Biomass-based hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, and particularly provides a biomass-based hard carbon negative electrode material and a preparation method and application thereof.The preparation method comprises the steps that biomass raw materials are pre-carbonized and then smashed, and a biomass precursor is obtained; the biomass precursor is soaked in alkali liquor, the concentration of the alkali liquor for soaking in the alkali liquor is 0.5-5 M, the time is 6-24 h, and filtering and drying are conducted after soaking; mixing the obtained material with an inorganic compound, and carrying out vacuum calcination, wherein the inorganic compound is one or more of sodium chloride, zinc chloride, nickel chloride, ferric chloride, cobalt chloride and copper chloride; carrying out acid pickling on the calcined material, and then washing with water until the pH is 5-7; and carrying out plasma treatment on the obtained material. The electrochemical performance of the negative electrode material is effectively improved by cooperatively controlling alkali liquor soaking to remove part of lignin, adding an inorganic compound for chambering and coating surface defects with plasmas, and the method can be used as the negative electrode material of the sodium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly to a biomass-based hard carbon anode material, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, the increasing demand for new energy vehicles has driven the power battery market, and there has been a situation of supply falling short of demand for power batteries. In addition, with the advancement of some photovoltaic and energy storage projects, energy storage batteries have also become a market hot spot. This change in the supply-demand relationship has directly led to a sharp rise in the price of lithium carbonate, and there has been a short-term fluctuation in the industrial chain. In order to fundamentally alleviate the shortage of lithium resources, it is very important to develop the next-generation electrochemical energy system. Sodium has resource advantages, and sodium-ion batteries are similar to lithium-ion batteries in principle. Sodium-ion batteries have excellent low-temperature performance and good rate performance, and have unique application scenarios. Therefore, sodium-ion batteries have become one of the most promising next-generation electrochemical energy systems.

[0003] Hard carbon materials are currently the preferred materials for the anodes of sodium-ion batteries. Biomass-derived hard carbon anode materials have a natural closed-pore structure and relatively low costs, and have become a research hotspot. The key to improving the performance of biomass-derived hard carbon anode materials lies in regulating the closed-pore structure of the materials. However, the current strategies for regulating the closed-pore structure are relatively single, and the electrochemical performance of the obtained hard carbon anode materials needs to be improved. Summary of the Invention

[0004] The present invention provides a biomass-based hard carbon anode material, a preparation method thereof, and an application thereof, to solve the defect that the electrochemical performance of the biomass-based hard carbon anode material in the prior art is not high, and to obtain a biomass-based hard carbon anode material with higher electrochemical performance.

[0005] In a first aspect, the present invention provides a preparation method of a biomass-based hard carbon anode material, comprising the following steps: (1) Pre-carbonizing a biomass raw material and then pulverizing it to obtain a biomass precursor; (2) Soaking the biomass precursor in an alkali solution, where the concentration of the alkali solution for soaking is 0.5 - 5M, the time is 6 - 24h, and after soaking, filtering and drying are carried out; (3) Mixing the material obtained in step (2) with an inorganic compound and then carrying out vacuum calcination, where the inorganic compound is one or more of sodium chloride, zinc chloride, nickel chloride, iron chloride, cobalt chloride, and copper chloride; (4) Pickling the calcined material and then washing it with water until the pH is 5 - 7; (5) Carrying out plasma treatment on the material obtained in step (4).

[0006] The main components of biomass are lignin, cellulose, and hemicellulose. The composition of these components directly affects the closed-pore structure of biomass-based hard carbon materials, thereby affecting the electrochemical performance of the materials. Therefore, the material performance can be improved by regulating the components of the biomass precursor.

