Preparation method of green and environment-friendly hard carbon negative electrode material for sodium ion battery

Abstract

The application discloses a green and environment-friendly preparation method of a sodium-ion battery hard carbon negative electrode material, and comprises the following steps: S1, pre-carbonization: biomass raw materials are pre-carbonized under a protective atmosphere to obtain pre-carbonized materials; S2, particle size control treatment: the pre-carbonized materials obtained in the step S1 are crushed and refined to obtain refined pre-carbonized materials; S3, preparation of a precursor material: the refined pre-carbonized materials obtained in the step S2, acid liquor and deionized water are stirred and dispersed to form a precursor slurry, and after temperature control sand milling, solid-liquid separation, water washing and drying, the precursor material is obtained; S4, high-temperature sintering: the precursor material obtained in the step S3 is high-temperature carbonized under a protective atmosphere to obtain a purified hard carbon material; and S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in the step S4 is high-temperature carbon coated to obtain a surface-coated hard carbon negative electrode material. The application has the characteristics of being green and environment-friendly, excellent in electrochemical performance and good in processability.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a green and environment-friendly preparation method of a hard carbon negative electrode material for sodium ion batteries. BACKGROUND

[0002] Compared with lithium ion batteries, sodium ion electrodes have the advantages of rich raw material resources, low manufacturing cost, good low-temperature performance, excellent safety performance and rate performance, and are a powerful supplement to lithium iron phosphate batteries and an excellent solution to replace lead-acid batteries. Among the many negative electrode technology routes of sodium ion batteries, the hard carbon negative electrode material has the advantages of wide raw material sources, low cost, low working potential, high capacity and good cycle stability, and is considered to be the best solution for the commercialization of sodium ion batteries.

[0003] At present, the cost and large-scale application of hard carbon materials are subject to the supply of hard carbon raw materials. The alternative carbon sources include biomass, chemical raw materials such as resins, and fossil raw materials such as coal and pitch. Among them, the biomass raw material has the advantages of wide source, low price, sufficient supply and renewable, and is considered to be an ideal choice for large-scale production of hard carbon.

[0004] The main component of the biomass raw material is carbon-containing organic matter, and these organic matters are formed into carbon materials through high-temperature pyrolysis. However, the biomass raw material naturally contains metals required for the growth of biomass, such as Fe, Na, K, Mg, Ca and the like. The impurities (ash) remaining in the hard carbon material will cause problems such as reduction of electronic conductivity of the material, alkaline pH, catalysis of irreversible decomposition of electrolyte, and influence on the cycle rate, processability and other properties of the battery.

[0005] The impurities in the hard carbon material exist in the form of metal oxides and metal salts, and are generally removed by a purification method of high-temperature reaction of strong acid in a reaction kettle. However, this method needs to use a large amount of acid, has high cost and serious environmental pollution, and is not conducive to commercial production and application. SUMMARY

[0006] The purpose of the present application is to provide a green and environment-friendly preparation method of a hard carbon negative electrode material for sodium ion batteries, which has the characteristics of green environmental protection, excellent electrochemical performance and good processability.

[0007] The present application can be realized by the following technical solutions:

[0008] The present application discloses a green and environment-friendly preparation method of a hard carbon negative electrode material for sodium ion batteries, comprising the following steps:

[0009] S1, pre-carbonization: pre-carbonizing the biomass raw material under a protective atmosphere to obtain a pre-carbonized material;

[0010] S2, particle size control treatment: crushing and refining the pre-carbonized material obtained in step S1 to obtain a refined pre-carbonized material;

[0011] S3, preparation of the precursor material: the refined pre-carbonization material obtained in step S2, acid liquid and deionized water are stirred and dispersed to form a precursor slurry, and after temperature control sanding, solid-liquid separation, water washing and drying, the precursor material is obtained; the acid liquid is hydrochloric acid; the addition amount of the acid liquid is 1-20wt.% of the mass of the pre-carbonization material, and the pH of the precursor slurry is 4-6; the solid content of the precursor slurry is 15-30%;

[0012] S4, high-temperature sintering: the precursor material obtained in step S3 is subjected to high-temperature carbonization in a protective atmosphere to obtain a purified hard carbon material;

[0013] S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in step S4 is subjected to high-temperature carbon coating to obtain a hard carbon negative electrode material coated on the surface.

[0014] In step S3 of the present application, non-water-soluble or acid-soluble impurities such as silicates cannot be dissolved into the aqueous solution. Such impurities will not be dissolved in the subsequent homogenate coating process, and will not be dissolved in the electrolyte after the preparation of the electrode, thereby not adversely affecting the processing process and the battery performance. The addition amount of the acid liquid and the pH of the slurry affect the effect of the present application: if the addition amount of hydrochloric acid is too small, the effect of the present application cannot be achieved; if the addition amount of hydrochloric acid is too high, the production equipment is increased, and a too low pH will corrode the equipment, which is not conducive to actual production application. The solid content of the slurry affects the effect of the present application: if the solid content of the slurry is low, the yield of a single sanding is low, which increases the production cost; if the solid content of the slurry is high, it is not conducive to the dissolution of metal impurities. The solid content of the slurry affects the effect of the present application.

