Three-dimensional network structure carbon material, preparation method and application thereof
By doping hard carbon materials with phosphorus and nitrogen dopant and conductive agents to form a three-dimensional network structure, the problems of insufficient conductivity and capacity of hard carbon materials in sodium-ion batteries are solved, and the conductivity and energy density of the materials are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2024-03-13
- Publication Date
- 2026-05-12
AI Technical Summary
Existing hard carbon materials used as anode materials for sodium-ion batteries suffer from problems such as low residual carbon content, low specific capacity, low compaction density, poor conductivity, and difficulty in homogenization and dispersion.
A three-dimensional network structure carbon material is used. By doping the hard carbon body with phosphorus and nitrogen-doped porous hard carbon and conductive agent, a glassy carbon coating layer is formed. Combined with high-temperature carbonization treatment, a porous amorphous carbon layer is formed, which optimizes the conductivity and structure of the material.
The material's conductivity, specific capacity, and compaction density were improved, its specific surface area was reduced, and its coating effect was enhanced, resulting in high energy density and good kinetic characteristics for sodium-ion batteries.
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Figure BDA0004738264550000121
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium-ion battery materials, and particularly relates to an amorphous carbon material with a three-dimensional network structure and high electrical conductivity, its preparation method, and its application. Background Technology
[0002] In recent years, lithium-ion batteries have been widely used in many fields such as electronic devices and automobiles due to their advantages such as high energy density, long cycle life, high operating voltage, and no memory effect. However, the shortage of lithium resources has limited the development of lithium-ion batteries.
[0003] Sodium-ion batteries and lithium-ion batteries both belong to the category of rechargeable batteries. They operate on similar principles, and sodium is widely available and inexpensive. The development of sodium-ion batteries can not only mitigate the price fluctuations of raw materials for lithium-ion batteries but also ensure compatibility with existing lithium-ion battery production equipment, thus possessing promising commercial prospects.
[0004] Sodium ions have a larger radius than lithium ions, while graphite has a smaller interlayer spacing. Therefore, commercially available graphite anodes are unsuitable for sodium-ion batteries. Hard carbon materials, with their disordered graphite microcrystalline structure and large interlayer spacing, allow alkali metal ions to enter the graphite interlayers, making them a good choice for sodium-ion battery anode materials. However, using hard carbon as a sodium-ion battery anode material faces several challenges, such as low residual carbon content, low specific capacity, low compaction density, poor conductivity, and difficulty in homogenization and dispersion. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a three-dimensional network structure carbon material, its preparation method and application.
[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:
[0007] A three-dimensional network structure carbon material includes a hard carbon substrate and a glassy carbon coating layer covering the surface of the hard carbon substrate. The hard carbon substrate is a spherical, phosphorus- and nitrogen-doped porous hard carbon with a three-dimensional network framework structure inside. A conductive agent is also doped into the three-dimensional network framework structure of the hard carbon substrate. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin. The conductive agent is at least one of carbon nanotubes, graphene, and acetylene black. More preferably, the conductive agent is graphene.
[0008] Preferably, in the above-mentioned three-dimensional network structure carbon material, the thickness of the glassy carbon coating layer is 0.006–0.12 μm, and the hard carbon body contains 3–8% phosphorus, 5–25% nitrogen, and 1–5% conductive agent by mass.
[0009] Preferably, the three-dimensional network structure carbon material described above has a particle size of 4–20 μm, a pore volume of 0.05–0.10 cc / g, and a specific surface area of 2–5 m². 2 The powder compaction density is above 1.05 g / cm under 5t pressure, and the powder conductivity is 100-400 S / cm measured at 25 MPa.
[0010] In the three-dimensional network carbon material of this invention: the conductivity of the material is improved by incorporating conductive agents and forming a glassy carbon film on the surface; the specific capacity of the material is improved by incorporating phosphorus to form a closed microporous structure, increase the interlayer spacing, and improve the specific capacity of the material; the compaction density of the material is improved by controlling the particles to be spherical; the electronegativity difference is increased by incorporating phosphorus and nitrogen, and at the same time, the phosphorus source and nitrogen source undergo dehydration condensation reactions with the carboxyl and hydroxyl groups in the cellulose molecules, respectively. The phosphorus source and nitrogen source bridge the cellulose, so that the cellulose molecules are connected together or folded to form a three-dimensional network structure. This structure serves as an adsorption site for the conductive agent, ensuring the dispersion and distribution of the conductive agent inside the material, effectively improving the conductivity of the material. Moreover, the pores formed during the folding and connection process of this structure increase the internal defects of the material and provide more adsorption sites; by controlling the particles to be spherical and forming a glassy carbon film on the surface, the specific surface area of the material is reduced and the surface properties of the material are optimized to improve the homogenization and dispersibility.
[0011] As a general inventive concept, the present invention also provides a method for preparing the above-mentioned three-dimensional network structure carbon material, comprising the following steps:
[0012] (1) Plant-derived cellulose is mixed with phosphorus and nitrogen sources, and then heat-treated under inert gas protection to obtain phosphorus and nitrogen-doped network cellulose;
[0013] (2) The phosphorus and nitrogen doped reticulated cellulose, water-soluble sugar and conductive agent are placed in a hydrothermal reactor and deionized water is added to carry out a hydrothermal reaction to obtain pyrolytic carbon balls;
[0014] (3) The pyrolytic carbon balls are pre-carbonized under inert gas protection to obtain porous pyrolytic carbon balls;
[0015] (4) The porous pyrolytic carbon balls, anhydrous ethanol and furan resin are mixed evenly and then dried and carbonized at high temperature under inert gas protection to obtain a three-dimensional network structure carbon material.