[0007] One aspect of the present invention is to control the concentration of the alkali solution and the soaking time to regulate the removal level of lignin in the precursor, thereby increasing the closed-pore volume in the hard carbon material and optimizing the storage and diffusion of sodium ions. Second, by introducing inorganic compounds as pore-expanding templates during the calcination process to assist in forming a closed-pore structure, thereby regulating the defect structure of the hard carbon material, increasing the sodium ion storage sites, and improving the electrochemical performance. Third, using plasma coating technology to repair surface defects and reduce the specific surface area of the material, thereby improving the first Coulombic efficiency of the material. Among them, the inorganic compound needs to be selected from the chlorides mentioned above. If other inorganic compounds are selected, the beneficial effects of the present invention cannot be achieved.

[0008] Further, the inorganic compound is one or more of nickel chloride, iron chloride, and cobalt chloride. Iron ions, cobalt ions, and nickel ions have higher valence states and are more capable of achieving the effect of pore expansion.

[0009] Further, in step (2), the alkali solution is a sodium hydroxide solution.

[0010] Further, in step (2), the concentration of the alkali solution is 0.5 - 1.5 M.

[0011] Further, in step (2), the soaking time of the alkali solution is 10 - 14 h.

[0012] Further, in step (3), the mass ratio of the material obtained in step (2) to the inorganic compound is 10 - 25:1. Optionally, the mass ratio of the material obtained in step (2) to the inorganic compound can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, or 25:1, etc. Of course, it can also be other values within the above range, which are not limited here. Preferably, the mass ratio of the material obtained in step (2) to the inorganic compound is 15 - 25:1, and more preferably 20 - 25:1.

[0013] Further, in step (3), the calcination temperature is 1000 - 1700 °C, the heating rate is 1 - 5 °C / min, and the holding time is 2 - 5 h. Further, in step (3), the calcination temperature is 1200 - 1400 °C, the heating rate is 3 - 5 °C / min, and the holding time is 2.5 - 3.5 h.

[0014] Further, in step (5), the temperature of the plasma treatment is 200 - 500 °C, the gas input rate is 5 - 15 mL / s, and the treatment time is 20 - 60 min. The gas used in the plasma treatment is methane, ethylene, or acetylene. Further still, in step (5), the temperature of the plasma treatment is 400 - 500 °C.

[0015] Further, in step (1), the biomass raw material is selected from one or more of coconut shell, bamboo powder, starch, and walnut shell, preferably bamboo powder and coconut shell; the temperature of the pre-carbonization is 200 - 750 °C, and the time is 2 - 10 h. The pre-carbonization is carried out under an inert gas. The inert gas can be nitrogen, helium, argon, etc.

[0016] The specific pre-carbonization temperature is related to the type of biomass raw material. When the biomass raw material is bamboo powder, the pre-carbonization temperature is 680 - 720 °C, preferably 700 °C; when the biomass raw material is coconut shell, the pre-carbonization temperature is 280 - 320 °C, preferably 300 °C.

[0017] Further, in step (4), the acid used for pickling is hydrochloric acid or a mixture of at least two of hydrochloric acid, nitric acid, and hydrofluoric acid, and the concentration of the acid solution is 0.5 - 2 M.

[0018] In some embodiments of the present invention, the method for preparing the biomass-based hard carbon anode material includes the following steps: (1) Pre-carbonize the biomass raw material at a temperature of 200 - 750 °C for 2 - 10 h, and crush the pre-carbonized biomass raw material to obtain a biomass precursor; (2) Immerse the biomass precursor in an alkali solution with a concentration of 0.5 - 5 M for 6 - 24 h, and filter and dry after immersion; (3) Mix the material obtained in step (2) with an inorganic compound at a mass ratio of 10 - 25:1 and then carry out vacuum calcination at a temperature of 1000 - 1700 °C, a heating rate of 1 - 5 °C / min, and a holding time of 2 - 5 h; (4) Immerse the calcined material in an acid solution with a concentration of 0.5 - 2 M for 6 - 24 h, wash the soaked sample with deionized water until the pH is 5 - 7, and dry.

