Biomass-based hard carbon composite negative electrode material and preparation method and application thereof

Abstract

The invention relates to a biomass-based hard carbon composite negative electrode material and a preparation method and application thereof. The sulfuric acid is used for treating biomass, so that long-chain cellulose, lignin and the like in the biomass material can be promoted to be broken into short chains; then the materials treated by sulfuric acid are subjected to a hydrothermal reaction, hydroxyl groups are introduced to the surfaces of cellulose, lignin and the like through the hydrothermal reaction, and the introduction of the hydroxyl groups can improve the uniformity of a condensation reaction between biomass and water-soluble organic matter, aldehyde groups of alcohol-soluble thermoplastic phenolic resin and hydroxyl groups on graphene; the interface adaptability of the water-soluble organic matter, the alcohol-soluble thermoplastic phenolic resin, the biomass carbon and the graphene is improved. The biomass-based hard carbon composite negative electrode material has high capacity and first coulombic efficiency, and also has excellent cycle performance.

Description

Technical Field

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

[0002] With the rapid development of the electric vehicle market, the demand for lithium-ion batteries has also surged. However, the lithium resources in the earth's crust are limited, which makes the cost of lithium-ion batteries high. At the same time, the working principle of sodium-ion batteries is similar to that of lithium-ion batteries. They have an energy density close to that of lithium-ion batteries. In addition, sodium-ion resources are abundant, evenly distributed, and low in cost. They are expected to be used in large-scale energy storage devices.

[0003] Hard carbon is the most commonly used negative electrode material for commercial sodium-ion batteries. At present, there are two main raw materials for the preparation of hard carbon, namely petroleum coal and biomass. Petroleum coal materials are widely available, and the hard carbon prepared has stable performance and high carbon yield, but due to its structural characteristics, its capacity is lower than other materials; biomass as a carbon source has become the preferred raw material for the preparation of hard carbon due to its environmental friendliness and low cost. However, the first coulombic efficiency and capacity of the hard carbon negative electrode materials currently developed are low, which seriously restricts the development of sodium-ion batteries. Therefore, it is urgent to develop a hard carbon negative electrode material with high capacity and first coulombic efficiency. Summary of the invention

[0004] In order to improve the problems of low first coulombic efficiency and capacity of biomass-based hard carbon negative electrode materials in the prior art, the present invention provides a biomass-based hard carbon composite negative electrode material and a preparation method and use thereof. The biomass-based hard carbon composite negative electrode material has high capacity and first coulombic efficiency, and also has excellent cycle performance.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] A method for preparing a biomass-based hard carbon composite negative electrode material, the preparation method comprising the following steps:

[0007] (1) mixing the biomass with a sulfuric acid aqueous solution, heating and stirring, filtering, and washing with water until neutral to obtain a pretreated product;

[0008] (2) mixing the pretreated product of step (1) with water to perform a hydrothermal reaction to obtain a hydrothermal reaction product;

[0009] (3) mixing, soaking, filtering and drying the hydrothermal reaction product of step (2) and the aqueous solution of water-soluble organic matter to obtain a solid component;

[0010] (4) mixing the dried solid component of step (3), ethanol, alcohol-soluble thermoplastic phenolic resin and graphene to obtain a mixed solution; stirring the mixed solution under heating conditions until the ethanol is completely volatilized to obtain a solid mixture;

[0011] (5) subjecting the solid mixture of step (4) to a curing reaction to obtain a cured product;

[0012] (6) Carbonizing the solidified product of step (5) to prepare the biomass-based hard carbon composite negative electrode material.

[0013] According to an embodiment of the present invention, in step (1), the source of the biomass is not particularly defined, and may be, for example, at least one of lychee wood, apple wood, poplar wood, bamboo, fruit shell, straw, coconut shell and corn cob.

[0014] According to an embodiment of the present invention, in step (1), the biomass is preferably washed biomass, for example, the biomass raw material is washed with water to remove impurities therein; after washing, the biomass is dried, for example, at 60-120°C for 8-12 hours.

