A method for preparing and using a resin / pitch-based hard carbon material

Abstract

The application provides a preparation method and application of a resin / bitumen-based hard carbon material, which comprises the following steps: pre-carbonizing phenolic resin to obtain a phenolic resin carbon material; performing first pre-oxidation on bitumen and an oxygen-containing organic polymer to obtain a first pre-oxidized bitumen material; performing second pre-oxidation on the phenolic resin carbon material and the first pre-oxidized bitumen material to obtain a resin / bitumen composite material precursor; and then performing high-temperature carbonization. In the first pre-oxidation process, the oxygen-containing organic polymer is introduced, the property difference between the oxygen-containing organic polymer and the bitumen is utilized to reduce the sintering probability of the bitumen, and the uniformity of the hard carbon material is improved; meanwhile, the oxygen atoms carried by the oxygen-containing organic polymer realize oxygen doping, and the active sites of the hard carbon material are increased; in the second pre-oxidation process, the oxygen atoms are introduced again for doping, meanwhile, the bitumen material and the resin carbon material which have both completed the first pre-oxidation are in contact with each other, can combine to form a large number of interfaces, and the property difference between the two is utilized to further inhibit the sintering of the bitumen.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode materials technology, and in particular to a method for preparing and applying a resin / asphalt-based hard carbon material. Background Technology

[0002] Driven by the goals of carbon peaking and carbon neutrality and the cost of lithium batteries, sodium-ion batteries have been rapidly developed in fields such as large-scale energy storage, low-speed electric vehicles, and start-stop batteries because they have the same working principle and similar structural composition as lithium-ion batteries, and have significant advantages in terms of raw material cost, high and low temperature performance, and safety performance.

[0003] Sodium-ion battery anode materials mainly include carbon materials, organic materials, and metal oxides. Carbon materials have become the mainstream choice for sodium-ion battery anodes due to their small expansion during charging and discharging and low cost. Carbon materials can generally be divided into graphite and amorphous carbon materials. Amorphous carbon materials are further classified into hard carbon and soft carbon materials based on their graphitization capability at 2600℃. Hard carbon has a short-range ordered and long-range disordered structure. Its closed-cell structure formed by the curling of graphite sheets, the interlayer gaps in graphite carbon, and defect sites can all effectively store sodium ions, giving it a high sodium storage capacity. It is the preferred material for sodium-ion battery anodes, and the selection and preparation of hard carbon precursors are key aspects of the industrialization of sodium-ion batteries.

[0004] Currently, the main precursors for preparing hard carbon are pitch-based, resin-based, biomass-based, and mineral-based. Among them, pitch-based precursors, as byproducts of petrochemical or coal chemical processes, are stable in source, inexpensive, and have low impurity content, making them the preferred raw material for industrialization. However, pitch-based materials suffer from severe sintering problems during carbonization, resulting in poor uniformity of the prepared hard carbon materials. This, in turn, leads to low initial coulombic efficiency and insufficient sodium storage capacity in sodium-ion batteries, limiting the industrial application of pitch-based hard carbon materials.

[0005] Therefore, developing a preparation method that can effectively inhibit pitch sintering and improve the electrochemical performance of hard carbon materials is of great practical significance. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing resin / asphalt-based hard carbon material to solve the problem of severe sintering of asphalt-based hard carbon material during carbonization in the prior art. At the same time, this invention will also provide a negative electrode sheet using the resin / asphalt-based hard carbon material as an active material and a sodium-ion battery using the negative electrode sheet.

[0007] To achieve the above and other related objectives, the present invention provides the following technical solutions: In a first aspect, this invention provides a method for preparing a resin / asphalt-based hard carbon material, wherein the pre-oxidation is carried out in two stages. By introducing an oxygen-containing organic polymer and phenolic resin carbon into the two pre-oxidation processes respectively, the sintering of the asphalt is effectively suppressed, while oxygen atom doping is achieved, increasing the active sites of the material. Specifically, the method includes the following steps: (1) Pre-carbonized phenolic resin: Phenolic resin is pre-carbonized, then crushed and sieved to obtain phenolic resin carbon material; (2) Primary pre-oxidation: The asphalt is mixed evenly with an oxygen-containing organic polymer, and then subjected to a first pre-oxidation under oxygen conditions to obtain a pre-oxidized asphalt material. After cooling, it is pulverized. (3) Secondary pre-oxidation: The phenolic resin carbon material obtained in step (1) and the pre-oxidized asphalt material obtained in step (2) are mixed evenly, and then a second pre-oxidation is carried out under oxygen conditions to obtain a resin / asphalt composite material precursor, which is then pulverized after cooling. (4) High-temperature carbonization: The resin / asphalt composite material precursor obtained in step (3) is subjected to high-temperature carbonization, cooled and then sieved to obtain resin / asphalt-based hard carbon material.

