Bamboo-based hard carbon materials and their preparation and application in sodium-ion batteries

Abstract

The present invention belongs to the field of anode materials, and specifically discloses a preparation method of a bamboo-based hard carbon material. The bamboo stems of 3-5-year-old bamboos are screened, cut into sections and peeled to obtain peeled bamboo tubes; the peeled bamboo tubes are placed in a modification solution for liquid-phase modification treatment, and then calcined in an oxygen-containing atmosphere for gas-solid modification treatment to obtain modified bamboo tubes; the modification solution is an aqueous solution containing at least one solute of permanganate, hypochlorite, hydrogen peroxide, hypochlorous acid, manganate, dichromate, etc.; the calcination temperature is 150-300 °C; the modified bamboo tubes are pre-carbonized, crushed and classified to obtain a precursor, and then carbonized to obtain the bamboo-based hard carbon material. The present invention also includes the material prepared by the above preparation method and its application. The material of the present invention can exhibit excellent electrochemical performance and uniformity.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and particularly relates to the field of anode active materials for sodium-ion batteries. Background Art

[0002] With the increasing demand for electric energy storage methods, sodium-ion batteries have gradually attracted people's attention due to their advantages such as low cost and high safety performance. More and more research institutions are industrializing them. However, due to the larger radius of the active ion Na in sodium-ion batteries compared to Li, it is difficult for materials suitable for lithium-ion insertion and extraction to meet the requirements of sodium-ion insertion and extraction. This is the main factor that seriously lags behind the commercial development of lithium-ion batteries for sodium-ion batteries.

[0003] In addition, biomass hard carbon materials have attracted much attention due to their wide raw material sources and low prices. Bamboo-based materials are even better because of the huge bamboo production in China, and they are one of the best raw materials for local biomass hard carbon materials in China. Some bamboo-based active materials have also been reported in the prior art. For example, Chinese patent document with publication number CN115849333A reports a preparation method of a bamboo-based hard carbon active electrode material. The bamboo raw material is pretreated in acid solution A to obtain pretreated bamboo raw material; the pretreated bamboo raw material is pyrolyzed to obtain pyrolyzed bamboo charcoal, and the bamboo tar during the pyrolysis process is collected; the pyrolyzed bamboo charcoal is treated with alkali solution B and acid solution C in any order to obtain pretreated bamboo charcoal; the bamboo tar and a cross-linking agent are used as precursor raw materials for cross-linking treatment to obtain a carbon shaping agent; the carbon shaping agent or its precursor raw material is mixed with the pretreated bamboo charcoal to obtain a mixture, and then two-stage roasting treatment is carried out to obtain the bamboo-based hard carbon active electrode material. Another example is the patent document with publication number WO2019062495A1, which discloses a carbon material and an asphalt-based anode material for sodium-ion batteries, their preparation methods and applications, and further records that the anode material of the sodium-ion battery is a composite carbon material with an ordered carbon structure or an asphalt-based massive or vertical channel-shaped material with irregular morphology coated on the surface. The types of carbon materials include charcoal materials and bamboo charcoal materials. The charcoal includes one or more mixtures obtained by mixing white charcoal, black charcoal, activated carbon and machine-made charcoal. The bamboo charcoal materials include Phyllostachys edulis, Phyllostachys glauca, Phyllostachys heterocycla, Phyllostachys praecox and Dendrocalamus giganteus, etc.

[0004] In summary, although some bamboo charcoal-based anode materials for sodium-ion batteries have been reported in the prior art, however, the electrochemical performance of existing bamboo-based materials needs to be improved, and in the prior art, less attention has been paid to the problem of the performance uniformity of bamboo-based materials. Summary of the Invention

[0005] Aiming at the problems of unsatisfactory electrochemical performance and performance uniformity of current bamboo-based hard carbon materials, the first object of the present invention is to provide a preparation method of bamboo-based hard carbon materials, aiming to prepare bamboo-based hard carbon materials with excellent performance uniformity and electrochemical performance.

[0006] The second object of the present invention is to provide a bamboo-based hard carbon material prepared by the above-mentioned preparation method.

[0007] The third object of the present invention is to provide the application of the above-mentioned bamboo-based hard carbon material as a negative electrode active material for sodium-ion batteries.

[0008] The fourth object of the present invention is to provide a sodium-ion battery and its negative electrode containing the above-mentioned bamboo-based hard carbon material.