[0015] According to an embodiment of the present invention, in step (1), during the process of mixing the biomass with the aqueous sulfuric acid solution, the sulfuric acid can break the long-chain cellulose and lignin components in the biomass into short chains. The presence of short-chain cellulose is conducive to inhibiting the directional growth of graphite crystallites, constructing more chaotic layer graphite microstructures, and inducing the formation of closed pores, which is conducive to obtaining high-capacity biomass-based hard carbon composite negative electrode materials. At the same time, the presence of short-chain cellulose is also conducive to introducing hydroxyl groups through hydrothermal reaction, thereby improving the interface composite effect of biomass carbon with graphene, water-soluble organic matter, and alcohol-soluble thermoplastic phenolic resin, and is conducive to generating a carbon precursor with a cross-linked network structure, thereby achieving the effect of further improving the capacity of the biomass-based hard carbon composite negative electrode material.

[0016] According to an embodiment of the present invention, in step (1), in order to allow the biomass to fully contact with sulfuric acid and to break as many components as possible such as long-chain cellulose and lignin in the biomass into short chains, the biomass is preferably crushed, for example, the washed and dried biomass is sent to a crusher for crushing to obtain biomass particles of 16-60 mesh.

[0017] According to an embodiment of the present invention, in step (1), the heating and stirring temperature is 40-60°C, for example, 50°C; the heating and stirring time is 1-3 hours, for example, 2 hours. The heating and stirring conditions are more conducive to the cleavage of long-chain cellulose and lignin components in the biomass by sulfuric acid.

[0018] According to an embodiment of the present invention, in step (1), the filtration is, for example, suction filtration or centrifugation.

[0019] According to an embodiment of the present invention, in step (1), the mass concentration of the aqueous sulfuric acid solution is 60%-65%, for example, 61%, 62%, 63% or 64%; the feed ratio of the biomass to the aqueous sulfuric acid solution is (40-60) g / L, that is, 40-60 g of biomass is added to 1 L of aqueous sulfuric acid solution with a concentration of 60%-65%.

[0020] According to an embodiment of the present invention, in step (2), the mass ratio of the pretreated product of step (1) to water is 1:(12-20), for example, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20.

[0021] According to an embodiment of the present invention, in step (2), the temperature of the hydrothermal reaction is 120-160°C, for example, 120°C, 130°C, 140°C, 150°C or 160°C.

[0022] According to an embodiment of the present invention, in step (2), the hydrothermal reaction time is 4-12 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0023] According to an embodiment of the present invention, in step (2), hydroxyl groups can be introduced on the surfaces of cellulose and lignin through a hydrothermal reaction, and the introduction of hydroxyl groups can improve the uniformity of the condensation reaction between biomass and water-soluble organic matter, aldehyde groups of alcohol-soluble thermoplastic phenolic resin, and hydroxyl groups on graphene, improve the interface adaptability of water-soluble organic matter, alcohol-soluble thermoplastic phenolic resin, biomass carbon and graphene, improve the interface composite effect, and promote the generation of a carbon precursor with a cross-linked network structure, which is conducive to obtaining a biomass-based hard carbon composite negative electrode material with a high capacity.

[0024] According to an embodiment of the present invention, in step (3), the water-soluble organic matter is selected from one or a mixture of carboxymethyl starch, acetic starch, hydroxymethyl cellulose, polyacrylamide, and polyvinyl pyrrolidone.

[0025] According to an embodiment of the present invention, in step (3), the concentration of the water-soluble organic matter in the aqueous solution of the water-soluble organic matter is 10wt%-50wt%, for example, 10wt%, 20wt%, 30wt%, 40wt% or 50wt%.

[0026] According to an embodiment of the present invention, in step (3), the feed ratio of the hydrothermal reaction product of step (2) to the aqueous solution of water-soluble organic matter is (30-50) g / L, for example, 30 g / L, 35 g / L, 40 g / L, 45 g / L or 50 g / L. Exemplarily, 30-50 g of the hydrothermal reaction product of step (2) is added to 1 L of an aqueous solution of water-soluble organic matter having a concentration of 10 wt%-50 wt%.

[0027] According to an embodiment of the present invention, in step (3), the soaking time is 12-24 hours, for example, 12 hours, 16 hours, 18 hours or 24 hours.

[0028] According to an embodiment of the present invention, in step (3), the immersion is immersion at normal pressure.

