Sodium-ion battery regenerated hard carbon material, preparation method and application thereof

Abstract

The application discloses a regenerated hard carbon material for sodium ion batteries, a preparation method and application thereof, relates to the technical field of battery material recycling, and meets the following conditions: the interplanar spacing d002 of the regenerated hard carbon material is 0.37 nm to 0.38 nm, the half-height width in the X-ray diffraction spectrum of the regenerated hard carbon material is 0.83° to 0.89°, and the graphitization degree of the regenerated hard carbon material is 17.6% to 18.9%. According to the performance test parameters of the regenerated hard carbon material, the integrity of the stacking structure of the disordered carbon skeleton and the microcrystalline domain of the regenerated hard carbon material for the sodium ion batteries in the scheme can be obtained, the interplanar spacing d002 of the regenerated hard carbon meets the optimized sodium storage range of 0.37 nm to 0.38 nm, the surface defects are small, and therefore, the high-value application of the regenerated hard carbon is ensured.

Description

Technical Field

[0001] This application relates to the technical field of battery material recycling, specifically to a sodium-ion battery regenerated hard carbon material, its preparation method, and its application. Background Technology

[0002] With the large-scale development of the sodium-ion battery industry, the number of retired sodium-ion batteries has increased year by year. If they are discarded directly, it will not only waste resources, but also pose an environmental pollution risk due to impurities in the electrode materials and electrolyte residues. Therefore, the high-value recycling and utilization of hard carbon from waste batteries is of great significance to promoting the green and circular development of the sodium-ion battery industry.

[0003] In some related technologies, firstly, traditional acid washing processes often use strong acids for a one-time treatment, which can easily lead to the collapse of the microcrystalline structure or voids in hard carbon materials, severely affecting the electrochemical performance of regenerated hard carbon materials. Secondly, water-based solution treatment can only remove surface by-reaction products of hard carbon materials, and is unable to remove deeply embedded metal impurities and stubborn silicates, resulting in insufficient purity of the regenerated material and limiting its high-end applications. Thirdly, the regeneration process only focuses on impurity removal and lacks targeted repair of the key sodium storage structure of hard carbon, resulting in core indicators such as the initial discharge specific capacity and coulombic efficiency of regenerated hard carbon being significantly lower than those of newly manufactured materials. Fourthly, the process has environmental hazards or excessively high costs, making it difficult to achieve industrial-scale promotion. Summary of the Invention

[0004] In order to solve at least one of the problems mentioned in the background art, this application provides a sodium-ion battery regenerated hard carbon material, a preparation method and its application. The method uses a stepwise treatment with an acid solution of increasing concentration to ensure the integrity of the disordered carbon skeleton and the stacked structure of microcrystalline domains in the regenerated hard carbon material. At the same time, the two acid solutions can gradually and directionally remove impurities in the regenerated hard carbon material and improve the purity of the regenerated hard carbon material.

[0005] The specific technical solutions provided in this application are as follows: In a first aspect, a regenerated hard carbon material for sodium-ion batteries is provided, wherein the interplanar spacing d002 of the regenerated hard carbon material is 0.37 nm to 0.38 nm, the full width at half maximum (FWHM) of the X-ray diffraction pattern of the regenerated hard carbon material is 0.83° to 0.89°, and the degree of graphitization of the regenerated hard carbon material is 17.6% to 18.9%.

[0006] In one specific embodiment, the specific surface area of ​​the recycled hard carbon material is 4.2 m² / g to 4.5 m² / g.

[0007] Secondly, a method for preparing regenerated hard carbon material for sodium-ion batteries is provided, the method comprising: S1. Separate waste sodium-ion batteries to obtain negative electrode sheets, and grind, clean and screen the negative electrode sheets to obtain hard carbon coarse powder; S2. The hard carbon powder is added to the first acid solution for reaction, and then filtered and washed to obtain the primary processed product; S3. The primary treatment product is added to the second acid solution for reaction, and then filtered and washed to obtain the fluoride-free secondary treatment product. S4. Add sodium citrate aqueous solution to the secondary processed product for desorption treatment, and then filter and dry to obtain hard carbon intermediate; S5. Anneal the hard carbon intermediate under inert gas protection and cool it to obtain the recycled hard carbon material.

[0008] In one specific embodiment, the reaction process in S1 includes: The negative electrode sheet is treated with ultrasonic grinding-ultrasonic assisted peeling at 50℃~80℃ and 20kHz~40kHz for 15min~30min to peel the hard carbon active material from the current collector surface, and the peeled hard carbon active material is passed through a 200-mesh sieve to obtain the hard carbon coarse powder. And / or, the reaction process in S2 includes: The coarse hard carbon powder is added to the first acid solution and stirred for 60 to 90 minutes at a temperature of 40°C to 60°C to remove metallic impurities from the surface of the coarse hard carbon powder. Then, it is filtered and washed until neutral to obtain the first-stage processed product.

[0009] In one specific embodiment, the reaction process in S3 includes: The primary processed product is added to the second acid solution and stirred for 120 min to 180 min at a temperature of 50℃ to 70℃ to remove the inner layer impurities of the primary processed product. After filtration, it is washed with deionized water to obtain the secondary processed product. And / or, the S4 process includes: The desorption process involves ultrasonic treatment at 30℃~50℃ for 30min~60min to remove electrolyte decomposition products and by-reaction residues adsorbed on the surface of hard carbon. The material is then filtered and vacuum dried at 80℃~100℃ for 4h~6h to obtain the hard carbon intermediate.

