Retired lithium battery recovered graphite reconstructed sp2 / sp3 hybrid synergistic sodium battery hard carbon negative electrode material as well as method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and relates to a decommissioned lithium battery recovered graphite reconstructed sp2 / sp3 hybrid synergistic sodium battery hard carbon negative electrode material as well as a method and application of the decommissioned lithium battery recovered graphite reconstructed sp2 / sp3 hybrid synergistic sodium battery hard carbon negative electrode material. The preparation method comprises the following steps: (1) carrying out oxidation layer expansion and micro-explosion pore-forming on waste graphite by using a supercritical fluid technology to assist an oxidizing liquid; (2) carrying out secondary pore structure regulation and control by using a pore-forming agent; (3) washing with ethanol and acid liquor until the solution is neutral, and centrifugally drying; and (4) the electrochemical stability and conductivity are improved through high-temperature carbonization. The treatment method disclosed by the invention is simple to operate, green and environment-friendly in reaction process and low in recovery cost, realizes low-pollution conversion from the waste graphite to the sodium-ion battery sp2 / sp3 hybrid synergistic carbon negative electrode material, improves the electrochemical performance, and provides a new thought for battery recovery and development of the sodium-ion battery carbon negative electrode material.

Description

Technical Field

[0001] This invention relates to the technical field of sodium-ion batteries, and more particularly to a method for recycling retired lithium-ion batteries using graphite reconstructing sp. 2 / sp 3 Hybridized synergistic sodium-ion hard carbon anode materials, their preparation methods, and applications. Background Technology

[0002] As the global energy structure shifts towards renewable energy, sodium-ion batteries have become an important supplement to lithium-ion batteries due to their abundant resources and low cost. However, the large ionic radius of sodium ions makes their embedding in traditional graphite anodes difficult, resulting in insufficient interlayer spacing (graphite d 002 The kinetic hysteresis and low reversible capacity caused by the ≈0.34 nm atom density severely restrict its practical application. To address this, researchers have focused on materials such as hard carbon and heteroatom-doped carbon, but their high raw material costs (such as phenolic resins and biomass precursors) and geographical limitations restrict their large-scale development.

[0003] On the other hand, with the peak of lithium-ion battery retirement approaching, the recycling and reuse of graphite from retired lithium-ion batteries has become an urgent issue. Traditional recycling processes often employ high-temperature incineration or strong acid leaching (such as HF, concentrated H2SO4), which can purify graphite, but suffer from problems such as high energy consumption, release of toxic gases, and damage to the microstructure, making it difficult to directly use recycled graphite in sodium battery systems. Recent studies have attempted to increase interlayer spacing through oxidation (such as H2O2, KMnO4 oxidation), but conventional liquid-phase oxidation easily introduces excessive oxygen-containing functional groups (C=O, -COOH), leading to a decrease in initial efficiency (<60%) and deterioration in cycle stability. In addition, if residual metallic impurities (Cu, Al, etc.) in the recycled graphite are not completely removed, they will trigger side reactions and exacerbate capacity decay.

[0004] To address the aforementioned challenges, this invention proposes a supercritical carbon dioxide (SC-CO2)-assisted strategy for the regeneration and structural control of graphite recovered from retired lithium batteries, achieving an innovative breakthrough through multi-scale collaborative design. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a method for recycling decommissioned lithium-ion batteries using graphite reconstructing sp. 2 / sp 3 The preparation method of hybrid synergistic sodium-electric hard carbon anode material has the advantages of being green and environmentally friendly, economical and practical, having excellent performance, and being strategic.

[0006] The second objective of this invention is to provide a method for recycling decommissioned lithium-ion batteries using graphite reconstructed sp. 2 / sp 3 Hybridized synergistic sodium-carbon hard anode materials have the advantages of large interlayer spacing and abundant pores.

[0007] The third objective of this invention is to provide a method for recycling decommissioned lithium-ion batteries using graphite reconstructed sp. 2 / sp 3 The application of hybrid synergistic sodium-carbon anode materials ensures that sodium-ion batteries can have excellent electrochemical performance when used as anode materials.

