A method for directly regenerating waste lithium iron phosphate positive electrode material based on lignin light-assisted, regenerated lithium iron phosphate positive electrode material and application

Abstract

The application discloses a kind of based on lignin light-assisted direct regeneration method of waste lithium iron phosphate positive material and regeneration lithium iron phosphate positive material and application, belong to lithium ion battery technical field.The method includes: waste lithium iron phosphate powder, lignin, lithium source is mixed, solvent is added, and dispersion treatment is obtained Uniform mixed solution;Uniform mixed solution is repaired by light-heat synergic auxiliary, and the lithium iron phosphate positive material slurry after repair is obtained;The lithium iron phosphate positive material slurry after repair is separated and dried, and the regeneration lithium iron phosphate positive material is obtained.The application is innovatively with the lignin of biomass waste source as illumination response and electron transfer participant, under the premise that the skeleton of waste lithium iron phosphate positive material is completed, by mild means, synchronous lithium supplement, Fe 3+ Valence state regulation, Fe Li Anti-position defect inhibition, impurity phase removal and electrochemical performance recovery are realized.The application also discloses the regeneration lithium iron phosphate positive material prepared by the above method and application.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration, as well as the regenerated lithium iron phosphate cathode materials and their applications. Background Technology

[0002] Among the various lithium-ion battery technologies, lithium iron phosphate (LFP) batteries, due to their absence of precious metals such as cobalt and nickel, possess extremely high safety, excellent cycle performance, and significant cost advantages. In recent years, their market share in power batteries and energy storage has rapidly expanded, gradually gaining a dominant position. However, as the first batch of mass-produced new energy vehicle power batteries (with a typical lifespan of 5-8 years) and energy storage systems gradually enter their retirement cycle, the number of spent lithium iron phosphate (SLFP) batteries is growing exponentially. Forecasts indicate that millions of tons of spent lithium iron phosphate batteries will be generated globally by the end of 2025, and this rapid upward trend is expected to continue over the next decade.

[0003] Improper disposal of spent lithium iron phosphate batteries can trigger a dual crisis of resources and the environment: on the one hand, it causes a serious waste of key resources such as lithium, phosphorus, and iron; on the other hand, the electrolyte and its organic components pose a potential threat to the ecological environment. Current industry research revolves around balancing the three core aspects of "recycling rate, economic efficiency, and environmental friendliness." On the one hand, it focuses on developing mature technological pathways such as battery pretreatment, cathode material recycling, full leaching recycling, selective lithium extraction, and reuse of recycled materials to solidify the industry's technological foundation. On the other hand, it actively explores emerging processes such as the comprehensive recycling of phosphorus-iron-lithium ternary cathode materials and high-temperature solid-phase remediation, striving to break through the technical bottleneck of single-element recycling and achieve a closed-loop utilization of spent battery resources across the entire chain.

[0004] Currently, recycling technologies for spent lithium-ion batteries are mainly divided into two categories: pyrometallurgy and hydrometallurgy. Pyrometallurgy involves high-temperature smelting to remove organic matter from the battery through pyrolysis, while simultaneously reducing valuable metals to alloy phases. This method has a relatively simple process flow, lower requirements for battery pretreatment, and can handle various battery types. However, its disadvantages are also significant: extremely high energy consumption (recycling 1 kg of cathode material requires up to 18.4 MJ) and generates a large amount of greenhouse gases; at high temperatures, lithium elements in lithium iron phosphate easily enter the slag phase, leading to low recovery rates and resource waste; furthermore, this method directly and completely destroys the material's crystal structure, yielding only basic metal elements or alloys, and cannot directly recover the high-value-added cathode material itself.

[0005] Hydrometallurgy is a method that uses chemical reagents such as acids and alkalis to leach waste electrode materials, transferring valuable metal ions into a solution, and then separating and purifying them through chemical steps such as extraction and precipitation. Compared to pyrometallurgy, hydrometallurgy has a higher recovery rate for elements such as lithium and relatively lower energy consumption. However, its process is lengthy and complex, requiring large amounts of strong acids and alkalis, and inevitably generating large amounts of wastewater and waste residue containing heavy metal ions and high salinity, posing a risk of secondary pollution. Furthermore, this method is costly; the cost of recovering 1 kg of lithium iron phosphate cathode material is approximately US$2.4.

