Preparation Method, Negative Electrode Material and Application of a Biomass Composite Hard Carbon Negative Electrode Material

Abstract

The present invention relates to a biomass composite hard carbon anode material, a preparation method thereof and an application. The preparation method of the biomass composite hard carbon anode material comprises: crushing a biomass material, mixing a metal salt and an organic carbon source, drying and crushing to obtain a biomass precursor material; transferring the biomass precursor material into an inert gas for high-temperature calcination, and cooling to obtain a biomass hard carbon material; soaking the biomass hard carbon material in an acid solution, drying, mixing with one of a boron source, a sulfur source, a phosphorus source and a nitrogen source, treating under microwave, washing with deionized water until the pH value remains unchanged, and drying to obtain the biomass composite hard carbon anode material. The present invention forms a composite biomass hard carbon material with organic hard carbon coating biomass hard carbon. The biomass hard carbon inhibits the side reaction between the biomass carbon and the electrolyte by the method of surface coating with organic carbon, and further dopes elements on the surface to improve the conductivity of the material itself, so that the prepared material has a high initial efficiency, excellent rate performance and cycling performance.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a preparation method of a biomass composite hard carbon negative electrode material, the negative electrode material and applications thereof. Background Art

[0002] In recent years, energy and environmental problems have become bottleneck problems restricting the development of human society. On the one hand, the excessive consumption of traditional fossil energy has gradually been unable to meet the increasing energy demand of human society. On the other hand, the accompanying environmental problems have gradually become a difficult problem hindering social progress. Therefore, promoting the development and application of green new energy has become the mainstream.

[0003] With the development of technology and the progress of human society, the demand for equipment such as portable electronic devices and electric vehicles, and large-scale energy storage engineering fields has increased day by day. Since lithium-ion batteries entered the vision of humans, they have now been widely used in various related industries, showing remarkable prospects. However, problems such as the high cost of lithium-ion batteries and resource shortages have limited their development and application to a certain extent. Sodium-ion batteries and lithium-ion batteries were basically studied by scholars at the same time. Sodium resources are rich in reserves and evenly distributed. Existing research has proved that the performance of sodium-ion batteries can be comparable to that of lithium-ion batteries. Sodium-ion batteries meet the current energy demand of humans and have gradually become a hot research topic.

[0004] Currently, graphite is already the most widely used commercial negative electrode material for lithium-ion batteries. However, the atomic radius of sodium ions is larger than that of lithium ions, and it is difficult for them to enter the graphite layer. Therefore, the sodium storage performance of graphite is poor. Hard carbon materials, due to their larger interlayer spacing than graphite, are conducive to the storage and insertion / extraction of sodium ions and can maintain good stability during the insertion / extraction process of sodium ions. They are suitable as negative electrode materials for sodium-ion batteries. Moreover, biomass hard carbon materials have attracted extensive research from scholars due to their wide sources, green pollution-free nature, and low price. However, problems such as poor reversibility and low initial efficiency in the cycle exist. Therefore, it is necessary to develop a biomass hard carbon material with low cost, high initial efficiency, high sodium storage capacity, and good reversibility.

[0005] As disclosed in CN113948681A, a biomass-based hard carbon compound composite material, its preparation method and uses, the specific steps of the preparation method of a biomass-based hard carbon compound composite material are as follows: Step 1: Clean the biomass precursor, soak it in deionized water, perform ultrasonic treatment, and then dry it. After drying, crush it to obtain particulate matter A; Step 2: Mix particulate matter A and B evenly to obtain mixture C, where B is a non-metal element and / or a non-metal compound; Step 3: Add mixture C to H and mix evenly, where H is a mixture of one or more metal salts, and the mass ratio of A to H is 1:(1 - 10), to obtain mixture D; Step 4: Under an oxygen-free environment, first keep mixture D at a low temperature for heat preservation, and then raise the temperature for carbonization to obtain product E; Step 5: Immerse the obtained product E in an acid solution, stir it, and perform ultrasonic treatment, and then wash it until it is neutral, and filter it by suction to obtain solid product F; Step 6: Dry F to obtain the biomass-based hard carbon compound composite material. The biomass-based hard carbon compound composite material has no organic carbon coating, and there are many steps, resulting in a relatively low first efficiency in sodium-ion batteries. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to provide a biomass hard carbon material with low cost, high first efficiency, high sodium storage capacity and good reversibility.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] A preparation method of a biomass composite hard carbon negative electrode material, comprising the following steps:

[0009] S1. Crush the biomass material, mix it with a metal salt and an organic carbon source in a certain mass ratio, add an appropriate amount of water and mix evenly, and then obtain the biomass precursor material after drying and crushing;

[0010] S2. Place the biomass precursor material under an inert gas, and after two calcinations, cool it to obtain the biomass hard carbon material;

[0011] S3. Immerse the biomass hard carbon material in an acid solution, dry it, then mix the material evenly with one or several of a boron source, a sulfur source, a phosphorus source and a nitrogen source, treat it under an inert gas microwave, wash it with deionized water until the pH value remains unchanged, and dry it to obtain the biomass composite hard carbon negative electrode material.

[0012] Beneficial effects: The present invention selects biomass materials and organic carbon sources as raw materials, which are green, environmentally friendly, widely sourced, low-cost, and have a stable supply, and can meet large-scale industrial production. Through the further catalysis of iron, cobalt, and nickel elements on the biomass precursor material after two high-temperature calcinations, a composite biomass hard carbon material with organic hard carbon coated on biomass hard carbon is formed. The biomass hard carbon inhibits the side reaction between biomass carbon and the electrolyte by coating organic carbon on the surface, removes the residual metal on the surface by acid treatment, and further dopes boron, sulfur, phosphorus, and nitrogen elements on the surface to improve the conductivity of the material itself, so that the prepared biomass composite hard carbon anode material has a high initial efficiency, excellent rate performance, and cycling performance.

[0013] Preferably, the biomass material in the step S1 includes one or more of walnut shells, rice husks, banana peels, melon seed shells, pinecones, cotton, coconut shells, seaweeds, wheat straws, peanut shells, lotus leaves, peat.

[0014] Preferably, the metal salt in the step S1 is one or more of FeCl3, Fe(NO3)3, Fe2(SO4)3, CoCl2, CoBr2, CoI2, CoCO3, Co(NO3)2, CoSO4, NiSO4, NiCl2, NiBr2, NiI2.

[0015] Preferably, the organic carbon source in the step S1 can be one or more of glucose, asphalt, epoxy resin.

[0016] Preferably, the mass ratio of the biomass material, organic carbon source, and metal salt in the step S1 is (0.60 - 0.98):(0.01 - 0.35):(0.01 - 0.05).

[0017] Preferably, the drying temperature in the step S1 is 80 - 100 °C, and the time is 48 h.

[0018] Preferably, the inert gas in the step S2 includes one or more of nitrogen, argon.

[0019] Preferably, the two calcinations are first at 200 - 400 °C for 2 - 4 h, and then the temperature is raised to 1000 - 1600 °C,

[0020] and calcined for 8 - 12 h.

[0021] Preferably, the acid solution in the step S3 is hydrochloric acid or sulfuric acid, the concentration is 1 - 6 mol / L, and the soaking time is 1 - 2 h.

[0022] Preferably, in the step S3, microwave treatment is carried out at 500 - 2000 W for 5 - 15 min in an inert gas.

[0023] Preferably, in step S3, the boron source includes one or more of boron oxide and boric acid, the sulfur source includes one or more of thiourea and magnesium sulfate, the phosphorus source includes phosphoric acid, and the nitrogen source includes one or more of nitric acid, urea, and ammonium nitrate.

[0024] Preferably, the mass ratio of the material to the mixture of the boron source, sulfur source, phosphorus source, and nitrogen source in step S3 is 1:(0.2 - 1).

[0025] The present invention also provides a biomass composite hard carbon anode material obtained by the above preparation method.

[0026] The present invention also provides an application of the biomass composite hard carbon anode material obtained by the above preparation method in the anode material of a sodium-ion battery.