[0009] The electrochemical performance of existing bamboo-based hard carbon materials needs to be improved, and the performance uniformity is poor. Aiming at this problem, the present invention provides the following improvement solutions, specifically:

[0010] A preparation method of bamboo-based hard carbon materials, the steps include:

[0011] Step (1): Bamboo raw material regulation

[0012] Select the bamboo stems of 3-5-year-old bamboo, cut them into sections and remove the skin to obtain peeled bamboo tubes;

[0013] Step (2): Liquid-phase - gas-phase modification

[0014] Place the peeled bamboo tubes in a modification liquid for liquid-phase modification treatment, and then carry out roasting in an oxygen-containing atmosphere for gas-solid modification (also known as gas-phase modification) treatment to obtain modified bamboo tubes; the modification liquid is an aqueous solution containing at least one solute of permanganate, hypochlorite, hydrogen peroxide, hypochlorous acid, manganate, dichromate, etc.; the roasting temperature is 150-300 °C;

[0015] Step (3): Carbonization

[0016] Carry out pre-carbonization and crushing classification on the modified bamboo tubes to obtain a precursor, and then carbonize to obtain the bamboo-based hard carbon material.

[0017] Aiming at the problems that bamboo-based hard carbon materials are difficult to adapt to the use requirements of sodium-ion batteries, the sodium battery performance is unsatisfactory, and the performance uniformity is unsatisfactory, etc., the present invention innovatively conducts regulation treatments such as bamboo age and skin removal on bamboo raw materials, and then pre-performs liquid-phase modification in the above-mentioned modifier, and then performs gas-phase roasting modification treatment. In this way, synergy can be achieved, which can not only help to construct a microstructure and active sites suitable for sodium-ion batteries and improve the performance of sodium-ion batteries, but also unexpectedly improve the performance uniformity of the materials.

[0018] The regulation of the age of the bamboo raw material and peeling in the present invention is the key to synergistically improving the electrochemical performance and uniformity in cooperation with the two-stage liquid-phase / gas-phase modification.

[0019] In the present invention, the bamboo at the age of 3 - 5 refers to Phyllostachys edulis at the growth age of 3 - 5; preferably Phyllostachys edulis at the growth age of 3 - 4.

[0020] Preferably, the length of the peeled bamboo tube is 30 - 50 cm and the diameter is 3 - 12 cm.

[0021] In the present invention, innovatively selecting the bamboo raw material at the said age and further cooperating with the direct combined control of peeling and cutting into sections contribute to further synergistically improving the sodium battery performance and performance uniformity of the prepared material.

[0022] In the present invention, on the basis of the innovative regulation of the bamboo raw material, further cooperating with the two-stage modification process of first liquid phase and then gas phase is beneficial to synergistically improving the adaptation effect of the prepared material to sodium ions and also beneficial to improving the performance uniformity of the material.

[0023] The research of the present invention also shows that innovatively controlling the components in the modification liquid, for example, controlling the solute of the modification liquid to be a mixture containing hydrogen peroxide and hypochlorous acid, helps to further improve the adaptation advantage of the prepared material to sodium ions and helps to further improve the performance and uniformity.

[0024] Preferably, in the said solute, the weight ratio of hydrogen peroxide to hypochlorous acid is 0.1 - 2:1.

[0025] In the present invention, in step (2), in the modification liquid, the weight content of the solute is 1 - 10 wt%.

[0026] Preferably, during the liquid-phase modification treatment, the peeled bamboo tube is completely immersed in the modification liquid.

[0027] Preferably, the temperature during the liquid-phase modification treatment is 20 - 35 °C.

[0028] Preferably, the time of the liquid-phase modification treatment is 1 - 12 h.

[0029] In the present invention, the oxygen-containing atmosphere is an atmosphere containing oxygen, preferably pure oxygen, air, or a mixture of oxygen and a protective gas.

[0030] Preferably, the oxygen content in the oxygen-containing atmosphere is 5 - 15 v%.

[0031] Preferably, the flow rate of the oxygen-containing atmosphere is above 50 sccm, preferably 100 - 300 sccm.

[0032] In the present invention, the roasting temperature can be 150 - 250 °C.

