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

Abstract

This invention discloses a bamboo-based hard carbon anode material, its preparation method, and its application, comprising the following steps: (1) pretreating block bamboo raw materials in high-temperature steam and then drying them to obtain pretreated bamboo raw materials; (2) pre-carbonizing the pretreated bamboo raw materials under an inert protective atmosphere to obtain preliminary bamboo charcoal material; (3) acid treating the preliminary bamboo charcoal material in an acid solution to obtain pretreated bamboo charcoal material; (4) mixing the pretreated bamboo charcoal material with an activator and activating it at low temperature under an inert atmosphere to obtain modified bamboo charcoal material; (5) carbonizing the modified bamboo charcoal material under an inert protective atmosphere to obtain bamboo-based hard carbon anode material. This invention can homogenize physicochemical differences, improve quality uniformity and stability, exhibit better electrochemical performance in sodium batteries, and improve its fast-charging performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery anode materials, and particularly relates to a bamboo-based hard carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of modern technology, the severe environmental pollution and energy crisis caused by the combustion of traditional fossil fuels have made the development of renewable and clean energy sources an urgent priority. Lithium-ion batteries, due to their high energy density and long cycle life, are widely used in portable electronic devices and electric vehicles. However, with the development of the lithium battery industry, the demand for lithium is increasing, while lithium resources are unevenly distributed and have low abundance in the bottom shell, thus becoming an obstacle to the large-scale deployment of lithium-ion batteries. Therefore, developing new, abundant metal-ion batteries with similar working principles to lithium-ion batteries is a major alternative. Sodium resources are abundant and inexpensive, giving them a significant cost advantage. Therefore, sodium-ion batteries are expected to become an effective alternative to lithium-ion batteries in the energy storage field.

[0003] For sodium-ion battery anode materials, hard carbon is currently the most commonly used material. However, the reversible specific capacity of hard carbon materials commonly used in production lines is less than 300 mAh / g. Therefore, developing high-capacity, high-efficiency hard carbon for sodium-ion batteries is a current research hotspot. Biomass materials are characterized by their abundant resources, renewability, and environmental friendliness, and have been widely used as precursors for carbon material preparation. From the perspective of green environmental protection and resource recycling, using biological waste as a precursor to prepare electrode materials turns waste into treasure, which has significant research value and development potential. In addition, during the pyrolysis and carbonization process, biomass precursors will inherit and retain their morphology and structural characteristics to a certain extent, thus enabling the preparation of carbon electrode materials with unique structures, compositions, and properties.

[0004] However, different biomass materials possess different physicochemical characteristics, presenting different technical challenges in their preparation of hard char. For instance, bamboo raw materials suffer from poor radial uniformity and contain numerous electrochemically undesirable components, making it difficult to prepare hard char materials with ideal performance. Therefore, specialized bamboo-based hard char development methods are required. While existing technologies offer some approaches to bamboo-based hard char preparation, they pay less attention to issues such as the quality uniformity and unsatisfactory fast-charging performance caused by the unique physicochemical characteristics of bamboo. Summary of the Invention

[0005] 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 bamboo-based hard carbon anode material, its preparation method and application.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for preparing a bamboo-based hard carbon anode material includes the following steps: (1) The block bamboo raw material is placed in high temperature steam for pretreatment and then dried to obtain pretreated bamboo raw material; the high temperature steam contains acid additives and oxidants, and the temperature of the high temperature steam is 100~250℃ and the pressure is 1~30MPa. (2) The pretreated bamboo raw material is pre-carbonized under an inert protective atmosphere to obtain preliminary bamboo charcoal material; (3) The preliminary bamboo charcoal material is placed in an acid solution for acid treatment to obtain pretreated bamboo charcoal material; (4) The pretreated bamboo charcoal material is mixed with an activator and activated at low temperature in an inert atmosphere to obtain the modified bamboo charcoal material; the activator is at least one of alkali metal hydroxide, alkali metal carbonate, and metal chloride; the temperature of the low-temperature activation is 600~1000℃. (5) The modified bamboo charcoal material is carbonized under an inert protective atmosphere to obtain bamboo-based hard carbon anode material.

[0007] Furthermore, the acid additive in step (1) is at least one of hydrofluoric acid, sulfuric acid, nitric acid, hydrochloric acid, and acetic acid.

[0008] Furthermore, the oxidant in step (1) is at least one of hydrogen peroxide, potassium permanganate, potassium dichromate, potassium chlorate, sodium perchlorate, sodium hypochlorite, and ammonium persulfate.