[0006] For lithium iron phosphate batteries, the economic viability of the two traditional recycling pathways mentioned above faces a particularly severe challenge. Unlike ternary materials containing expensive cobalt and nickel, lithium iron phosphate cathode materials have relatively low elemental value. Using costly pyrometallurgical or hydrometallurgical processes to break them down into basic raw materials such as iron salts, phosphates, and lithium carbonate may result in a final product value that is unlikely to cover the costs of the complex recycling process, thus creating an "economically infeasible" dilemma. Therefore, academia and industry urgently need a more economically and environmentally efficient recycling method. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration, as well as the regenerated lithium iron phosphate (RLFP) cathode material and its applications.

[0008] The technical solution of the present invention is as follows:

[0009] First, the present invention provides a direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration, comprising the following steps:

[0010] Waste lithium iron phosphate powder, lignin, and lithium source are mixed, and a solvent is added to disperse the mixture to obtain a uniform solution.

[0011] Photothermal synergistic assisted repair of a homogeneous mixture yields a repaired lithium iron phosphate cathode material slurry.

[0012] The lithium iron phosphate cathode material slurry was separated and dried to obtain regenerated lithium iron phosphate cathode material;

[0013] The solvent is a liquid medium that can dissolve the lithium source but not the lignin, and the waste lithium iron phosphate powder is dispersed in the solvent in the form of solid particles.

[0014] This invention provides a direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration. Unlike traditional high-energy-consuming and high-polluting recycling processes (such as high-temperature solid-state sintering and high-temperature, high-pressure hydrothermal lithium replenishment), this method innovatively uses lignin from biomass waste as a participant in photo-responsive and electron transfer processes. While ensuring the integrity of the waste lithium iron phosphate cathode material framework, it achieves simultaneous lithium replenishment and Fe2+ regeneration through a gentle approach—based on a multiple mechanism of "photo-induced gentle reduction + uniform lithium replenishment in the solvent system + synergistic repair of defects / impure phases." 3+ Price regulation, Fe Li This method suppresses anti-site defects, removes impurity phases, and restores electrochemical performance. It eliminates the need for high temperatures and pressures and avoids the use of strong acids and bases, offering significant advantages such as low energy consumption, environmental friendliness, and ease of large-scale application. It provides a practical new approach for the direct regeneration of waste lithium iron phosphate cathode materials.

[0015] Preferably, the solvent is an alcohol solvent and / or water.

[0016] More preferably, the alcohol solvent is one or more of ethylene glycol, glycerol, or 1,2-propanediol.

[0017] Preferably, the lithium source is one or both of lithium hydroxide and lithium acetate.

[0018] Preferably, the mass ratio of waste lithium iron phosphate powder, lignin and lithium source is (10~30):(30~50):(1~5), and the amount of solvent used is the amount that forms a uniform mixture of waste lithium iron phosphate powder, lignin and lithium source.

[0019] More preferably, the mass ratio of waste lithium iron phosphate powder, lignin and lithium source is (15~26):(38~45):(2~4).

[0020] The preferred mass ratio of waste lithium iron phosphate powder, lignin and lithium source is 20:40:3.

[0021] Preferably, the preparation steps of waste lithium iron phosphate powder include: pre-treating waste lithium iron phosphate cathode sheets to obtain waste lithium iron phosphate powder.

[0022] More preferably, the pretreatment includes: discharging, removing the adhesive, and washing and drying.

[0023] Preferably, the dispersion process includes ultrasonic dispersion.

[0024] Preferably, the photothermal synergistic assisted repair includes: maintaining a temperature of 70~90℃ with continuous stirring, and reacting continuously for 6~8 hours under ultraviolet light irradiation.

[0025] Preferably, the separation and drying process includes: hot filtration of the lithium iron phosphate cathode material slurry to separate the solid product; washing to remove the solvent and soluble substances from the surface of the solid product; and drying.

[0026] More preferably, the drying process includes drying under vacuum conditions at a temperature of 55-65°C for 10-24 hours.

[0027] Second, the present invention provides a regenerated lithium iron phosphate cathode material prepared by the above-mentioned direct regeneration method.

