Battery preparation method based on sodium pyrophosphate iron regeneration material and hard carbon regeneration material

Abstract

This application discloses a battery preparation method based on recycled sodium iron pyrophosphate and recycled hard carbon materials, relating to the field of battery material recycling technology. The method includes pretreatment of retired sodium-ion batteries to obtain recycled sodium iron pyrophosphate and hard carbon materials, acid washing, complexation and impurity removal, and low-temperature sintering of the recycled sodium iron pyrophosphate to obtain recycled sodium iron pyrophosphate, desorption treatment of the hard carbon material in a supercritical carbon dioxide system, followed by segmental carbonization to obtain recycled hard carbon material, and assembly of the battery based on the above recycled materials. This method avoids structural collapse of the regenerated cathode material, while simultaneously replenishing sodium vacancies and improving ionic conductivity. The method also involves gently removing the SEI film from the hard carbon anode in a supercritical carbon dioxide environment, preventing damage to the hard carbon structure, increasing sodium ion insertion sites, and preserving the disordered carbon skeleton of the hard carbon, thus ensuring that the battery prepared from the recycled material possesses considerable coulombic efficiency and cycle life.

Description

Technical Field

[0001] This application relates to the technical field of batteries, specifically to a battery preparation method based on recycled sodium iron pyrophosphate and recycled hard carbon. Background Technology

[0002] In some related technologies, the recycling of positive and negative electrode materials from retired batteries is crucial. Sodium iron pyrophosphate positive electrode materials are prone to structural collapse, metal leaching, and impurity adhesion after retirement. Meanwhile, hard carbon negative electrodes from retired batteries easily form thick and unstable SEI films during cycling, and simultaneously adsorb electrolyte decomposition products. Traditional physical stripping methods easily damage the microporous structure of hard carbon, leading to a decrease in the initial coulombic efficiency of regenerated hard carbon and a shortened cycle life. Furthermore, existing recycling technologies mostly target either the positive or negative electrode separately, failing to achieve synergistic regeneration of both materials, thus hindering the development of batteries based on the synergistic effect of recycled positive and negative electrode materials. Summary of the Invention

[0003] In order to solve at least one of the problems mentioned in the background art, this application provides a battery preparation method based on sodium iron pyrophosphate recycled material and hard carbon recycled material. A thin carbon layer is formed by carbonization with sodium carbon repair agent to coat the positive electrode particles, which suppresses structural collapse and replenishes sodium vacancies, thereby improving ionic conductivity. The SEI film of the hard carbon negative electrode is gently removed in a supercritical carbon dioxide environment, avoiding damage to the hard carbon structure.

[0004] The specific technical solutions provided in this application are as follows: In a first aspect, a battery preparation method based on recycled sodium iron pyrophosphate and recycled hard carbon is provided, comprising the following steps: Retired sodium-ion batteries are pretreated to obtain sodium iron pyrophosphate and hard carbon retired materials; The decommissioned sodium ferric pyrophosphate is sequentially acid-washed and impurity-removed with a complexing agent to obtain purified cathode material. The purified cathode material is then mixed with a sodium carbonate repair agent to obtain cathode mixture. The cathode mixture is then sintered to obtain regenerated sodium ferric pyrophosphate. In a supercritical carbon dioxide system, the decommissioned hard carbon material is desorbed using a fluorocarbonate desorbent to obtain desorbed hard carbon. The desorbed hard carbon is then mixed with an activator to obtain a negative electrode mixture. The negative electrode mixture is then subjected to segmented carbonization to obtain regenerated hard carbon material. A positive electrode is prepared based on the regenerated sodium iron pyrophosphate, and a negative electrode is prepared based on the regenerated hard carbon material. The positive electrode, the negative electrode, the electrolyte, and the separator are then assembled to form a sodium-ion battery.

[0005] In one specific embodiment, in a supercritical carbon dioxide system, the desorbed hard carbon material is desorbed using a fluorocarbonate desorbent to obtain desorbed hard carbon, specifically including: The degraded hard carbon material is placed in the fluorocarbonate desorbent and treated for 1 to 2 hours to obtain the desorbed hard carbon; the supercritical carbon dioxide system conditions are a temperature of 35°C to 45°C and a pressure of 8 MPa to 12 MPa.

[0006] In one specific embodiment, the amount of the fluorocarbonate desorbent is 0.5wt%~1wt%, based on the mass of the hard carbon decommissioned material; And / or, the fluorocarbonate desorbent is fluoroethylene carbonate; And / or, the mass ratio of the desorbed hard carbon to the activator is 100:(10~15); And / or, the activator is sodium bicarbonate.

[0007] In one specific embodiment, the negative electrode mixture is subjected to segmented carbonization to obtain regenerated hard carbon material, specifically including: Under an inert atmosphere, the negative electrode mixture undergoes a first-stage carbonization and a second-stage carbonization. The first-stage carbonization conditions are: heating to 400℃~500℃ at a heating rate of 3℃ / min~5℃ / min and holding for 1h~1.5h; the second-stage carbonization conditions are: heating to 900℃~1000℃ at a heating rate of 5℃ / min~8℃ / min and holding for 1.5h~2h. After natural cooling, the mixture is washed with deionized water until neutral and then vacuum dried to obtain the regenerated hard carbon material. The vacuum drying temperature is 70℃~90℃ and the time is 10h~12h.

[0008] In one specific embodiment, the decommissioned sodium iron pyrophosphate material is subjected to acid cleaning and impurity removal with a complexing agent to obtain a purified cathode material, specifically including: The decommissioned sodium iron pyrophosphate material was placed in a 0.1 mol / L to 0.3 mol / L phosphoric acid solution and stirred at 30°C to 50°C for 1 to 1.5 hours to obtain an acid-washed material. The acid-washed material was then added to a 0.05 mol / L to 0.1 mol / L ethylenediaminetetraacetic acid complexing agent solution and stirred at 50°C to 60°C for 0.5 to 1 hour to obtain a complexed and purified material. The purified material was washed with deionized water and then vacuum-dried at 60°C to 80°C for 8 to 10 hours to obtain the purified cathode material.

[0009] In one specific embodiment, the amount of phosphoric acid solution used is 3 mL / g to 8 mL / g, based on the mass of the decommissioned sodium iron pyrophosphate material; And / or, the amount of the ethylenediaminetetraacetic acid complexing agent is 2 mL / g to 5 mL / g, based on the mass of the decommissioned sodium ferric pyrophosphate.

[0010] In one specific embodiment, the mass ratio of the purified positive electrode material to the sodium carbonate remediation agent is 100:(5~10); And / or, the sodium carbonate remedial agent comprises glucose and sodium dihydrogen phosphate, wherein the mass ratio of glucose to sodium dihydrogen phosphate is (1~5):1.

[0011] In one specific embodiment, sintering the positive electrode mixture to obtain regenerated sodium ferric pyrophosphate specifically includes: Under an inert atmosphere, the positive electrode mixture is heated to 550°C to 650°C at a heating rate of 2°C / min to 5°C / min, held at that temperature for 2 to 3 hours, and then naturally cooled to obtain the regenerated sodium pyrophosphate.

