Method for preparing hard and soft carbon core-shell material based on biomass depolymerization technology and application of hard and soft carbon core-shell material

Abstract

The invention belongs to the technical field of carbon materials, and relates to a method for preparing a hard and soft carbon core-shell material based on a biomass depolymerization technology and application of the hard and soft carbon core-shell material, the preparation method comprises the following steps: (1) crushing, sieving and deliming biomass, (2) depolymerizing the delimed biomass, and (3) carrying out redox reaction on the depolymerized biomass and asphalt to obtain the hard and soft carbon core-shell material. And (4) carrying out high-temperature carbonization on the pre-coated intermediate in an inert gas to obtain the hard and soft carbon core-shell material which is used for the negative electrode of the sodium-ion battery. According to the preparation method, the biomass is depolymerized, so that the surface of the biomass is rich in functional groups, then the surface of the biomass is coated with the asphalt more uniformly and stably by utilizing an oxidation-reduction reaction between the biomass and the functional groups of the asphalt, and the hard and soft carbon core-shell negative electrode material with high initial coulombic efficiency and excellent cycling stability is prepared.

Description

Technical Field

[0001] The invention relates to a method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology and application thereof, belonging to the technical field of carbon materials. Background Art

[0002] Sodium-ion batteries have become an important candidate technology for large-scale energy storage systems due to their excellent rate performance, low cost, high safety and wide temperature adaptability. Among the many negative electrode materials, hard carbon is considered to be the most promising negative electrode material for large-scale industrialization due to its advantages such as low working potential, low cost and stable structure. However, hard carbon has problems such as low first coulombic efficiency and poor cycle stability due to its complex structure and many defects. Soft carbon has a more ordered structure and fewer defects. Surface coating of hard carbon with soft carbon can effectively improve the first coulombic efficiency and cycle stability of hard carbon. At the same time, hard-soft carbon composites can also retain the high specific capacity characteristics of hard carbon.

[0003] Biomass is a natural and cheap raw material composed of hemicellulose, cellulose and lignin. Hard carbon materials derived from biomass are also widely used in the field of electrochemical energy storage due to their low cost and environmental friendliness. However, the components of lignin, cellulose and hemicellulose in natural biomass are mainly bonded together in the form of hydrogen bonds, forming a strong hydrogen bond network between molecules, which makes it a huge challenge to finely control the structure of hard carbon materials and achieve precise coating of soft carbon. Therefore, it is very important to develop a method for preparing hard and soft carbon core-shell materials with uniform coating and stable structure using biomass depolymerization technology. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology and its application, by depolymerizing the cross-linked structure of the three components of hemicellulose, cellulose and lignin in the biomass, fully exposing the functional groups of each component, and utilizing them to undergo redox reaction with asphalt rich in functional groups to achieve uniform and stable coating, thereby solving the problems of low first-cycle coulombic efficiency and poor cycle stability of hard carbon negative electrode materials for sodium ion batteries.

[0005] In order to achieve the above-mentioned invention object and solve the problems existing in the prior art, the technical solution adopted by the present invention is: a method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology, comprising the following steps: Step 1: Soak 20-50 g of biomass in a mixed solution of 300-500 mL of water and 300-500 mL of ethanol, clean it with ultrasound for 1-3 h, and then place it in a forced air drying oven at 70-90 °C. oC drying, crushing the dried biomass with a grinder, passing through a 250-400 mesh sieve, weighing 10-20 g of the sieved biomass, and adding 400-500 mL of 8-10 mol / L reagent for deashing, stirring for 4-8 h, filtering, and placing in a forced air drying oven at 70-90 o C drying to obtain deashed biomass; the biomass is selected from one of bamboo, bagasse, ramie or ginkgo leaf, and the reagent is selected from one of hydrochloric acid, sulfuric acid, hydrofluoric acid or sodium hydroxide solution; Step 2: Weigh 2-5 g of the deashed biomass from step 1 and place it in a container. Then place the container in a tube furnace and heat it at 5-10 °C under an argon atmosphere. o C / min heating rate to 200~500 o C, keeping warm for 1-3 h, so that the cross-linked structures between hemicellulose, cellulose and lignin of the biomass are depolymerized and their functional groups are fully exposed, and then cooled to room temperature to obtain biomass with rich functional groups on the surface after depolymerization, wherein the container is selected from one of a graphite crucible and a corundum boat; Step 3: Weigh 50-100 mg of asphalt and dissolve it in 30-50 mL of solvent. After stirring for 1-2 h, add 1-2 g of depolymerized biomass and continue stirring for 2-6 h. During this process, the depolymerized biomass and asphalt undergo redox reaction, making the asphalt uniformly and stably coated on the biomass. Then, at 60-100 o C to dry the solvent to obtain a pre-coated intermediate, wherein the solvent is selected from one of dichloromethane, toluene, xylene or tetrahydrofuran; Step 4: Weigh 1-2 g of the pre-coated intermediate obtained in step 3 and place it in a container. Then place the container in a tube furnace and heat it at 5-10 °C under an argon atmosphere. o C / min heating to 1000~1500 o C, keep warm for 1-3 h, and then cool to room temperature to obtain a hard-soft carbon core-shell material, wherein the container is selected from a graphite crucible or a corundum boat.

