A biomass hard carbon anode material, its preparation method and application

Abstract

The present invention discloses a biomass hard carbon anode material, a preparation method thereof and an application. The present invention uses waste biomass as a raw material, and only through pretreatment with an organic acid of an appropriate concentration, the selective dissolution and regulation of hemicellulose in plants can be realized under the condition of not destroying the natural structure of plants, while retaining the cellulose and lignin components. Then, through two-step carbonization and acid-base treatment, a biomass hard carbon anode material with improved performance can be obtained, so that the assembled sodium-ion battery has excellent electrochemical performance. At a current density of 50 mA / g, the initial discharge capacity is 286-345 mAh / g, the initial Coulomb efficiency is 92-95%, and the cycle capacity is stable. The method can be used as a general strategy to optimize the electrochemical performance of biomass hard carbon, and the preparation process has low cost, simple process, and is conducive to large-scale application for producing high-performance sodium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion battery energy storage, and specifically relates to a biomass hard carbon negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the global climate change problem caused by the extensive use of fossil fuels, humans have made great efforts to find new energy storage and utilization technologies. Among the existing and efficient energy storage devices, secondary batteries are considered high-energy-density storage systems and are ideal choices for portable electronic devices, hybrid electric vehicles, and large industrial devices. Lithium-ion batteries occupy the main market of current secondary batteries. However, due to the limited lithium ore resources, the prices of lithium battery materials represented by lithium carbonate fluctuate greatly with the market. Compared with lithium, sodium resources have the advantages of rich reserves, wide distribution, and low price, and are expected to be used for large-scale energy storage.

[0003] In sodium-ion batteries, the negative electrode material plays an important role in storing sodium ions. Traditional graphite negative electrodes are difficult to be applied to sodium-ion batteries due to their low sodium storage capacity. Hard carbon materials are difficult to be graphitized even at temperatures above 2500°C. They have more pores and larger interlayer spacings inside, enabling sodium ions with larger ionic radii to freely intercalate and deintercalate, and thus have a higher sodium storage capacity. Moreover, hard carbon materials are widely sourced and low-cost, especially the hard carbon derived from biomass materials often has the property of being renewable, which has attracted the attention of researchers. Currently, reports on biomass-derived hard carbon materials mainly include Physalis peruviana shells, walnut shells, peanut shells, straw, etc. However, currently, sodium-ion batteries prepared from biomass-derived hard carbon materials all require complex hard carbon material preparation processes (such as complex pretreatment processes, organic matter coating and doping processes) to improve the performance of the prepared sodium-ion batteries, and it is difficult to meet the requirements of commercial sodium-ion battery materials for negative electrodes in large-scale production. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects and deficiencies existing in the prior art, and to provide a preparation method of a biomass hard carbon negative electrode material.

[0005] The second purpose of the present invention is to provide a biomass hard carbon negative electrode material prepared by the above-mentioned preparation method.

[0006] The third purpose of the present invention is to provide the application of the above-mentioned biomass hard carbon negative electrode material in the preparation of sodium-ion batteries.

[0007] The fourth purpose of the present invention is to provide a sodium-ion battery.

[0008] The above-mentioned purposes of the present invention are achieved by the following technical solutions:

[0009] The present invention first provides a method for preparing a biomass hard carbon anode material, comprising the following steps:

[0010] S1. Crushing and sieving the waste biomass, pretreating it with a 10-50 wt% organic acid solution to selectively remove hemicellulose while retaining cellulose and lignin, washing with water and drying to obtain a biomass hard carbon precursor;

[0011] S2. Performing pre-carbonization treatment on the biomass hard carbon precursor obtained in step S1 under an inert atmosphere to obtain a preliminary biomass hard carbon material;

[0012] S3. Sequentially performing alkali treatment and acid treatment on the preliminary biomass hard carbon material obtained in step S2, washing until neutral, drying, and performing carbonization treatment under an inert atmosphere to obtain a hard carbon anode material for sodium-ion batteries.

[0013] Wherein, the organic acid solution is a solution prepared by diluting the corresponding organic acid with deionized water, and wt% is w / w.