[0016] In the above preparation method, preferably, in step (1), the plant-derived cellulose is reed cellulose;
[0017] The phosphorus source is at least one of phosphoric acid, monomethyl phosphate, diammonium hydrogen phosphate, and phytic acid.
[0018] The nitrogen source is at least one of urea, putrescine, and hexamethylenediamine;
[0019] The mass ratio of plant-derived cellulose to phosphorus source is 100:20 to 100:40; the mass ratio of plant-derived cellulose to nitrogen source is 100:80 to 100:100. Within this range, the phosphorus source ensures that it reacts in excess with cellulose. During the subsequent hydrothermal reaction, the excess phosphorus source dissolves in the water and is evenly distributed within the spheres during spheroidization, serving as a pore-forming agent for pore formation during subsequent pre-carbonization. However, excessive phosphorus source is not advisable, otherwise it will lead to excessively large pore sizes, affecting the material's initial efficiency. Excessive nitrogen source is wasteful, while insufficient nitrogen source will affect the reaction.
[0020] More preferably, the phosphorus source is phytic acid, which has a relatively high phosphorus content. Each phytic acid molecule has 6 RP(=O)(OH)2 structures, which form a more complex network structure after esterification with the fiber, increasing the number of internal defects in the material and significantly improving its capacity.
[0021] In the above preparation method, preferably, in step (1), the stirring rate during the mixing process is 200-300 rpm and the stirring time is 0.5-1 h.
[0022] In the above preparation method, preferably, in step (1), the heat treatment includes first heating to 150-170°C at a heating rate of 5-10°C / min, holding at that temperature for 0.5-1h, and then heating to 180-200°C and holding at that temperature for 0.5-1h.
[0023] In the above preparation method, preferably, in step (2), the water-soluble sugar is at least one of sucrose, trehalose, raffinose, mesotriose, and dextrin; since phosphorus sources such as phosphate are oxidizing, choosing these non-reducing sugars can prevent possible side reactions, and at the same time, heating can ensure complete dissolution during the hydrothermal process.
[0024] The mass ratio of phosphorus and nitrogen-doped reticular cellulose to water-soluble sugar is 1:2 to 1:3. The amount of water-soluble sugar added should not be too low, otherwise the reticular cellulose may not be completely wrapped when carbon spheres are formed. The amount of water-soluble sugar added should not be too high, otherwise the proportion of dopant may be reduced, weakening the doping effect.
[0025] The mass ratio of phosphorus and nitrogen-doped reticulated cellulose to conductive agent is 100:1 to 100:3. The amount of conductive agent added should not be too high, as this will reduce the content of hard carbon responsible for providing capacity and affect the material's capacity and other properties. The amount of conductive agent added should not be too low, as this will not significantly improve the conductivity. The mass ratio of phosphorus and nitrogen-doped reticulated cellulose to deionized water is 1:3 to 1:6.
[0026] In the above preparation method, preferably, in step (2), the temperature of the hydrothermal reaction is 200-300°C, the holding time of the hydrothermal reaction is 24-72h, and the filling rate of the hydrothermal reactor is 70%-80% during the hydrothermal reaction.
[0027] In the above preparation method, preferably, in step (3), the pre-carbonization temperature is 400-650℃ and the holding time is 2-6h.
[0028] In the above preparation method, preferably, in step (4), the furan resin is at least one of furfuryl alcohol resin and furfural resin, with a solid content of 55-70% and a residual carbon content of 25-30%.
[0029] The mass ratio of the porous pyrolytic carbon balls to anhydrous ethanol is 1:1.2 to 1:1.5; the mass ratio of the pyrolytic carbon balls to furan resin is 100:2 to 100:6.
[0030] In the above preparation method, preferably, in step (4), the drying temperature is 75-90°C and the drying time is 24-48h.
[0031] In the above preparation method, preferably, in step (4), the high-temperature carbonization includes first heating to 400-650°C at a heating rate of 2-10°C / min, holding for 1-3 hours, and then heating to 1200-1800°C and holding for 2-6 hours.