[0019] (5) Put the material obtained in step (4) into a plasma fluidized bed for treatment at a plasma treatment temperature of 200 - 500 °C, a gas input rate of 5 - 15 mL / s, and a treatment time of 20 - 60 min, and then carry out depolymerization and sieving to obtain the hard carbon anode material.

[0020] More preferably, in step (1), the biomass raw material is bamboo powder and the pre-carbonization temperature is 700 °C; In step (2), the alkali solution is sodium hydroxide with a concentration of 1 M; the soaking time of the alkali solution is 12 h; In step (3), the mass ratio of the material obtained in step (2) to the inorganic compound is 20:1, and the calcination temperature is 1300 °C; In step (4), the acid used for pickling is hydrochloric acid or at least two of hydrochloric acid, nitric acid, and hydrofluoric acid in combination, the acid concentration is 1 M, and the soaking time is 12 h.

[0021] In step (5), the gas used for plasma treatment is methane, and the treatment temperature is 450 °C.

[0022] In a second aspect, the present invention provides a biomass-based hard carbon negative electrode material prepared by the above preparation method.

[0023] The biomass-based hard carbon negative electrode material obtained by the present invention has good electrochemical performance. Under relatively optimal conditions, the specific capacity of the obtained biomass-based hard carbon negative electrode material can reach 335 mA h g -1 at 0.1 C, and the initial Coulombic efficiency can reach 93%.

[0024] In a third aspect, the present invention provides a sodium ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the active material of the negative electrode comprises the above biomass-based hard carbon negative electrode material.

[0025] Since the biomass-based hard carbon negative electrode material of the present invention has good specific capacity and initial Coulombic efficiency, it is helpful for improving the performance of sodium ion batteries and can be applied to sodium ion batteries. In the sodium ion battery, the positive electrode material, separator, electrolyte (solid or liquid), and solvents, binders, matrices, etc. involved in the negative electrode can all adopt the materials commonly used in sodium ion batteries. For example, the sodium salt electrolyte is selected from any one of NaClO4 and NaPF6, and the solvent is selected from any one of ethylene carbonate, diethyl carbonate, propylene carbonate, and dimethyl carbonate.

[0026] The present invention provides a biomass-based hard carbon negative electrode material, its preparation method, and application. By synergistically controlling the removal of part of the lignin by alkali solution soaking, adding inorganic compounds to expand pores, and plasma coating surface defects, the electrochemical performance of the biomass-based hard carbon negative electrode material is effectively improved, and it can be used as the negative electrode material of sodium ion batteries. Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is the SEM image of the hard carbon negative electrode material obtained in Example 1 of the present invention.

[0029] Figure 2 It is the TEM image of the hard carbon negative electrode material obtained in Example 1 of the present invention. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] For those technical or conditions not specified in the embodiments, they shall be in accordance with the technologies or conditions described in the literature in this field or in accordance with the product specifications. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through regular channels.

[0032] Example 1 This example provides a biomass-based hard carbon negative electrode material, and its preparation steps are as follows: Select bamboo powder as the biomass, with a pre-carbonization temperature of 700 °C, a heating rate of 5 °C / min, and a pre-carbonization time of 10 h. Then put the pre-carbonized bamboo powder into a jet mill for pulverization to obtain the pulverized bamboo powder precursor.

[0033] Soak the above sample in 1M sodium hydroxide solution for 12 h, and then filter and dry.

[0034] Mix the dried powder with ferric chloride with a mass ratio of 20:1. After mixing, put it into a vacuum sintering furnace for calcination. The calcination temperature is 1300 °C, the heating rate is 5 °C / min, and the holding time is 3 h.

[0035] Soak the calcined and carbonized sample in 1M hydrochloric acid solution for 12 h, then wash it with deionized water until the pH is 5 - 7, and dry.

[0036] Put the above sample into a plasma fluidized bed for treatment, introduce methane gas at a flow rate of 10 mL / s, with a heating rate of 5 °C / min, a sintering temperature of 450 °C, hold for 40 min, cool to room temperature and then take it out for depolymerization and sieving to obtain a hard carbon anode material.