[0014] Biomass materials mainly include cellulose, hemicellulose, and lignin components. In the present invention, selective removal of hemicellulose in different waste biomasses is achieved through pretreatment with an organic acid at an appropriate concentration while retaining cellulose and lignin. While maintaining the natural structure of the biomass, hemicellulose is removed as much as possible while retaining cellulose and lignin. The results show that after retaining cellulose and lignin and removing hemicellulose, a significant improvement in electrochemical performance can be promoted, thereby realizing the optimized regulation of the sodium storage performance of the biomass hard carbon anode material. Compared with inorganic acid pretreatment or without organic acid pretreatment, the performance of the sodium-ion battery assembled with the biomass hard carbon anode material prepared by organic acid pretreatment is improved. In particular, both the initial discharge capacity and the first Coulombic efficiency are significantly increased, and the specific capacity is high and the cycle stability is good. However, after pretreatment with a higher concentration of organic acid, cellulose in the biomass is retained, but more lignin is removed, and the performance improvement effect of the sodium-ion battery assembled with the biomass hard carbon anode material prepared is worse than that of pretreatment with a lower concentration of organic acid. Further, regulating the biomass components (selectively removing and retaining cellulose and lignin) through organic acid pretreatment to improve electrochemical performance (capacity, first-cycle Coulombic efficiency) is a general and effective method, which is suitable for optimizing the performance of hard carbon materials prepared from different biomasses. Although plant precursors have their own morphological distributions and are affected by their growth environments. Different precursors result in different proportions, distribution morphologies, and element ratios of cellulose, hemicellulose, and lignin in the biomass; after carbonization, the pore structures and distributions are different, and the layer spacings are different, ultimately leading to capacity differences. Although different biomasses exhibit different performances, selective removal of hemicellulose by organic acid pretreatment can improve the electrochemical performance of the biomass, but the improvement effects are different. The results of the present invention show that selective regulation of hemicellulose by pretreatment with an appropriate concentration of organic acid can be used as a universal strategy for optimizing the electrochemical performance of biomass hard carbon.

[0015] Further, the waste biomass is selected from one or more of Chinese fan palm, straw, and banana peel.

[0016] Preferably, the waste biomass is Chinese fan palm, and the first Coulombic efficiency of the sodium-ion battery assembled with the Chinese fan palm-based hard carbon anode material prepared in the present invention can be as high as 94.7%.

[0017] Further preferably, the Chinese fan palm is selected from one or more of Chinese fan palm stem, Chinese fan palm leaf, and Chinese fan palm root.

[0018] More preferably, the Chinese fan palm is Chinese fan palm stem.

[0019] Further, in step S1, the biomass is washed, dried, and then subjected to crushing and sieving; the drying temperature is 60-120°C, the drying time is 6-24 h, and preferably dried at 80°C for 12 h.

[0020] Further, the specification of the sieving is 40 to 100 mesh, preferably 60 mesh.

[0021] Further, the organic acid includes but is not limited to acetic acid, formic acid, glycolic acid or pyruvic acid.

[0022] Preferably, the organic acid is formic acid.

[0023] Further, the concentration of the organic acid solution in step S1 is 10 wt% to 30 wt%.

[0024] Preferably, the organic acid solution in step S1 is 10 wt%.

[0025] Further, the pretreatment temperature of the organic acid solution in step S1 is 30 to 100 °C, the treatment time is 0.5 to 5 h, and the solid-liquid ratio (g / mL) is 1:3 to 10.

[0026] Preferably, the pretreatment temperature of the organic acid solution in step S1 is 60 °C, the time is 1 h, and the solid-liquid ratio (g / mL) is 1:8.

[0027] Further, the pre-carbonization treatment in step S2 is calcination at 400 to 800 °C for 1 to 5 h.

[0028] Further, the heating rate of the pre-carbonization treatment is 1 to 10 °C / min.

[0029] Preferably, the inert atmosphere is argon or helium, preferably argon.

[0030] Preferably, the pre-carbonization treatment is calcination at 400 to 700 °C for 3 h.

[0031] Preferably, the heating rate of the pre-carbonization treatment is 3 to 5 °C / min.

[0032] Further, the alkali concentration in the alkali treatment in step S3 is 2 to 15 wt%, and the alkali treatment time is 1 to 5 h.

[0033] Preferably, the alkali solution used in the alkali treatment in step S3 is potassium hydroxide or sodium hydroxide.