[0028] Third, the present invention provides an application of the above-mentioned recycled lithium iron phosphate cathode material in lithium-ion batteries.

[0029] The beneficial effects of this invention are:

[0030] (1) Significantly improved uniformity and material performance. This invention, by employing a specific solvent system combined with a dispersion process, constructs a highly uniform and stable solid-liquid reaction interface in the early stage of repair, realizing uniform contact and mass transfer of lithium source, lignin and waste lithium iron phosphate powder at the microscale. This fundamentally solves the problems of low repair efficiency and incomplete material performance recovery caused by uneven local lithium replenishment in traditional direct regeneration processes, significantly improving the overall uniformity and process controllability of the repair process, and laying a key foundation for obtaining highly consistent and high-performance regenerated lithium iron phosphate cathode materials.

[0031] (2) Valence state regulation and defect repair are achieved under mild conditions, significantly reducing energy consumption and risk. This invention utilizes the reversible redox activity of lignin under light to construct a reduction environment capable of photoinduced charge / electron transfer. Fe is achieved in a mild system at low temperature, normal pressure, and without added reducing agents, in synergistic effect with a lithium source. 3+ To Fe 2+ The selective backtracking effectively suppresses the formation and accumulation of high-iron impurities such as FePO4; at the same time, it promotes the growth of Li + Uniform re-intercalation and lattice-order reconstruction significantly reduced lithium vacancies and Fe... Li The concentration of antisite defects restored the one-dimensional diffusion channels for lithium ions in the olivine structure. Compared with existing technologies that rely on high-temperature reducing atmospheres, strong reducing agents, or high-temperature and high-pressure hydrothermal conditions, this invention significantly reduces process energy consumption and operational risks, providing a new approach for the green and low-energy direct regeneration of waste lithium iron phosphate.

[0032] (3) Short process, fully enclosed process, and strong environmental friendliness. The present invention adopts a short process and fully enclosed process of "one-pot solvent phase photo-repair + solid-liquid separation". Lithium replenishment, valence state regulation, defect repair and structural reconstruction are completed in a single solvent phase. There is no need to introduce corrosive chemical reagents such as strong acids and strong alkalis for leaching and separation, which avoids excessive damage to the main structure of lithium iron phosphate olivine. Thus, while achieving efficient regeneration, it significantly reduces the generation of high salt and heavy metal waste liquid and the burden of subsequent treatment, and greatly improves the green environmental protection and overall sustainability of the process.

[0033] (4) The "waste-to-waste" synergistic remediation pathway boasts low overall cost and outstanding sustainability. Unlike existing regeneration strategies that rely on a single "lithium replenishment-annealing" process, this invention innovatively couples three key remediation steps—lithium replenishment, valence / impure phase regulation, and defect repair—within a single mild photochemical system. Lignin, a widely available and inexpensive waste biomass, is used as the key functional component to construct a closed-loop "waste-to-waste" remediation pathway. This pathway offers significant advantages in terms of low energy consumption, short process, and environmental friendliness, reducing process complexity and cost while enhancing the overall green sustainability of the regeneration process and products. Attached Figure Description

[0034] Figure 1 The images show the X-ray diffraction (XRD) patterns of waste lithium iron phosphate (SLFP) powder and the recycled lithium iron phosphate (RLFP) cathode material obtained in Example 1.

[0035] Figure 2 The image shows the refined XRD pattern of the regenerated lithium iron phosphate cathode material obtained in Example 1.

[0036] Figure 3 Fourier transform infrared (FT-IR) spectra of waste lithium iron phosphate powder and the recycled lithium iron phosphate cathode material obtained in Example 1.

[0037] Figure 4 This is a scanning electron microscope (SEM) image of waste lithium iron phosphate powder.

[0038] Figure 5 Here is a SEM image of the regenerated lithium iron phosphate cathode material obtained in Example 1;

[0039] Figure 6 The rate cycling diagram shows the ratio of waste lithium iron phosphate powder to the recycled lithium iron phosphate cathode material obtained in Example 1.

[0040] Figure 7A comparison chart of the long-cycle performance of waste lithium iron phosphate powder and the recycled lithium iron phosphate cathode material obtained in Example 1 at 1C rate;

[0041] Figure 8 The charge-discharge curves are for waste lithium iron phosphate powder and the recycled lithium iron phosphate cathode material obtained in Example 1.

