A high-capacity, high-compaction biomass-based hard carbon composite negative electrode material, a preparation method and application thereof

Abstract

The application provides a high-capacity and high-compaction biomass-based hard carbon composite negative electrode material and a preparation method and application thereof. Biomass is treated with sulfuric acid to promote the breaking of long-chain cellulose, lignin and the like in the biomass material into short chains, reduce the graphitization degree of pyrolysis carbon, and increase the closed pore content of the pyrolysis carbon. Subsequently, ball milling treatment is used to enhance the destruction of the pre-carbonization precursor, introduce local structural defects or shear orientation on the surface of the pre-carbonization precursor, and prepare hard carbon with high closed pore content and high defect active sites after carbonization treatment of the pre-carbonization precursor, thereby effectively improving the capacity of the biomass-based hard carbon composite negative electrode material. The biomass-based hard carbon composite negative electrode material can have high capacity and high compaction density, and also has excellent first coulombic efficiency and cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode materials for sodium ion batteries, and particularly relates to a biomass-based hard carbon composite negative electrode material with high capacity and high compaction, and a preparation method and application thereof. BACKGROUND

[0002] The content of lithium element in the earth's crust is limited, which cannot meet the demand of large-scale application of lithium ion batteries. Sodium element resources are abundant and evenly distributed, and sodium ion batteries have become the focus of attention of the scientific and industrial communities. Hard carbon, as an amorphous carbon, has a larger interlayer spacing than graphite, and the disordered structure of hard carbon provides more defects, vacancies and more sodium storage sites, so it is the most promising industrialized negative electrode material for sodium ion batteries.

[0003] Biomass is the preferred raw material for preparing hard carbon due to its environmental friendliness and low cost. However, the existing biomass-based hard carbon negative electrode material has low capacity and low compaction density (only 1.0 g / cm 3 ), which leads to a low energy density of the obtained sodium ion battery. Therefore, it is particularly urgent to improve the capacity and compaction density of the biomass-based hard carbon composite negative electrode material. SUMMARY

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

[0005] The purpose of the application is achieved by the following technical solutions:

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

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

[0008] (2) performing a pre-carbonization treatment on the pretreated product of step (1) under a nitrogen atmosphere to obtain a pre-carbonization precursor;

[0009] (3) performing a ball milling treatment on the pre-carbonization precursor of step (2), and then performing a carbonization treatment under a nitrogen atmosphere to obtain hard carbon particles;

[0010] (4) Put the pitch into a reaction kettle and heat to 120-160℃, then add SnCl4 under stirring, react for 0.5-1 hour, then introduce argon into the reaction kettle, continue to heat to 330-390℃ under argon protection, and keep for 2-6 hours to obtain the modified pitch;

[0011] (5) Mix the modified pitch of step (4) with the hard carbon particles of step (3) to perform secondary granulation reaction;

[0012] (6) Perform carbonization treatment on the reaction product of step (5) under nitrogen atmosphere to obtain the biomass-based hard carbon composite negative electrode material.

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

[0014] According to the embodiment of the present application, in step (1), the biomass is preferably cleaned biomass, for example, the biomass raw material is cleaned using water to remove impurity components therein; and the cleaned biomass is dried, for example, dried at 60-120℃ for 8-12 hours.

[0015] According to the embodiment of the present application, in step (1), in the process of mixing the biomass with the sulfuric acid aqueous solution, the sulfuric acid can break long-chain cellulose and lignin components in the biomass into short chains, reduce the degree of graphitization of the pyrolytic carbon, and at the same time, can also improve the closed pore content of the pyrolytic carbon, which is beneficial to obtain the biomass-based hard carbon composite negative electrode material with high capacity.

[0016] According to the embodiment of the present application, in step (1), in order to make the biomass fully contact with the sulfuric acid and make as many long-chain cellulose and lignin components in the biomass as possible to break into short chains, the biomass is preferably subjected to crushing treatment, for example, the cleaned and dried biomass is sent into a crusher to perform crushing treatment to obtain biomass particles with 16-60 meshes.