[0015] Further, in step S3, the temperature of sanding is 30-80℃, and during the sanding process, the slurry will gradually heat up due to grinding heat, and cooling water needs to be passed to control the temperature of the sanding machine at a suitable value. On the one hand, high temperature can promote the reaction of hydrochloric acid and metal impurities in the carbon material, and promote the dissolution of metal impurities; on the other hand, if the temperature is too high and exceeds the maintenance temperature of the equipment, it will affect the service life of the equipment; the sanding time is 1-6h, and the D50 of the ground precursor material is 3-10μm.

[0016] Further, in step S3, the water washing of the precursor material is to pH 6-7; the solid-liquid separation method is centrifugation and / or pressure filtration, which separates the metal impurities dissolved in the aqueous solution from the hard carbon material, and the water washing process further washes away the water-soluble impurities on the surface of the hard carbon material; through acid dissolution and water system, part of the metal impurities are converted into chloride salt, and the boiling point of the chloride salt is usually lower; the drying method is one or more of the following: air oven drying, flash drying, vacuum oven drying, tunnel type drying oven, double-cone dryer, belt dryer and rake dryer.

[0017] Further, in step S5, the high-temperature carbon-coating method is one or more of chemical vapor deposition (CVD), liquid coating, and high-temperature solid-phase coating; and the raw material for the high-temperature carbon coating is a carbon source free of metal impurities, and the carbon source is one or more of pitch, phenol-formaldehyde resin, PVP, PVA, dopamine, glucose, PAA, citric acid, phenol, benzene, toluene, and acetylene.

[0018] Further, in step S5, the amount of the carbon layer in the high-temperature carbon coating is 0.5-5 wt.% of the weight of the hard carbon material. If the carbon layer is too thin, a uniform and complete coating layer cannot be formed on the surface of the hard carbon material; and if the amount of the carbon coating is too large, the production cost is increased. The heating rate is 1-10 ℃ / min, the carbonization temperature is 600-1100 ℃, and the carbonization time is 1-3 h.

[0019] Specifically, the carbon layer coated on the surface of the hard carbon material is pure carbon, and a uniform and dense carbon layer is formed on the surface of the hard carbon material. On the one hand, the carbon layer separates the internal biomass carbon material from the electrolyte, further avoiding the adverse effects of the unremoved impurities in the biomass hard carbon material on the battery performance; and on the other hand, the coating layer reduces the specific surface area of the biomass hard carbon material, reduces the contact area between the material surface and the electrolyte, and improves the first cycle efficiency, cycle performance, and storage performance of the battery.

[0020] Further, in step S4, the high-temperature carbonization conditions are as follows: the heating rate is 0.5-10 ℃ / min, the carbonization temperature is 1100-1500 ℃, and the carbonization time is 2-5 h. During the high-temperature carbonization process, the part of the chloride salt that has not been removed from the material is gasified in the inert gas stream under the action of high temperature and is carried away from the material, achieving the purpose of further purifying the hard carbon material.

[0021] Further, in step S2, the pre-carbonization material is crushed and refined to a D50 of 5-20 μm, and the crushing method is one or more of jaw crushing, roller crushing, air flow crushing, mechanical grinding, ball grinding, Raymond grinding, and stirring grinding.

[0022] Further, in step S1, the carbonization conditions are as follows: the heating rate is 1-20 ℃ / min, the carbonization temperature is 300-900 ℃, and the carbonization time is 1-5 h.

[0023] Specifically, the carbonization conditions affect the effect of the present application. In this process, the organic matter in the biomass is gradually carbonized and cracked, and the metal elements are converted into inorganic salts. If the carbonization temperature is low, the metal elements cannot be completely converted into inorganic salts, and it is difficult to remove them in the subsequent process; and if the carbonization temperature is too high, the pores of the carbon material collapse and close under the action of high temperature, so that the inorganic salts are wrapped inside the carbon material and are difficult to remove.

[0024] Further, in step S1, the biomass raw material is one or two or more of walnut shell, nut shell, apricot shell, straw, reed, coffee shell, coconut shell, bamboo, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, fir, oak, anthracite, lignite, sub-bituminous coal.

[0025] Further, in steps S1 / S4 and S5, the protective atmosphere is nitrogen and / or argon.

[0026] The green and environmentally-friendly sodium-ion battery hard carbon negative electrode material preparation method has the following beneficial effects:

[0027] First, green and environmentally-friendly, the present application uses sanding medium and material particles, and the intense friction and impact between material particles promote the dissolution of metal impurities, without the need to use a large amount of strong acid high-temperature reaction, so the process is green and environmentally-friendly and low in cost.

