Preparation method of high-yield sodium ion battery hard carbon negative electrode material

Abstract

The invention discloses a preparation method of a high-yield sodium ion battery hard carbon negative electrode material, which comprises the following steps: S1, pretreatment: crushing and sieving a carbon-containing raw material to obtain the carbon-containing raw material; s2, premixing: uniformly mixing the carbon-containing raw material obtained in the step S1, a carbonizing agent and conductive carbon to obtain a mixed precursor; s3, low-temperature sintering: performing low-temperature sintering on the mixed precursor obtained in the step S2 in a protective atmosphere to obtain a low-temperature carbonized material; s4, crushing and refining: crushing and refining the low-temperature carbonized material obtained in the step S3 to obtain a crushed and refined low-temperature carbonized material; and S5, high-temperature sintering: carrying out high-temperature sintering on the refined low-temperature carbonized material obtained in the step S4 in a protective atmosphere to obtain a finished product of the hard carbon negative electrode material. The preparation method of the high-yield sodium ion battery hard carbon negative electrode material has the characteristics of high yield, green and environment-friendly process and excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for sodium-ion batteries, and specifically refers to a preparation method of a hard carbon negative electrode material for sodium-ion batteries with high yield. Background Art

[0002] Energy and environment are major issues faced by the world today. Affected by issues such as the drastic fluctuations in global lithium prices, resource distribution, and reserves, the sodium-ion battery industry has gradually received attention. However, the commonly used graphite-based negative electrode materials in lithium-ion batteries cannot be applied to sodium-ion batteries.

[0003] Currently, among the negative electrode materials for sodium-ion batteries, hard carbon has characteristics such as high sodium storage capacity, low working potential, and good cycle performance, and is the mainstream choice for industrialization at present. Hard carbon materials are mainly obtained by high-temperature pyrolysis of carbon-containing raw materials in an oxygen-free environment. The main chemical components of the carbon-containing raw materials are elements such as C, H, and O, which undergo carbonization, dehydrogenation, graphitization and other reactions under the action of high temperature, and thus decompose and transform into gaseous, liquid and solid products.

[0004] Specifically, the gaseous products mainly include hydrogen, carbon monoxide, carbon dioxide, tar, etc.; the liquid products mainly include wood vinegar, water, etc.; the solid product is mainly hard carbon. The high-temperature pyrolysis of carbon-containing raw materials produces a large amount of gaseous and liquid products, resulting in a low yield of hard carbon products, driving up production costs and being unfavorable for commercial promotion.

[0005] In addition, the gaseous products contain a large amount of tar, and its main components are large molecular weight aromatic substances. Tar gradually condenses during the emission process, is easy to adhere to the inner walls of the furnace and pipelines, causing pipeline blockage and equipment corrosion, and posing a hazard to the safe operation of the equipment. Currently, the combustion method is usually used to treat tar waste, with quite high energy consumption and a large amount of carbon dioxide gas emitted during combustion. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a hard carbon negative electrode material for sodium-ion batteries with high yield, which has the characteristics of high yield, green and environmentally friendly process, and excellent electrochemical performance.

[0007] The present invention can be realized through the following technical solutions:

[0008] The present invention discloses a preparation method of a hard carbon negative electrode material for sodium-ion batteries with high yield, including the following steps:

[0009] S1. Pretreatment: Crushing and sieving the carbon-containing raw material to obtain the carbon-containing raw material;

[0010] S2. Premixing: Uniformly mixing the carbon-containing raw material obtained in step S1, the carbonizing agent, and the conductive carbon to obtain a mixed precursor;

[0011] S3. Low-temperature sintering: The mixed precursor obtained in step S2 is sintered at low temperature in a protective atmosphere to obtain a low-temperature carbonized material;

[0012] S4. Crushing and refining: The low-temperature carbonized material obtained in step S3 is crushed and refined to obtain a crushed and refined low-temperature carbonized material;

[0013] S5. High-temperature sintering: The refined low-temperature carbonized material obtained in step S4 is sintered at high temperature in a protective atmosphere to obtain a finished hard carbon negative electrode material.

[0014] In the present invention, the conductive carbon has a high degree of graphitization, induces the carbonization of the carbon-containing raw material, effectively reduces the carbonization temperature, improves the carbonization degree, and increases the yield of the hard carbon product; at the same time, the conductive carbon is coupled with the carbon-containing raw material, and finally forms a highly cross-linked three-dimensional network structure in the hard carbon material, which serves as a conductive network, improves the electronic conductivity of the hard carbon material, and further enhances the rate performance of the hard carbon negative electrode material.

[0015] Further, in step S3, the low-temperature sintering is a staged sintering, which includes a first stage, a second stage, and a third stage. The treatment temperature in the first stage is 150 - 250 °C, and the treatment time is 0.5 - 5 h; the treatment temperature in the second stage is 250 - 350 °C, and the treatment time is 0.5 - 3 h; the treatment temperature in the third stage is 400 - 700 °C, and the treatment time is 0.5 - 3 h.