[0008] In step (1), the pre-carbonization temperature of the phenolic resin is 600~800℃; after crushing and sieving, the particle size D50 of the phenolic resin carbon material is controlled to be less than or equal to 20μm.

[0009] In step (2), asphalt powder with a softening point of 180~250℃ is selected.

[0010] In step (2), the oxygen-containing organic polymer is selected from at least one of polyoxymethylene, polyethylene oxide, polycarbonate, polyvinyl acetate, polylactic acid, polybutylene succinate, and polyvinyl butyral. Preferably, it is at least one of polyoxymethylene, polycarbonate, and polyvinyl butyral, and more preferably, it is polycarbonate.

[0011] In step (2), the mass ratio of the asphalt to the oxygen-containing organic polymer is 10:1 to 1:1.

[0012] In step (2), the particle size D50 of the asphalt and the oxygen-containing organic polymer is 50μm~150μm, preferably 100μm.

[0013] In step (2), the conditions for the first pre-oxidation are: oxidation temperature of 270~420℃, heating rate of 1~2℃ / min, and holding time of 240~480min.

[0014] In step (2), after the first pre-oxidation is completed and cooled, the pre-oxidized asphalt composite material is taken out and crushed to control the particle size D50 to be less than or equal to 20 μm.

[0015] In step (3), the mass ratio of the phenolic resin carbon material to the primary pre-oxidized asphalt material is 10:1 to 1:2.

[0016] In step (3), the conditions for the second pre-oxidation are: the oxidation temperature is 400~600℃, which is lower than the pre-carbonization temperature of phenolic resin in step (1), the heating rate is 1~2℃ / min, and the holding time is 120~240min.

[0017] In step (3), after the second pre-oxidation is completed, the material is cooled and pulverized to control the particle size of the resin / asphalt composite material to be less than or equal to 10 μm.

[0018] In step (4), the conditions for high-temperature carbonization are: carbonization temperature of 1000~1500℃, heating rate of 1~5℃ / min, and holding time of 60~360min.

[0019] In step (4), a protective gas is introduced throughout the high-temperature carbonization process until cooling is completed. The protective gas includes at least one of nitrogen, argon, and helium.

[0020] In step (4), after high-temperature carbonization is completed, the resin / asphalt-based hard carbon material is obtained by passing it through a 325-mesh sieve.

[0021] In a second aspect, the present invention provides a resin / asphalt-based hard carbon material, which is prepared by the above-described preparation method. The material has an amorphous structure with short-range order and long-range disorder, high oxygen atom doping content, abundant active sites, and no obvious sintering agglomeration phenomenon, exhibiting excellent material uniformity.

[0022] In a third aspect, the present invention provides a negative electrode sheet, wherein the negative electrode sheet uses the above-mentioned resin / asphalt-based hard carbon material as the active material.

[0023] Furthermore, the negative electrode sheet also includes a binder and a conductive agent. The mass ratio of the active material, binder, and conductive agent is 93.0%:2.0%:5.0%, wherein the conductive agent is carbon black (SP), and the binder is a compound system of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), with a mass ratio of CMC to SBR of 2.0%:2.0% (SBR solid content 40%).

[0024] In a fourth aspect, the present invention provides a sodium-ion battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the negative electrode is the aforementioned negative electrode sheet. This sodium-ion battery, at a current density of 0.1C, exhibits an initial charge specific capacity greater than 360.7 mAh / g, an initial discharge specific capacity of 340-370 mAh / g, and an initial efficiency of 88%-93%.

