Lithium supplement agent for regeneration of positive electrode material of waste lithium iron phosphate battery
By using 2,5-thiophene dimethyl diborate tetralithium salt as a lithium replenishing agent, combined with dissolution-evaporation-gelling and low-temperature and high-temperature heat treatment steps, the structural defects of waste lithium iron phosphate batteries were successfully repaired, the battery performance was improved, the problem of poor performance of recycled materials in the existing technology was solved, and an efficient and environmentally friendly recycling process was realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-09
- Publication Date
- 2026-03-17
AI Technical Summary
Existing recycling technologies for spent lithium iron phosphate batteries are unable to effectively repair structural defects in the materials, resulting in poor capacity recovery and long-cycle stability of the recycled materials. Furthermore, traditional methods pose risks of high energy consumption and secondary pollution.
Using 2,5-thiophene dimethyl diborate tetralithium salt (C4Li4B2O4S) as a lithium replenishing agent, lithium replenishment, structural repair and performance improvement are completed simultaneously through a one-step regeneration process, including dissolution-drying-paste preparation, ball milling coating and low-temperature pre-activation and high-temperature reconstruction steps, to form a highly conductive residual carbon layer and uniform lithium release.
It achieves efficient regeneration of spent lithium iron phosphate batteries, significantly improves electrochemical performance, and has the potential for industrialization due to its simple process and environmental friendliness.
Smart Images
Figure CN121688198A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery material recycling and reuse technology, specifically a method for efficiently repairing and regenerating waste lithium iron phosphate (LiFePO4) cathode materials using novel organic lithium salts, thereby achieving synergistic improvement of the electrochemical performance of waste LiFePO4 materials through lithium compensation, crystal structure repair, and element doping. Background Technology
[0002] With the explosive growth of the global new energy vehicle industry and the rapid expansion of the large-scale electrochemical energy storage market, the demand for lithium-ion batteries is increasing daily. Lithium iron phosphate (LiFePO4) batteries, due to their superior safety, long cycle life, and cost advantages, have become one of the mainstream technologies for power and energy storage batteries. However, LiFePO4 batteries typically have a lifespan of 5-8 years, meaning that a massive wave of retired batteries is expected in the foreseeable future. How to environmentally friendly and cost-effectively dispose of these used batteries has become a major challenge related to sustainable resource utilization and environmental protection.
[0003] From a resource perspective, waste LiFePO4 cathode materials still contain valuable elements such as lithium, iron, and phosphorus. Direct disposal or low-value treatment not only causes serious environmental pollution but also represents a huge waste of scarce strategic resources, especially lithium. Therefore, recycling waste LiFePO4 materials to achieve a closed loop "from waste to resource" is of paramount strategic importance for ensuring the security of my country's lithium resource supply chain and promoting the development of a circular economy.
[0004] Currently, the recycling and regeneration methods for waste LiFePO4 materials are mainly divided into three categories: pyrometallurgical recycling, hydrometallurgical recycling, and direct regeneration. Pyrometallurgical recycling is complex, energy-intensive, and prone to lithium volatilization at high temperatures, potentially generating harmful waste gases, making it neither economically nor environmentally sound. Hydrometallurgical recycling typically uses strong acids to leach valuable metal elements from the cathode material, followed by chemical precipitation and other methods to resynthesize the material. This process is lengthy, generates large amounts of wastewater and waste residue, poses a risk of secondary pollution, and completely destroys the olivine crystal structure of LiFePO4 during the process, failing to fully utilize its original material framework.