[0006] The hard and soft carbon core-shell materials prepared by the method are used in negative electrode materials for sodium ion batteries.

[0007] The beneficial effects of the present invention are: a method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology and its application, wherein the preparation method comprises the following steps: (1) crushing and screening the biomass, deashing treatment, (2) depolymerizing the deashed biomass, (3) subjecting the depolymerized biomass to an oxidation-reduction reaction with asphalt to obtain a pre-coated intermediate, and (4) carbonizing the pre-coated intermediate at high temperature under an argon atmosphere to obtain a hard and soft carbon core-shell material. The present invention has the following advantages: First, the ash is first removed by acid or alkali elution of the biomass, and then the cross-linked structure of the three components of hemicellulose, cellulose and lignin in the biomass is depolymerized by controlling the depolymerization temperature, eliminating the intermolecular forces and fully exposing the functional groups of each component, and then a redox reaction is carried out with asphalt rich in functional groups to achieve uniform and stable coating, and finally a hard and soft carbon core-shell material with high first coulomb efficiency and high cycle stability is obtained after high-temperature carbonization. Second, the biomass and asphalt raw materials used in the preparation process of the present invention are cheap and widely available, and are suitable for large-scale production; the present invention uses a graphite crucible for carbonization in a tubular furnace, which is conducive to increasing the carbon yield. Third, compared with the existing process, the preparation technology of the present invention only requires the biomass to be depolymerized under low temperature conditions to achieve uniform and stable coating, which has the characteristics of low energy consumption, low equipment requirements, and a simple and controllable process. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a SEM photograph of the hard and soft carbon core-shell material in Example 1 of the present invention.

[0009] Figure 2 This is a SEM photograph of the bagasse after depolymerization in Example 1 of the present invention.

[0010] Figure 3 This is a SEM photograph of the hard and soft carbon core-shell material of Example 3 of the present invention.

[0011] Figure 4 This is the XRD diagram of the hard and soft carbon core-shell material of Example 1 of the present invention.

[0012] Figure 5 This is the XRD diagram of the hard and soft carbon core-shell material of Example 3 of the present invention.

[0013] Figure 6 3 is a charge and discharge curve diagram of the hard and soft carbon core-shell material in Example 1 of the present invention.

[0014] Figure 7 3 is a charge and discharge curve diagram of the hard and soft carbon core-shell material in Example 3 of the present invention.

[0015] Figure 8 1 is a cyclic stability diagram of the hard and soft carbon core-shell material in Example 1 of the present invention.

[0016] Figure 9This is a cyclic stability diagram of the hard and soft carbon core-shell material in Example 3 of the present invention.

[0017] Figure 10 This is a SEM photograph of bagasse after depolymerization in Example 5 of the present invention.

[0018] Figure 11 This is a SEM photograph of bagasse after depolymerization in Example 6 of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the embodiments. Example 1

[0020] Step 1: Soak 50 g of bagasse in a mixed solution of 500 mL of water and 400 mL of ethanol, clean it with ultrasound for 2 h, and then place it in a forced air drying oven at 80 °C. o C drying, crushing the dried bagasse with a pulverizer, passing through a 300-mesh sieve, weighing 20 g of the sieved bagasse, adding 500 mL of 10 mol / L hydrofluoric acid solution to deash, stirring for 6 h, filtering, and placing in a forced air drying oven for 80 o C drying to obtain deashed bagasse.