[0008] The technical solution adopted by this invention to solve its technical problem is: A method for recycling graphite from retired lithium batteries 2 / sp 3 The preparation method of hybrid synergistic sodium-electric hard carbon anode material includes the following steps: Step 1: Collect waste graphite and use supercritical fluid technology to assist in oxidation and layer expansion with oxidizing liquid, and create micro-explosion pores; Step 2: Secondary pore structure regulation using pore-forming agents; Step 3: Remove impurities sequentially with ethanol (to remove oxidizing liquids such as H2O2 solution) and acidic solution (to remove residual metal ions), and wash with deionized water until neutral to obtain the carbon precursor; Step 4: Carbon precursor is carbonized at high temperature to obtain sp 2 / sp 3 Hybridized carbon anode materials for sodium-ion batteries.

[0009] By employing the above technical solution, exfoliation and pore formation are first achieved using a supercritical fluid such as SC-CO2 assisted by an oxidizing liquid such as H2O2. SC-CO2's high diffusivity and low surface tension allow it to penetrate the graphite interlayers and assist in exfoliation, combined with rapid pressure relief to achieve micro-explosive pore formation. Furthermore, SC-CO2 can replace toxic solvents: it can replace HF / HCl, achieving environmentally friendly impurity removal and surface modification. In addition, H2O2 decomposes to generate ·OH free radicals, which attack the C / C bonds between graphite layers, introducing oxygen-containing groups (-OH, -COOH) and expanding the interlayer spacing. A secondary pore-forming process is performed on the graphite using KOH solution immersion, providing more active sites. Immersion in ethanol and acid effectively removes a series of impurities inherent in the graphite itself and those generated by subsequent processes. Further carbonization forms sp... 2 / sp 3 Hybridized synergistic carbon materials are used to obtain green, environmentally friendly, recyclable electrode materials with ideal electrochemical performance.

[0010] Furthermore, the waste graphite in step 1 originates from retired lithium-ion batteries, discarded lithium-ion batteries, and lithium-ion batteries with deteriorated performance, preferably obtained by dismantling lithium-ion batteries. More preferably, after dismantling the lithium-ion battery, the graphite negative electrode coating of the lithium-ion pouch battery is scraped off with a scraper to obtain a graphite negative electrode mixture, which is waste graphite.

[0011] Further, in step 1, the oxidizing liquid is at least one of H2O2, HNO3, H2SO4, and KMnO7 solutions. More preferably, the mass of the oxidizing substance in the oxidizing liquid is 2-4 times the mass of the waste graphite, and the oxidizing substance is at least one of H2O2, HNO3, H2SO4, and KMnO7. The oxidizing liquid is preferably an H2O2 solution. More preferably, the mass fraction of the H2O2 solution is 5-30%, and the mass ratio of H2O2 to waste graphite in the solution is 2-4:1.

[0012] Further, in step 1, the supercritical fluid in the supercritical fluid technology is at least one of CO2, N2, and CH4, and the supercritical conditions are the conditions for maintaining it as a supercritical fluid, more preferably: a temperature of 40-60 °C, a pressure of 6-15 MPa, and a treatment time of 4-36 hours, more preferably 12-24 hours. More preferably, when the supercritical fluid is CO2, the temperature is not lower than 40 °C and the pressure is not lower than 7.38 MPa, so that it is in a supercritical fluid state.

[0013] Further, in step 1, the method for supercritical fluid technology-assisted oxidative liquid oxidation layer expansion includes: Step 1.1: Place the waste graphite in an oxidizing liquid, with the mass ratio of the oxidizing substance to the waste graphite in the solution being 2-4:1. Place the solution in an ultrasonic instrument to uniformly disperse the graphite interlayer oxidation and exfoliation, and obtain a mixed solution. More preferably, the oxidizing liquid is an H2O2 solution with a mass fraction of 5-30%, and the oxidizing substance in the solution is H2O2; More preferably, the power range of the ultrasonic instrument is 100-300 W, and the ultrasonic time is 1-3 h; Step 1.2: Transfer the mixed solution obtained in Step 1.1 into a supercritical reactor; Step 1.3: Introduce CO2 gas at 7.3-8 MPa into the supercritical reactor described in Step 1.2, and keep it at 43-55 °C for 4-36 h, more preferably 12-24 h; Step 1.4: Open the supercritical knob of the supercritical reactor after the heat preservation described in Step 1.3 to quickly release pressure and induce micro-explosion to create pores.