[0009] Furthermore, the pre-carbonization temperature in step (2) is 350~650℃, and the pre-carbonization time is 2~7h.

[0010] Furthermore, the acid solution in step (3) includes at least two of HF, sulfuric acid, nitric acid, HCl, and acetic acid.

[0011] Furthermore, in step (4), the mass ratio of the pretreated bamboo charcoal material to the activator is 1:0.1~1.

[0012] Furthermore, the carbonization process in step (5) includes two heat preservation stages, wherein the temperature of the first heat preservation stage is 700~1000℃ and the time is 1~3h; the temperature of the second heat preservation stage is 1100~1500℃ and the time is 2~6h.

[0013] The present invention also provides a bamboo-based hard carbon anode material, which is prepared by the preparation method described above.

[0014] The present invention also provides a negative electrode for a sodium-ion battery, which comprises the aforementioned bamboo-based hard carbon negative electrode material.

[0015] The present invention also provides a sodium-ion battery comprising the aforementioned negative electrode.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention pre-treats bamboo raw materials in high-temperature steam mixed with acid additives and oxidants to remove soluble low-quality components, inorganic impurities, and some soluble metal salts, reducing ash content and decreasing the content of components in the carbon material that are not essential for electrochemical performance. Furthermore, the pyrolysis of components such as bamboo tar helps prevent clogging of the pre-carbonization equipment during subsequent pre-carbonization, improving carbon yield and other effects. Additionally, the permeation of steam into the bamboo raw materials generates different bamboo fiber microstructures, making the bamboo more uniform and regulating its pore structure and surface chemical properties, contributing active sites for subsequent energy storage. The resulting cross-linked structure increases oxygen atom content, thereby improving the rate performance and capacity retention of hard carbon materials.

[0017] The pre-carbonized bamboo charcoal material is purified by acid to fully remove impurities from the preliminary biomass carbon material and reduce ash content including potassium, calcium, magnesium, silicon, sodium, etc., to obtain pre-treated bamboo charcoal material.

[0018] Pretreated bamboo charcoal material is activated at low temperature with an activator to obtain modified bamboo charcoal material. The activator reacts with the carbon in the biomass carbon material to produce gas and other substances. The gas escape increases the porosity in the material, leaving pores, thereby regulating and reorganizing the pore structure. This is beneficial to improving the sodium storage performance of the final biomass carbon anode material for sodium-ion batteries and increasing its specific capacity.

[0019] The preparation method described in this invention can endow the prepared material with special physicochemical characteristics, solve the problem of hard carbon preparation caused by the physicochemical characteristics of bamboo raw materials, homogenize physicochemical differences, improve quality uniformity and stability, and the material with the aforementioned characteristics can unexpectedly exhibit excellent sodium ion compatibility, and can exhibit better electrochemical performance in sodium batteries, improving its fast charging performance and other properties. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a charge-discharge curve diagram of Example 1; Figure 2 This is the SEM image of Example 1. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] In some specific embodiments, the preparation method of the bamboo-based hard carbon anode material of the present invention includes the following steps: Step (1): The block bamboo raw material is placed in high-temperature steam for pretreatment, and then dried to obtain pretreated bamboo raw material. The high-temperature steam contains acid additives and oxidants, which are generated by heating and boiling an aqueous solution containing acid additives and oxidants.

[0026] In some embodiments, the bamboo raw material is cut into bamboo blocks with a thickness of 2-5 mm, a width of 2-5 mm, and a length of 5-10 mm.

[0027] In some embodiments, the temperature of the high-temperature steam is 100~250℃, the steam pressure is 1~30MPa, and the pretreatment time is 0.5~5h. Controlling the temperature, pressure, and other parameters within the above range helps to further homogenize the physicochemical characteristics of the bamboo raw material, and can further improve the quality uniformity and fast-charging performance of the prepared bamboo-based hard carbon material.

[0028] In some embodiments, the acid additive is at least one of hydrofluoric acid, sulfuric acid, nitric acid, hydrochloric acid, and acetic acid. The oxidant is at least one of hydrogen peroxide, potassium permanganate, potassium dichromate, potassium chlorate, sodium perchlorate, sodium hypochlorite, and ammonium persulfate. Besides removing surface impurities, the acid additive further loosens the stubborn impurity structure inside the bamboo block, paving the way for subsequent deep acid washing and impurity removal. Under high pressure and acid, the closed carbon layer of the bamboo-based material is partially opened, exposing some active reaction sites between the carbon layers. Oxidation of the bamboo-based material by the oxidant can cause oxidation reactions on the surface of the bamboo-based material and in the branches between the carbon layers, improving electrochemical performance.