[0028] Second, excellent electrochemical performance, the sanding process promotes the dissolution of metal impurities, high-temperature carbonization further evaporates the chlorides, and the surface is coated with a carbon layer with high purity, which further avoids the adverse effects of metal impurities and effectively reduces the specific surface area of the hard carbon material, thereby achieving the purpose of improving the first-week efficiency and cycle performance of the hard carbon material.

[0029] Third, good processability, the present application can make the pH of the hard carbon material neutral, and in the homogenization process of the pole piece, the poor flowability of the slurry caused by the alkalinity of the material is avoided. DETAILED DESCRIPTION

[0030] In order to enable the personnel in the technical field to better understand the technical solutions of the present application, the product of the present application is further described in detail below in combination with embodiments.

[0031] The present application discloses a green and environmentally-friendly sodium-ion battery hard carbon negative electrode material preparation method, comprising the following steps:

[0032] S1, pre-carbonization: pre-carbonizing the biomass raw material under a protective atmosphere to obtain a pre-carbonized material;

[0033] S2, particle size control treatment: crushing and refining the pre-carbonized material obtained in step S1 to obtain a refined pre-carbonized material;

[0034] S3, preparation of a precursor material: stirring and dispersing the refined pre-carbonized material obtained in step S2, an acid solution and deionized water to form a precursor slurry, and then performing solid-liquid separation, water washing and drying after temperature control sanding to obtain a precursor material; the acid solution is hydrochloric acid; the addition amount of the acid solution is 1-20wt.% of the mass of the pre-carbonized material, the pH of the precursor slurry is 4-6, and the solid content of the precursor slurry is 15-30%;

[0035] S4, high-temperature sintering: the precursor material obtained in step S3 is subjected to high-temperature carbonization in a protective atmosphere to obtain a purified hard carbon material;

[0036] S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in step S4 is subjected to high-temperature carbon coating to obtain a hard carbon negative electrode material with surface coating.

[0037] Further, in step S3, the sanding temperature is 30-80℃, the sanding time is 1-6h, and the grinding to the D50 of the precursor material is 3-10μm.

[0038] Further, in step S3, the water washing to the pH of the precursor material is 6-7; the solid-liquid separation method is centrifugation and / or pressure filtration; and the drying method is one or more of a forced air oven drying, flash drying, vacuum oven drying, tunnel drying oven, double-cone dryer, belt dryer, and rake dryer.

[0039] Further, in step S5, the high-temperature carbon coating method is one or more of chemical vapor deposition, liquid phase coating, and high-temperature solid phase coating; and the raw material for the high-temperature carbon coating is a carbon source without metal impurities, which is one or more of pitch, phenol formaldehyde resin, PVP, PVA, dopamine, glucose, PAA, citric acid, phenol, benzene, toluene, and acetylene.

[0040] Further, in step S5, the amount of the carbon layer in the high-temperature coated carbon is 0.5-5wt.% of the weight of the hard carbon material; the heating rate is 1-10℃ / min, the carbonization temperature is 600-1100℃, and the carbonization time is 1-3h.

[0041] Further, in step S4, the high-temperature carbonization conditions are: the heating rate is 0.5-10℃ / min, the carbonization temperature is 1100-1500℃, and the carbonization time is 2-5h.

[0042] Further, in step S2, the grinding and refining to the D50 of the pre-carbonization material is 5-20μm, and the grinding method is one or more of a jaw crusher, a roller crusher, an air flow mill, a mechanical mill, a ball mill, a Raymond mill, and a stirring mill.

[0043] Further, in step S1, the carbonization conditions are: the heating rate is 1-20℃ / min, the carbonization temperature is 300-900℃, and the carbonization time is 1-5h.

[0044] Further, in step S1, the biomass raw material is one or more of walnut shell, nut shell, apricot shell, straw, reed, coffee shell, coconut shell, bamboo, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, fir wood, oak, anthracite, lignite, and sub-bituminous coal.

[0045] Further, in steps S1 / S4 and S5, the protective atmosphere is nitrogen and / or argon.

[0046] Embodiment 1

[0047] The embodiment relates to a green and environment-friendly preparation method of a sodium-ion battery hard carbon negative electrode material, and comprises the following steps.

[0048] S1, pre-carbonization: biomass raw materials are pre-carbonized under a protective atmosphere to obtain pre-carbonized materials. Specifically, the carbonization conditions are as follows: the heating rate is 20 ℃ / min, the carbonization temperature is 600 ℃, and the carbonization time is 1 h. The biomass raw materials are walnut shells, nut shells, apricot shells, straw, and reed.