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

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

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

[0020] According to an embodiment of the present application, in step (2), the temperature of the pre-carbonization treatment is 300-500℃, for example, 300℃, 350℃, 400℃, 450℃ or 500℃; the time of the pre-carbonization is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0021] According to an embodiment of the present application, in step (2), after the pre-carbonization treatment, the product is preferably cooled to room temperature in the furnace.

[0022] According to an embodiment of the present application, in step (2), the pre-carbonization treatment can effectively remove low-melting-point volatile substances in the biomass, and thus the treatment is beneficial to obtaining a biomass-based hard carbon composite negative electrode material with high capacity and high compactness.

[0023] According to an embodiment of the present application, in step (2), the product obtained after the pre-carbonization treatment is preferably subjected to a crushing treatment to obtain a pre-carbonization precursor with a median particle size of 5-8 μm. The crushing treatment is beneficial to the ball milling process, and can ensure the sufficient destruction of the pre-carbonization precursor in the ball milling process and the introduction of local structural defects or shear orientation on the surface of the pre-carbonization precursor.

[0024] According to an embodiment of the present application, in step (3), the rotation speed of the ball milling treatment is 400-900 revolutions per minute, for example, 400 revolutions per minute, 500 revolutions per minute, 600 revolutions per minute, 700 revolutions per minute, 800 revolutions per minute or 900 revolutions per minute; the time of the ball milling treatment is 1-8 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0025] According to an embodiment of the present application, in step (3), the temperature of the carbonization treatment is 1200-1600℃, for example, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃ or 1600℃; the time of the carbonization is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0026] According to an embodiment of the present application, in step (3), after the carbonization treatment, the product is preferably cooled to room temperature in the furnace.

[0027] According to an embodiment of the present application, in step (3), the median particle size of the hard carbon particles is 3-5 μm, for example 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0028] According to an embodiment of the present application, in step (3), the ball milling treatment can enhance the damage to the pre-carbonized precursor, and introduce local structural defects or shear orientation on the surface of the pre-carbonized precursor, so that the pre-carbonized precursor can be carbonized to prepare hard carbon particles with more closed pores and more defect active sites, which is beneficial to improve the capacity of the biomass-based hard carbon composite negative electrode material.

[0029] According to an embodiment of the present application, in step (4), the softening point of the pitch is 65-75℃, for example 65℃, 70℃ or 75℃.

[0030] According to an embodiment of the present application, in step (4), the content of water in the pitch is 2-3 wt%, for example 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt% or 3 wt%.

[0031] According to an embodiment of the present application, in step (4), during the reaction, the SnCl4 reacts with water in the pitch to generate nano-SnO2 particles, and the generated nano-SnO2 particles are uniformly distributed in the pitch to prepare the modified pitch. The in-situ synthesis method of nano-SnO2 particles of the present application can make the nano-SnO2 particles uniformly distributed in the pitch, and in the subsequent carbonization process, the nano-SnO2 is reduced to metal Sn and uniformly distributed in the amorphous carbon after carbonization of the pitch, and the amorphous carbon exists on the surface of the hard carbon particles, which is beneficial to improve the compaction density of the hard carbon composite negative electrode material; at the same time, the introduction of metal Sn can also improve the capacity of the biomass-based hard carbon composite negative electrode material.

[0032] According to an embodiment of the present application, in step (4), the softening point of the modified pitch is 100-150℃, for example 100℃, 110℃, 120℃, 130℃, 140℃ or 150℃.

[0033] According to an embodiment of the present application, in step (4), the mass ratio of SnCl4 to pitch is (2-12):100, for example 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100 or 12:100.

[0034] Exemplarily, the pitch is put into a reaction kettle and heated to 120℃, 130℃, 140℃, 150℃ or 160℃. At this temperature, the reaction is carried out for 0.5-1 hour, SnCl4 reacts with water in the pitch to generate nano SnO2 particles, and the generated nano SnO2 particles are uniformly distributed in the pitch.