[0010] In one specific embodiment, the first acid solution is a hydrochloric acid solution, the concentration of the first acid solution is 5wt%~8wt%, and the liquid-solid ratio of the first acid solution to the hard carbon powder satisfies (10~15):1mL / g.

[0011] In one specific embodiment, the concentration of the second acid solution is 15wt%~20wt%, the liquid-to-solid ratio of the second acid solution to the primary treatment product is (8~12):1mL / g, the second acid solution is a mixture of hydrochloric acid and hydrofluoric acid, and the volume ratio of hydrochloric acid to hydrofluoric acid in the mixture satisfies (2~6):1. And / or, the concentration of sodium citrate is 0.5wt%~1.0wt%, and the liquid-to-solid ratio of the secondary treatment product to the sodium citrate satisfies (5~8):1mL / g.

[0012] In one specific embodiment, the annealing reaction in S5 includes: The first stage of annealing involves heating at a rate of 5℃ / min to 8℃ / min to 800℃ to 1000℃ and holding at that temperature for 120min to 240min. The second stage of annealing involves heating at a rate of 2℃ / min to 3℃ / min to 1500℃ to 1800℃ and holding at that temperature for 180min to 240min.

[0013] In one specific embodiment, the recycled hard carbon material is subjected to airflow classification treatment so that the particle size D50 of the treated recycled hard carbon material meets the requirements of 7μm~9μm and the particle size D90 ≤30μm.

[0014] And / or, the initial discharge specific capacity of the battery containing the recycled hard carbon material is greater than or equal to 328 mAh / g, and the initial coulombic efficiency of the battery containing the recycled hard carbon material is greater than 91%.

[0015] Thirdly, a sodium-ion battery is provided, the sodium-ion battery comprising the sodium-ion battery regenerated hard carbon material as described above, or the sodium-ion battery comprising a material prepared by the method for preparing the sodium-ion battery regenerated hard carbon material as described above.

[0016] The embodiments of this application have the following beneficial effects: The embodiments of this application provide a regenerated hard carbon material with a crystal plane spacing d002 of 0.37 nm to 0.38 nm, and a full width at half maximum (FWHM) of 0.83° to 0.89° in the X-ray diffraction pattern of the regenerated hard carbon material. The degree of graphitization of the regenerated hard carbon material is 17.6% to 18.9%. Based on the above performance test parameters of the regenerated hard carbon material, the integrity of the disordered carbon skeleton and microcrystalline domain stacking structure of the regenerated hard carbon material in the sodium-ion battery of this scheme can be obtained. Furthermore, the crystal plane spacing d002 of the regenerated hard carbon meets the optimized sodium storage range of 0.37 nm to 0.38 nm, and the surface defects are small, thereby ensuring the high-value application of regenerated hard carbon. Attached Figure Description

[0017] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the method for preparing regenerated hard carbon materials for sodium-ion batteries in this application; Figure 2 The XRD diffraction patterns of Examples 1 and 2 of this application are shown below. Figure 3 The XRD diffraction patterns are those of Comparative Examples 1 and 2 of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The "range" disclosed herein is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0021] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0022] Unless otherwise specified in this disclosure, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0023] In this disclosure, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] This application provides a regenerated hard carbon material for sodium-ion batteries. The interplanar spacing d002 of the regenerated hard carbon material is 0.37 nm to 0.38 nm. Specifically, the interplanar spacing d002 of the regenerated hard carbon material is set to 0.370 nm, 0.371 nm, 0.372 nm, 0.373 nm, 0.374 nm, 0.375 nm, 0.376 nm, 0.377 nm, 0.378 nm, 0.379 nm, 0.380 nm, or any combination of two of the above values. In this solution, XRD testing is performed on the regenerated hard carbon material to obtain the interplanar spacing d002 parameter of 0.37 nm to 0.38 nm, which meets the optimal sodium storage range and ensures that the hard carbon material has sufficient sodium storage active sites.

[0026] Furthermore, the full width at half maximum (FWHM) of the X-ray diffraction pattern of the regenerated hard carbon material satisfies 0.83°~0.89°. Specifically, the FWHM of the regenerated hard carbon material is selected as 0.83°, 0.84°, 0.85°, 0.86°, 0.87°, 0.88°, 0.89°, or any two of the above values. The FWHM of the XRD peak is closely related to the crystallite size and structural disorder of the hard carbon material, indicating that the structure can provide abundant defect sites and nanopores for sodium ion adsorption, while maintaining a certain short-range order to ensure electronic conductivity. Excessive order (such as soft carbon) will lead to low sodium storage capacity; excessive disorder will affect conductivity and cycle life. The FWHM range reflects the balance between local order and global disorder in the "vortex structure", which helps to achieve a synergy between high capacity and good rate performance.

[0027] The degree of graphitization of the regenerated hard carbon material is between 17.6% and 18.9%. Specifically, the degree of graphitization of the regenerated hard carbon material is selected as 17.6%, 17.7%, 17.8%, 17.9%, 18.0%, 18.1%, 18.2%, 18.3%, 18.4%, 18.5%, 18.6%, 18.7%, 18.8%, 18.9%, or any two of the above values. The degree of graphitization reflects the development degree of graphite-like microcrystals in the carbon material. A low degree of graphitization in this range means that the main body of the material is an amorphous carbon structure, rich in turbulent layers, defect sites, and nanopores, providing multiple storage mechanisms for sodium ions, such as adsorption, intercalation, or pore filling, to increase the total capacity. The degree of graphitization indicates the presence of a small number of short-range ordered graphite microcrystals. These microcrystals can act as "bridges" for electron conduction, improving the overall conductivity, while avoiding volume expansion and cyclic degradation caused by excessive graphitization.