[0016] In step S3, during this process, the carbonizing agent chemically combines with small molecule organic substances such as C 6 H 5 OH, CH 3 OH and other small molecule organic substances produced by the high-temperature cracking of the organic raw material. The volatile small molecule organic substances are further polycondensed into non-volatile organic macromolecules, and at the same time, they are polycondensed with the functional groups in the residual carbon, thereby increasing the yield of the low-temperature carbonized material and reducing the emission of organic gases. Step S3 uses a staged carbonization process to reduce the yield of volatile organic small molecules in each stage, making it easier for them to undergo polycondensation reactions and remain in the solid-phase product.

[0017] Further, in step S3, the pressure of the low-temperature sintering is controlled at 100 - 250 Pa. The sintering pressure affects the effect of the present invention: if the sintering pressure is too low, the small molecule organic substances produced by cracking are directly discharged, resulting in a low yield of the solid-phase product; if the sintering pressure is too high, the volatile gases in the product are not discharged in time, accumulate in the furnace in large quantities, and a large amount of tar adheres to the inner walls of the furnace and the pipeline, causing pipeline blockage and equipment corrosion, and posing a hazard to the safe operation of the equipment.

[0018] Further, in step S2, the carbonizing agent is one or more of sulfuric acid, nitric acid, oxalic acid, citric acid, phosphoric acid, formic acid, acetic acid, fruit acid, tartaric acid; the addition amount of the carbonizing agent is 1-10.0 wt.% of the addition amount of the carbon-containing raw material. The addition amount of the carbonizing agent affects the effect of the present invention: if the amount of the carbonizing agent is insufficient, there will be no sufficient amount of -OH or -COOH group functional groups to chemically combine with small molecule organic substances such as C 6 H 5 OH, CH3OH, etc., and the purpose of reducing the volatilization of organic gases and increasing the yield cannot be achieved; if the addition amount of the carbonizing agent is too high, it will affect the microstructure of the carbon material and have an adverse effect on the performance of the material.

[0019] Further, in step S2, the conductive carbon is carbon nanotubes and / or graphene, the carbon nanotubes are one or more of single-walled carbon nanotubes, oligomeric-walled carbon nanotubes, multi-walled carbon nanotubes, and the graphene is monolayer graphene and / or multilayer graphene; the addition amount of the conductive carbon is 0.1-3.0 wt.% of the addition amount of the carbon-containing raw material. If the addition amount of the conductive carbon is too low, a sufficient conductive network cannot be formed inside the carbon material, and the purpose of improving the electronic conductivity of the hard carbon material and further improving the rate performance of the hard carbon negative electrode material cannot be achieved; if the addition amount of the conductive carbon is too high, the specific surface area of the finished material will be too large, affecting the first efficiency of the material.

[0020] Further, in step S5, the conditions for high-temperature sintering are: the heating rate is 1-5 °C / min, the sintering temperature is 1100-1500 °C, and the sintering time is 1-5 h.

[0021] Further, in step S1, the carbon-containing raw material is one or more of walnut shells, coffee shells, nut shells, wheat straw, phenolic resin, epoxy resin, furfural resin, glucose, sucrose, starch, poplar, pine, bamboo, straw, corn cobs, anthracite, bituminous coal, lignite, semi-anthracite; the mesh number of the sieve for sieving ≥ 10 meshes. Specifically, if the mesh number of the sieve is too small and the pore size is too large, the particle size of the carbon-containing raw material will be too large, which is not conducive to subsequent uniform mixing.

[0022] Further, in step S2, the mixing method includes solid-phase mixing and liquid-phase mixing.

[0023] Further, in step S4, the pulverizing method is one or more of a pair-roll machine, a mechanical mill, a jet mill, a Raymond mill, a ball mill; the volume median diameter D50 after pulverization is 4-12 μm.

[0024] Further, in steps S3 and S5, the protective atmosphere is argon and / or nitrogen.

[0025] The preparation method of a hard carbon negative electrode material for a sodium-ion battery with high yield of the present invention has the following beneficial effects:

[0026] First, high yield. During the low-temperature sintering process, the carbonizing agent and conductive carbon can significantly increase the yield of the final hard carbon product, thus significantly reducing the production cost per ton of the product. During the low-temperature sintering process, C 6 H 5 OH, CH 3 OH and other small-molecule organic substances are generated by the high-temperature pyrolysis of organic raw materials. The -OH or -COOH group functional groups in the carbonizing agent chemically combine with the volatile small-molecule organic substances generated by high-temperature pyrolysis to recapture the volatile substances back into the internal solid-phase system; the carbon material in the conductive carbon further catalyzes carbonization, thereby increasing the yield of low-temperature carbonized materials and reducing the emission of organic gases.