[0035] Exemplarily, the heating is continued under argon protection to 330℃, 340℃, 350℃, 360℃, 370℃, 380℃ or 390℃. At this temperature, the reaction is carried out for 2-6 hours, the pitch in the system can be polymerized, which can greatly improve the softening point of the pitch, which is beneficial to obtaining a carbonized product with high residual carbon value after carbonization, thereby improving the stability of the secondary particle structure of the biomass-based hard carbon composite negative electrode material.

[0036] According to the embodiment of the present application, in step (5), the secondary granulation reaction is carried out in a granulation kettle.

[0037] According to the embodiment of the present application, in step (5), the secondary granulation reaction can realize the secondary granulation of the hard carbon particles, and realize the preparation of the biomass-based hard carbon composite negative electrode material with a secondary particle structure; specifically, in the reaction process, the modified pitch can be uniformly coated on the surface of the single-particle hard carbon particles with a small particle size (D 50 3-5 μm), and the single-particle hard carbon particles with a small particle size are bonded together to obtain the biomass-based hard carbon composite negative electrode material with a secondary particle structure of the amorphous carbon layer coated on the surface of the single particle.

[0038] According to the embodiment of the present application, in step (5), the mass ratio of the modified pitch to the hard carbon particles is (8-15):100, for example, 8:100, 9:100, 10:100, 11:100, 12:100, 13:100, 14:100 or 15:100.

[0039] According to the embodiment of the present application, in step (5), the temperature of the reaction is 450-650℃, for example, 450℃, 500℃, 550℃, 600℃ or 650℃; and the time of the reaction is 2-8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0040] According to the embodiment of the present application, in step (5), after the reaction treatment is completed, the cooling to room temperature is preferably carried out with the furnace.

[0041] According to the embodiment of the present application, in step (6), the temperature of the carbonization treatment is 800-1000℃, for example, 800℃, 850℃, 900℃, 950℃ or 1000℃; and the time of the carbonization is 2-6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0042] According to an embodiment of the present application, in step (6), after the carbonization treatment, the carbonized biomass is preferably cooled down to room temperature in the furnace.

[0043] The present application also provides a biomass-based hard carbon composite negative electrode material prepared by the above method.

[0044] According to an embodiment of the present application, the biomass-based hard carbon composite negative electrode material comprises hard carbon, nano-Sn particles and amorphous carbon.

[0045] According to an embodiment of the present application, the biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles and amorphous carbon.

[0046] According to an embodiment of the present application, the nano-Sn particles are distributed in the amorphous carbon.

[0047] According to an embodiment of the present application, the biomass-based hard carbon composite negative electrode material has a secondary particle structure, and the amorphous carbon binds the small particle size (D 50 hard carbon into a biomass-based hard carbon composite negative electrode material having a secondary particle structure (D 50 of 8-12 μm.

[0048] According to an embodiment of the present application, the median particle size of the nano-Sn particles is 25-35 nm, for example 30 nm.

[0049] According to an embodiment of the present application, the median particle size of the biomass-based hard carbon composite negative electrode material is 8-12 μm.

[0050] According to an embodiment of the present application, the median particle size of the hard carbon is 3-5 μm.

[0051] The present application also provides the use of the above biomass-based hard carbon composite negative electrode material for a sodium-ion battery, preferably for preparing a negative electrode of a sodium-ion battery.

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

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

[0054] The present application has the following advantages:

[0055] The application can promote the breaking of long-chain cellulose, lignin and the like in the biomass material into short chains by using sulfuric acid treatment, reduce the degree of graphitization of pyrolysis carbon, and increase the closed pore content of pyrolysis carbon; then, the damage to the pre-carbonized precursor is enhanced by ball milling treatment, so that local structural defects or shear orientation are introduced on the surface of the pre-carbonized precursor, and the pre-carbonized precursor can be carbonized to prepare hard carbon with more closed pores and more defect active sites, thereby effectively improving the capacity of the biomass-based hard carbon composite negative electrode material.

