Method for preparing ultrahigh-capacity hard carbon material through strong oxidant pore forming and application of ultrahigh-capacity hard carbon material

Abstract

The invention provides a method for preparing an ultrahigh-capacity hard carbon material through strong oxidant pore forming and application of the ultrahigh-capacity hard carbon material, and the preparation method comprises the following steps: firstly, performing low-temperature carbonization and acid pickling treatment on a biomass raw material to obtain a pre-carbonized material, then oxidizing the pre-carbonized material through a strong oxidant, and finally performing high-temperature carbonization to obtain the ultrahigh-capacity hard carbon material. According to the invention, the mechanism that biomass raw materials are pre-carbonized to generate oxygen-containing compounds and other impurities is utilized, and the oxygen-containing compounds and other impurities are removed through acid pickling to form a pre-carbonized material with a porous structure; meanwhile, by controlling the addition amount of the strong oxidant, more defect and closed pore structures are formed in the hard carbon material structure, so that the reversible capacity and the first effect of the prepared hard carbon material are comprehensively improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant and its application. Background Technology

[0002] The resurgence of sodium-ion batteries represents a strategic choice for the energy storage sector in addressing resource security, cost control, and the need for diversified technological approaches. Leveraging breakthroughs in materials science (especially hard carbon anodes), it is rapidly evolving from an alternative technology into a practical product with strong competitiveness in specific areas, and is expected to work alongside lithium-ion batteries to build a more resilient and sustainable green energy storage future.

[0003] Hard carbon, also known as non-graphitized carbon, is a type of amorphous carbon material that is difficult to transform into a graphite crystalline structure even under high-temperature heat treatment. Its precursors are typically polymers, biomass, or resins rich in cross-linked structures. During pyrolysis, the molecular chains are difficult to rearrange in an orderly manner, resulting in a highly disordered carbon structure. With increasing global focus on energy storage costs and resource sustainability, hard carbon, thanks to its wide availability of raw materials and compatibility with sodium batteries, is moving from the laboratory to the forefront of industrialization, becoming a crucial material foundation for next-generation energy storage systems.

[0004] However, the industrial application of existing hard carbon materials still faces two major bottlenecks: First, the sodium storage capacity is limited, which is difficult to meet the needs of high-energy-density sodium-ion batteries; second, the first-cycle coulombic efficiency is low, mainly due to irreversible reactions caused by excessive defects and residual impurities on the material surface, as well as the confinement of sodium ions in disordered pores. This not only reduces the energy conversion efficiency of the battery, but also affects the cycle stability.

[0005] Therefore, there is an urgent need to find a method for preparing hard carbon that can improve the reversible sodium storage capacity of hard carbon while stabilizing the first-cycle coulombic efficiency, which is of great significance for promoting the sustainable development of the energy storage field. 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 ultra-high capacity hard carbon materials by creating pores with a strong oxidant, which solves the problem of limited sodium storage capacity of hard carbon materials in the prior art and improves the problem of low initial efficiency of sodium-ion batteries; at the same time, this invention will also provide an ultra-high capacity hard carbon material; in addition, this invention will also provide applications of the ultra-high capacity hard carbon material.

[0007] To achieve the above and other related objectives, the present invention provides the following technical solutions: In a first aspect, the present invention provides a method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant, comprising the following steps: S1. Using biomass materials as raw materials, after crushing and pretreatment, the materials are placed under inert gas protection for pre-carbonization treatment to obtain pre-carbonized materials. S2. The pre-carbonized material obtained in step S1 is sequentially acid-washed in hydrochloric acid, hydrofluoric acid and nitric acid for a certain period of time, then washed and filtered with deionized water, and dried to obtain porous pre-carbonized material. S3. The porous pre-carbonized material and the strong oxidant are ball-milled and mixed evenly in proportion to obtain the composite product; S4. The composite product obtained in step S3 is placed under inert gas protection for carbonization treatment to obtain ultra-high capacity hard carbon material.