[0027] Second, the process is green and environmentally friendly. The amount of waste such as tar generated during the low-temperature pyrolysis process is significantly reduced, reducing the consumption of natural gas for burning tar and lowering energy consumption. Moreover, most of the carbon atoms are retained in the hard carbon product during the low-temperature pyrolysis process, reducing the emission of atmospheric carbon dioxide.

[0028] Third, excellent electrochemical performance. The conductive carbon and the carbon-containing raw material are coupled to form a highly cross-linked three-dimensional network structure, which serves as a conductive network to improve the electronic conductivity of the hard carbon material, thereby enhancing the rate performance of the hard carbon anode material. Specific embodiments

[0029] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the products of the present invention will be further described in detail below in conjunction with embodiments.

[0030] The present invention discloses a method for preparing a hard carbon anode material for a sodium-ion battery with high yield, comprising the following steps:

[0031] S1. Pretreatment: Crushing and sieving the carbon-containing raw material to obtain the carbon-containing raw material;

[0032] S2. Premixing: Uniformly mixing the carbon-containing raw material, carbonizing agent, and conductive carbon obtained in step S1 to obtain a mixed precursor;

[0033] S3. Low-temperature sintering: Low-temperature sintering the mixed precursor obtained in step S2 in a protective atmosphere to obtain a low-temperature carbonized material;

[0034] S4. Crushing and refining: Crushing and refining the low-temperature carbonized material obtained in step S3 to obtain a crushed and refined low-temperature carbonized material;

[0035] S5. High-temperature sintering: High-temperature sintering the refined low-temperature carbonized material obtained in step S4 in a protective atmosphere to obtain the finished hard carbon anode material.

[0036] Further, in step S3, the low-temperature sintering is carried out in a staged manner, which includes a first stage, a second stage, and a third stage. The treatment temperature in the first stage is 150 - 250 °C, and the treatment time is 0.5 - 5 h; the treatment temperature in the second stage is 250 - 350 °C, and the treatment time is 0.5 - 3 h; the treatment temperature in the third stage is 400 - 700 °C, and the treatment time is 0.5 - 3 h.

[0037] Further, in step S3, the pressure of the low-temperature sintering is controlled to be 100 - 250 Pa.

[0038] Further, in step S2, the carbonizing agent is one or more of sulfuric acid, nitric acid, oxalic acid, citric acid, phosphoric acid, formic acid, acetic acid, fruit acid, tartaric acid; the addition amount of the carbonizing agent is 1 - 10.0 wt.% of the addition amount of the carbon-containing raw material.

[0039] Further, in step S2, the conductive carbon is carbon nanotubes and / or graphene. The carbon nanotubes are one or more of single-walled carbon nanotubes, oligomeric-walled carbon nanotubes, multi-walled carbon nanotubes, and the graphene is monolayer graphene and / or multilayer graphene; the addition amount of the conductive carbon is 0.1 - 3.0 wt.% of the addition amount of the carbon-containing raw material.

[0040] Further, in step S5, the conditions for high-temperature sintering are: the heating rate is 1 - 5 °C / min, the sintering temperature is 1100 - 1500 °C, and the sintering time is 1 - 5 h.

[0041] Further, in step S1, the carbon-containing raw material is one or more of walnut shell, coffee shell, nut shell, wheat straw, phenolic resin, epoxy resin, furfural resin, glucose, sucrose, starch, poplar, pine, bamboo, straw, corn cob, anthracite, bituminous coal, lignite, semi-anthracite; the mesh number of the sieve for sieving is ≥ 10 mesh.

[0042] Further, in step S2, the mixing method includes solid-phase mixing and liquid-phase mixing.

[0043] Further, in step S4, the pulverizing method is one or more of a pair-roll mill, mechanical mill, air classifier mill, Raymond mill, ball mill; the volume median diameter D50 after pulverization is 4 - 12 μm.

[0044] Further, in steps S3 and S5, the protective atmosphere is argon and / or nitrogen.

[0045] Example 1

[0046] This example relates to a preparation method of a hard carbon negative electrode material for a sodium-ion battery with high yield, including the following steps:

[0047] S1. Pretreatment: Crush and screen the carbon-containing raw material to obtain the carbon-containing raw material. Specifically, the carbon-containing raw material is walnut shell, coffee shell, nut shell, wheat straw, phenolic resin.

[0048] S2. Premixing: Uniformly solid-phase mix the carbon-containing raw material, carbonizing agent, and conductive carbon obtained in step S1 to obtain a mixed precursor. Specifically, the carbonizing agent is sulfuric acid and nitric acid, and the addition amount of the carbonizing agent is 10.0 wt.% of the addition amount of the carbon-containing raw material; the conductive carbon is carbon nanotubes and graphene, the carbon nanotubes are single-walled carbon nanotubes and oligomeric-walled carbon nanotubes, and the graphene is single-layer graphene and multi-layer graphene; the addition amount of the conductive carbon is 2.0 wt.% of the addition amount of the carbon-containing raw material.