[0014] Further, in step 2, the pore-forming agent is a KOH solution; more preferably, the concentration of the KOH solution is 1-5 mol / L (M), even more preferably 2 mol / L; more preferably, the mass ratio of KOH to graphite in the solution is 1-7:1; more preferably, KOH solid is added to 100 ml of deionized water to make its concentration 2 M and to prepare for the subsequent secondary pore-forming, and 1-3 g of graphite mixture is added to this KOH solution (the mass ratio of KOH to graphite in the solution is 1-7:1), and magnetically stirred for 4-20 h, the reaction time is 4-20 hours, and the temperature is 30-80℃; more preferably, the stirring speed is 300-1000 rpm.

[0015] Further, in step 3, the ethanol volume concentration is 95%; and / or the acidic solution is at least one of HCl, HNO3, and H2SO4, more preferably a mixed solution of HCl and HNO3, more preferably the concentrations of HCl and HNO3 in the mixed solution are 1-3 mol / L; more preferably the mass ratio of acidic solution to graphite is 1-4:1; more preferably the acid soaking time is 1-12 hours, and the temperature is 30-80℃; more preferably, the product after soaking and washing is centrifuged, washed with deionized water, and the resulting graphite mixture is placed in a forced-air drying oven or oven for drying and later use.

[0016] Further, in step 3, the impurity removal method includes: washing with ethanol after pore formation, preferably with an ethanol volume concentration of 95%, to remove residual H2O2 solution, etc.; acidic solution impurity removal using a 1-3M HCl and HNO3 mixed solution, soaking for 1-12 hours at a temperature of 30-80℃, to remove metallic impurities such as Li, Cu, Al, and K (metallic impurities 0.1%-4%); and controlling the final pH value at 6-7 during water washing and centrifugation. The preferred drying conditions after centrifugation are 80℃ for 12 hours to obtain a graphite oxide mixture with a purity ≥99%.

[0017] Furthermore, step 4 includes placing a porcelain boat containing a graphite mixture into a tube furnace, and controlling the tube furnace to operate at 1-10 °C / min under an inert atmosphere. -1 The temperature is increased to 300-900°C at a rate of [missing information], and calcined at a constant temperature for 1-3 hours. After calcination at a constant temperature, the temperature is cooled to room temperature to obtain the electrode material. More preferably, the inert atmosphere is at least one of nitrogen, helium, and argon.

[0018] Furthermore, the structural parameters of the prepared material are: interlayer spacing 0.3-0.5 nm, specific surface area 30-100 m². 2 / g, porosity 20%-40%, sp 3 / (sp 2 +sp 35%-40%, oxygen-containing groups (-OH, -COOH) 3%-10%.

[0019] To achieve the second objective mentioned above, the present invention provides the following technical solution: A method for recycling graphite from retired lithium batteries 2 / sp 3 Hybridized synergistic sodium-ion hard carbon anode material, prepared according to any of the preparation methods described above.

[0020] By adopting the above technical solution, graphite provides the basic carbon layer. Supercritical carbon dioxide assists in the oxidation of graphite by H2O2, attacking the C-C bonds between graphite layers and introducing oxygen-containing groups (-OH, -COOH) to expand the interlayer spacing of carbon. Furthermore, after secondary pore formation with KOH, the carbon layer exposes more porous structures, has larger sodium storage sites, and possesses good ionic conductivity.

[0021] To achieve the third objective mentioned above, the present invention provides the following technical solution: A method for recycling graphite from retired lithium batteries 2 / sp 3 Application of hybrid synergistic sodium-ion battery hard carbon anode material, and application of electrode materials prepared according to the described method in sodium-ion batteries.

[0022] By adopting the above technical solutions, the electrochemical performance of sodium-ion batteries is guaranteed, and a solution is provided for the recycling of green waste graphite and its application in the anode of sodium-ion batteries.

[0023] In summary, compared with the prior art, the beneficial effects of the present invention are as follows: 1. The method of this invention uses graphite recovered from retired lithium-ion batteries as raw material. The process involves supercritical fluid cleaning (such as SC-CO2) to expand the layers and create pores, secondary pore formation and regulation with KOH, acid washing to remove impurities, and finally high-temperature carbonization to optimize the graphite structure. This allows the graphite to achieve its desired spline properties. 2 The hybrid orbital structure partially transforms into one suitable for Na + stored sp 3 Hybrid orbital structures are used to obtain novel electrode materials with high rate capability and low recycling cost.

