A method for electronic state reconstruction and interface engineering regeneration of retired lithium iron phosphate based on pi-conjugated interface reconstruction mediator

Abstract

This invention relates to the field of regenerated resources of retired lithium-ion batteries, and discloses a method for electronic state reconstruction and interface engineering regeneration of retired lithium iron phosphate based on π-conjugated interface reconstruction dielectrics. The method involves mixing retired lithium iron phosphate cathode powder with a repair medium and conducting an in-situ interface engineering reaction under mild conditions. The repair medium includes a π-conjugated interface reconstruction dielectric capable of in-situ repair and a lithium salt. The reaction utilizes the delocalized π-electron system formed by the polymerization of the π-conjugated interface reconstruction dielectric to perform orbital hybridization with defect sites in the retired lithium iron phosphate, thereby eliminating localized polaron traps and reconstructing electron transport paths, while simultaneously filling lattice lithium vacancies. After the reaction, the mixture is subjected to solid-liquid separation, and the resulting solid is washed and dried to obtain regenerated lithium iron phosphate cathode material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery recycling and regeneration technology, specifically relating to a method for electronic state reconstruction and interface engineering regeneration of retired lithium iron phosphate based on π-conjugated interface reconstruction dielectric. Background Technology

[0002] With the rapid development of electric vehicles and energy storage systems, lithium iron phosphate (LFP) batteries have become one of the mainstream power batteries due to their high safety, long cycle life, and low cost. However, as a large number of batteries gradually enter their retirement period, how to achieve efficient and high-value recycling has become a key problem that the industry urgently needs to solve. Currently, the recycling of retired LFP batteries mainly follows two technical routes: hydrometallurgy and direct regeneration. Although hydrometallurgy can recover elements such as lithium and iron, its process is complex, energy-intensive, and environmentally polluting, and the added value of the products is low. In contrast, direct regeneration technology directly restores the performance of the cathode material through lithium replenishment and structural repair, and has the potential advantages of short process, low energy consumption, and good economic benefits, thus being regarded as a more promising recycling direction. To achieve truly efficient and high-level direct regeneration, it is essential to first thoroughly understand the failure mechanism of LFP in long-term cycling. Although the stable PO bond framework in its crystal lattice gives the material excellent cycle stability, and the lifespan of commercial products can typically reach more than 2000 cycles, the capacity will gradually decay with the extension of the usage time. When it drops to 70%–80% of the initial capacity, it is generally considered to have reached its service life. The capacity degradation of lithium iron phosphate (LFP) batteries is not caused by a single factor, but rather by the coupled effects of multiple mechanisms. Irreversible loss of active lithium is a core issue during battery cycling: the solid electrolyte interphase (SEI) film continuously forming on the negative electrode surface and the positive electrode-electrolyte (CEI) interphase film on the positive electrode surface constantly consume lithium salts, preventing some extracted lithium ions from returning to the crystal lattice and causing permanent loss of active lithium. Simultaneously, the thickening of the negative electrode interphase film exacerbates polarization and can even induce lithium dendrite growth, further aggravating lithium loss. As active lithium is continuously lost, a large number of lithium vacancies are generated in the crystal lattice. Under the combined effects of electrochemical cycling and thermal disturbance, some iron ions may migrate to these lithium vacancies, forming lithium iron antisite defects. Since the radius of iron ions is much larger than that of lithium ions, and lithium ions diffuse along one-dimensional channels in LFP, these defects severely hinder the lithium ion insertion / extraction kinetics and further induce the formation of more defects, driving the transformation of ferrous iron to ferric iron. This results in the formation of an electrochemically inert iron phosphate phase near the particle surface, thereby reducing the active region and increasing interfacial impedance. Furthermore, the accumulation of lattice stress caused by repeated lithium ion insertion / extraction during cycling can also lead to microcracks within the particles. Cracks not only isolate some active materials from the conductive network and cause them to become inactive, but also provide a new interface for electrolyte penetration and side reactions, accelerating the growth of the interfacial film and forming a vicious cycle of "active lithium loss - structural degradation" that exacerbates each other.