[0029] In some embodiments, the concentration of the acid additive in the aqueous solution containing the acid additive and the oxidant is 30-40 wt%, and the concentration of the oxidant is 8-15 wt%.

[0030] Step (2): The pretreated bamboo raw material obtained in step (1) is pre-carbonized, crushed and sieved under an inert protective atmosphere (such as nitrogen or inert gas) to obtain preliminary bamboo charcoal material.

[0031] In some embodiments, the pre-carbonization temperature is 350~650℃; the pre-carbonization heating rate is 2~10℃ / min; and the pre-carbonization time is 2~7h.

[0032] Step (3): Place the preliminary bamboo charcoal material obtained in step (2) in an acid solution for acid treatment, then wash and dry to obtain pretreated bamboo charcoal material.

[0033] In some embodiments, the acid solution is a mixed acid solution, comprising at least two mixtures of HF, sulfuric acid, nitric acid, HCl, and acetic acid. Preferably, a mixed acid solution of HF and sulfuric acid is selected. More preferably, the HF concentration in the mixed acid solution is 35-45 wt%, and the HCl concentration is 25-35 wt%. The initial mass ratio of bamboo charcoal material to the mixed acid solution is 1:5-10. The purification time in the mixed acid is 1-3 hours with stirring. A single acid cannot completely remove ash impurities; different acids target different elements, and the synergistic effect of mixed acids is better.

[0034] In some embodiments, the material is washed with 100 to 300 times its volume of water after mixed acid treatment.

[0035] Step (4): Mix the pretreated bamboo charcoal material obtained in step (3) with an activator and perform low-temperature activation in an inert atmosphere to obtain the modified bamboo charcoal material.

[0036] In some embodiments, the activator is at least one of alkali metal hydroxide, alkali metal carbonate, and metal chloride. Specifically, the alkali metal hydroxide is at least one of potassium hydroxide and sodium hydroxide, the alkali metal carbonate is at least one of potassium carbonate, sodium carbonate, and lithium carbonate, and the metal chloride is at least one of zinc chloride, magnesium chloride, calcium chloride, and ferric chloride.

[0037] Preferably, it is an alkali metal hydroxide, more preferably a mixture of an alkali metal hydroxide and a carbonate. When the activator is KOH, NaOH, or KHCO3... 3、 K2CO3, NaCO 3、 At least one or more of ZnCl2, preferably KOH.

[0038] Preferably, the mass ratio of pretreated bamboo charcoal material to activator is 1:0.1~1.

[0039] Preferably, the mixing method is mechanical mixing or liquid phase (H2O as solvent) mixing.

[0040] Preferably, the low-temperature activation temperature is 600~1000℃. Preferably, the heating rate for low-temperature activation is 2~15℃ / min. Preferably, the low-temperature activation time is 1~5h. Preferably, the low-temperature activation is performed using any one of a box furnace, tube furnace, rotary furnace, or microwave oven; more preferably, a tube furnace is selected. During the low-temperature activation process, elements such as K will volatilize under high-temperature combustion.

[0041] Step (5): The modified bamboo charcoal material obtained in (4) is carbonized under an inert protective atmosphere to obtain a bamboo-based hard carbon anode material for sodium-ion batteries.

[0042] In some embodiments, the carbonization process includes two holding stages, wherein the temperature of the first holding stage is 700~1000℃ and the time is 1~3h; the temperature of the second holding stage is 1100~1500℃ and the time is 2~6h. In the 700-1000℃ pre-carbonization stage, moisture and volatiles are removed, and a preliminary disordered carbon skeleton is formed; in the 1100-1500℃ carbonization stage, at high temperature, the remaining carbon layer undergoes a "thermal condensation" reaction, truly transforming the basically disordered carbon precursor into hard carbon material.

[0043] This invention involves pretreating bamboo raw materials in a pressurized atmosphere containing acid and oxidant vapors, followed by pre-carbonization, mixed acid treatment, activation, and carbonization. This process unexpectedly achieves synergy, fully utilizing the physicochemical structural characteristics of bamboo raw materials, selectively retaining beneficial electrochemical components, and selectively removing harmful components. Furthermore, it homogenizes the structure, thereby synergistically improving the quality uniformity of the process and significantly enhancing the fast-charging performance of the material.