[0024] 2. In the electrode material of the present invention, graphite provides the basic carbon layer, and supercritical fluid such as SC-CO2 assisted oxidizing liquid such as H2O2 oxidizes graphite to increase the interlayer spacing of the carbon layer. Furthermore, KOH creates pores and provides abundant porosity, resulting in more sodium storage sites. By utilizing the intrinsic structure of graphite, it possesses excellent rate performance.

[0025] 3. This invention effectively improves the electrochemical performance of sodium-ion batteries by applying electrode materials to them, and provides a solution for recycling graphite from retired lithium-ion batteries for use as the negative electrode in sodium-ion batteries. Attached Figure Description

[0026] Figure 1 These are XRD patterns of the electrode materials in Embodiment 1 and Comparative Example 1 of the present invention; Figure 2 This is a SEM image of the electrode material in Embodiment 1 of the present invention; Figure 3 This is a SEM image of the electrode material of Comparative Example 1 of the present invention; Figure 4 The first 76 cycles of the electrode material in Comparative Example 1 of this invention; Figure 5 The first 76 cycles of the electrode material in Example 1 of this invention are shown. Detailed Implementation

[0027] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention's content can all achieve the stated reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0029] This invention discloses a method for reconstructing graphite sp from decommissioned lithium batteries. 2 / sp 3 A method for preparing hybrid synergistic sodium-ion hard carbon anode materials includes the following steps: Step 1: Collect waste graphite and use supercritical fluid technology to assist in oxidation and layer expansion with oxidizing liquid, and create micro-explosion pores; Step 2: Secondary pore structure regulation using pore-forming agents; Step 3: Wash sequentially with ethanol (to remove H2O2 solution), acidic solution (to remove residual metal ions), and deionized water until neutral; Step 4: Obtain sp through high-temperature carbonization 2 / sp 3 Hybridized carbon anode materials for sodium-ion batteries.

[0030] The present invention also discloses the application of the electrode material prepared by the above method in sodium-ion batteries.

[0031] Example 1

[0032] This invention discloses a method for reconstructing graphite from decommissioned lithium batteries. 2 / sp 3 A method for preparing hybrid synergistic sodium-ion hard carbon anode materials includes the following steps: An oxidizing liquid A is selected and added to the supercritical reactor. The oxidizing liquid is an H2O2 solution (mass fraction 30%).

[0033] Step 1: Scrape off the graphite negative electrode coating of the lithium-ion soft-pack battery. Collect the scraped graphite as waste graphite and place it in a supercritical reactor. Add liquid A (the mass ratio of A to waste graphite in the solution is 2:1). Then, introduce CO2 to reach a pressure of 7.5 MPa. Place it in an oven, adjust the temperature to 43℃, and keep it at that temperature for 12 hours. Quickly open the supercritical knob to release the pressure and collect the graphite.

[0034] Step 2: Prepare 100 ml of deionized water by adding KOH solid to make the concentration 2 M, in preparation for the next secondary pore formation. Add 2 g of the graphite mixture sample collected in Step 1 to this KOH solution and apply magnetic stirring (500 rpm) simultaneously. The reaction time is 4 h and the temperature is 50 ℃.

[0035] Step 3: After centrifugation, the collected graphite is immersed in a 95% ethanol solution (immersion time 2 h) to remove residual H2O2 solution, and centrifugation is continued. Then, it is placed in solution B for metal element removal. Solution B is a mixed solution of HCl and HNO3, with both HCl and HNO3 concentrations of 1M. When using, a certain amount of this mixed solution is taken, and graphite is added to make the mass ratio of solution to graphite 2:1; the immersion time is 3 h, and the immersion temperature is 60 ℃. After immersion in solution B, the product is collected by centrifugation and washed with deionized water until the pH reaches 7. The collected graphite is then dried in an oven for later use.

[0036] Step 4: First, place the porcelain boat containing graphite into the tube furnace. Under the protection of N2 atmosphere, control the tube furnace to operate at 5 °C / min. -1 The temperature was increased to 900 °C at a certain rate, and calcined at a constant temperature for 2 h. After calcination at a constant temperature, the temperature was cooled to room temperature to obtain the electrode material (the mass ratio of waste graphite to electrode material is 5:2).