[0032] In the preparation method of this invention, a compound containing a phosphite group (RP(=O)(OH)2) is used as a phosphorus source, and a compound containing two or more amino groups (R-NH2) is used as a nitrogen source. Reed cellulose contains abundant hydroxyl and carboxyl groups. The phosphorus and nitrogen sources react with reed cellulose in a molten state after heating: the molten nitrogen source acts as a solvent, and the phosphorus source provides an acidic environment. Under acidic conditions, the carboxyl groups in the reed cellulose and the amino groups in the nitrogen source undergo a dehydration condensation reaction to form R2-O-HN-R1-NH-O-R3. The structure, where R1 represents the functional group connecting two nitrogen atoms, and R2 and R3 represent different parts of the same cellulose molecule or two different cellulose molecules, undergoes an esterification reaction upon heating with the hydroxyl groups of the phosphorus source and reed cellulose to form the R2-O-PR4(=O)-O-R3 structure. Here, R4 represents the atom or functional group connecting the phosphorus atom, and R2 and R3 represent different parts of the same cellulose molecule or two different cellulose molecules. The phosphorus and nitrogen sources react to fold, deform, or randomly connect multiple cellulose molecules, forming a three-dimensional structure. The 1D network structure removes excess nitrogen source by subsequent heating to above the boiling point of the nitrogen source, which can then be collected and reused through condensation. During the pretreatment of the hydrothermal reaction, a conductive agent is incorporated into the network fibers through liquid-phase doping. During the hydrothermal reaction, water-soluble sugars use the conductive agent-doped network fibers as templates to grow carbon spheres, encapsulating the network fibers and conductive agent within the carbon spheres. In the pre-carbonization process, a phosphorus source acts as a pore-forming agent, etching the carbon spheres through its oxidizing and dehydrating properties to form porous carbon spheres. The internal network fibers form a network-like pyrolytic carbon skeleton. Later... The carbon spheres are then coated with a layer of furan resin through liquid-phase coating. The solvent is dried while the furan resin is cured. Finally, the surface furan resin film is transformed into a glassy carbon film through segmented high-temperature carbonization. Under high temperature, the carbon layer spacing shrinks, graphite-like microcrystals grow, and the carbon layers rearrange. This transforms the internal porous pyrolytic carbon spheres into porous hard carbon spheres, while the open pore ports shrink, deform, or even close, forming a closed microporous structure. Under high temperature, the network pyrolytic carbon skeleton transforms into a network hard carbon skeleton, resulting in a three-dimensional network structure with high electrical conductivity and porous amorphous carbon sphere material.
[0033] As a general inventive concept, the present invention provides an application of the above-described three-dimensional network structure carbon material or the three-dimensional network structure carbon material prepared by the above-described preparation method in sodium-ion batteries.
[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0035] (1) The three-dimensional network structure carbon material of the present invention is doped with nitrogen element (χ). N =3.04), nitrogen has a higher χ² value than carbon (χ² = 3.04). C The electronegativity of phosphorus (χ² = 2.55) can improve the electrical conductivity of carbon materials; at the same time, the doping of phosphorus (χ² = 2.55) can enhance the conductivity of carbon materials.P =2.19) has a lower electronegativity than carbon, and its interaction with nitrogen can further improve the conductivity of the material; phosphorus atoms have a larger radius than carbon atoms, which can expand the interlayer spacing and create defect sites, providing more sodium storage sites and improving the material capacity; moreover, the phosphorus source has oxidizing and dehydrating properties at high temperatures, and as a pore-forming agent, it reacts with carbon to form a COP associated structure, enabling hard carbon to obtain a large number of PO network structures and pores. After the pores close, more internal micropores are formed, increasing the number of defect points inside the carbon spheres, providing more sites for sodium ion adsorption, and effectively improving the material capacity.
[0036] (2) The three-dimensional network framework structure in the three-dimensional network carbon material of the present invention serves as a carrier for dopants, which helps the dopants to disperse and distribute within the material. Furthermore, its disordered network structure increases the number of internal defect points in the carbon spheres, enabling the material to adsorb more sodium ions and improve its capacity. The conductive agent is doped onto the internal network hard carbon framework of the material, ensuring its dispersion and distribution within the material. The internally incorporated conductive agent significantly reduces the powder resistance of the material, optimizes the kinetic characteristics of the sodium-ion battery, and improves the conductivity of the material.
[0037] (3) The glassy carbon film coating on the surface of the three-dimensional network structure carbon material of the present invention helps to close the pore size of the material, forming a closed microporous structure, preventing capacity and first-efficiency loss caused by excessive surface area of the carbon material, and improving the coating effect; glassy carbon has good conductivity, which helps to improve the overall conductivity of the carbon material. Spherical porous hard carbon helps to reduce the specific surface area of the material, improve the coating effect, and the spherical particles are more regular, with higher compaction density and vibration density, thus improving the energy density of the material.
[0038] (4) The preparation method of the present invention has a simple synthesis process, strong operability, low raw material cost, and is easy to achieve mass production and commercialization.
[0039] (5) The sodium-ion battery prepared by using the three-dimensional network structure carbon material of the present invention as the negative electrode material of sodium-ion battery has a first reversible capacity of more than 360 mAh / g at 0.1C and a first charge-discharge efficiency of more than 85% at 0.1C. Detailed Implementation
[0040] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.
[0041] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0042] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.
[0043] Example 1:
[0044] A three-dimensional network structure carbon material of the present invention includes a hard carbon body and a glassy carbon coating layer covering the surface of the hard carbon body. The hard carbon body is a spherical, phosphorus and nitrogen-doped porous hard carbon with a three-dimensional network skeleton structure inside. The hard carbon body with a three-dimensional network skeleton structure is also doped with a conductive agent, graphene. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin.
[0045] The preparation method of the three-dimensional network structure carbon material in this embodiment includes the following steps:
[0046] (1) Cellulose extracted from reeds was placed in a VC high-speed mixer with phosphoric acid and urea in a ratio of 100:20:100 and stirred at a stirring rate of 300 rpm for 0.5 h. Then it was placed in a rotary kiln and heated to 150 °C at a heating rate of 10 °C / min under nitrogen protection. After holding at this temperature for 0.5 h, it was heated to 200 °C at a heating rate of 10 °C / min and held for 1 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained.