[0021] Step 2: Weigh 4 g of the deashed bagasse from step 1 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating rate to 350 o C, keep warm for 2 h to depolymerize the cross-linked structures of hemicellulose, cellulose and lignin in the bagasse and fully expose the functional groups of each component. Then cool to room temperature to obtain bagasse with rich functional groups on the surface after depolymerization.

[0022] Step 3: Weigh 100 mg of asphalt and dissolve it in 50 mL of dichloromethane solution. After stirring for 1 h, add 2 g of the depolymerized bagasse in step 2 and continue stirring for 2 h. During this process, the bagasse and asphalt undergo redox reaction, so that the asphalt is evenly and stably coated on the bagasse. Then, at 60 o The dichloromethane solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0023] Step 4: Weigh 2 g of the pre-coated intermediate obtained in step 3 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating up to 1300 o C, keep warm for 3 h, and then cool to room temperature to obtain a hard-soft carbon core-shell material. It was applied to the negative electrode material of sodium ion battery and the electrochemical performance was tested: at 20 mA g -1 The current density is 325 mAh g-1 The high reversible specific capacity of the material is as high as 91.1% for the first coulombic efficiency and 99.4% for the capacity retention after 250 cycles. Figure 1 As shown, the SEM photos of depolymerized bagasse are as follows Figure 2 As shown, the XRD spectrum is Figure 4 As shown, the charge and discharge curves are Figure 6 As shown, the cyclic stability is Figure 8 shown. Example 2

[0024] Step 1: Soak 50 g of bagasse in a mixed solution of 400 mL of water and 400 mL of ethanol, clean it with ultrasound for 2 h, and then place it in a forced air drying oven at 80 °C. o C drying, crushing the dried bagasse with a pulverizer, passing through a 400-mesh sieve, weighing 15 g of the sieved bagasse, adding 500 mL of 8 mol / L hydrochloric acid solution to deash, stirring for 7 h, filtering, and placing in a forced air drying oven for 80 o C drying to obtain deashed bagasse.

[0025] Step 2: Weigh 4 g of the deashed bagasse from step 1 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating rate to 350 o C, keep warm for 2 h to depolymerize the cross-linked structures of hemicellulose, cellulose and lignin in the bagasse and fully expose the functional groups of each component. Then cool to room temperature to obtain bagasse with rich functional groups on the surface after depolymerization.

[0026] Step 3: Weigh 100 mg of asphalt and dissolve it in 50 mL of dichloromethane solution. After stirring for 1 h, add 2 g of the depolymerized bagasse in step 2 and continue stirring for 4 h. During this process, the bagasse and the asphalt undergo a redox reaction, so that the asphalt is evenly and stably coated on the bagasse. Then, the asphalt is heated to 60 °C. o The dichloromethane solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0027] Step 4: Weigh 1 g of the pre-coated intermediate obtained in step 3 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 5 °C under an argon atmosphere. o C / min heating up to 1400 o C, kept warm for 3 h, and then cooled to room temperature to obtain a hard-soft carbon core-shell material. Example 3

[0028] Step 1: Soak 50 g of bagasse in a mixed solution of 500 mL of water and 500 mL of ethanol, clean it with ultrasound for 2 h, and then place it in a forced air drying oven at 80 °C. o C drying, crushing the dried bagasse with a pulverizer, passing through a 300-mesh sieve, weighing 20 g of the sieved bagasse, adding 500 mL of 10 mol / L hydrofluoric acid solution to deash, stirring for 6 h, filtering, and placing in a forced air drying oven for 80 o C drying to obtain deashed bagasse.

[0029] Step 2: Weigh 4 g of the deashed bagasse from step 1 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating rate to 200 o C, keep warm for 2 h to depolymerize the cross-linked structures of hemicellulose, cellulose and lignin in the bagasse and fully expose the functional groups of each component. Then cool to room temperature to obtain bagasse with rich functional groups on the surface after depolymerization.