[0005] Direct regeneration is an emerging technology. Its core concept is to restore the electrochemical performance of materials by replenishing lost lithium and repairing structural defects. However, existing direct regeneration technologies also have significant drawbacks. After long-term cycling, waste LiFePO4 materials not only suffer lithium loss, but their crystal structure also deteriorates due to the loss of lithium. +Irreversible damage occurs due to lattice stress from extraction / intercalation, Fe-Li antisite defects, and trace Fe dissolution. Traditional lithium replenishers can only replenish lithium and cannot effectively repair these deep structural defects, resulting in poor capacity recovery and long-cycle stability of recycled materials. Therefore, traditional direct regeneration processes still require the addition of other materials to improve the performance of recycled materials, making this method uneconomical. Thus, there is an urgent need in the field to develop a novel, multifunctional regeneration process that can simultaneously repair structural defects in materials and potentially further improve their performance, thereby overcoming the performance bottleneck of existing direct regeneration technologies. Summary of the Invention
[0006] To address the problems mentioned in the background section, this invention provides a novel organic lithium salt, 2,5-thiophenediylbisborate tetralithium salt (C4Li4B2O4S), as a core remediation agent for the direct regeneration of waste lithium iron phosphate cathode materials. The 2,5-thiophenediylbisborate tetralithium salt (C4Li4B2O4S) molecule integrates three functions: lithium source, structural repair, and performance enhancement through doping.
[0007] Through this "one-step, multi-effect" design, the "lithium replenishment," "structural repair," and "performance enhancement" of waste LiFePO4 materials were successfully completed simultaneously in a one-step regeneration process, ultimately yielding regenerated LiFePO4 cathode materials with excellent electrochemical performance. This method is simple, environmentally friendly, and energy-efficient, opening up a new technological path for the high-value-added resource utilization of waste lithium iron phosphate batteries.
[0008] To achieve the above objectives, the present invention provides the following technical solution:
[0009] This invention provides a lithium replenishing agent for the regeneration of cathode materials from waste lithium iron phosphate batteries. The lithium replenishing agent is a tetralithium salt of 2,5-thiophene dimethyl diborate with the chemical formula C4Li4B2O4S.
[0010] This invention also provides an application of the 2,5-thiophene dimethyl diboronate tetralithium salt described above in the lithium replenishment and repair of waste lithium iron phosphate cathode materials. Through lithium replenishment, structural repair, and elemental doping, waste lithium iron phosphate cathode materials are effectively regenerated, and their electrochemical performance is further improved.
[0011] This invention also provides a method for lithium replenishment and repair of waste lithium iron phosphate cathode materials based on tetralithium 2,5-thiophene dimethyl diboronate, comprising the following steps:
[0012] Step 1: Add 2,5-thiophene dihydric acid to deionized water, heat and stir to dissolve until fully dissolved, then add lithium hydroxide, heat and stir to react. Observe that no precipitate forms, indicating the reaction is complete. Continue heating and stirring to evaporate water until the solution becomes a paste, and finally dry completely to form a solid, ensuring the formation of a high-purity, uniform organic tetralithium salt solid. Then transfer the solid to a vacuum oven and dry it at 80°C. Finally, a pale yellow or white powder, C4Li4B2O4S, is obtained. During ball milling, the tetralithium salt is uniformly coated and penetrated into the S-LFP surface. The ball milling slurry is dried at 80°C and then ground to ensure solid homogeneity.
[0013] Step 2: Place waste lithium iron phosphate (S-LFP) and C4Li4B2O4S in a ball mill jar, add anhydrous ethanol (dispersion medium) and milling beads, and then ball mill. After ball milling, dry the slurry and then grind it to obtain powder.
[0014] Step 3: The powder obtained in Step 2 is calcined at high temperature in an argon atmosphere, naturally cooled to room temperature, and then ground to obtain the regenerated lithium iron phosphate cathode material (R-LFP).
[0015] Furthermore, in step one, the mass ratio of 2,5-thiophene dimethyl diboronic acid to lithium hydroxide is 10:1 to 1:10; the temperature is controlled at 50-150℃ to ensure complete dissolution and uniform ion exchange.
[0016] Furthermore, in step two, the amount of C4Li4B2O4S added is based on the amount of lithium deficiency in the waste lithium iron phosphate powder, and 2%-40% molar fraction of lithium source (lithium in C4Li4B2O4S) needs to be added.
[0017] Furthermore, in step three, the high-temperature calcination includes a two-stage heat treatment to repair S-LFP: the first stage: holding at 200-450℃ for 2-4 h to promote the decomposition of C4Li4B2O4S and release active lithium, repairing the lattice vacancies of lithium-depleted LFP; the second stage: holding at 500-900℃ for 6-12 h to complete the LFP structure reconstruction, nucleation / recrystallization, and form R-LFP.