[0027] The advantages of the present invention are as follows: The present invention selects biomass materials and organic carbon sources as raw materials, which are green, environmentally friendly, widely sourced, low-cost, and have a stable supply, and can meet large-scale industrial production. Through two high-temperature calcinations, the iron, cobalt, and nickel elements further catalyze the biomass precursor material to form a composite biomass hard carbon material with organic hard carbon coating biomass hard carbon. The biomass hard carbon inhibits the side reaction between the biomass carbon and the electrolyte by coating the surface with organic carbon, removes the residual metal on the surface by acid treatment, and further dopes boron, sulfur, phosphorus, and nitrogen elements on the surface to improve its conductivity. The prepared biomass composite hard carbon anode material has a high initial efficiency, a high reversible capacity, and excellent rate performance. Description of the Drawings

[0028] Figure 1 is the XRD pattern of the biomass composite hard carbon anode material prepared in Example 1 of the present invention;

[0029] Figure 2 is the SEM image of the biomass composite hard carbon anode material prepared in Example 1 of the present invention;

[0030] Figure 3 is the TEM image of the biomass composite hard carbon anode material prepared in Example 1 of the present invention;

[0031] Figure 4 is the first charge-discharge curve of the sodium-ion battery prepared from the biomass composite hard carbon anode material prepared in Example 1 of the present invention. Detailed Embodiments

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0033] Example 1

[0034] The present invention provides a method for preparing a biomass composite hard carbon anode material, which includes the following steps:

[0035] S1. Clean the walnut shells with deionized water, then crush them. Mix FeCl3 and glucose in a mass ratio of 0.90:0.02:0.08, add an appropriate amount of water and mix evenly. Dry in an oven at 80°C for 48h to obtain a biomass precursor material;

[0036] S2. Place the biomass precursor material in an open atmosphere tube furnace. Under an argon atmosphere (flow rate of 80 sccm), heat it at a rate of 5°C / min to 200°C, calcine for 2h, then heat it at a rate of 4°C / min to 1000°C, calcine for 12h, and naturally cool to room temperature to obtain a biomass hard carbon material;

[0037] S3. Immerse the biomass hard carbon material in a 2mol / L hydrochloric acid solution for 1h, then dry it. Mix the obtained material with urea in a mass ratio of 1:0.2 and mix evenly. After treating it under an inert gas of 500W microwave for 10min, wash it with deionized water until the pH value remains unchanged, and then dry it in an oven at 80°C for 24h to obtain the biomass composite hard carbon anode material.

[0038] Figure 1 The XRD pattern of the biomass composite hard carbon anode material prepared in Example 1 is shown. The carbon layer spacing is 0.392nm, which is much larger than the carbon layer spacing of graphite (0.335nm), and can more effectively accommodate the insertion and extraction of sodium ions.

[0039] Figure 2 The SEM image of the biomass composite hard carbon anode material prepared in Example 1 is shown. There are hard carbon particles with a size of 0.5 - 10um, and a mesoporous structure can be observed on the surface.

[0040] Figure 3 The TEM image of the biomass composite hard carbon anode material prepared in Example 1 is shown. The material is amorphous hard carbon, and there are uniform carbon layer stripes on the outer layer.

[0041] The biomass composite hard carbon anode material prepared in Example 1 was mixed with conductive carbon black and polyvinylidene chloride in a mass ratio of 8:1:1, and then an appropriate amount of N-methylpyrrolidone was added. After mixing evenly, it was coated on a copper foil and dried in a vacuum oven at 80 °C. After rolling and cutting, an electrode sheet was obtained. A Na sheet was used as the negative electrode, the electrolyte was a mixed system containing 1 M NaClO / (EC + DMC) (volume ratio 1:1), the separator was a glass fiber separator, and a button cell was assembled and formed in a glove box filled with argon.

[0042] Figure 4 The first charge-discharge curves of the sodium-ion battery prepared from the biomass composite hard carbon anode material prepared in Example 1 are shown. The first discharge specific capacity is 320.33 mAh / g, the first charge specific capacity is 291.01 mAh / g, and the first efficiency is 90.85%. Moreover, it can be seen from the figure that the reversible capacity still remains at a relatively high level after 100 cycles.