[0049] S2, particle size control treatment: the pre-carbonized materials obtained in step S1 are crushed and refined to obtain refined pre-carbonized materials. Specifically, the pre-carbonized materials are crushed and refined to a D50 of 5-20 μm, and the crushing mode is impact crushing and roller crushing; the protective atmosphere is nitrogen.

[0050] S3, preparation of a precursor material: the refined pre-carbonized materials obtained in step S2, acid liquor, and deionized water are stirred and dispersed to form a precursor slurry, and then temperature-controlled sand milling is performed, followed by solid-liquid separation, water washing, and drying to obtain a precursor material; the acid liquor is hydrochloric acid; the addition amount of the acid liquor is 20 wt.% of the mass of the pre-carbonized materials, the pH of the precursor slurry is 5, and the solid content of the precursor slurry is 15%. Specifically, the sand milling temperature is 80 ℃, the sand milling time is 3 h, the grinding is performed to a D50 of 3-10 μm of the precursor material; the water washing is performed to a pH of 6 of the precursor material; the solid-liquid separation mode is centrifugation; and the drying mode is drum oven drying.

[0051] S4, high-temperature sintering: the precursor material obtained in step S3 is high-temperature carbonized under a protective atmosphere to obtain a purified hard carbon material. Specifically, the high-temperature carbonization conditions are as follows: the heating rate is 0.5 ℃ / min, the carbonization temperature is 1500 ℃, and the carbonization time is 4 h; and the protective atmosphere is nitrogen.

[0052] S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in step S4 is high-temperature carbon coated to obtain a surface-coated hard carbon negative electrode material. Specifically, the high-temperature carbon coating mode is chemical vapor deposition; the raw material for the high-temperature carbon coating is a carbon source free of metal impurities, and the carbon source is pitch or phenolic resin; the amount of the carbon layer in the high-temperature coated carbon is 0.5 wt.% of the weight of the hard carbon material; the heating rate is 10 ℃ / min, the carbonization temperature is 800 ℃, and the carbonization time is 1 h; and the protective atmosphere is nitrogen.

[0053] Embodiment 2

[0054] The embodiment relates to a green and environment-friendly preparation method of a sodium-ion battery hard carbon negative electrode material.

[0055] S1, pre-carbonization: biomass raw materials are pre-carbonized under a protective atmosphere to obtain pre-carbonized materials. Specifically, the carbonization conditions are as follows: a temperature rising rate is 10 DEG C / min, a carbonization temperature is 300 DEG C, and a carbonization time is 5 h. The biomass raw materials are walnut shells, nut shells, anthracite, lignite, and sub-bituminous coal.

[0056] S2, particle size control treatment: the pre-carbonized materials obtained in the step S1 are crushed and refined to obtain refined pre-carbonized materials. Specifically, the pre-carbonized materials are crushed and refined to have a D50 of 5-20 mu m, and the crushing mode is Raymond mill or stirring mill; the protective atmosphere is argon.

[0057] S3, preparation of a precursor material: the refined pre-carbonized materials obtained in the step S2, acid liquor and deionized water are stirred and dispersed to form a precursor slurry, and after temperature control sand milling, solid-liquid separation, water washing and drying, a precursor material is obtained; the acid liquor is hydrochloric acid; the addition amount of the acid liquor is 10 wt.% of the mass of the pre-carbonized materials, the pH of the precursor slurry is 4, and the solid content of the precursor slurry is 30%. Specifically, the sand milling temperature is 60 DEG C, the sand milling time is 1 h, the grinding is performed to the precursor material to have a D50 of 3-10 mu m; the water washing is performed to the precursor material to have a pH of 7; the solid-liquid separation mode is pressure filtration; and the drying mode is air oven drying or flash drying.

[0058] S4, high-temperature sintering: the precursor material obtained in the step S3 is high-temperature carbonized under a protective atmosphere to obtain a purified hard carbon material. Specifically, the high-temperature carbonization conditions are as follows: a temperature rising rate is 5 DEG C / min, a carbonization temperature is 1100 DEG C, and a carbonization time is 5 h; and the protective atmosphere is argon.

[0059] S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in the step S4 is high-temperature carbon coated to obtain a surface-coated hard carbon negative electrode material. Specifically, the high-temperature carbon coating mode is chemical vapor deposition, liquid phase coating or high-temperature solid phase coating; the high-temperature carbon coating raw material is a carbon source free of metal impurities, and the carbon source is dopamine, glucose or PAA; the amount of the carbon layer in the high-temperature coated carbon is 2 wt.% of the weight of the hard carbon material; a temperature rising rate is 1 DEG C / min, a carbonization temperature is 1100 DEG C, and a carbonization time is 2 h; and the protective atmosphere is argon.

[0060] Embodiment 3

[0061] The embodiment relates to a green and environment-friendly preparation method of a sodium-ion battery hard carbon negative electrode material, which comprises the following steps.