[0033] Preferably, the calcination process includes two-stage treatment. Among them, the temperature of the first stage is 150-180 °C, and the flow rate of the oxygen-containing atmosphere is 100-150 sccm; the temperature of the second stage is 200-250 °C, and the flow rate of the oxygen-containing atmosphere is 200-250 sccm. The research of the present invention finds that the two-stage treatment, further combined with the combined control of the temperature and atmosphere of the two-stage treatment, can unexpectedly further construct the structure and sites suitable for sodium-ion batteries, which helps to further improve the sodium battery performance.

[0034] Preferably, the calcination time is 1-4 h. When the preferred two-stage treatment is adopted, the time of each stage can be 1-2 h.

[0035] In the present invention, the modified bamboo tube is pre-carbonized, then crushed and classified to obtain a precursor, and then carbonized to obtain the bamboo-based hard carbon material.

[0036] In the present invention, the pre-carbonization and carbonization processes are carried out in a protective gas, and the protective gas is at least one of nitrogen and inert gas;

[0037] Preferably, the protective gas is also allowed to contain at least one of hydrogen and CO;

[0038] Preferably, the temperature of the pre-carbonization is 400-700 °C, and further can be 500-600 °C;

[0039] Preferably, the time of the pre-carbonization is 1-4 h;

[0040] Preferably, the particle size of the precursor obtained by crushing and classifying after pre-carbonization is 3-20 μm;

[0041] Preferably, the precursor is pre-treated with acid before carbonization;

[0042] Preferably, the temperature of the carbonization is 800-1500 °C, and further can be 1300-1400 °C;

[0043] Preferably, the time of the carbonization is 2-8 h.

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

[0045] In the present invention, thanks to the preparation method, the prepared material can be given a special microstructure and active sites, which can make it show a better sodium-ion adaptation effect, help to further improve the sodium battery performance, and in addition, can also improve the performance uniformity of the material.

[0046] The present invention also includes an application of the bamboo-based hard carbon material prepared by the preparation method, using it as a negative electrode active material for preparing a sodium-ion battery.

[0047] In the present invention, based on known processes, the bamboo-based hard carbon material prepared by the preparation method of the present invention can be used as the negative electrode active material to prepare the required sodium-ion battery. For example, the bamboo-based hard carbon material, a conductive agent, and a binder can be mixed to obtain a negative electrode material, and then it can be loaded on a current collector by coating to form a negative electrode. Then, the negative electrode, a separator, and a positive electrode are assembled in combination to obtain the required battery.

[0048] In the present invention, except for using the bamboo-based hard carbon material described in the present invention as the negative electrode active material, other operations, parameters, and components can be conventional selections and adjustments based on existing principles.

[0049] The present invention also provides a negative electrode of a sodium-ion battery, which includes a current collector and a negative electrode material loaded thereon. The negative electrode material contains the bamboo-based hard carbon material prepared by the preparation method described in the present invention;

[0050] In the present invention, the negative electrode material further contains a binder and a conductive agent;

[0051] In the present invention, in the negative electrode material, the content of the bamboo-based hard carbon material is above 60 wt.%, preferably 70 - 90 wt.%.

[0052] The present invention also provides a sodium-ion battery, which includes a positive electrode, a separator, and a negative electrode assembled in sequence, and the negative electrode is the negative electrode described in the present invention.

[0053] Beneficial effects

[0054] In the present invention, the bamboo raw materials are innovatively regulated and processed in terms of bamboo age, peeling, etc. Subsequently, liquid-phase modification is first carried out in the modifier, and then gas-phase roasting modification treatment is carried out. In this way, synergy can be achieved, which can not only help to construct a microstructure and active sites suitable for sodium-ion batteries and improve the performance of sodium-ion batteries, but also unexpectedly improve the material property uniformity. Brief description of the drawings

[0055] Figure 1 SEM diagram of the hard carbon material finally obtained in Example 1.

[0056] Figure 2 XRD diagram of the hard carbon material finally obtained in Example 1.

[0057] Figure 3 First-cycle charge and discharge diagram of the sodium-ion battery assembled with the hard carbon material finally obtained in Example 1. Detailed description of the specific embodiments

[0058] To better understand the present invention, the following further illustrates the present invention through embodiments. The embodiments are only used to explain the present invention and do not constitute a limitation to the present invention.