[0025] As described above, the preparation method and application of the resin / asphalt-based hard carbon material of the present invention have the following beneficial effects: 1. In the first pre-oxidation process, the present invention introduces an oxygen-containing organic polymer, which reduces the probability of asphalt sintering by utilizing the difference in properties between the oxygen-containing organic polymer and asphalt, which is beneficial to improving the uniformity of hard carbon materials; at the same time, the oxygen atoms of the oxygen-containing organic polymer enable oxygen doping, increase the active sites of hard carbon materials, improve conductivity, and enhance sodium storage capacity and rate performance. The pre-carbonized phenolic resin carbon is mixed with the primary pre-oxidized asphalt material for secondary pre-oxidation. The secondary pre-oxidation process can introduce oxygen atoms again, further optimizing the material structure. In addition, during the secondary pre-oxidation process, the asphalt material and resin carbon material that have completed the primary pre-oxidation come into contact with each other and can combine to form a large number of interfaces. The difference in properties between the two can be used to further inhibit asphalt sintering and further improve the material uniformity, thereby improving the capacity and first coulombic efficiency of hard carbon.

[0026] 2. In steps (1) and (2), the present invention performs a first pre-oxidation on phenolic resin and asphalt at different temperatures to maximize the alteration of their properties, thereby enabling them to more effectively prevent the sintering of asphalt materials during the second pre-oxidation process. Simultaneously, by controlling the temperature of the second pre-oxidation to be lower than the temperature of the phenolic resin pre-carbonization, secondary pyrolysis or graphitization of the phenolic resin carbon can be avoided, allowing it to continue to exert its physical barrier effect and thoroughly inhibit asphalt sintering from a spatial structural perspective. This temperature also allows the asphalt to undergo a mild cross-linking reaction during the second oxidation process. The oxygen-containing functional groups (-OH, -COOH) generated on the surface will form hydrogen bonds or covalent bonds with the active sites on the surface of the phenolic resin carbon. This interfacial bonding will not break due to high temperature, allowing the phenolic resin carbon and asphalt particles to form a stable structure, ensuring the uniformity of the final hard carbon material.

[0027] 3. This invention employs a step-by-step process of primary pre-oxidation, pulverization, secondary pre-oxidation, pulverization, and carbonization to maximize the sintering inhibition effect of pre-oxidation. Multiple pulverization processes ensure the uniformity of material particle size and avoid agglomeration problems after sintering. At the same time, the introduction of oxygen-containing organic polymers during the primary pre-oxidation process and the introduction of pre-carbonized resin carbon materials during the secondary pre-oxidation process provide favorable conditions for preventing the sintering of asphalt materials, ultimately resulting in a significant increase in sodium storage capacity and initial coulombic efficiency. Attached Figure Description

[0028] Figure 1 The first charge-discharge curves of the sodium-ion batteries prepared for Example 1 and Comparative Example 1 at a current density of 0.1C are shown.

[0029] Figure 2 The graph shows the retention rate of the sodium-ion battery prepared in Example 1 at 1C cycling. Detailed Implementation

[0030] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0031] Example 1 A method for preparing a resin / asphalt-based hard carbon material specifically includes the following steps: S1. Place the phenolic resin in a carbonization furnace for pre-carbonization. Raise the temperature to 600℃ at a rate of 3℃ / min, then keep it at that temperature for 2 hours. After it cools naturally to room temperature, take it out and pulverize it using an air jet mill. The particle size D50 of the pulverized resin is controlled to be around 10μm.

[0032] S2. Add asphalt with a D50 of 100μm and polyoxymethylene with a D50 of 100μm to the mixer in a mass ratio of 3:1. Mix them evenly at 100 revolutions / min for 60 minutes. Then, take them out and put them into a carbonization furnace for the first pre-oxidation. Raise the temperature to 300℃ at a heating rate of 2℃ / min and keep it at that temperature for 1 hour. After naturally cooling to room temperature, take them out and pulverize them with an air jet mill. The particle size D50 of the pulverized particles is controlled at about 10μm.

[0033] S3. The pre-oxidized asphalt with a particle size D50 of 10 μm obtained in step S2 and the pre-carbonized phenolic resin carbon with a particle size D50 of 10 μm obtained in step S1 are added to the mixer at a mass ratio of 5:1. The mixture is then stirred at 120 revolutions / min for 150 min until homogeneous. After stirring, the mixture is removed and placed in a carbonization furnace for a second pre-oxidation. The temperature is raised to 450°C at a heating rate of 2°C / min and then kept at that temperature for 2 hours. After naturally cooling to room temperature, the mixture is removed and pulverized using an air jet mill. The particle size D50 of the pulverized mixture is controlled to be around 7 μm.

