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

Abstract

The application belongs to the technical field of battery materials, and more particularly relates to a biomass hard carbon negative electrode material and a preparation method and application thereof. The preparation method of the biomass hard carbon negative electrode material provided in the application mixes biomass powder and a coating agent at a first rotating speed for a first time, so that the biomass powder and the coating agent are uniformly mixed, and frictional heat generation is reduced, thereby avoiding uneven mixing caused by melting of the coating agent. Then, the biomass powder and the coating agent are mixed at a second rotating speed for a second time, so that the coating agent on the surface of the biomass powder is melted to achieve a coating fusion effect, and adhesion between particles is avoided. Finally, heat treatment is performed to obtain the biomass hard carbon negative electrode material. The application improves the micro-morphology of the biomass hard carbon negative electrode material, improves the electrochemical performance thereof, improves the processing performance of the battery cell end, and has the characteristics of low cost, wide raw material sources, simple preparation steps, low equipment requirements, and large-scale preparation.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and more specifically, relates to a biomass hard carbon anode material, its preparation method and application. Background Technology

[0002] With the widespread application of lithium-ion batteries in electric vehicles, mobile phones, computers, and other electronic products, the demand for lithium is increasing year by year. However, global lithium reserves are extremely limited, unevenly distributed, and costly, severely restricting the development of low-cost, high-performance energy storage devices. Sodium and lithium are in the same group, and sodium possesses similar electrochemical properties to lithium. Moreover, sodium is abundant and inexpensive. Therefore, sodium-ion batteries are the next generation of rechargeable batteries for commercial application after lithium-ion batteries.

[0003] Currently, the preparation of hard carbon anode materials for sodium-ion batteries mainly uses biomass such as coconut shells, walnut shells, straw, and bamboo as precursors. Usually, biomass is used as the carbon source, and hard carbon materials are obtained through steps such as crushing, acid washing, water washing, and sintering. However, the particle size of biomass materials is currently too large, and the microstructure is mostly irregular. This reduces the capacity, cycle stability, and initial coulombic efficiency of hard carbon materials, and also reduces the processing performance of subsequent cell-end processes such as pulping and coating. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to provide a biomass hard carbon anode material, its preparation method and application, aiming to solve the technical problems of low charge-discharge specific capacity, low initial coulombic efficiency and high processing difficulty when applying it to sodium-ion batteries.

[0005] To achieve the above objectives, this application provides a method for preparing a biomass hard carbon anode material, comprising the following steps:

[0006] Biomass powder and a coating agent are mixed at a first rotation speed for a first time, and then mixed at a second rotation speed for a second time to perform solid-phase coating fusion, thereby obtaining a precursor material; wherein the first rotation speed is less than the second rotation speed, and the first time is greater than the second time.

[0007] The above-mentioned precursor material was subjected to heat treatment to obtain the above-mentioned biomass hard carbon anode material.

[0008] Preferably, the first rotational speed is less than or equal to 550 rpm; and / or,

[0009] The second speed mentioned above is greater than or equal to 900 rpm; and / or,

[0010] The first time mentioned above is greater than or equal to 1 hour; and / or,

[0011] The second time mentioned above is less than or equal to 30 minutes.

[0012] More preferably, the first rotational speed is 400 rpm to 500 rpm; and / or,

[0013] The second speed mentioned above is 900 rpm to 950 rpm; and / or,

[0014] The aforementioned first time period is 1 hour to 1.5 hours; and / or,

[0015] The second time mentioned above is 10 min to 30 min.

[0016] Preferably, the ash content of the above-mentioned biomass powder is less than or equal to 3%.

[0017] Preferably, the median particle size of the above-mentioned biomass powder is 4 μm to 7 μm.

[0018] More preferably, the maximum particle size of the above-mentioned biomass powder is less than 20 μm.

[0019] Preferably, the biomass is selected from at least one of coconut shell, walnut shell, straw, bamboo, starch, white sugar, fruit shell, and lignin.

[0020] Preferably, the coating agent is asphalt, and the asphalt is selected from at least one of high softening point asphalt, medium softening point asphalt and low softening point asphalt.

[0021] Preferably, the mass ratio of the above-mentioned biomass powder to the above-mentioned coating agent is 100:(2-4).

[0022] Preferably, the heat treatment is carried out under a protective atmosphere, wherein the protective atmosphere includes at least one of nitrogen, argon, neon, helium, xenon or krypton.