[0062] S1, pre-carbonization: the biomass raw material is pre-carbonized under a protective atmosphere to obtain a pre-carbonized material. Specifically, the carbonization conditions are: a heating rate of 1 ℃ / min, a carbonization temperature of 900 ℃, and a carbonization time of 3 h. The biomass raw material is walnut shell, nut shell, apricot shell, straw, anthracite, lignite, and sub-bituminous coal.

[0063] S2, particle size control treatment: the pre-carbonized material obtained in step S1 is crushed and refined to obtain a refined pre-carbonized material. Specifically, the pre-carbonized material is crushed and refined to a D50 of 5-20 μm, and the crushing method is air flow powder and mechanical grinding; the protective atmosphere is nitrogen and argon.

[0064] S3, preparation of a precursor material: the refined pre-carbonized material obtained in step S2, acid solution, and deionized water are stirred and dispersed to form a precursor slurry, and after temperature control sand milling, solid-liquid separation, water washing, and drying, a precursor material is obtained; the acid solution is hydrochloric acid; the addition amount of the acid solution is 1 wt.% of the mass of the pre-carbonized material, and the pH of the precursor slurry is 6; the solid content of the precursor slurry is 23%. Specifically, the sand milling temperature is 30 ℃, the sand milling time is 6 h, and the grinding is performed to a D50 of 3-10 μm of the precursor material; the water washing is performed to a pH of 6.5 of the precursor material; the solid-liquid separation method is centrifugation and / or pressure filtration; and the drying method is vacuum oven drying and tunnel type drying furnace.

[0065] S4, high-temperature sintering: the precursor material obtained in step S3 is high-temperature carbonized under a protective atmosphere to obtain a purified hard carbon material. Specifically, the high-temperature carbonization conditions are: a heating rate of 0.5 ℃ / min, a carbonization temperature of 1500 ℃, and a carbonization time of 3 h; and the protective atmosphere is nitrogen and argon.

[0066] S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in step S4 is high-temperature carbon coated to obtain a surface-coated hard carbon negative electrode material. Specifically, the high-temperature carbon coating method is chemical vapor deposition, liquid phase coating, and high-temperature solid phase coating; the high-temperature carbon coating raw material is a carbon source free of metal impurities, and the carbon source is PAA, citric acid, phenol, benzene, toluene, and acetylene; the amount of the carbon layer in the high-temperature coated carbon is 0.5 wt.% of the weight of the hard carbon material; the heating rate is 10 ℃ / min, the carbonization temperature is 900 ℃, and the carbonization time is 1 h; and the protective atmosphere is nitrogen and argon.

[0067] Example 4

[0068] The present embodiment relates to a green and environmentally friendly preparation method of a sodium ion battery hard carbon negative electrode material, comprising the following steps:

[0069] S1, pre-carbonization: the biomass raw material is pre-carbonized under a protective atmosphere to obtain a pre-carbonized material. Specifically, the carbonization conditions are: a heating rate of 5 ℃ / min, a carbonization temperature of 700 ℃, and a carbonization time of 2 h. The biomass raw material is reed, coffee shell, coconut shell, bamboo, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, and cedar.

[0070] S2, particle size control treatment: the pre-carbonized material obtained in step S1 is crushed and refined to obtain a refined pre-carbonized material. Specifically, the pre-carbonized material is crushed and refined to a D50 of 5-20 μm, the crushing mode is impact, roller, and stirring mill; the protective atmosphere is nitrogen and argon.

[0071] S3, preparation of a precursor material: the refined pre-carbonized material obtained in step S2, acid solution, and deionized water are stirred and dispersed to form a precursor slurry, and after temperature control sand milling, solid-liquid separation, water washing, and drying, a precursor material is obtained; the acid solution is hydrochloric acid; the addition amount of the acid solution is 5wt.% of the mass of the pre-carbonized material, the pH of the precursor slurry is 5, and the solid content of the precursor slurry is 20%. Specifically, the sand milling temperature is 70 ℃, the sand milling time is 2 h, the grinding is to a D50 of 3-10 μm of the precursor material; the water washing is to a pH of 6 of the precursor material; the solid-liquid separation mode is centrifugation and / or pressure filtration; and the drying mode is flash drying and rake dryer.

[0072] S4, high-temperature sintering: the precursor material obtained in step S3 is high-temperature carbonized under a protective atmosphere to obtain a purified hard carbon material. Specifically, the high-temperature carbonization conditions are: a heating rate of 3 ℃ / min, a carbonization temperature of 1300 ℃, and a carbonization time of 4 h; and the protective atmosphere is nitrogen and argon.