[0003] However, most current direct regeneration methods primarily focus on replenishing chemical components and restoring the macroscopic crystal structure, often neglecting the deeper damage caused by cycling within the material—namely, the degradation of electron transport properties. For example, patent CN118398760A uses a hydrothermal method at 80-120 °C for repair. Lithium iron phosphate has poor intrinsic conductivity, and its charge transport relies on the "small polaron hopping" mechanism. When the polymerization repair temperature is relatively high, the lithium vacancies and trivalent iron localized states formed by long-term cycling can induce strong local lattice distortion, forming deep-level "polaron traps," which severely restrict the coordinated transport of electrons and ions. Simply replenishing lithium cannot eliminate these defects at the electronic structure level, which is the fundamental reason why the performance recovery of traditional recycled materials is still unsatisfactory in practical applications such as high-rate and long-cycle applications. Therefore, developing a regeneration strategy that can not only repair the material composition and macroscopic structure but also rebuild its internal efficient electron transport channels has become a key breakthrough for achieving truly high-performance regeneration of retired lithium iron phosphate. Summary of the Invention

[0004] To address the insufficient recovery of electron transport performance in existing regeneration technologies for decommissioned lithium iron phosphate (LFP) batteries, this invention proposes a method for electronic state reconstruction and interface engineering regeneration of LFP batteries based on π-conjugated interface reconstruction of the dielectric. This method, utilizing mild low-temperature liquid-phase conditions, not only achieves lithium vacancy backfilling and crystal structure repair but also eliminates localized polaron traps and reconstructs efficient electron transport channels by constructing an organic-inorganic hybrid interface, thereby achieving a comprehensive recovery and enhancement of the material's electrochemical performance.

[0005] This invention is achieved through the following technical solution:

[0006] A method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction of dielectric conductors, characterized by the following steps:

[0007] Step S1: After disassembling, peeling and crushing the retired lithium iron phosphate cathode sheet, retired lithium iron phosphate powder is obtained.

[0008] Step S2, Pre-wetting and Adsorption: The retired lithium iron phosphate powder obtained in step S1 is uniformly dispersed in a pre-wetting solution containing a monomer with a π-conjugated interface reconstructed dielectric, and a suspension system is obtained by ultrasonication.

[0009] The solution is a mixed solvent of deionized water and low-carbon alcohol, with a monomer concentration of 0.01-0.1 mol / L; the π-conjugated interface reconstruction dielectric is an organic compound that can form a delocalized π-electron conjugated system through in-situ oxidative polymerization under mild conditions.

[0010] Step S3, Interface Coupling and Initiation of Polymerization: A lithium salt solution is added to the suspension system in step S2 to obtain a mixed system. The lithium salt is selected from lithium compounds that can highly dissociate in the mixed solvent and release active lithium. The molar ratio of the lithium salt to the monomer of the π-conjugated interface reconstructing dielectric is (0.8-1.5):1. The mixed system is then polymerized in a reactor at a polymerization temperature of 30-75 °C.

[0011] Step S4, Dynamic Repair and Functional Layer Growth: The polymerization temperature is maintained for 2-10 hours to carry out the in-situ interface repair reaction. This process is accompanied by the continuous growth and cross-linking of polymer chains, ultimately forming a continuous, dense, and chemically bonded conjugated polymer functional coating layer with a thickness of 2-20 nm on the surface of the decommissioned lithium iron phosphate particles. Simultaneously, free lithium ions in the mixed solution spontaneously fill lattice vacancies under charge balance and concentration gradient, achieving repair.

[0012] Step S5, ripening and structural relaxation: After the reaction is complete, stop heating, keep stirring, and allow the reaction system to slowly cool to room temperature over 30-60 minutes to allow the newly formed interface structure to fully relax and stabilize.

[0013] Step S6, separation and post-processing of functionalized materials: The reaction mixture obtained in step S5 is centrifuged, washed, and freeze-dried under vacuum to obtain regenerated lithium iron phosphate cathode material.

[0014] Preferably, the ultrasonic temperature in step S2 is 10-30 ℃, the ultrasonic power is 100-300 W, and the ultrasonic time is 10-30 minutes, so that the monomer molecules can fully penetrate and physically adsorb onto the surface cracks, pores and defects of the powder particles.