[0018] Furthermore, in step three, the temperature is steadily increased at a rate of 2-20℃ / min under an argon atmosphere to reduce excessive carbonization or lattice collapse of the material. An inert atmosphere is used to prevent Li volatilization, oxidation, and migration loss of B / S elements.
[0019] Compared with the prior art, the beneficial effects of the present invention are:
[0020] (1) This invention is the first to apply 2,5-thiophene dimethyl diborate tetralithium salt (C4Li4B2O4S) as a lithium replenisher / dopant in the field of battery repair. This material integrates the synergistic functions of lithium replenishment, bulk doping and surface modification: its high lithium content can efficiently replenish active lithium; S and B elements can be incorporated into the lattice or surface to form SO and BO bonds, enhancing the structural stability of the material; at the same time, the remaining components can form a highly conductive residual carbon layer during calcination, significantly improving electronic conductivity, thereby achieving a triple improvement of structural reconstruction, conductivity enhancement and capacity recovery.
[0021] (2) The present invention adopts a unique route of "dissolving-evaporating-paste". By controlling the solvent to evaporate to a paste state, the component segregation caused by rapid drying is effectively avoided, and finally high-purity, high-dispersion and highly reactive C4Li4B2O4S powder is obtained, which is significantly better than traditional solid-phase lithium salts.
[0022] (3) In the ball milling process, the present invention uses ethanol solvent to form a flexible organic coating layer of C4Li4B2O4S on the surface of waste lithium iron phosphate (LFP) particles. This layer can release lithium and other active elements in situ and uniformly during subsequent heat treatment, making the lithium replenishment process more gentle and controllable, and avoiding explosive reactions.
[0023] (4) This invention employs a two-step method combining low-temperature pre-activation and high-temperature reconstruction. The low-temperature stage promotes the initial decomposition of lithium salts and Li + Pre-diffusion into the LFP lattice; the high-temperature stage drives complete lattice rearrangement, thereby significantly improving the capacity recovery rate and structural integrity of the material.
[0024] (5) The organic lithium salt used in this invention is simple to prepare and has high safety. It does not rely on metallic lithium or other dangerous reducing agents and has excellent process compatibility and potential for large-scale industrial promotion. Attached Figure Description
[0025] Figure 1 The image shows the XRD pattern of C4Li4B2O4S synthesized in Example 1.
[0026] Figure 2 XRD patterns of untreated waste lithium iron phosphate cathode material and the repaired and regenerated lithium iron phosphate material in Example 1 are compared.
[0027] Figure 3 The first charge-discharge specific capacity-voltage curves of untreated waste lithium iron phosphate cathode material, the repaired and regenerated lithium iron phosphate material in Example 1, and LFP virgin material are shown at a rate of 0.05C. Detailed Implementation
[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0029] Example 1
[0030] 2 g of 2,5-thiophene dimethyl diboronic acid was weighed and placed in a beaker. 100 mL of deionized water was added, and the solution was dissolved completely under stirring at 100 °C and 600 rpm. Then, 1 g of lithium hydroxide was added to the solution, the beaker was sealed, and stirring was maintained at 100 °C until the reaction system became clear and no precipitate formed, indicating a complete reaction. The resulting solution was transferred to an evaporating dish, stirred continuously at 100 °C, and evaporated to a paste-like consistency. The paste was then completely dried to obtain a solid. The solid product was transferred to a vacuum drying oven and dried under vacuum at 80 °C for 24 h to obtain a pale yellow or white C4Li4B2O4S powder. The obtained C4Li4B2O4S powder was characterized by XRD. Figure 1 The XRD pattern of C4Li4B2O4S synthesized in Example 1 shows that the product exhibits high-resolution diffraction peaks, indicating good crystallinity, and no obvious impurity peaks or broadened background signals were observed. This demonstrates that the wet chemical synthesis route can stably prepare C4Li4B2O4S powder with uniform structure and high purity. This result verifies that the method can obtain the target product under mild conditions, laying the foundation for its subsequent application as a lithium replenishment agent in the structural repair of spent lithium iron phosphate materials.