[0042] Figure 9 The recycled lithium iron phosphate cathode material obtained in Example 1 [ Figure 9 (a) in the middle and waste lithium iron phosphate powder [ Figure 9 The AC impedance spectrum of (b) in [the text]. Detailed Implementation

[0043] The specific embodiments listed in this invention are merely examples, and the invention is not limited to the specific embodiments described below. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of this invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of this invention should be covered within its scope. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are commercially available conventional products. To better illustrate this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this invention can be practiced even without certain specific details. In other embodiments, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the main points of this invention.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Unless otherwise specified, all units used in this specification are International Standard Units (SI), and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors unavoidable in industrial production.

[0045] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0046] I. Examples and Comparative Examples

[0047] Example 1

[0048] This embodiment provides a direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration, including the following steps:

[0049] S1. Raw material pretreatment: Waste lithium iron phosphate cathode sheets were thoroughly discharged in 0.5 mol / L NaCl electrolyte, and then the cathode active material was stripped off; the obtained cathode active material was soaked in N-methylpyrrolidone (NMP) solution for 24 h to remove poly(vinylidene fluoride) [PVDF] binder; then it was repeatedly washed three times with ethanol and deionized water, and vacuum dried at 80℃ for 12 h to obtain dry waste lithium iron phosphate powder.

[0050] S2. Preparation of homogeneous mixture: 200 mg of waste lithium iron phosphate powder obtained from S1, 400 mg of lignin and 30 mg of lithium hydroxide were mixed, 30 mL of ethylene glycol was added as solvent, and the mixture was ultrasonically dispersed in an ultrasonic device for 30 min to obtain a homogeneous mixture.

[0051] S3. Photothermal Synergistic Assisted Repair: The homogeneous mixture obtained in S2 is placed in a reaction vessel, kept at 80°C and continuously stirred, and reacted continuously for 7 hours under ultraviolet light irradiation to obtain the repaired lithium iron phosphate cathode material slurry.

[0052] S4. Separation and Drying: The repaired lithium iron phosphate cathode material slurry obtained in S3 is filtered while hot to separate the solid product; then it is washed three times with deionized water and ethanol alternately to remove residual solvent and soluble matter; finally, the solid is dried under vacuum at 60°C for 24 hours to obtain the regenerated lithium iron phosphate cathode material.

[0053] Example 2

[0054] This embodiment provides a direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration, including the following steps:

[0055] S1. Raw material pretreatment: Same as in Example 1, to obtain dry waste lithium iron phosphate powder.

[0056] S2. Preparation of homogeneous mixture: 300 mg of waste lithium iron phosphate powder obtained from S1, 480 mg of lignin and 46 mg of lithium acetate were mixed, 40 mL of 1,2-propanediol was added as solvent, and the mixture was ultrasonically dispersed in an ultrasonic device for 30 min to obtain a homogeneous mixture.

[0057] S3. Photothermal Synergistic Assisted Repair: The homogeneous mixture obtained in S2 is placed in a reaction vessel, kept at 90°C and continuously stirred, and reacted continuously for 8 hours under ultraviolet light irradiation to obtain the repaired lithium iron phosphate cathode material slurry.

[0058] S4. Separation and drying: Same as in Example 1, omitted here, to obtain regenerated lithium iron phosphate cathode material.

[0059] Comparative Example 1

[0060] This comparative example is used to verify the role of "lignin photoinduced electron transfer / mild reduction" in Fe valence state recovery and defect repair. Except for the absence of lignin, the remaining steps are the same as in Example 1. The steps include:

[0061] S1. Raw material pretreatment: Same as in Example 1, to obtain dry waste lithium iron phosphate powder.

[0062] S2. Preparation of homogeneous mixture: 200 mg of waste lithium iron phosphate powder obtained from S1 and 30 mg of lithium hydroxide were mixed, 30 mL of ethylene glycol was added as a solvent, and the mixture was ultrasonically dispersed in an ultrasonic device for 30 min to obtain a homogeneous mixture.

[0063] S3. Photothermal Synergistic Assisted Repair: The homogeneous mixture obtained in S2 is placed in a reaction vessel, kept at 100℃ and continuously stirred, and reacted continuously for 8 hours under ultraviolet light irradiation to obtain the repaired lithium iron phosphate cathode material slurry.