[0023] Preferably, the heating rate of the above heat treatment is 1℃ / min to 5℃ / min, the heat treatment temperature is 1200℃ to 1500℃, and the heat treatment time is 1.5h to 3h.

[0024] More preferably, before mixing the biomass powder and the coating agent at the first rotation speed for the first time, the method further includes vibrating sieving of the biomass powder and / or vibrating sieving of the biomass powder to remove magnetism.

[0025] This application provides a biomass hard carbon anode material prepared using the above-described preparation method.

[0026] This application provides a sodium-ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode contains the aforementioned biomass hard carbon negative electrode material.

[0027] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages:

[0028] (1) The preparation method of the biomass hard carbon anode material provided in this application involves mixing biomass powder and a coating agent at a first rotation speed for a first time to ensure uniform mixing and reduce frictional heat generation, thus preventing uneven mixing caused by coating agent melting. Then, the mixture is mixed at a second rotation speed for a second time to achieve solid-phase coating fusion and obtain a precursor material. Rapid frictional heat generation allows the coating agent on the surface of the biomass powder to melt, achieving a coating fusion effect and preventing particle adhesion. Finally, heat treatment is performed to obtain the biomass hard carbon anode material. This application improves the microstructure of the biomass hard carbon anode material while enhancing its electrochemical performance and improving its cell-end processing performance.

[0029] (2) In the preferred embodiment, this application controls the particle size of biomass powder, the mass ratio of biomass powder to coating agent, the magnitude of the first rotation speed and the second rotation speed, and the length of the first time and the second time, etc., to reduce the amount of coating agent while effectively improving the coating integrity. The resulting biomass hard carbon anode material has a regular appearance, high sphericity, and good processing performance. When applied to sodium-ion batteries, it has the advantages of large charge-discharge specific capacity and high first-cycle charge-discharge efficiency.

[0030] (3) In the preferred embodiment, when the biomass hard carbon anode material prepared from untreated biomass raw materials is applied to a sodium-ion battery, the charge-discharge specific capacity can reach 300.31 mAh / g, and the first-cycle charge-discharge efficiency can reach 85.54%. That is, the electrochemical performance of the biomass hard carbon anode material can be significantly improved without acid washing of the biomass raw materials. The preparation method provided by this application has the characteristics of wide availability of raw materials, low cost, simple operation steps, low energy consumption in the preparation process, low equipment requirements, environmental friendliness, and large-scale preparation capability. Attached Figure Description

[0031] Figure 1 This is an electron microscope image of the biomass powder prepared in Example 1 of this application;

[0032] Figure 2 It is the charge / discharge specific capacity of the battery assembled in Embodiment 1 of this application. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0034] Currently, acid-washed biomass materials are commonly used to prepare biomass hard carbon anode materials suitable for sodium-ion batteries. However, acid washing is costly and causes significant pollution, hindering large-scale mass production. Therefore, this application provides a method for preparing biomass hard carbon anode materials, comprising the following steps:

[0035] Biomass powder and a coating agent are mixed at a first rotation speed for a first time, and then mixed at a second rotation speed for a second time to perform solid-phase coating fusion, thereby obtaining a precursor material; wherein the first rotation speed is less than the second rotation speed, and the first time is greater than the second time.

[0036] The above-mentioned precursor material was subjected to heat treatment to obtain the above-mentioned biomass hard carbon anode material.

[0037] In some embodiments, the first rotational speed is less than or equal to 550 rpm; and / or,

[0038] The second speed mentioned above is greater than or equal to 900 rpm; and / or,

[0039] The first time mentioned above is greater than or equal to 1 hour; and / or,

[0040] The second time mentioned above is less than or equal to 30 minutes.

[0041] In a preferred embodiment, the first rotation speed is 400 rpm to 500 rpm; and / or the first time is 1 h to 1.5 h, which can ensure that the biomass powder and the coating agent are fully mixed, and can reduce frictional heat generation and avoid uneven mixing caused by the melting of the coating agent.

[0042] In a preferred embodiment, the second rotation speed is 900 rpm to 950 rpm; and / or the second time is 10 min to 30 min. By rapidly generating heat through friction, the coating agent mixed on the surface of the biomass powder melts, achieving the effect of coating and fusion. This also avoids adhesion between particles, prevents sintering and agglomeration during subsequent heat treatment, reduces negative impacts on the heat treatment effect, and ensures that the hard carbon anode material obtained has a complete morphology and high uniformity.