[0034] S4. The particle size D50 of 7 μm obtained in step S3 is placed into a carbonization furnace for high-temperature carbonization. The temperature is increased to 1400℃ at a heating rate of 2℃ / min, and held for 2 hours. After natural cooling to room temperature, the material is passed through a 325-mesh sieve to obtain resin / asphalt-based hard carbon material.

[0035] The resin / asphalt-based hard carbon material prepared above is used as an active material in the preparation of sodium-ion batteries, including the following steps: Weigh out 9.3g, 0.2g, 0.3g, and 0.5g of resin / asphalt-based hard carbon composite material, CMC, SP, and SBR (40% solid content) respectively in a mass ratio of 93.0%:2.0%:3.0%:2.0%, and add them sequentially to a beaker while stirring. Add an appropriate amount of deionized water and stir for 6 hours until a uniform slurry is formed. Use a four-sided coater to evenly coat the slurry onto the surface of copper foil. Dry the slurry in a vacuum drying oven at 80℃ for 12 hours. Then, cut the Cu foil coated with active material into circular pieces with a diameter of 12mm and transfer them to a glove box for later use.

[0036] The half-cell assembly was carried out in an Ar atmosphere glove box. The negative electrode used was the aforementioned resin / asphalt-based hard carbon electrode. The electrolyte was a 1.0 mol / L commercial electrolyte with the following formulation: NaPF6 dissolved in EC:DMC = 1:1 by volume. The counter electrode was a metallic Na sheet. The battery case was of CR2032 specification. The battery was assembled into a coin cell and then charge-discharge tests were conducted at a current density of 0.1C (1C = 300 mAh / g) and at different rates.

[0037] Example 2 A method for preparing a resin / asphalt-based hard carbon material specifically includes the following steps: S1. Place the phenolic resin in a carbonization furnace for pre-carbonization. Raise the temperature to 800℃ at a rate of 3℃ / min, then keep it at that temperature for 2 hours. After it cools naturally to room temperature, take it out and pulverize it using an air jet mill. The particle size D50 of the pulverized resin is controlled to be around 10μm.

[0038] S2. Add asphalt with a D50 of 100μm and polyoxymethylene with a D50 of 100μm to the mixer in a mass ratio of 3:1. Mix them evenly at 100 revolutions / min for 60 minutes. Then, take them out and put them into a carbonization furnace for the first pre-oxidation. Raise the temperature to 300℃ at a heating rate of 2℃ / min and keep it at that temperature for 1 hour. After naturally cooling to room temperature, take them out and pulverize them with an air jet mill. The particle size D50 of the pulverized particles is controlled at about 10μm.

[0039] S3. The pre-oxidized asphalt with a particle size D50 of 10 μm obtained in step S2 and the pre-carbonized phenolic resin carbon with a particle size D50 of 10 μm obtained in step S1 are added to the mixer at a mass ratio of 5:1. The mixture is then stirred at 120 revolutions / min for 150 min until homogeneous. After stirring, the mixture is removed and placed in a carbonization furnace for a second pre-oxidation. The temperature is raised to 450°C at a heating rate of 2°C / min and then kept at that temperature for 2 hours. After naturally cooling to room temperature, the mixture is removed and pulverized using an air jet mill. The particle size D50 of the pulverized mixture is controlled to be around 7 μm.

[0040] S4. The particle size D50 of 7 μm obtained in step S3 is placed into a carbonization furnace for high-temperature carbonization. The temperature is increased to 1400℃ at a heating rate of 2℃ / min, and held for 2 hours. After natural cooling to room temperature, the material is passed through a 325-mesh sieve to obtain resin / asphalt-based hard carbon material.

[0041] The resin / asphalt-based hard carbon material prepared above is used as an active material in the preparation of sodium-ion batteries, including the following steps: Weigh out 9.3g, 0.2g, 0.3g, and 0.5g of resin / asphalt-based hard carbon composite material, CMC, SP, and SBR (40% solid content) respectively in a mass ratio of 93.0%:2.0%:3.0%:2.0%, and add them sequentially to a beaker while stirring. Add an appropriate amount of deionized water and stir for 6 hours until a uniform slurry is formed. Use a four-sided coater to evenly coat the slurry onto the surface of copper foil. Dry the slurry in a vacuum drying oven at 80℃ for 12 hours. Then, cut the Cu foil coated with active material into circular pieces with a diameter of 12mm and transfer them to a glove box for later use.