[0064] S4. Separation and Drying: The repaired lithium iron phosphate cathode material slurry obtained in S3 was filtered while hot to separate the solid product; then it was washed three times with deionized water and ethanol alternately to remove residual solvent and soluble matter; finally, the solid was dried under vacuum at 60°C for 24 hours to obtain regenerated lithium iron phosphate cathode material-1.

[0065] Comparative Example 2

[0066] This comparative example is used to verify the role of "lighting" in stimulating lignin to participate in electron transfer, promoting Fe valence state reversion, and synergistic defect repair. Except for the absence of light exposure during the reaction, the remaining steps are consistent with Example 1, including the following steps:

[0067] S1. Raw material pretreatment: Same as in Example 1, to obtain dry waste lithium iron phosphate powder.

[0068] S2. Preparation of homogeneous mixture: Same as in Example 1, to obtain homogeneous mixture.

[0069] S3. Heat treatment: The homogeneous mixture obtained in S2 is placed in a reaction vessel, kept at 100℃ and continuously stirred for 8 hours to obtain the repaired lithium iron phosphate cathode material slurry.

[0070] S4. Separation and Drying: The repaired lithium iron phosphate cathode material slurry obtained in S3 was filtered while hot to separate the solid product; then it was washed three times with deionized water and ethanol alternately to remove residual solvent and soluble matter; finally, the solid was dried under vacuum at 60°C for 24 hours to obtain regenerated lithium iron phosphate cathode material-2.

[0071] Comparative Example 3

[0072] This comparative example is used to verify the role of "lithium source supplementation" in restoring the Li / Fe stoichiometry, promoting lithium-ion reintercalation, and reconstructing the crystal structure. Except for the absence of a lithium source, the remaining steps are the same as in Example 1. These include the following steps:

[0073] S1. Raw material pretreatment: Same as in Example 1, to obtain dry waste lithium iron phosphate powder.

[0074] S2. Preparation of homogeneous mixture: 200 mg of waste lithium iron phosphate powder obtained from S1 and 400 mg of lignin were mixed, 30 mL of ethylene glycol was added as a solvent, and the mixture was ultrasonically dispersed in an ultrasonic device for 30 min to obtain a homogeneous mixture.

[0075] S3. Photothermal Synergistic Assisted Repair: The homogeneous mixture obtained in S2 is placed in a reaction vessel, kept at 100℃ and continuously stirred, and reacted continuously for 8 hours under ultraviolet light irradiation to obtain the repaired lithium iron phosphate cathode material slurry.

[0076] S4. Separation and Drying: The repaired lithium iron phosphate cathode material slurry obtained in S3 was filtered while hot to separate the solid product; then it was washed three times with deionized water and ethanol alternately to remove residual solvent and soluble matter; finally, the solid was dried under vacuum at 60°C for 24 hours to obtain regenerated lithium iron phosphate cathode material-3.

[0077] II. Performance Testing and Characterization

[0078] Micromorphology

[0079] Figure 1 The images show the XRD patterns of waste lithium iron phosphate powder and the recycled lithium iron phosphate cathode material obtained in Example 1. Figure 2 The XRD pattern of the recycled lithium iron phosphate cathode material obtained in Example 1 shows that the ferric phase (such as FePO4) is only present in the XRD pattern of the waste lithium iron phosphate powder, but not in the recycled lithium iron phosphate cathode material. This indicates that the repair process effectively eliminated the ferric phase in the waste lithium iron phosphate powder, achieving structural repair. Further analysis using FT-IR... Figure 3 Analysis shows that in the recycled lithium iron phosphate cathode material obtained in Example 1, the cathode material located at 1250 cm⁻¹... -1 With 681cm -1 The peak of the high-speed rail phase disappears and is located at 969~974cm. -1 The nearby peaks show a blue shift, indicating that Fe Li The reduction of reaction defects.