[0029] According to an embodiment of the present invention, in step (3), the hydrothermal reaction product of step (2) and the aqueous solution of water-soluble organic matter are mixed under stirring conditions, and then the hydrothermal reaction product of step (2) is completely immersed in the aqueous solution of water-soluble organic matter, that is, the aqueous solution of water-soluble organic matter completely covers the hydrothermal reaction product.

[0030] According to an embodiment of the present invention, in step (3), after the soaking is completed, the aqueous solution of water-soluble organic matter is removed by filtering, and then dried.

[0031] According to an embodiment of the present invention, in step (3), by immersing the product of the hydrothermal reaction in an aqueous solution of water-soluble organic matter, sufficient mixing of the hydrothermal reaction product of step (2) and the water-soluble organic matter can be achieved, which is beneficial to improving the reaction uniformity of the subsequent condensation reaction (curing reaction). At the same time, the introduction of water-soluble organic matter is also beneficial to obtaining a biomass-based hard carbon composite negative electrode material with a high capacity.

[0032] According to an embodiment of the present invention, in step (4), the mass volume ratio of the dried solid component of step (3) to ethanol is (25-35) g / L, for example, 25 g / L, 26 g / L, 28 g / L, 30 g / L, 32 g / L or 35 g / L. Exemplarily, 25-35 g of the dried solid component of step (3) is added to 1 L of ethanol.

[0033] According to an embodiment of the present invention, in step (4), the mass ratio of the dried solid component of step (3) to the alcohol-soluble thermoplastic phenolic resin is 1:(0.1-0.3), for example, 1:0.1, 1:0.2 or 1:0.3.

[0034] According to an embodiment of the present invention, in step (4), the mass ratio of the graphene to the dried solid component of step (3) is (0.1-0.3):100, for example, 0.1:100, 0.2g:100 or 0.3g:100.

[0035] According to an embodiment of the present invention, in step (4), the heating temperature is 60-100°C, for example, 60°C, 70°C, 80°C, 90°C or 100°C.

[0036] According to an embodiment of the present invention, in step (4), the mixing method of step (4) enables the dried solid components of step (3) (specifically the hydrothermal reaction product of step (2) and the water-soluble organic matter) to be fully and evenly mixed with the alcohol-soluble thermoplastic phenolic resin and graphene, which is beneficial to improving the reaction uniformity of the subsequent condensation reaction (curing reaction).

[0037] According to an embodiment of the present invention, in step (4), the mixing is performed under ultrasonic conditions.

[0038] According to an embodiment of the present invention, in step (4), the alcohol-soluble thermoplastic phenolic resin can be purchased from commercial sources or prepared by methods known in the art.

[0039] According to an embodiment of the present invention, in step (5), the solidified product is a solidified product of a cross-linking reaction between biomass, water-soluble organic matter, alcohol-soluble thermoplastic phenolic resin and graphene.

[0040] According to an embodiment of the present invention, in step (5), the temperature of the curing reaction is 120-180°C, for example, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C or 180°C; the time of the curing reaction is 12-20 hours, for example, 12 hours, 14 hours, 16 hours, 18 hours or 20 hours.

[0041] According to an embodiment of the present invention, in step (5), the curing reaction is carried out in a vacuum drying oven.

[0042] According to an embodiment of the present invention, in step (6), the carbonization treatment is performed under a protective atmosphere, such as nitrogen or argon.

[0043] According to an embodiment of the present invention, in step (6), the temperature of the carbonization treatment is 1000-1500° C., for example, 1000° C., 1100° C., 1200° C., 1300° C. or 1400° C. The time of the carbonization treatment is 1-6 hours, preferably 2-4 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0044] According to an embodiment of the present invention, in step (6), after the carbonization treatment is completed, it is preferably cooled to room temperature in the furnace.

[0045] According to an embodiment of the present invention, in step (6), the product after the carbonization treatment is preferably pulverized to obtain a biomass-based hard carbon composite negative electrode material with a median particle size of 5-8 μm.

[0046] According to an embodiment of the present invention, the water-soluble organic matter can form a closed-pore structure after carbonization, and the existence of the closed-pore structure is beneficial to improving the capacity of the biomass-based hard carbon composite negative electrode material.