[0034] More preferably, the alkali treatment in step S3 is soaking in a 10 wt% sodium hydroxide solution for 1 h.

[0035] Further, the acid concentration in the acid treatment in step S3 is 0.5 to 6 mol / L, and the acid treatment time is 1 to 5 h.

[0036] Preferably, the acid solution in the acid treatment in step S3 is any one of hydrochloric acid, nitric acid or sulfuric acid.

[0037] Further preferably, the acid treatment in step S3 is soaking in a 1 mol / L nitric acid solution for 0.5 h.

[0038] Preferably, in step S3, the preliminary biomass hard carbon material is subjected to alkali treatment. After acid treatment, it needs to be washed, dried, and then calcined for the second time, i.e., carbonized.

[0039] Preferably, the drying temperature is 60 - 120 °C and the drying time is 6 - 24 h; more preferably, it is dried at 80 °C for 12 h.

[0040] Further, the carbonization treatment in step S3 is calcination at 1000 - 1500 °C for 1 - 6 h.

[0041] Further, the heating rate of the carbonization treatment is 2 - 5 °C / min.

[0042] Preferably, the carbonization treatment is heating to 1400 °C at a rate of 3 °C / min and calcining for 2 h.

[0043] The present invention also provides a biomass hard carbon negative electrode material prepared by any of the above - described methods.

[0044] The present invention also provides the application of the biomass hard carbon negative electrode material in the preparation of sodium - ion batteries.

[0045] The present invention also provides a sodium - ion battery, including a negative electrode material, and the active material of the negative electrode material is the above - mentioned biomass hard carbon negative electrode material.

[0046] Further, in the sodium - ion battery, the negative electrode is prepared by uniformly grinding the above - mentioned biomass hard carbon negative electrode material and sodium carboxymethylcellulose as a binder in a mass ratio of 9:1, uniformly mixing with deionized water as a solvent, and coating on a copper foil, and then vacuum - drying at 80 °C for 12 h.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention uses waste biomass as a raw material and pretreats it with an organic acid of appropriate concentration. Under the condition of not destroying the natural structure of plants, the selective dissolution and regulation of hemicellulose in plants are realized while retaining cellulose and lignin components, which can improve the electrochemical performance of the biomass hard carbon negative electrode material, thereby realizing the optimized regulation of the sodium - storage performance of the biomass hard carbon negative electrode material, and enabling the biomass hard carbon negative electrode material to exhibit more excellent electrochemical performance in the assembled sodium - ion battery.

[0049] (2) The method for preparing the biomass hard carbon anode of the present invention is simple. By only pre-treating with organic acids in the early stage to regulate the composition of plant components of biomass, and then through two-step carbonization and acid-base treatment, a biomass hard carbon anode material with improved performance can be obtained, enabling the assembled sodium-ion battery to have excellent electrochemical performance and a higher first-cycle Coulombic efficiency. The selective regulation of hemicellulose by pre-treatment with organic acids at an appropriate concentration in the present invention can be used as a general strategy to optimize the electrochemical performance of biomass hard carbon, and the preparation process has low cost and simple process, which is conducive to large-scale application in the production of high-performance sodium-ion batteries.

[0050] (3) For the sodium-ion battery prepared based on the biomass hard carbon anode material of the present invention, at a current density of 50 mA / g, the first discharge capacity is 286 - 346 mAh / g, the first Coulombic efficiency is 92 - 95%, and the cycle capacity is stable. Among them, the sodium-ion battery prepared from the Livistona chinensis hard carbon anode material has the highest first discharge capacity of 345.2 mAh / g, the first Coulombic efficiency reaches 94.7%, and the cycle capacity is stable, indicating that the biomass hard carbon anode material of the present invention has good prospects in the industrial application of sodium-ion batteries. Description of the Drawings

[0051] Figure 1 The first charge-discharge capacity curve diagram of the biomass hard carbon anode material for sodium-ion battery prepared in Example 1.

[0052] Figure 2 The charge-discharge capacity and Coulombic efficiency curve diagram of the biomass hard carbon anode material for sodium-ion battery prepared in Example 1.