[0042] The half-cell assembly was carried out in an Ar atmosphere glove box. The negative electrode used was the aforementioned resin / asphalt-based hard carbon electrode. The electrolyte was a 1.0 mol / L commercial electrolyte with the following formulation: NaPF6 dissolved in EC:DMC = 1:1 by volume. The counter electrode was a metallic Na sheet. The battery case was of CR2032 specification. The battery was assembled into a coin cell and then charge-discharge tests were conducted at a current density of 0.1C (1C = 300 mAh / g) and at different rates.

[0043] Example 3 A method for preparing a resin / asphalt-based hard carbon material specifically includes the following steps: S1. Place the phenolic resin in a carbonization furnace for pre-carbonization. Raise the temperature to 600℃ at a rate of 3℃ / min, then keep it at that temperature for 2 hours. After it cools naturally to room temperature, take it out and pulverize it using an air jet mill. The particle size D50 of the pulverized resin is controlled to be around 10μm.

[0044] S2. Add asphalt with a D50 of 100μm and polycarbonate with a D50 of 100μm to the mixer in a mass ratio of 3:1. Mix them evenly at 100 revolutions / min for 60 minutes. Then, take them out and put them into a carbonization furnace for the first pre-oxidation. Raise the temperature to 300℃ at a heating rate of 2℃ / min and keep it at that temperature for 1 hour. After naturally cooling to room temperature, take them out and pulverize them with an air jet mill. The particle size D50 of the pulverized particles is controlled at about 10μm.

[0045] S3. The pre-oxidized asphalt with a particle size D50 of 10 μm obtained in step S2 and the pre-carbonized phenolic resin carbon with a particle size D50 of 10 μm obtained in step S1 are added to the mixer at a mass ratio of 5:1. The mixture is then stirred at 120 revolutions / min for 150 min until homogeneous. After stirring, the mixture is removed and placed in a carbonization furnace for a second pre-oxidation. The temperature is raised to 450°C at a heating rate of 2°C / min and then kept at that temperature for 2 hours. After naturally cooling to room temperature, the mixture is removed and pulverized using an air jet mill. The particle size D50 of the pulverized mixture is controlled to be around 7 μm.

[0046] S4. The particle size D50 of 7 μm obtained in step S3 is placed into a carbonization furnace for high-temperature carbonization. The temperature is increased to 1400℃ at a heating rate of 2℃ / min, and held for 2 hours. After natural cooling to room temperature, the resin / asphalt-based hard carbon composite material is obtained by passing it through a 325-mesh sieve.

[0047] The resin / asphalt-based hard carbon composite material prepared above is used as the active material in the preparation of sodium-ion batteries, including the following steps: Weigh out 9.3g, 0.2g, 0.3g, and 0.5g of resin / asphalt-based hard carbon composite material, CMC, SP, and SBR (40% solid content) respectively in a mass ratio of 93.0%:2.0%:3.0%:2.0%, and add them sequentially to a beaker while stirring. Add an appropriate amount of deionized water and stir for 6 hours until a uniform slurry is formed. Use a four-sided coater to evenly coat the slurry onto the surface of copper foil. Dry the slurry in a vacuum drying oven at 80℃ for 12 hours. Then, cut the Cu foil coated with active material into circular pieces with a diameter of 12mm and transfer them to a glove box for later use.

[0048] The half-cell assembly was carried out in an Ar atmosphere glove box. The negative electrode used was the aforementioned resin / asphalt-based hard carbon electrode. The electrolyte was a 1.0 mol / L commercial electrolyte with the following formulation: NaPF6 dissolved in EC:DMC = 1:1 by volume. The counter electrode was a metallic Na sheet. The battery case was of CR2032 specification. The battery was assembled into a coin cell and then charge-discharge tests were conducted at a current density of 0.1C (1C = 300 mAh / g) and at different rates.

[0049] Example 4 A method for preparing a resin / asphalt-based hard carbon material specifically includes the following steps: S1. Place the phenolic resin in a carbonization furnace for pre-carbonization. Raise the temperature to 600℃ at a rate of 3℃ / min, then keep it at that temperature for 2 hours. After it cools naturally to room temperature, take it out and pulverize it using an air jet mill. The particle size D50 of the pulverized resin is controlled to be around 10μm.