[0056] The application also uses modified asphalt containing tin dioxide, and coats the modified asphalt on the surface of single-particle hard carbon with a small particle size (D 50 The application also uses modified asphalt containing tin dioxide, and coats the modified asphalt on the surface of single-particle hard carbon with a small particle size (D 50 The application also uses modified asphalt containing tin dioxide, and coats the modified asphalt on the surface of single-particle hard carbon with a small particle size (D 50 The application also uses modified asphalt containing tin dioxide, and coats the modified asphalt on the surface of single-particle hard carbon with a small particle size (D DETAILED DESCRIPTION

[0057] The preparation method of the application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application. Any technology achieved based on the above description of the application is covered within the scope of protection intended by the application.

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

[0059] Example 1

[0060] (1) 100g of coconut shell was cleaned and dried at 70℃, and then preliminarily broken to obtain 50-mesh granular material A;

[0061] (2) 100g of the granular material A was put into 2L of an aqueous sulfuric acid solution (63wt%) and heated and stirred at 45℃ for 3h, then washed with deionized water, filtered or centrifuged until the mixed solution was neutral, then subjected to solid-liquid separation, and the solid material was dried at 100℃ after separation to obtain powder B;

[0062] (3) 100g of the powder B was pre-carbonized at 500℃ for 2h under a nitrogen atmosphere, and after cooling to room temperature, the pre-carbonized precursor was obtained after crushing treatment;

[0063] (4) After high-speed ball milling (500 rpm) of the pre-carbonized precursor for 3 h, carbonization was carried out at 1400 °C under a nitrogen atmosphere for 2 h. After cooling to room temperature, hard carbon particles were obtained;

[0064] (5) 100 g of pitch (softening point 65 °C) was placed in a reaction kettle and heated to 150 °C. Under stirring (500 rpm), 6 g of SnCl4was added to the molten pitch and reacted for 0.5 h. Then, the reaction kettle was sealed and argon was introduced. Stirring was continued and the temperature was increased to 360 °C. The reaction was continued for 5 h to obtain modified pitch (softening point 100 °C);

[0065] (6) 15 g of the modified pitch of step (5) was mixed with 100 g of the hard carbon particles of step (4) to obtain a uniform mixture. The mixture was then stirred in a granulation kettle at 600 °C for 5 h. After cooling to room temperature, carbonization was carried out at 800 °C under a nitrogen atmosphere for 5 h to obtain a biomass-based hard carbon composite negative electrode material.

[0066] The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles and amorphous carbon. The nano-Sn particles are distributed in the amorphous carbon. The biomass-based hard carbon composite negative electrode material has a secondary particle structure. The amorphous carbon binds the small particle size (D 50 3-5 pm) hard carbon into a biomass-based hard carbon composite negative electrode material with a secondary particle structure (D 50 8-12 pm).

[0067] Example 2

[0068] (1) 100 g of litchi wood was washed and dried at 100 °C. After preliminary crushing, 30 mesh granular material A was obtained;

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

[0070] (3) 100 g of powder B was pre-carbonized at 400 °C under a nitrogen atmosphere for 5 h. After cooling to room temperature, the pre-carbonized precursor was obtained after crushing;

[0071] (4) After high-speed ball milling (450 rpm) of the pre-carbonized precursor for 3 h, carbonization was carried out at 1200 °C under a nitrogen atmosphere for 6 h. After cooling to room temperature, hard carbon particles were obtained;

[0072] (5) 100 g of pitch (softening point 70 °C) was put into a reactor and heated to 120 °C, 12 g of SnCl4 was added into the molten pitch under stirring (500 r / min) for 0.5 h, then the reactor was sealed and argon was introduced, the stirring was continued and the temperature was raised to 380 °C for 3 h to obtain modified pitch (softening point 110 °C);

[0073] (6) 10 g of modified pitch of step (5) was mixed with 100 g of hard carbon particles of step (4) uniformly, then the mixture was stirred at 480 °C for 5 h in a granulator, cooled to room temperature, and then carbonized at 900 °C for 5 h under nitrogen atmosphere to obtain biomass-based hard carbon composite negative electrode material.

[0074] The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles and amorphous carbon. The nano-Sn particles are distributed in the amorphous carbon. The biomass-based hard carbon composite negative electrode material has a secondary particle structure, and the amorphous carbon binds the small particle size (D 50 3-5 μm) hard carbon into a biomass-based hard carbon composite negative electrode material with a secondary particle structure (D 50 8-12 μm).