[0008] Furthermore, in step S1, the biomass material is selected from one or more of peanut shells, jackfruit shells, coconut shells, durian shells, and mangosteen shells. This invention uses these abundant and environmentally friendly biomass sources as raw materials, resulting in low cost, low energy consumption, and high cost-effectiveness of the obtained hard carbon material.

[0009] Hard carbon prepared from biomass raw materials is rich in oxygen-containing functional groups. During pyrolysis, these groups form nanoparticles or oxygen-containing compounds that can expand the carbon layer, catalyze the formation of graphitized microcrystals, and leave behind abundant nanopores after subsequent acid leaching. This porous structure is crucial for sodium storage. During carbonization, oxygen atoms in these molecules can be partially retained in the carbon framework, forming natural oxygen doping, increasing surface defects and active sites in the material, which is beneficial for improving the surface adsorption capacity of sodium ions.

[0010] Furthermore, in step S1, the temperature of the pre-carbonization treatment is 400~600℃, the time of the pre-carbonization treatment is 3~5h, and the heating rate is 3~5℃ / min.

[0011] Furthermore, in step S1, the inert gas includes nitrogen, argon, or a nitrogen-argon mixture.

[0012] Furthermore, in step S2, the concentrations of hydrochloric acid, hydrofluoric acid, and nitric acid are all 0.1~3 mol / L. Preferably, the concentrations of the hydrochloric acid, hydrofluoric acid, and nitric acid solutions are all 1 mol / L.

[0013] Furthermore, in step S2, stirring is performed during the pickling process, and the pickling stirring time is 6~12 hours.

[0014] This invention involves sequentially acid-washing pre-carbonized materials in hydrochloric acid, hydrofluoric acid, and nitric acid solutions. This process thoroughly removes impurities such as oxides from the pre-carbonized material, generating nanopores. By controlling the acid dosage and acid-washing time, the cost is lower, and it is easier to achieve large-scale industrial production. During the acid-washing process, if the solution acidity is too low and the time is too short, impurities cannot be completely removed; if the acidity is too high and the time is too long, too much acid will remain, affecting the next step. This invention, through reasonable control of the acid dosage and acid-washing time, can thoroughly remove impurities and generate sufficient nanopores without over-washing, which would lead to a loose structure and a significant reduction in sodium storage performance.

[0015] Furthermore, in step S2, the acid-washed product is washed with deionized water and then transferred to a vacuum oven for drying at a temperature of 80~120℃ for 24~36h.

[0016] Furthermore, in step S3, the strong oxidant includes at least one of pyridine-N-oxide, sodium hypochlorite, potassium hypochlorite, and hydrogen peroxide.

[0017] Furthermore, the strong oxidant is preferably pyridine-N-oxide. Sodium hypochlorite and potassium hypochlorite have extremely strong oxidizing activity and violent reactions, making it difficult to precisely control the degree of oxidation; while pyridine-N-oxide has a mild and controllable oxidizing intensity. Its oxidation effect mainly targets the unsaturated carbon bonds and weak oxygen-containing functional groups in the pre-carbonized material, directionally breaking and reconstructing the structure; even at an addition ratio close to the upper limit (e.g., 1:1), it will not cause severe damage to the carbon skeleton. The oxidizing activity of hydrogen peroxide is greatly affected by environmental factors. During ball milling and subsequent carbonization, it is prone to decomposition and failure, leading to fluctuations in oxidation efficiency; while pyridine-N-oxide has stronger chemical stability. It will not spontaneously decompose during the ball milling (room temperature) and pretreatment stages before high-temperature carbonization. The dosage of oxidant can be precisely controlled, the oxidation effect is stable and repeatable, no additional control of the reaction environment is required, and the process tolerance is higher.

[0018] Compared to other strong oxidants, pyridine-N-oxides have the core advantages of solving problems such as over- or under-oxidation, uneven dispersion, residual impurities, and complex processes associated with other oxidants. Furthermore, through the dual effects of pore formation and nitrogen doping, they maximize the sodium storage capacity, first-cycle coulombic efficiency, and cycle stability of hard carbon materials. This makes them the optimal oxidant choice for preparing ultra-high capacity hard carbon materials, better meeting the comprehensive requirements of the sodium-ion battery industry for material performance, process stability, and environmental friendliness. As a strong oxidant, pyridine-N-oxides achieve a synergistic balance of "controllable oxidation, interfacial compatibility, residue-free characteristics, and dual effects of pore formation and nitrogen doping."