[0053] Figure 3 The XRD diagram of the biomass hard carbon anode materials prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0054] Figure 4 The comparison diagram of charge-discharge curves of the biomass hard carbon anode materials treated with inorganic acids in Example 1 and Comparative Examples 4 and 5. Detailed Embodiments

[0055] The following further illustrates the present invention in conjunction with the drawings of the specification and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

[0056] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0057] Example 1

[0058] A preparation method of a Livistona chinensis hard carbon anode material, comprising the following steps:

[0059] (1) Clean 5 g of Livistona chinensis stems with pure water, dry them under vacuum, then crush the Livistona chinensis stems and pass them through a 60-mesh sieve. Subsequently, treat them with 40 mL of an organic acid solution with a concentration of 10 wt%, at a treatment temperature of 60 °C for 1 h; wash and dry with deionized water to obtain a precursor of the biomass hard carbon material; the organic acid is formic acid;

[0060] (2) Place the precursor material obtained in step (1) in a tubular furnace for pre-carbonization, and calcine it at a rate of 3 °C / min from room temperature to 600 °C for 3 h in an argon atmosphere to obtain a preliminary biomass hard carbon material;

[0061] (3) Place the preliminary biomass hard carbon material obtained in step (2) in a NaOH solution with a concentration of 10 wt% and stir for 1 h for alkali treatment;

[0062] (4) Add 6 mol / L nitric acid solution to the solution obtained in step (3), wash it with deionized water until neutral, filter and dry, then transfer it to a vacuum oven for further drying at 80 °C for 12 h;

[0063] (5) Place the dried biomass hard carbon material obtained in step (4) in a tubular furnace, and calcine it at a rate of 3 °C / min from room temperature to 1400 °C for 2 h in an argon atmosphere to obtain a biomass hard carbon negative electrode material for sodium-ion batteries.

[0064] Example 2

[0065] The difference between this example and Example 1 is that the concentration of the organic acid solution in step (1) is 30 wt%.

[0066] Example 3

[0067] The difference between this example and Example 1 is that the concentration of the organic acid solution in step (1) is 50 wt%.

[0068] Example 4

[0069] The difference between this example and Example 1 is that the biomass raw material is waste banana peel.

[0070] Example 5

[0071] The difference between this example and Example 1 is that the biomass raw material is waste straw.

[0072] Example 6

[0073] The difference between this example and Example 1 is that the concentration of the organic acid solution in step (1) is 30 wt%, the material-liquid ratio is 1:9, the pre-carbonization temperature is 700 °C, and the concentration of the acid solution after pre-carbonization is 6 mol / L hydrochloric acid.

[0074] Example 7

[0075] The difference between this example and Example 1 is that: the concentration of the organic acid solution in step (1) is 80 wt%, the ratio of material to liquid is 1:7, and the concentration of the alkali solution after pre-carbonization is 12 wt% NaOH.

[0076] Example 8

[0077] The difference between this example and Example 1 is that: the organic acid in step (1) is pyruvic acid, the concentration is 10 wt%, the ratio of material to liquid is 1:8, and the concentration of the alkali solution after pre-carbonization is 12 wt% NaOH.

[0078] Example 9

[0079] The difference between this example and Example 1 is that: the organic acid in step (1) is pyruvic acid, the concentration is 30 wt%, the ratio of material to liquid is 1:10, and the pre-carbonization temperature is 500 °C.

[0080] Comparative Example 1

[0081] The difference between this comparative example and Example 1 is that: after the biomass raw material, Chinese fan palm leaves, are crushed and screened, without any treatment, they are directly put into a carbonization furnace and carbonized at a high temperature of 1300 °C for 2 h in a nitrogen atmosphere to obtain a hard carbon material.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 1 is that: in step (1), the biomass raw material, Chinese fan palm stems, is not treated with an organic acid.

[0084] Comparative Example 3

[0085] The difference between this comparative example and Example 1 is that: the concentration of the organic acid solution in step (1) is 80 wt%.

[0086] Comparative Example 4

[0087] The difference between this comparative example and Example 1 is that: in step (1), the biomass raw material, Chinese fan palm stems, is treated with an inorganic acid, and the inorganic acid is hydrochloric acid with a concentration of 30 wt%.

[0088] Comparative Example 5

[0089] The difference between this comparative example and Example 1 is that: in step (1), the biomass raw material, Chinese fan palm stems, is treated with an inorganic acid, and the inorganic acid is sulfuric acid with a concentration of 20 wt%.

