Method for preparing biomass hard carbon material by ball-milling oxidation and oxygen-rich roasting in cooperation, biomass hard carbon material and sodium ion battery

Abstract

This invention discloses a method for preparing biomass hard carbon materials through ball milling, oxidation, and oxygen-enriched calcination: biomass is sequentially mixed with an oxidizing agent and subjected to ball milling, calcined in an oxygen-enriched atmosphere, carbonized at low temperature under a protective atmosphere, chemically purified, and then carbonized at high temperature under a protective atmosphere to obtain a biomass hard carbon anode material. This invention also discloses a biomass hard carbon material prepared by ball milling and oxygen-enriched calcination, and a sodium-ion battery. The biomass hard carbon material preparation process of this invention is simple, has low production cost, and exhibits high sodium storage capacity, thus accelerating the industrialization of biomass-based hard carbon.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and particularly relates to a method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, as well as the biomass hard carbon materials and sodium-ion batteries. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries have advantages such as low cost, abundant sodium resources, and excellent safety performance, and are considered one of the most promising energy storage systems. Among them, carbon-based anodes are recognized as the most commercially promising anode materials, especially biomass-based hard carbon materials, which have attracted widespread attention due to their abundant precursor sources and low prices. However, current biomass-based hard carbon materials suffer from problems such as low sodium storage capacity and poor cycle performance. Furthermore, the current preparation methods for biomass-based hard carbon materials also have some technical problems. For example, patent application CN202210603915.6 discloses a biomass hard carbon based on low crystalline cellulose content, its preparation method, and its application. This method involves pretreating biomass through acid hydrolysis and alkaline hydrolysis, followed by carbonization and pyrolysis under an inert atmosphere to prepare biomass-derived hard carbon with high closed-pore ratio. However, due to the use of chemical reagents, it is not environmentally friendly, and its process is complex and has high production costs. Patent application CN202410068005.1 discloses a biomass hard carbon anode material, its preparation method, and its application. It involves pre-carbonizing agricultural waste in an inert atmosphere, then blending it with a modifier for modification, followed by high-temperature carbonization after impurity removal to obtain the hard carbon material. However, the modifier used is difficult to remove during impurity removal, affecting the sodium storage performance of the hard carbon material. Patent application CN202110907187.3 discloses a sodium-ion battery carbon anode material based on waste wood chips and its preparation method. It uses waste wood chips as a precursor and pre-carbonizes them in air. However, the oxygen concentration is too low, the carbonization time is too short, and the biomass cannot fully contact oxygen, resulting in insufficient pre-oxidation. Furthermore, the temperature and time distribution during the carbonization process cannot be precisely controlled, affecting the quality and performance of the final product. Additionally, it has high energy consumption, which is not suitable for practical production. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a method for preparing biomass hard carbon materials by ball milling oxidation and oxygen-enriched calcination, as well as biomass hard carbon materials and sodium-ion batteries.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0005] A method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination includes the following steps:

[0006] (1) After mixing the biomass with an oxidizing agent, the mixture is ball-milled; the oxidizing agent is at least one of hydrogen peroxide, concentrated sulfuric acid, and persulfate.

[0007] (2) The ball-milled oxidation product obtained after step (1) is placed in an oxygen-enriched atmosphere for calcination treatment; wherein the oxygen concentration in the oxygen-enriched atmosphere is not less than 30%;

[0008] (3) The roasted product obtained after step (2) is subjected to low-temperature carbonization treatment under a protective atmosphere;

[0009] (4) The low-temperature carbonization product obtained after step (3) is chemically purified;

[0010] (5) The low-temperature carbonization product obtained by chemical purification in step (4) is subjected to high-temperature carbonization under a protective atmosphere to obtain biomass hard carbon anode material.

[0011] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, in step (2), the oxygen-enriched atmosphere is a mixture of oxygen and nitrogen, the calcination temperature is 150-350℃, and the holding time is 4-48h. The calcination temperature should not be too low, otherwise the pre-oxidation will be insufficient, the cross-linking will be insufficient, and the material properties will be affected; the calcination temperature should not be too high, otherwise combustion will occur, affecting the yield.