[0075] Example 3

[0076] (1) 100 g of bamboo was washed and dried at 80 °C, and then preliminarily broken to obtain 50 mesh granular material A;

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

[0078] (3) 100 g of powder B was pre-carbonized at 500 °C for 3 h under nitrogen atmosphere, and then cooled to room temperature, crushed and treated to obtain pre-carbonized precursor;

[0079] (4) The pre-carbonized precursor was high-speed ball milled (550 revolutions per minute) for 6 h, and then carbonized at 1350 °C for 4 h under nitrogen atmosphere, and then cooled to room temperature to obtain hard carbon particles;

[0080] (5) 100 g of pitch (softening point 72 °C) was put into a reactor and heated to 140 °C, 10 g of SnCl4 was added into the molten pitch under stirring (500 r / min) for 0.5 h, then the reactor was sealed and argon was introduced, the stirring was continued and the temperature was raised to 380 °C for 3 h to obtain modified pitch (softening point 135 °C);

[0081] (6) 8 g of the modified pitch of step (5) is mixed with 100 g of the hard carbon particles of step (4) uniformly, and then stirred and reacted at 600°C for 5 hours in a granulation kettle, cooled to room temperature; then carbonized at 900°C for 5 hours under a nitrogen atmosphere, cooled to room temperature, to obtain a biomass-based hard carbon composite negative electrode material.

[0082] The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles, and amorphous carbon. The nano-Sn particles are distributed in the amorphous carbon. The biomass-based hard carbon composite negative electrode material has a secondary particle structure, and the amorphous carbon binds the small particle diameter (D 50 3-5 μm) hard carbon into a biomass-based hard carbon composite negative electrode material with a secondary particle structure (D 50 8-12 μm).

[0083] Example 4

[0084] (1) 100 g of straw is washed and dried at 80°C, and then preliminarily broken to obtain 40-mesh granular material A;

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

[0086] (3) 100 g of the powder B is pre-carbonized at 500°C for 3 h under a nitrogen atmosphere, and then cooled to room temperature. After crushing, a pre-carbonized precursor is obtained;

[0087] (4) The pre-carbonized precursor is high-speed ball milled (650 revolutions per minute) for 4 h, and then carbonized at 1400°C for 4 h under a nitrogen atmosphere. After cooling to room temperature, hard carbon particles are obtained;

[0088] (5) 100 g of pitch (softening point 75°C) is put into a reaction kettle and heated to 140°C. Under stirring conditions (500 r / min), 12 g of SnCl4 is added to the molten pitch and reacted for 0.5 h. Then the reaction kettle is sealed and argon is introduced. The stirring is continued, and the temperature is increased to 360°C. The reaction is continued for 6 h to obtain modified pitch (softening point 150°C);

[0089] (6) 8 g of the modified pitch of step (5) is mixed with 100 g of the hard carbon particles of step (4) uniformly, and then stirred and reacted at 600°C for 5 hours in a granulation kettle, cooled to room temperature; then carbonized at 900°C for 5 hours under a nitrogen atmosphere, cooled to room temperature, to obtain a biomass-based hard carbon composite negative electrode material.

[0090] The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles and amorphous carbon. The nano-Sn particles are distributed in the amorphous carbon. The biomass-based hard carbon composite negative electrode material has a secondary particle structure, and the amorphous carbon binds the small particle size (D 50 is 3-5 μm) hard carbon into a secondary particle structure (D 50 is 8-12 μm) biomass-based hard carbon composite negative electrode material.