[0047] (2) The phosphorus and nitrogen doped reticulated cellulose prepared in step (1) is placed in a hydrothermal reactor with sucrose, graphene and deionized water in a mass ratio of sucrose: reticulated cellulose: graphene: deionized water = 300:100:1:450. The hydrothermal reactor is filled with 80% of its capacity. The mixture is stirred until the sucrose is completely dissolved and the cellulose and graphene are uniformly dispersed in the solution. The reactor is then sealed and heated to 250°C at a heating rate of 5°C / min. The temperature is maintained for 48 hours. After cooling to room temperature, pyrolytic carbon balls with graphene doping and a three-dimensional reticulated carbon skeleton inside are obtained.
[0048] (3) The graphene-phosphorus nitrogen-doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 500°C at 5°C / min under nitrogen protection. They are then held at this temperature for 2 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0049] (4) The porous pyrolytic carbon balls, anhydrous ethanol, and furfuryl alcohol resin prepared in step (3) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfuryl alcohol resin = 100:120:2 and stirred at a stirring rate of 40 rpm for 2 h. Then, the mixture is placed in an oven and dried at 90°C for 24 h under nitrogen protection. After cooling to room temperature, a furfuryl alcohol resin-porous pyrolytic carbon ball composite precursor is obtained.
[0050] (5) The composite precursor prepared in step (3) is placed in a box furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection. The temperature is held for 2 hours, and then heated to 1600°C at a heating rate of 5°C / min. The temperature is held for 2 hours for high-temperature carbonization. After cooling to room temperature, a three-dimensional network structure carbon material is obtained.
[0051] Example 2:
[0052] A three-dimensional network structure carbon material of the present invention includes a hard carbon body and a glassy carbon coating layer covering the surface of the hard carbon body. The hard carbon body is a spherical, phosphorus and nitrogen-doped porous hard carbon with a three-dimensional network framework structure inside. The hard carbon body with a three-dimensional network framework structure is also doped with conductive carbon nanotubes. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin.
[0053] The preparation method of the three-dimensional network structure carbon material in this embodiment includes the following steps:
[0054] (1) Cellulose extracted from reeds was placed in a VC high-speed mixer with phosphoric acid and urea in a ratio of 100:40:100 and stirred at a stirring rate of 300 rpm for 0.5 h. Then it was placed in a rotary kiln and heated to 150 °C at a heating rate of 10 °C / min under nitrogen protection. After holding at the temperature for 0.5 h, it was heated to 200 °C at a heating rate of 10 °C / min and held for 1 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained.
[0055] (2) White dextrin, phosphorus and nitrogen doped reticulated cellulose, carbon nanotubes and deionized water prepared in step (1) are placed in a hydrothermal reactor at a mass ratio of white dextrin: reticulated cellulose: carbon nanotubes: deionized water = 200:100:1:500. The hydrothermal reactor is filled with 80% of its capacity. The mixture is stirred until the white dextrin is completely dissolved and the cellulose and carbon nanotubes are uniformly dispersed in the solution. The reactor is then sealed and heated to 200°C at a heating rate of 5°C / min. The temperature is maintained for 48 hours and then cooled to room temperature to obtain pyrolytic carbon balls doped with carbon nanotubes and having a three-dimensional reticulated carbon skeleton inside.
[0056] (3) The carbon nanotube-phosphorus nitrogen doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 450°C at 5°C / min under nitrogen protection. They are then held at the temperature for 2 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0057] (4) Porous pyrolytic carbon balls, anhydrous ethanol, and furfuryl alcohol resin were placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfuryl alcohol resin = 100:120:2 and stirred at a stirring rate of 40 rpm for 2 h. Then, the mixture was placed in an oven and dried at 90 °C for 24 h under nitrogen protection. After cooling to room temperature, a furfuryl alcohol resin-porous pyrolytic carbon ball composite precursor was obtained.
[0058] (5) The composite precursor was placed in a box furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection. The temperature was held for 2 hours, and then heated to 1400°C at a heating rate of 5°C / min. The temperature was held for 2 hours to carry out high-temperature carbonization. The material was then cooled to room temperature to obtain a three-dimensional network structure carbon material.
[0059] Example 3:
[0060] A three-dimensional network structure carbon material of the present invention includes a hard carbon body and a glassy carbon coating layer covering the surface of the hard carbon body. The hard carbon body is a spherical, phosphorus and nitrogen-doped porous hard carbon with a three-dimensional network skeleton structure inside. The hard carbon body with a three-dimensional network skeleton structure is also doped with a conductive agent, graphene. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin.
[0061] The preparation method of the three-dimensional network structure carbon material in this embodiment includes the following steps:
[0062] (1) Cellulose extracted from reeds was placed in a VC high-speed mixer with phosphoric acid and putrescine in a ratio of 100:40:80 and stirred at a stirring rate of 300 rpm for 0.5 h. Then it was placed in a rotary kiln and heated to 150 °C at a heating rate of 10 °C / min under nitrogen protection. After holding at the temperature for 0.5 h, it was heated to 180 °C at a heating rate of 10 °C / min and held for 0.5 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained.
