropwise under ice bath conditions. The reaction is maintained at a low temperature and then the temperature is raised to continue the reaction. After adjusting the pH of the reaction solution, the functional monomer is obtained after extraction, drying, filtering, vacuum distillation, washing, and vacuum drying.

3. The preparation method according to claim 1, characterized in that The chain transfer agent in step S1 is prepared by dissolving sodium lignin sulfonate and a thiocarbonyl-containing compound in N,N-dimethylformamide, reacting under nitrogen protection, precipitating the reaction solution in acetone, filtering, washing and vacuum drying.

4. The preparation method according to claim 1, characterized in that In step S1, the components by weight include 24-28 parts of functional monomers, 5-8 parts of chain transfer agents, 80-100 parts of N,N-dimethylformamide, 64-70 parts of acrylonitrile, 0.4-0.6 parts of ammonium persulfate, and 0.08-0.12 parts of azobisisobutyronitrile.

5. The preparation method according to claim 1, characterized in that In step S2, the components are 9-11 parts by weight of nano-molybdenum trioxide and 14-16 parts by weight of zinc acetate dihydrate.

6. The preparation method according to claim 1, characterized in that In step S3, the weight ratio of the copolymer is 28-32 parts, the core-shell template is 14-16 parts, the sodium chloride is 19-23 parts and the polymethyl methacrylate microspheres is 18-22 parts. In step S4, the mixed gas is composed of ammonia and argon in a volume ratio of 1: (6-8).

7. The preparation method according to claim 2, characterized in that In step A1, the components, by weight, include 45-55 parts of 2-pyridinecarboxaldehyde, 22-28 parts of 4-aminopyridine, 90-100 parts of anhydrous ethanol, and 1-3 parts of lanthanum trifluoromethanesulfonate.

8. The preparation method according to claim 2, characterized in that In step A2, the components are 5-7 parts of the intermediate, 35-40 parts of tetrahydrofuran, and 18-22 parts of a 30-35 wt% tetrahydrofuran solution of phenylphosphonic dichloride.

9. The preparation method according to claim 3, characterized in that In the chain transfer agent preparation step, the components include 18-22 parts by weight of sodium lignin sulfonate, 4-6 parts by weight of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]valeric acid and 90-100 parts by weight of N,N-dimethylformamide.

10. A porous carbon negative electrode material for lithium ion batteries, characterized in that: The porous carbon negative electrode material for lithium ion batteries is prepared by the preparation method of any one of claims 1 to 9.