[0037] Figure 1 It is the SEM image of the hard carbon anode material obtained in Example 1. Figure 2 It is the TEM image of the hard carbon anode material obtained in Example 1.

[0038] Example 2 This example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Select bamboo powder as the biomass, with a pre-carbonization temperature of 700 °C, a heating rate of 5 °C / min, and a pre-carbonization time of 10 h. Then put the pre-carbonized bamboo powder into a jet mill for pulverization to obtain a pulverized bamboo powder precursor.

[0039] Soak the above sample in 1 M sodium hydroxide solution for 12 h, and then filter and dry.

[0040] Mix the dried powder with cobalt chloride in a mass ratio of 20:1, put the mixture into a vacuum sintering furnace for sintering, with a calcination temperature of 1300 °C, a heating rate of 5 °C / min, and a holding time of 3 h.

[0041] Soak the calcined and carbonized sample in 1 M hydrochloric acid solution for 12 h, then wash it with deionized water until the pH is 5 - 7, and dry.

[0042] Put the above sample into a plasma fluidized bed for treatment, introduce methane gas at a flow rate of 10 mL / s, with a heating rate of 5 °C / min, a sintering temperature of 450 °C, hold for 40 min, cool to room temperature and then take it out for depolymerization and sieving to obtain a hard carbon anode material.

[0043] Example 3 This example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Select bamboo powder as the biomass, with a pre-carbonization temperature of 700 °C, a heating rate of 5 °C / min, and a pre-carbonization time of 10 h. Then put the pre-carbonized bamboo powder into a jet mill for pulverization to obtain a pulverized bamboo powder precursor.

[0044] Soak the above sample in 1 M sodium hydroxide solution for 12 h, and then filter and dry.

[0045] Mix the dried powder with nickel chloride at a mass ratio of 20:1. After mixing, put it into a vacuum sintering furnace for sintering. The calcination temperature is 1300 °C, the heating rate is 5 °C / min, and the holding time is 3 h.

[0046] Immerse the calcined and carbonized sample in 1 M hydrochloric acid solution for 12 h, then wash it with deionized water until the pH is 5 - 7. Dry the sample and put it into a plasma fluidized bed for treatment. Pass methane gas into it at a flow rate of 10 mL / s, with a heating rate of 5 °C / min, a sintering temperature of 450 °C, and hold for 40 min. After cooling to room temperature, take it out for depolymerization and sieving to obtain the hard carbon anode material.

[0047] Example 4 This example provides a biomass-based hard carbon anode material. The difference in its preparation method from that of Example 1 is that the mass ratio of the dried powder to ferric chloride is 25:1.

[0048] Example 5 This example provides a biomass-based hard carbon anode material. The difference in its preparation method from that of Example 1 is that the mass ratio of the dried powder to ferric chloride is 15:1.

[0049] Example 6 This example provides a biomass-based hard carbon anode material. The difference in its preparation method from that of Example 1 is that the mass ratio of the dried powder to ferric chloride is 10:1.

[0050] Example 7 This example provides a biomass-based hard carbon anode material. The difference in its preparation method from that of Example 1 is that the mass ratio of the dried powder to ferric chloride is 5:1.

[0051] Example 8 This example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Select coconut shell as the biomass, with a pre-carbonization temperature of 300 °C, a heating rate of 5 °C / min, and a pre-carbonization time of 3 h. Then put the pre-carbonized coconut shell into a jet mill for grinding to obtain the ground coconut shell precursor.

[0052] Immerse the above sample in 1 M sodium hydroxide solution for 12 h, then filter and dry.

[0053] Mix the dried powder with ferric chloride at a mass ratio of 20:1. After mixing, put it into a vacuum sintering furnace for sintering. The calcination temperature is 1300 °C, the heating rate is 5 °C / min, and the holding time is 3 h.