[0012] Oxygen-enriched calcination enables cross-linking of organic macromolecules in biomass, forming more carbonyl functional groups and facilitating the formation of highly randomly oriented nanostructures during subsequent carbonization. In general, oxygen-enriched calcination enhances the degree of cross-linking of macromolecules in biomass, suppresses graphitization during carbonization, and yields more disordered hard carbon materials. Hard carbon materials prepared by oxygen-enriched calcination pretreatment have higher carbonyl content, increased interlayer spacing, and significantly improved sodium storage capacity. The O / C ratio of the material is reduced, the calorific value is increased, the yield of high-temperature carbonization is improved, the overall yield is increased, and the production cost is reduced. The oxygen concentration in the oxygen-enriched atmosphere should not be less than 30%. If the oxygen concentration is low, the contact between oxygen and biomass is poor, resulting in insufficient oxidation and cross-linking of biomass, which in turn affects electrochemical performance. To further ensure sufficient oxidation during the oxygen-enriched calcination process, this invention introduces an oxidizing agent during ball milling to achieve preliminary oxidation of the biomass.

[0013] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation and oxygen-enriched calcination, preferably, in step (1), the ball milling speed is 200-600 rpm and the ball milling time is not less than 12 h.

[0014] During ball milling, long-chain molecules in biomass can be broken down through physical action, and weaker chemical bonds (hydrogen bonds) can be severed through shear force, effectively reducing the degree of polymerization of biomass organic molecules. Mechanical force can promote the generation of free radicals in biomass molecules, which can then react with other molecules to form new chemical bonds. The heat and pressure generated during ball milling cause certain functional groups in biomass to react and form new chemical bonds, thus achieving preliminary cross-linking of biomass components.

[0015] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, in step (1), the ratio of biomass to oxidizing agent is 20:1 to 2:1.

[0016] Introducing oxidizing agents during ball milling can promote the initial oxidation of biomass. Taking hydrogen peroxide as an example, the initial oxidation process of biomass is explained. Under alkaline conditions, hydrogen peroxide will dissociate to generate peroxyhydroxyl ions, as shown in formula (1). Peroxyhydroxyl anions will act on the lignin side chain, forming hydroxylated products from the propene structure with double bond structure, and generating hydroxyl radicals, as shown in formula (2). The hydroxylated intermediate will undergo chain scission reaction, resulting in a decrease in the degree of polymerization, as shown in formula (3).

[0017] H2O2+OH - ⇌ H2O+HOO - (1)

[0018] R-CH=H-CH2-Ar+HOO - → R-CH(OH)-CH2-Ar+HO·(2)

[0019] R-CH(OH)-CH2-Ar→ R-CHO+HO-CH2-Ar(3)

[0020] In this context, R-CH=H-CH2-Ar represents the allyl structure on the lignin side chain, Ar represents the aromatic ring structure of lignin, and R-CH(OH)-CH2-Ar is a hydroxylation intermediate.

[0021] Hydrogen peroxide will further dissociate with peroxyhydroxy anion to generate hydroxyl radicals and superoxide anion radicals, as shown in formula (4). Hydroxyl radicals can effectively oxidize the β-O-4 ether bond between lignin and hemicellulose and the ester bond of lignin, as shown in formulas (5) and (6), to achieve preliminary pre-oxidation.

[0022] H2O2+HOO - → HO·+·O 2- +H2O (4)

[0023] Ar-O-CH2-Ar1+HO·→ Ar-OH+Ar1-CHO (5)

[0024] Ar-COO-R+HO· → Ar-COOH+RH (6)

[0025] In Ar-O-CH2-Ar1, two aromatic compounds (Ar and Ar1) are linked by a β-O-4 ether bond. The hydroxyl radical interacts with the ether bond, causing it to break and form a phenol (Ar-OH) and an aldehyde (Ar1-CHO). Ar-COO-R represents an ester bond in lignin. Ar is the aromatic ring of lignin, and R is the fatty acid chain. The hydroxyl radical interacts with the ester bond, causing it to break and form a carboxylic acid (Ar-COOH) and the corresponding alcohol or hydrocarbon (RH).

[0026] The residual hydrogen peroxide will decompose into oxygen and water during the roasting process, as shown in formula (7), which is beneficial for the pre-oxidation of biomass.

[0027] H2O2→ H2O+O2(7)

[0028] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, in step (2), the gas flow rate of the oxygen-enriched atmosphere is 0.1-4 L / h.