[0019] Furthermore, the mass ratio of the porous pre-carbonized material to the strong oxidant is 1:0.1~1.

[0020] By controlling the ratio of pre-carbonized material to strong oxidant, the prepared hard carbon material exhibits richer defects and nanopores. When used as a negative electrode material in sodium-ion batteries, it can adsorb and fill more sodium ions, significantly improving the battery's sodium storage capacity. When the strong oxidant dosage is low, the porous pre-carbonized material cannot be deeply oxidized, resulting in fewer defects and nanopores generated during subsequent carbonization. When the strong oxidant dosage is high, excessive defects easily form on the hard carbon surface, leading to irreversible capacity loss. Therefore, this invention promotes a good bond between the porous pre-carbonized material and the strong oxidant by controlling the mass ratio, ensuring that the final hard carbon material is suitable for storing sufficient sodium ions while guaranteeing reversible capacity release. Preferably, the mass ratio of the porous pre-carbonized material to the strong oxidant is 1:0.5.

[0021] Furthermore, in step S3, the ball milling time is 4~8 hours.

[0022] Furthermore, in step S4, the carbonization temperature is 1200~1600℃, the carbonization time is 2~3h, and the heating rate is 3~5℃ / min.

[0023] Furthermore, in step S4, the inert gas is selected from nitrogen, argon, or a nitrogen-argon mixture.

[0024] In a second aspect, the present invention provides an ultra-high capacity hard carbon material prepared by the above method.

[0025] A third aspect of the present invention provides a negative electrode sheet, wherein the negative electrode sheet uses the aforementioned ultra-high capacity hard carbon material as the negative electrode active material. The negative electrode sheet is prepared by the following steps: T1. A negative electrode slurry is prepared by mixing ultra-high capacity hard carbon material, conductive agent and binder in a certain proportion. T2. The negative electrode slurry is coated onto the current collector and dried to obtain the negative electrode sheet.

[0026] Furthermore, in step T1, the mass ratio of hard carbon material, conductive agent, and binder is (7~8):(2~1):1. Preferably, the mass ratio of hard carbon material, conductive agent, and binder is 7:2:1 or 8:1:1.

[0027] Furthermore, in step T1, the conductive agent includes conductive carbon black. The binder includes any one of sodium carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), and sodium alginate; preferably sodium carboxymethyl cellulose (CMC). The solvent used for polyvinylidene fluoride (PVDF) is N-methylpyrrolidone (NMP); the solvent used for sodium carboxymethyl cellulose (CMC) and sodium alginate is water.

[0028] Furthermore, in step T2, the current collector is a copper foil or an aluminum foil; preferably an aluminum foil.

[0029] Furthermore, in step T2, the drying temperature is 80~120℃, and the drying time is 12~24h.

[0030] 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.

[0031] In one embodiment of the present invention, the electrolyte comprises a sodium salt and a non-aqueous solvent. The sodium salt is any one of NaClO4 and NaPF6; the non-aqueous solvent is any one or a combination of ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), and dimethyl carbonate (DMC). In the electrolyte, the concentration of the sodium salt is 0.8~1.5 mol / L.

[0032] Preferably, when the sodium salt is NaClO4, the non-aqueous solvent is a mixture of EC and DEC with a volume ratio of 1:1, or PC is used as the non-aqueous solvent; when the sodium salt is NaPF6, the non-aqueous solvent is a mixture of EC, DMC and DEC with a volume ratio of 1:1:1, or a mixture of EC and PC with a volume ratio of 1:1 is used as the non-aqueous solvent.