[0015] And / or, the lower alcohol is one or more of ethanol, isopropanol or methanol.

[0016] Preferably, in step S3, initiating polymerization of the mixture in the reactor specifically involves transferring the mixture to a reactor with precise temperature control and stirring functions, stirring at a rate of 100-600 rpm under an inert or air atmosphere, and then programming the temperature to 30-75 ℃ at a rate of 0.5-2 ℃ / min.

[0017] Preferably, the temperature program is as follows: first, the temperature is increased to 40-50℃ at 1℃ / min and held at that temperature for 1-2 hours to complete polymerization initiation and initial coating; then, the temperature is increased to the target temperature at 0.5℃ / min to complete deep repair and functional layer densification.

[0018] Preferably, in step S4, the monomers adsorbed at the defect sites undergo in-situ polymerization, while lithium ions diffuse back into the lattice vacancies under the influence of electrostatics and concentration gradient. The polymer chains grown by polymerization undergo strong pd orbital hybridization between their delocalized π-electron system and the localized polaron traps on the material surface. Electrons are injected from the highest occupied molecular orbitals of the polymer into the defect state, eliminating the trap energy level and converting the bound electrons into the extended state.

[0019] Preferably, step S6 specifically involves: centrifuging the reaction mixture obtained in step S5 at a speed of 3000-8000 rpm for 5-15 minutes; washing the resulting solid precipitate with deionized water, ethanol, and acetone alternately using ultrasonic washing for 2-4 times each to thoroughly remove unreacted monomers, salts, and oligomers; placing the washed wet material in a vacuum freeze dryer, pre-freezing it at -40 to -20 ℃ for 2-4 hours, and then sublimating it under a vacuum of ≤10 Pa for 12-24 hours to obtain regenerated lithium iron phosphate cathode material.

[0020] Preferably, the freeze-drying process is as follows: maintain at -30°C for 3 hours, then increase the temperature to 0°C at 0.5°C / min and maintain for 5 hours, and finally increase the temperature to 25°C at 1°C / min and maintain until the end.

[0021] Preferably, the π-conjugated interface reconstruction dielectric is one or more of N-methylpyrrole, 3,4-ethylenedioxythiophene, aniline, o-phenylenediamine and its derivatives.

[0022] A regenerated lithium iron phosphate cathode material is prepared by the above method. Its particle surface has a continuous, dense and thickness-controllable functional coating layer composed of chemically bonded conjugated polymers rich in delocalized π electrons. The lithium vacancies inside the material are effectively filled and the local polaron traps are eliminated.

[0023] A lithium-ion battery comprising the above-mentioned recycled lithium iron phosphate cathode material.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The regeneration method of this invention achieves a paradigm shift from "composition-structure repair" to "functional-electronic state repair". Unlike existing technologies that only focus on lithium replenishment and crystallographic recovery, this invention introduces delocalized π-electron donors through low-temperature polymerization repair to perform in-situ interface engineering, directly intervening in the electronic structural root causes of material failure. The conjugated polymer layer formed by polymerization has a delocalized π-electron cloud that can undergo strong orbital hybridization with the localized states at the surface and near-surface defects of the decommissioned material, thereby neutralizing highly active defect sites at the electronic state level from the very beginning of the repair process. This process simultaneously completes interface cleaning, electronic compensation, and structural pre-stabilization in a single, mild system, laying an atomic-scale foundation for subsequent deep functional recovery.

[0026] (2) This invention can target and eliminate the core bottleneck restricting charge transport—the "polaron trap"—through low-temperature polymerization repair, fundamentally rebuilding efficient electron transport channels. Long-term cycling of lithium vacancies within the material can stably form localized polaron traps, severely hindering the intrinsic conductivity mechanism based on "small polaron jumps." In this invention, the delocalized π orbitals of the conjugated polymer selectively hybridize with the localized states of the polaron traps, releasing charge carriers bound by the lattice distortion field and converting them into electrons that can rapidly migrate in the extended π system. This electronic state reconstruction process directly opens up the charge transport micropaths blocked by defects, significantly reducing the charge transfer impedance and activation energy of the material, achieving "functional repair" of its intrinsic conductivity—something that traditional high-temperature solid-state lithium replenishment methods cannot achieve.