[0090] Comparative Example 6

[0091] The difference between this comparative example and Example 4 is that: in step (1), the biomass raw material, banana peel, is not treated with an organic acid.

[0092] Comparative Example 7

[0093] The difference between this comparative example and Example 5 lies in that: in step (1), the biomass raw material straw is not treated with organic acid.

[0094] Test Example

[0095] The plant components of the biomass pretreated with organic acid in Examples 1-5 and pretreated in different ways in Comparative Examples 1-7 were determined. The contents of cellulose, hemicellulose, and lignin in the plant components were determined by the NREL method, and the measurement results are shown in Table 1. In addition, the assembled sodium-ion batteries in Examples 1-5 and Comparative Examples 1-7 were tested for their electrochemical performance. The sodium-ion battery was prepared by uniformly mixing the hard carbon negative electrode material and a binder (sodium carboxymethylcellulose) in a mass ratio of 9:1 using a small ball mill, and then adding an appropriate amount of deionized water and uniformly mixing to obtain an electrode slurry; the electrode slurry was coated on a current collector and vacuum-dried and then stamped to obtain a battery negative electrode sheet. The prepared battery negative electrode sheet was assembled with metallic sodium, a glass fiber separator, an electrolyte, a battery case, a gasket, a spring piece, etc. to form a sodium-ion battery. The test conditions were a current density of 50 mA / g and a voltage range of 0-3 V, and the test results are shown in Table 2.

[0096] Table 1 Masses of the three major components of the biomass after pretreatment in Examples 1-5 and Comparative Examples 1-7

[0097]

[0098]

[0099] Table 2 Electrochemical performance of the assembled sodium-ion batteries in Examples 1-5 and Comparative Examples 1-7

[0100]

[0101] As can be seen from Table 1, compared with the untreated organic acid (Comparative Examples 1-2, 6-7), after pretreatment with organic acid, the mass of hemicellulose in the biomass decreased significantly, while the masses of cellulose and lignin remained unchanged or decreased slightly. After pretreatment with high-concentration organic acid (Comparative Example 3) and inorganic acid (Comparative Examples 4 and 5), the masses of hemicellulose and lignin in the biomass decreased significantly. Therefore, the results show that pretreatment with an appropriate concentration of organic acid can selectively remove hemicellulose in different waste biomasses and retain cellulose and lignin, while inorganic acid and treatment with too high a concentration of organic acid cannot.

[0102] As can be seen from Table 2, the sodium-ion batteries assembled with the hard carbon anodes prepared in Examples 1-5 have excellent battery performance. Their initial discharge capacity is 286-346 mAh / g, the first Coulombic efficiency is 92-95%, and the cycling plateau capacity (2nd) (<0.1V) is 180-228 mAh / g. Comparing the hard carbon anodes prepared from the same waste biomass (Examples 1-3 vs. Comparative Examples 1-3, Examples 4-5 vs. Comparative Examples 6-7), the battery performance of the sodium-ion batteries assembled with the hard carbon anodes prepared by organic acid pretreatment is significantly higher than that of the sodium-ion batteries assembled with the hard carbon anodes without organic acid pretreatment. However, the improvement effect of the battery performance of the sodium-ion batteries assembled with the hard carbon anodes prepared by high-concentration organic acid pretreatment is not as good as that of low-concentration organic acid pretreatment. Inorganic acid pretreatment (Comparative Examples 4-5) cannot achieve selective removal of hemicellulose and is prone to destroying the natural structure of plants, resulting in hard carbon anodes with low capacity and Coulombic efficiency. Therefore, the above results show that regulating the biomass components by appropriate concentration of organic acid pretreatment (selectively removing and retaining cellulose and lignin) to improve the electrochemical performance (capacity, first-cycle Coulombic efficiency) is a general and effective method, which is suitable for optimizing the performance of hard carbon materials prepared from different biomasses.