[0047] According to an embodiment of the present invention, the carbide formed after carbonization of the alcohol-soluble thermoplastic phenolic resin has good consistency and better short-range order than biomass carbon, and can show a higher first coulombic efficiency, which is beneficial to improving the first coulombic efficiency of biomass-based hard carbon composite negative electrode materials.

[0048] According to an embodiment of the present invention, during the carbonization process, the aromatic rings near the graphene have a strong tendency to grow along the graphene layer, which will cause local graphitization of the hard carbon, reduce the specific surface area of ​​the hard carbon, and help improve the first coulombic efficiency of the biomass-based hard carbon composite negative electrode material.

[0049] The present invention also provides a biomass-based hard carbon composite negative electrode material prepared by the above method.

[0050] According to an embodiment of the present invention, the biomass-based hard carbon composite negative electrode material includes hard carbon and graphene.

[0051] The present invention also provides the use of the above-mentioned biomass-based hard carbon composite negative electrode material, which is used in sodium ion batteries, preferably used to prepare the negative electrode of sodium ion batteries.

[0052] The present invention also provides a negative electrode for a sodium ion battery, wherein the negative electrode comprises the above-mentioned biomass-based hard carbon composite negative electrode material.

[0053] The present invention also provides a sodium ion battery, which comprises the above-mentioned biomass-based hard carbon composite negative electrode material.

[0054] Beneficial effects of the present invention:

[0055] The present invention utilizes sulfuric acid to treat biomass, which can promote the breaking of long-chain cellulose and lignin in the biomass material into short chains; then the material treated with sulfuric acid is subjected to a hydrothermal reaction, and hydroxyl groups are introduced on the surfaces of cellulose and lignin through the hydrothermal reaction. The introduction of hydroxyl groups can improve the uniformity of the condensation reaction between the biomass and the water-soluble organic matter, the aldehyde group of the alcohol-soluble thermoplastic phenolic resin, and the hydroxyl group on the graphene, improve the interface adaptability of the water-soluble organic matter, the alcohol-soluble thermoplastic phenolic resin, the biomass carbon and the graphene, improve the interface composite effect, and generate a carbon precursor with a cross-linked network structure.

[0056] The short-chain cellulose in the carbon precursor is also conducive to inhibiting the directional growth of graphite crystallites, constructing more chaotic graphite microstructures, and inducing the formation of closed pores, which can show higher capacity. The carbonization of water-soluble organic matter can also form closed pores, further improving the capacity of hard carbon. The carbon material formed after carbonization of alcohol-soluble thermoplastic phenolic resin has good consistency and better short-range order than biomass-based carbon, and can show higher first coulombic efficiency. During the carbonization process, the aromatic rings near the graphene have a strong growth arrangement along the graphene layer, which will cause local graphitization of the hard carbon, reduce the specific surface area of ​​the hard carbon, and further improve the first coulombic efficiency of the biomass-based hard carbon composite negative electrode material. DETAILED DESCRIPTION

[0057] The preparation method of the present invention will be described in further detail below in conjunction with specific examples. It should be understood that the following examples are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0058] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0059] Example 1

[0060] (1) 500 g of coconut shells were washed, dried at 80° C., and then preliminarily crushed to obtain 40-mesh particles A;

[0061] (2) 100 g of granular material A is put into 2 L of sulfuric acid aqueous solution (concentration of 63 wt%), heated and stirred at 45° C. for 3 h, then rinsed with deionized water, filtered or centrifuged until the mixed solution is neutral, and then solid-liquid separation is performed. After separation, the solid material is dried at 100° C. to obtain powder B;

[0062] (3) Mixing 100 g of powder B prepared in step (2) with 1500 g of water and subjecting the mixture to a hydrothermal reaction at 140° C. for 6 h to obtain powder C;

[0063] (4) soaking 100 g of powder C obtained in step (3) in 2 L of an aqueous solution of carboxymethyl starch (with a concentration of 35 wt%) and drying the solution to obtain powder D;

[0064] (5) dispersing 100 g of powder D obtained in step (4) in 4 L of anhydrous ethanol and stirring the mixture evenly, adding 30 g of alcohol-soluble thermoplastic phenolic resin and stirring the mixture thoroughly, and then adding 0.3 g of graphene. After ultrasonic dispersion, the mixture is continuously stirred at 60° C. until the ethanol is completely evaporated, thereby obtaining a mixture;

[0065] (6) placing the mixture of step (5) in a vacuum drying oven and heating at 150° C. for 20 hours to obtain a cured product;

[0066] (7) The solidified product of step (6) is subjected to high-temperature carbonization at 1200° C. for 3 h, cooled to room temperature, and crushed to obtain a biomass-based hard carbon composite negative electrode material.