[0044] The present invention also provides a bamboo-based hard carbon anode material prepared by the aforementioned preparation method.

[0045] The present invention also provides a negative electrode for a sodium-ion battery, comprising the aforementioned bamboo-based hard carbon negative electrode material. For example, the aforementioned bamboo-based hard carbon negative electrode material can be composited with a binder and coated onto a current collector to serve as a negative electrode sheet for a sodium-ion battery.

[0046] The present invention also provides a sodium-ion battery, comprising the negative electrode, the separator, and the positive electrode sequentially combined.

[0047] The following are specific examples: Example 1 Step 1: Cut the bamboo raw material into bamboo blocks 2-5mm thick, 2-5mm wide, and 5-10mm long. Place the bamboo blocks in a stainless steel steamer and introduce high-temperature steam mixed with hydrochloric acid and hydrogen peroxide (generated by heating and boiling an aqueous solution containing hydrochloric acid and hydrogen peroxide, with an HCl concentration of 37.5% and an H2O2 concentration of 10%) into the steamer. The steam pressure is 10 MPa and the temperature reaches 120℃. The bamboo blocks stay in the steamer for 0.5 hours. Then, the bamboo segments are removed from the steamer and placed in an oven to dry for 5 hours to obtain pretreated bamboo raw material. Step 2: Place the pretreated bamboo raw material obtained in Step 1 into a tube furnace and pre-carbonize it by heating it to 500℃ at 3℃ / min and holding it for 2 hours under an argon atmosphere. Then, put the pre-carbonized bamboo charcoal material into an airflow mill for grinding and pass it through a 200-mesh sieve to obtain 200-mesh preliminary bamboo charcoal material. Step 3: Place the preliminary bamboo charcoal material obtained in Step 2 into a mixed acid solution of HCl and HF. The concentration of HF in the mixed acid solution is 40% and the concentration of HCl is 31% (the mass ratio of preliminary bamboo charcoal material to mixed acid solution is 1:7). Stir for 2 hours, then wash with 200 times the amount of pure water until the waste liquid is neutral. After filtration, the material is dried and then transferred to a vacuum drying oven at 50°C for 12 hours to obtain pretreated bamboo charcoal material. Step 4: Mix the pretreated bamboo charcoal material obtained in Step 3 with the activator KOH at a mass ratio of 1:0.3, transfer it to a tube furnace, use argon as a protective gas, and heat it from room temperature to 950℃ at a rate of 5℃ / min for 2 hours to obtain the modified bamboo charcoal material. Step 5: Place the modified bamboo charcoal material obtained in Step 4 into a tube furnace. Under an argon atmosphere, first heat the material to 700℃ at 10℃ / min and hold for 1 hour, then heat it to 1400℃ at 3℃ / min and continue holding for 3 hours to obtain bamboo-based hard carbon anode material for sodium-ion batteries.

[0048] Button power test: The prepared negative electrode material, acetylene black, CMC, and SBR were uniformly mixed in a mass ratio of 95.5:1:1.5:2. A slurry was prepared using deionized water as a solvent and then coated onto copper foil. The slurry was dried at 60°C and then cut into 1cm diameter circular pieces to load the active material onto a current collector. A sodium sheet was used as the counter electrode, and the electrolyte was NP-027 type with NaPF6 as the solute. The cells were assembled into CR2032 coin cells in an argon-filled glove box. Charge-discharge tests were conducted at room temperature (25°C) in the voltage range of 0.01~3.0V. The current density was 12mA / g, the first-cycle reversible specific capacity (0.1C) was 343.8 mAh / g, the first-cycle coulombic efficiency was 90.7%, the rate performance (5C / 0.1C) was 20.6%, and the average voltage was 0.208. Figure 1 This is a charge-discharge curve diagram of Example 1.

[0049] Gray content test: Weigh 1 ± 0.0010 g of the sample (the prepared negative electrode material) into an ash dish and spread it out. Place the ash dish rack into the isothermal zone of a muffle furnace with a temperature below 100℃, leaving a gap of about 15 mm in the furnace door. Heat the furnace to 850 ± 10℃ at a heating rate of 5℃ / min and calcine for 3 hours. Remove the ash dish, cool it in air for about 5 minutes, then transfer it to a desiccator to cool to room temperature before weighing. The ash content of the bamboo-based hard carbon material was found to be 0.06%.