[0043] In some embodiments, the ash content of the above-mentioned biomass powder is less than or equal to 3%.

[0044] In some embodiments, the median particle size of the above-mentioned biomass powder is 4 μm to 7 μm.

[0045] In a preferred embodiment, the maximum particle size of the biomass powder is less than 20 μm.

[0046] This application does not limit the source of the biomass powder. For example, the biomass powder can be a commercially available product or can be obtained by crushing biomass raw materials. In some embodiments, the biomass can be selected from at least one of coconut shells, walnut shells, straw, bamboo, starch, sugar, fruit shells, and lignin. Those skilled in the art can choose conventional crushing methods to crush the biomass raw materials. Crushing methods include, but are not limited to, one or more of mechanical methods such as bead milling, impact, shearing, and airflow impact.

[0047] In some embodiments, the above-mentioned biomass raw materials may also be subjected to acid washing to reduce their ash content, for example, the ash content may be reduced by less than or equal to 3%, such as reaching 0.3% to 0.5% or less than 0.3%. The acid washing treatment can adopt conventional acid washing operations in the art, and this application does not limit the type and concentration of acid solution, acid washing time and temperature, etc. in the acid washing treatment.

[0048] In some embodiments, the median particle size of the biomass powder is 4μm to 7μm, which allows the coating agent to fully and completely coat the biomass powder without increasing the specific surface area of ​​the subsequently prepared biomass hard carbon anode material and without affecting its first charge-discharge efficiency when applied to sodium-ion batteries.

[0049] In some embodiments, the coating agent used in this application is asphalt. This application does not have special requirements for the asphalt used; any asphalt known in the art can be used, including but not limited to high softening point asphalt, medium softening point asphalt, and low softening point asphalt. In some specific embodiments of this application, the asphalt used was purchased from Xinjiang Zhongtan New Material Technology Co., Ltd., and the product model is petroleum-based coated asphalt ZT280.

[0050] In some embodiments, the mass ratio of the biomass powder to the coating agent is 100:(2-4), which makes the biomass powder and the coating agent mixed evenly, improves the integrity of the coating, and prevents agglomeration after heat treatment, thereby improving the electrochemical performance of the hard carbon anode material subsequently prepared.

[0051] In some embodiments, the heat treatment is performed under a protective atmosphere, wherein the protective atmosphere includes at least one of nitrogen, argon, neon, helium, xenon, or krypton.

[0052] In some embodiments, the heating rate of the above heat treatment is 1℃ / min to 5℃ / min, the temperature is 1200℃ to 1500℃, and the time is 1.5h to 3h. If the heat treatment temperature is too low or the heat treatment time is too short, it will reduce the number of closed pores in the hard carbon anode material and increase the specific surface area, resulting in a decrease in capacity. If the heat treatment temperature is too high or the heat treatment time is too long, over-sintering will occur, resulting in serious graphitization problems in the hard carbon anode material and affecting the capacity of the hard carbon anode material.

[0053] This application does not limit the equipment or heating method of the above-mentioned "heat treatment". The above-mentioned heat treatment usually adopts one or more of the following: box furnace, pusher furnace, roller furnace, tunnel furnace, rotary furnace, etc. The heat treatment heating method is generally one or more of the following: resistance wire heating, silicon carbide rod and silicon molybdenum rod heating.

[0054] In some embodiments, before mixing the biomass powder and the coating agent at the first rotation speed for the first time, the biomass powder is further subjected to a vibratory sieving process. This process can improve the flowability of the biomass powder, reduce agglomeration, and improve the subsequent processability of the biomass powder. It should be understood that this application does not limit the frequency and time of the vibratory sieving. Those skilled in the art can select appropriate vibratory sieving frequencies and times based on actual experimental conditions (such as vibratory sieving instruments), all of which are within the scope of protection of this application.

[0055] In other embodiments, before mixing the biomass powder with the coating agent at a first rotation speed for a first time, the biomass powder is further subjected to a vibratory sieving and demagnetization treatment.

[0056] In a preferred embodiment, the above demagnetization process is performed several times, preferably 1 to 5 times. In a specific embodiment of this application, the magnetic field strength of the above demagnetization process is 8000 Gs to 10000 Gs. Excessive magnetic material can lead to self-discharge of the battery. During the charging and discharging process, it will gradually nucleate and grow with temperature changes, precipitate during cycling, generate metal dendrites, and pierce the separator. As excellent conductors of electrons, magnetic materials can cause short circuits in the battery and affect its thermal stability. The above demagnetization process of this application can remove magnetic materials such as iron, cobalt, nickel, zinc, copper, and manganese from biomass powder, thereby reducing the content of magnetic materials in biomass powder and ultimately reducing the content of magnetic materials in biomass hard carbon anode materials.