[0037] Example 2-19

[0038] Based on Example 1, the supercritical temperature and pressure, supercritical holding time, type of oxidizing liquid, mass ratio of oxidizing liquid to graphite, acid washing and impurity removal liquid, and reaction temperature were changed as shown in Table 1 below:

[0039] Comparative Example 1

[0040] A ceramic boat containing graphite recycled from retired lithium-ion batteries was placed inside a tube furnace. Under a nitrogen atmosphere, the furnace was controlled to operate at 5°C per minute. -1 The temperature was increased to 900°C at a certain rate, and after constant temperature calcination for 2 hours, it was cooled to room temperature to obtain the electrode material.

[0041] Comparative Example 2

[0042] Graphite recovered from retired lithium-ion batteries was soaked in a 1M HCl solution for 3 hours at 60°C. After centrifugation to neutral, the solution was collected and dried. A ceramic boat containing the graphite mixture was placed in a tube furnace, and the furnace was heated at 5°C per minute under a nitrogen atmosphere. -1 The temperature was increased to 900°C at a certain rate, and after constant temperature calcination for 2 hours, it was cooled to room temperature to obtain the electrode material.

[0043] Comparative Example 3

[0044] Graphite recovered from retired lithium-ion batteries was soaked in a 1M HCl solution for 3 hours at 60°C. After centrifugation to neutral, the solution was collected and dried. A ceramic boat containing the graphite mixture was placed in a tube furnace, and the furnace was heated at 5°C per minute under a nitrogen atmosphere. -1 The temperature was increased to 300°C at a constant rate, calcined at a constant temperature for 2 hours, and then cooled to room temperature to obtain the electrode material.

[0045] Comparative Example 4

[0046] Graphite recovered from retired lithium-ion batteries was soaked in a 1M HCl solution for 3 hours at 60°C. After centrifugation to neutral, the solution was collected and dried. A ceramic boat containing the graphite mixture was placed in a tube furnace, and the furnace was heated at 5°C per minute under a nitrogen atmosphere. -1The temperature was increased to 600°C at a constant rate, calcined at a constant temperature for 2 hours, and then cooled to room temperature to obtain the electrode material.

[0047] Comparative Example 5

[0048] Based on Example 1, the experimental conditions and proportions remain unchanged, except that the supercritical gas CO2 is replaced with N2.

[0049] Comparative Example 6

[0050] Based on Example 1, the experimental conditions and proportions remain unchanged, except that the supercritical gas CO2 is replaced with CH4.

[0051] Comparative Example 7

[0052] Based on Example 1, the experimental conditions and proportions remained unchanged, but the pore-forming agent KOH was replaced with Na2CO3.

[0053] Comparative Example 8

[0054] Based on Example 1, the experimental conditions and proportions remained unchanged, but the pore-forming agent KOH was replaced with ZnCl2.

[0055] Comparative Example 9

[0056] Based on Example 1, the experimental conditions and proportions remained unchanged, but the pore-forming agent KOH was replaced with SiO2.

[0057] Comparative Example 10

[0058] The graphite recovered from retired lithium-ion batteries is used directly in the electrode material without any processing.

[0059] Comparative Example 11

[0060] Based on Example 1, the experimental conditions and proportions remain unchanged, but the order of operations in Step 1 and Step 2 is reversed.

[0061] Performance testing The electrode materials prepared in Examples 1-19 and Comparative Examples 1-6 were homogenized and coated with Super P and CMC in a mass ratio of 8:1:1 to form electrode sheets. The coated electrode sheets were dried in a vacuum drying oven at 120 °C for 12 h to ensure complete removal of the solvent, and then cut into circular electrode sheets with a diameter of 12 mm. A sodium metal sheet was used as the negative electrode, and the aforementioned prepared SP... 2 / sp 3A hybrid synergistic carbon anode material was used as the positive electrode, and the cells were assembled into a 2032 type coin cell. The electrolyte was 1M NaPF6 inDME = 100 vol%, and the separator was a glass fiber separator. The half-cell was assembled in the following order: positive electrode shell, positive electrode sheet, separator, electrolyte, sodium foil, gasket, spring sheet, and negative electrode shell, and then sealed using a fully automated sealing machine. After the cells were allowed to stand for 24 hours, electrochemical tests were performed using a Xinweihe electrochemical workstation. All electrochemical tests were conducted at 25°C. o The test was conducted under conditions C, primarily including constant current charge-discharge testing at a current density of 50 mA g. -1 The battery's first-cycle discharge specific capacity, first-cycle coulombic efficiency, and cycle performance were tested under the specified conditions.