[0031] The spent lithium iron phosphate (LFP) pouch cells were produced by Wanxiang A123 Company, and their capacity had decayed to approximately 70% of their initial capacity (below 80% is considered a waste battery). Using the separated spent LFP cathode material as a baseline, 0.365 g of the synthesized C4Li4B2O4S lithium replenisher was precisely weighed according to its lithium deficiency and placed together with 4 g of S-LFP in a ball mill jar. 30 mL of anhydrous ethanol and an appropriate amount of milling beads were added, and the mixture was ball-milled at 500 r / min for 3 h. After ball milling, the slurry was collected, dried completely in an 80℃ forced-air drying oven, and then ground to obtain a uniform mixed powder.
[0032] The dried mixed powder was placed in a ceramic boat and then placed in a tube furnace for heat treatment under an argon atmosphere. First, the temperature was increased to 350 °C at a rate of 10 °C / min and held for 2 h to achieve preliminary decomposition of the lithium salt and pre-diffusion of lithium ions. Then, the temperature was increased to 700 °C at the same rate and held for 6 h to complete lattice reconstruction and repair. After the reaction, the furnace was allowed to cool naturally to room temperature, and the resulting material was ground to obtain the regenerated lithium iron phosphate cathode material (RLFP). XRD characterization tests were performed on both the untreated waste lithium iron phosphate material and the regenerated lithium iron phosphate material. Figure 2 The XRD patterns of the two materials are shown. It can be seen that the diffraction peaks in SLFP correspond to LiFePO4 (LFP, JCPDS No. 83-2092) and FePO4 (FP, JCPDS No. 65-0258); while the diffraction peaks of RLFP are consistent with those of LiFePO4 (LFP, JCPDS No. 83-2092), indicating that the structure of RLFP was completely restored after the repair.
[0033] Regenerated LFP material, conductive agent, and binder were mixed at a mass ratio of 7:2:1 to prepare the positive electrode. A lithium metal sheet was used as the counter electrode, a Celgard 2400 polypropylene porous membrane as the separator, and a 1 mol / L LiPF6 EC / DEC mixed solution (volume ratio 1:1) was used as the electrolyte. A 2032 coin cell was assembled in an argon atmosphere glove box (H2O < 0.01 ppm, O2 < 0.01 ppm). The assembled cells were then subjected to charge-discharge tests. Figure 3 The first charge-discharge specific capacity-voltage curves of untreated waste lithium iron phosphate (SLFP), repaired and regenerated lithium iron phosphate (RLFP), and unused new LFP (NLFP) materials at a rate of 0.05C are shown. It can be concluded that the performance of RLFP (155 mAh / g) is restored to about 95% of that of NLFP (163 mAh / g).
[0034] Example 2
[0035] Weigh 3 g of 2,5-thiophenedimethylbisboronic acid into a beaker, add 100 mL of deionized water, and dissolve it completely under stirring at 100 °C and 600 r / min. Then, add 1 g of lithium hydroxide to the solution, seal the beaker, and maintain stirring at 100 °C until the reaction system is clear and no precipitate forms, indicating a complete reaction. Transfer the resulting solution to an evaporating dish, and evaporate and concentrate it to a paste under continuous stirring at 100 °C, finally drying completely to obtain a solid. Transfer the solid product to a vacuum drying oven and vacuum dry at 80 °C for 24 h to obtain a pale yellow or white C4Li4B2O4S powder.
[0036] Based on waste lithium iron phosphate, 0.365 g of the synthesized C4Li4B2O4S lithium supplement was accurately weighed according to its lithium deficiency and placed together with 4 g SLFP in a ball mill jar. 30 mL of anhydrous ethanol and an appropriate amount of milling beads were added, and the mixture was ball-milled at 500 r / min for 3 h. After ball milling, the slurry was collected and dried completely in an 80 ℃ forced-air drying oven. After grinding, a uniform mixed powder was obtained.