[0012] In one specific embodiment, the decommissioned sodium-ion battery is pretreated to obtain decommissioned sodium iron pyrophosphate and hard carbon materials, specifically including: Disassembling the retired sodium-ion battery yields used positive electrode material and used negative electrode material. The used positive electrode material is placed in a 0.5 mol / L to 1 mol / L citric acid solution at a temperature of 50°C to 70°C for 1 to 2 hours, the aluminum foil substrate is peeled off, and then filtered to obtain the retired sodium iron pyrophosphate material. The used negative electrode material is placed in a 1:1 volume ratio mixture of ethanol and water at a temperature of 40°C to 60°C and ultrasonically cleaned for 30 to 60 minutes. The aluminum foil substrate is peeled off, and then filtered to obtain the retired hard carbon material.

[0013] In a second aspect, a battery is provided, which is prepared by the battery preparation method described above based on sodium iron pyrophosphate recycled material and hard carbon recycled material.

[0014] The embodiments of this application have the following beneficial effects: The positive electrode material from retired batteries is subjected to acid cleaning and complexation to remove impurities. Acid cleaning removes aluminum and iron oxide impurities adhering to the surface of the positive electrode material, while complexation removes trace amounts of Cu. 2+ Ni 2+Heavy metal ions are removed, and then a sodium-carbon repair agent is used for structural repair. This allows the sodium-carbon repair agent to form a thin carbon layer that coats the positive electrode particles through carbonization, inhibiting structural collapse. Simultaneously, the sodium-carbon repair agent can fill sodium vacancies, repairing the crystal structure of Na2FeP2O7 and improving ionic conductivity. Furthermore, the high diffusion effect of supercritical carbon dioxide is used to fully remove the SEI film, effectively preventing damage to the hard carbon structure. A staged activation agent is used to form precise micropores, increasing sodium ion insertion sites while preserving the disordered carbon skeleton of the hard carbon, thus improving the battery's initial coulombic efficiency and cycle stability. Attached Figure Description

[0015] 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.

[0016] Figure 1 This application provides a method for preparing a battery based on recycled sodium iron pyrophosphate and recycled hard carbon. Figure 2 SEM image of the regenerated sodium pyrophosphate after remediation; Figure 3 The XRD patterns of sodium iron pyrophosphate cathode material before and after repair are shown in the comparison. Figure 4 SEM image of hard carbon scrap; Figure 5 SEM image of the recycled hard carbon material after treatment in Example 1; Figure 6 The images show the XRD patterns of hard carbon scrap before and after repair. Detailed Implementation

[0017] 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.

[0018] 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 a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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 ​​of 1 and 2 are listed, and if maximum range values ​​of 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 application, 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.

[0019] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0020] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0021] In this application, 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.

[0022] 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.

[0023] This application provides a battery preparation method based on recycled sodium iron pyrophosphate and recycled hard carbon, including the following steps: S1. Pre-treat retired sodium-ion batteries to obtain sodium iron pyrophosphate retired materials and hard carbon retired materials.

[0024] Specifically, the process includes: S1.1, dismantling retired sodium-ion batteries to obtain used positive and negative electrode materials; dismantling the retired sodium-ion batteries, removing the outer casing and electrolyte, and separating the positive and negative electrode materials; recovering the solvent from the electrolyte by distillation; the positive electrode material includes an aluminum foil substrate and a sodium iron pyrophosphate active layer, and the negative electrode material includes an aluminum foil substrate and a hard carbon active layer. S1.2, placing the used positive electrode material in a 0.5 mol / L~1 mol / L citric acid solution at a temperature of 50℃~70℃ for 1h~2h, peeling off the aluminum foil substrate, and then filtering to obtain the retired sodium iron pyrophosphate material.

[0025] S1.3 Place the old negative electrode material in a 1:1 volume ratio of ethanol and water, at a temperature of 40℃~60℃, and ultrasonically clean for 30min~60min. Peel off the aluminum foil substrate and then filter to obtain hard carbon decommissioned material.

[0026] S2. The retired sodium iron pyrophosphate material is sequentially acid-washed and impurities are removed with a complexing agent to obtain purified cathode material. The purified cathode material is mixed with a sodium carbonate repair agent to obtain cathode mixture. The cathode mixture is sintered to obtain regenerated sodium iron pyrophosphate.

[0027] The decommissioned sodium iron pyrophosphate was placed in a 0.1 mol / L to 0.3 mol / L phosphoric acid solution and stirred at 30℃ to 50℃ for 1 h to 1.5 h to obtain the acid-washed material. The acid-washed material was added to a 0.05 mol / L to 0.1 mol / L ethylenediaminetetraacetic acid complexing agent solution and stirred at 50℃ to 60℃ for 0.5 h to 1 h to obtain the complexed and impurity-removed material. The purified cathode material is obtained by washing the material with deionized water and then vacuum drying it at a temperature of 60℃~80℃ for 8h~10h.

[0028] The amount of phosphoric acid solution used is 3 mL / g to 8 mL / g, based on the mass of the decommissioned sodium ferric pyrophosphate; and / or the amount of ethylenediaminetetraacetic acid complexing agent used is 2 mL / g to 5 mL / g, based on the mass of the decommissioned sodium ferric pyrophosphate.

[0029] The positive electrode mixture is sintered to obtain regenerated sodium ferric pyrophosphate, specifically including: Under an inert atmosphere, the positive electrode mixture is heated to 550℃~650℃ at a heating rate of 2℃ / min~5℃ / min, held at that temperature for 2h~3h, and then naturally cooled to obtain regenerated sodium pyrophosphate.

[0030] Using a weak acid for cleaning avoids the problem of dissolving the cathode material structure caused by strong acid cleaning. Simultaneously, the complexing agent EDTA can remove trace heavy metal ions, such as Cu. 2+ Ni 2+ This ensures stable ion transport, thereby improving the electrochemical performance of the regenerated material.

[0031] Furthermore, the mass ratio of the purified cathode material to the sodium carbon repair agent is 100:(5~10). Preferably, the mass ratio of the purified cathode material to the sodium carbon repair agent is 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or any two of the above values. The sodium carbon repair agent includes glucose and sodium dihydrogen phosphate, and the mass ratio of glucose to sodium dihydrogen phosphate is (1~5):1. Specifically, the mass ratio of glucose to sodium dihydrogen phosphate is 1:1, 2:1, 3:1, 4:1, 5:1, or any two of the above values. The purified cathode material and the repair agent are mixed and sintered at low temperature under a nitrogen atmosphere. The glucose carbonizes to form a thin carbon layer that coats the cathode particles, inhibiting structural collapse. The sodium dihydrogen phosphate replenishes sodium vacancies, repairs the crystal structure of Na2FeP2O7, improves ionic conductivity, and ensures the cycle stability of the regenerated material when used in the battery.

[0032] S3. In a supercritical carbon dioxide system, fluorinated carbonate desorbents are used to desorb retired hard carbon materials to obtain desorbed hard carbon. The desorbed hard carbon is then mixed with an activator to obtain a negative electrode mixture. The negative electrode mixture is then subjected to segmented carbonization to obtain regenerated hard carbon materials.