[0057] This application provides a biomass hard carbon anode material prepared using the above-described preparation method.

[0058] This application also provides a sodium-ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode contains the aforementioned biomass hard carbon negative electrode material.

[0059] The above technical solutions are described in detail below with reference to specific embodiments. It should be understood that these are merely exemplary and not intended to limit this application. Materials of the same or similar type, model, quality, properties, or functions as the reagents and instruments described below can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments and comparative examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments and comparative examples are commercially available.

[0060] The following are examples and comparative examples:

[0061] Example 1

[0062] S1. Coconut shells with an ash content of 2.24% were crushed, and then the particle size of the coconut shell powder was determined using a Malvern Mastersizer 2000E laser particle size analyzer according to GB / T 19077-2016, Particle Size Distribution Laser Diffraction Method. The measured particle size of the coconut shell powder was D50 = 5.56 μm and Dmax = 15.14 μm (see...). Figure 1 ).

[0063] S2. The coconut shell powder processed in S1 is demagnetized by vibrating sieve with a vibration frequency of 30Hz, a sieve mesh size of 325 mesh, and an 8000Gs demagnetizing rod connected to the discharge port.

[0064] S3. The demagnetized coconut shell powder and asphalt (petroleum-based coated asphalt ZT280) from S2 are added to a fusion machine at a mass ratio of 100:2 to obtain the precursor material through solid-phase coating fusion. First, the coconut shell powder and asphalt are mixed at a low speed (first stage) of 400 rpm for 1 hour to ensure uniform mixing. The temperature inside the fusion machine at this time is 30℃. Then, a high-speed treatment is performed at 950 rpm for 15 minutes (second stage). Rapid friction heat is used to melt the asphalt coating on the surface of the coconut shell powder, achieving the coating fusion effect. The temperature inside the fusion machine at this time is 53℃.

[0065] S4. The above precursor material is calcined at high temperature in a nitrogen atmosphere. The sintering temperature is 1300℃, the heating rate is 1℃ / min, and the sintering time is 2h to obtain the biomass hard carbon anode material.

[0066] Example 2

[0067] The biomass raw material in step S1 is acid-washed coconut shells with an ash content of 0.25%, and the other operations are the same as in Example 1.

[0068] Example 3

[0069] The biomass raw material in step S1 is biomass straw, and the other operations are the same as in Example 1.

[0070] Example 4

[0071] In step S1, the particle size of the coconut shell powder is D50 = 4.1 μm and Dmax = 14 μm, and other operations are the same as in Example 1.

[0072] Example 5

[0073] In step S1, the particle size of the coconut shell powder is D50 = 7.0 μm and Dmax = 16 μm, and other operations are the same as in Example 1.

[0074] Example 6

[0075] In step S3, the mass ratio of coconut shell powder to asphalt is 100:4, and other operations are the same as in Example 1.

[0076] Example 7

[0077] In step S3, the first stage of low-speed mixing is performed at a speed of 500 rpm for 1 hour, and the second stage of high-speed mixing is performed at a speed of 900 rpm for 30 minutes. Other operations are the same as in Example 1.

[0078] Example 8

[0079] In step S3, the first stage of low-speed mixing is performed at a speed of 400 rpm for 1.5 h. In step S4, the heat treatment temperature is 1200℃. Other operations are the same as in Example 1.

[0080] Example 9

[0081] In step S4, the heat treatment temperature is 1500℃ and the sintering time is 1.5h. Other operations are the same as in Example 1.

[0082] Example 10

[0083] In step S4, the heating rate of the heat treatment process is 5°C / min, the sintering time is 3h, and other operations are the same as in Example 1.

[0084] Comparative Example 1

[0085] In step S1, the particle size of the coconut shell powder is D50 = 8 μm and Dmax = 28.9 μm. Other operations are the same as in Example 1.

[0086] Comparative Example 2

[0087] In step S3, coconut shell powder and asphalt are added to a fusion machine for one-step solid-phase coating fusion. The rotation speed is 400 rpm and the processing time is 75 min. Other operations are the same as in Example 1.