[0080] Figure 4The SEM image of the waste lithium iron phosphate powder shows that the waste lithium iron phosphate particles still maintain a spherical secondary particle morphology, but their surface is significantly roughened, accompanied by local cracking, depressions, and debris adhesion. This indicates that the particle surface structure has deteriorated during the cycle failure process, and the particle integrity has decreased. In contrast, the recycled lithium iron phosphate cathode material obtained in Example 1 ( Figure 5 The particles exhibit more regular morphology, with a more complete ellipsoidal outline, enhanced surface continuity, and a significant reduction in obvious cracks and damaged areas. This indicates that the regeneration process effectively repairs the surface damage of waste lithium iron phosphate powder at the structural level, improves the integrity of the particle structure, and thus provides more stable interfacial conditions for subsequent lithium-ion transport, consistent with the recovery of the material's electrochemical performance.

[0081] Electrochemical performance

[0082] Table 1 shows the electrochemical test results of the recycled lithium iron phosphate cathode materials obtained in Example 1 and Comparative Examples 1-3.

[0083] Table 1. Electrochemical test results of the recycled lithium iron phosphate cathode materials obtained in Example 1 and Comparative Examples 1-3

[0084]

[0085] Table 1 shows that there is a synergistic effect among the addition of lignin, photothermal synergistic repair, and the addition of a lithium source in the remediation process of waste lithium iron phosphate cathode materials. Specifically, the electrochemical performance of the materials obtained in Comparative Example 1 (photothermal synergistic repair + lithium source), Comparative Example 2 (lignin + lithium source), and Comparative Example 3 (lignin + photothermal synergistic repair) is significantly lower than that in Example 1 (lignin + photothermal synergistic repair + lithium source). This result indicates that relying on any two of these conditions alone cannot achieve sufficient repair; only the synergistic effect of all three can significantly improve the electrochemical performance of the recycled materials, proving that the elements in this remediation system have irreplaceable complementarity and synergy.

[0086] Figure 6The rate cycling diagrams for waste lithium iron phosphate powder and the recycled lithium iron phosphate cathode material obtained in Example 1 show that the recycled lithium iron phosphate powder exhibits excellent electrochemical performance across a wide rate range of 0.1–10C, demonstrating good specific capacity maintenance and rate response capabilities, indicating superior electrode reaction kinetics. Particularly at 1C, the recycled lithium iron phosphate discharge specific capacity reaches 142.7 mAh / g, a significant increase of approximately 36.9% compared to untreated waste lithium iron phosphate (104.2 mAh / g). This capacity is not only significantly better than the original failed material but also reaches or even slightly exceeds the level of current mainstream commercial lithium iron phosphate cathode materials. More notably, at high rates (such as 5C and 10C), the recycled lithium iron phosphate still maintains good specific capacity output, indicating that it retains a fast electron transport channel and low lithium-ion diffusion resistance under high-rate charge-discharge conditions. This improvement mainly stems from the targeted repair of the "failure chain" of retired lithium iron phosphate, achieved by the present invention, where the lithium source provides Li... + On the one hand, lignin participates in charge / electron transfer processes under light illumination, synergistically promoting Fe valence state reversion and lattice reorganization, thereby restoring reversible lithium intercalation / deintercalation activity and reaction accessibility. Specific capacity is significantly enhanced, and long-term decay is slower.

[0087] Figure 7 This is a comparison chart of the long-term cycling performance of waste lithium iron phosphate powder and the regenerated lithium iron phosphate cathode material obtained in Example 1 at 1C rate. It can be seen that the regenerated lithium iron phosphate cathode material obtained in Example 1 retains a capacity of 81% after 500 charge-discharge cycles at 1C rate, while the waste lithium iron phosphate powder, under the same conditions, only retains 53.9% of its capacity. This indicates that the regeneration method proposed in this invention can effectively delay the performance degradation of materials during long-term cycling.

[0088] Specifically, waste lithium iron phosphate powder has many structural defects and high Fe content. 3+ An unstable electrode interface, due to its proportions, often leads to continuous loss of active lithium and exacerbated interfacial side reactions during long-term cycling, resulting in sustained structural / interface degradation and rapid capacity decay. This invention addresses this issue by repairing lattice vacancies through lithium replenishment and by promoting Fe production in a light-induced lignin system. 3+ By mitigating and suppressing the formation of inactive phases and the accumulation of defects, the method effectively slows down polarization growth and interfacial instability, thus maintaining a high reversible capacity even under long-term cycling. This fully demonstrates the significant advantages of the method in improving the durability and cycle life of recycled materials.