[0033] In a supercritical carbon dioxide system, desorbed hard carbon material is desorbed using fluorocarbonate desorbents to obtain desorbed hard carbon. Specifically, the desorbed hard carbon material is placed in a fluorocarbonate desorbent for 1 to 2 hours to obtain desorbed hard carbon. The supercritical carbon dioxide system conditions are a temperature of 35°C to 45°C and a pressure of 8 MPa to 12 MPa.

[0034] Specifically, the temperature in the supercritical carbon dioxide system is set to 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, or any combination of two of the above values; the pressure is set to 8MPa, 9MPa, 10MPa, 11MPa, 12MPa, or any combination of two of the above values. Through the supercritical carbon dioxide system in this embodiment, and in conjunction with the use of fluorocarbonate desorbents, the SEI membrane, whose main components are organic carbonate salts and fluorides, is fully removed under the high diffusivity of supercritical carbon dioxide, resulting in filtered hard carbon after membrane removal.

[0035] Furthermore, the dosage of the fluorocarbonate desorbent is 0.5wt%~1wt%, based on the weight of the hard carbon decommissioned material. Specifically, the dosage of the fluorocarbonate desorbent is 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, or any two of the above values. The fluorocarbonate desorbent is fluoroethylene carbonate. In this embodiment, after the SEI film on the surface of the hard carbon negative electrode is removed, the hard carbon material is reconstructed with micropores. This is achieved by setting the mass ratio of desorbed hard carbon to activator to be 100:(10~15), and the activator being sodium bicarbonate. Specifically, the mass ratio of desorbed hard carbon to activator is 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, or any combination of two of these values. The mixture of desorbed hard carbon and activator is then subjected to staged carbonization under an inert atmosphere. Supercritical carbon dioxide gently removes the SEI film, avoiding damage to the hard carbon structure. Then, combined with staged activation using sodium bicarbonate, precise micropores are formed, increasing sodium ion insertion sites while preserving the disordered carbon skeleton of the hard carbon, ensuring the electrochemical performance of the regenerated hard carbon material.

[0036] The process involves segmented carbonization of the negative electrode mixture to obtain regenerated hard carbon material. Specifically, this includes: first-stage carbonization and second-stage carbonization of the negative electrode mixture under an inert atmosphere; the first-stage carbonization conditions are: heating to 400℃~500℃ at a heating rate of 3℃ / min~5℃ / min and holding for 1h~1.5h; the second-stage carbonization conditions are: heating to 900℃~1000℃ at a heating rate of 5℃ / min~8℃ / min and holding for 1.5h~2h; after natural cooling, washing with deionized water until neutral, and vacuum drying to obtain regenerated hard carbon material; wherein the vacuum drying temperature is 70℃~90℃ and the time is 10h~12h.

[0037] Based on the above-mentioned segmented carbonization process, in the first stage, sodium bicarbonate decomposes to produce carbon dioxide and water, which initially creates pores; in the second stage of carbonization, the micropores are further reconstructed, and the micropore size is concentrated in 0.6nm~0.7nm, which is suitable for sodium ion intercalation and achieves the battery's first coulombic efficiency ≥88%, which meets the charging and discharging efficiency standard of soft-pack batteries.

[0038] It should be noted that the inert atmosphere in this embodiment includes one or more of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).

[0039] S4. Prepare a positive electrode based on recycled sodium iron pyrophosphate, prepare a negative electrode based on recycled hard carbon material, and assemble the positive electrode, negative electrode, electrolyte and separator to form a sodium-ion battery.

[0040] The preparation of positive electrode sheets based on recycled sodium iron pyrophosphate includes: mixing recycled sodium iron pyrophosphate positive electrode material, conductive carbon black, and polyvinylidene fluoride in a preset mass ratio, adding N-methylpyrrolidone to form a slurry, coating it onto an aluminum foil current collector, vacuum drying at 80℃~100℃ for 6h~8h, and rolling to obtain a recycled positive electrode sheet. The recycled positive electrode sheet is adapted to the size of a soft-pack battery, and the electrode sheet thickness is adjusted to 100μm~150μm according to the specifications of the soft-pack battery.

[0041] The preparation of negative electrode sheets based on recycled hard carbon materials includes: mixing recycled hard carbon negative electrode materials, Ketjen black, and styrene-butadiene rubber in a preset mass ratio, adding deionized water to make a slurry, coating it on an aluminum foil current collector, vacuum drying at a temperature of 80℃~100℃ for 6h~8h, and rolling to obtain a recycled negative electrode sheet. The recycled negative electrode sheet is adapted to the size of a soft-pack battery, and the electrode sheet thickness is adjusted to 80μm~120μm according to the specifications of the soft-pack battery.

[0042] With 1 mol / L NaPF 6 / Ethylene carbonate (EC)-dimethyl carbonate (DMC) (volume ratio 1:1) is used as the electrolyte, and glass fiber is used as the separator (thickness 20μm~30μm). The soft-pack battery is assembled in an argon glove box using a stacking process. After encapsulation, settling, formation, and aging, the finished regenerated sodium-ion soft-pack battery is obtained. The regenerated sodium-ion soft-pack battery has a single cell capacity of 20Ah and a nominal voltage of 3.4V, which is suitable for energy storage and power battery scenarios.

[0043] Corresponding to the above embodiments, this application provides a battery prepared by the above-described method for preparing a battery based on recycled sodium iron pyrophosphate and recycled hard carbon.

[0044] Example 1 S1. Separation and pretreatment of positive and negative electrodes of retired sodium-ion pouch cells.

[0045] (1) Ten Na2FeP2O7 / hard carbon soft-pack sodium-ion batteries (20Ah, 3.4V each) with capacity decay to 58% of their initial capacity after 1000 cycles were selected. The outer shell was removed, and the electrolyte was collected and the EC and DMC solvents were recovered by distillation (recovery efficiency 92.3%). The positive electrode (aluminum foil substrate + sodium iron pyrophosphate active layer, total mass 120g) and the negative electrode (aluminum foil substrate + hard carbon active layer, total mass 80g) were separated. (2) Pretreatment of positive electrode sheet: Prepare 500 mL of 0.8 mol / L citric acid solution, immerse the positive electrode sheet in it, soak at 60℃ for 1.5 h, stir at 200 r / min, peel off the aluminum foil substrate during the process (aluminum foil recovery rate 98.5%), vacuum filter (vacuum degree ≤10 Pa) to obtain 48.6 g of crude product of sodium iron pyrophosphate positive electrode recovery material; (3) Pretreatment of negative electrode sheet: Prepare 500 mL of ethanol-water mixed solution (volume ratio 1:1), immerse the negative electrode sheet in it, and ultrasonically clean it at 50°C for 45 min (ultrasonic power 300W). Peel off the aluminum foil substrate (aluminum foil recovery rate 99.2%), and vacuum filter to obtain 29.8 g of hard carbon negative electrode recovery crude product.

[0046] S2. Preparation of regenerated sodium ferric pyrophosphate.