[0028] In one specific embodiment, the specific surface area of ​​the recycled hard carbon material is between 4.2 m² / g and 4.5 m² / g. Specifically, the specific surface area of ​​the recycled hard carbon material is set to 4.2 m² / g, 4.25 m² / g, 4.3 m² / g, 4.35 m² / g, 4.4 m² / g, 4.45 m² / g, or a range of any two of the above values. Specific surface area refers to the external surface area of ​​a substance per unit mass or unit volume. In this embodiment, the specific surface area of ​​the hard carbon refers to the external surface area per unit mass. Through the above specific surface area range, it can be confirmed that impurities in the microporous structure of the recycled hard carbon material in this embodiment are effectively removed, and the pore structure is intact, further ensuring the sodium storage capacity of the hard carbon material.

[0029] Corresponding to the above embodiments, this application provides a method for preparing regenerated hard carbon materials for sodium-ion batteries, such as... Figure 1 As shown, the method includes the following steps: S1 Pretreatment: Separate waste sodium-ion batteries to obtain negative electrode sheets, and grind, clean and screen the negative electrode sheets to obtain hard carbon coarse powder.

[0030] Specifically, after disassembling and discharging the waste sodium-ion batteries, the batteries are disassembled when the voltage is ≤0.05V. Hard carbon negative electrode sheets are then separated. A mechanical grinding-ultrasonic assisted peeling method is used to treat the negative electrode sheets at 50℃~80℃ and 20kHz~40kHz for 15min~30min to peel the hard carbon active material from the copper current collector surface. The peeled hard carbon active material is then passed through a 200-mesh sieve to obtain hard carbon coarse powder. The 200-mesh sieve process can remove the current collector and large impurities.

[0031] S2. Primary treatment in gradient purification process: Hard carbon coarse powder is added to the first acid solution for reaction, and then filtered and washed to obtain the primary treatment product.

[0032] Specifically, coarse hard carbon powder is added to a first acid solution and stirred for 60-90 minutes at 40℃~60℃ to remove metallic impurities from the surface of the coarse hard carbon powder. The powder is then filtered and washed until neutral to obtain the primary processed product, i.e., washed to pH=6-7. The first acid solution reacts with the loose metallic impurities on the surface of the coarse hard carbon powder to remove Fe, Ca, and Mg impurities.

[0033] The first acid solution is a hydrochloric acid solution with a concentration of 5wt% to 8wt%. The liquid-to-solid ratio of the first acid solution to the coarse carbon powder is (10~15):1mL / g. Specifically, the concentration of the first acid solution is set to 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, or any two of the above values. The liquid-to-solid ratio of the first acid solution to the coarse carbon powder is set to 10:1mL / g, 11:1mL / g, 12:1mL / g, 13:1mL / g, 14:1mL / g, 15:1mL / g, or any two of the above values.

[0034] S3. Secondary treatment in gradient purification process: The product of primary treatment is added to the second acid solution for reaction, and then filtered and washed to obtain the fluoride-free secondary treatment product.

[0035] Specifically, the primary treatment product is added to the second acid solution and stirred for 120-180 minutes at 50℃~70℃ to remove inner impurities from the primary treatment product. After filtration, it is washed with deionized water until no fluoride ions remain, yielding the secondary treatment product, which is negative for fluoride ion test strips. The second acid solution can specifically remove stubborn impurities such as Si and Al embedded deep within the hard carbon material, as well as silicates, to further purify the hard carbon material.

[0036] In this embodiment, the concentration of the second acid solution is 15wt%~20wt%, and the liquid-to-solid ratio of the second acid solution to the primary treatment product satisfies (8~12):1mL / g. The second acid solution is a mixture of hydrochloric acid and hydrofluoric acid, and the volume ratio of hydrochloric acid to hydrofluoric acid in the mixture satisfies (2~6):1. Specifically, the concentration of the second acid solution is set to 15wt%, 15.5wt%, 16wt%, 16.5wt%, 17wt%, 17.5wt%, 18wt%, 18.5wt%, 19wt%, 19.5wt%, 20wt%, or a range consisting of any two of the above values. The liquid-to-solid ratio of the second acid solution to the primary treatment product is set to 8:1 mL / g, 8.5:1 mL / g, 9:1 mL / g, 9.5:1 mL / g, 10:1 mL / g, 10.5:1 mL / g, 11:1 mL / g, 11.5:1 mL / g, 12:1 mL / g, or any combination of two of the above values. When the second acid solution is a mixture of hydrochloric acid and hydrofluoric acid, the volume ratio of hydrochloric acid to hydrofluoric acid satisfies 2:1, 3:1, 4:1, 5:1, 6:1, or any combination of two of the above values. By controlling the liquid-to-solid ratio of the second acid solution to the primary treatment product to meet the above values, it is ensured that Fe, Ca, and Mg-related impurities in the primary treatment product can be completely treated.

[0037] S4. Tertiary treatment in gradient purification process: Add sodium citrate aqueous solution to the secondary treatment product for desorption treatment, and then filter and dry to obtain hard carbon intermediate.

[0038] The desorption process involves ultrasonic treatment at 30℃~50℃ for 30min~60min to remove electrolyte decomposition products and by-reaction residues adsorbed on the hard carbon surface. The product is then filtered and vacuum dried at 80℃~100℃ for 4h~6h to obtain the hard carbon intermediate. The concentration of sodium citrate is 0.5wt%~1.0wt%, and the liquid-to-solid ratio of the secondary treatment product to sodium citrate is (5~8):1mL / g. Specifically, the concentration of sodium citrate is set to 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, 0.75wt%, 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt%, 1wt%, or any two of the above values; the liquid-solid ratio of the secondary treatment product to sodium citrate is set to 5:1mL / g, 5.5:1mL / g, 6:1mL / g, 6.5:1mL / g, 7:1mL / g, 7.5:1mL / g, 8:1mL / g, or any two of the above values. The secondary treatment product is further desorbed using sodium citrate of the above concentrations to obtain a high-purity hard carbon intermediate.