[0088] Comparative Example 3

[0089] In step S3, coconut shell powder and asphalt are added to a fusion machine for one-step solid-phase coating fusion. The rotation speed is 750 rpm and the processing time is 75 min. Other operations are the same as in Example 1.

[0090] Comparative Example 4

[0091] In step S3, coconut shell powder and asphalt are added to a fusion machine for one-step solid-phase coating fusion. The rotation speed is 950 rpm and the processing time is 75 min. Other operations are the same as in Example 1.

[0092] Comparative Example 5

[0093] In step S4, the heat treatment temperature is 1100℃, and the other operations are the same as in Example 1.

[0094] Comparative Example 6

[0095] The heat treatment time in step S4 is 1 hour, and the other operations are the same as in Example 1.

[0096] Comparative Example 7

[0097] In step S1, the biomass raw material is acid-washed coconut shell with an ash content of 0.25%. In step S3, coconut shell powder and asphalt are added to a fusion machine for one-step solid-phase coating fusion. The rotation speed is 400 rpm and the processing time is 75 min. Other operations are the same as in Example 1.

[0098] Comparative Example 8

[0099] In step S3, the mass ratio of coconut shell powder to asphalt is 100:5, and other operations are the same as in Example 1. During the experiment, it was found that the precursor material obtained in step S3 agglomerated after heat treatment, affecting subsequent processing. In practical applications, an additional crushing process is required, which will increase processing difficulty and manufacturing costs.

[0100] The biomass hard carbon anode materials prepared in Examples 1-10 and Comparative Examples 1-7 were mixed with conductive carbon black and a binder to form a slurry. This slurry was uniformly coated onto aluminum foil and dried to form an electrode. A sodium sheet was used as the counter electrode, and a glass fiber membrane was selected as the separator. A mixed solution of 1 mol / L NaPF6 and ethylene carbonate (EC): dimethyl carbonate (DEC) = 1:1 vol.% was used as the electrolyte to form a coin cell. The test conditions were as follows: the first discharge test was performed by discharging to 0.01V at 20 mA / g, followed by recharging to 2.5V, and the test was conducted under a constant temperature of 25℃. The test results are shown in Table 1.

[0101] Table 1. Performance of the batteries assembled in Examples 1-10 and Comparative Examples 1-7

[0102] Group Charge / discharge specific capacity (mAh / g) First-cycle charge / discharge efficiency (%) Example 1 300.31 85.54 Example 2 327.10 86.53 Example 3 297.47 83.55 Example 4 298.01 85.01 Example 5 296.25 85.19 Example 6 297.32 85.62 Example 7 299.11 86.97 Example 8 294.00 85.56 Example 9 299.86 85.07 Example 10 299.91 86.44 Comparative Example 1 280.67 81.62 Comparative Example 2 279.12 83.12 Comparative Example 3 275.42 81.84 Comparative Example 4 271.45 81.91 Comparative Example 5 266.64 82.58 Comparative Example 6 284.68 82.04 Comparative Example 7 303.98 82.11

[0103] As can be seen from Table 1, the charge-discharge specific capacity and first-cycle charge-discharge efficiency of the batteries assembled using the biomass hard carbon anode materials prepared in Examples 1-10 are higher than those of Comparative Examples 1-6, indicating that the biomass hard carbon materials prepared by the preparation method provided in this application can improve the capacity of the material and improve the processing performance of the cell end.

[0104] Specifically, comparing Example 1 and Comparative Example 1, it was found that the charge / discharge specific capacity of the battery assembled in Comparative Example 1 was 280.67 mAh / g, and the first-cycle charge / discharge efficiency was 81.62%, both significantly lower than those in Example 1 (charge / discharge specific capacity is shown in Example 1). Figure 2 The reason for this may be that the biomass powder prepared in Comparative Example 1 had an excessively large particle size (coconut shell powder particle size D50 = 7.7 μm, Dmax = 28.9 μm), which made it difficult for the asphalt to fully coat the biomass powder, thus affecting the capacity of the hard carbon material applied to the battery.