[0047] (1) Take 40g of crude positive electrode material, add 200mL of 0.2mol / L phosphoric acid solution, stir at 40℃ for 1.2h (stirring rate 200r / min) to complete the weak acid cleaning; then add 100mL of 0.08mol / L EDTA solution, stir at 55℃ for 0.8h to complex and remove trace amounts of Cu. 2+ Ni 2+ The material was repeatedly washed with deionized water until pH=7.0 (3 washes, 100mL water each time), and then vacuum dried at 80℃ for 9h (vacuum degree ≤10Pa) to obtain 37.2g of purified positive electrode material (recovery rate 93.0%). ICP-OES testing showed that the aluminum impurity content was 0.06%, and the Cu content was... 2+ Content 0.003%, Ni 2+ Content 0.002%; (2) The purified positive electrode recycled material and the repair agent were mixed at a mass ratio of 100:8. The repair agent was prepared by mixing glucose and sodium dihydrogen phosphate at a mass ratio of 3:1 (2.32 g glucose and 0.77 g sodium dihydrogen phosphate). The mixture was placed in a tube furnace, and nitrogen gas was introduced (flow rate 50 mL / min). The temperature was raised to 600°C at a rate of 3°C / min, held for 2.5 h, and then naturally cooled to room temperature to obtain 36.8 g of regenerated sodium iron pyrophosphate positive electrode material suitable for soft-pack batteries (total recovery rate 91.0%). XRD test showed that the crystallinity was 91.2%, which was close to that of the fresh material (93%), and there were no impurities. The ionic conductivity was 1.4 × 10⁻⁶. -3 S / cm.

[0048] S3, Preparation of recycled hard carbon materials.

[0049] (1) Take 20g of hard carbon recovery crude product, put it into a supercritical carbon dioxide treatment device, add 0.16g of 0.8wt% FEC desorbent, control the temperature at 40℃ and the pressure at 10MPa, and treat it at constant temperature and pressure for 1.5h. After filtration, 19.2g of hard carbon after membrane removal was obtained (recovery rate 96.0%). XPS test showed that the fluorine content was 0.15% and the SEI membrane removal rate was 97.3%. (2) The hard carbon after demolding was mixed with sodium bicarbonate at a mass ratio of 100:12 (2.30 g of sodium bicarbonate), placed in a tube furnace, and nitrogen gas was introduced (flow rate 50 mL / min). The temperature was first increased to 450°C at 4°C / min and held for 1.2 h; then increased to 950°C at 6°C / min and held for 1.8 h; after natural cooling, it was washed with deionized water until pH=7.0 (washed 3 times, each time with 50 mL of water), and vacuum dried at 80°C for 11 h (vacuum degree ≤10 Pa) to obtain 18.5 g of regenerated hard carbon anode material suitable for soft-pack batteries (total recovery rate 92.5%); BET test showed that the specific surface area was 482 m². 2 / g, micropore volume 0.19cm³ 3 / g, with micropore sizes concentrated in the range of 0.64nm to 0.66nm.

[0050] S4. Assemble the positive electrode, negative electrode, electrolyte, and separator to form a sodium-ion battery.

[0051] (1) Preparation of positive electrode slurry: Regenerated sodium pyrophosphate, SuperP and PVDF are mixed in a mass ratio of 85:10:5 (8.5g of regenerated sodium pyrophosphate, 1.0g of SuperP and 0.5g of PVDF), 20mL of N-methylpyrrolidone (NMP) is added, and the mixture is stirred until a uniform slurry is formed (stirring speed 3000r / min, stirring time 30min). The mixture is coated on a 15μm aluminum foil current collector (coating thickness 120μm), vacuum dried at 90℃ for 7h (vacuum degree ≤10Pa), and rolled (pressure 5MPa) to obtain the regenerated positive electrode sheet; (2) Preparation of negative electrode slurry: Regenerated hard carbon, Ketjen black and SBR are mixed in a mass ratio of 90:5:5 (9.0g of regenerated hard carbon, 0.5g of Ketjen black and 0.5g of SBR), 25mL of deionized water is added, and the mixture is stirred until a uniform slurry is formed (stirring speed 3000r / min, stirring time 30min). The mixture is coated on a 10μm aluminum foil current collector (coating thickness 100μm), vacuum dried at 90℃ for 7h (vacuum degree ≤10Pa), and rolled (pressure 3MPa) to obtain the regenerated negative electrode sheet; (3) Assembly of soft-pack batteries: Using 1mol / L NaPF6 / EC-DMC (volume ratio 1:1) as electrolyte and glass fiber as separator (thickness 20μm), soft-pack batteries (single capacity 20Ah, nominal voltage 3.4V) are assembled in an argon glove box using a stacking process. The electrolyte volume is adjusted to 5mL according to the specifications of the soft-pack battery. After encapsulation, standing for 12h, formation (0.05C constant current charging to 3.8V, standing for 30min, 0.05C constant current discharge to 2.0V), and aging for 24h, the finished regenerated sodium-ion soft-pack battery is obtained. Test Results: Using the CT-4000 battery testing system, at 0.1C rate, the regenerated positive electrode showed an initial discharge specific capacity of 98 mAh / g and a capacity recovery rate of 98%; at 0.5C rate, after 1000 cycles, the capacity retention rate was 91%; the regenerated hard carbon showed an initial coulombic efficiency of 89.5% and an initial irreversible capacity of 10.2 mAh / g; at 0.5C rate, after 200 cycles, the capacity retention rate was 93.8%; the sodium ion diffusion coefficient was 8.9 × 10⁻⁶. -11 cm 2 / s; The regenerated soft-pack battery has an energy density of 123Wh / kg, a capacity retention rate of 87% at -20℃, and shows no fire or leakage during needle penetration and extrusion tests, meeting sealing performance standards; the total energy consumption is 88kWh / kg, and wastewater discharge is only 4.8% of that of traditional processes. The regenerated hard carbon has a specific capacity of 328mAh / g, an initial coulombic efficiency of 87.2%, and an Al impurity content of 0.06% in the positive electrode.

[0052] The positive electrode uses a glucose-sodium dihydrogen phosphate composite repair agent to simultaneously achieve carbon layer coating and sodium vacancy repair, taking into account both structural stability and ionic conductivity, and is suitable for the high-rate charge and discharge requirements of pouch batteries. The hard carbon uses supercritical CO2 defilming and sodium bicarbonate segmented activation to precisely reconstruct a microporous structure suitable for sodium ion intercalation, achieving a micropore size of 0.6nm~0.7nm. This addresses the performance degradation problem of recycled materials from a mechanistic perspective, meeting the long-cycle and high-safety requirements of pouch batteries.

[0053] Furthermore, this solution utilizes recycled materials from retired pouch batteries as raw materials, significantly reducing the preparation cost of fresh positive and negative electrode materials. The simplified process reduces equipment wear and reagent consumption, while ensuring the recycled materials meet performance standards. The integrated process of positive and negative electrode separation, pretreatment, purification and repair, and regeneration assembly employs a stacking process adapted to pouch battery assembly, eliminating the need to separate independent recycling production lines. It is compatible with existing sodium-ion pouch battery recycling equipment, requiring minimal modification and investment, and enabling large-scale production. The electrolyte solvent is recovered through distillation, further improving resource utilization.