[0062] The performance test results are as follows:

[0063] Analysis of the data obtained from the table, compared with Comparative Examples 1-4 and Comparative Example 10, shows that after the treatment in Examples 1 and others, the sp of waste graphite... 3 / (sp 2 +sp 3 The proportion of Na increases, among which interlayer spacing, specific surface area, porosity, and oxygen-containing functional groups are beneficial to Na. + The storage structure has been greatly improved. Correspondingly, as can be seen in Comparative Examples 5-9 and 11, its sp... 3 / (sp 2 +sp 3The proportion of sodium ions also increased, and their performance was improved compared to Comparative Examples 1-4 and 10. Comparative Examples 5-6 replaced supercritical fluids N2 and CH4, but their effect was inferior to that of supercritical fluid CO2. This is because N2 and CH4 have poor diffusion capabilities and higher surface tension characteristics than supercritical fluid CO2, making them unable to effectively penetrate the graphite interlayers and assist in exfoliation. However, they were still significantly better than Comparative Examples 1-4 and 10, and still had certain advantages compared to other comparative examples. Comparative Examples 7-9 used other pore-forming agents, which improved performance to some extent, but their effect was still significantly inferior to that of pore-forming agent KOH. This was because the lack of synergistic pore-forming effect of strong alkaline etching and high-temperature gas generation made it difficult to form suitable sodium ions. The optimized pore structure for transport; Comparative Example 10 did not undergo layer expansion, pore formation, and impurity removal processes, and its effect was far lower than that of Example 1; Comparative Example 11 first used KOH to form pores and then used supercritical CO2 to expand the layers and form pores, and the effect was significantly worse than the original order. This is because the strong alkaline etching of KOH will destroy the integrity of the graphite interlayer structure, resulting in loose and aggregated layers. Subsequently, supercritical carbon dioxide cannot accurately penetrate the interlayer to play a layer expansion role, and it cannot form a synergistic structure of "optimized interlayer spacing + interconnected pores" adapted to sodium ion transport. In the end, although the electrochemical performance of the material is improved compared with Comparative Example 10, it is significantly lower than that of Example 1 under the same conditions.

[0064] Figure 1 The XRD patterns of Comparative Example 1 and Example 1 show that acid washing effectively removed the metallic impurities contained in the waste graphite itself and those generated subsequently.

[0065] The electrode material obtained in Example 1, i.e., sp 2 / sp 3 The hybrid cooperating carbon was scanned under a scanning electron microscope, and the scanning results are as follows: Figure 2 As shown Figure 3 This is the SEM image for Comparative Example 1.

[0066] Following the directional reconstruction and pore-forming agent treatment in Example 1, the regular layered structure of the original graphite underwent significant expansion and porosity evolution, with a marked increase in interlayer spacing. Simultaneously, some sp² crystal domains were reconstructed into sp² / sp³ hybridized quasi-amorphous carbon frameworks. This structural modulation benefited from the abundant pore structure introduced by the pore-forming agent and the synergistic effect of topological defects and edge functional groups. The expanded layer structure and surface porosity jointly enhanced the Na₂O₃ content. + The adsorption and diffusion kinetics are well understood, while the retained sp² conjugated network ensures an efficient electron transport path. Comparative Example 1 (untreated decommissioned graphite) has local defects due to aging, but its main body is still a regular and dense graphite crystal phase with narrow interlayer spacing, making it difficult for sodium ions to insert and diffuse, ultimately exhibiting extremely poor sodium storage performance and unsuitable for sodium-ion battery anodes.

[0067] Figure 4 and Figure 5 The cycling graphs of the coin cell sodium-ion half-cells assembled in Comparative Example 1 and Example 1 for the first 76 cycles show that the initial discharge capacity increased by 90 mAh g⁻¹. -1 Furthermore, the reversible capacity was increased by 40 mAh g. -1 It exhibits high capacity retention and slow capacity decay. Other embodiments of the present invention have comparable or even superior effects.