[0105] As can be seen from Examples 1 and Comparative Examples 2-4, the battery assembly of the biomass hard carbon anode material prepared by one-step coating and fusion using low rotation speed (400 rpm) in Comparative Example 2, medium rotation speed (750 rpm) in Comparative Example 3, and high rotation speed (950 rpm) in Comparative Example 4 all exhibited lower charge-discharge specific capacity and first-cycle charge-discharge efficiency than that of Example 1. Compared to Comparative Examples 2-4, this application adjusts the one-step coating and fusion to a two-stage coating and fusion. The first stage involves low-speed, long-duration mixing to ensure thorough mixing of the coconut shell powder and asphalt. Furthermore, the low rotation speed reduces frictional heat generation, keeping the asphalt in a solid state and preventing uneven mixing due to asphalt melting. The second stage involves high-speed, short-duration mixing, where rapid frictional heat generation melts the asphalt mixed on the surface of the coconut shell powder, achieving the coating and fusion effect. This also prevents particle adhesion and agglomeration during subsequent sintering, thus avoiding negative impacts on the sintering results. The preparation method provided in this application ensures the uniformity of the biomass hard carbon material and improves its capacity.

[0106] As can be seen from Example 1 and Comparative Examples 5 and 6, the charge-discharge specific capacity and first-cycle charge-discharge efficiency of the batteries assembled with the biomass hard carbon anode materials prepared in Comparative Examples 5 and 6 are lower than those in Example 1. The reason may be that the heat treatment temperature is too low or the heat treatment time is too short, which will reduce the number of closed pores in the hard carbon anode material and increase the specific surface area, thereby reducing the charge-discharge specific capacity of the sodium-ion battery assembled with the hard carbon anode material.

[0107] As can be seen from Example 1 and Comparative Example 7, when the biomass hard carbon anode material prepared from untreated biomass raw materials is applied to sodium-ion batteries, the charge-discharge specific capacity can reach 300.31 mAh / g, and the first-cycle charge-discharge efficiency can reach 85.54%, which is basically the same as that of Comparative Example 7. This means that this application can significantly improve the electrochemical performance of the biomass hard carbon anode material without acid washing of the biomass raw materials, and it has the characteristics of low cost and environmental friendliness. Combined with Example 2 and Comparative Example 7, it can be seen that the method provided in this application can further improve the electrochemical performance of the prepared biomass hard carbon anode material.

[0108] In summary, the preparation method provided in this application, by controlling the particle size of the biomass powder, the mass ratio of biomass powder to the coating agent, the magnitudes of the first and second rotational speeds, and the durations of the first and second time intervals, can produce biomass hard carbon anode materials with regular morphology and high uniformity. When applied to sodium-ion batteries, these materials exhibit advantages such as high charge-discharge specific capacity and high first-cycle charge-discharge efficiency. Furthermore, this application is characterized by a wide availability of raw materials, low energy consumption, low equipment requirements, and the ability to be prepared on a large scale.

[0109] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A preparation method of a biomass hard carbon negative electrode material applied to a sodium ion battery, characterized in that, The method comprises the following steps: mixing the biomass powder with a coating agent at a first rotating speed for a first time, and then mixing at a second rotating speed for a second time to perform solid phase coating fusion, to obtain a precursor material; wherein the biomass powder has a median particle size of 4-7 μm; the mass ratio of the biomass powder to the coating agent is 100:(2-4); the first rotating speed is 400-500 rpm; the second rotating speed is 900-950 rpm; the first time is 1-1.5 h; the second time is 10-30 min; the biomass is selected from at least one of coconut shell, walnut shell, straw, bamboo, starch, white sugar, fruit shell, and lignin; the coating agent is pitch; and no external heating is used in the process of solid phase coating fusion; heat treating the precursor material to obtain the biomass hard carbon negative electrode material; the heat treatment is performed at a temperature of 1200-1500 °C for 1.5-3 h.

2. The production method according to claim 1, characterized by, The ash content of the biomass powder is less than or equal to 3%.

3. The preparation method according to claim 1, characterized in that, The heat treatment is performed in a protective atmosphere, and the gas of the protective atmosphere comprises at least one of nitrogen, argon, neon, helium, xenon, or krypton; The heat treatment has a heating rate of 1-5 °C / min.

4. The production method according to any one of claims 1 to 3, characterized by, Before the step of mixing the biomass powder with a coating agent at a first rotating speed for a first time, the method further comprises a vibration screening treatment of the biomass powder, and / or a magnetic removal treatment of the biomass powder.

5. The biomass hard carbon negative electrode material prepared by the preparation method of any one of claims 1-3.

6. A sodium-ion battery, characterized in that, The sodium ion battery comprises a positive electrode and a negative electrode, wherein the negative electrode contains the biomass hard carbon negative electrode material of claim 5. The sodium ion battery comprises a positive electrode and a negative electrode, wherein the negative electrode contains the biomass hard carbon negative electrode material of claim 5.

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