[0054] SEM analysis was performed on the regenerated sodium ferric pyrophosphate after the treatment method described in Example 1. The test results are as follows: Figure 2 As shown, the regenerated sodium iron pyrophosphate cathode material exists in the form of irregular polyhedral particle agglomeration with a particle size of about 0.5μm~1.5μm. The surface is covered with flocculent carbonaceous products, indicating that a carbonaceous coating layer is formed on the particle surface after glucose carbonization.

[0055] The XRD patterns of the sodium iron pyrophosphate cathode material before and after repair were compared, and the results are as follows: Figure 3As shown, before repair (gray curve), due to structural collapse and impurity residue after decommissioning, the characteristic peaks are weak in intensity, broadened in shape, with some peaks shifted, low crystallinity, and structural distortion. After repair (black curve), the characteristic peaks are significantly stronger and sharper, all peaks perfectly match the standard Na2FeP2O7 crystal phase, no impurity phases are generated, and the crystallinity is restored to 89%~92% (close to 93% of fresh material). The results indicate that the gradient purification process of this invention can effectively remove impurities, and the composite repair agent and low-temperature sintering process can accurately repair sodium vacancies and crystal structure, completely preserving the orthorhombic crystal framework of sodium iron pyrophosphate, providing a reliable structural guarantee for the cathode material to achieve high capacity recovery rate and long cycle stability.

[0056] SEM tests were performed on the decommissioned hard carbon material in Example 1 and the treated recycled hard carbon material, respectively. The test results are as follows: Figure 4 and Figure 5 As shown, it can be concluded that Figure 4 (Before restoration) The surface of the decommissioned hard carbon was covered with a large amount of SEI film and organic residue, presenting a flocculent and filamentous impurity accumulation pattern. The original microporous structure was obscured, the particles were severely aggregated, and the disordered carbon skeleton was wrapped by impurities, making it unable to effectively participate in the sodium ion insertion / extraction reaction. Figure 5 (After repair): After gentle defilming with supercritical carbon dioxide and staged activation with sodium bicarbonate, impurities on the hard carbon surface were completely removed, leaving a smooth and clean surface with the disordered carbon skeleton intact, without structural damage or pulverization. Simultaneously, uniformly distributed nanoscale micropores formed on the surface, precisely controlling the pore structure and significantly increasing the number of sodium ion insertion sites, providing a structural basis for efficient sodium storage. XRD patterns of the hard carbon material before and after repair were compared, and the results are as follows: Figure 6 As shown, hard carbon, as a typical amorphous carbon material, exhibits two broadened characteristic peaks at ~26° and ~44°, corresponding to the (002) and (100) / (101) crystal planes, respectively. Before repair (gray curve), the characteristic peak intensity was weak and the peak shape was broadened due to the influence of the SEI film and organic residue coverage, and the order of the carbon skeleton was obscured. After repair (black curve), the characteristic peak intensity was significantly improved and the peak shape was sharper, indicating that the supercritical carbon dioxide gentle defilming completely removed the surface impurities and the order of the hard carbon skeleton was restored; at the same time, the (002) peak position did not shift, and the carbon interlayer spacing (d) was restored. 002 The wavelength (≈0.37nm~0.38nm) remained stable, verifying that the staged activation process, while constructing precise micropores, completely preserved the disordered carbon framework and sodium storage adaptation structure of hard carbon, providing structural assurance for efficient sodium ion insertion / extraction.

[0057] Example 2 The difference between this embodiment and Embodiment 1 is that the positive electrode gradient purification uses a 0.1 mol / L phosphoric acid solution, stirred at 30°C for 1.5 h, and an EDTA concentration of 0.05 mol / L, stirred at 50°C for 1 h; the positive electrode structure repair temperature is 550°C, kept at that temperature for 3 h, and the repair agent addition ratio is 100:5.

[0058] The hard carbon SEI membrane was removed at 35℃ and 8MPa, with FEC added at 0.5wt% for 2 hours. The sodium bicarbonate addition ratio for hard carbon micropore reconstruction was 100:10. The first stage was held at 400℃ for 1.5 hours, and the second stage was held at 900℃ for 2 hours. The coating thickness of the soft-pack battery was adjusted to 100μm for the positive electrode and 80μm for the negative electrode, with an electrolyte volume of 4.5mL. The remaining experimental conditions were the same as in Example 1, with 3 parallel samples set up, and the average value of the test results was taken.

[0059] Test results: The recovery rate of the purified cathode material was 91.5%, the aluminum impurity content was 0.07%, the crystallinity of the regenerated cathode was 89.5%, and the ionic conductivity was 1.2 × 10⁻⁶. -3 S / cm, first discharge specific capacity 95mAh / g, capacity recovery rate 95%, capacity retention rate 90% after 1000 cycles at 0.5C.

[0060] The regenerated hard carbon has a specific capacity of 318 mAh / g, a recovery rate of 95.2% after hard carbon membrane removal, an SEI membrane removal rate of 95.0%, and a specific surface area of ​​455 m². 2 / g, micropore size 0.63nm~0.67nm, initial coulombic efficiency 88%, capacity retention 92% after 200 cycles; regenerated pouch battery energy density 120Wh / kg, capacity retention 85% at -20℃, initial coulombic efficiency of 85.2% for the whole cell, safety performance meets standards; total energy consumption 80kWh / kg, slightly lower than Example 1, suitable for pouch battery applications in low-cost energy storage scenarios.

[0061] Example 3 The difference between this embodiment and Embodiment 1 is that the positive electrode gradient purification uses a 0.3 mol / L phosphoric acid solution, stirred at 50°C for 1 h, and an EDTA concentration of 0.1 mol / L, stirred at 60°C for 0.5 h; the positive electrode structure repair temperature is 650°C, kept at that temperature for 2 h, and the repair agent addition ratio is 100:10.

[0062] The hard carbon SEI membrane was removed at 45℃ and 12MPa, with FEC added at 1.0wt% for 1 hour. The hard carbon micropore reconstruction involved a sodium bicarbonate addition ratio of 100:15. The first stage was held at 500℃ for 1 hour, and the second stage at 1000℃ for 1.5 hours. The coating thickness of the soft-pack battery was adjusted to 150μm for the positive electrode and 120μm for the negative electrode, with an electrolyte volume of 5.5mL. All other experimental conditions were the same as in Example 1, with three parallel samples, and the average value of the test results was taken.

[0063] Test results: The recovery rate of the purified positive electrode material was 93.5%, the aluminum impurity content was 0.05%, the crystallinity of the regenerated positive electrode was 92.0%, and the ionic conductivity was 1.5 × 10⁻⁶. -3 S / cm, first-cycle discharge specific capacity 100mAh / g, capacity recovery rate 100%, capacity retention rate 92% after 1000 cycles at 0.5C.