[0054] The calcined and carbonized sample was immersed in 1 M hydrochloric acid solution for 12 h, then washed with deionized water until the pH reached 5 - 7, and dried.

[0055] The above sample was placed in a plasma fluidized bed for treatment. Methane gas was introduced at a flow rate of 10 mL / s, the heating rate was 5 °C / min, the sintering temperature was 450 °C, and it was kept at this temperature for 40 min. After cooling to room temperature, it was taken out for depolymerization and sieving to obtain the hard carbon anode material.

[0056] Example 9 This example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Coconut shell was selected as the biomass. The pre-carbonization temperature was 300 °C, the heating rate was 5 °C / min, and the pre-carbonization time was 3 h. Then the pre-carbonized coconut shell was put into a jet mill for grinding to obtain the ground coconut shell precursor.

[0057] The above sample was immersed in 1 M sodium hydroxide solution for 12 h, then filtered and dried.

[0058] The dried powder was mixed with cobalt chloride in a mass ratio of 20:1. After mixing, it was put into a vacuum sintering furnace for sintering. The calcination temperature was 1300 °C, the heating rate was 5 °C / min, and the holding time was 3 h.

[0059] The calcined and carbonized sample was immersed in 1 M hydrochloric acid solution for 12 h, then washed with deionized water until the pH reached 5 - 7, and dried.

[0060] The above sample was placed in a plasma fluidized bed for treatment. Methane gas was introduced at a flow rate of 10 mL / s, the heating rate was 5 °C / min, the sintering temperature was 450 °C, and it was kept at this temperature for 40 min. After cooling to room temperature, it was taken out for depolymerization and sieving to obtain the hard carbon anode material.

[0061] Example 10 This example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Coconut shell was selected as the biomass. The pre-carbonization temperature was 300 °C, the heating rate was 5 °C / min, and the pre-carbonization time was 3 h. Then the pre-carbonized coconut shell was put into a jet mill for grinding to obtain the ground coconut shell precursor.

[0062] The above sample was immersed in 1 M sodium hydroxide solution for 12 h, then filtered and dried.

[0063] The dried powder was mixed with nickel chloride in a mass ratio of 20:1. After mixing, it was put into a vacuum sintering furnace for sintering. The calcination temperature was 1300 °C, the heating rate was 5 °C / min, and the holding time was 3 h.

[0064] The calcined and carbonized sample was immersed in 1 M hydrochloric acid solution for 12 h, then washed with deionized water until the pH was 5 - 7, and dried.

[0065] The above sample was placed in a plasma fluidized bed for treatment, methane gas was introduced at a flow rate of 10 mL / s, the heating rate was 5 °C / min, the sintering temperature was 450 °C, held for 40 min, and after cooling to room temperature, it was taken out for depolymerization and sieving to obtain the hard carbon anode material.

[0066] Comparative Example 1 This comparative example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Bamboo powder was selected as the biomass, the pre-carbonization temperature was 700 °C, the heating rate was 5 °C / min, the pre-carbonization time was 10 h, and then the pre-carbonized bamboo powder was put into a jet mill for pulverization to obtain the pulverized bamboo powder precursor.

[0067] The bamboo powder precursor was mixed with ferric chloride at a mass ratio of 20:1, and after mixing, it was put into a vacuum sintering furnace for sintering. The calcination temperature was 1300 °C, the heating rate was 5 °C / min, and the holding time was 3 h.

[0068] The calcined and carbonized sample was immersed in 1 M hydrochloric acid solution for 12 h, then washed with deionized water until the pH was 5 - 7, and dried.

[0069] The above sample was placed in a plasma fluidized bed for treatment, methane gas was introduced at a flow rate of 10 mL / s, the heating rate was 5 °C / min, the sintering temperature was 450 °C, held for 40 min, and after cooling to room temperature, it was taken out for depolymerization and sieving to obtain the hard carbon anode material.