[0059] The preparation process of the typical bamboo-based hard carbon material of the present invention, for example, includes the following steps:

[0060] Step 1: Select 3- to 4-year-old moso bamboos and perform sectional treatment;

[0061] Step 2: Select bamboo tubes within a certain diameter range;

[0062] Step 3: Remove the bamboo skin;

[0063] Step 4: Immerse the bamboo tubes in a modification liquid (the first-stage liquid-phase modification);

[0064] Step 5: Wash the bamboo tubes and then dry them;

[0065] Step 6: Perform roasting modification treatment on the bamboo tubes in an oxygen-containing atmosphere (the second-stage gas-phase modification);

[0066] Step 7: Perform pre-carbonization under a protective atmosphere;

[0067] Step 8: Crush and classify to form a biomass hard carbon precursor.

[0068] Step 9: Pickle the precursor and then dry it.

[0069] Step 10: Perform high-temperature carbonization on the pickled and dried precursor to obtain the hard carbon material corresponding to the precursor.

[0070] Further, in the above Step 1, the sectional length of the sectional treatment is 30-50 cm;

[0071] Further, in the above Step 2, the diameter range of the selected bamboo tubes is 3-12 cm;

[0072] Further, in the above Step 3, the thickness of the peeled outer skin can be determined according to the characteristics of the bamboo, and it is only necessary to remove the surface green layer. For example, it can be 1-5 mm;

[0073] Further, in the above Step 4, the modification liquid is one or more of potassium permanganate solution, potassium hypochlorite solution, hydrogen peroxide, hypochlorous acid, potassium manganate, and dichromate solution;

[0074] Further, in the above Step 4, the solute concentration of the modification liquid is 1%-10%;

[0075] Further, in the above Step 4, it is only necessary to completely immerse the bamboo tubes in the modification liquid. For example, the mass of the modification liquid is 10-100 times the mass of the bamboo tubes;

[0076] Further, in the step 4, the soaking time of the bamboo tube in the modification liquid is 2 - 8 hours;

[0077] Further, in the step 5, the water washing dosage is 50 - 400 times the weight of the bamboo tube;

[0078] Further, in the step 5, the water washing time is 1 - 4 hours;

[0079] Further, in the step 5, the drying temperature is 60 - 120 °C;

[0080] Further, in the step 5, the drying time is 4 - 18 h;

[0081] Further, in the step 6, the oxygen concentration in the second - stage gas - phase modification is 5 - 15%;

[0082] Further, in the step 6, the other atmosphere except oxygen in the second - stage gas - phase modification is one or more of nitrogen, argon, and helium;

[0083] In the present invention, there is no special requirement for the flow rate of the atmosphere in the second - stage gas - phase modification. Considering the processing efficiency and cost, it can be further above 50 sccm, and further can be 100 - 300 sccm.

[0084] Further, in the step 6, the temperature of the second - stage gas - phase modification is 150 - 300 °C, and further can be 150 - 200 °C;

[0085] Further, in the step 6, the time of the second - stage gas - phase modification is 1 - 4 hours;

[0086] Further, in the step 7, the protective atmosphere for pre - carbonization is one or more of nitrogen, argon, and helium;

[0087] Further, in the step 7, the temperature of pre - carbonization is 400 - 700 °C;

[0088] Further, in the step 7, the time of pre - carbonization is 2 - 6 hours;

[0089] Further, in the step 8, the crushing time is 0.5 - 4 hours;

[0090] Further, in the step 8, the particle size after classification is 3 - 20 μm;

[0091] Further, in the step 9, the acid used for pickling the precursor is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, hypochlorous acid, etc.;

[0092] Further, in the step 9, the concentration of the acid during the pickling process of the precursor is 5 - 30%;

[0093] Further, in step 9, the mass ratio of the acid solution to the precursor during the pickling of the precursor is 2:1 - 10:1;

[0094] Further, in step 9, the pickling time of the precursor is 4 - 24 hours;

[0095] Further, in step 9, the drying temperature of the precursor is 60 - 120 °C;

[0096] Further, in step 9, the drying time of the precursor is 4 - 24 hours;

[0097] Further, in step 10, the protective atmosphere for high-temperature carbonization is one or more of nitrogen, argon, and helium;

[0098] Further, in step 10, the high-temperature carbonization temperature is 800 - 1500 °C;

[0099] Further, in step 10, the high-temperature carbonization time is 2 - 8 hours.

[0100] The present invention innovatively regulates through the bamboo age and peeling method of bamboo raw materials, and further cooperates with the above-mentioned liquid-phase - gas-phase two-stage modification treatment, so as to achieve synergy, improve the sodium ion adaptation performance of the material, improve the sodium battery performance of the material. In addition, it also helps to improve the uniformity of the material structure and properties, and further improve the uniformity of the material.