[0050] Example 2 Compared with Example 1, the only difference is that the steam pretreatment process in step one is changed. In the pretreatment, high-temperature steam mixed with hydrofluoric acid, nitric acid and hydrogen peroxide is introduced and the steam pressure is adjusted to 15 MPa.

[0051] Other processing procedures, conditions, and electrochemical and ash determination methods are the same as in Example 1. Specifically: The current density was 12 mA / g, the first-cycle reversible specific capacity (0.1C) was 353.6 mAh / g, the first-cycle coulombic efficiency was 91.9%, the rate performance (5C / 0.1C) was 24.7%, and the average voltage was 0.223. The ash content of the obtained bamboo-based hard carbon material was 0.04%.

[0052] Example 3 Compared to Example 1, the only difference is that the type and proportion of the activator in step four are changed. The experimental groups are: Group A: The activator is KOH, and the mass ratio of pretreated bamboo charcoal material to KOH is 1:1. Group B: The activators are KOH and ZnCl2, and the mass ratio of pretreated bamboo charcoal material to activator is 1:1.

[0053] Other processing procedures, conditions, and electrochemical measurement methods are the same as in Example 1. Specifically: The current density was 12 mA / g. Group A had a first-cycle reversible specific capacity (0.1C) of 346.5 mAh / g, a first-cycle coulombic efficiency of 92.3%, a rate performance (5C / 0.1C) of 22.7%, an average voltage of 0.202, and an ash content of 0.06%. Group B had a first-cycle reversible specific capacity (0.1C) of 348.5 mAh / g, a first-cycle coulombic efficiency of 92.1%, a rate performance (5C / 0.1C) of 24.9%, an average voltage of 0.231, and an ash content of 0.05%.

[0054] Example 4 Compared to Example 1, the only difference is that the pretreatment, activation, and two-stage carbonization temperatures and times were changed. The experimental groups are as follows:

[0055] Other processing procedures, conditions, and electrochemical and ash content determination methods are the same as in Example 1. Specific data are as follows:

[0056] Comparative Example 1 Compared with Example 1, the only difference is that tree bark is used instead of bamboo material; all other operations and parameters are the same as in Example 1.

[0057] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity (0.1C) was 306.5 mAh / g, first-cycle coulombic efficiency was 88.6%, rate performance (5C / 0.1C) was 18.6%, average voltage was 0.186, and ash content was 0.24%.

[0058] Comparative Example 2 Compared with Example 1, the only difference is that step one was not performed. Instead, the bamboo raw material was washed with water and then directly proceeded to step two and subsequent processing.

[0059] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity (0.1C) was 270.6 mAh / g, first-cycle coulombic efficiency was 73.4%, rate performance (5C / 0.1C) was 9.3%, average voltage was 0.154, and ash content was 1.13%.

[0060] Comparative Example 3 Compared with Example 1, the only difference is that in step one, the water vapor solidification treatment is not performed. Instead, the bamboo raw material is soaked in water with the same concentration of acid and oxidant and kept at 120°C for 0.5 hours. All other operations and parameters are the same as in Example 1.

[0061] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity (0.1C) was 273.1 mAh / g, first-cycle coulombic efficiency was 74.6%, rate performance (5C / 0.1C) was 9.8%, average voltage was 0.153, and ash content was 0.95%.

[0062] Comparative Example 4 Compared with Example 1, the only difference is that in step one, the steam pretreatment does not increase the steam pressure (i.e., atmospheric pressure), while the other operations and parameters are the same as in Example 1.

[0063] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity (0.1C) was 290.2 mAh / g, first-cycle coulombic efficiency was 87.4%, rate performance (5C / 0.1C) was 11.4%, average voltage was 0.168, and ash content was 0.781%.

[0064] Comparative Example 5A Compared with Example 1, the only difference is that in step one, an oxidant is added to the water vapor pretreatment, but no acid is added. All other operations and parameters are the same as in Example 1.

[0065] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity was 274.2 mAh / g, first-cycle coulombic efficiency was 76.6%, rate performance (5C / 0.1C) was 9.3%, average voltage was 0.153, and ash content was 0.854%.

[0066] Comparative Example 5B Compared with Example 1, the only difference is that in step one, acid is added to the water vapor pretreatment, but no oxidant is added. All other operations and parameters are the same as in Example 1.