[0030] Step 3: Weigh 100 mg of asphalt and dissolve it in 50 mL of dichloromethane solution. After stirring for 1 h, add 2 g of the depolymerized bagasse in step 2 and continue stirring for 2 h. During this process, the bagasse and asphalt undergo redox reaction, so that the asphalt is evenly and stably coated on the bagasse. Then, at 60 o The dichloromethane solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0031] Step 4: Weigh 2 g of the pre-coated intermediate obtained in step 3 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating up to 1300 o C, keep warm for 3 h, and then cool to room temperature to obtain a hard-soft carbon core-shell material. It was applied to the negative electrode material of sodium ion battery and the electrochemical performance was tested: at 20 mA g -1 The current density is 284 mAh g -1 The reversible specific capacity of the hard and soft carbon core-shell material is shown in the SEM photo. Figure 3 As shown, the XRD spectrum is Figure 5 As shown, the charge and discharge curves are Figure 7 As shown, the cyclic stability is Figure 9 shown. Example 4

[0032] Step 1: Soak 40 g of ramie in a mixed solution of 400 mL of water and 500 mL of ethanol, clean it with ultrasound for 2 h, and then place it in a forced air drying oven at 80 °C.o C drying, crushing the dried ramie with a grinder, passing through a 300-mesh sieve, weighing 20 g of the sieved ramie, adding 500 mL of 10 mol / L hydrofluoric acid solution to deash, continuing to stir for 8 h, filtering, and placing in a forced air drying oven for 80 o C. drying to obtain deashed ramie; Step 2: Weigh 4 g of the deashed ramie in step 1 and place it in a corundum boat. Then place the corundum boat in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating rate to 350 o C, keep warm for 2 h, so that the cross-linked structures of hemicellulose, cellulose and lignin in ramie are depolymerized and the functional groups of each component are fully exposed. Then it is cooled to room temperature to obtain ramie with rich functional groups on the surface after depolymerization.

[0033] Step 3: Weigh 100 mg of asphalt and dissolve it in 50 mL of xylene solution. After stirring for 1 h, add 2 g of ramie depolymerized in step 2 and continue stirring for 4 h. During this process, ramie and asphalt undergo redox reaction, so that the asphalt is evenly and stably coated on the ramie. Then, at 100 o The xylene solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0034] Step 4: Weigh 2 g of the pre-coated intermediate obtained in step 3 and place it in a corundum boat. Then place the corundum boat in a tube furnace and heat it at 10 o C / min heating up to 1200 o C, kept warm for 3 h, and then cooled to room temperature to obtain a hard-soft carbon core-shell material. Example 5

[0035] Step 1: Soak 40 g of bagasse in a mixed solution of 500 mL of water and 400 mL of ethanol, clean it with ultrasound for 2 h, and then place it in a forced air drying oven at 80 °C. o C drying, crushing the dried bagasse with a pulverizer, passing through a 300-mesh sieve, weighing 20 g of the sieved bagasse, adding 500 mL of 10 mol / L hydrofluoric acid solution to deash, stirring for 6 h, filtering, and placing in a forced air drying oven for 80 o C. drying to obtain deashed bagasse; Step 2: Weigh 4 g of the deashed bagasse from step 1 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating rate to 450 oC, keep warm for 3 h to depolymerize the cross-linked structures of the three components of hemicellulose, cellulose and lignin in the bagasse and fully expose the functional groups of each component. Then cool to room temperature to obtain bagasse with rich functional groups on the surface after depolymerization.

[0036] Step 3: Weigh 100 mg of asphalt and dissolve it in 50 mL of xylene solution. After stirring for 1 h, add 2 g of the depolymerized bagasse in step 2 and continue stirring for 2 h. During this process, the bagasse and asphalt undergo redox reaction, so that the asphalt is evenly and stably coated on the bagasse. Then, heat the mixture at 60 °C. o The xylene solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0037] Step 4: Weigh 2 g of the pre-coated intermediate obtained in step 3 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating up to 1300 o C, kept warm for 2 h, and then cooled to room temperature to obtain a hard-soft carbon core-shell material. Figure 10 shown. Example 6