[0073] S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in step S4 is high-temperature carbon coated to obtain a surface-coated hard carbon negative material. Specifically, the high-temperature carbon coating mode is chemical vapor deposition, liquid phase coating, and high-temperature solid phase coating; the high-temperature carbon coating raw material is a carbon source free of metal impurities, and the carbon source is pitch, phenolic resin, PVP, PVA, dopamine, and glucose; the amount of the carbon layer in the high-temperature coated carbon is 4wt.% of the weight of the hard carbon material; the heating rate is 3 ℃ / min, the carbonization temperature is 700 ℃, and the carbonization time is 1.5 h; and the protective atmosphere is nitrogen and argon.

[0074] Example 5

[0075] This example relates to a green and environmentally friendly method for preparing a sodium ion battery hard carbon negative material, comprising the following steps:

[0076] S1, pre-carbonization: the biomass raw material is pre-carbonized under a protective atmosphere to obtain a pre-carbonized material. Specifically, the carbonization conditions are: a heating rate of 15 ℃ / min, a carbonization temperature of 400 ℃, and a carbonization time of 4 h. The biomass raw material is walnut shell, nut shell, apricot shell, and straw.

[0077] S2, particle size control treatment: the pre-carbonized material obtained in step S1 is crushed and refined to obtain a refined pre-carbonized material. Specifically, the pre-carbonized material is crushed and refined to a D50 of 5-20 μm, and the crushing method is impact crushing; the protective atmosphere is nitrogen and argon.

[0078] S3, preparation of a precursor material: the refined pre-carbonized material obtained in step S2, acid solution, and deionized water are stirred and dispersed to form a precursor slurry, and after temperature control sand milling, solid-liquid separation, water washing, and drying, a precursor material is obtained; the acid solution is hydrochloric acid; the addition amount of the acid solution is 15 wt.% of the mass of the pre-carbonized material, the pH of the precursor slurry is 4, and the solid content of the precursor slurry is 20%. Specifically, the sand milling temperature is 60 ℃, the sand milling time is 4 h, the grinding is performed to a D50 of 3-10 μm of the precursor material; the water washing is performed to a pH of 6 of the precursor material; the solid-liquid separation method is centrifugation and / or pressure filtration; and the drying method is a drum belt dryer or a rake dryer.

[0079] S4, high-temperature sintering: the precursor material obtained in step S3 is high-temperature carbonized under a protective atmosphere to obtain a purified hard carbon material. Specifically, the high-temperature carbonization conditions are: a heating rate of 3 ℃ / min, a carbonization temperature of 1400 ℃, and a carbonization time of 4 h; and the protective atmosphere is nitrogen and argon.

[0080] S5, high-temperature carbon coating: the surface of the purified hard carbon material obtained in step S4 is high-temperature carbon coated to obtain a surface-coated hard carbon negative electrode material. Specifically, the high-temperature carbon coating method is chemical vapor deposition, liquid phase coating, and high-temperature solid phase coating; the high-temperature carbon coating raw material is a carbon source free of metal impurities, and the carbon source is glucose, PAA, citric acid, phenol, benzene, toluene, or acetylene; the amount of the carbon layer in the high-temperature coated carbon is 4 wt.% of the weight of the hard carbon material; the heating rate is 3 ℃ / min, the carbonization temperature is 1000 ℃, and the carbonization time is 2 h; and the protective atmosphere is nitrogen and argon.

[0081] Application Example 1

[0082] This example relates to an ion battery hard carbon negative electrode material. The preparation process includes the following steps:

[0083] S1, pre-carbonization: the coconut shell raw material is pre-carbonized under a nitrogen gas atmosphere, the heating rate is 5 ℃ / min, the carbonization temperature is 700 ℃, and the carbonization time is 3, to obtain a pre-carbonized material.

[0084] S2, particle size control process: the pre-carbonized material obtained in step S1 is crushed and refined in sequence using a roll mill and a mechanical mill, and the pre-carbonized material with a D50 of 10 μm is obtained.

[0085] S3, preparation of a precursor material: the crushed pre-carbonized material obtained in step S2, acid solution and deionized water are stirred and dispersed in a dispersion tank to obtain a precursor slurry, wherein the amount of hydrochloric acid added is 10 wt.% of the amount of pre-carbonized material added, the pH of the slurry is 4.5, and the solid content of the slurry is 25%. Subsequently, sand milling is performed: the temperature of sand milling is 60°C, the time is 1.5, and the material is ground to a D50 of 5 μm. Subsequently, centrifugation, water washing to pH = 6, and drying in a blast oven are performed to obtain a precursor material.

[0086] S4, high-temperature sintering: the precursor material obtained in step S3 is subjected to high-temperature carbonization under a nitrogen gas atmosphere, the heating rate is 2 ℃ / min, the carbonization temperature is 1400 ℃, and the carbonization time is 3 h, to obtain a purified hard carbon material;

[0087] S5, high-temperature carbon coating: using acetylene as a coating agent, coating is performed in a CVD manner, the coating atmosphere is argon, the coating temperature is 800°C, and the deposition time is 1 h, to obtain a hard carbon negative electrode material coated on the surface.