[0039] S5. Structural reconstruction process: The hard carbon intermediate is annealed under inert gas protection and cooled to obtain the recycled hard carbon material.

[0040] In this embodiment, the annealing reaction includes: a first-stage annealing, where the temperature is increased to 800℃~1000℃ at a heating rate of 5℃ / min~8℃ / min and held for 120min~240min to repair surface defects in the hard carbon material; and a second-stage annealing, where the temperature is increased to 1500℃~1800℃ at a heating rate of 2℃ / min~3℃ / min and held for 180min~240min, followed by natural cooling to room temperature to obtain regenerated hard carbon material. Through the above process, the interlayer spacing d002 is further controlled to 0.370 nm~0.380 nm to ensure that the interlayer spacing during hard carbon processing allows for the insertion and extraction of sodium ions. Simultaneously, the pore structure parameters are optimized to ensure the structural stability of the hard carbon material, thereby ensuring that the subsequently prepared battery has high reversible capacity, good cycle stability, and rate performance.

[0041] The restructured hard carbon material is subjected to air classification to ensure that the particle size D50 of the treated recycled hard carbon material meets the requirements of 7μm~9μm and the particle size D90 ≤ 30μm, which meets the requirements of superior grade particle size, and finally obtains high-performance recycled hard carbon products.

[0042] Based on the above processing steps, it can be seen that the first acid solution, the second acid solution, and the sodium citrate aqueous solution in this scheme can not only dissolve the loose side reaction products on the surface, but also penetrate into the micropores and grain boundaries of hard carbon, removing impurities that are tightly bound to the carbon skeleton. It can precisely remove different types of impurities, such as elemental metals, oxides, and silicates, thereby ensuring that the recycled hard carbon material maintains high purity and meets its battery-grade application requirements. This results in the battery containing the recycled hard carbon material having an initial discharge specific capacity of greater than or equal to 328 mAh / g and an initial coulombic efficiency of greater than 91%.

[0043] In this embodiment, the interplanar spacing d002 of the regenerated hard carbon material is 0.37 nm to 0.38 nm, and the full width at half maximum (FWHM) of the X-ray diffraction pattern of the regenerated hard carbon material is 0.83° to 0.89°. The graphitization degree of the regenerated hard carbon material is 17.6% to 18.9%. It can be seen that this solution not only effectively removes impurities, but also ensures that the crystal planes of the hard carbon material remain intact and grow stably with a clear pore structure. This ensures that when applied to sodium-ion batteries, the material has abundant sodium storage active sites, thereby achieving the high efficiency of sodium-ion batteries.

[0044] Corresponding to the above embodiments, this application provides a sodium-ion battery, which includes the sodium-ion battery regenerated hard carbon material as described above, or the sodium-ion battery includes the material prepared by the above method for preparing sodium-ion battery regenerated hard carbon material.

[0045] Example 1 S1. Pretreatment: Take retired sodium-ion batteries (hard carbon negative electrode system), discharge them to a voltage ≤0.05V and then disassemble them to obtain hard carbon negative electrode sheets; place the electrode sheets in a ball mill and grind them for 30 minutes, then transfer them to an ultrasonic cleaner and sonicate them at 60℃ and 30kHz for 20 minutes. Collect the hard carbon coarse powder through a 200-mesh sieve. The basic data test results of retired sodium-ion batteries are shown in Table 1. S2. Gradient purification: Primary treatment: Add all the coarse hard carbon powder to 1000mL of 6wt% dilute hydrochloric acid, stir at 50℃ for 75min, filter, and wash with deionized water until pH=6.5. S3, Secondary treatment: Add the filter residue to 800mL of 18wt% hydrochloric acid-hydrofluoric acid mixture (volume ratio 3:1), stir at 60℃ for 150min, filter and wash until no fluoride ions are present, i.e., the fluoride ion test paper is negative. S4. Tertiary treatment: Add the product to 500 mL of an aqueous solution containing 0.8 wt% trisodium citrate, sonicate at 40 °C for 45 min, filter, and vacuum dry at 90 °C for 5 h to obtain the hard carbon intermediate. S5. Structural Reconstruction: The hard carbon intermediate is placed in an argon-protected tube furnace, heated to 900℃ at 6℃ / min and held for 120min, then heated to 1600℃ at 2.5℃ / min and held for 200min. After natural cooling, the gas flow is staged, and D50=8μm and D90=28μm are controlled.

[0046] The regenerated hard carbon material prepared above was subjected to relevant performance tests. The test results are as follows: the ash content of the regenerated hard carbon is 0.08%, the total content of Fe, Ca, Mg and Si is 185ppm, d002=0.375nm, the initial discharge specific capacity is 328mAh / g, the initial coulombic efficiency is 93.1%, and the capacity retention rate after 1000 cycles is 88%, which meets the requirements of Grade I product.