[0091] Comparative Example 1

[0092] (1) 200 g of coconut shell was washed and dried at 70°C, and after drying, preliminary crushing was performed to obtain 50 mesh granular material A;

[0093] (2) 100 g of granular material A was pre-carbonized at 500°C for 2 h under a nitrogen atmosphere, and after cooling to room temperature, crushing treatment was performed to obtain a pre-carbonized precursor;

[0094] (3) The pre-carbonized precursor was high-speed ball milled (500 rpm) for 3 h, and after cooling to room temperature, carbonization was performed at 1400°C for 2 h under a nitrogen atmosphere to obtain hard carbon particles (D 50 is 3-5 μm);

[0095] (4) 100 g of pitch (softening point 65°C) was placed in a reaction kettle and heated to 150°C, and under stirring conditions (500 r / min), 6 g of SnCl4 was added to the molten pitch and reacted for 0.5 h, and then the reaction kettle was sealed and argon was introduced, and stirring was continued, and the temperature was increased to 360°C and the reaction was continued for 5 h to obtain modified pitch (softening point 90°C);

[0096] (5) 15 g of the modified pitch of step (4) was uniformly mixed with 100 g of the hard carbon particles of step (3), and then granulation was performed in a granulation kettle at 600°C for 5 h under stirring, and after cooling to room temperature, carbonization was performed at 800°C for 5 h under a nitrogen atmosphere to obtain a biomass-based hard carbon composite negative electrode material.

[0097] The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles and amorphous carbon. The nano-Sn particles are distributed in the amorphous carbon. The biomass-based hard carbon composite negative electrode material has a secondary particle structure, and the amorphous carbon binds the small particle size (D 50 is 3-5 μm) hard carbon into a secondary particle structure (D 50 is 8-12 μm) biomass-based hard carbon composite negative electrode material.

[0098] Comparative Example 2

[0099] (1) 100 g of coconut shell was washed and dried at 70°C, and after drying, preliminary crushing was performed to obtain 50 mesh granular material A;

[0100] (2) 100 g of the granular material A was put into 2 L of an aqueous sulfuric acid solution (63 wt%) and stirred at 45°C for 3 h, then washed with deionized water, suction filtered or centrifuged until the mixture was neutral, then subjected to solid-liquid separation, and the solid material was dried at 100°C after the separation to obtain powder B;

[0101] (3) 100 g of the powder B was pre-carbonized at 500°C for 2 h under a nitrogen atmosphere, and after cooling to room temperature, the pre-carbonized precursor (D 50 with a particle size of 3-5 μm) was obtained after crushing;

[0102] (4) The pre-carbonized precursor was carbonized at 1400°C for 2 h under a nitrogen atmosphere, and after cooling to room temperature, hard carbon particles were obtained;

[0103] (5) 100 g of pitch (softening point 65°C) was put into a reaction kettle and heated to 150°C, and 6 g of SnCl4 was added to the molten pitch under stirring (500 r / min) for 0.5 h, then the reaction kettle was sealed and argon was introduced, and the stirring was continued to heat to 360°C for 5 h to obtain modified pitch (softening point 90°C);

[0104] (6) 15 g of the modified pitch of step (5) was uniformly mixed with 100 g of the hard carbon particles of step (4), and then stirred at 600°C for 5 h in a granulation kettle, and cooled to room temperature; then carbonized at 800°C for 5 h under a nitrogen atmosphere, and cooled to room temperature to obtain a biomass-based hard carbon composite negative electrode material.

[0105] The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles and amorphous carbon. The nano-Sn particles are distributed in the amorphous carbon. The biomass-based hard carbon composite negative electrode material has a secondary particle structure, and the amorphous carbon binds the hard carbon with a small particle size (D 50 of 3-5 μm) into a biomass-based hard carbon composite negative electrode material (D 50 of 8-12 μm) with a secondary particle structure.

[0106] Comparative Example 3

[0107] (1) 100 g of coconut shell was washed and dried at 70°C, and after drying, it was preliminarily crushed to obtain 50-mesh granular material A;

[0108] (2) 100 g of the granular material A was put into 2 L of an aqueous sulfuric acid solution (63 wt%) and stirred at 45°C for 3 h, then washed with deionized water, suction filtered or centrifuged until the mixture was neutral, then subjected to solid-liquid separation, and the solid material was dried at 100°C after the separation to obtain powder B;

[0109] (3) 100 g of the powder B was pre-carbonized at 500°C for 2 h under nitrogen atmosphere, and after cooling to room temperature, the pre-carbonized precursor was obtained by crushing treatment;