[0033] As described above, the method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant according to the present invention and its application have the following beneficial effects: 1. This invention utilizes biomass raw materials rich in oxygen-containing functional groups to prepare hard carbon. During pyrolysis, these materials form nanoparticles or oxygen-containing compounds that can "expand" the carbon layer, catalyze the formation of graphitized microcrystals, and leave behind abundant nanopores after subsequent acid washing. This pore structure is crucial for sodium storage. Furthermore, during carbonization, oxygen atoms in these molecules can be partially retained in the carbon framework, forming natural oxygen doping, increasing surface defects and active sites in the material, which is beneficial for improving the surface adsorption capacity of sodium ions.

[0034] 2. This invention removes impurities such as oxides from the pre-carbonized material by sequentially rinsing it in hydrochloric acid, hydrofluoric acid, and nitric acid solutions, thereby generating nanopores. By controlling the amount of acid and the stirring time, impurities can be thoroughly removed and sufficient nanopores can be generated without over-rinsing, which would result in a loose structure and a significant reduction in sodium storage performance. Moreover, it is lower in cost and easier to achieve large-scale industrial production.

[0035] 3. This invention preferentially uses pyridine-N-oxide as a strong oxidant, which not only solves the problems of over- or under-oxidation, uneven dispersion, residual impurities, and complex processes of other oxidants, but also maximizes the sodium storage capacity, first-cycle coulombic efficiency, and cycle stability of hard carbon materials through the dual effects of pore formation and nitrogen doping. It is the optimal oxidant choice for preparing ultra-high capacity hard carbon materials, and is more in line with the comprehensive requirements of sodium-ion battery industrialization for material performance, process stability, and environmental protection.

[0036] 4. By adjusting the ratio of pre-carbonized material to strong oxidant, the present invention prepares hard carbon material with more defects and nanopores. When used as a negative electrode material for sodium-ion batteries, it can adsorb and fill more sodium ions, which can greatly improve the sodium storage capacity of the battery.

[0037] 5. The preparation method of the present invention is simple to operate and has a short process flow, making it suitable for large-scale industrial production; the prepared hard carbon material has the characteristics of high defects and porosity, which can greatly improve the sodium storage performance when applied to sodium-ion batteries. Attached Figure Description

[0038] Figure 1 This is a SEM image of the ultra-high capacity hard carbon material prepared in Example 2 of the present invention.

[0039] Figure 2 This is the first coulombic efficiency diagram of the sodium-ion battery prepared in Example 2 of the present invention. Detailed Implementation

[0040] 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.

[0041] Example 1 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. The pre-carbonized material obtained in step S1 is transferred to a beaker and acid-washed by stirring with 1 mol / L hydrochloric acid, hydrofluoric acid and nitric acid for 8 hours in sequence. Finally, it is washed with deionized water, filtered, and placed in a vacuum oven to dry at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material obtained in step S2, transfer it to a ball mill jar, add 0.1g of the strong oxidant pyridine-N-oxide, and ball mill for 6h to obtain the composite material. S4. The composite material obtained in step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0042] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0043] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 320.1mAh / g, and the first coulombic efficiency was 91.1%.

[0044] Example 2 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. The pre-carbonized material obtained in step S1 is transferred to a beaker and acid-washed by stirring with 1 mol / L hydrochloric acid, hydrofluoric acid and nitric acid for 8 hours in sequence. Finally, it is washed with deionized water, filtered, and placed in a vacuum oven to dry at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material obtained in step S2, transfer it to a ball mill jar, add 0.5g of the strong oxidant pyridine-N-oxide, and ball mill for 6h to obtain the composite material. S4. The composite material obtained in step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0045] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0046] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 403.1mAh / g, and the first coulombic efficiency was 93.6%.

[0047] Example 3 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. The pre-carbonized material obtained in step S1 is transferred to a beaker and acid-washed by stirring with 1 mol / L hydrochloric acid, hydrofluoric acid and nitric acid for 8 hours in sequence. Finally, it is washed with deionized water, filtered, and placed in a vacuum oven to dry at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material obtained in step S2, transfer it to a ball mill jar, add 1g of the strong oxidant pyridine-N-oxide, and ball mill for 6h to obtain the composite material. S4. The composite material obtained in step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0048] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0049] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 310.2mAh / g, and the first coulombic efficiency was 88.2%.