[0029] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, in step (3), the temperature of the low-temperature carbonization treatment is 400-800℃, and the holding time is 1-4 h. During the low-temperature carbonization process, the temperature is usually low, mainly used to remove volatiles in the precursor, and at the same time to perform preliminary carbonization of the material to form a preliminary carbon structure. This stage helps to improve the loading amount and yield during the second stage of carbonization, and at the same time, to allow the hard carbon structure to be initially formed, providing a stable foundation for subsequent carbonization. In this invention, after low-temperature carbonization, high-temperature carbonization is also carried out. This two-stage carbonization method can more accurately control the temperature and time. Through crushing and particle size control, it helps to improve the control of the specific surface area and median particle size of the hard carbon, thereby obtaining a higher quality hard carbon product, and can save energy consumption, reduce production costs, and meet the requirements of industrial production.

[0030] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, the biomass is first soaked, washed, and dried, and then subjected to oxygen-enriched calcination.

[0031] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, the biomass is one of bamboo, reed, coconut shell, and fruit shell; the soaking time is 1-8 hours; the drying temperature is 50-100℃, and the drying time is 6-24 hours.

[0032] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation and oxygen-enriched calcination, preferably, in step (4), the chemical impurity removal includes alkaline leaching and acid leaching. The reagent used in the alkaline leaching is selected from one or more mixed solutions of sodium hydroxide, potassium hydroxide, and ammonia water. The reagent used in the acid leaching is selected from one or more mixed solutions of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid.

[0033] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation and oxygen-enriched calcination, preferably, in step (5), the high-temperature carbonization temperature is 1000-1600℃ and the holding time is 1-4 h.

[0034] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, in steps (3) and (5), the protective atmosphere is at least one of nitrogen and argon, and the gas flow rate of the protective atmosphere is 0.1-4 L / h.

[0035] In the above-mentioned method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, preferably, the D50 of the biomass hard carbon material is 2-15 μm.

[0036] Based on a general inventive concept, the present invention also provides a biomass hard carbon material, which is prepared by the above-described preparation method.

[0037] Based on a general inventive concept, the present invention also provides a sodium-ion battery comprising the above-described biomass hard carbon material.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) This invention uses biomass, which is abundant and inexpensive, as raw material. By mixing and ball milling with oxidizing reagents, the degree of polymerization of macromolecules in biomass can be reduced, more free radicals can be exposed, which is conducive to the oxidation of oxygen-enriched roasting process. It can also preliminarily oxidize the β-O-4 ether bond between lignin and hemicellulose and the ester bond of lignin. Then, the ball-milled and oxidized material is subjected to oxygen-enriched roasting treatment, which makes the organic molecules in biomass crosslinked, inhibits the degree of graphitization in the carbonization process, and the prepared hard carbon material is more disordered and has excellent sodium storage performance.

[0040] (2) The present invention uses oxygen-enriched roasting pretreatment to reduce the O / C ratio, increase the yield of subsequent carbonization processes, reduce energy consumption, increase carbon yield, and effectively reduce production costs.

[0041] (3) When the biomass hard carbon material of the present invention is used as a carbon-based negative electrode to prepare sodium-ion batteries, it has advantages such as high sodium storage capacity and excellent cycle performance.

[0042] Overall, the preparation process of the biomass hard carbon material of the present invention is simple, the production cost is low, and the sodium storage capacity is high, which accelerates the industrialization process of biomass-based hard carbon. Attached Figure Description

[0043] Figure 1 This is the XRD pattern of the biomass-based hard carbon material prepared in Example 1 of this invention.

[0044] Figure 2 This is a TEM image of the biomass-based hard carbon material prepared in Example 1 of this invention.

[0045] Figure 3 This is the first charge-discharge curve of the biomass-based hard carbon material prepared in Example 1 of this invention. Detailed Implementation

[0046] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0047] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0048] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0049] The following examples and comparative examples involve a hard carbon yield of carbon material = (mass of the prepared hard carbon material / mass of the original biomass) * 100%.

[0050] Example 1:

[0051] A method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination according to the present invention includes the following steps:

[0052] (1) Raw material processing: Soak bamboo in distilled water for 2 hours, wash it, dry it at 80℃ for 18 hours, and pre-crush it;

[0053] (2) Ball milling oxidation: The pre-crushed bamboo was mixed with a hydrogen peroxide solution with a pH of 11 and a concentration of 0.3 g / mL at a solid-liquid ratio of 1:1 g / mL and ball milled at a speed of 400 rpm for 24 h.