[0110] (4) After high-speed ball milling (500 rpm) of the pre-carbonized precursor for 3 h, the hard carbon particles (D 50 with a particle size of 8-12 μm) were obtained by carbonization at 1400°C for 2 h under nitrogen atmosphere, and after cooling to room temperature;

[0111] (5) 100 g of pitch (softening point 65°C) was put into a reaction kettle and heated to 150°C, and 6 g of SnCl4 was added into the molten pitch under stirring (500 r / min) for 0.5 h, then the reaction kettle was sealed and argon was introduced, and the stirring was continued, and the temperature was increased to 360°C for 5 h to obtain modified pitch (softening point 100°C);

[0112] (6) 15 g of the modified pitch of step (5) was mixed with 100 g of the hard carbon particles of step (4) to obtain a biomass-based hard carbon composite negative electrode material (D 50 with a particle size of 8-12 μm) by carbonization at 800°C for 5 h under nitrogen atmosphere, and after cooling to room temperature, the biomass-based hard carbon composite negative electrode material was obtained by dispersing.

[0113] The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles and amorphous carbon. The nano-Sn particles are distributed in the amorphous carbon. The amorphous carbon is coated on the surface of the biomass-based hard carbon composite negative electrode material.

[0114] The biomass-based hard carbon composite negative electrode materials prepared in the above examples 1-4 and comparative examples 1-3 were used as negative electrode materials of sodium ion batteries, and electrochemical performance tests were carried out, and the method was as follows:

[0115] The biomass-based hard carbon composite negative electrode material, the conductive agent Super P, the binder sodium carboxymethyl cellulose (CMC) and the water-based binder (SBR) were weighed in a mass ratio of 95:2:1.5:1.5, and after being ground in a maroon mortar, a small amount of deionized water was added to mix a uniform black paste slurry, and the slurry was coated on a copper foil current collector as a test electrode, and a metal sodium sheet was used as a comparative electrode to assemble a button cell. The electrolyte was 1M sodium hexafluorophosphate dissolved in a volume ratio of 1:1 of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solution, 5wt.% of fluoroethylene carbonate (FEC) was added as an additive, glass fiber was used as a separator, and CR2032 type stainless steel was used as a battery shell to assemble a button cell. The capacity and the first coulombic efficiency were tested at a constant rate of 0.1C in the voltage range of 0.01-3.0V.

[0116] The biomass-based hard carbon composite negative material prepared in the examples and Comparative Examples 1-3 was used as a negative electrode, a nickel-iron-manganese sodium was used as a positive electrode, and a 1M-NaPF6+EC:DEC:DMC (volume ratio 1:1:1) solution was used as an electrolyte to assemble a full cell in a laminated manner. The full cell was subjected to charge-discharge detection at room temperature at a rate of 1C, and the voltage range was 1.5-3.9V. The cycle performance was tested.

[0117] Table 1: Electrochemical performance of biomass-based hard carbon composite negative materials

[0118]

[0119] As can be seen from Table 1, the biomass-based hard carbon composite negative material prepared in the present application has good high capacity, compaction density, first coulombic efficiency, and cycle performance.

[0120] 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, a low amount of closed pores, and a significant reduction in the capacity of the biomass-based hard carbon composite negative material prepared. Comparative Example 2 did not use ball milling treatment, which cannot introduce local structural defects or shear orientation on the surface of the pre-carbonization precursor, and cannot obtain hard carbon with a large amount of closed pores and a large number of defect active sites, thereby reducing the capacity of the biomass-based hard carbon composite negative material. Comparative Example 3 did not perform secondary granulation, which cannot obtain biomass-based hard carbon composite negative material with secondary particle structure, and cannot improve the compaction density and cycle performance of the hard carbon composite negative material.