[0101] Example 1

[0102] Step 1: Select 3 - 4-year-old Moso bamboo and cut it into sections with a length of 45 cm;

[0103] Step 2: Select bamboo tubes with a diameter range of 5 - 8 cm;

[0104] Step 3: Use a machine to remove 2 mm of bamboo skin;

[0105] Step 4: Use a 3% hydrogen peroxide and hypochlorous acid mixed solution (modifying solution, the weight ratio of hydrogen peroxide to hypochlorous acid is 0.5:1) that is 50 times the mass of the bamboo tube to soak the bamboo tube for 4 hours;

[0106] Step 5: Wash the bamboo tube with tap water that is 200 times the mass of the bamboo tube, and then dry it at 80 °C for 8 h to remove moisture;

[0107] Step 6: Configure a nitrogen and air mixture with an oxygen content (modifying atmosphere, where the oxygen content is 10 v%, and the flow rate is 200 sccm), and keep the bamboo tube obtained in step 5 modified at 200 °C for 2 hours in the above-mentioned atmosphere to obtain a modified bamboo tube;

[0108] Step 7: Perform pre-carbonization at 500 °C for 4 hours under an argon atmosphere;

[0109] Step 8: Crushing and classification, and taking the precursor particles with D50 in the range of 5 - 8 μm.

[0110] Step 9: Put the precursor into 15% hydrochloric acid with a liquid - solid ratio of 6:1 ml / g for pickling for 16 hours, then wash it with a filter press until neutral and filter dry the water, and bake it at 100 °C for 12 hours.

[0111] Step 10: Keep the pickled and baked precursor at 1400 °C for 4 hours for high - temperature carbonization (in an Ar atmosphere) to obtain the corresponding hard - carbon material of the precursor.

[0112] Example 2

[0113] Compared with Example 1, the difference is only that the bamboo raw materials and properties are adjusted, and the experimental groups are as follows:

[0114] Group A: Phyllostachys pubescens with a bamboo age of 3 - 4 years, segmented at a length of 35 cm, screening bamboo tubes with a diameter range of 5 - 8 cm, and using a machine to remove 4 mm of bamboo skin;

[0115] Group B: Phyllostachys pubescens with a bamboo age of 3 - 4 years, segmented at a length of 40 cm, screening bamboo tubes with a diameter range of 5 - 8 cm, and using a machine to remove 3 mm of bamboo skin.

[0116] In the above groups, other operations and parameters are the same as those in Example 1.

[0117] Example 3

[0118] Compared with Example 1, the difference is only that the composition and concentration of the modification liquid are changed, and the experimental groups are as follows:

[0119] A: The solute in the modification liquid is H2O2, and the concentration of the solute in the modification liquid is the same as that in Example 1;

[0120] B: The solute in the modification liquid is hypochlorous acid, and the concentration of the solute in the modification liquid is the same as that in Example 1;

[0121] In the above groups, other operations and parameters are the same as those in Example 1.

[0122] Example 4

[0123] Compared with Example 1, the difference is only that the processing conditions in Step 6 are changed, and the experimental group is as follows:

[0124] Group A: The volume of oxygen in the atmosphere during the modification stage is 15 v%;

[0125] Group B: The modification temperature is 250 °C and the time is 3 h;

[0126] C: Two-stage gradient treatment: the temperature of the first stage is 150 °C, the flow rate is 100 sccm, and the holding time is 1 h; the temperature of the second stage is 200 °C, the flow rate is 200 sccm, and the holding time is 1 h, obtaining a modified bamboo tube;

[0127] In the above groups, other operations and parameters are the same as those in Example 1.

[0128] Example 5

[0129] Compared with Example 1, the difference is only that the temperature of pre-carbonization is changed to 600 °C and the time is 3 h; in the above groups, other operations and parameters are the same as those in Example 1.

[0130] Example 6

[0131] Compared with Example 1, the difference is only that the temperature of carbonization is changed to 1300 °C and the carbonization time is 6 hours; in the above groups, other operations and parameters are the same as those in Example 1.

[0132] Comparative Example 1

[0133] Compared with Example 1, the difference is only that the peeling treatment in Step 3 is not carried out, and other operations and parameters are the same as those in Example 1.