[0063] (2) Trehalose, phosphorus and nitrogen doped reticulated cellulose, graphene and deionized water prepared in step (1) were placed in a hydrothermal reactor at a mass ratio of trehalose: reticulated cellulose: graphene: deionized water = 300:100:3:450. The hydrothermal reactor was filled to 80%. The mixture was stirred until the trehalose was completely dissolved and the cellulose and graphene were uniformly dispersed in the solution. The reactor was then sealed and heated to 300°C at a heating rate of 5°C / min. The temperature was kept constant for 48 hours and then cooled to room temperature to obtain pyrolytic carbon balls doped with graphene and with a three-dimensional reticulated carbon skeleton inside.
[0064] (3) The graphene-phosphorus nitrogen doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 550°C at a heating rate of 5°C / min under nitrogen protection. They are then held at this temperature for 2 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0065] (4) The porous pyrolytic carbon balls, anhydrous ethanol, and furfuryl alcohol resin prepared in step (3) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfuryl alcohol resin = 100:150:6. The mixture is stirred at a stirring rate of 40 rpm for 2 h. Then it is placed in an oven and dried at 80 °C for 36 h under nitrogen protection. After cooling to room temperature, a furfuryl alcohol resin-porous pyrolytic carbon ball composite precursor is obtained.
[0066] (5) The composite precursor is placed in a box furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection. The temperature is held for 2 hours, and then heated to 1500°C at a heating rate of 5°C / min. The temperature is held for 2 hours to carry out high-temperature carbonization. The material is then cooled to room temperature to obtain a three-dimensional network structure carbon material.
[0067] Example 4:
[0068] A three-dimensional network structure carbon material of the present invention includes a hard carbon body and a glassy carbon coating layer covering the surface of the hard carbon body. The hard carbon body is a spherical, phosphorus and nitrogen-doped porous hard carbon with a three-dimensional network skeleton structure inside. The hard carbon body with the three-dimensional network skeleton structure is also doped with a conductive agent, acetylene black. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin.
[0069] The preparation method of the three-dimensional network structure carbon material in this embodiment includes the following steps:
[0070] (1) The cellulose extracted from reeds was placed in a VC high-speed mixer with phytic acid and putrescine in a ratio of 100:30:100 and stirred at a stirring rate of 300 rpm for 0.5 h. Then it was placed in a rotary kiln and heated to 150 °C at a heating rate of 10 °C / min under nitrogen protection. After holding at the temperature for 0.5 h, it was heated to 170 °C at a heating rate of 10 °C / min and held for 1 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained.
[0071] (2) The mesotriose, phosphorus and nitrogen doped reticulated cellulose, acetylene black and deionized water prepared in step (1) are placed in a hydrothermal reactor at a mass ratio of mesotriose: reticulated cellulose: acetylene black: deionized water = 200:100:1:500. The hydrothermal reactor is filled with 80% of its capacity. The mixture is stirred until the mesotriose is completely dissolved and the cellulose and acetylene black are evenly dispersed in the solution. The reactor is then sealed and heated to 200°C at a heating rate of 5°C / min. The temperature is maintained for 72 hours. After cooling to room temperature, pyrolytic carbon balls with acetylene black doping and a three-dimensional reticulated carbon skeleton inside are obtained.
[0072] (3) The acetylene black-phosphorus nitrogen doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 450°C at a heating rate of 5°C / min under nitrogen protection. They are then held at this temperature for 3 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0073] (4) The porous pyrolytic carbon balls, anhydrous ethanol, and furfural resin prepared in step (3) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfural resin = 100:120:3. The mixture is stirred at a stirring rate of 40 rpm for 2 hours. Then it is placed in an oven and dried at 75°C for 48 hours under nitrogen protection. After cooling to room temperature, a furfural resin-porous pyrolytic carbon ball composite precursor is obtained.
[0074] (5) The furfural resin-porous pyrolytic carbon ball composite precursor prepared in step (4) is placed in a box furnace and heated to 550°C at a heating rate of 5°C / min under nitrogen protection. The temperature is held for 2 hours and then heated to 1200°C at a heating rate of 5°C / min. The temperature is held for 4 hours to carry out high-temperature carbonization. The material is then cooled to room temperature to obtain a three-dimensional network structure carbon material.
[0075] Example 5:
[0076] A three-dimensional network structure carbon material of the present invention includes a hard carbon body and a glassy carbon coating layer covering the surface of the hard carbon body. The hard carbon body is a spherical, phosphorus and nitrogen-doped porous hard carbon with a three-dimensional network skeleton structure inside. The hard carbon body with the three-dimensional network skeleton structure is also doped with a conductive agent, acetylene black. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin.
[0077] The preparation method of the three-dimensional network structure carbon material in this embodiment includes the following steps:
[0078] (1) Cellulose extracted from reeds was placed in a VC high-speed mixer with monomethyl phosphate and hexamethylenediamine in a ratio of 100:40:100 and stirred at a stirring rate of 300 rpm for 0.5 h. Then it was placed in a rotary kiln and heated to 170 °C at 10 °C / min under nitrogen protection. After holding at the temperature for 0.5 h, it was heated to 200 °C at 10 °C / min and held for 1 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained.