[0049] S3. Low-temperature sintering: Low-temperature sinter the mixed precursor obtained in step S2 in a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the low-temperature sintering is staged sintering, and this staged sintering includes a first stage, a second stage, and a third stage. The treatment temperature in the first stage is 250 °C, and the treatment time is 3 h; the treatment temperature in the second stage is 250 °C, and the treatment time is 3 h; the treatment temperature in the third stage is 550 °C, and the treatment time is 0.5 h; the pressure control for low-temperature sintering is 250 Pa; the protective atmosphere is argon and nitrogen.

[0050] S4. Crushing and refining: Crush and refine the low-temperature carbonized material obtained in step S3 to obtain a crushed and refined low-temperature carbonized material. Specifically, the crushing method is a roll crusher; the volume median diameter D50 after crushing is 4 - 12 μm.

[0051] S5. High-temperature sintering: Perform high-temperature sintering on the refined low-temperature carbonized material obtained in step S4 in a protective atmosphere to obtain a finished hard carbon negative electrode material. Specifically, the conditions for high-temperature sintering are: the heating rate is 5 °C / min, the sintering temperature is 1300 °C, the sintering time is 1 h, and the protective atmosphere is argon or nitrogen.

[0052] Example 2

[0053] This example relates to a method for preparing a hard carbon negative electrode material for a sodium-ion battery with high yield, including the following steps:

[0054] S1. Pretreatment: Crush and screen the carbon-containing raw material to obtain the carbon-containing raw material. Specifically, the carbon-containing raw material is walnut shell, coffee shell, nut shell, wheat straw, straw, corn cob, anthracite, bituminous coal, lignite, semi-anthracite.

[0055] S2. Premixing: The carbon-containing raw material, carbonizing agent, and conductive carbon obtained in step S1 are uniformly mixed in a liquid phase to obtain a mixed precursor. Specifically, the carbonizing agent is phosphoric acid, formic acid, acetic acid, fruit acid, tartaric acid, and the addition amount of the carbonizing agent is 5.0 wt.% of the addition amount of the carbon-containing raw material; the conductive carbon is carbon nanotubes, and the carbon nanotubes are single-walled carbon nanotubes and multi-walled carbon nanotubes; the addition amount of the conductive carbon is 0.1 wt.% of the addition amount of the carbon-containing raw material.

[0056] S3. Low-temperature sintering: The mixed precursor obtained in step S2 is sintered at a low temperature in a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the low-temperature sintering is a staged sintering, which includes a first stage, a second stage, and a third stage. The treatment temperature in the first stage is 200 °C, and the treatment time is 0.5 h; the treatment temperature in the second stage is 350 °C, and the treatment time is 2 h; the treatment temperature in the third stage is 400 °C, and the treatment time is 3 h; the pressure of the low-temperature sintering is controlled at 200 Pa; the protective atmosphere is argon.

[0057] S4. Crushing and refining: The low-temperature carbonized material obtained in step S3 is crushed and refined to obtain a crushed and refined low-temperature carbonized material. Specifically, the crushing method is air jet milling; the volume median diameter D50 after crushing is 4 - 12 μm.

[0058] S5. High-temperature sintering: The refined low-temperature carbonized material obtained in step S4 is sintered at a high temperature in a protective atmosphere to obtain a finished hard carbon anode material. Specifically, the conditions for high-temperature sintering are: the heating rate is 3 °C / min, the sintering temperature is 1100 °C, the sintering time is 5 h, and the protective atmosphere is argon and nitrogen.

[0059] Example 3

[0060] This example relates to a method for preparing a hard carbon anode material for a sodium-ion battery with high yield, including the following steps:

[0061] S1. Pretreatment: The carbon-containing raw material is crushed and sieved to obtain a carbon-containing raw material. Specifically, the carbon-containing raw material is walnut shell, coffee shell, nut shell, furfural resin, glucose, sucrose, starch, poplar, pine, bamboo, straw, corn cob.

[0062] S2. Premixing: The carbon-containing raw material, carbonizing agent, and conductive carbon obtained in step S1 are uniformly mixed in a solid phase to obtain a mixed precursor. Specifically, the carbonizing agent is citric acid, phosphoric acid, fruit acid, tartaric acid, and the addition amount of the carbonizing agent is 1 wt.% of the addition amount of the carbon-containing raw material; the conductive carbon is carbon graphene, and the graphene is single-layer graphene and multi-layer graphene; the addition amount of the conductive carbon is 3.0 wt.% of the addition amount of the carbon-containing raw material.