[0088] The obtained material is subjected to electrochemical performance testing according to the following method: hard carbon material, Super P, CMC, and SBR are mixed into a uniform slurry at a mass ratio of 94:1.5:2:2.5, the black slurry is coated on a copper foil using a 120 um four-side coater, and then the film is dried in a 100°C vacuum drying oven for 2 hours. The electrode film is punched into a circular sheet with a radius of 0.6 mm using a sheet punching machine, a metal sodium is used as a counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) is used as an electrolyte, and a PP / PE / PP three-layer separator is used as a separator, to assemble a CR2016 type button cell in a glove box. The button cell is subjected to constant current charge and discharge testing, the current density is 0.1C (1C=300 mAh / g), and the voltage range is 2-0.005 V.

[0089] Comparative Example 1 (without sand milling)

[0090] This example relates to an ion battery hard carbon negative electrode material. The preparation process thereof includes the following steps:

[0091] S1, pre-carbonization: the coconut shell raw material is pre-carbonized under a nitrogen gas atmosphere, the heating rate is 5 ℃ / min, the carbonization temperature is 700 ℃, and the carbonization time is 3, to obtain a pre-carbonized material.

[0092] S2, fineness control treatment: the pre-carbonized material obtained in step S1 is crushed and refined in sequence using a pair of rollers and a mechanical mill, and the pre-carbonized material with a D50 of 5 μm is obtained.

[0093] S3, high-temperature sintering: the precursor material obtained in step S2 is subjected to high-temperature carbonization under a nitrogen gas atmosphere, the heating rate is 2 ℃ / min, the carbonization temperature is 1400 ℃, and the carbonization time is 3 h, to obtain a purified hard carbon material;

[0094] S4, high-temperature carbon coating: using acetylene as a coating agent, coating is performed in a CVD manner, the coating atmosphere is argon, the coating temperature is 800 ℃, and the deposition time is 1 h, to obtain a hard carbon negative electrode material coated on the surface.

[0095] The obtained material is subjected to electrochemical performance testing according to the following method: hard carbon material, Super P, CMC, and SBR are mixed into a slurry in a mass ratio of 94:1.5:2:2.5, the black slurry is coated on a copper foil using a 120 um four-side coater, and then the film is dried in a 100 ℃ vacuum drying oven for 2 hours. The electrode film is punched into a circular sheet with a radius of 0.6 mm using a sheet puncher, metal sodium is used as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) is used as the electrolyte, and a PP / PE / PP three-layer separator is used to assemble a CR2016 type button cell in a glove box. The above button cell is subjected to constant current charge and discharge testing, the current density is 0.1C (1C=300 mAh / g), and the voltage range is 2-0.005 V.

[0096] Comparative Example 2 (without coating)

[0097] This example relates to an ion battery hard carbon negative electrode material. The preparation process includes the following steps:

[0098] S1, pre-carbonization: the coconut shell raw material is pre-carbonized under a nitrogen gas atmosphere, the heating rate is 5 ℃ / min, the carbonization temperature is 700 ℃, and the carbonization time is 3, to obtain a pre-carbonized material.

[0099] S2, fineness control treatment: the pre-carbonized material obtained in step S1 is crushed and refined in sequence using a pair of rollers and a mechanical mill, and the pre-carbonized material with a D50 of 10 μm is obtained.

[0100] S3, Preparation of the precursor material: the crushed pre-carbonization material obtained in step S2, acid solution and deionized water were stirred and dispersed in a dispersion tank, wherein the added amount of hydrochloric acid was 10 wt.% of the added amount of the pre-carbonization material, the pH of the slurry was 4.5; the solid content of the slurry was 25%. Then sand milling was carried out: the temperature of sand milling was 60°C, the time was 1.5, and the material was ground to a D50 of 5 μm. Then centrifugation, water washing to pH = 6, and air oven drying were carried out to obtain the precursor material.

[0101] S4, High-temperature sintering: the precursor material obtained in step S3 was subjected to high-temperature carbonization under nitrogen gas, the heating rate was 2 ℃ / min, the carbonization temperature was 1400 ℃, and the carbonization time was 3 h to obtain a purified hard carbon material;

[0102] The obtained material was subjected to electrochemical performance test according to the following method: hard carbon material, Super P, CMC, SBR were mixed into a slurry in a mass ratio of 94:1.5:2:2.5, then the black slurry was coated on a copper foil using a 120 um four-side coater, and then the film was dried in a 100°C vacuum drying oven for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6 mm using a sheet puncher, sodium metal was used as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) was used as the electrolyte, and PP / PE / PP three-layer separators were used to assemble CR2016 type button cells in a glove box. The above button cells were subjected to constant current charge and discharge test, the current density was 0.1C (1C = 300 mAh / g), and the voltage range was 2-0.005 V.