[0038] Step 1: Soak 50 g of bagasse in a mixed solution of 400 mL of water and 400 mL of ethanol, clean it with ultrasound for 3 h, and then place it in a forced air drying oven at 80 °C. o C drying, crushing the dried bagasse with a pulverizer, passing through a 400-mesh sieve, weighing 20 g of the sieved bagasse, adding 500 mL of 10 mol / L hydrofluoric acid solution to deash, stirring for 6 h, filtering, and placing in a forced air drying oven for 80 o C. drying to obtain deashed bagasse; Step 2: Weigh 4 g of the deashed bagasse from step 1 and place it in a corundum boat. Then place the corundum boat in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating rate to 250 o C, keep warm for 3 h to depolymerize the cross-linked structures of the three components of hemicellulose, cellulose and lignin in the bagasse and fully expose the functional groups of each component. Then cool to room temperature to obtain bagasse with rich functional groups on the surface after depolymerization.

[0039] Step 3: Dissolve 100 mg of asphalt in 50 mL of dichloromethane solution, stir for 1 h, then add 2 g of the depolymerized bagasse in step 2, and continue stirring for 2 h. During this process, the bagasse and asphalt undergo redox reaction, so that the asphalt is evenly and stably coated on the bagasse. o The dichloromethane solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0040] Step 4: Weigh 2 g of the pre-coated intermediate obtained in step 3 and place it in a corundum boat. Then place the corundum boat in a tube furnace and heat it at 10 o C / min heating up to 1300 o C, kept warm for 3 h, and then cooled to room temperature to obtain hard-soft carbon core-shell material. Figure 11 shown. Example 7

[0041] Step 1: Soak 40 g of ginkgo leaves in a mixed solution of 500 mL of water and 400 mL of ethanol, clean them by ultrasonic for 2 h, and then place them in a forced air drying oven at 80 °C. o C drying, using a grinder to grind the dried ginkgo leaves, through a 300-mesh sieve, weighing 20 g of the sieved ginkgo leaves, adding 500 mL of 8 mol / L sulfuric acid solution to deash, continuing to stir for 8 h, filtering, and placing in a forced air drying oven for 80 o C. drying to obtain deashed ginkgo leaves; Step 2: Weigh 4 g of the deashed ginkgo leaves from step 1 and place them in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating rate to 350 o C, keep warm for 2 h to depolymerize the cross-linked structures of the three components of hemicellulose, cellulose and lignin in the ginkgo leaves and fully expose the functional groups of each component. Then cool to room temperature to obtain ginkgo leaves with rich functional groups on the surface after depolymerization.

[0042] Step 3: Weigh 50 mg of asphalt and dissolve it in 40 mL of tetrahydrofuran solution. After stirring for 2 h, add 2 g of the depolymerized ginkgo leaves in step 2 and continue stirring for 6 h. During this process, the depolymerized ginkgo leaves and asphalt undergo redox reaction, making the asphalt uniformly and stably coated on the ginkgo leaves. Then, at 100 o The tetrahydrofuran solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0043] Step 4: Weigh 2 g of the pre-coated intermediate obtained in step 3 and place it in a graphite crucible. Then place the graphite crucible in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating up to 1300 o C, kept warm for 3 h, and then cooled to room temperature to obtain a hard-soft carbon core-shell material. Example 8

[0044] Step 1: Soak 50 g of bamboo in a mixed solution of 400 mL of water and 400 mL of ethanol, clean it with ultrasound for 2 h, and then place it in a forced air drying oven at 90 °C. oC drying, crushing the dried bamboo with a grinder, passing through a 300-mesh sieve, weighing 20 g of the sieved bamboo, adding 400 mL of 8 mol / L sodium hydroxide solution to deash, continuing to stir for 6 h, filtering, and placing in a forced air drying oven at 90 o C. drying to obtain deashed bamboo; Step 2: Weigh 3 g of the deashed bamboo from step 1 and place it in a corundum boat. Then place the corundum boat in a tube furnace and heat it at 5 °C under an argon atmosphere. o C / min heating rate to 450 o C, keep warm for 2 h to depolymerize the cross-linked structures of the three components of bamboo, hemicellulose, cellulose and lignin, fully expose the functional groups of each component, and then cool to room temperature to obtain bamboo with rich functional groups on the surface after depolymerization.