[0064] The regenerated hard carbon has a specific capacity of 332 mAh / g, a recovery rate of 96.5% after hard carbon membrane removal, an SEI membrane removal rate of 97.2%, and a specific surface area of ​​498 m². 2 / g, micropore size 0.64nm~0.65nm, initial coulombic efficiency 90%, capacity retention 94% after 200 cycles; regenerated pouch battery energy density 125Wh / kg, capacity retention 88% at -20℃, initial coulombic efficiency 87.8% for the whole cell, with optimal safety and rate performance; total energy consumption 95kWh / kg, suitable for pouch battery applications in power battery scenarios.

[0065] Example 4 The difference between this embodiment and Example 1 is that the concentration of FEC desorbent in the supercritical carbon dioxide system is set to 0.5 wt% (based on the mass of crude hard carbon recycled material). The other experimental conditions are completely the same as in Example 1. Three parallel samples are set for each group, and the test results are taken as the average value.

[0066] Example 5 The difference between this embodiment and Example 1 is that the concentration of the FEC desorbent in the supercritical carbon dioxide system is set to 1.0 wt% (based on the mass of the crude hard carbon recovery material). All other experimental conditions are identical to those in Example 1. Three parallel samples are set for each group, and the average value of the test results is taken. The test results for Examples 1, 4, and 5 are shown in Table 1. Table 1. Test results for Examples 1, 4, and 5.

[0067] Based on the data in Table 1, it can be concluded that when the FEC desorbent concentration is selected within the range of 0.5wt% to 1.0wt%, the SEI film removal rate in this embodiment reaches over 95%, and the initial coulombic efficiency of the regenerated hard carbon material obtained after the treatment reaches over 87.2%. The minimum capacity retention rate of the regenerated hard carbon after 200 cycles is over 91%, further verifying that the treatment method in this embodiment can effectively regenerate the regenerated sodium iron pyrophosphate cathode material and regenerated hard carbon material in the retired battery. Furthermore, for the battery prepared by combining the regenerated sodium iron pyrophosphate cathode material and regenerated hard carbon material, the SEI film removal rate and hard carbon electrochemical performance gradually improve with increasing FEC desorbent concentration within the range of 0.5wt% to 1.0wt%. However, the performance improvement slows down after the concentration exceeds 0.8wt%. Considering both process cost and performance, 0.8wt% is the optimal concentration.

[0068] Example 6 The difference between this embodiment and Example 1 is that the mass ratio of hard carbon to sodium bicarbonate after demolding is set to 100:10, three sets of variables are set, and the remaining experimental conditions are completely consistent with Example 1. Three parallel samples are set for each group, and the average value of the test results is taken.

[0069] Example 7 The difference between this embodiment and embodiment 1 is that the mass ratio of hard carbon to sodium bicarbonate after demolding is set to 100:15, three sets of variables are set, and the remaining experimental conditions are completely consistent with those of embodiment 1. Three parallel samples are set for each group, and the test results are taken as average values. The test results of embodiment 1, embodiment 6 and embodiment 7 are shown in Table 2.

[0070] Table 2 Test results for Examples 1, 6 and 7

[0071] Based on the test results in Table 2, it can be concluded that, according to the scheme in this embodiment, increasing the amount of sodium bicarbonate can improve the specific surface area and micropore volume of hard carbon. However, when the mass ratio exceeds 100:12, the micropores on the hard carbon surface are prone to excessive expansion, leading to a decrease in structural stability and a slight decline in cycle performance. The optimal mass ratio is 100:12. This further verifies that, based on the scheme in this embodiment, supercritical carbon dioxide gently removes the SEI film, avoiding damage to the hard carbon structure. Then, combined with the staged activation of sodium bicarbonate, precise micropores are formed, and the micropore size range of the regenerated hard carbon material meets the requirements of 0.62nm~0.68nm, which improves the sodium ion insertion sites while preserving the disordered carbon skeleton of hard carbon, ensuring the electrochemical performance of the regenerated hard carbon material.

[0072] Example 8 The difference between this embodiment and Embodiment 1 is that the first stage carbonization conditions in the segmented carbonization of the negative electrode mixture are set at a temperature of 400℃ and a holding time of 1.5h, and the second stage carbonization conditions are set at a temperature of 900℃ and a holding time of 2.0h. The remaining experimental conditions are completely consistent with those in Embodiment 1. Three parallel samples are set for each group, and the average value of the test results is taken.

[0073] Example 9 The difference between this embodiment and Embodiment 1 is that the first stage carbonization condition in the segmented carbonization of the negative electrode mixture is set at 500℃ for 1.0 h, and the second stage carbonization condition is set at 1000℃ for 1.5 h. All other experimental conditions are completely consistent with Embodiment 1. Three parallel samples were set for each group, and the average value of the test results was taken. The test results of Embodiments 1, 8, and 9 are shown in Table 3. The other test results of Embodiments 4 to 9 are summarized in Table 4.

[0074] Table 3 Test results of Examples 1, 8 and 9

[0075] Based on the data in Table 3, it can be concluded that the segmented carbonization method in this embodiment involves the decomposition of sodium bicarbonate to produce carbon dioxide and water in the first stage, which initially creates pores; the second stage of carbonization further reconstructs the micropores. The segmented carbonization conditions of holding at 450℃ for 1.2h in the first stage and at 950℃ for 1.8h in the second stage can achieve a balance between hard carbon crystallinity, microporous structure and energy consumption, with the highest sodium ion diffusion efficiency and the lowest cycle decay rate.

[0076] Table 4 Summary of test results from Examples 4 to 9

[0077] Comparative Example 1 Corresponding to the above embodiments, the difference between Comparative Example 1 and Example 1 is that the existing conventional process processes the recycled sodium iron pyrophosphate cathode material but does not process the hard carbon anode before assembling the soft-pack battery. The specific steps are as follows: S1. Pretreatment of retired sodium-ion batteries, the same as in Example 1, to obtain 48.6g of crude sodium iron pyrophosphate cathode material; S2. Strong acid leaching: Add 40g of crude positive electrode recovery material to 200mL of 2mol / L sulfuric acid solution, stir at 80℃ for 2h (stirring rate 200r / min), filter, add 1mol / L sodium hydroxide to adjust pH to 7.5, precipitate to obtain a mixture of iron and sodium hydroxide, filter and dry to obtain 32.8g of solid product; S3. High-temperature calcination: 32.8g of the precipitated product was mixed with 10g of sodium dihydrogen phosphate, and the mixture was heated to 850℃ at 5℃ / min in air atmosphere and held for 4h to obtain 28.5g of traditional recycled cathode material (total recovery rate 71.2%). XRD test showed that the crystallinity was 78.3% and a small amount of impurity phase (Fe2O3) was present. ICP-OES test showed that the aluminum impurity content was 0.35% and the total heavy metal ion content was 0.08%. S4. Assembly and testing of pouch cells: Using the fresh hard carbon anode, electrolyte and pouch cell assembly process (stacking, encapsulation, formation and aging) of Example 1, the performance of the regenerated cathode and pouch cells was tested. Three parallel samples were set up and the average value of the test results was taken.