[0079] (2) Merinotriose, phosphorus and nitrogen doped reticulated cellulose, acetylene black and deionized water prepared in step (1) are placed in a hydrothermal reactor at a mass ratio of menotriose:reticulated cellulose:acetylene black:deionized water = 200:100:1:500. The hydrothermal reactor is filled with 80% of its capacity. The mixture is stirred until the menotriose is completely dissolved and the cellulose and acetylene black are evenly dispersed in the solution. The reactor is then sealed and heated to 200°C at 5°C / min. The temperature is maintained for 72 hours. After cooling to room temperature, pyrolytic carbon balls with acetylene black doping and a three-dimensional reticulated carbon skeleton are obtained.
[0080] (3) The acetylene black-phosphorus nitrogen doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 450°C at 5°C / min under nitrogen protection. They are then held at this temperature for 3 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0081] (4) The porous pyrolytic carbon balls, anhydrous ethanol, and furfural resin prepared in step (3) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfural resin = 100:120:3. The mixture is stirred at a stirring rate of 40 rpm for 2 h. Then it is placed in an oven and dried at 75°C for 48 h under nitrogen protection. After cooling to room temperature, a furfural resin-porous pyrolytic carbon ball composite precursor is obtained.
[0082] (5) The composite precursor prepared in step (4) is placed in a box furnace and heated to 550°C at 5°C / min under nitrogen protection. The temperature is held for 2 hours, and then heated to 1400°C at 2°C / min for 6 hours to carry out high-temperature carbonization. The material is then cooled to room temperature to obtain a three-dimensional network structure carbon material.
[0083] Example 6:
[0084] A three-dimensional network structure carbon material of the present invention includes a hard carbon body and a glassy carbon coating layer covering the surface of the hard carbon body. The hard carbon body is a spherical, phosphorus and nitrogen-doped porous hard carbon with a three-dimensional network framework structure inside. The hard carbon body with a three-dimensional network framework structure is also doped with conductive carbon nanotubes. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin.
[0085] The preparation method of the three-dimensional network structure carbon material in this embodiment includes the following steps:
[0086] (1) Cellulose extracted from reeds was placed in a VC high-speed mixer with ammonium dihydrogen phosphate and hexamethylenediamine in a ratio of 100:20:100 and stirred at a stirring rate of 300 rpm for 0.5 h. Then it was placed in a rotary kiln and heated to 170 °C at 10 °C / min under nitrogen protection. After holding at the temperature for 0.5 h, it was heated to 200 °C at 10 °C / min and held for 1 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained.
[0087] (2) Raffinose, phosphorus and nitrogen doped reticulated cellulose, carbon nanotubes and deionized water prepared in step (1) are placed in a hydrothermal reactor at a mass ratio of raffinose: reticulated cellulose: carbon nanotubes: deionized water = 200:100:2:500. The hydrothermal reactor is filled with 70% of its capacity. The mixture is stirred until the raffinose is completely dissolved and the cellulose and carbon nanotubes are evenly dispersed in the solution. The reactor is then sealed and heated to 200°C at 5°C / min. The temperature is maintained for 48 hours. After cooling to room temperature, pyrolytic carbon balls with carbon nanotubes and a three-dimensional reticulated carbon skeleton are obtained.
[0088] (3) The carbon nanotube-phosphorus nitrogen doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 650°C at 5°C / min under nitrogen protection. They are then held at the temperature for 3 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0089] (4) The porous pyrolytic carbon balls, anhydrous ethanol, and furfural resin prepared in step (3) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfural resin = 100:150:6. The mixture is stirred at a stirring rate of 40 rpm for 2 h. Then it is placed in an oven and dried at 90°C for 24 h under nitrogen protection. After cooling to room temperature, a furfural resin-porous pyrolytic carbon ball composite precursor is obtained.
[0090] (5) The composite precursor prepared in step (4) is placed in a box furnace and heated to 650°C at 5°C / min under nitrogen protection. The temperature is held for 2 hours, and then heated to 1500°C at 5°C / min for 6 hours for high-temperature carbonization. The carbon material is cooled to room temperature to obtain a three-dimensional network structure carbon material.
[0091] Example 7:
[0092] A three-dimensional network structure carbon material of the present invention includes a hard carbon body and a glassy carbon coating layer covering the surface of the hard carbon body. The hard carbon body is a spherical, phosphorus and nitrogen-doped porous hard carbon with a three-dimensional network skeleton structure inside. The hard carbon body with a three-dimensional network skeleton structure is also doped with a conductive agent, graphene. The glassy carbon coating layer is an amorphous carbon layer formed by high-temperature carbonization of furan resin.
[0093] The preparation method of the three-dimensional network structure carbon material in this embodiment includes the following steps:
[0094] (1) Cellulose extracted from reeds, phytic acid and urea were placed in a VC high-speed mixer in a ratio of 100:40:100 and stirred at a stirring rate of 300 rpm for 0.5 h. Then, the mixture was placed in a rotary kiln and heated to 150 °C at 10 °C / min under nitrogen protection. After being kept at the temperature for 0.5 h, it was heated to 200 °C at 10 °C / min and kept at the temperature for 1 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained.