[0043] Example 2

[0044] The present invention provides a preparation method of a biomass composite hard carbon anode material, which includes the following steps:

[0045] S1. The melon seedshells were cleaned with deionized water, then crushed, and Co(NO3)2 and pitch were mixed in a mass ratio of 0.60:0.05:0.35, and an appropriate amount of water was added and mixed evenly. After drying in an oven at 90 °C for 48 h, a biomass precursor material was obtained.

[0046] S2. The biomass precursor material was placed in an open-type atmosphere tube furnace. Under an argon atmosphere (flow rate 80 sccm), it was heated to 300 °C at a rate of 5 °C / min and calcined for 3 h, then heated to 1200 °C at a rate of 4 °C / min and calcined for 10 h, and naturally cooled to room temperature to obtain a biomass hard carbon material.

[0047] S3. The biomass hard carbon material was soaked in a 1 mol / L sulfuric acid solution for 2 h, then dried. After the obtained material was mixed evenly with phosphoric acid in a mass ratio of 1:0.6, it was treated under an inert gas 500 W microwave for 15 min, washed with deionized water until the pH value remained unchanged, and then dried in an oven at 80 °C for 24 h to obtain the biomass composite hard carbon anode material.

[0048] The biomass composite hard carbon negative electrode material prepared in Example 2 was mixed with conductive carbon black and polyvinylidene chloride in a mass ratio of 8:1:1, and then an appropriate amount of N-methylpyrrolidone was added, mixed evenly, coated on a copper foil, dried in a vacuum oven at 80°C, and rolled and cut to obtain an electrode sheet. Na sheet was used as the negative electrode, the electrolyte was a mixed system containing 1M NaClO / (EC+DMC) (volume ratio of 1:1), and the diaphragm was a glass fiber diaphragm. The button battery was assembled in a glove box filled with argon.

[0049] Example 3

[0050] The present invention provides a method for preparing a biomass composite hard carbon negative electrode material, comprising the following steps:

[0051] S1. Clean the coconut shell with deionized water, grind it into powder, mix it with NiSO4 and epoxy resin in a mass ratio of 0.98:0.01:0.01, add appropriate amount of water and mix thoroughly, and dry it in an oven at 100°C for 48 hours to obtain a biomass precursor material.

[0052] S2. Place the biomass precursor material in an open atmosphere tubular furnace, heat it to 400°C at a rate of 5°C / min under a nitrogen atmosphere (flow rate of 80sccm), calcine it for 2h, then heat it to 1400°C at a rate of 4°C / min, calcine it for 9h, and naturally cool it to room temperature to obtain a biomass hard carbon material.

[0053] S3. Soak the obtained hard carbon material in a 4 mol / L hydrochloric acid solution for 2 hours and dry it. Mix the obtained material with magnesium sulfate in a mass ratio of 1:0.8, treat it with a microwave at 800 W for 15 minutes under an inert atmosphere, wash it with deionized water until the pH value remains unchanged, and dry it in an oven at 80°C for 24 hours to obtain a biomass composite hard carbon negative electrode material.

[0054] The biomass composite hard carbon negative electrode material prepared in Example 3 was mixed with conductive carbon black and polyvinylidene chloride in a mass ratio of 8:1:1, and then an appropriate amount of N-methylpyrrolidone was added and mixed evenly. Coated on copper foil and dried in a vacuum oven at 80°C. The electrode sheet was obtained by rolling and cutting, and the Na sheet was used as the negative electrode. The electrolyte was a mixed system containing 1M NaClO / (EC+DMC) (volume ratio of 1:1), and the diaphragm was a glass fiber diaphragm. The button battery was assembled in a glove box filled with argon.

[0055] Example 4

[0056] The present invention provides a method for preparing a biomass composite hard carbon negative electrode material, comprising the following steps:

[0057] S1. Clean the pinecones with deionized water, grind them into powder, and mix them with FeCl3 and glucose at a mass ratio of 0.90:0.02:0.08. Add an appropriate amount of water and mix well. Dry in an oven at 90 °C for 48 h to obtain a biomass precursor material;

[0058] S2. Place the biomass precursor material in an open-type atmosphere tube furnace. Under an argon atmosphere (flow rate: 80 sccm), heat it at a rate of 5 °C / min to 200 °C and calcine for 4 h. Then heat it at a rate of 4 °C / min to 1600 °C and calcine for 8 h. Naturally cool to room temperature to obtain a biomass hard carbon material;

[0059] S3. Immerse the obtained hard carbon material in a 6 mol / L hydrochloric acid solution for 1 h, then dry it. Mix the obtained material with ammonium nitrate at a mass ratio of 1:1 evenly. After microwave treatment at 2000 W for 5 min under an inert atmosphere, wash it with deionized water until the pH value remains unchanged, and then dry it in an oven at 80 °C for 24 h to obtain a biomass composite hard carbon negative electrode material.