[0067] Example 2

[0068] (1) 500 g of litchi wood was washed, dried at 100° C., and then preliminarily crushed to obtain 30-mesh particles A;

[0069] (2) 100 g of granular material A is added to 1.8 L of sulfuric acid aqueous solution (concentration of 62 wt%), heated and stirred at 45° C. for 1 h, then rinsed with deionized water, filtered or centrifuged until the mixed solution is neutral, and then solid-liquid separation is performed. After separation, the solid material is dried at 100° C. to obtain powder B;

[0070] (3) 100 g of powder B prepared in step (2) was mixed with 1600 g of water and subjected to hydrothermal reaction at 150° C. for 6 h to obtain powder C;

[0071] (4) 100 g of powder C prepared in step (3) was soaked in 3 L of an aqueous solution of acetic acid starch (with a concentration of 42 wt%) and then dried to obtain powder D;

[0072] (5) dispersing 100 g of powder D obtained in step (4) in 3.8 L of anhydrous ethanol and stirring the mixture, adding 24 g of an alcohol-soluble thermoplastic phenolic resin and stirring the mixture thoroughly, and then adding 0.2 g of graphene. After ultrasonic dispersion, the mixture is continuously stirred at 80° C. until the ethanol is completely evaporated, thereby obtaining a mixture;

[0073] (6) placing the mixture of step (5) in a vacuum drying oven and heating at 130° C. for a curing reaction for 18 hours to obtain a cured product;

[0074] (7) The solidified product of step (6) is subjected to high-temperature carbonization at 1400° C. for 2 h, cooled to room temperature, and crushed to obtain a biomass-based hard carbon composite negative electrode material.

[0075] Example 3

[0076] (1) 500 g of bamboo was washed, dried at 80° C., and then preliminarily crushed to obtain 50-mesh particles A;

[0077] (2) 100 g of granular material A is put into 2.2 L of sulfuric acid aqueous solution (concentration of 60 wt%), heated and stirred at 48° C. for 1.5 h, then rinsed with deionized water, filtered or centrifuged until the mixed solution is neutral, and then solid-liquid separation is performed. After separation, the solid material is dried at 70° C. to obtain powder B;

[0078] (3) 100 g of powder B prepared in step (2) was mixed with 1400 g of water and subjected to hydrothermal reaction at 160° C. for 4 h to prepare powder C;

[0079] (4) soaking 100 g of powder C obtained in step (3) in 2 L of an aqueous solution of carboxymethyl starch (with a concentration of 35 wt%) and drying the solution to obtain powder D;

[0080] (5) dispersing 100 g of powder D obtained in step (4) in 3.5 L of anhydrous ethanol and stirring the mixture, adding 12 g of an alcohol-soluble thermoplastic phenolic resin and stirring the mixture thoroughly, and then adding 0.15 g of graphene. After ultrasonic dispersion, the mixture is continuously stirred at 60° C. until the ethanol is completely evaporated, thereby obtaining a mixture;

[0081] (6) placing the mixture of step (5) in a vacuum drying oven and heating at 150° C. for 24 hours to obtain a cured product;

[0082] (7) The solidified product of step (6) is subjected to high-temperature carbonization at 1300° C. for 3 h, cooled to room temperature, and crushed to obtain a biomass-based hard carbon composite negative electrode material.