[0050] S2. Add asphalt with a D50 of 100μm and polyoxymethylene with a D50 of 100μm to the mixer in a mass ratio of 3:1. Mix them evenly at 100 revolutions / min for 60 minutes. Then take it out and put it into the carbonization furnace for the first pre-oxidation. Raise the temperature to 400℃ at a heating rate of 2℃ / min and keep it at that temperature for 1 hour. After naturally cooling to room temperature, take it out and pulverize it with an air jet mill. The particle size D50 of the pulverized particles is controlled at about 10μm.

[0051] S3. The pre-oxidized asphalt with a particle size D50 of 10 μm obtained in step S2 and the pre-carbonized phenolic resin carbon with a particle size D50 of 10 μm obtained in step S1 are added to the mixer at a mass ratio of 5:1. The mixture is then stirred at 120 revolutions / min for 150 min until homogeneous. After stirring, the mixture is removed and placed in a carbonization furnace for a second pre-oxidation. The temperature is raised to 450°C at a heating rate of 2°C / min and then kept at that temperature for 2 hours. After naturally cooling to room temperature, the mixture is removed and pulverized using an air jet mill. The particle size D50 of the pulverized mixture is controlled to be around 7 μm.

[0052] S4. The particle size D50 of 7 μm obtained in step S3 is placed into a carbonization furnace for high-temperature carbonization. The temperature is increased to 1400℃ at a heating rate of 2℃ / min, and held for 2 hours. After natural cooling to room temperature, the material is passed through a 325-mesh sieve to obtain resin / asphalt-based hard carbon material.

[0053] The resin / asphalt-based hard carbon composite material prepared above is used as an active material in the preparation of sodium-ion batteries, including the following steps: Weigh out 9.3g, 0.2g, 0.3g, and 0.5g of resin / asphalt-based hard carbon composite material, CMC, SP, and SBR (40% solid content) respectively in a mass ratio of 93.0%:2.0%:3.0%:2.0%, and add them sequentially to a beaker while stirring. Add an appropriate amount of deionized water and stir for 6 hours until a uniform slurry is formed. Use a four-sided coater to evenly coat the slurry onto the surface of copper foil. Dry the slurry in a vacuum drying oven at 80℃ for 12 hours. Then, cut the Cu foil coated with active material into circular pieces with a diameter of 12mm and transfer them to a glove box for later use.

[0054] The half-cell assembly was carried out in an Ar atmosphere glove box. The negative electrode used was the aforementioned resin / asphalt-based hard carbon electrode. The electrolyte was a 1.0 mol / L commercial electrolyte with the following formulation: NaPF6 dissolved in EC:DMC = 1:1 by volume. The counter electrode was a metallic Na sheet. The battery case was of CR2032 specification. The battery was assembled into a coin cell and then charge-discharge tests were conducted at a current density of 0.1C (1C = 300 mAh / g) and at different rates.

[0055] Example 5 A method for preparing a resin / asphalt-based hard carbon material specifically includes the following steps: S1. Place the phenolic resin in a carbonization furnace for pre-carbonization. Raise the temperature to 600℃ at a rate of 3℃ / min, then keep it at that temperature for 2 hours. After it cools naturally to room temperature, take it out and pulverize it using an air jet mill. The particle size D50 of the pulverized resin is controlled to be around 10μm.

[0056] S2. Add asphalt with a D50 of 100μm and polyoxymethylene with a D50 of 100μm to the mixer in a mass ratio of 3:1. Mix them evenly at 100 revolutions / min for 60 minutes. Then, take them out and put them into a carbonization furnace for the first pre-oxidation. Raise the temperature to 300℃ at a heating rate of 2℃ / min and keep it at that temperature for 1 hour. After naturally cooling to room temperature, take them out and pulverize them with an air jet mill. The particle size D50 of the pulverized particles is controlled at about 10μm.