[0027] (3) This invention achieves synergistic regeneration and enhancement of both atomic-scale electronic structure and macroscopic electrode performance through low-temperature polymerization repair. Through precise interface orbital engineering, the regenerated material not only restores the complete olivine crystal structure and uniform iron valence state, but also constructs an organic-inorganic strong coupling interface on the particle surface that combines physical protection and ultrafast electronic conduction. This interface layer effectively compensates for the intrinsic low conductivity of lithium iron phosphate, promoting uniform lithium ion insertion / extraction and the reversibility of the two-phase transition. At the same time, this stable interface can significantly suppress the continuous decomposition and side reactions of the electrolyte, fundamentally improving the application performance and durability of the material under high-rate, long-cycle, and harsh high and low temperature conditions.

[0028] (4) The process of this invention combines precise repair capability with good engineering adaptability. The method uses liquid phase and low temperature reaction conditions, avoiding problems such as high energy consumption, grain coarsening, and lithium volatilization caused by high-temperature sintering. By flexibly controlling the type and concentration of delocalized π electron donors and parameters such as reaction temperature and time, this method can be applied to retired lithium iron phosphate materials with different degrees of decay and different sources, showing excellent batch stability and potential for large-scale application. The regenerated lithium iron phosphate cathode material has a complete structure and pure interface, and its electrochemical performance is fully restored or even surpasses that of the original material. For example, the discharge specific capacity can reach 166 mAh·g at a 0.2 C rate. -1 The above results show that the capacity retention rate exceeds 85% after 500 cycles at a high rate of 5C, and the cycle stability and low-temperature performance are significantly better than traditional recycled materials, providing a reliable technical solution for the high-value and high-performance direct regeneration of retired lithium iron phosphate batteries. Attached Figure Description

[0029] Figure 1 The calculation results of Fe 3d orbital density of states (DOS) of Example 1 and retired lithium iron phosphate cathode materials are compared to reveal the differences in the degree of electronic state reconstruction.

[0030] Figure 2 The XRD spectra of the regenerated lithium iron phosphate cathode materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are compared to demonstrate the influence of different regeneration methods on the crystal structure recovery effect.

[0031] Figure 3 The transmission electron microscope (TEM) and high-resolution images of the recycled lithium iron phosphate cathode materials of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are compared to show the differences in the interface microstructure.

[0032] Figure 4 The comparison of Fe 2p X-ray photoelectron spectroscopy (XPS) spectra of the recycled lithium iron phosphate cathode materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 reflects the differences in the iron valence state on the surface.

[0033] Figure 5 This is a comparison of the performance of the recycled lithium iron phosphate cathode materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 under different charge and discharge rates.

[0034] Figure 6 This is a comparison of the long-cycle performance of recycled lithium iron phosphate cathode materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 at a 5 C rate. Detailed Implementation

[0035] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0036] These and other aspects of the embodiments of the present invention will become clear from the following description and accompanying drawings. In these descriptions and drawings, some specific embodiments of the present invention are specifically disclosed to illustrate some ways of implementing the principles of the embodiments of the present invention; however, it should be understood that the scope of the embodiments of the present invention is not limited thereto.

[0037] The cathode powder from retired lithium-ion batteries used comes from a new energy company in Hunan Province, and its main component is retired lithium iron phosphate.

[0038] Example 1

[0039] A method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction of the dielectric conductor includes the following steps:

[0040] S1. Refined Pretreatment of Retired Materials: Retired lithium iron phosphate cathode sheets were manually disassembled and immersed in dimethyl carbonate to remove the electrolyte. The aluminum foil was then peeled off to obtain the cathode material coating. The coating material was first coarsely crushed using a jaw crusher, and then pulverized to a D50 of approximately 5 μm using an air jet mill. The resulting powder was placed in a tube furnace under nitrogen protection, heated to 250°C at a rate of 3 °C / min, held at that temperature for 2 hours, and then allowed to cool naturally to obtain pretreated retired lithium iron phosphate powder.