[0047] Example 2 S1. Pretreatment: After the retired sodium-ion battery is discharged and disassembled, the hard carbon electrode sheet is ultrasonically treated at 50℃ and 25kHz for 25 minutes, then ground and collected as coarse powder through a 200-mesh sieve. S2~S4, gradient purification: primary treatment with 7wt% dilute hydrochloric acid (50℃, 90min), secondary treatment with 16wt% hydrochloric acid-hydrofluoric acid mixture (65℃, 140min), tertiary treatment with 0.6wt% trisodium citrate aqueous solution (35℃, 50min), and vacuum drying at 100℃ for 4h. S5. Structural reconstruction: Under an argon atmosphere, the temperature is increased to 850℃ at 7℃ / min and held for 120min, then increased to 1700℃ at 3℃ / min and held for 180min. The airflow is controlled in stages, with D50=9μm.

[0048] The recycled hard carbon material prepared above was subjected to relevant performance tests. The test results are as follows: the ash content of the recycled hard carbon is 0.07%, the total impurity content is 172ppm, the initial discharge specific capacity is 332mAh / g, and the initial coulombic efficiency is 93.9%, which meets the requirements of the superior grade.

[0049] Example 3 S1. Pretreatment: Take retired sodium-ion batteries from the same batch as in Example 1, discharge them to a voltage ≤0.05V, then disassemble them and separate the hard carbon negative electrode sheets. Grind the electrode sheets in a ball mill for 30 minutes, then transfer them to an ultrasonic cleaner and sonicate them at 60°C and 30kHz for 20 minutes. Collect 100g of coarse hard carbon powder by passing it through a 200-mesh sieve. S2. Gradient Purification: Primary Treatment: Add all the coarse hard carbon powder to 1000 mL of 5 wt% dilute hydrochloric acid (liquid-solid ratio 10:1), stir at 50℃ for 80 min, filter, and wash with deionized water until pH=6.5; S3. Secondary Treatment: Add the filter residue to 800 mL of 18 wt% hydrochloric acid-hydrofluoric acid mixture (volume ratio 3:1, liquid-solid ratio 8.4:1), stir at 60℃ for 150 min, filter, and wash until the fluoride ion test paper is negative; S4. Tertiary Treatment: Add the product to 500 mL of 0.8 wt% trisodium citrate aqueous solution (liquid-solid ratio 5.6:1), sonicate at 40℃ for 45 min, filter, and vacuum dry at 90℃ for 5 h to obtain the hard carbon intermediate; S5. Structural Reconstruction: Place the hard carbon intermediate in an argon-protected tube furnace, heat to 900℃ at 6℃ / min and hold for 120 min, then heat at 2.5℃ / min... Heat to 1600℃ and hold for 200 minutes. After natural cooling, the airflow is staged, and D50=7.8μm and D90=27.6μm are controlled.

[0050] Example 4 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: First-stage treatment: add all coarse hard carbon powder to 1000mL of 8wt% dilute hydrochloric acid (liquid-solid ratio 10:1), stir at 50℃ for 70min, filter and wash until pH=6.5; S3~S5. Second-stage treatment, third-stage treatment and structural reconstruction steps are all consistent with Example 1. After airflow classification, control D50=8.2μm and D90=28.3μm.

[0051] Example 5 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: First-stage treatment: add all coarse hard carbon powder to 1000mL of 4wt% dilute hydrochloric acid (liquid-solid ratio 10:1), stir at 50℃ for 100min, filter and wash until pH=6.5; S3~S5. Second-stage treatment, third-stage treatment and structural reconstruction steps are all consistent with Example 1. After airflow classification, control D50=8.5μm and D90=29.1μm.

[0052] Example 6 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: First-stage treatment: add all coarse hard carbon powder to 1000mL of 10wt% dilute hydrochloric acid (liquid-solid ratio 10:1), stir at 50℃ for 60min, filter and wash until pH=6.5; S3~S5. Second-stage treatment, third-stage treatment and structural reconstruction steps are all consistent with Example 1. After airflow classification, control D50=7.9μm and D90=27.8μm.

[0053] Example 7 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: First-stage treatment: consistent with Example 1 (6wt% dilute hydrochloric acid, stirring at 50℃ for 75min); S3. Second-stage treatment: add the filter residue to 800mL of 15wt% hydrochloric acid-hydrofluoric acid mixture (volume ratio 3:1, liquid-solid ratio 8.4:1), stir at 60℃ for 160min, filter and wash until fluoride ions are removed; S4~S5. Tertiary treatment and structural reconstruction steps are consistent with Example 1, after airflow classification, control D50=8.1μm and D90=28.5μm.

[0054] Example 8 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: Primary treatment: consistent with Example 1; S3. Secondary treatment: add the filter residue to 800mL of 20wt% hydrochloric acid-hydrofluoric acid mixture (volume ratio 3:1, liquid-solid ratio 8.4:1), stir at 60℃ for 140min, filter and wash until fluoride ions are removed; S4~S5. Tertiary treatment and structural reconstruction steps are consistent with Example 1, after airflow classification, control D50=7.7μm and D90=27.3μm.

[0055] Example 9 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: Primary treatment: consistent with Example 1; S3. Secondary treatment: add the filter residue to 800mL of 14wt% hydrochloric acid-hydrofluoric acid mixture (volume ratio 3:1, liquid-solid ratio 8.4:1), stir at 60℃ for 180min, filter and wash until fluoride ions are removed; S4~S5. Tertiary treatment and structural reconstruction steps are consistent with Example 1, after airflow classification, control D50=8.6μm and D90=29.4μm.

[0056] Example 10 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: Primary treatment: consistent with Example 1; S3. Secondary treatment: add the filter residue to 800mL of 22wt% hydrochloric acid-hydrofluoric acid mixture (volume ratio 3:1, liquid-solid ratio 8.4:1), stir at 60℃ for 130min, filter and wash until fluoride ions are removed; S4~S5. Tertiary treatment and structural reconstruction steps are consistent with Example 1, after airflow classification, control D50=7.5μm and D90=26.9μm.