[0067] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity was 273.9 mAh / g, first-cycle coulombic efficiency was 78.2%, rate performance (5C / 0.1C) was 8.4%, average voltage was 0.152, and ash content was 0.773%.

[0068] Comparative Example 6 Compared with Example 1, the only difference is that the order of steps one and two is reversed. That is, the bamboo raw material is pre-carbonized under the conditions of step two, then steam treatment is performed under the conditions of step one, and then step three and subsequent treatments are performed.

[0069] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity was 2285.6 mAh / g, first-cycle coulombic efficiency was 81.2%, rate performance (5C / 0.1C) was 11.8%, average voltage was 0.172, and ash content was 0.38%.

[0070] Comparative Example 7 Compared with Example 1, the only difference is that the treatment in step three is replaced with an alkali treatment: the initial bamboo charcoal material is placed in a NaOH solution and stirred for 2 hours.

[0071] All other operations and parameters are the same as in Example 1.

[0072] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity was 287.1 mAh / g, first-cycle coulombic efficiency was 86.3%, rate performance (5C / 0.1C) was 13.3%, average voltage was 0.17, and ash content was 0.895%.

[0073] Comparative Example 8 Compared with Example 1, the only difference is that step four is omitted, and the material from step three is directly processed in step five. All other operations and parameters are the same as in Example 1.

[0074] The test was conducted according to the method in Example 1, and the results were as follows: current density was 12 mA / g, first-cycle reversible specific capacity was 204.1 mAh / g, first-cycle coulombic efficiency was 56.2%, rate performance (5C / 0.1C) was 2.6%, average voltage was 0.094, and ash content was 0.17%.

[0075] Figure 2 This is the SEM image of Example 1.

[0076] The main impurity element contents of the hard carbon materials obtained in Example 1 and the comparative example are shown in the table below:

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a bamboo-based hard carbon anode material, characterized in that, The steps include the following: (1) The block bamboo raw material is placed in high temperature steam for pretreatment and then dried to obtain pretreated bamboo raw material; the high temperature steam contains acid additives and oxidants, and the temperature of the high temperature steam is 100~250℃ and the pressure is 1~30MPa. (2) The pretreated bamboo raw material is pre-carbonized under an inert protective atmosphere to obtain preliminary bamboo charcoal material; (3) The preliminary bamboo charcoal material is placed in an acid solution for acid treatment to obtain pretreated bamboo charcoal material; (4) The pretreated bamboo charcoal material is mixed with an activator and activated at low temperature in an inert atmosphere to obtain the modified bamboo charcoal material; the activator is at least one of alkali metal hydroxide, alkali metal carbonate, and metal chloride; the temperature of the low-temperature activation is 600~1000℃. (5) The modified bamboo charcoal material is carbonized under an inert protective atmosphere to obtain bamboo-based hard carbon anode material.

2. The method for preparing bamboo-based hard carbon anode material according to claim 1, characterized in that, The acid additive in step (1) is at least one of hydrofluoric acid, sulfuric acid, nitric acid, hydrochloric acid, and acetic acid.

3. The method for preparing bamboo-based hard carbon anode material according to claim 1, characterized in that, The oxidant in step (1) is at least one of hydrogen peroxide, potassium permanganate, potassium dichromate, potassium chlorate, sodium perchlorate, sodium hypochlorite, and ammonium persulfate.

4. The method for preparing bamboo-based hard carbon anode material according to claim 1, characterized in that, The pre-carbonization temperature in step (2) is 350~650℃, and the pre-carbonization time is 2~7h.

5. The method for preparing bamboo-based hard carbon anode material according to claim 1, characterized in that, The acid solution in step (3) includes at least two of HF, sulfuric acid, nitric acid, HCl, and acetic acid.

6. The method for preparing bamboo-based hard carbon anode material according to claim 1, characterized in that, In step (4), the mass ratio of the pretreated bamboo charcoal material to the activator is 1:0.1~1.

7. The method for preparing bamboo-based hard carbon anode material according to claim 1, characterized in that, The carbonization process in step (5) includes two heat preservation stages, wherein the temperature of the first heat preservation stage is 700~1000℃ and the time is 1~3h; the temperature of the second heat preservation stage is 1100~1500℃ and the time is 2~6h.

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

9. A negative electrode for a sodium-ion battery, characterized in that, It comprises the bamboo-based hard carbon anode material as described in claim 8.

10. A sodium-ion battery, characterized in that, It comprises the negative electrode as described in claim 9.

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