[0041] S2. Pre-wetting and adsorption: Weigh 1.00 g of the above pretreated powder and disperse it in 50 ml of a solvent consisting of deionized water and ethanol in a 1:1 volume ratio. Add pyrrole monomer to make the monomer concentration in the system 0.05 mol / L. Treat under ultrasonic conditions of 25 ℃ and 200 W for 20 minutes.

[0042] S3. Interfacial Coupling and Initiation of Polymerization: The above suspension was transferred to a reactor equipped with a stirrer, condenser, and nitrogen inlet. A 0.25 mol / L lithium chloride aqueous solution was prepared. Under stirring (300 rpm) and a nitrogen atmosphere, the lithium chloride solution (calculated based on a pyrrole:LiCl molar ratio of 0.85:1) was added dropwise to the system. The reaction system was heated to 45 °C at a rate of 1 °C / min and stirred at a constant temperature for 1.5 hours. Subsequently, the temperature was further increased to 65 °C at a rate of 0.5 °C / min.

[0043] S4. Dynamic repair and functional layer growth: Maintain the reaction by reacting at this temperature for 4 hours.

[0044] S5. Curing and structural relaxation: After the reaction is complete, stop heating, maintain stirring and nitrogen atmosphere, and allow the reaction system to cool naturally to room temperature within 1 hour.

[0045] S6. Separation and post-processing of functionalized materials: Pour the reaction mixture into centrifuge tubes and centrifuge at 5000 rpm for 10 minutes, discarding the supernatant. Wash the solid precipitate sequentially with deionized water, anhydrous ethanol, and acetone, each ultrasonically for 10 minutes. Transfer the washed wet material to a freeze dryer tray and maintain at -30 °C for 3 hours. Then, increase the temperature to 0 °C at 0.5 °C / min and maintain for 5 hours. Finally, increase the temperature to 25 °C at 1 °C / min and maintain until the end of the process. The final regenerated lithium iron phosphate cathode material is obtained.

[0046] Example 2

[0047] The only difference between this embodiment and Example 1 is that the polymerization temperature is replaced with 30 °C.

[0048] Example 3

[0049] The only difference between this embodiment and Example 1 is that the polymerization temperature is replaced with 75 °C.

[0050] Example 4

[0051] The only difference between this embodiment and Example 1 is that the monomer is replaced with 3,4-ethylenedioxythiophene monomer.

[0052] Example 5

[0053] The only difference between this embodiment and Example 1 is that the monomer is replaced with aniline monomer.

[0054] Example 6

[0055] The only difference between this embodiment and Example 1 is that the monomer is replaced with o-phenylenediamine monomer.

[0056] Comparative Example 1

[0057] A method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction of the dielectric conductor includes the following steps:

[0058] S1. Weigh 1.00 g of decommissioned lithium iron phosphate cathode powder from the same source as in Example 1. To restore it to the standard stoichiometric ratio of lithium iron phosphate, a sufficient amount of lithium carbonate is weighed out as a lithium source according to stoichiometric calculations. Simultaneously, to promote diffusion and reaction during sintering, an additional 5 wt.% of glucose is added as a carbon source. The cathode powder, lithium carbonate, and glucose are manually ground and mixed in an agate mortar for 40 minutes until uniformly mixed.

[0059] S2. Place the uniformly mixed powder in an alumina crucible and perform heat treatment under an argon atmosphere. First, heat to 350 °C at 5 °C / min and hold for 2 hours to decompose glucose and form a reducing atmosphere. Then, continue heating to 650 °C at 5 °C / min and hold for 10 hours to drive the lithium source to diffuse into the bulk phase of the decommissioned material and achieve structural reconstruction.

[0060] S3. After heat treatment, allow the material to cool naturally to room temperature under a protective atmosphere. Gently grind the resulting sintered product to obtain lithium iron phosphate cathode material regenerated by the traditional solid-phase lithium replenishment method.

[0061] Comparative Example 2

[0062] The only difference between this comparative example and Example 1 is that the pyrrole monomer is replaced with glucose;

[0063] Comparative Example 3

[0064] The only difference between this comparative example and Example 1 is that the polymerization temperature was replaced with 80°C.