[0050] Example 4 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. Transfer the pre-carbonized material obtained in step S1 to a beaker, and wash it with 0.1 mol / L hydrochloric acid, hydrofluoric acid and nitric acid in sequence for 6 hours. Finally, wash and filter it with deionized water, place it in a vacuum oven and dry it at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material obtained in step S2, transfer it to a ball mill jar, add 0.1g of the strong oxidant pyridine-N-oxide, and ball mill for 6h to obtain the composite material. S4. The composite material obtained in step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0051] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0052] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 320.7mAh / g, and the first coulombic efficiency was 90.4%.

[0053] Example 5 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. The pre-carbonized material obtained in step S1 is transferred to a beaker and acid-washed by stirring with 3 mol / L hydrochloric acid, hydrofluoric acid and nitric acid for 12 h in sequence. Finally, it is washed with deionized water, filtered, and placed in a vacuum oven to dry at 100℃ for 24 h to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material from step S2, transfer it to a ball mill jar, add 0.1g of the strong oxidant pyridine-N-oxide, and ball mill for 6 hours to obtain the composite material. S4. The composite material from step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0054] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0055] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 298.5mAh / g, and the first coulombic efficiency was 89.1%.

[0056] Example 6 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. The pre-carbonized material obtained in step S1 is transferred to a beaker and acid-washed by stirring with 1 mol / L hydrochloric acid, hydrofluoric acid and nitric acid for 8 hours in sequence. Finally, it is washed with deionized water, filtered, and placed in a vacuum oven to dry at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material obtained in step S2, transfer it to a ball mill jar, add 0.1g of strong oxidant sodium hypochlorite, and ball mill for 6 hours to obtain the composite material. S4. The composite material obtained in step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0057] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0058] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 310.5mAh / g, and the first coulombic efficiency was 90.0%.

[0059] Example 7 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. The pre-carbonized material obtained in step S1 is transferred to a beaker and acid-washed by stirring with 1 mol / L hydrochloric acid, hydrofluoric acid and nitric acid for 8 hours in sequence. Finally, it is washed with deionized water, filtered, and placed in a vacuum oven to dry at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material obtained in step S2, transfer it to a ball mill jar, add 0.1g of strong oxidant potassium hypochlorite, and ball mill for 6 hours to obtain the composite material. S4. The composite material obtained in step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0060] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0061] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 307.2mAh / g, and the first coulombic efficiency was 89.1%.

[0062] Example 8 A method for preparing ultra-high capacity hard carbon materials by creating pores using a strong oxidant includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. The pre-carbonized material obtained in step S1 is transferred to a beaker and acid-washed by stirring with 1 mol / L hydrochloric acid, hydrofluoric acid and nitric acid for 8 hours in sequence. Finally, it is washed with deionized water, filtered, and placed in a vacuum oven to dry at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material obtained in step S2, transfer it to a ball mill jar, add 0.1g of the strong oxidant hydrogen peroxide, and ball mill for 6 hours to obtain the composite material. S4. The composite material obtained in step S3 is transferred to a tube furnace and calcined at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain an ultra-high capacity hard carbon material. The ultra-high capacity hard carbon material prepared above was used as the negative electrode active material. It was mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1, and water solvent was added to make a negative electrode slurry. The slurry was coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet was obtained by rolling and punching.

[0063] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0064] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 296.2mAh / g, and the first coulombic efficiency was 87.6%.

[0065] Comparative Example A method for preparing a hard carbon material includes the following steps: S1. Crush 5g of durian shells using a crusher, place them in a corundum ceramic boat, transfer them to a tube furnace, and calcine them at a heating rate of 5℃ / min to 500℃ for 4 hours under a nitrogen protective atmosphere to obtain pre-carbonized material. S2. Transfer the pre-carbonized material obtained in step S1 to a beaker, wash and filter it with deionized water, place it in a vacuum oven, and dry it at 100°C for 24 hours to obtain a porous pre-carbonized material. S3. Take 1g of the porous pre-carbonized material from step S2, transfer it to a ball mill jar, and ball mill for 6 hours to obtain the ball-milled material. S4. Transfer the ball-milled material from step S3 to a tube furnace, and calcine it at 1400°C for 2 hours under a nitrogen protective atmosphere at a heating rate of 5°C / min to obtain a hard carbon material. The hard carbon material prepared above is used as the negative electrode active material. It is mixed evenly with sodium carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 8:1:1. Water solvent is added to make a negative electrode slurry, which is coated on aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. The negative electrode sheet is obtained by rolling and punching.