[0063] S3. Low-temperature sintering: The mixed precursor obtained in step S2 is sintered at a low temperature in a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the low-temperature sintering is a staged sintering, which includes a first stage, a second stage and a third stage. The treatment temperature in the first stage is 150 °C and the treatment time is 5 h; the treatment temperature in the second stage is 300 °C and the treatment time is 0.5 h; the treatment temperature in the third stage is 700 °C and the treatment time is 2 h; the pressure control for the low-temperature sintering is 100 Pa; the protective atmosphere is nitrogen.

[0064] S4. Crushing and refining: The low-temperature carbonized material obtained in step S3 is crushed and refined to obtain a crushed and refined low-temperature carbonized material. Specifically, the crushing method is ball milling; the volume median diameter D50 after crushing is 4 - 12 μm.

[0065] S5. High-temperature sintering: The refined low-temperature carbonized material obtained in step S4 is sintered at a high temperature in a protective atmosphere to obtain a finished hard carbon anode material. Specifically, the conditions for the high-temperature sintering are: the heating rate is 1 °C / min, the sintering temperature is 1500 °C, the sintering time is 3 h, and the protective atmosphere is argon and nitrogen.

[0066] Example 4

[0067] This example relates to a method for preparing a hard carbon anode material for a sodium-ion battery with high yield, which includes the following steps:

[0068] S1. Pretreatment: The carbon-containing raw material is crushed and sieved to obtain a carbon-containing raw material. Specifically, the carbon-containing raw material is walnut shell, coffee shell, nut shell, wheat straw, glucose, sucrose, starch, poplar wood, pine wood.

[0069] S2. Premixing: The carbon-containing raw material, carbonizing agent, and conductive carbon obtained in step S1 are uniformly mixed in a liquid phase to obtain a mixed precursor. Specifically, the carbonizing agents are citric acid, phosphoric acid, formic acid, and the addition amount of the carbonizing agent is 3.0 wt.% of the addition amount of the carbon-containing raw material; the conductive carbon is carbon nanotubes and graphene, the carbon nanotubes are single-walled carbon nanotubes, and the graphene is multi-layer graphene; the addition amount of the conductive carbon is 1.0 wt.% of the addition amount of the carbon-containing raw material.

[0070] S3. Low-temperature sintering: The mixed precursor obtained in step S2 is sintered at a low temperature in a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the low-temperature sintering is a staged sintering, which includes a first stage, a second stage and a third stage. The treatment temperature in the first stage is 180 °C and the treatment time is 4 h; the treatment temperature in the second stage is 320 °C and the treatment time is 1 h; the treatment temperature in the third stage is 600 °C and the treatment time is 1 h; the pressure control for the low-temperature sintering is 180 Pa; the protective atmosphere is argon and nitrogen.

[0071] S4. Crushing and Refining: Crush and refine the low-temperature carbonized material obtained in step S3 to obtain a crushed and refined low-temperature carbonized material. Specifically, the crushing method is a pair-roller mill or a Raymond mill; the volume median particle size D50 after crushing is 4 - 12 μm.

[0072] S5. High-temperature Sintering: Sinter the refined low-temperature carbonized material obtained in step S4 under a protective atmosphere to obtain a finished hard carbon negative electrode material. Specifically, the conditions for high-temperature sintering are: the heating rate is 2 °C / min, the sintering temperature is 1200 °C, the sintering time is 4 h, and the protective atmosphere is argon and nitrogen.

[0073] Example 5

[0074] This example relates to a method for preparing a hard carbon negative electrode material for a sodium-ion battery with high yield, including the following steps:

[0075] S1. Pretreatment: Crush and screen the carbon-containing raw material to obtain a carbon-containing raw material. Specifically, the carbon-containing raw material is walnut shell, coffee shell, epoxy resin, furfural resin, glucose, sucrose, starch, poplar, pine, bamboo, straw.

[0076] S2. Premixing: Uniformly mix the carbon-containing raw material, carbonizing agent, and conductive carbon obtained in step S1 in solid phase and liquid phase to obtain a mixed precursor. Specifically, the carbonizing agent is sulfuric acid, phosphoric acid, formic acid, fruit acid, tartaric acid, and the addition amount of the carbonizing agent is 8.0 wt.% of the addition amount of the carbon-containing raw material; the conductive carbon is carbon nanotube and graphene, the carbon nanotube is oligomeric wall carbon nanotube or multi-wall carbon nanotube, and the graphene is single-layer graphene; the addition amount of the conductive carbon is 2.0 wt.% of the addition amount of the carbon-containing raw material.

[0077] S3. Low-temperature Sintering: Sinter the mixed precursor obtained in step S2 at low temperature in a protective atmosphere to obtain a low-temperature carbonized material. Specifically, the low-temperature sintering is staged sintering, which includes a first stage, a second stage, and a third stage. The treatment temperature in the first stage is 220 °C, and the treatment time is 2 h; the treatment temperature in the second stage is 280 °C, and the treatment time is 2 h; the treatment temperature in the third stage is 500 °C, and the treatment time is 2 h; the pressure control for low-temperature sintering is 220 Pa; the protective atmosphere is argon and nitrogen.