[0065] Figure 1 The image shows a comparison of the Fe 3d density of states (DOS) spectra of the materials before and after the repair treatment in Example 1. Before treatment, a sharp local DOS peak appeared near the Fermi level in the decommissioned lithium iron phosphate, corresponding to small polarons locked in shallow-level traps within the material. However, this characteristic peak disappeared in the DOS spectrum of the regenerated lithium iron phosphate, confirming the electron injection effect of polypyrrole, which effectively reduced the localized trivalent iron at the small polarons to divalent iron, reversing the increase in surface oxidation state caused by cycling. Similar phenomena were observed in Examples 2, 3, 4, 5, and 6, where the sharp local DOS peak near the Fermi level of the decommissioned lithium iron phosphate disappeared in the Fe 3d DOS spectrum.

[0066] Figure 2 XRD spectra of the regenerated lithium iron phosphate cathode materials of Examples 1, 1, 2, and 3 were compared. In Comparative Example 2, due to the use of glucose to replace pyrrole monomer, iron phosphate impurity phase peaks were present at 18.12°, 23.78°, and 30.9°, proving that non-conjugated carbon sources could not achieve crystal structure repair. In Comparative Example 3, due to the polymerization temperature rising to 80°C, the impurity phase peaks were partially weakened but still remained, indicating that excessive self-polymerization led to incomplete lithium vacancy backfilling. In Comparative Example 1, the impurity phase disappeared after high-temperature solid-phase lithium replenishment, but the diffraction peaks broadened significantly. In Example 1, the impurity phase was completely eliminated and the (311) crystal plane diffraction peak had the narrowest half-width, indicating the best crystal integrity. This proved that the iron phosphate phase could be completely eliminated after repair. The diffraction peaks in the regenerated lithium iron phosphate sample matched well with the lithium iron phosphate standard card, and no impurity peaks were found, proving that no additional impurities were introduced during the regeneration process, ensuring the purity of the regenerated sample.

[0067] Figure 3 The images show a comparison of transmission electron microscopy (TEM) images of the regenerated lithium iron phosphate cathode materials from Examples 1, 1, 2, and 3. Comparative Example 2 exhibits an amorphous carbon deposition layer of uneven thickness and disordered structure, with no chemical bonding to the substrate and blurred lattice fringes. Comparative Example 3 shows a loose, porous, and unevenly thick polypyrrole coating layer, confirming the presence of an over-crosslinked structure. Comparative Example 1 shows localized carbon accumulation and lattice distortion regions on its surface, with poor coating layer continuity. Example 1 presents a uniform, continuous, dense, and chemically bonded polypyrrole coating layer with clear and complete lattice fringes underneath, indicating optimal interface coupling. This demonstrates that the crystallinity of the lithium iron phosphate crystals was restored after repair, and in-situ polypyrrole coating was successfully achieved.

[0068] Figure 4 The following is a comparison of the Fe 2p XPS spectra of the regenerated lithium iron phosphate cathode materials from Examples 1, 1, 2, and 3. In Comparative Example 2, due to the use of glucose instead of pyrrole monomer, the Fe 2p peak exhibits a characteristic of ferric iron, demonstrating that non-conjugated carbon sources cannot achieve surface electronic state repair. Although Comparative Example 3 suffered from excessive interface reconstruction due to improper polymerization temperature, the ferric iron component on the surface was completely eliminated. After high-temperature reduction, Comparative Example 1 showed a surface dominated by ferrous iron with a slight ferric iron shoulder peak. The Fe 2p peak in Example 1 exhibited a single ferrous iron characteristic peak with the narrowest half-width at half-maximum (HWHM), indicating that the delocalized π electrons of polypyrrole effectively injected into surface defect states, reducing ferric iron to ferrous iron and achieving homogenization repair of the surface electronic structure.

[0069] Figure 5 This section compares the performance of recycled lithium iron phosphate cathode materials from Examples 1, 1, 2, and 3 at different charge / discharge rates. Comparative Example 2 shows a discharge specific capacity of 92.9 mAh·g at a 5C rate. -1 This demonstrates that glucose cannot construct an effective electron transport channel; in Comparative Example 3, the loose coating layer formed by excessive self-aggregation increases interfacial impedance, resulting in only 113.7 mAh·g⁻¹ release at 5 C. -1 Furthermore, the polarization voltage increased significantly; Comparative Example 1 had a capacity of 118.4 mAh·g at 5 C. -1 The rate performance is improved compared to retired materials, but it is limited by the intrinsic low conductivity; the discharge specific capacities of Example 1 at 0.1 C / 0.2 C / 1 C / 2 C / 5 C are 162.1 / 161.2 / 158.7 / 152.6 / 137.4 mAh·g, respectively. -1 The rate performance is significantly better than that of the comparative examples. This indicates that the delocalized electron channels constructed from polypyrrole significantly improve the charge transport dynamics of the material, making it suitable for high-power applications.