[0083] Example 4

[0084] (1) 500 g of straw was washed, dried at 80°C, and then preliminarily crushed to obtain 40-mesh particles A;

[0085] (2) 100 g of granular material A is put into 2.2 L of sulfuric acid aqueous solution (concentration of 63 wt%), heated and stirred at 45° C. for 1 h, then rinsed with deionized water, filtered or centrifuged until the mixed solution is neutral, and then solid-liquid separation is performed. After separation, the solid material is dried at 100° C. to obtain powder B;

[0086] (3) 100 g of powder B prepared in step (2) was mixed with 1800 g of water and subjected to hydrothermal reaction at 140° C. for 6 h to obtain powder C;

[0087] (4) soaking 100 g of powder C in step (3) in 2 L of an aqueous solution of carboxymethyl starch (with a concentration of 42 wt%) and drying the solution to obtain powder D;

[0088] (5) dispersing 100 g of powder D obtained in step (4) in 4 L of anhydrous ethanol and stirring the mixture uniformly, adding 24 g of alcohol-soluble thermoplastic phenolic resin and stirring the mixture thoroughly, and then adding 0.22 g of graphene, and stirring the mixture continuously at 60° C. after ultrasonic dispersion until the ethanol is completely evaporated to obtain a mixture;

[0089] (6) placing the mixture of step (5) in a vacuum drying oven and heating at 150° C. for 24 hours to obtain a cured product;

[0090] (7) The solidified product of step (6) is subjected to high-temperature carbonization at 1200° C. for 3 h, cooled to room temperature, and crushed to obtain a biomass-based hard carbon composite negative electrode material.

[0091] Comparative Example 1

[0092] (1) 500 g of coconut shells were washed, dried at 80° C., and then preliminarily crushed to obtain 40-mesh particles A;

[0093] (2) 100 g of the granular material A prepared in step (1) was mixed with 1500 g of water and subjected to a hydrothermal reaction at 140° C. for 6 h to prepare a powder C;

[0094] (3) 100 g of powder C prepared in step (2) was soaked in 2 L of an aqueous solution of carboxymethyl starch (with a concentration of 35 wt%) and then dried to obtain powder D;

[0095] (4) dispersing 100 g of powder D obtained in step (3) in 4 L of anhydrous ethanol and stirring the mixture evenly, adding 30 g of alcohol-soluble thermoplastic phenolic resin and stirring the mixture thoroughly, and then adding 0.3 g of graphene, and stirring the mixture continuously at 60° C. after ultrasonic dispersion until the ethanol is completely evaporated to obtain a mixture;

[0096] (5) placing the mixture of step (4) in a vacuum drying oven and heating at 150° C. for 20 hours to obtain a cured product;

[0097] (6) The solidified product of step (5) is subjected to high-temperature carbonization at 1200° C. for 3 h, cooled to room temperature, and crushed to obtain a biomass-based hard carbon composite negative electrode material.

[0098] Comparative Example 2

[0099] (1) 500 g of coconut shells were washed, dried at 80° C., and then preliminarily crushed to obtain 40-mesh particles A;

[0100] (2) 100 g of granular material A is put into 2 L of sulfuric acid aqueous solution (concentration of 63 wt%), heated and stirred at 45° C. for 3 h, then rinsed with deionized water, filtered or centrifuged until the mixed solution is neutral, and then solid-liquid separation is performed. After separation, the solid material is dried at 100° C. to obtain powder B;

[0101] (3) 100 g of powder B prepared in step (2) was soaked in 2 L of an aqueous solution of carboxymethyl starch (with a concentration of 35 wt%) and then dried to obtain powder D;

[0102] (4) dispersing 100 g of powder D obtained in step (3) in 4 L of anhydrous ethanol and stirring the mixture evenly, adding 30 g of alcohol-soluble thermoplastic phenolic resin and stirring the mixture thoroughly, and then adding 0.3 g of graphene, and stirring the mixture continuously at 60° C. after ultrasonic dispersion until the ethanol is completely evaporated to obtain a mixture;

[0103] (5) placing the mixture of step (4) in a vacuum drying oven and heating at 150° C. for 20 hours to obtain a cured product;

[0104] (6) The solidified product of step (5) is subjected to high-temperature carbonization at 1200° C. for 3 h, cooled to room temperature, and crushed to obtain a biomass-based hard carbon composite negative electrode material.