[0068] The above-described embodiment 1 is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for recycling retired lithium-ion batteries using graphite reconstructing sp 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... Includes the following steps: Step 1: Collect waste graphite and use supercritical fluid technology to assist in oxidation and layer expansion with oxidizing liquid, and create micro-explosion pores; Step 2: Secondary pore structure regulation using pore-forming agents; Step 3: Remove impurities sequentially with ethanol and acidic solution, and wash with water until neutral; Step 4: High-temperature carbonization to obtain sp 2 / sp 3 Hybridized synergistic carbon anode materials.

2. The method for recycling and reconstructing graphite sp from decommissioned lithium batteries according to claim 1 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... The waste graphite in step 1 originates from retired lithium-ion batteries, waste lithium-ion batteries, and lithium-ion batteries with deteriorated performance.

3. The method for recycling decommissioned lithium batteries using graphite reconstructing sp as described in claim 1 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... In step 1, the supercritical fluid is at least one of CO2, N2, and CH4, and the supercritical conditions are those that maintain the supercritical fluid state, with a treatment time of 4-36 hours. The oxidizing liquid is at least one of H2O2, HNO3, H2SO4, and KMnO7 solutions, and the mass of the oxidizing substance in the solution is 2-4 times the mass of the waste graphite.

4. The method for recycling graphite from decommissioned lithium batteries according to claim 3 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... The method for supercritical fluid technology-assisted oxidative liquid oxidation layer expansion in step 1 includes: Step 1.1: Place the waste graphite in an H2O2 solution with a mass fraction of 5-30% and a mass ratio of H2O2 to waste graphite of 2-4:

1. Place the solution in an ultrasonic instrument to uniformly disperse the graphite and perform interlayer oxidation and exfoliation to obtain a mixed solution. Step 1.2: Transfer the resulting mixed solution into a supercritical reactor; Step 1.3: Introduce CO2 gas at 7.3-8 MPa into the supercritical reactor and maintain the temperature at 43-55 °C for 4-36 h; Step 1.4: Rapidly depressurize the supercritical reactor to induce micro-explosion and create pores.

5. The method for recycling decommissioned lithium batteries using graphite reconstructing sp as described in claim 1 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... In step 2, the pore-forming agent is a KOH solution with a concentration of 1-5 mol / L. The mass ratio of KOH to graphite in the solution is 1-7:

1. Magnetic stirring is applied simultaneously at a speed of 300-1000 rpm for 4-20 hours at a temperature of 30-80℃.

6. The method for recycling decommissioned lithium batteries using graphite reconstructing sp as described in claim 1 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... In step 3, the ethanol volume concentration is 95%; the acidic solution is at least one of HCl, HNO3, and H2SO4 solutions, the acidic solution soaking time is 1-12 hours, and the temperature is 30-80℃; the mixture is washed with water until the pH value is 6-7, and dried to obtain a graphite oxide mixture with a purity ≥99%.

7. The method for recycling and reconstructing graphite sp from decommissioned lithium batteries according to claim 1 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... The high-temperature carbonization conditions in step 4 are as follows: under an inert atmosphere, at 1-10℃ min. -1 The temperature is increased to 300~900℃ at a rate of [temperature value], and held for 1~3 hours.

8. The method for recycling decommissioned lithium batteries using graphite reconstructing sp as described in claim 1 2 / sp 3 A method for developing hybrid synergistic sodium-based hard carbon anode materials, characterized in that... The structural parameters of the prepared material are: interlayer spacing 0.3-0.5 nm, specific surface area 30-100 m². 2 / g, porosity 20%-40%, sp 3 / (sp 2 +sp 3 5%-40%, oxygen-containing groups 3%-10%.

9. A method for preparing recycled graphite sp from decommissioned lithium batteries according to any one of claims 1-8 2 / sp 3 Hybridized synergistic sodium-carbon hard anode material.

10. A method for preparing recycled graphite sp from decommissioned lithium batteries according to any one of claims 1-8 2 / sp 3 Application of hybrid synergistic sodium-carbon hard anode materials in sodium-ion batteries.

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