[0070] Figure 6This section compares the long-cycle performance of recycled lithium iron phosphate cathode materials from Examples 1, 1, 2, and 3 at a 5C rate. Comparative Example 2 had an initial capacity of 102.3 mAh·g. -1 After 200 cycles, the concentration rapidly decreased to 30 mAh·g. -1 The following showed no repair effect; Comparative Example 3 had an initial capacity of 105 mAh·g. -1 However, due to severe pyrrole self-polymerization, the actual proportion of active material was low, resulting in a lower capacity than in Example 1; Comparative Example 1 had an initial capacity of 109.8 mAh·g. -1 It maintained 84.9 mAh·g after 500 laps. -1 The retention rate was 76.3%, and the cycle stability was moderate; the initial discharge capacity of Example 1 was 138.2 mAh·g. -1 After 500 cycles, it maintains 122 mAh·g -1 The material retained 88.4% of its structure, exhibiting optimal performance over high-rate, long-cycle conditions. This demonstrates that the interface engineering regeneration strategy of this invention effectively restored the structural integrity of the material and suppressed cycle decay.

[0071] In summary, the regeneration method proposed in this invention, based on π-conjugated interface reconstruction of the dielectric in-situ interface engineering, simultaneously achieves compositional compensation, structural repair, and electron transport function reconstruction of retired lithium iron phosphate materials by constructing a strongly coupled organic-inorganic interface under low-temperature liquid phase conditions. This method not only effectively removes surface impurities and fills lithium vacancies, but also fundamentally eliminates "polaron traps" through orbital hybridization of the delocalized π-electron system with the localized trivalent iron state, thus overcoming the microscopic bottleneck of charge transport. The pre-constructed conductive polymer coating layer simultaneously serves as a physical barrier and an ultrafast electron channel, significantly improving the material's interface stability, lithium-ion diffusion kinetics, and electronic conductivity. This invention features mild process conditions, a simple flow, and strong adaptability. The resulting regenerated material achieves synergistic improvements in capacity, rate performance, and long-cycle stability, providing a groundbreaking technical path for the high-performance, high-value regeneration of retired lithium iron phosphate batteries that combines scientific merit, economic viability, and industrial feasibility.

Claims

1. A method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction of the dielectric conductor, characterized in that, Specifically, the steps include the following: Step S1: After disassembling, peeling and crushing the retired lithium iron phosphate cathode sheet, retired lithium iron phosphate powder is obtained. Step S2, Pre-wetting and Adsorption: The retired lithium iron phosphate powder obtained in step S1 is uniformly dispersed in a pre-wetting solution containing a monomer with a π-conjugated interface reconstructed dielectric, and a suspension system is obtained by ultrasonication. The solution is a mixed solvent of deionized water and low-carbon alcohol, with a monomer concentration of 0.01-0.1 mol / L; the π-conjugated interface reconstruction dielectric is an organic compound that can form a delocalized π-electron conjugated system through in-situ oxidative polymerization under mild conditions. Step S3, Interface Coupling and Initiation of Polymerization: A lithium salt solution is added to the suspension system in step S2 to obtain a mixed system. The lithium salt is selected from lithium compounds that can highly dissociate in the mixed solvent and release active lithium. The molar ratio of the lithium salt to the monomer of the π-conjugated interface reconstructing dielectric is (0.8-1.5):