[0060] Mix the biomass composite hard carbon negative electrode material prepared in Example 4 with conductive carbon black and polyvinylidene chloride at a mass ratio of 8:1:1, and then add an appropriate amount of N-methylpyrrolidone and mix evenly. Coat it on a copper foil and dry it in a vacuum oven at 80 °C. After rolling and cutting, an electrode sheet is obtained. Use a Na sheet as the negative electrode, the electrolyte is a mixed system containing 1 M NaClO / (EC + DMC) (volume ratio: 1:1), the separator is a glass fiber separator, and an assembled coin cell is formed in a glove box filled with argon.

[0061] Comparative Example 1

[0062] S1. Clean the walnut shells with deionized water, grind them into powder, and mix them with glucose at a mass ratio of 0.92:0.08. Add an appropriate amount of water and mix well. Dry in an oven at 90 °C for 48 h to obtain a biomass precursor material;

[0063] S2. Place the biomass precursor material in an open-type atmosphere tube furnace. Under an argon atmosphere (flow rate: 80 sccm), heat it at a rate of 5 °C / min to 200 °C and calcine for 2 h. Then heat it at a rate of 4 °C / min to 1200 °C and calcine for 8 h. Naturally cool to room temperature to obtain a biomass hard carbon material;

[0064] S3. Immerse the biomass hard carbon material in a 2 mol / L hydrochloric acid solution for 2 h, then dry it. Mix the material with urea at a mass ratio of 1:0.2 evenly. After microwave treatment at 1000 W for 10 min under an inert atmosphere, wash it with deionized water until the pH value remains unchanged, and then dry it in an oven at 80 °C for 24 h to obtain a biomass composite hard carbon negative electrode material.

[0065] The biomass composite hard carbon anode material prepared in Comparative Example 1 was mixed with conductive carbon black and polyvinylidene chloride in a mass ratio of 8:1:1, and then an appropriate amount of N-methylpyrrolidone was added and mixed evenly. It was coated on a copper foil and dried in a vacuum oven at 80 °C. After rolling and cutting, an electrode sheet was obtained. A Na sheet was used as the anode, the electrolyte was a mixed system containing 1 M NaClO / (EC + DMC) (volume ratio 1:1), the separator was a glass fiber separator, and a button cell was assembled and formed in a glove box filled with argon.

[0066] Comparative Example 2

[0067] S1. The walnut shell was cleaned with deionized water, ground into powder and mixed with FeCl3 in a mass ratio of 0.98:0.02, and an appropriate amount of water was added and mixed thoroughly. It was dried in an oven at 80 °C for 48 h to obtain a biomass precursor material;

[0068] S2. The biomass precursor material was placed in an open-type atmosphere tube furnace. Under an argon atmosphere (flow rate 80 sccm), it was heated to 200 °C at a rate of 5 °C / min and calcined for 2 h, then heated to 1200 °C at a rate of 4 °C / min and calcined for 8 h, and naturally cooled to room temperature to obtain a biomass hard carbon material;

[0069] S3. The biomass hard carbon material was immersed in a 2 mol / L hydrochloric acid solution for 2 h and then dried. After the material was mixed evenly with urea in a mass ratio of 1:0.2, it was treated with 1000 W microwave in an inert atmosphere for 10 min, washed with deionized water until the pH value remained unchanged, and then dried in an oven at 80 °C for 24 h to obtain a biomass composite hard carbon anode material.