[0078] S4. Crushing and Refining: Crush and refine the low-temperature carbonized material obtained in step S3 to obtain a crushed and refined low-temperature carbonized material. Specifically, the crushing method is a Raymond mill or a ball mill; the volume median particle size D50 after crushing is 4 - 12 μm.

[0079] S5. High-temperature sintering: The refined low-temperature carbonized material obtained in step S4 is subjected to high-temperature sintering under a protective atmosphere to obtain the finished hard carbon negative electrode material. Specifically, the conditions for high-temperature sintering are as follows: the heating rate is 4 °C / min, the sintering temperature is 1200 °C, the sintering time is 4 h, and the protective atmosphere is argon and nitrogen.

[0080] Application Example 1

[0081] S1. Pretreatment: The bamboo chip raw material is crushed and screened through a 10-mesh sieve to obtain bamboo powder raw material with a certain fineness.

[0082] S2. Premixing: The bamboo powder, phosphoric acid, and multi-walled carbon nanotubes obtained in step S1 are uniformly mixed to obtain a mixed precursor. Among them, the addition amounts of phosphoric acid and multi-walled carbon nanotubes are 5.0 and 1.0 wt.% of the addition amount of bamboo powder, respectively.

[0083] S3. Low-temperature sintering: The mixed precursor obtained in step S2 is sintered in a nitrogen atmosphere. The treatment temperature in the first stage is 200 °C, the treatment time is 2 h, the treatment temperature in the second stage is 300 °C, the treatment time is 1.5 h; the treatment temperature in the third stage is 500 °C, the treatment time is 2 h, and the furnace pressure is 150 Pa.

[0084] S4. Crushing and refining: The low-temperature carbonized material obtained in step S3 is crushed by air jet milling to a low-temperature carbonized material with a D50 of 6 μm.

[0085] S5. High-temperature sintering: The refined low-temperature carbonized material obtained in step S4 is subjected to high-temperature sintering in a nitrogen gas atmosphere. The heating rate is 3 °C / min, the sintering temperature is 1300 °C, and the sintering time is 2 h to obtain the finished hard carbon negative electrode material.

[0086] The obtained material was tested for electrochemical performance according to the following method: The hard carbon material, Super P, CMC, and SBR were mixed into a homogeneous slurry in a mass ratio of 94:1.5:2:2.5, and then the black slurry was coated on the copper foil using a 120-μm four-sided coater. Then, the film was dried in a vacuum drying oven at 100 °C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine, with metallic sodium as the counter electrode, 1 mol / L NaClO 4 EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator was used to assemble a CR2016-type button cell in a glove box. The above-mentioned button cell was subjected to a constant current charge-discharge test, with a current density of 0.1 C (1 C = 300 mAh / g) and a voltage range of 1 - 0.005 V.

[0087] Comparative Example 1

[0088] S1. Pretreatment: Crush the bamboo chip raw material and sieve it through a 10-mesh sieve to obtain bamboo powder raw material with a certain fineness.

[0089] S2. Premixing: Uniformly mix the bamboo powder obtained in step S1 and multi-walled carbon nanotubes to obtain a mixed precursor. Among them, the addition amount of multi-walled carbon nanotubes is 1.0 wt.% of the addition amount of bamboo powder.

[0090] S3. Low-temperature sintering: Sinter the mixed precursor obtained in step S2 in a nitrogen atmosphere. The treatment temperature in the first stage is 200 °C, and the treatment time is 2 h. The treatment temperature in the second stage is 300 °C, and the treatment time is 1.5 h. The treatment temperature in the third stage is 500 °C, and the treatment time is 2 h. The pressure in the furnace is 150 Pa.

[0091] S4. Crushing and refining: Use air jet milling to crush the low-temperature carbonized material obtained in step S3 into low-temperature carbonized material with D50 of 6 μm.

[0092] S5. High-temperature sintering: Perform high-temperature sintering on the refined low-temperature carbonized material obtained in step S4 in a nitrogen gas atmosphere. The heating rate is 3 °C / min, the sintering temperature is 1300 °C, and the sintering time is 2 h to obtain the finished hard carbon negative electrode material.

[0093] The obtained material is tested for electrochemical performance according to the following method: The hard carbon material, Super P, CMC, and SBR are mixed into a homogeneous slurry according to the mass ratio of 94:1.5:2:2.5, and then the black slurry is coated on the copper foil using a 120-μm four-sided coater. Then, the film is dried in a vacuum drying oven at 100 °C for 2 hours. Use a punching machine to punch the electrode film into a circular piece with a radius of 0.6 mm, use metallic sodium as the counter electrode, 1 mol / L NaClO 4 EC+DEC (1:1 vol%) as the electrolyte, and the separator is a three-layer PP / PE / PP separator, and a CR2016 type button battery is assembled in a glove box. Perform constant current charge and discharge tests on the above button battery, with a current density of 0.1 C (1 C = 300 mAh / g) and a voltage range of 1 - 0.005 V.