1. The mixed system is then polymerized in a reactor at a polymerization temperature of 30-75 °C. Step S4, Dynamic Repair and Functional Layer Growth: The polymerization temperature is maintained for 2-10 hours to carry out the in-situ interface repair reaction. This process is accompanied by the continuous growth and cross-linking of polymer chains, ultimately forming a continuous, dense, and chemically bonded conjugated polymer functional coating layer with a thickness of 2-20 nm on the surface of the decommissioned lithium iron phosphate particles. Simultaneously, free lithium ions in the mixed solution spontaneously fill lattice vacancies under charge balance and concentration gradient, achieving repair. Step S5, ripening and structural relaxation: After the reaction is complete, stop heating, keep stirring, and allow the reaction system to slowly cool to room temperature over 30-60 minutes to allow the newly formed interface structure to fully relax and stabilize. Step S6, separation and post-processing of functionalized materials: The reaction mixture obtained in step S5 is centrifuged, washed, and freeze-dried under vacuum to obtain regenerated lithium iron phosphate cathode material.

2. The method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction of the dielectric as described in claim 1, characterized in that, In step S2, the ultrasonic temperature is 10-30 ℃, the ultrasonic power is 100-300 W, and the ultrasonic time is 10-30 minutes, so that the monomer molecules can fully penetrate and physically adsorb onto the surface cracks, pores and defects of the powder particles. And / or, the lower alcohol is one or more of ethanol, isopropanol or methanol.

3. A method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction dielectric as described in claim 1 or 2, characterized in that, In step S3, initiating polymerization of the mixture in the reactor specifically involves transferring the mixture to a reactor with precise temperature control and stirring functions, stirring at a rate of 100-600 rpm under an inert or air atmosphere, and then programming the temperature to 30-75 ℃ at a rate of 0.5-2 ℃ / min.

4. The method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction dielectric as described in claim 3, characterized in that, The specific temperature rise procedure is as follows: first, the temperature is raised to 40-50℃ at a rate of 1℃ / min and held at that temperature for 1-2 hours to complete polymerization initiation and initial coating; then, the temperature is raised to the target temperature at a rate of 0.5℃ / min to complete deep repair and densification of the functional layer.

5. The method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction dielectric as described in claim 1, characterized in that, In step S4, the monomers adsorbed at the defect sites undergo in-situ polymerization, while lithium ions diffuse back into the lattice vacancies under the influence of electrostatics and concentration gradient. The polymer chains grown by polymerization undergo strong pd orbital hybridization between their delocalized π-electron system and the localized polaron traps on the material surface. Electrons are injected from the highest occupied molecular orbitals of the polymer into the defect state, eliminating the trap energy level and converting the bound electrons into the extended state.

6. The method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction dielectric as described in claim 1, characterized in that, Step S6 specifically involves: centrifuging the reaction mixture obtained in step S5 at a speed of 3000-8000 rpm for 5-15 minutes; washing the resulting solid precipitate with deionized water, ethanol, and acetone alternately using ultrasonic washing for 2-4 times each to thoroughly remove unreacted monomers, salts, and oligomers; placing the washed wet material in a vacuum freeze dryer, pre-freezing it at -40 to -20 ℃ for 2-4 hours, and then sublimating it under a vacuum of ≤10 Pa for 12-24 hours to obtain regenerated lithium iron phosphate cathode material.

7. The method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction dielectric as described in claim 6, characterized in that, The freeze-drying process is as follows: hold at -30℃ for 3 hours, then increase the temperature to 0℃ at 0.5℃ / min and hold for 5 hours, and finally increase the temperature to 25℃ at 1℃ / min and hold until the end.

8. The method for electronic state reconstruction and interface engineering regeneration of decommissioned lithium iron phosphate based on π-conjugated interface reconstruction of the dielectric as described in claim 1, characterized in that, The π-conjugated interface reconstruction dielectric is one or more of N-methylpyrrole, 3,4-ethylenedioxythiophene, aniline, o-phenylenediamine and their derivatives.

9. A recycled lithium iron phosphate cathode material, characterized in that, The particles prepared by the method described in any one of claims 1-8 have a continuous, dense and thickness-controllable functional coating layer on their surface composed of a chemically bonded, conjugated polymer rich in delocalized π electrons, and the lithium vacancies inside the material are effectively filled and the local polaron traps are eliminated.

10. A lithium-ion battery, characterized in that, It includes the recycled lithium iron phosphate cathode material as described in claim 9.

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