[0066] Using a sodium sheet as the counter electrode, the aforementioned negative electrode was assembled into a 2032 button cell in a glove box under an argon protective atmosphere where the water and oxygen contents were both less than 0.1 ppm. The electrolyte used contained NaClO4 as the sodium salt at a concentration of 1 mol / L, and a 1:1 volume ratio mixture of EC and DEC as the non-aqueous solvent.

[0067] Tests showed that at 27℃ and a current density of 15mA / g, the first charge capacity was 270.3mAh / g, and the first coulombic efficiency was 80.4%.

[0068] As can be seen from the test results of the above 7 embodiments, the hard carbon material prepared in Example 2 has the best performance.

[0069] Comparing Example 2 with Examples 1 and 3, it can be seen that the amount of strong oxidant added in step S3 affects the surface and internal structure of the hard carbon, thereby affecting the electrochemical performance of the hard carbon material. By controlling the ratio of pre-carbonized material to strong oxidant, the prepared hard carbon material has more defects and nanopores. When used as a negative electrode material for sodium-ion batteries, it can adsorb and fill more sodium ions, which can greatly improve the sodium storage capacity of the battery. When the amount of strong oxidant is too small, the porous pre-carbonized material cannot be deeply oxidized, and fewer defects and nanopores are generated in the subsequent carbonization process. When the amount of strong oxidant is too large, too many defects are easily formed on the surface of the hard carbon, resulting in irreversible capacity loss. Therefore, this invention promotes a good combination between the porous pre-carbonized material and the strong oxidant by controlling the mass ratio of the porous pre-carbonized material to the strong oxidant, so that the final hard carbon material is suitable for storing sufficient sodium ions on the one hand, and ensures reversible capacity release on the other. The optimal mass ratio of porous pre-carbonized material to strong oxidant is 1:0.5.

[0070] Comparing Example 1 with Examples 4 and 5, it can be seen that the concentrations of hydrochloric acid, hydrofluoric acid, and nitric acid, as well as the pickling time in step S2, affect the formation of defects in hard carbon materials. By controlling the concentrations and pickling time, the cost is lower and large-scale industrial production is easier to achieve. During the pickling process, if the acidity of the solution is too low and the time is too short, impurities cannot be completely removed. If the acidity is too high and the time is too long, too much acid will remain, affecting the next step. Therefore, it is necessary to control the acid concentration and pickling time to ensure the removal of impurities and the stability of the structure. The most preferred concentrations are 1 mol / L for hydrochloric acid, hydrofluoric acid, and nitric acid, and the pickling time is 8 hours.

[0071] Comparing Example 1 with the comparative example, it can be seen that the acid washing in step S2 and the strong oxidant in step S3 affect the structure of the hard carbon, thereby affecting its sodium storage performance. Therefore, the present invention enables the hard carbon material to exhibit optimal electrochemical performance by controlling the acid washing and the addition of strong oxidants.

[0072] Comparing Example 1 with Examples 6, 7, and 8 reveals that the choice of strong oxidant affects the performance of hard carbon materials. Pyridine-N-oxide, through directional oxidation and uniform dispersion, constructs a highly efficient sodium storage structure of micropores (sodium storage) + mesopores (mass transfer) + moderate defects (active sites), achieving a pore utilization rate close to 100%, thus resulting in the highest capacity. In contrast, chlorine-containing oxidants (sodium hypochlorite, potassium hypochlorite), due to their intense oxidation and uneven dispersion, form a structure of macropores + ineffective micropores + excessive defects, resulting in low sodium ion storage efficiency, and some sodium ions are trapped in disordered pores, leading to a decrease in reversible capacity. Hydrogen peroxide, due to insufficient oxidation efficiency, forms only a small number of pores on the surface, with a dense interior and limited sodium storage space, resulting in the lowest capacity.