[0057] S3. The pre-oxidized asphalt with a particle size D50 of 10 μm obtained in step S2 and the pre-carbonized phenolic resin carbon with a particle size D50 of 10 μm obtained in step S1 are added to the mixer at a mass ratio of 1:1. The mixture is then stirred at 120 revolutions / min for 150 min until homogeneous. After stirring, the mixture is removed and placed in a carbonization furnace for a second pre-oxidation. The temperature is raised to 450°C at a heating rate of 2°C / min and then kept at that temperature for 2 hours. After naturally cooling to room temperature, the mixture is removed and pulverized using an air jet mill. The particle size D50 of the pulverized mixture is controlled to be around 7 μm.

[0058] S4. The particle size D50 of 7 μm obtained in step S3 is placed into a carbonization furnace for high-temperature carbonization. The temperature is increased to 1400℃ at a heating rate of 2℃ / min, and held for 2 hours. After natural cooling to room temperature, the material is passed through a 325-mesh sieve to obtain resin / asphalt-based hard carbon material.

[0059] The resin / asphalt-based hard carbon composite material prepared above is used as an active material in the preparation of sodium-ion batteries, including the following steps: Weigh out 9.3g, 0.2g, 0.3g, and 0.5g of resin / asphalt-based hard carbon composite material, CMC, SP, and SBR (40% solid content) respectively in a mass ratio of 93.0%:2.0%:3.0%:2.0%, and add them sequentially to a beaker while stirring. Add an appropriate amount of deionized water and stir for 6 hours until a uniform slurry is formed. Use a four-sided coater to evenly coat the slurry onto the surface of copper foil. Dry the slurry in a vacuum drying oven at 80℃ for 12 hours. Then, cut the Cu foil coated with active material into circular pieces with a diameter of 12mm and transfer them to a glove box for later use.

[0060] The half-cell assembly was carried out in an Ar atmosphere glove box. The negative electrode used was the aforementioned resin / asphalt-based hard carbon electrode. The electrolyte was a 1.0 mol / L commercial electrolyte with the following formulation: NaPF6 dissolved in EC:DMC = 1:1 by volume. The counter electrode was a metallic Na sheet. The battery case was of CR2032 specification. The battery was assembled into a coin cell and then charge-discharge tests were conducted at a current density of 0.1C (1C = 300 mAh / g) and at different rates.

[0061] Example 6 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 only in that the oxygen-containing organic polymer is polyethylene oxide.

[0062] Example 7 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 only in that the oxygen-containing organic polymer is polyvinyl acetate.

[0063] Example 8 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 only in that the oxygen-containing organic polymer is polylactic acid.

[0064] Example 9 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 only in that the oxygen-containing organic polymer is polybutylene succinate.

[0065] Example 10 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 only in that the oxygen-containing organic polymer is polyvinyl butyral.

[0066] Comparative Example 1 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 in that: polyoxymethylene is not added in S2, while the rest of the steps are the same as in Example 1, and the obtained battery material is tested using the same method as in Example 1.

[0067] Comparative Example 2 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 in that: no pre-carbonized phenolic resin is added in S3, while the rest of the steps are the same as in Example 1, and the obtained battery material is tested using the same method as in Example 1.

[0068] Comparative Example 3 A method for preparing a resin / asphalt-based hard carbon material, which differs from Example 1 in that: secondary pre-oxidation is not performed in S3, while the rest of the steps are the same as in Example 1, and the obtained battery material is tested using the same method as in Example 1.

[0069] Performance testing The sodium-ion batteries prepared in Examples 1-10 and Comparative Examples 1-3 were subjected to electrochemical performance tests, and the test results are shown in Table 1.