[0070] The biomass composite hard carbon anode material prepared in Comparative Example 2 was mixed with conductive carbon black and polyvinylidene chloride in a mass ratio of 8:1:1, and then an appropriate amount of N-methylpyrrolidone was added and mixed evenly. It was coated on a copper foil and dried in a vacuum oven at 80 °C. After rolling and cutting, an electrode sheet was obtained. A Na sheet was used as the anode, the electrolyte was a mixed system containing 1 M NaClO / (EC + DMC) (volume ratio 1:1), the separator was a glass fiber separator, and a button cell was assembled and formed in a glove box filled with argon.

[0071] Comparative Example 3

[0072] S1. The walnut shell was cleaned with deionized water and crushed, and mixed with FeCl3 and glucose in a mass ratio of 0.90:0.02:0.08, and an appropriate amount of water was added and mixed thoroughly. It was dried in an oven at 80 °C for 48 h to obtain a biomass precursor material;

[0073] S2. Place the biomass precursor material in an open atmosphere tube furnace. Under an argon atmosphere (flow rate: 80 sccm), heat it to 200 °C at a rate of 5 °C / min and calcine for 2 h. Then heat it to 1200 °C at a rate of 4 °C / min and calcine for 8 h. Naturally cool it to room temperature to obtain the biomass hard carbon material;

[0074] S3. Immerse the biomass hard carbon material in a 2 mol / L hydrochloric acid solution for 2 h, then dry it. After drying, subject the material to 1000 W microwave treatment in an inert atmosphere for 10 min. Wash it with deionized water until the pH value remains unchanged, and then dry it in an oven at 80 °C for 24 h to obtain the biomass composite hard carbon anode material.

[0075] Mix the biomass composite hard carbon anode material prepared in Comparative Example 3 with conductive carbon black and polyvinylidene chloride in a mass ratio of 8:1:1. Then add an appropriate amount of N-methylpyrrolidone and mix evenly. Coat it on a copper foil and dry it in a vacuum oven at 80 °C. After rolling and cutting, obtain the electrode sheet. Use a Na sheet as the anode, the electrolyte is a mixed system containing 1 M NaClO / (EC + DMC) (volume ratio 1:1), the separator is a glass fiber separator, and assemble a button cell in a glove box filled with argon.

[0076] Comparative Example 4

[0077] S1. Wash the walnut shells with deionized water, crush them, and dry them in an oven at 80 °C for 48 h to obtain the biomass precursor material;

[0078] S2. Place the biomass precursor material in an open atmosphere tube furnace. Under an argon atmosphere (flow rate: 80 sccm), heat it to 200 °C at a rate of 5 °C / min and calcine for 2 h. Then heat it to 1200 °C at a rate of 4 °C / min and calcine for 8 h. Naturally cool it to room temperature to obtain the biomass hard carbon material.

[0079] Mix the biomass composite hard carbon anode material prepared in Comparative Example 4 with conductive carbon black and polyvinylidene chloride in a mass ratio of 8:1:1. Then add an appropriate amount of N-methylpyrrolidone and mix evenly. Coat it on a copper foil. Dry it in a vacuum oven at 80 °C. After rolling and cutting, obtain the electrode sheet. Use a Na sheet as the anode, the electrolyte is a mixed system containing 1 M NaClO / (EC + DMC) (volume ratio 1:1), the separator is a glass fiber separator, and assemble a button cell in a glove box filled with argon.

[0080] Test the electrochemical performance of the 8 sodium-ion batteries prepared in Examples 1-4 and Comparative Examples 1-4. The test results are shown in Table 1.

[0081] Table 1 Electrochemical performance of sodium-ion batteries

[0082] Example Initial charge specific capacity Initial discharge specific capacity Initial efficiency Example 1 291.01 mAh / g 320.33 mAh / g 90.85％ Example 2 289.54 mAh / g 318.45 mAh / g 90.92％ Example 3 294.38 mAh / g 325.07 mAh / g 90.55％ Example 4 288.34 mAh / g 317.89 mAh / g 90.70％ Comparative example 1 252.01 mAh / g 287.0 mAh / g 87.81％ Comparative example 2 240.56 mAh / g 290.73 mAh / g 82.74％ Comparative example 3 253.42 mAh / g 286.56 mAh / g 88.44％ Comparative example 4 134.56 mAh / g 275.53 mAh / g 48.83％