[0095] (2) Sucrose, phosphorus and nitrogen doped reticulated cellulose, graphene, and deionized water prepared in step (1) are placed in a hydrothermal reactor at a mass ratio of sucrose: reticulated cellulose: graphene: deionized water = 300:100:1:300. The hydrothermal reactor is filled with 70% of its capacity. The mixture is stirred until the sucrose is completely dissolved and the cellulose and graphene are uniformly dispersed in the solution. The reactor is then sealed and heated to 300°C at 5°C / min. The temperature is maintained for 48 hours. After cooling to room temperature, pyrolytic carbon balls with graphene doping and a three-dimensional reticulated carbon skeleton inside are obtained.
[0096] (3) The graphene-phosphorus nitrogen-doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 400°C at 5°C / min under nitrogen protection. They are then held at this temperature for 2 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0097] (4) The porous pyrolytic carbon balls, anhydrous ethanol, and furfural resin prepared in step (3) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfural resin = 100:120:2 and stirred at a stirring rate of 40 rpm for 2 h. Then, the mixture is placed in an oven and dried at 90°C for 24 h under nitrogen protection. After cooling to room temperature, a furfural resin-porous pyrolytic carbon ball composite precursor is obtained.
[0098] (5) The composite precursor prepared in step (4) is placed in a box furnace and heated to 600°C at 5°C / min under nitrogen protection, and held at the temperature for 2 hours. Then, the temperature is increased to 1500°C at 5°C / min and held at the temperature for 2 hours for high-temperature carbonization. After cooling to room temperature, a three-dimensional network structure carbon material is obtained.
[0099] Comparative Example 1:
[0100] The only difference between this comparative example and Example 1 is that the conductive agent graphene is not added in step (2) of the preparation process. The other processes and parameters are the same as those in Example 1.
[0101] Comparative Example 2:
[0102] The only difference between this comparative example and Example 1 is that furfuryl alcohol resin is not added in step (4) of the preparation process; the other processes and parameters are the same as in Example 1.
[0103] Comparative Example 3:
[0104] The only difference between this comparative example and Example 1 is that the cellulose extracted from reeds was not treated with nitrogen and phosphorus elements during the preparation process; the other processes and parameters are the same as in Example 1.
[0105] Comparative Example 4:
[0106] The only difference between this comparative example and Example 1 is that, in the preparation process, carbon balls were not formed by hydrothermal method. Instead, sucrose, reticulated fiber, and conductive agent were mixed by solid-phase mixing. That is, the operation in step (2) is to place sucrose and the phosphorus and nitrogen doped reticulated cellulose and graphene prepared in step (1) in a VC high-speed mixer at a mass ratio of sucrose: reticulated cellulose: graphene = 300:100:1 and mix them thoroughly at a stirring rate of 300 rpm for 1 hour. The remaining steps are the same as in Example 1.
[0107] Comparative Example 5:
[0108] The preparation method of the carbon material in this comparative example is as follows:
[0109] (1) Sucrose, graphene, phosphoric acid, urea, and deionized water were placed in a hydrothermal reactor at a mass ratio of sucrose:graphene:deionized water:phosphoric acid:urea = 400:1:450:20:100. The hydrothermal reactor was filled to 80%. The mixture was stirred until the sucrose, phosphoric acid, and urea were completely dissolved and the graphene was uniformly dispersed in the solution. The reactor was then sealed and heated to 250°C at 5°C / min. The temperature was kept constant for 48 hours. After cooling to room temperature, pyrolytic carbon balls containing phosphorus, nitrogen, and graphene were obtained.
[0110] (2) The pyrolytic carbon balls prepared in step (1) are placed in a box furnace and heated to 500°C at 5°C / min under nitrogen protection. They are then held at this temperature for 2 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls.
[0111] (3) The pyrolytic carbon balls, anhydrous ethanol, and furfuryl alcohol resin prepared in step (2) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfuryl alcohol resin = 100:120:2 and stirred at a stirring rate of 40 rpm for 2 h. Then, the mixture is placed in an oven and dried at 90°C for 24 h under nitrogen protection. After cooling to room temperature, the furfuryl alcohol resin-pyrolytic carbon ball composite precursor is obtained.
[0112] (4) The composite precursor prepared in step (3) is placed in a box furnace and heated to 600°C at 5°C / min under nitrogen protection, and held at the temperature for 2 hours. Then, the temperature is increased to 1600°C at 5°C / min and held at the temperature for 2 hours for high-temperature carbonization. After cooling to room temperature, the finished amorphous carbon balls are obtained.
[0113] Comparative Example 6:
[0114] The preparation method of the carbon material in this comparative example is as follows:
[0115] (1) Cellulose, sucrose and deionized water were placed in a hydrothermal reactor at a mass ratio of sucrose:cellulose:deionized water = 300:100:450. The hydrothermal reactor was filled to 80%. The mixture was stirred until the sucrose was completely dissolved and the cellulose was evenly dispersed in the solution. The reactor was then sealed and heated to 250°C at 5°C / min. The temperature was kept constant for 48 hours. After cooling to room temperature, pyrolytic carbon balls 1 were obtained.
[0116] (2) Place the pyrolytic carbon ball 1 in a box furnace and heat it to 500°C at 5°C / min under nitrogen protection. Hold it at the temperature for 2 hours for pre-carbonization. After cooling to room temperature, take it out to obtain the pyrolytic carbon ball 2.