[0057] Example 11 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2~S3. Primary and secondary treatment steps are consistent with Example 1; S4. Tertiary treatment: add the product to 500mL of 0.5wt% trisodium citrate aqueous solution (liquid-solid ratio 5.6:1), sonicate at 40℃ for 50min, filter, and vacuum dry at 90℃ for 5h; S5. Structural reconstruction: consistent with Example 1, control D50=8.3μm and D90=28.8μm after airflow classification.

[0058] Example 12 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2~S3. Primary and secondary treatment steps are consistent with Example 1; S4. Tertiary treatment: add the product to 500mL of 1.0wt% trisodium citrate aqueous solution (liquid-solid ratio 5.6:1), sonicate at 40℃ for 40min, filter, and vacuum dry at 90℃ for 5h; S5. Structural reconstruction: consistent with Example 1, control D50=7.6μm and D90=27.1μm after airflow classification.

[0059] Example 13 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2~S3. Primary and secondary treatment steps are consistent with Example 1; S4. Tertiary treatment: add the product to 500mL of 0.4wt% trisodium citrate aqueous solution (liquid-solid ratio 5.6:1), sonicate at 40℃ for 60min, filter, and vacuum dry at 90℃ for 5h; S5. Structural reconstruction: consistent with Example 1, control D50=8.7μm and D90=29.6μm after airflow classification.

[0060] Example 14 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2~S3. Primary and secondary treatment steps are consistent with Example 1; S4. Tertiary treatment: add the product to 500mL of 1.2wt% trisodium citrate aqueous solution (liquid-solid ratio 5.6:1), sonicate at 40℃ for 35min, filter, and vacuum dry at 90℃ for 5h; S5. Structural reconstruction: consistent with Example 1, control D50=7.4μm and D90=26.7μm after airflow classification.

[0061] Comparative Example 1 Corresponding to the above embodiments, in this embodiment: the same batch of hard carbon coarse powder is treated once with 20wt% concentrated hydrochloric acid, stirred at 70℃ for 240min, washed and dried, and then directly annealed at 1600℃ for 200min; other treatment processes are the same as in Embodiment 1.

[0062] Performance testing of the treated recycled hard carbon material revealed that the hard carbon structure exhibited localized pore collapse, with an ash content of 0.15%, an initial discharge specific capacity of 295 mAh / g, an initial coulombic efficiency of 83.1%, a capacity retention rate of 79% after 500 cycles, and a capacity retention rate of less than 50% after 1000 cycles. The performance was significantly lower than that of the embodiments of the present invention.

[0063] Comparative Example 2 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. Gradient purification: Primary treatment: add 100g of coarse hard carbon powder to 1000mL of 8wt% dilute hydrochloric acid (liquid-solid ratio 10:1), stir at 50℃ for 90min, filter and wash until pH=6.5; S3. No secondary acid treatment, directly proceed to tertiary treatment: add the product of primary treatment to 500mL of 0.8wt% trisodium citrate aqueous solution (liquid-solid ratio 5.6:1), sonicate at 40℃ for 45min, filter and vacuum dry at 90℃ for 5h; S4. Structural reconstruction: Consistent with Example 1, after airflow classification, control D50=9.5μm and D90=32.4μm.

[0064] Comparative Example 3 S1. Pretreatment: Completely consistent with Example 1, collect 100g of coarse hard carbon powder; S2. No primary acid treatment, directly proceed to secondary treatment: add 100g of coarse hard carbon powder to 800mL of 18wt% hydrochloric acid-hydrofluoric acid mixture (volume ratio 3:1, liquid-solid ratio 8:1), stir at 60℃ for 180min, filter and wash until fluoride ions are removed; S3. Tertiary treatment: Consistent with Example 1 (0.8wt% trisodium citrate, sonication at 40℃ for 45min, vacuum drying at 90℃ for 5h); S4. Structural reconstruction: Consistent with Example 1, after airflow classification, control D50=9.8μm and D90=33.7μm.

[0065] Comparative Example 4 S1. Pretreatment: Completely consistent with Example 1, collect 100g of hard carbon coarse powder; S2~S3. Primary and secondary treatment steps are consistent with Example 1; S4. No tertiary treatment (no sodium citrate added): filter the secondary treatment product directly and vacuum dry at 90℃ for 5h to obtain hard carbon intermediate; S5. Structural reconstruction: consistent with Example 1, control D50=8.9μm and D90=30.2μm after airflow classification.

[0066] The testing methods for each set of embodiments are as follows: (1) Ash content test: Performed according to GB / T 17664-1999 "Determination of Ash Content in Carbon Materials"; (2) Impurity content test: determined by ICP-OES inductively coupled plasma atomic emission spectrometry; (3) Interplanar spacing test: The d002 value was calculated using the Bragg equation by X-ray diffraction (XRD); (4) Specific surface area test: BET nitrogen adsorption method was used; (5) Electrochemical performance test: The charge-discharge cycle test was completed on the Blue Battery test system.

[0067] Based on the above testing methods, the recycled hard carbon materials prepared in the above embodiments were subjected to relevant tests, and the test results are shown in Tables 2, 3, and 4, respectively. Table 1 shows the test results of various parameters of the hard carbon materials used in each set of embodiments, i.e., the negative electrode sheets of retired sodium-ion batteries. Note that Tables 2-1, 2-2, and 2-3 are continuations of Table 2. Table 3-1 is a continuation of Table 3, and Table 4-1 is a continuation of Table 4.

[0068] Table 1. Basic test data of the negative electrode sheet from the waste sodium-ion battery used in this embodiment.