[0083] Table 1

[0084] As can be seen from Table 1, the biomass composite hard carbon anode materials obtained by implementing the present invention all have relatively high initial discharge specific capacity, initial charge specific capacity and initial efficiency; while for the materials of Comparative Examples 1, 2 and 3, the initial charge-discharge specific capacity and initial efficiency are relatively low compared with those of the Examples. The main reason is that in Comparative Example 1, the metal salt was not used, which affected the interlayer spacing of the hard carbon and the coated carbon at the same temperature, resulting in a decrease in both the initial charge-discharge specific capacity and the initial efficiency also decreased. In Comparative Example 2, organic carbon coating was not used, and the side reaction between the hard carbon and the electrolyte was serious. Although it had a relatively high initial discharge specific capacity, the initial charge capacity and the initial efficiency both decreased; in Comparative Example 3, the performance of the biomass composite hard carbon anode material obtained without element doping and microwave activation was also poor, so the initial discharge specific capacity, initial charge specific capacity and initial efficiency also decreased. Comparative Example 4 only used biomass materials, and the initial discharge specific capacity, initial charge specific capacity and initial efficiency were lower than those of Comparative Examples 1-3.

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

Claims

1. A preparation method of a biomass composite hard carbon negative electrode material, characterized in that, It includes the following steps: S1. Crush the biomass material, mix it with metal salts and organic carbon sources in a certain mass ratio and add an appropriate amount of water to mix evenly. After drying and crushing, a biomass precursor material is obtained; the metal salt is one or more of FeCl3, Fe(NO3)3, Fe2(SO4)3, CoCl2, CoBr2, CoI2, Co(NO3)2, CoSO4, NiSO4, NiCl2, NiBr2, NiI2; the mass ratio of the biomass material, organic carbon source, and metal salt is (0.60 - 0.98):(0.01 - 0.35):(0.01 - 0.05); S2. Transfer the biomass precursor material under an inert gas. After two calcinations and cooling, a biomass hard carbon material is obtained; S3. Immerse the biomass hard carbon material in an acid solution, dry it, then mix the material evenly with one or several of a boron source, sulfur source, phosphorus source, and nitrogen source. After microwave treatment at 500 - 2000W for 5 - 15 min under an inert gas, wash it with deionized water until the pH value remains unchanged, and after drying, a biomass composite hard carbon negative electrode material is obtained.

2. The preparation method of the biomass composite hard carbon negative electrode material according to claim 1, characterized in that: The biomass material in step S1 includes one or several of walnut shells, rice husks, banana peels, melon seeds shells, pinecones, cotton, coconut shells, seaweeds, wheat straws, peanut shells, lotus leaves, peat.

3. The preparation method of the biomass composite hard carbon negative electrode material according to claim 1, characterized in that: The organic carbon source in step S1 is one or several of glucose, asphalt, epoxy resin.

4. The preparation method of the biomass composite hard carbon negative electrode material according to claim 1, wherein: The drying temperature in step S1 is 80 - 100°C, and the time is 48 h; the inert gas in step S2 includes one or several of nitrogen, argon; the two calcinations are first at 200 - 400°C for 2 - 4 h, and then the temperature is raised to 1000 - 1600°C for 8 - 12 h.

5. The preparation method of the biomass composite hard carbon negative electrode material according to claim 1, characterized in that: The acid solution in step S3 is hydrochloric acid or sulfuric acid, with a concentration of 1 - 6 mol / L, and the soaking time is 1 - 2 h.

6. The preparation method of the biomass composite hard carbon negative electrode material according to claim 1, wherein: The boron source in step S3 includes one or several of boron oxide, boric acid, the sulfur source includes one or several of thiourea, magnesium sulfate, the phosphorus source includes phosphoric acid, and the nitrogen source includes one or several of nitric acid, urea, and ammonium nitrate; the mass ratio of the material to the mixture of the boron source, sulfur source, phosphorus source, and nitrogen source is 1:(0.2 - 1).

7. A biomass composite hard carbon negative electrode material obtained by the preparation method according to any one of claims 1 - 6.

8. Application of the biomass composite hard carbon negative electrode material according to claim 7 in a negative electrode material of a sodium ion battery.

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