[0078] Test results: The first discharge specific capacity of the regenerated positive electrode was 78 mAh / g, with a capacity recovery rate of only 78%. After 1000 cycles at 0.5C, the capacity retention rate was 72%; the ionic conductivity was 4.8 × 10⁻⁶. -4 S / cm; the capacity retention rate of the pouch battery at -20℃ was 68%, and slight leakage was observed during the needle penetration test, indicating that the safety performance did not meet the standards; the process energy consumption was 210kWh / kg, which is 138.6% higher than that of Example 1; the wastewater discharge was 22 times that of Example 1, with COD=320mg / L, ammonia nitrogen 35mg / L, fluoride 12mg / L, containing heavy metal ions, resulting in high environmental treatment costs, and the negative electrode regeneration was not achieved, resulting in low resource utilization (only the positive electrode was recycled, and the negative electrode was discarded), which does not meet the requirements for green mass production of pouch batteries.

[0079] Comparative Example 2 Corresponding to the above embodiments, the difference between Comparative Example 2 and Example 1 is that sodium carbonate repair agent is not used, and low-temperature sintering is carried out directly. The other experimental conditions are completely consistent with those of Example 1. Three parallel samples are set up for each group, and the test results are taken as the average value.

[0080] Test results: The recovery rate of the positive electrode after purification was 93.0%, the crystallinity of the regenerated positive electrode was 82.5%, and the ionic conductivity was 6.5 × 10⁻⁶. - 4 The first-cycle discharge specific capacity was 82 mAh / g, with a capacity recovery rate of 82%. After 1000 cycles at 0.5C, the capacity retention rate was 65% (severe structural collapse occurred during cycling). The performance of the regenerated hard carbon was basically consistent with Example 1 (88% initial coulombic efficiency, 92% capacity retention rate after 200 cycles). The overall energy density of the regenerated pouch battery was 102 Wh / kg, a decrease of 17.1% compared to Example 1. After 500 cycles, the capacity decay reached 28%, failing to meet the requirements for long-cycle use of pouch batteries. The total energy consumption was 86 kWh / kg. The core problem was the lack of a carbon layer coating on the positive electrode, leading to structural collapse, ineffective repair of sodium vacancies, and insufficient ionic conductivity, highlighting the crucial role of carbon-sodium repair agents in the performance of the pouch battery's positive electrode.

[0081] Comparative Example 3 Corresponding to the above embodiments, the difference between Comparative Example 3 and Example 1 is that the hard carbon anode uses traditional high-temperature calcination for demolding, without supercritical CO2 demolding and sodium bicarbonate micropore reconstruction. The remaining experimental conditions are completely consistent with Example 1. Three parallel samples are set up for each group, and the test results are taken as the average value.

[0082] The specific steps for hard carbon processing are as follows: 20g of crude hard carbon anode material was placed in a tube furnace and heated to 600℃ at 5℃ / min under air atmosphere, held for 2 hours to remove the SEI film and organic impurities. After natural cooling, 17.2g of regenerated hard carbon was obtained (recovery rate 86.0%). BET testing showed a specific surface area of ​​285m². 2 / g, micropore volume 0.11cm³ 3 / g, with random micropore sizes (0.4nm~1.2nm) and a micropore structure retention rate of only 68.3%; XPS test showed that the fluorine content was 0.85% and the SEI membrane removal rate was 77.6%.

[0083] Test results: The initial coulombic efficiency of the regenerated hard carbon was 74%, the initial irreversible capacity was 22.5 mAh / g, and the capacity retention was 70% after 200 cycles at 0.5C rate; the sodium ion diffusion coefficient was 3.9 × 10⁻⁶. -11 cm 2 / s; The performance of the regenerated positive electrode is basically the same as that of Example 1 (90% capacity retention after 1000 cycles at 0.5C); The capacity of the regenerated pouch battery decreases by 35% after 500 cycles at 0.5C, which is much worse than that of Example 1 (capacity decrease ≤10% after 500 cycles). The voltage fluctuation is large during charging and discharging, which cannot meet the requirements for large-scale use of pouch batteries. This indicates that supercritical CO2 gentle demembranes and segmented micropore reconstruction can effectively retain the sodium storage activity of hard carbon and improve the overall performance of pouch batteries.

[0084] Based on Comparative Examples 1, 2, and 3, it can be found that the processing technology in this scheme can synergistically regenerate the positive and negative electrode materials in retired sodium-ion batteries. It has significant advantages in terms of the performance of recycled materials, energy consumption control, environmental protection, and resource utilization. The prepared positive and negative electrode materials are suitable for the assembly and performance requirements of pouch batteries.

[0085] Comparative Example 4 Corresponding to the above embodiments, the difference between Comparative Example 4 and Example 1 is that the concentration of FEC desorbent during the supercritical CO2 demembrane removal process is 1.5 wt%, while the rest is completely consistent with Example 1. Three parallel samples were set up, and the average value of the test results was taken.

[0086] The test results are as follows: SEI film removal rate: 97.5%; elemental analysis of the regenerated hard carbon surface: fluorine residue 0.25%; initial coulombic efficiency of regenerated hard carbon: 87.8%; capacity retention rate of regenerated hard carbon after 200 cycles: 89.6%; initial coulombic efficiency of the full cell: 85.1%; capacity decay rate of the pouch cell after 500 cycles: 13.2%.

[0087] Based on the above comparison schemes, it can be found that although the removal rate of SEI membrane can be further improved when the amount of FEC desorbent exceeds the range of 0.5wt%~1wt%, it will lead to an increase in fluorine residue, damage the chemical environment of hard carbon surface, and reduce sodium storage activity and cycle stability, thus verifying the rationality of limiting the FEC concentration range in this invention.

[0088] Comparative Example 5 Corresponding to the above embodiments, the difference between Comparative Example 5 and Example 1 is that the removal of hard carbon SEI membrane adopts a "subcritical CO2 + FEC" system (non-supercritical atmosphere). Specifically, the membrane removal system is: CO2 (subcritical state), temperature 25°C, pressure 5MPa, FEC dosage 0.8wt%, and treatment time 1.5h. The rest is completely consistent with Example 1. Three parallel samples were set up, and the average value of the test results was taken.

[0089] Test results: SEI membrane removal rate: 78.3%; fluorine content of regenerated hard carbon: 0.72%; specific surface area of ​​regenerated hard carbon: 395 m². 2 / g, initial coulombic efficiency of regenerated hard carbon: 82.5%, capacity retention after 200 cycles of regenerated hard carbon: 86.3%, energy density of pouch cell: 110Wh / kg, capacity decay rate after 500 cycles of pouch cell: 18.5%.

[0090] Based on the above comparison, it can be found that under a non-supercritical CO2 atmosphere, the diffusivity and solubility of CO2 decrease significantly, making it impossible to efficiently strip the SEI film. This leads to the destruction of the hard carbon structure, an increase in impurity residue, and electrochemical performance that is significantly inferior to the supercritical CO2 system of this invention. This highlights that the supercritical state is the core prerequisite for achieving mild and efficient film stripping.