[0069] As shown in Table 1, the ash content of the hard carbon material in the negative electrode of the retired sodium-ion battery reached 0.32 wt%, and the total impurity content reached 856 ppm. This indicates that the impurities in the untreated hard carbon material far exceed the ash and impurity requirements for battery-grade hard carbon materials. Furthermore, the interplanar spacing d002 in the untreated hard carbon material is 0.361 nm. This large d002 indicates a small interlayer spacing and poor structural stability in the hard carbon material structure, making it difficult for sodium ions to intercalate and deintercalate. This affects the sodium ion mobility during use, leading to a decrease in the capacity of the sodium-ion battery.

[0070] Table 2 Test results for each set of embodiments

[0071] Table 2-1 Test results for each set of examples

[0072] Table 2-2 Test results for each set of examples

[0073] Table 2-3 Test results for each set of examples

[0074] Based on the data in Table 2, it can be concluded that treating the material with different concentrations of the first and second acid solutions not only dissolves the loose by-reaction products on the surface of the material, but also penetrates into the micropores and grain boundaries of the hard carbon, removing impurities tightly bound to the carbon skeleton. When the concentrations of the first and second acid solutions and the sodium citrate concentration meet the corresponding ranges, the loose by-reaction products on the surface of the material and the impurities in the pores can be effectively removed. When the corresponding acid concentrations are adjusted to be less than or greater than the corresponding ranges, it can be found that when the concentration of the treatment solution is too low, the recovery rate of the regenerated hard carbon material decreases, and the total impurity content in the treated material reaches more than 300 ppm, indicating that the impurities have not been effectively removed.

[0075] Furthermore, by combining Comparative Examples 1 to 4, it can be found that when using a single acid for treatment, even if the acid concentration is within the optimized range, the impurity content in the hard carbon material obtained by the treatment is still very high. The total impurity content reached 428 ppm when only hydrochloric acid was used for treatment. This indicates that the single acid washing treatment lacks specificity and has a large difference in removal efficiency for different types of impurities, such as elemental metals, oxides and silicates, resulting in impurity residue.

[0076] Table 3 Physical performance test results for each set of embodiments

[0077] Table 3-1 Physical performance test results of each set of examples

[0078] Based on the XRD diffraction results of the regenerated hard carbon materials in Table 3, it is demonstrated that this type of hard carbon material can provide abundant defect sites and nanopores for sodium ion adsorption, while maintaining a certain short-range order to ensure electronic conductivity, which is consistent with the structural characteristics of high-quality hard carbon. Excessive order (such as soft carbon) leads to low sodium storage capacity, while excessive disorder affects conductivity and cycle life. Therefore, when the interplanar spacing d002 of the regenerated hard carbon material is controlled to be 0.37 nm to 0.38 nm, and the full width at half maximum (FWHM) of the X-ray diffraction pattern of the regenerated hard carbon material is 0.83° to 0.89°, the integrity of the disordered carbon skeleton and the stacked structure of the microcrystalline domains of the regenerated hard carbon material for sodium-ion batteries is ensured. It has an optimized sodium storage range, small surface defects, reasonable pore structure and conductive network, which enables the hard carbon material to maintain a high capacity at high current density. The FWHM reflects the balance between local order and global disorder in the "vortex structure", which helps to achieve the synergy of high capacity and good rate performance.

[0079] Tap density refers to the density when the dry powder particle group reaches its limit of packing density after applying external forces such as vibration. Combining the specific surface area and tap density of the recycled hard carbon material, it can be concluded that the micropore and mesopore structure in the recycled hard carbon material structure of this scheme is relatively complete and has not collapsed during the processing, thus preserving the pore structure required for sodium storage.

[0080] Table 4. XRD test results of recycled hard carbon materials

[0081] Table 4-1 XRD test results of recycled hard carbon materials

[0082] Furthermore, combining Table 4 and Figure 2 , Figure 3 It can be concluded that Figure 2The XRD diffraction patterns of the regenerated hard carbon materials from Examples 1 and 2 are shown. Both exhibit broad (002) characteristic diffraction peaks at 2θ≈23°~25°, corresponding to interplanar spacings d002 of 0.375 nm and 0.373 nm, respectively, consistent with the data in Table 4. The broad peaks and absence of sharp impurity peaks indicate that they retain the disordered carbon structure required for sodium storage in hard carbon, with a stable graphitization degree of 18.2%~18.8%. Furthermore, the differences in peak intensity and full width at half maximum (FWHM) between the two are small, confirming the excellent structural consistency of the regenerated hard carbon under these process parameters. Simultaneously, the degree of graphitization reflects the development of graphite-like microcrystals in the carbon material. A low degree of graphitization in this range implies that the material's main body is an amorphous carbon structure, rich in turbulent layers, defect sites, and nanopores, providing multiple storage mechanisms for sodium ions, such as adsorption, intercalation, or pore filling, to enhance the overall capacity.

[0083] Combining Examples 5, 6, 9, and 10, it can be observed that when graphitization is greater than 18.9% or less than 17.6%, weak impurity peaks appear in the XRD patterns of hard carbon materials, and the peaks become sharper when the degree of graphitization increases slightly. This verifies that the degree of graphitization reflects the development degree of graphite-like microcrystals in carbon materials. When the degree of graphitization is too low, the lack of graphite crystals reduces electron conduction, while when the graphite crystals are too high, the "bridges" become too crowded, which occupies the electron conduction path. Therefore, it is necessary to control the degree of graphitization to improve the overall conductivity, while avoiding the volume expansion and cyclic degradation caused by excessive graphitization.