[0070] Table 1. Electrochemical performance of sodium-ion batteries

[0071] According to the test results: 1. Compared with Example 1, Example 2 shows that the pre-carbonization temperature of phenolic resin is increased to 800℃, the phenolic resin is almost completely carbonized, the property deviation with asphalt is increased, the sintering inhibition effect in the secondary pre-oxidation is better, the first coulombic efficiency is increased to 93.1%, and the first discharge specific capacity is significantly improved. 2. Compared with Example 1, Example 3 replaces polyoxymethylene with polycarbonate. Polycarbonate has a higher pyrolysis temperature, is easier to maintain its shape during the first pre-oxidation, has a better sintering inhibition effect, and the first discharge specific capacity reaches 370.1 mAh / g, which is the highest among all examples. 3. Compared with Example 1, Example 4 shows that the primary pre-oxidation temperature of asphalt is too high, which leads to a reduction in volatile substances in asphalt, an increase in carbonization rate, and a decrease in the cross-linking and doping effects of secondary pre-oxidation. Therefore, the capacity and initial coulombic efficiency are slightly reduced. 4. Compared with Example 1, Example 5 increased the proportion of phenolic resin carbon material, further optimized the sintering inhibition effect, and improved the first coulombic efficiency and sodium storage capacity. 5. Comparative Example 1 did not add oxygen-containing organic polymers, had no effective oxygen doping and could not suppress the primary sintering of asphalt, resulting in the worst performance; Comparative Example 2 did not add phenolic resin carbon materials, and the secondary pre-oxidation resulted in single asphalt, which was prone to sintering and had poor electrochemical performance; Comparative Example 3 did not undergo secondary pre-oxidation, and the phenolic resin and asphalt sintered again during high-temperature carbonization, resulting in a significant reduction in capacity and initial coulombic efficiency.

[0072] The above test results fully demonstrate that the preparation method of the present invention can effectively inhibit the sintering of asphalt, significantly improve the sodium storage capacity and first coulombic efficiency of hard carbon materials, and the prepared hard carbon materials have excellent electrochemical performance.

[0073] In summary, this invention introduces an oxygen-containing organic polymer during the first pre-oxidation process. The difference in properties between the oxygen-containing organic polymer and asphalt reduces the probability of asphalt sintering, which is beneficial for improving the uniformity of hard carbon materials. Simultaneously, the oxygen atoms inherent in the oxygen-containing organic polymer enable oxygen doping, increasing the active sites of the hard carbon material. During the second pre-oxidation process, oxygen atoms are introduced again for doping. Simultaneously, the asphalt material and resin carbon material, both having undergone the first pre-oxidation, come into contact and form numerous interfaces, further inhibiting asphalt sintering by utilizing their property differences. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial applicability.

[0074] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a resin / asphalt-based hard carbon material, characterized in that, Includes the following steps: (1) Phenolic resin is pre-carbonized, then crushed and sieved to obtain phenolic resin carbon material; (2) Mix asphalt with oxygen-containing organic polymer evenly, and then perform the first pre-oxidation under oxygen conditions to obtain a pre-oxidized asphalt material. After cooling, crush it. (3) Mix the phenolic resin carbon material obtained in step (1) and the pre-oxidized asphalt material obtained in step (2) evenly, and then perform a second pre-oxidation under oxygen conditions to obtain a resin / asphalt composite material precursor. After cooling, crush it. (4) The resin / asphalt composite material precursor obtained in step (3) is subjected to high-temperature carbonization, cooled and sieved to obtain resin / asphalt-based hard carbon material.

2. The preparation method according to claim 1, characterized in that, In step (1), the pre-carbonization temperature of the phenolic resin is 600~800℃.

3. The preparation method according to claim 1, characterized in that, In step (2), asphalt powder with a softening point of 180~250℃ is selected.

4. The preparation method according to claim 1, characterized in that, In step (2), the oxygen-containing organic polymer is selected from at least one of polyoxymethylene, polyethylene oxide, polycarbonate, polyvinyl acetate, polylactic acid, polybutylene succinate, and polyvinyl butyral; the mass ratio of the asphalt to the oxygen-containing organic polymer is 10:1 to 1:

1.

5. The preparation method according to claim 1, characterized in that, The conditions for the first pre-oxidation are: oxidation temperature of 270~420℃, heating rate of 1~2℃ / min, and holding time of 240~480min.

6. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the phenolic resin carbon material to the primary pre-oxidized asphalt material is 10:1 to 1:

2.

7. The preparation method according to claim 1, characterized in that, In step (3), the conditions for the second pre-oxidation are: the oxidation temperature is 400~600℃, which is lower than the phenolic resin pre-carbonization temperature in step (1); the heating rate is 1~2℃ / min; and the holding time is 120~240min.

8. The preparation method according to claim 1, characterized in that, In step (4), the conditions for high-temperature carbonization are: carbonization temperature of 1000~1500℃, heating rate of 1~5℃ / min, and holding time of 60~360min.

9. A negative electrode sheet, characterized in that, The negative electrode sheet is prepared using a resin / asphalt-based hard carbon material prepared by the method described in any one of claims 1 to 8 as the active material.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode sheet described in claim 9.

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