[0089] Initial coulombic efficiency (ICE) is a crucial parameter for measuring the reversible lithium insertion / extraction ratio during the first charge / discharge cycle of a lithium-ion battery, directly impacting the battery's energy utilization and initial capacity performance. For example... Figure 8 As shown, the initial coulombic efficiency of the regenerated lithium iron phosphate cathode material obtained in Example 1 reached 96.9%, significantly higher than that of untreated waste lithium iron phosphate powder, exhibiting a lower irreversible capacity loss. This improvement can be explained from the perspective of "structure-interface synergy": the lithium replenishment and defect repair of the present invention reduce lithium traps and blocking sites inside the material, reducing "incomplete lithium intercalation" caused by transport obstruction in the first pass; at the same time, the gentle repair process can alleviate the side reaction active sites caused by the surface inactive phase / defects, reducing the active lithium consumed by electrolyte decomposition and repeated generation of unstable solid electrolyte interphase (SEI) / cathode electrolyte interphase (CEI).

[0090] Figure 9 The AC impedance spectra of the recycled lithium iron phosphate cathode material and waste lithium iron phosphate powder obtained in Example 1 show that the recycled lithium iron phosphate cathode material obtained in Example 1 [ Figure 9 The impedance of (a) in [the sample] is significantly lower than that of waste lithium iron phosphate powder. Figure 9 [b] in Example 1 shows that the regenerated lithium iron phosphate cathode material obtained in Example 1 has faster interfacial charge transfer, lower lithium ion diffusion resistance, and better electrochemical reaction kinetics.

[0091] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A method for direct regeneration of waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration, characterized in that, Includes the following steps: Waste lithium iron phosphate powder, lignin, and lithium source are mixed, and a solvent is added to disperse the mixture to obtain a uniform solution. The homogeneous mixture was subjected to photothermal synergistic assisted repair to obtain a repaired lithium iron phosphate cathode material slurry. The lithium iron phosphate cathode material slurry is separated and dried to obtain regenerated lithium iron phosphate cathode material; The solvent is a liquid medium that can dissolve the lithium source but cannot dissolve the lignin, and the waste lithium iron phosphate powder is dispersed in the solvent in the form of solid particles; The photothermal synergistic assisted repair includes: maintaining a temperature of 70~90℃ with continuous stirring, and reacting continuously for 6~8 hours under ultraviolet light irradiation.

2. The direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration according to claim 1, characterized in that, The solvent is an alcohol solvent and / or water.

3. The direct regeneration method for waste lithium iron phosphate cathode materials based on lignin photo-assisted regeneration according to claim 2, characterized in that, The alcohol solvent is one or more of ethylene glycol, glycerol, or 1,2-propanediol.

4. The direct regeneration method for waste lithium iron phosphate cathode material based on lignin photo-assisted regeneration according to claim 1, characterized in that, The lithium source is one or both of lithium hydroxide and lithium acetate.

5. The direct regeneration method for waste lithium iron phosphate cathode material based on lignin photo-assisted regeneration according to claim 1, characterized in that, The mass ratio of the waste lithium iron phosphate powder, the lignin, and the lithium source is (10~30):(30~50):(1~5), and the amount of solvent used is the amount that forms a uniform mixture of the waste lithium iron phosphate powder, the lignin, and the lithium source.

6. The direct regeneration method for waste lithium iron phosphate cathode material based on lignin photo-assisted regeneration according to claim 5, characterized in that, The mass ratio of the waste lithium iron phosphate powder, the lignin and the lithium source is (15~26):(38~45):(2~4).

7. The direct regeneration method for waste lithium iron phosphate cathode material based on lignin photo-assisted regeneration according to claim 1, characterized in that, The separation and drying process includes: hot filtration of the lithium iron phosphate cathode material slurry to separate the solid product; washing to remove the solvent and soluble substances from the surface of the solid product, followed by drying; the drying process includes: drying under vacuum conditions at a temperature of 55~65℃ for 10~24h.

8. A regenerated lithium iron phosphate cathode material prepared by the direct regeneration method as described in any one of claims 1-7.

9. The application of the regenerated lithium iron phosphate cathode material as described in claim 8 in lithium-ion batteries.

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