[0070] Comparative Example 2 This comparative example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Bamboo powder was selected as the biomass, the pre-carbonization temperature was 700 °C, the heating rate was 5 °C / min, the pre-carbonization time was 10 h, and then the pre-carbonized bamboo powder was put into a jet mill for pulverization to obtain the pulverized bamboo powder precursor.

[0071] The above sample was immersed in 1 M sodium hydroxide solution for 12 h, and then filtered and dried.

[0072] The dried powder was put into a vacuum sintering furnace for sintering. The calcination temperature was 1300 °C, the heating rate was 5 °C / min, and the holding time was 3 h.

[0073] The calcined and carbonized sample was immersed in 1 M hydrochloric acid solution for 12 h, then washed with deionized water until the pH was 5 - 7, and dried.

[0074] Put the above sample into a plasma fluidized bed for treatment. Methane gas is introduced at a flow rate of 10 mL / s, the heating rate is 5 °C / min, the sintering temperature is 450 °C, keep the temperature for 40 min, cool to room temperature and then take it out for depolymerization and sieving to obtain the hard carbon anode material.

[0075] Comparative Example 3 This comparative example provides a biomass-based hard carbon anode material, and its preparation steps are as follows: Select bamboo powder as the biomass, the pre-carbonization temperature is 700 °C, the heating rate is 5 °C / min, the pre-carbonization time is 10 h, and then put the pre-carbonized bamboo powder into an air-flow crusher for crushing to obtain the crushed bamboo powder precursor.

[0076] Put the above sample into 1 M sodium hydroxide solution and soak for 12 h, then filter and dry.

[0077] Mix the dried powder with ferric chloride, and their mass ratio is 20:1. After mixing, put it into a vacuum sintering furnace for sintering. The calcination temperature is 1300 °C, the heating rate is 5 °C / min, and the holding time is 3 h.

[0078] Put the sample after calcination and carbonization into 1 M hydrochloric acid solution and soak for 12 h, then wash with deionized water until the pH is 5 - 7, and dry to obtain the hard carbon anode material.

[0079] Comparative Example 4 This comparative example provides a negative electrode material Kureha type2.

[0080] Performance Test Assemble button cells with the hard carbon anode materials obtained from the above Examples 1 - 10 and Comparative Examples 1 - 4 for testing. The specific preparation method is as follows: Mix in an aqueous solution according to the mass ratio of hard carbon: SP (conductive carbon black): CMC (sodium carboxymethyl cellulose): SBR (styrene-butadiene rubber) = 94:1.5:1.5:3, the solid content of the slurry is 40 wt.%, then coat it evenly on the copper foil to obtain the negative electrode sheet. After drying, roll it with a pair of rollers with a spacing of 30 μm. Use metallic sodium as the counter electrode, the electrolyte system is 1.5 M NaPF6 dissolved in a solution of EC / DMC / DEC = 1 / 2 / 2, and the separator is Whatman glass fiber separator to assemble CR2032 button cells. Use the battery test system of Shenzhen Neware Electronic Co., Ltd. for room temperature testing. The test conditions: charge and discharge tests are carried out at 0.1 C, the voltage range is 0 - 1.5 V, and the test results are shown in Table 1.

[0081] Table 1

[0082] As can be seen from the above results, the present invention modifies biomass. By synergistically controlling the removal of part of lignin through alkaline solution soaking, adding inorganic compounds for pore expansion, and plasma coating surface defects, the electrochemical performance of the material is effectively improved. It can be used as the anode material for sodium-ion batteries and ensures that the material has good processing performance. The biomass-based hard carbon anode material prepared by the present invention has a specific capacity greater than 309 mA h g -1 at 0.1C, and can reach up to 335 mA h g -1 . The initial Coulombic efficiency is greater than or equal to 87% and can reach up to 93%.