[0091] Comparative Example 6 Corresponding to the above embodiments, the difference between Comparative Example 6 and Example 1 is that the negative electrode mixture undergoes a stage of carbonization to obtain regenerated hard carbon material. The specific carbonization conditions include heating to 950°C at a rate of 5°C / min and holding at that temperature for 3.0 hours. The rest are completely consistent with Example 1. Three parallel samples were set up, and the average value of the test results was taken. The test results of Comparative Examples 1 to 6 are summarized in Table 5.

[0092] Test results: Specific surface area of ​​regenerated hard carbon: 412 m² 2 / g, regenerated hard carbon micropore volume: 0.15cm³3 / g, with a randomized micropore size distribution ranging from 0.55 nm to 0.78 nm; initial coulombic efficiency of regenerated hard carbon: 85.7%; capacity retention after 200 cycles: 88.2%; sodium ion diffusion coefficient: 6.8 × 10⁻⁶. -11 cm 2 / s, capacity decay rate of pouch battery after 500 cycles: 15.7%.

[0093] Based on the above comparison schemes, it can be found that single-stage carbonization cannot achieve step-by-step control of "preliminary pore formation - precise reconstruction", resulting in disordered micropore size and insufficient structural stability of hard carbon, and a significant decrease in sodium ion transport efficiency and cycle performance, which verifies the necessity of segmented carbonization process.

[0094] Table 5 Summary of test results from Comparative Examples 1 to 6

[0095] 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.

[0096] 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 battery preparation method based on recycled sodium iron pyrophosphate and recycled hard carbon, characterized in that, Includes the following steps: Retired sodium-ion batteries were pretreated to obtain sodium iron pyrophosphate and hard carbon retired materials. The decommissioned sodium ferric pyrophosphate is sequentially acid-washed and impurity-removed with a complexing agent to obtain purified cathode material. The purified cathode material is then mixed with a sodium carbonate repair agent to obtain cathode mixture. The cathode mixture is then sintered to obtain regenerated sodium ferric pyrophosphate. In a supercritical carbon dioxide system, the decommissioned hard carbon material is desorbed using a fluorocarbonate desorbent to obtain desorbed hard carbon. The desorbed hard carbon is then mixed with an activator to obtain a negative electrode mixture. The negative electrode mixture is then subjected to segmented carbonization to obtain regenerated hard carbon material. A positive electrode is prepared based on the regenerated sodium iron pyrophosphate, and a negative electrode is prepared based on the regenerated hard carbon material. The positive electrode, the negative electrode, the electrolyte, and the separator are then assembled to form a sodium-ion battery.

2. The method according to claim 1, characterized in that, In a supercritical carbon dioxide system, the desorbed hard carbon material is desorbed using a fluorocarbonate desorbent to obtain desorbed hard carbon, specifically including: The desorbed hard carbon material is placed in the fluorocarbonate desorbent and treated for 1 to 2 hours to obtain the desorbed hard carbon. The conditions for the supercritical carbon dioxide system are a temperature of 35℃~45℃ and a pressure of 8MPa~12MPa.

3. The method according to claim 1 or 2, characterized in that, The amount of the fluorocarbonate desorbent is 0.5wt%~1wt%, based on the mass of the hard carbon decommissioned material; And / or, the fluorocarbonate desorbent is fluoroethylene carbonate; And / or, the mass ratio of the desorbed hard carbon to the activator is 100:(10~15); And / or, the activator is sodium bicarbonate.

4. The method according to claim 1 or 2, characterized in that, The negative electrode mixture is subjected to segmented carbonization to obtain regenerated hard carbon material, specifically including: The negative electrode mixture is subjected to a first stage of carbonization and a second stage of carbonization under an inert atmosphere; The conditions for the first stage of carbonization are: heating to 400℃~500℃ at a heating rate of 3℃ / min~5℃ / min, and holding at that temperature for 1h~1.5h; The conditions for the second stage of carbonization are as follows: heating to 900℃~1000℃ at a heating rate of 5℃ / min~8℃ / min, holding at that temperature for 1.5h~2h, naturally cooling, washing with deionized water until neutral, and vacuum drying to obtain the regenerated hard carbon material. The vacuum drying temperature is 70℃~90℃, and the time is 10h~12h.

5. The method according to claim 1 or 2, characterized in that, The decommissioned sodium iron pyrophosphate material is subjected to acid cleaning and impurity removal with a complexing agent to obtain purified cathode material, specifically including: The decommissioned sodium iron pyrophosphate material was placed in a 0.1 mol / L to 0.3 mol / L phosphoric acid solution and stirred at 30℃ to 50℃ for 1 h to 1.5 h to obtain the acid-washed material. The acid-washed material is added to a 0.05 mol / L to 0.1 mol / L ethylenediaminetetraacetic acid complexing agent solution and stirred at 50℃ to 60℃ for 0.5 h to 1 h to obtain the complexed and impurity-removed material. The purified material is obtained by washing the purified material with deionized water and then vacuum drying it at a temperature of 60℃~80℃ for 8h~10h.

6. The method according to claim 5, characterized in that, The amount of phosphoric acid solution used is 3 mL / g to 8 mL / g, based on the mass of the decommissioned sodium iron pyrophosphate material; And / or, the amount of the ethylenediaminetetraacetic acid complexing agent is 2 mL / g to 5 mL / g, based on the mass of the decommissioned sodium ferric pyrophosphate.

7. The method according to claim 1 or 2, characterized in that, The mass ratio of the purified positive electrode material to the sodium carbonate repair agent is 100:(5~10); And / or, the sodium carbonate remedial agent comprises glucose and sodium dihydrogen phosphate, wherein the mass ratio of glucose to sodium dihydrogen phosphate is (1~5):

1.

8. The method according to claim 7, characterized in that, The positive electrode mixture is sintered to obtain regenerated sodium ferric pyrophosphate, specifically including: Under an inert atmosphere, the positive electrode mixture is heated to 550°C to 650°C at a heating rate of 2°C / min to 5°C / min, held at that temperature for 2 to 3 hours, and then naturally cooled to obtain the regenerated sodium pyrophosphate.

9. The method according to claim 1 or 2, characterized in that, Pretreatment of retired sodium-ion batteries yields sodium iron pyrophosphate and hard carbon retired materials, specifically including: Disassembling the retired sodium-ion battery yields used positive electrode material and used negative electrode material; The spent positive electrode material is placed in a citric acid solution with a concentration of 0.5 mol / L to 1 mol / L at a temperature of 50°C to 70°C for 1 to 2 hours. The aluminum foil substrate is then peeled off and filtered to obtain the decommissioned sodium iron pyrophosphate material. The old negative electrode material was placed in a mixture of ethanol and water with a volume ratio of 1:1, and ultrasonically cleaned at a temperature of 40℃~60℃ for 30min~60min. The aluminum foil substrate was then peeled off, and the hard carbon decommissioned material was obtained by filtration.

10. A battery, characterized in that, The battery is prepared by any one of the battery preparation methods based on sodium iron pyrophosphate recycled material and hard carbon recycled material as described in any one of claims 1 to 9.

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