[0045] Step 3: Weigh 100 mg of asphalt and dissolve it in 50 mL of toluene solution. After stirring for 1 h, add 1 g of the depolymerized bamboo in step 2 and continue stirring for 6 h. During this process, the depolymerized bamboo and asphalt undergo redox reaction, making the asphalt uniformly and stably coated on the bamboo. o The toluene solution was evaporated to dryness at 400 °C to obtain the pre-coated intermediate.

[0046] Step 4: Weigh 1 g of the pre-coated intermediate obtained in step 3 and place it in a corundum boat. Then place the corundum boat in a tube furnace and heat it at 10 °C under an argon atmosphere. o C / min heating up to 1200 o C, kept warm for 3 h, and then cooled to room temperature to obtain a hard-soft carbon core-shell material.

Claims

1. A method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology, characterized in that: The following steps are involved: Step 1, weighing biomass, soaking it in a mixed solution of water and ethanol, ultrasonically cleaning it, drying it, crushing it and sieving it, and deashing the crushed and sieved biomass; Step 2, weighing the deashed biomass into a container, and adjusting the depolymerization temperature to depolymerize the cross-linked structures of the three components of hemicellulose, cellulose and lignin in the biomass, eliminating the intermolecular forces and fully exposing the functional groups of each component; Step 3, using a solvent to dissolve the asphalt rich in functional groups, adding the biomass depolymerized in step 2 to the asphalt solution, stirring and mixing them thoroughly to allow the two to undergo a redox reaction, and then evaporating the solvent to obtain a pre-coated intermediate; Step 4: Carbonize the pre-coated intermediate at high temperature under an argon atmosphere to obtain a hard-soft carbon core-shell material.

2. The method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology according to claim 1, characterized in that: Weigh 20-50 g of biomass and soak it in a mixed solution of 300-500 mL of water and 300-500 mL of ethanol. After ultrasonic cleaning for 1-3 h, place it in a forced air drying oven at 70-90 °C. o C drying, crushing the dried biomass with a grinder, passing through a 250-400 mesh sieve, weighing 10-20 g of the sieved biomass, and adding 400-500 mL of 8-10 mol / L reagent for deashing, stirring for 4-8 h, filtering, and placing in a forced air drying oven at 70-90 o C drying to obtain deashed biomass, wherein the biomass in step 1 is selected from one of bamboo, bagasse, ramie or ginkgo leaf, and the reagent is selected from one of hydrochloric acid, sulfuric acid, hydrofluoric acid or sodium hydroxide solution.

3. The method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology according to claim 1, characterized in that: Weigh 2-5 g of the deashed biomass in step 1 and place it in a container. Then place the container in a tube furnace and heat it at 5-10 °C under an argon atmosphere. o C / min heating rate to 200~500 o C, keep warm for 1-3 h, so that the cross-linked structures of the three components of hemicellulose, cellulose and lignin in the biomass are depolymerized and the functional groups of each component are fully exposed, and then cooled to room temperature to obtain biomass with rich functional groups on the surface after depolymerization, and the container is selected from one of a graphite crucible or a corundum boat.

4. The method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology according to claim 1, characterized in that: Weigh 50-100 mg of asphalt and dissolve it in 30-50 mL of solvent. After stirring for 1-2 h, add 1-2 g of the depolymerized biomass in step 2 and continue stirring for 2-6 h. During this process, the depolymerized biomass and asphalt undergo redox reaction, making the asphalt uniformly and stably coated on the biomass. Then, at 60-100 o C to dry the solvent to obtain a pre-coated intermediate, wherein the solvent is selected from one of dichloromethane, toluene, xylene or tetrahydrofuran.

5. The method for preparing hard and soft carbon core-shell materials based on biomass depolymerization technology according to claim 1, characterized in that: Weigh 1-2 g of the pre-coated intermediate obtained in step 3 and place it in a container. Then place the container in a tube furnace and heat it at 5-10 °C under an argon atmosphere. o C / min heating to 1000~1500 o C, keep warm for 1-3 h, and then cool to room temperature to obtain a hard-soft carbon core-shell material, wherein the container is selected from a graphite crucible or a corundum boat.

6. Use of the hard and soft carbon core-shell material prepared according to the method of claims 1 to 5 in negative electrode materials for sodium ion batteries.

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