[0083] It should be noted that, in this disclosure, the endpoints and any values in the disclosed ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0084] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "specific implementation manners", or "some specific implementation manners" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a biomass-based hard carbon negative electrode material, characterized in that: The following steps are involved: (1) Pre-carbonizing the biomass raw material and then crushing it to obtain a biomass precursor; (2) soaking the biomass precursor in an alkali solution with an alkali solution concentration of 0.5 to 5 M for 6 to 24 hours, and filtering and drying after soaking; (3) mixing the material obtained in step (2) with an inorganic compound and then calcining in vacuum, wherein the inorganic compound is one or more of sodium chloride, zinc chloride, nickel chloride, ferric chloride, cobalt chloride and copper chloride; (4) The calcined material is acid washed and then washed with water until the pH is 5-7; (5) The material obtained in step (4) is subjected to plasma treatment.

2. The method for preparing a biomass-based hard carbon negative electrode material according to claim 1, characterized in that: In step (3), the mass ratio of the material obtained in step (2) to the inorganic compound is 10-25:

1.

3. The method for preparing a biomass-based hard carbon negative electrode material according to claim 2, characterized in that: In step (3), the calcination temperature is 1000-1700°C, the heating rate is 1-5°C / min, and the holding time is 2-5h.

4. The method for preparing a biomass-based hard carbon negative electrode material according to claim 1, characterized in that: In step (5), the temperature of the plasma treatment is 200-500° C., the gas input is 5-15 mL / s, and the treatment time is 20-60 min.

5. The method for preparing a biomass-based hard carbon negative electrode material according to claim 1, characterized in that: In step (1), the biomass raw material is selected from one or more of coconut shells, bamboo powder, starch and walnut shells; The pre-carbonization temperature is 200-750° C., and the time is 2-10 hours; the pre-carbonization is carried out under an inert gas.

6. The method for preparing a biomass-based hard carbon negative electrode material according to claim 5, characterized in that: The biomass raw material is bamboo powder, and the pre-carbonization temperature is 680-720°C; The biomass raw material is coconut shell, and the pre-carbonization temperature is 280-320°C.

7. The method for preparing a biomass-based hard carbon negative electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) pre-carbonizing the biomass raw material at a pre-carbonization temperature of 200-750°C for a pre-carbonization time of 2-10 hours, and crushing the pre-carbonized biomass raw material to obtain a biomass precursor; (2) soaking the biomass precursor in alkali solution, wherein the concentration of the alkali solution is 0.5-5M, the soaking time is 6-24 hours, and filtering and drying after soaking; (3) mixing the material obtained in step (2) with an inorganic compound in a mass ratio of 10 to 25:1 and calcining in vacuum at a calcination temperature of 1000 to 1700°C, a heating rate of 1 to 5°C / min, and a holding time of 2 to 5 hours; (4) Soaking the calcined material in an acid solution with a concentration of 0.5-2M for 6-24 hours. The soaked sample is washed with deionized water until the pH is 5-7 and dried. (5) The material obtained in step (4) is placed in a plasma fluidized bed for treatment, the plasma treatment temperature is 200-500°C, the gas input is 5-15 mL / s, the treatment time is 20-60 min, and then depolymerized and sieved to obtain a hard carbon negative electrode material.

8. The method for preparing a biomass-based hard carbon negative electrode material according to claim 7, characterized in that: In step (1), the biomass raw material is bamboo powder, and the pre-carbonization temperature is 700°C; In step (2), the alkali solution is sodium hydroxide with a concentration of 1M; the alkali solution soaking time is 12h; In step (3), the mass ratio of the material obtained in step (2) to the inorganic compound is 20:1, and the calcination temperature is 1300° C.; In step (4), the acid solution is hydrochloric acid or a mixture of at least two of hydrochloric acid, nitric acid, and hydrofluoric acid, the concentration is 1 M, and the immersion time is 12 h; In step (5), the gas used for plasma treatment is methane, and the treatment temperature is 450°C.

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

10. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte, wherein the active material of the negative electrode comprises the biomass-based hard carbon negative electrode material according to claim 9.

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