[0094] Comparative Example 2

[0095] S1. Pretreatment: Crush the bamboo chip raw material and sieve it through a 10-mesh sieve to obtain bamboo powder raw material with a certain fineness.

[0096] S2. Premixing: Uniformly mix the bamboo powder obtained in step S1 and phosphoric acid to obtain a mixed precursor. Among them, the addition amounts of phosphoric acid are 5.0 and 1.0 wt.% of the addition amount of bamboo powder.

[0097] S3. Low-temperature sintering: Sinter the mixed precursor obtained in step S2 in a nitrogen atmosphere. The treatment temperature in the first stage is 200 °C, the treatment time is 2 h, the treatment temperature in the second stage is 300 °C, the treatment time is 1.5 h; the treatment temperature in the third stage is 500 °C, the treatment time is 2 h, and the furnace pressure is 150 Pa.

[0098] S4. Crushing and refining: Use air-flow pulverization to crush the low-temperature carbonized material obtained in step S3 into low-temperature carbonized material with a D50 of 6 μm.

[0099] S5. High-temperature sintering: Perform high-temperature sintering on the refined low-temperature carbonized material obtained in step S4 in a nitrogen gas atmosphere. The heating rate is 3 °C / min, the sintering temperature is 1300 °C, and the sintering time is 2 h to obtain the finished hard carbon negative electrode material.

[0100] The obtained material is tested for electrochemical performance according to the following method: The hard carbon material, Super P, CMC, and SBR are mixed into a homogeneous slurry in a mass ratio of 94:1.5:2:2.5, and then the black slurry is coated on the copper foil using a 120-μm four-sided coater. Then, the film is dried in a vacuum drying oven at 100 °C for 2 hours. Use a punching machine to punch the electrode film into a disc with a radius of 0.6 mm, use metallic sodium as the counter electrode, and 1 mol / L NaClO 4 EC+DEC (1:1 vol%) as the electrolyte, and the separator is a three-layer PP / PE / PP separator, and assemble it into a CR2016 type button battery in a glove box. Perform a constant current charge-discharge test on the above button battery, with a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 1 - 0.005 V.

[0101] Comparative Example 3

[0102] S1. Pretreatment: Crush the bamboo chip raw material and screen it through a 10-mesh sieve to obtain bamboo powder raw material with a certain fineness.

[0103] S2. Low-temperature sintering: Sinter the bamboo powder raw material obtained in step S1 in a nitrogen atmosphere. The treatment temperature in the first stage is 200 °C, the treatment time is 2 h, the treatment temperature in the second stage is 300 °C, the treatment time is 1.5 h; the treatment temperature in the third stage is 500 °C, the treatment time is 2 h, and the furnace pressure is 150 Pa.

[0104] S3. Crushing and refining: Use air-flow pulverization to crush the low-temperature carbonized material obtained in step S2 into low-temperature carbonized material with a D50 of 6 μm.

[0105] S4. High-temperature sintering: The refined low-temperature carbonized material obtained in step S3 is subjected to high-temperature sintering in a nitrogen gas atmosphere at a heating rate of 3 °C / min, a sintering temperature of 1300 °C, and a sintering time of 2 h to obtain the finished hard carbon negative electrode material.

[0106] The obtained material is tested for its electrochemical performance according to the following method: After mixing hard carbon material, Super P, CMC, and SBR into a homogeneous slurry in a mass ratio of 94:1.5:2:2.5, the black slurry is coated on copper foil using a 120-μm four-sided coater, and then the film is dried in a vacuum drying oven at 100 °C for 2 hours. The electrode film is punched into discs with a radius of 0.6 mm using a punching machine, with metallic sodium as the counter electrode, 1 mol / L NaClO 4 EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, and assembled into a CR2016 type button cell in a glove box. The above-mentioned button cell is subjected to constant current charge-discharge testing with a current density of 0.1 C (1 C = 300 mAh / g) and a voltage range of 1 - 0.005 V.

[0107] The first-week charge specific capacity and first-week efficiency of Application Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 measured by constant current charge-discharge testing are 331.4, 304.5, 326.4, and 294.9 mAh / g, and 91.6%, 90.8%, 91.3%, and 91.5% respectively. The higher sodium storage capacity of the application example and Comparative Example 2 is attributed to the doping of phosphorus atoms by phosphoric acid in the hard carbon material, which broadens the carbon layer spacing and increases the sodium storage active sites, thereby improving the sodium storage capacity of the hard carbon material.