[0121] The above describes embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

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 biomass with sulfuric acid aqueous solution, heating and stirring, filtering, and washing to neutral to obtain a pretreated product; (2) performing pre-carbonization treatment on the pretreated product of step (1) under a nitrogen atmosphere to obtain a pre-carbonization precursor; (3) performing ball milling treatment on the pre-carbonization precursor of step (2), and then performing carbonization treatment under a nitrogen atmosphere to obtain hard carbon particles; (4) placing pitch into a reaction kettle and heating to 120-160℃, adding SnCl4 under stirring, reacting for 0.5-1 hour, then introducing argon into the reaction kettle, continuously heating to 330-390℃ under argon protection, and keeping for 2-6 hours to obtain modified pitch; (5) mixing the modified pitch of step (4) with the hard carbon particles of step (3) to perform secondary granulation reaction; (6) performing carbonization treatment on the reaction product of step (5) under a nitrogen atmosphere to obtain a biomass-based hard carbon composite negative electrode material.

2. The method for preparing the biomass-based hard carbon composite anode material according to claim 1, wherein, In step (1), the biomass is at least one of litchi wood, apple wood, poplar wood, bamboo, fruit shell, straw, coconut shell, and corn cob; In step (1), the temperature of the heating and stirring is 40-60℃; and the time of the heating and stirring is 1-3 hours. In step (1), the mass concentration of the sulfuric acid aqueous solution is 60%-65%; and the feeding ratio of the biomass to the sulfuric acid aqueous solution is (40-60) g / L.

3. The preparation method of the biomass-based hard carbon composite anode material according to claim 1, wherein, In step (2), the temperature of the pre-carbonization treatment is 300℃-500℃; and the time of the pre-carbonization is 1-6 hours. In step (2), the product obtained after the pre-carbonization treatment is crushed to obtain a pre-carbonization precursor with a median particle size of 5-8 μm.

4. The method for preparing the biomass-based hard carbon composite anode material according to claim 1, wherein, In step (3), the rotating speed of the ball milling treatment is 400-900 revolutions per minute; and the time of the ball milling treatment is 1-8 hours. In step (3), the temperature of the carbonization treatment is 1200℃-1600℃; and the time of the carbonization is 1-6 hours. In step (3), the median particle size of the hard carbon particles is 3-5 μm.

5. The method of producing a biomass-based hard carbon composite negative electrode material according to any one of claims 1 to 4, wherein In step (4), the softening point of the pitch is 65-75℃. In step (4), the content of water in the pitch is 2-3 wt%. In step (4), the mass ratio of SnCl4 to pitch is (2-12):

100.

6. The method of producing a biomass-based hard carbon composite negative electrode material according to any one of claims 1 to 4, wherein In step (5), the mass ratio of the modified pitch to the hard carbon particles is (8-15):

100. In step (5), the temperature of the reaction is 450-650℃; and the time of the reaction is 2-8 hours.

7. The method of producing a biomass-based hard carbon composite negative electrode material according to any one of claims 1 to 4, wherein In step (6), the temperature of the carbonization treatment is 800-1000℃; and the time of the carbonization is 2-6 hours.

8. The biomass-based hard carbon composite negative electrode material prepared by the method of any one of claims 1-7.

9. The biomass-based hard carbon composite anode material of claim 8, wherein, The biomass-based hard carbon composite negative electrode material comprises hard carbon, nano-Sn particles, and amorphous carbon.

10. The biomass-based hard carbon composite anode material of claim 8, wherein, The biomass-based hard carbon composite negative electrode material is a composite of hard carbon, nano-Sn particles, and amorphous carbon.

11. The biomass-based hard carbon composite anode material according to claim 9 or 10, wherein, The nano-Sn particles are distributed in the amorphous carbon.

12. The biomass-based hard carbon composite anode material of claim 9, wherein, The biomass-based hard carbon composite negative electrode material has a secondary particle structure, and the amorphous carbon bonds the hard carbon into the biomass-based hard carbon composite negative electrode material with a secondary particle structure.

13. The biomass-based hard carbon composite anode material of claim 9 or 10, wherein, The median particle size of the nano Sn particles is 25-35 nm; the median particle size of the biomass-based hard carbon composite negative electrode material is 8-12 μm; and the median particle size of the hard carbon is 3-5 μm. 14.A negative electrode for a sodium ion battery, comprising the biomass-based hard carbon composite negative electrode material according to any one of claims 8-13. 15.A sodium ion battery, comprising the biomass-based hard carbon composite negative electrode material according to any one of claims 8-13.

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