[0054] (3) Oxygen-enriched roasting: The ball-milled and oxidized bamboo is added to a heating furnace and roasted at 250°C for 24 hours at a heating rate of 5°C / min under an oxygen-enriched atmosphere. The oxygen-enriched atmosphere is a mixture of 50% oxygen and 50% argon, and the flow rate of the mixture is 0.3 L / h. After roasting, the mixture is cooled to room temperature to obtain the oxygen-enriched roasting product.

[0055] (4) Low-temperature carbonization: The oxygen-enriched roasting product was heated to 500℃ at a heating rate of 5℃ / min under the protection of argon gas for low-temperature carbonization. The carbonization holding time was 2 h, the argon gas flow rate was 0.3 L / h, and the low-temperature carbonized product was obtained after cooling to room temperature.

[0056] (5) Impurity removal treatment: The low-temperature carbonization product is first treated with an alkaline leaching solution of 5 mol / L sodium hydroxide for 5 h; then treated with an acid leaching solution of 1 mol / L hydrochloric acid and 3 mol / L hydrofluoric acid for 5 h to remove impurity elements and obtain the impurity-removed product.

[0057] (6) High-temperature carbonization: The impurity-removed product obtained in step (5) is heated to 1500℃ under the protection of argon gas at a heating rate of 5℃ / min for high-temperature carbonization. The carbonization holding time is 2 h, the argon gas flow rate is 0.3 L / h, and the high-temperature carbonized product is obtained after cooling to room temperature.

[0058] (7) Grinding and classification: The high-temperature carbonization products are subjected to air jet milling to obtain D 50 Materials with a thickness of 10 μm are called biomass-based hard carbon materials.

[0059] The carbon yield of the hard carbon material prepared in this embodiment is 29.33%.

[0060] The XRD pattern of the biomass-based hard carbon material prepared in this embodiment is as follows: Figure 1 As shown in the XRD pattern, two severely broadened diffraction peaks appear near 23° and 43°, which correspond to the diffraction crystal planes (002) and (101) respectively, indicating that the material prepared in this embodiment belongs to amorphous carbon material.

[0061] TEM images of the biomass-based hard carbon material prepared in this invention are shown below. Figure 2 As shown in the figure, the biomass-based hard carbon material prepared in this embodiment has a high degree of disorder and a large number of closed-pore structures.

[0062] The hard carbon material prepared in this embodiment was used as the active material for the negative electrode of a sodium-ion battery in the preparation of sodium-ion batteries, and its electrochemical performance was measured:

[0063] The hard carbon material powder prepared in this embodiment was mixed evenly with acetylene black and PVDF at a mass ratio of 90:5:5. Then, an appropriate amount of organic solvent NMP was added and the mixture was ground to form a slurry. The evenly ground slurry was then uniformly coated onto a current collector copper foil, dried, and cut into circular electrode sheets. The electrode sheets were dried at 120°C for 6 hours under vacuum conditions and then transferred to a glove box for later use.

[0064] The simulated battery assembly was performed in an Ar atmosphere glove box, using metallic sodium as the counter electrode and a CR2032 coin cell assembled with 1 mole of NaPF6 dissolved in 1 L of a 1:1 volume ratio solution of ethylene carbonate and diethyl carbonate as the electrolyte. Constant current charge-discharge mode was used, and charge-discharge tests were conducted at a current density of 0.1C. Figure 3 As shown, under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity is 325.41 mAh / g, the first-cycle coulombic efficiency is 87.13%, and the capacity retention rate is as high as 95.80% after 100 cycles at a current density of 1.0 C.

[0065] Example 2:

[0066] A method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination according to the present invention includes the following steps:

[0067] (1) Raw material processing: Soak coconut shells in distilled water for 2 hours, wash them, dry them at 90℃ for 12 hours, and pre-crush them;

[0068] (2) Ball milling oxidation: The pre-crushed coconut shells were mixed with a hydrogen peroxide solution with a pH of 10 and a concentration of 0.2 g / mL at a solid-liquid ratio of 1:1 g / mL, and ball milled at a speed of 400 rpm for 16 h.