[0084] Figure 3 The XRD patterns of Comparative Example 1 and Comparative Example 2 are as follows: In Comparative Example 1, the (002) peak shifted to 2θ≈24.9° with traditional single acid washing, corresponding to d002=0.358nm. The peak shape became sharper, and as shown in Table 4, the graphitization degree increased to 32.5%, indicating that the traditional process caused the collapse of the disordered structure of hard carbon. In Comparative Example 2, the (002) peak shifted to 2θ≈24.3° without secondary acid treatment, and the baseline fluctuated greatly and weak impurity peaks appeared, confirming that the lack of secondary acid purification would lead to the deterioration of hard carbon structure and the presence of impurity residues.

[0085] Although preferred embodiments have been described in this application, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0086] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A regenerated hard carbon material for sodium-ion batteries, characterized in that, The interplanar spacing d002 of the recycled hard carbon material is 0.37 nm to 0.38 nm, and the full width at half maximum (FWHM) of the X-ray diffraction pattern of the recycled hard carbon material is 0.83° to 0.89°. The degree of graphitization of the recycled hard carbon material is 17.6% to 18.9%.

2. The sodium-ion battery regenerated hard carbon material according to claim 1, characterized in that, The specific surface area of ​​the recycled hard carbon material is 4.2 m² / g to 4.5 m² / g.

3. A method for preparing regenerated hard carbon material for sodium-ion batteries according to claim 1 or 2, characterized in that, The method includes: S1. Separate waste sodium-ion batteries to obtain negative electrode sheets, and grind, clean and screen the negative electrode sheets to obtain hard carbon coarse powder; S2. The hard carbon powder is added to the first acid solution for reaction, and then filtered and washed to obtain the primary processed product; S3. The primary processed product is added to the second acid solution for reaction, and then filtered and washed to obtain the fluoride-free secondary processed product. S4. Add sodium citrate aqueous solution to the secondary processed product for desorption treatment, and then filter and dry to obtain hard carbon intermediate; S5. Anneal the hard carbon intermediate under inert gas protection and cool it to obtain the recycled hard carbon material.

4. The method for preparing regenerated hard carbon material for sodium-ion batteries according to claim 3, characterized in that, The reaction process in S1 includes: The negative electrode sheet is treated with ultrasonic grinding-ultrasonic assisted peeling at 50℃~80℃ and 20kHz~40kHz for 15min~30min to peel the hard carbon active material from the current collector surface, and the peeled hard carbon active material is passed through a 200-mesh sieve to obtain the hard carbon coarse powder. And / or, the reaction process in S2 includes: The coarse hard carbon powder is added to the first acid solution and stirred for 60 to 90 minutes at a temperature of 40°C to 60°C to remove metallic impurities from the surface of the coarse hard carbon powder. Then, it is filtered and washed until neutral to obtain the first-stage processed product.

5. The method for preparing regenerated hard carbon material for sodium-ion batteries according to claim 3, characterized in that, The reaction process in S3 includes: The primary processed product is added to the second acid solution and stirred for 120 min to 180 min at a temperature of 50℃ to 70℃ to remove the inner layer impurities of the primary processed product. After filtration, it is washed with deionized water to obtain the secondary processed product. And / or, the S4 process includes: The desorption process involves ultrasonic treatment at 30℃~50℃ for 30min~60min to remove electrolyte decomposition products and by-reaction residues adsorbed on the surface of hard carbon. The material is then filtered and vacuum dried at 80℃~100℃ for 4h~6h to obtain the hard carbon intermediate.

6. The method for preparing regenerated hard carbon material for sodium-ion batteries according to claim 3 or 4, characterized in that, The first acid solution is a hydrochloric acid solution with a concentration of 5wt%~8wt% and a liquid-to-solid ratio of the first acid solution to the hard carbon powder of (10~15):1mL / g.

7. The method for preparing regenerated hard carbon material for sodium-ion batteries according to claim 5, wherein the concentration of the second acid solution is 15wt%~20wt%, the liquid-solid ratio of the second acid solution to the primary treatment product satisfies (8~12):1mL / g, the second acid solution is a mixture of hydrochloric acid and hydrofluoric acid, and the volume ratio of hydrochloric acid to hydrofluoric acid in the mixture satisfies (2~6):1; And / or, the concentration of sodium citrate is 0.5wt%~1.0wt%, and the liquid-to-solid ratio of the secondary treatment product to the sodium citrate satisfies (5~8):1mL / g.

8. The method for preparing regenerated hard carbon material for sodium-ion batteries according to claim 3, characterized in that, The annealing reaction in S5 includes: The first stage of annealing involves heating at a rate of 5℃ / min to 8℃ / min to 800℃ to 1000℃ and holding at that temperature for 120min to 240min. The second stage of annealing involves heating at a rate of 2℃ / min to 3℃ / min to 1500℃ to 1800℃ and holding at that temperature for 180min to 240min.

9. The method for preparing regenerated hard carbon material for sodium-ion batteries according to any one of claims 3 to 5, characterized in that, The recycled hard carbon material is subjected to airflow classification treatment so that the particle size D50 of the treated recycled hard carbon material meets the requirements of 7μm~9μm and the particle size D90≤30μm; And / or, the initial discharge specific capacity of the battery containing the recycled hard carbon material is greater than or equal to 328 mAh / g, and the initial coulombic efficiency of the battery containing the recycled hard carbon material is greater than 91%.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery regenerated hard carbon material as described in claim 1 or 2, or the sodium-ion battery includes the material prepared by the method for preparing the sodium-ion battery regenerated hard carbon material as described in any one of claims 3 to 9.

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