[0105] Comparative Example 3

[0106] (1) 500 g of coconut shells were washed, dried at 80° C., and then preliminarily crushed to obtain 40-mesh particles A;

[0107] (2) 100 g of granular material A is put into 2 L of sulfuric acid aqueous solution (concentration of 63 wt%), heated and stirred at 45° C. for 3 h, then rinsed with deionized water, filtered or centrifuged until the mixed solution is neutral, and then solid-liquid separation is performed. After separation, the solid material is dried at 100° C. to obtain powder B;

[0108] (3) Mixing 100 g of powder B prepared in step (2) with 1500 g of water and subjecting the mixture to a hydrothermal reaction at 140° C. for 6 h to obtain powder C;

[0109] (4) soaking 100 g of powder C obtained in step (3) in 2 L of an aqueous solution of carboxymethyl starch (with a concentration of 35 wt%) and drying the solution to obtain powder D;

[0110] (5) dispersing 100 g of powder C obtained in step (4) in 4 L of anhydrous ethanol and stirring evenly, adding 30 g of alcohol-soluble thermoplastic phenolic resin and stirring thoroughly, and then ultrasonically dispersing and continuously stirring at 60° C. until the ethanol is completely evaporated to obtain a mixture;

[0111] (6) placing the mixture of step (5) in a vacuum drying oven and heating at 150° C. for 20 hours to obtain a cured product;

[0112] (7) The solidified product of step (6) is subjected to high-temperature carbonization at 1200° C. for 3 h, cooled to room temperature, and crushed to obtain a biomass-based hard carbon composite negative electrode material.

[0113] The biomass-based hard carbon composite negative electrode material prepared in the above examples and comparative examples was used as the negative electrode material of the sodium ion battery, and the electrochemical performance test was performed as follows:

[0114] The biomass-based hard carbon composite negative electrode material, conductive agent Super P, binder sodium carboxymethyl cellulose (CMC) and aqueous binder (SBR) of the above examples were weighed in a mass ratio of 95:2:1.5:1.5, and after being fully ground in an agate mortar, a small amount of deionized water was added to mix to form a uniform black paste slurry. The slurries were coated on a copper foil current collector as a test electrode, and a metal sodium sheet was used as a reference electrode to assemble into a button cell. The electrolyte was 1M sodium hexafluorophosphate dissolved in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. 5wt.% of fluoroethylene carbonate (FEC) was added to the electrolyte as an additive, glass fiber was used as a separator, and CR2032 stainless steel was used as a battery casing to assemble into a button cell, and the capacity and first coulombic efficiency were tested at a constant rate of 0.1C in a voltage range of 0.01-3.0V.

[0115] The biomass-based hard carbon composite negative electrode material prepared in the embodiment and the comparative example was used as the negative electrode, the sodium ion battery layered oxide was used as the positive electrode, and 1M-NaPF6+EC:DEC:DMC (volume ratio 1:1:1) solution was used as the electrolyte to assemble a full battery in a stacked manner. The room temperature charge and discharge test was carried out at a rate of 1C with a voltage range of 1.5-3.9V to test the cycle performance.

[0116] Table 1 Electrochemical performance of biomass-based hard carbon composite anode materials

[0117]

[0118] It can be seen from Table 1 that the biomass-based hard carbon composite negative electrode material prepared by the present invention has good high capacity, first coulombic efficiency and cycle performance.

[0119] Comparative Example 1 did not use sulfuric acid to treat the biomass, and the long-chain cellulose and lignin in the biomass were not destroyed, resulting in a high degree of graphitization in the pyrolytic carbon and a low content of closed pores, causing the capacity of the prepared biomass-based hard carbon composite negative electrode material to be greatly reduced.

[0120] In Comparative Example 2, no hydrothermal reaction was performed and no hydroxyl groups were introduced into the biomass, resulting in a lower content of closed pores formed in the pyrolyzed carbon, causing the capacity of the biomass-based hard carbon composite negative electrode material to be reduced; and the biomass, water-soluble organic matter and phenolic resin were not uniformly cured, resulting in a reduction in the cycle performance of the biomass-based hard carbon composite negative electrode material.

[0121] In Comparative Example 3, graphene was not added, and the hard carbon generated during the carbonization process had a high degree of disorder, resulting in a decrease in the first-effect coulombic efficiency of the prepared biomass-based hard carbon composite negative electrode material.