[0069] (3) Oxygen-enriched roasting: The ball-milled and oxidized coconut shells are added to a heating furnace and roasted at 180°C for 18 hours at a heating rate of 5°C / min under an oxygen-enriched atmosphere. The oxygen-enriched atmosphere is a mixture of 50% oxygen and 50% argon, and the flow rate of the mixture is 0.3 L / h. After roasting, the mixture is cooled to room temperature to obtain the oxygen-enriched roasting product.

[0070] (4) Low-temperature carbonization: The oxygen-enriched roasting product was heated to 500℃ at a heating rate of 5℃ / min under the protection of argon gas for low-temperature carbonization. The carbonization holding time was 2 h, the argon gas flow rate was 0.3 L / h, and the low-temperature carbonized product was obtained after cooling to room temperature.

[0071] (5) Impurity removal treatment: The low-temperature carbonization product is first treated with an alkaline leaching treatment of 4 mol / L sodium hydroxide solution for 6 h; then treated with an acid leaching treatment of 2 mol / L hydrochloric acid solution for 6 h to remove impurity elements and obtain the impurity-removed product.

[0072] (6) High-temperature carbonization: The purified product was heated to 1400℃ under the protection of argon gas at a heating rate of 5℃ / min for high-temperature carbonization. The carbonization holding time was 3h, the argon gas flow rate was 0.3 L / h, and the high-temperature carbonized product was obtained after cooling to room temperature.

[0073] (7) Grinding and classification: The high-temperature carbonization products are subjected to air jet milling to obtain D 50 Materials with a thickness of 12 μm are biomass-based hard carbon materials.

[0074] The carbon yield of the hard carbon material prepared in this embodiment is 28.83%.

[0075] The biomass-based hard carbon material of this embodiment was used as the active material for the negative electrode of a sodium-ion battery in the preparation of the sodium-ion battery, and electrochemical charge-discharge tests were conducted. The preparation process and testing methods were the same as in Example 1. The results are as follows: under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity was 319.23mAh / g, the first-cycle coulombic efficiency was 86.90%, and the capacity retention rate after 100 cycles at a current density of 1.0C was 95.17%.

[0076] Example 3:

[0077] A method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination according to the present invention includes the following steps:

[0078] (1) Raw material processing: Soak bamboo in distilled water for 4 hours, wash it, dry it at 90℃ for 12 hours, and pre-crush it;

[0079] (2) Ball milling oxidation: The pre-crushed bamboo was mixed with a hydrogen peroxide solution with a pH of 11 and a concentration of 0.4 g / mL at a solid-liquid ratio of 1:1 g / mL and ball milled at 300 rpm for 24 h.

[0080] (3) Oxygen-enriched roasting: The ball-milled and oxidized bamboo is added to a heating furnace and roasted at 200°C for 24 hours at a heating rate of 5°C / min under an oxygen-enriched atmosphere. The oxygen-enriched atmosphere is a mixture of 80% oxygen and 20% argon, and the flow rate of the mixture is 0.3 L / h. After roasting, the mixture is cooled to room temperature to obtain the oxygen-enriched roasting product.

[0081] (4) Low-temperature carbonization: The oxygen-enriched roasting product was heated to 600℃ at a heating rate of 5℃ / min under the protection of argon gas for low-temperature carbonization. The carbonization holding time was 2 h, the argon gas flow rate was 0.3 L / h, and the low-temperature carbonized product was obtained after cooling to room temperature.

[0082] (5) Impurity removal treatment: The low-temperature carbonization product is first treated with an alkaline leaching solution of 5 mol / L sodium hydroxide for 5 h; then treated with an acid leaching solution of 1 mol / L hydrochloric acid and 3 mol / L hydrofluoric acid for 5 h to remove impurity elements and obtain the impurity-removed product.

[0083] (6) High-temperature carbonization: The purified product is heated to 1500℃ under the protection of argon gas at a heating rate of 5℃ / min for high-temperature carbonization. The carbonization holding time is 3h, the argon gas flow rate is 0.3 L / h, and the high-temperature carbonized product is obtained after cooling to room temperature.

[0084] (7) Grinding and classification: The high-temperature carbonization products are subjected to air jet milling to obtain D 50 Materials with a thickness of 12 μm are biomass-based hard carbon materials.