[0073] Meanwhile, pyridine-N-oxides have no impurity residues, controllable defects, the lowest irreversible capacity, and nitrogen doping enhances conductivity, resulting in high ion transport efficiency and optimal first-time efficiency; chlorine-containing oxidant residues of Cl... — K + Impurities can trigger side reactions, and excessive defects can lead to an increase in irreversible adsorption. Insufficient oxidation of hydrogen peroxide can result in poor conductivity of the material and damage to the local carbon skeleton, leading to a high proportion of irreversible capacity and thus the lowest initial efficiency.

[0074] In summary, this invention provides a method for preparing ultra-high capacity hard carbon materials using a strong oxidant to create pores, and its application. This method first utilizes biomass raw materials to obtain pre-carbonized materials through low-temperature carbonization and acid washing. Then, the pre-carbonized materials are oxidized with a strong oxidant, and finally, high-temperature carbonization yields an ultra-high capacity hard carbon material. This invention utilizes the mechanism of oxygen-containing compounds and other impurities generated during the pre-carbonization of biomass raw materials. Acid washing removes these impurities, forming a porous pre-carbonized material. Simultaneously, by controlling the amount of strong oxidant added, more defects and closed-pore structures are formed in the hard carbon material structure, comprehensively improving the reversible capacity and initial efficiency of the prepared hard carbon material. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value.

[0075] 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 ultra-high capacity hard carbon materials by creating pores with a strong oxidant, characterized in that, Includes the following steps: S1. Using biomass materials as raw materials, after crushing and pretreatment, the materials are placed under inert gas protection for pre-carbonization treatment to obtain pre-carbonized materials. S2. The pre-carbonized material obtained in step S1 is sequentially acid-washed in hydrochloric acid, hydrofluoric acid and nitric acid for a certain period of time, then washed and filtered with deionized water, and dried to obtain porous pre-carbonized material. S3. The porous pre-carbonized material and the strong oxidant are ball-milled and mixed evenly in proportion to obtain the composite product; S4. The composite product obtained in step S3 is placed under inert gas protection for carbonization treatment to obtain ultra-high capacity hard carbon material.

2. The method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant according to claim 1, characterized in that, In step S1, the biomass material is selected from one or more of peanut shells, jackfruit shells, coconut shells, durian shells, and mangosteen shells.

3. The method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant according to claim 1, characterized in that, In step S1, the temperature of the pre-carbonization treatment is 400~600℃, and the time of the pre-carbonization treatment is 3~5h.

4. The method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant according to claim 1, characterized in that, In step S2, the concentrations of hydrochloric acid, hydrofluoric acid, and nitric acid are all 0.1~3 mol / L, and the acid washing stirring time is 6~12 h.

5. The method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant according to claim 1, characterized in that, In step S3, the strong oxidant includes at least one of pyridine-N-oxide, sodium hypochlorite, potassium hypochlorite, and hydrogen peroxide.

6. The method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant according to claim 5, characterized in that, In step S3, the mass ratio of the porous pre-carbonized material to the strong oxidant is 1:0.1~1.

7. The method for preparing ultra-high capacity hard carbon materials by creating pores with a strong oxidant according to claim 1, characterized in that, In step S4, the carbonization temperature is 1200~1600℃, the carbonization time is 2~3h, and the heating rate is 3~5℃ / min.

8. A high-capacity hard carbon material, characterized in that, It is prepared by the method of preparing ultra-high capacity hard carbon material by pore formation with strong oxidant as described in any one of claims 1 to 7.

9. A negative electrode sheet, characterized in that, The negative electrode sheet uses the ultra-high capacity hard carbon material as described in claim 8 as the negative electrode active material, and the negative electrode sheet is prepared by the following steps: T1. A negative electrode slurry is prepared by mixing ultra-high capacity hard carbon material, conductive agent and binder in a certain proportion. T2. The negative electrode slurry is coated onto the current collector and dried to obtain the negative electrode sheet.

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

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