[0122] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a biomass-based hard carbon composite negative electrode material, wherein: The preparation method comprises the following steps: (1) mixing the biomass with a sulfuric acid aqueous solution, heating and stirring, filtering, and washing with water until neutral to obtain a pretreated product; (2) mixing the pretreated product of step (1) with water to perform a hydrothermal reaction to obtain a hydrothermal reaction product; (3) mixing, soaking, filtering and drying the hydrothermal reaction product of step (2) and the aqueous solution of water-soluble organic matter to obtain a solid component; (4) mixing the dried solid component of step (3), ethanol, alcohol-soluble thermoplastic phenolic resin and graphene to obtain a mixed solution; stirring the mixed solution under heating conditions until the ethanol is completely volatilized to obtain a solid mixture; (5) subjecting the solid mixture of step (4) to a curing reaction to obtain a cured product; (6) Carbonizing the solidified product of step (5) to prepare the biomass-based hard carbon composite negative electrode material.

2. The method for preparing a biomass-based hard carbon composite negative electrode material according to claim 1, wherein: In step (1), the biomass is at least one of lychee wood, apple wood, poplar wood, bamboo, fruit shell, straw, coconut shell and corn cob; And / or, in step (1), the temperature of the heating and stirring is 40-60° C., for example, 50° C.; the time of the heating and stirring is 1-3 hours; And / or, in step (1), the mass concentration of the aqueous sulfuric acid solution is 60%-65%; the feed ratio of the biomass to the aqueous sulfuric acid solution is (40-60) g / L.

3. The method for preparing a biomass-based hard carbon composite negative electrode material according to claim 1 or 2, wherein: In step (2), the mass ratio of the pretreated product of step (1) to water is 1:(12-20); And / or, in step (2), the temperature of the hydrothermal reaction is 120-160°C; And / or, in step (2), the hydrothermal reaction time is 4-12 hours.

4. The method for preparing a biomass-based hard carbon composite negative electrode material according to any one of claims 1 to 3, wherein: In step (3), the water-soluble organic matter is selected from one or a mixture of carboxymethyl starch, acetic starch, hydroxymethyl cellulose, polyacrylamide, and polyvinyl pyrrolidone; and / or, in step (3), the concentration of the water-soluble organic matter in the aqueous solution of the water-soluble organic matter is 10wt%-50wt%; And / or, in step (3), the feed ratio of the hydrothermal reaction product of step (2) to the aqueous solution of the water-soluble organic matter is (30-50) g / L; And / or, in step (3), the soaking time is 12-24 hours.

5. The method for preparing a biomass-based hard carbon composite negative electrode material according to any one of claims 1 to 4, wherein: In step (4), the mass volume ratio of the dried solid component of step (3) to ethanol is (25-35) g / L; And / or, in step (4), the mass ratio of the dried solid component of step (3) to the alcohol-soluble thermoplastic phenolic resin is 1:(0.1-0.3); And / or, in step (4), the mass of the graphene and the solid component after drying in step (3) is (0.1-0.3):100; And / or, in step (4), the heating temperature is 60-100°C.

6. The method for preparing a biomass-based hard carbon composite negative electrode material according to any one of claims 1 to 5, wherein: In step (5), the solidified product is a solidified product of a cross-linking reaction between biomass, water-soluble organic matter, alcohol-soluble thermoplastic phenolic resin and graphene; And / or, in step (5), the temperature of the curing reaction is 120-180° C.; the time of the curing reaction is 12-20 hours.

7. The method for preparing a biomass-based hard carbon composite negative electrode material according to any one of claims 1 to 6, wherein: In step (6), the carbonization treatment is carried out under a protective atmosphere, and the protective atmosphere is nitrogen or argon; And / or, in step (6), the temperature of the carbonization treatment is 1000-1500° C.; the time of the carbonization treatment is 1-6 hours; And / or, in step (6), the product after carbonization is pulverized to obtain a biomass-based hard carbon composite negative electrode material with a median particle size of 5-8 μm.

8. The biomass-based hard carbon composite negative electrode material prepared by the method according to any one of claims 1 to 7. Preferably, the biomass-based hard carbon composite negative electrode material comprises hard carbon and graphene.

9. A negative electrode for a sodium ion battery, the negative electrode comprising the biomass-based hard carbon composite negative electrode material according to claim 8.

10. A sodium ion battery, comprising the biomass-based hard carbon composite negative electrode material according to claim 8.

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