[0085] The carbon yield of the hard carbon material prepared in this embodiment is 28.26%.

[0086] The biomass-based hard carbon material prepared in this embodiment was used as the active material for the negative electrode of a sodium-ion battery. Electrochemical charge-discharge tests were conducted, and the preparation process and testing methods were the same as in Example 1. The results are as follows: Under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity was 320.87mAh / g, the first-cycle coulombic efficiency was 86.30%, and the capacity retention rate after 100 cycles at a current density of 1.0C was 94.88%.

[0087] Comparative Example 1:

[0088] The difference between this comparative example and Example 1 is that there is no oxygen-enriched roasting pretreatment; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0089] (1) Raw material processing: Soak bamboo in distilled water for 2 hours, wash it, dry it at 80℃ for 18 hours, and pre-crush it;

[0090] (2) Ball milling oxidation: The pre-crushed bamboo was mixed with a hydrogen peroxide solution with a pH of 11 and a concentration of 0.3 g / mL at a solid-liquid ratio of 1:1 g / mL and ball milled at a speed of 400 rpm for 24 h.

[0091] (3) Low-temperature carbonization: The material oxidized by ball milling in step (2) is heated to 500°C under the protection of argon gas at a heating rate of 5°C / min for low-temperature carbonization. The carbonization holding time is 2 h, the flow rate of argon gas is 0.3 L / h, and the low-temperature carbonized product is obtained after cooling to room temperature.

[0092] (4) Impurity removal treatment: The low-temperature carbonization product is first treated with an alkaline leaching solution of 5 mol / L sodium hydroxide for 5 h; then treated with an acid leaching solution of 1 mol / L hydrochloric acid and 3 mol / L hydrofluoric acid for 5 h to remove impurity elements and obtain the impurity-removed product.

[0093] (5) High-temperature carbonization: The purified product was heated to 1500℃ under the protection of argon gas at a heating rate of 5℃ / min for high-temperature carbonization. The carbonization holding time was 2 h and the argon gas flow rate was 0.3 L / h. After cooling to room temperature, the high-temperature carbonized product was obtained.

[0094] (6) Grinding and classification: The high-temperature carbonization products are subjected to air jet milling to obtain D 50 Materials with a thickness of 10 μm are called biomass-based hard carbon materials.

[0095] The carbon yield of the hard carbon material prepared in this comparative example was 24.43%.

[0096] The biomass-based hard carbon material of this comparative example was used as the active material for the negative electrode of a sodium-ion battery in the preparation of the battery, and electrochemical charge-discharge tests were conducted. The preparation process and testing methods were the same as in Example 1. The results are as follows: under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity was 291.09mAh / g, the first-cycle coulombic efficiency was 82.66%, and the capacity retention rate after 100 cycles at a current density of 1.0C was only 82.90%.

[0097] Comparative Example 2:

[0098] The difference between this comparative example and Example 1 is that there is no oxidative ball milling treatment; the remaining steps are the same as in Example 1.

[0099] (1) Raw material processing: Soak bamboo in distilled water for 2 hours, wash it, dry it at 80℃ for 18 hours, and pre-crush it;

[0100] (2) Oxygen-enriched roasting: The pre-crushed bamboo is added to a heating furnace and roasted at 250°C for 24 hours at a heating rate of 5°C / min under an oxygen-enriched atmosphere. The oxygen-enriched atmosphere is a mixture of 50% oxygen and 50% argon, and the flow rate of the mixture is 0.3 L / h. After roasting, the mixture is cooled to room temperature to obtain the oxygen-enriched roasting product.

[0101] (3) Low-temperature carbonization: The oxygen-enriched roasting product was heated to 500℃ at a heating rate of 5℃ / min under the protection of argon gas for low-temperature carbonization. The carbonization holding time was 2 h, the argon gas flow rate was 0.3 L / h, and the low-temperature carbonized product was obtained after cooling to room temperature.

[0102] (4) Impurity removal treatment: The low-temperature carbonization product is first treated with an alkaline leaching solution of 5 mol / L sodium hydroxide for 5 h; then treated with an acid leaching solution of 1 mol / L hydrochloric acid and 3 mol / L hydrofluoric acid for 5 h to remove impurity elements and obtain the impurity-removed product.