[0117] (3) Place the pyrolytic carbon ball 2 in a box furnace, raise the temperature to 600°C at 5°C / min under nitrogen protection, hold the temperature for 2 hours, then continue to raise the temperature to 1600°C at 5°C / min and hold the temperature for 2 hours to carry out high-temperature carbonization. After cooling to room temperature, the finished amorphous carbon ball is obtained.
[0118] The carbon materials prepared in Examples 1-7 and Comparative Examples 1-6 were used as anode materials for sodium-ion batteries and then assembled into anode materials for sodium-ion batteries. The performance test data are detailed in Table 1.
[0119] Table 1. Performance data of carbon materials and their prepared sodium-ion batteries in the examples and comparative examples.
[0120]
[0121] The experimental data in Table 1 show that:
[0122] Comparing Example 1 with Comparative Example 1, it can be seen that the addition of the conductive agent greatly increases the powder conductivity of the material.
[0123] Comparing Example 1 and Comparative Example 2, it can be seen that the glassy carbon film on the surface can help to form a closed microporous structure, avoid excessive surface defects that lead to a large specific surface area and low first efficiency and capacity, and the formation of the glassy carbon material on the surface also has a certain impact on the conductivity of the material.
[0124] Comparing Example 1 and Comparative Example 4, it can be seen that spherical shapes can significantly improve the compaction density of the powder.
[0125] Comparing Example 1 and Comparative Example 5, it can be seen that the construction of the reticulated hard carbon skeleton enables the conductive agent to be better dispersed inside the carbon material, resulting in a better incorporation effect of the conductive agent. Furthermore, the incorporation of the reticulated hard carbon skeleton also affects the capacity. This may be because the reticulated hard carbon skeleton creates more defects inside the material, providing more sodium storage sites, thereby increasing the specific capacity of the material.
[0126] Comparing Comparative Example 3 and Comparative Example 5, it can be seen that the incorporation of phosphorus and nitrogen elements has a significant impact on the capacity of the material. This may be because the phosphorus source undergoes oxidation and dehydration at high temperatures, forming a COP associated structure after reacting with carbon. This results in the carbon spheres acquiring a large number of PO network structures and micropores. After the pores close, more internal micropores are formed, providing more sites for the adsorption of sodium ions. Furthermore, the incorporation of phosphorus and nitrogen elements also has a certain impact on the conductivity of the material.
[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.
Claims
1. A method for preparing a three-dimensional network structure carbon material, characterized in that, Includes the following steps: (1) The cellulose extracted from reeds was placed in a VC high-speed mixer with phosphoric acid and urea in a ratio of 100:20:100 and stirred at a stirring rate of 300 rpm for 0.5 h. Then it was placed in a rotary kiln and heated to 150 °C at a heating rate of 10 °C / min under nitrogen protection. After holding at this temperature for 0.5 h, it was heated to 200 °C at a heating rate of 10 °C / min and held at this temperature for 1 h. After cooling to room temperature, phosphorus and nitrogen doped network cellulose was obtained. (2) The phosphorus and nitrogen doped reticulated cellulose prepared in step (1) is placed in a hydrothermal reactor with sucrose, graphene and deionized water in a mass ratio of sucrose: reticulated cellulose: graphene: deionized water = 300:100:1:
450. The hydrothermal reactor is filled with 80% of its capacity. The mixture is stirred until the sucrose is completely dissolved and the cellulose and graphene are uniformly dispersed in the solution. The reactor is then sealed and heated to 250°C at a heating rate of 5°C / min. The temperature is kept constant for 48 hours. After cooling to room temperature, pyrolytic carbon balls with graphene doping and a three-dimensional reticulated carbon skeleton inside are obtained. (3) The graphene-phosphorus nitrogen doped pyrolytic carbon balls prepared in step (2) are placed in a box furnace and heated to 500°C at 5°C / min under nitrogen protection. They are then held at the temperature for 2 hours for pre-carbonization. After cooling to room temperature, they are taken out to obtain porous pyrolytic carbon balls. (4) The porous pyrolytic carbon balls, anhydrous ethanol, and furfuryl alcohol resin prepared in step (3) are placed in a high-speed shear machine at a mass ratio of porous pyrolytic carbon balls: anhydrous ethanol: furfuryl alcohol resin = 100:120:2 and stirred at a stirring rate of 40 rpm for 2 h. Then, they are placed in an oven and dried at 90°C for 24 h under nitrogen protection. After cooling to room temperature, a furfuryl alcohol resin-porous pyrolytic carbon ball composite precursor is obtained. (5) The composite precursor prepared in step (4) is placed in a box furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection. The temperature is held for 2 hours, and then heated to 1600°C at a heating rate of 5°C / min. The temperature is held for 2 hours for high-temperature carbonization. After cooling to room temperature, a three-dimensional network structure carbon material is obtained.
2. A three-dimensional network structure carbon material, characterized in that, It is prepared by the preparation method described in claim 1.
3. The application of a three-dimensional network structure carbon material prepared by the preparation method as described in claim 1 or the three-dimensional network structure carbon material as described in claim 2 in a sodium-ion battery.