[0103] The test results of ash content test of Example 1, Comparative Example 1 and Comparative Example 2 were 0.6%, 2.5% and 0.7% respectively. It showed that the sand milling plus acid process could significantly reduce the content of impurities in the hard carbon material.

[0104] The pH test results showed that the pH of Example 1, Comparative Example 1 and Comparative Example 2 was 7.5, 10.6 and 8.1 respectively. It showed that the sand milling plus acid and surface coating process could effectively reduce the pH of the hard carbon material, and thus improve the processability of the material.

[0105] The nitrogen adsorption-desorption test results showed that the specific surface area of Example 1, Comparative Example 1 and Comparative Example 2 was 4.3, 5.3 and 10.6 m 2 / g respectively, indicating that the surface coating process could effectively reduce the specific surface area of the material.

[0106] The constant current charge-discharge test measured the first week charge specific capacity of example 1, comparative example 1 and comparative example 2 was 301, 290 and 287 mAh / g, respectively, and the first week coulombic efficiency was 92.3, 91.1 and 87.4%, respectively, indicating that increasing the purity of the hard carbon material and reducing the surface area of the material can effectively improve the week-to-week coulombic efficiency of the hard carbon material.

[0107] The constant current charge-discharge test measured the capacity retention rate of example 1, comparative example 1 and comparative example 2 after 200 cycles was 89.4, 82.3 and 79.4%, respectively, indicating that sand milling plus acid and surface coating process can effectively improve the cycle performance of the hard carbon material.

[0108] The above examples are only specific embodiments of the present application, which are described in detail, but cannot be construed as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.

Claims

1. A method for preparing a green and environmentally friendly hard carbon anode material for sodium-ion batteries, characterized in that... Includes the following steps: S1. Pre-carbonization: Biomass raw materials are pre-carbonized under a protective atmosphere to obtain pre-carbonized material; the pre-carbonization conditions are: heating rate of 1-20 ℃ / min, carbonization temperature of 300-900 ℃, and carbonization time of 1-5 h. S2. Particle size control treatment: The pre-carbonized material obtained in step S1 is crushed and refined to obtain refined pre-carbonized material; S3. Preparation of precursor material: The refined pre-carbonized material obtained in step S2, acid solution, and deionized water are stirred and dispersed to form a precursor slurry. After temperature-controlled sand milling, solid-liquid separation, water washing, and drying are performed to obtain the precursor material. The acid solution is hydrochloric acid. The amount of acid solution added is 1-20 wt.% of the mass of the pre-carbonized material. The pH of the precursor slurry is 4-6. The solid content of the precursor slurry is 15-30%. The sand milling temperature is 30-80℃, the sand milling time is 1-6 h, and the D50 of the precursor material is ground to 3-10 μm. S4. High-temperature sintering: The precursor material obtained in step S3 is carbonized at high temperature under a protective atmosphere to obtain purified hard carbon material; the conditions for high-temperature carbonization are: heating rate of 0.5-10 ℃ / min, carbonization temperature of 1100-1500 ℃, and carbonization time of 2-5 h. S5. High-Temperature Carbon Coating: The purified hard carbon material obtained in step S4 is subjected to high-temperature carbon coating to obtain a surface-coated hard carbon anode material; the high-temperature carbon coating method is one or more of chemical vapor deposition, liquid phase coating, and high-temperature solid phase coating; the raw material for high-temperature carbon coating is a carbon source free of metal impurities, which is one or more of asphalt, phenolic resin, PVP, PVA, dopamine, glucose, PAA, citric acid, phenol, benzene, toluene, and acetylene; the amount of carbon layer in high-temperature carbon coating is 0.5-5 wt.% of the weight of the hard carbon material; the heating rate is 1-10 ℃ / min, the carbon coating temperature is 600-1100℃, and the carbon coating time is 1-3 h.

2. The method for preparing the green and environmentally friendly hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In step S3, the precursor material is washed with water until the pH of the precursor material is 6-7; the solid-liquid separation method is centrifugation and / or pressure filtration; the drying method is one or more of the following: forced-air oven drying, flash drying, vacuum oven drying, tunnel drying oven, double cone dryer, belt dryer, and rake dryer.

3. The method for preparing the green and environmentally friendly hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In step S2, the pre-carbonized material is pulverized and refined to a D50 of 5-20 μm. The pulverization method is one or more of the following: jaw crusher, roller mill, air jet mill, mechanical mill, ball mill, Raymond mill, and stirred mill.

4. The method for preparing the green and environmentally friendly hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In step S1, the biomass raw materials are one or more of the following: walnut shells, nut shells, apricot shells, straw, reeds, coffee shells, coconut shells, bamboo, poplar, eucalyptus, pine, fruit wood, fir, oak, anthracite, lignite, and bituminous coal.

5. The method for preparing the green and environmentally friendly hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In steps S1, S4 and S5, the protective atmosphere is nitrogen and / or argon.