[0103] (5) High-temperature carbonization: The impurity-removed product obtained in step (4) is heated to 1500℃ under the protection of argon gas at a heating rate of 5℃ / min for high-temperature carbonization. The carbonization holding time is 2 h, the argon gas flow rate is 0.3 L / h, and the high-temperature carbonized product is obtained after cooling to room temperature.

[0104] (6) Grinding and classification: The high-temperature carbonization products are subjected to air jet milling to obtain D 50 Materials with a thickness of 10 μm are called biomass-based hard carbon materials.

[0105] The carbon yield of the hard carbon material prepared in this comparative example was 28.78%.

[0106] The biomass-based hard carbon material of this comparative example was used as the active material for the negative electrode of a sodium-ion battery in the preparation of the battery, and electrochemical charge-discharge tests were conducted. The preparation process and testing methods were the same as in Example 1. The results are as follows: under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity was 310.30 Ah / g, the first-cycle coulombic efficiency was 85.92%, and the capacity retention rate after 100 cycles at a current density of 1.0 C was 91.09%.

[0107] Comparative Example 3:

[0108] The difference between this comparative example and Example 1 is that the oxygen-enriched roasting pretreatment is replaced with air roasting. The remaining steps are the same as in Example 1. The specific steps are as follows:

[0109] (1) Raw material processing: Soak bamboo in distilled water for 2 hours, wash it, dry it at 80℃ for 18 hours, and pre-crush it;

[0110] (2) Ball milling oxidation: The pre-crushed bamboo was mixed with a hydrogen peroxide solution with a pH of 11 and a concentration of 0.3 g / mL at a solid-liquid ratio of 1:1 g / mL and ball milled at a speed of 400 rpm for 24 h.

[0111] (3) Air roasting: The ball-milled and oxidized bamboo was added to a heating furnace and roasted at 250°C for 24 hours in an air atmosphere at a heating rate of 5°C / min. The flow rate of the mixed gas was 0.3 L / h. After roasting, the mixture was cooled to room temperature to obtain the roasted product.

[0112] (4) Low-temperature carbonization: The calcined product was heated to 500℃ under the protection of argon gas at a heating rate of 5℃ / min for low-temperature carbonization. The carbonization holding time was 2 h, the argon gas flow rate was 0.3 L / h, and the low-temperature carbonized product was obtained after cooling to room temperature.

[0113] (5) Impurity removal treatment: The low-temperature carbonization product is first treated with an alkaline leaching solution of 5 mol / L sodium hydroxide for 5 h; then treated with an acid leaching solution of 1 mol / L hydrochloric acid and 3 mol / L hydrofluoric acid for 5 h to remove impurity elements and obtain the impurity-removed product.

[0114] (6) High-temperature carbonization: The purified product is heated to 1500℃ under the protection of argon gas at a heating rate of 5℃ / min for high-temperature carbonization. The carbonization holding time is 2 h and the argon gas flow rate is 0.3 L / h. After cooling to room temperature, the high-temperature carbonized product is obtained.

[0115] (7) Grinding and classification: The high-temperature carbonization products are subjected to air jet milling to obtain D 50 Materials with a thickness of 10 μm are called biomass-based hard carbon materials.

[0116] The carbon yield of the hard carbon material prepared in this comparative example was 26.89%.

[0117] The biomass-based hard carbon material of this comparative example was used as the active material for the negative electrode of a sodium-ion battery in the preparation of the battery, and electrochemical charge-discharge tests were conducted. The preparation process and testing methods were the same as in Example 1. The results are as follows: under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity was 309.45Ah / g, the first-cycle coulombic efficiency was 84.71%, and the capacity retention rate after 100 cycles at a current density of 1.0C was 90.31%.

[0118] Comparative Example 4:

[0119] The difference between this comparative example and Example 1 is that the carbonization process is a single-stage carbonization; the remaining steps are the same as in Example 1. The specific steps are as follows:

[0120] (1) Raw material processing: Soak bamboo in distilled water for 2 hours, wash it, dry it at 80℃ for 18 hours, and pre-crush it;

[0121] (2) Ball milling oxidation: The pre-crushed bamboo was mixed with a hydrogen peroxide solution with a pH of 11 and a concentration of 0.3 g / mL at a solid-liquid ratio of 1:1 g / mL and ball milled at a speed of 400 rpm for 24 h.