[0108] The capacity retention rates of Application Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 at high current (5 C) are 84.6, 73.2, 68.5, and 84.3 respectively. The higher capacity retention rates of Application Example 1 and Comparative Example 2 are attributed to the formation of a three-dimensional network structure by conductive carbon inside the hard carbon material, which acts as a conductive network to improve the electronic conductivity of the hard carbon material, thereby enhancing the rate performance of the hard carbon negative electrode material.

[0109] The product yields of Application Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are 34.5%, 22.4%, 25.1%, and 18.3% respectively. The higher product yield of Application Example 1 indicates that the carbonizing agent and conductive carbon can significantly improve the final yield of the hard carbon product during the low-temperature sintering process.

[0110] Table 1 Performance test results

[0111] Yield (%) Specific capacity (mAh / g) Initial efficiency (%) Retention rate of 5C capacity (%) Application Example 1 34.5 331.4 91.6 84.6 Comparative Example 1 22.4 304.5 90.8 84.3 Comparative Example 2 25.1 326.4 91.3 68.5 Comparative Example 3 18.3 294.9 91.5 73.6

[0112] The above embodiments are only specific embodiments of the present invention, and the description thereof is relatively specific and detailed. However, it should not be construed as limiting the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these obvious alternative forms all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-yield hard carbon negative electrode material for a sodium ion battery, characterized in that The following steps are involved: S1. Pretreatment: crushing and sieving the carbon-containing raw material to obtain the carbon-containing raw material; S2, premixing: uniformly mixing the carbon-containing raw material, carbonizing agent and conductive carbon obtained in step S1 to obtain a mixed precursor; S3, low temperature sintering: sintering the mixed precursor obtained in step S2 at low temperature in a protective atmosphere to obtain a low temperature carbonized material; S4, crushing and refining: crushing and refining the low-temperature carbonized material obtained in step S3 to obtain a crushed and refined low-temperature carbonized material; S5, high temperature sintering: the refined low temperature carbonized material obtained in step S4 is subjected to high temperature sintering under a protective atmosphere to obtain a finished hard carbon negative electrode material.

2. The method for preparing a high-yield hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S3, the low-temperature sintering is a staged sintering, which includes a first stage, a second stage and a third stage. The treatment temperature of the first stage is 150-250°C, and the treatment time is 0.5-5h; the treatment temperature of the second stage is 250-350°C, and the treatment time is 0.5-3h; the treatment temperature of the third stage is 400-700°C, and the treatment time is 0.5-3h.

3. The method for preparing a high-yield hard carbon negative electrode material for a sodium ion battery according to claim 2, characterized in that: In step S3, the pressure of low temperature sintering is controlled to be 100-250 Pa.

4. The method for preparing a high-yield hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S2, the carbonizing agent is one or more of sulfuric acid, nitric acid, oxalic acid, citric acid, phosphoric acid, formic acid, acetic acid, fruit acid, and tartaric acid; the amount of the carbonizing agent added is 1-10.0wt.% of the amount of the carbon-containing raw material added.

5. The method for preparing a high-yield hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S2, the conductive carbon is carbon nanotubes and / or graphene, the carbon nanotubes are one or more of single-walled carbon nanotubes, oligo-walled carbon nanotubes, and multi-walled carbon nanotubes, and the graphene is single-layer graphene and / or multi-layer graphene; the added amount of the conductive carbon is 0.1-3.0wt.% of the added amount of the carbon-containing raw material.

6. The method for preparing a high-yield hard carbon negative electrode material for sodium ion batteries according to claim 1, characterized in that: In step S5, the high temperature sintering conditions are: heating rate of 1-5°C / min, sintering temperature of 1100-1500°C, and sintering time of 1-5h.

7. The method for preparing a high-yield hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S1, the carbon-containing raw material is one or more of walnut shells, coffee shells, nut shells, wheat straw, phenolic resin, epoxy resin, furfural resin, glucose, sucrose, starch, poplar, pine, bamboo, straw, corn cobs, anthracite, bituminous coal, lignite, and semi-anthracite; and the mesh number of the sieve is ≥10 meshes.

8. The method for preparing a high-yield hard carbon negative electrode material for sodium ion batteries according to claim 1, characterized in that: In step S2, the mixing method includes solid phase mixing and liquid phase mixing.

9. The method for preparing a high-yield hard carbon negative electrode material for sodium ion batteries according to claim 1, characterized in that: In step S4, the pulverizing method is one or more of a roller mill, a mechanical mill, an air flow mill, a Raymond mill, and a ball mill; and the volume median particle size D50 after pulverization is 4-12 μm.

10. The method for preparing a high-yield hard carbon negative electrode material for sodium ion batteries according to claim 9, characterized in that: In steps S3 and S5, the protective atmosphere is argon and / or nitrogen.