[0134] Comparative Example 2

[0135] Compared with Example 1, the difference is only that Step 6 (the gas-phase modification treatment step) is not carried out, and other operations and parameters are the same as those in Example 1.

[0136] Comparative Example 3

[0137] Compared with Example 1, the difference is only that in Step 1, 6-7-year-old Phyllostachys pubescens is selected, and other operations and parameters are the same as those in Example 1.

[0138] Comparative Example 4

[0139] Compared with Example 1, the difference is only that Step 4 (the liquid-phase modification treatment) is omitted, and other operations and parameters are the same as those in Example 1.

[0140] Comparative Example 5

[0141] Compared with Example 1, the difference is only that the modification liquid in Step 4 is a 3% nitric acid solution, and other operations and parameters are the same as those in Example 1.

[0142] Comparative Example 6

[0143] Compared with Example 1, the difference is only that the order of Steps 6 and 4 is reversed. For example, after Step 3, Step 6 is carried out, then Steps 4 and 5, and then Step 7 and subsequent operations. Other operations and parameters are the same as those in Example 1.

[0144] Comparative Example 7

[0145] Compared with Example 1, the difference is that moso bamboos aged 6 - 7 years are selected and the peeling treatment in Step 3 is not carried out, and other operations and parameters are the same as those in Example 1.

[0146] The hard carbon materials prepared in the above cases, conductive carbon Super - P, CMC, and SBR are mixed in a ratio of 95:1.5:1.5:2, with water as the solvent. After mixing evenly, it is coated on a copper foil and dried in a vacuum oven at 80°C. After rolling, it is cut into circular electrode sheets with a diameter of 1 cm. Sodium sheets are used as the negative electrode, the electrolyte is NaPF6 lipid electrolyte of model NP - 001, and the separator is a glass fiber separator. A button cell is assembled in a glove box filled with argon. The charge - discharge performance of the 7 sodium - ion batteries prepared is tested, and the test results are shown in Table 1.

[0147] The electrochemical performance test data of each case are shown in Table 1:

[0148] Table 1

[0149]

[0150]

[0151] It can be seen from Table 1 that Examples 1 - 6 all have a relatively high first - cycle reversible specific capacity of more than 300 mAh / g, and the first - cycle efficiency is about 90%, with excellent performance.

[0152] Table 2 shows the specific surface area, ash content, and particle size D50 test data (Table 2) of the hard carbon materials prepared from the biomass hard - carbon precursors in the examples and comparative examples of the present invention.

[0153] Table 2

[0154]

[0155]

[0156] It can be seen from Table 2 that according to the technical solution of the present invention, the examples all have relatively low specific surface area and ash content parameters. The raw materials retaining the bamboo skin and those with a larger bamboo age and a thicker bamboo diameter have too high ash content. Moreover, the specific surface area of the hard carbon materials prepared from raw materials with a larger bamboo age, a thicker bamboo diameter, and those not treated with the modification liquid will be relatively large.

[0157] Repeat the process of each case 5 times, and evaluate the process uniformity by testing the variance:

[0158] The calculation formula of the variance is:

[0159]

[0160] Table 3 shows the specific surface area, ash content, particle size D50, first-cycle reversible specific capacity, first-efficiency test data and variance results of the hard carbon materials prepared from 5 randomly selected different batches of biomass hard carbon precursors in Example 1 and Comparative Example 7 (Table 3).

[0161] Table 3

[0162]

[0163]

[0164] It can be seen from Table 3 that according to the technical solution of the present invention, the 5 randomly selected different batches of samples in Example 1 not only have relatively low specific surface area and ash content parameters, but also the variance values of specific surface area, ash content, particle size, first-cycle reversible specific capacity of coin cell and first efficiency are all smaller than those of the comparative example, indicating that the raw material treatment scheme in Example 1 can better maintain the batch consistency of the raw materials.

Claims

1. A preparation method of a bamboo-based hard carbon material, characterized in that the steps Comprising: Step (1): Bamboo raw material regulation Select the bamboo stems of 3-5-year-old bamboo, cut into sections and peel off the skin to obtain peeled bamboo tubes; Step (2): Liquid-phase - gas-phase modification Place the peeled bamboo tubes in a modification liquid for liquid-phase modification treatment, and then conduct calcination in an oxygen-containing atmosphere for gas-solid modification treatment to obtain modified bamboo tubes; the modification liquid is an aqueous solution containing at least one solute of permanganate, hypochlorite, hydrogen peroxide, hypochlorous acid, manganate, dichromate, etc.; the calcination temperature is 150-300 °C; Step (3): Carbonization Pre-carbonize the modified bamboo tubes, crush and classify them to obtain a precursor, and then carbonize to obtain the bamboo-based hard carbon material.

2. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The 3-5-year-old bamboo is Phyllostachys pubescens with a growth age of 3-5 years.

3. The preparation method of the bamboo-based hard carbon material according to claim 2, wherein, The length of the peeled bamboo tube is 30-50 cm, and the diameter is 3-12 cm.

4. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, In step (2), in the modification liquid, the solute includes hydrogen peroxide and hypochlorous acid.

5. The preparation method of the bamboo-based hard carbon material according to claim 4, characterized in that, In the solute, the weight ratio of hydrogen peroxide to hypochlorous acid is 0.1-2:

1.

6. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, In step (2), in the modification liquid, the weight content of the solute is 1-10 wt%.

7. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, During the liquid-phase modification treatment, the peeled bamboo tubes are completely immersed in the modification liquid.

8. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The temperature during the liquid-phase modification treatment is 20-35 °C.

9. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The time of the liquid-phase modification treatment is 1-12 h.

10. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The oxygen-containing atmosphere is an atmosphere containing oxygen.

11. The preparation method of the bamboo-based hard carbon material according to claim 10, characterized in that, The oxygen-containing atmosphere is pure oxygen, air, or a mixed gas of oxygen - protective gas.

12. The preparation method of the bamboo-based hard carbon material according to claim 10, wherein, The oxygen content in the oxygen-containing atmosphere is 5-15 vol%.

13. The preparation method of the bamboo-based hard carbon material according to claim 10, characterized in that, The flow rate of the oxygen-containing atmosphere is above 50 sccm.

14. The preparation method of the bamboo-based hard carbon material according to claim 13, characterized in that, The flow rate of the oxygen-containing atmosphere is 100-300 sccm.

15. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The calcination process includes two-stage treatment processes. Among them, the temperature of the first stage is 150-180 °C, and the flow rate of the oxygen-containing atmosphere is 100-150 sccm; the temperature of the second stage is 200-250 °C, and the flow rate of the oxygen-containing atmosphere is 200-250 sccm.

16. The preparation method of the bamboo-based hard carbon material according to claim 1, wherein, The calcination time is 1-4 h.

17. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The pre-carbonization and carbonization processes are carried out in a protective gas, and the protective gas is at least one of nitrogen and inert gas.

18. The preparation method of the bamboo-based hard carbon material according to claim 17, wherein, In the protective gas, it also contains at least one of hydrogen and CO.

19. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The pre-carbonization temperature is 400-700 °C.

20. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The pre-carbonization time is 1-4 h.

21. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The particle size of the precursor obtained by crushing and classifying after pre-carbonization is 3-20 μm.

22. The preparation method of the bamboo-based hard carbon material according to claim 1, wherein, The precursor is pre-treated with acid before carbonization.

23. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The carbonization temperature is 800-1500 °C.

24. The preparation method of the bamboo-based hard carbon material according to claim 1, characterized in that, The carbonization time is 2-8 h.

25. A bamboo-based hard carbon material prepared by the preparation method according to any one of claims 1-24.

26. Use of the bamboo-based hard carbon material prepared by the preparation method according to any one of claims 1-24, characterized in that, Using it as a negative electrode active material for preparing a sodium-ion battery.

27. The negative electrode of a sodium-ion battery includes a current collector and a negative electrode material loaded thereon, characterized in that, The negative electrode material contains the bamboo-based hard carbon material prepared by the preparation method according to any one of claims 1-24.

28. The negative electrode of the sodium ion battery according to claim 27, characterized in that, In the negative electrode material, it also contains a binder and a conductive agent.

29. The negative electrode of the sodium ion battery according to claim 28, characterized in that, In the negative electrode material, the content of the bamboo-based hard carbon material is above 60 wt%.

30. The negative electrode of the sodium-ion battery according to claim 29, characterized in that, In the negative electrode material, the content of the bamboo-based hard carbon material is 70-90 wt%.

31. A sodium-ion battery, comprising a positive electrode, a separator and a negative electrode which are sequentially compounded, characterized in that, The negative electrode is the negative electrode of the sodium-ion battery according to any one of claims 27-30.

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