[0122] (3) Oxygen-enriched roasting: The ball-milled and oxidized bamboo is added to a heating furnace and roasted at 250°C for 24 hours at a heating rate of 5°C / min under an oxygen-enriched atmosphere. The oxygen-enriched atmosphere is a mixture of 50% oxygen and 50% argon, and the flow rate of the mixture is 0.3 L / h. After roasting, the mixture is cooled to room temperature to obtain the oxygen-enriched roasting product.

[0123] (4) High-temperature carbonization: The oxygen-enriched roasting product was heated to 1500℃ under the protection of argon at a heating rate of 5℃ / min for high-temperature carbonization. The carbonization holding time was 2 h and the argon gas flow rate was 0.3 L / h. After cooling to room temperature, the high-temperature carbonized product was obtained.

[0124] (5) Impurity removal treatment: The high-temperature carbonization product is first treated with an alkaline leaching solution of 5 mol / L sodium hydroxide for 5 h; then treated with an acid leaching solution of 1 mol / L hydrochloric acid and 3 mol / L hydrofluoric acid for 5 h to remove impurity elements and obtain the impurity-removed product.

[0125] (6) Crushing and classifying: The impurities are subjected to air jet milling to obtain D 50 Materials with a thickness of 10 μm are called biomass-based hard carbon materials.

[0126] The carbon yield of the hard carbon material prepared in this comparative example was 29.50%.

[0127] The biomass-based hard carbon material of this comparative example was used as the active material for the negative electrode of a sodium-ion battery in the preparation of the sodium-ion battery, and electrochemical charge-discharge tests were conducted. The preparation process and testing methods were the same as in Example 1. The results are as follows: under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity was 315.03Ah / g, the first-cycle coulombic efficiency was 85.35%, and the capacity retention rate after 100 cycles at a current density of 1.0C was 93.99%.

Claims

1. A method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination, characterized in that, Includes the following steps: (1) After mixing biomass with an oxidizing agent, the mixture is ball-milled; the oxidizing agent is at least one of hydrogen peroxide, concentrated sulfuric acid, and persulfate; the mass ratio of biomass to the oxidizing agent is 20:1 to 2:1; the ball milling speed is 200-600 rpm, and the ball milling time is not less than 12 h; (2) The ball-milled oxidation product obtained after step (1) is placed in an oxygen-enriched atmosphere for calcination treatment; wherein the oxygen concentration in the oxygen-enriched atmosphere is not less than 30%; (3) The roasted product obtained after step (2) is subjected to low-temperature carbonization treatment under a protective atmosphere; (4) The low-temperature carbonization product obtained after step (3) is chemically purified; (5) The low-temperature carbonization product obtained by chemical purification in step (4) is subjected to high-temperature carbonization under a protective atmosphere to obtain biomass hard carbon anode material.

2. The method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination as described in claim 1, characterized in that, In step (2), the oxygen-enriched atmosphere is a mixture of oxygen and nitrogen, the calcination temperature is 150-350℃, and the holding time is 4-48h; the gas flow rate of the oxygen-enriched atmosphere is 0.1-4 L / h.

3. The method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination as described in claim 1, characterized in that, In step (3), the temperature of the low-temperature carbonization treatment is 400-800℃, and the holding time is 1-4 h.

4. The method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination as described in claim 1, characterized in that, The biomass is at least one of bamboo, reeds, coconut shells, and fruit shells.

5. The method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination as described in claim 1, characterized in that, In step (4), the chemical impurity removal includes alkaline leaching and acid leaching. The reagent used in the alkaline leaching is selected from one or more mixed solutions of sodium hydroxide, potassium hydroxide, and ammonia water. The reagent used in the acid leaching is selected from one or more mixed solutions of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid.

6. The method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination as described in claim 1, characterized in that, In step (5), the high-temperature carbonization temperature is 1000-1600℃ and the holding time is 1-4 h.

7. The method for preparing biomass hard carbon materials by ball milling oxidation combined with oxygen-enriched calcination as described in claim 1, characterized in that, In steps (3) and (5), the protective atmosphere is at least one of nitrogen and argon, and the gas flow rate of the protective atmosphere is 0.1-4 L / h.

8. A biomass hard carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. A sodium-ion battery, characterized in that, Including the biomass hard carbon material as described in claim 8.

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