[0103] The first charge-discharge capacity curves of the biomass hard carbon anode material for the sodium-ion battery prepared in Example 1 are as Figure 1 shown, indicating that the biomass hard carbon anode material for the sodium-ion battery has excellent cycling reversibility and a high plateau capacity. The high plateau capacity indicates that the material has a rich closed-pore structure for sodium storage (since the closed pores in hard carbon are the main sodium storage sites and the corresponding plateau capacity <0.1V; when the capacity at a voltage <0.1V is high, it can reflect that there are more closed pores in the hard carbon). Figure 2 It is the charge-discharge capacity and Coulombic efficiency curve diagram of the biomass hard carbon anode material for the sodium-ion battery prepared in Example 1, indicating its good cycling stability and high reversibility.

[0104] Figure 3 It is the XRD of the biomass hard carbon anode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. The shift of the characteristic peaks in the figure shows that the hard carbon obtained by organic acid treatment has a larger interlayer spacing. Combining the results in Table 1, it can be seen that the increase in the interlayer spacing of the biomass hard carbon anode material is beneficial to the insertion and extraction of sodium, improving the capacity of the sodium-ion battery prepared therefrom.

[0105] Figure 4Comparing the charge-discharge curves of the samples of Example 1 and Comparative Examples 4 and 5 after being treated with inorganic acids, it can be seen that the charge-discharge capacity of the hard carbon anode material treated with organic acids is higher than that of inorganic acids. Combining the results in Table 1, it shows that organic acids selectively remove the amount of hemicellulose in plants while the mass of cellulose and lignin remains unchanged or slightly decreases, constructing a microporous structure after sintering while retaining the original three-dimensional structure of the cellulose and lignin components, providing more sodium storage sites and higher capacity.

[0106] In summary, the selective removal of hemicellulose in plants can be achieved by treating with organic acids of appropriate concentration in the present invention, while retaining cellulose and lignin, which is beneficial to increasing the layer spacing and forming more micropores during the high-temperature carbonization process, promoting the improvement of electrochemical performance; compared with inorganic acid pretreatment, high-concentration organic acid pretreatment or without organic acid pretreatment, the performance of sodium-ion batteries assembled with biomass hard carbon anode materials prepared by organic acid pretreatment is improved, especially the initial discharge capacity and the first Coulombic efficiency are both significantly improved, and the specific capacity is high and the cycle stability is good. The selective regulation of hemicellulose by organic acids of appropriate concentration in the present invention can be used as a general strategy to optimize the electrochemical performance of biomass hard carbon.

[0107] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. Any modifications, equivalent replacements, and improvements made within the ideas and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a biomass hard carbon negative electrode material, characterized in that: The following steps are involved: S1. The waste biomass is crushed and sieved, pretreated with 10-50wt% organic acid solution to selectively remove hemicellulose and retain cellulose and lignin, washed and dried to obtain a biomass hard carbon precursor; S2. The biomass hard carbon precursor obtained in step S1 is pre-carbonized under an inert atmosphere to obtain a preliminary biomass hard carbon material; S3. The preliminary biomass hard carbon material obtained in step S2 is sequentially subjected to alkali treatment and acid treatment, washed to neutrality, dried, and carbonized under an inert atmosphere to obtain a sodium ion battery hard carbon negative electrode material; The organic acid in step S1 is acetic acid, formic acid, glycolic acid or pyruvic acid; The pretreatment temperature of the organic acid solution in step S1 is 30-100° C., the treatment time is 0.5-5 h, and the material-liquid ratio of the waste biomass to the organic acid solution is 1 g:3-10 mL.

2. The preparation method according to claim 1, characterized in that: The waste biomass in step S1 is selected from one or more of fan palm, straw, and banana peel.

3. The preparation method according to claim 1, characterized in that: The pre-carbonization treatment in step S2 is calcination at 400-800° C. for 1-5 hours.

4. The preparation method according to claim 1, characterized in that: In step S3, the alkali concentration in the alkali treatment is 2-15wt%, and the alkali treatment time is 1-5h; the acid concentration in the acid treatment is 0.5-6mol / L, and the acid treatment time is 1-5h.

5. The preparation method according to claim 1, characterized in that: The carbonization treatment in step S3 is calcination at 1000-1500° C. for 1-6 hours.

6. The biomass hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the biomass hard carbon negative electrode material according to claim 6 in the preparation of sodium ion batteries.

8. A sodium ion battery comprising a negative electrode material, characterized in that: The active material of the negative electrode material is the biomass hard carbon negative electrode material according to claim 6.

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