[0037] The dried mixed powder was placed in a ceramic boat and then placed in a tube furnace for heat treatment under an argon atmosphere. First, the temperature was increased to 350 °C at a rate of 5 °C / min and held for 2 h to achieve preliminary decomposition of the lithium salt and pre-diffusion of lithium ions. Then, the temperature was increased to 500 °C at the same rate and held for 6 h to complete lattice reconstruction and repair. After the reaction, the furnace was allowed to cool naturally to room temperature, and the regenerated lithium iron phosphate cathode material was obtained after grinding.
[0038] Example 3
[0039] Weigh 4 g of 2,5-thiophenediylbisboronic acid into a beaker, add 100 mL of deionized water, and dissolve it completely under stirring at 100 °C and 600 r / min. Then, add 1 g of lithium hydroxide to the solution, seal the beaker, and maintain stirring at 100 °C until the reaction system is clear and no precipitate forms, indicating a complete reaction. Transfer the resulting solution to an evaporating dish, and evaporate and concentrate it to a paste under continuous stirring at 100 °C, finally drying completely to obtain a solid. Transfer the solid product to a vacuum drying oven and vacuum dry at 80 °C for 24 h to obtain a pale yellow or white C4Li4B2O4S powder.
[0040] Based on waste lithium iron phosphate, 0.365 g of the synthesized C4Li4B2O4S lithium supplement was accurately weighed according to its lithium deficiency and placed together with 4 g of S-LFP in a ball mill jar. 30 mL of anhydrous ethanol and an appropriate amount of milling beads were added, and the mixture was ball-milled at 500 r / min for 3 h. After ball milling, the slurry was collected and dried completely in an 80 ℃ forced-air drying oven. After grinding, a uniform mixed powder was obtained.
[0041] The dried mixed powder was placed in a ceramic boat and then placed in a tube furnace for heat treatment under an argon atmosphere. First, the temperature was increased to 350 °C at a rate of 10 °C / min and held for 2 h to achieve preliminary decomposition of the lithium salt and pre-diffusion of lithium ions. Then, the temperature was increased to 900 °C at the same rate and held for 6 h to complete lattice reconstruction and repair. After the reaction, the furnace was allowed to cool naturally to room temperature, and the regenerated lithium iron phosphate cathode material was obtained after grinding.
[0042] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0043] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.
Claims
1. A lithium supplement for the regeneration of positive electrode materials of waste lithium iron phosphate batteries, characterized in that, The lithium supplement agent is 2,5-thiophenediyl bisboric acid tetralithium salt, and the chemical formula is C4Li4B2O4S.
2. The application of 2,5-thiophenediyl bisboric acid tetralithium salt in the lithium supplement and repair of waste lithium iron phosphate positive electrode material according to claim 1.
3. A method for lithium supplement and repair of waste lithium iron phosphate cathode material based on 2, 5-thiophenediyl bisboronic acid tetralithium salt, characterized in that, The method comprises the following steps: Step one: 2,5-thiophenediyl bisboric acid is added into deionized water, heated and stirred to dissolve, then lithium hydroxide is added, heated and stirred to react, and after the reaction, the reaction product is evaporated into a paste or solid, and dried at 80℃ to obtain C4Li4B2O4S; Step two: the waste lithium iron phosphate and C4Li4B2O4S are placed in a ball mill tank, anhydrous ethanol is added for ball milling, the ball milling speed is 200-700 r / min, and the ball milling time is 10-300 min, then the slurry is dried and ground to obtain a powder; Step three: the powder obtained in step two is high-temperature calcined under an argon atmosphere, naturally cooled to room temperature, and ground to obtain a regenerated lithium iron phosphate positive electrode material.
4. The method according to claim 3, wherein the 2,5-thiophenediylbisboronic acid tetralithium salt-based lithium supplementing and repairing method for the spent lithium iron phosphate cathode material is characterized in that, In step one, the mass ratio of 2,5-thiophenediyl bisboric acid to lithium hydroxide is 10:1-1:10, and the temperature is controlled at 50-150℃.
5. The method according to claim 3, wherein the lithium supplementing and repairing method for the spent lithium iron phosphate cathode material based on 2,5-thiophenediyl diborate tetralithium salt is characterized in that, In step two, the added C4Li4B2O4S is 2%-40% of the lithium deficiency of the waste lithium iron phosphate powder.
6. The method according to claim 3, wherein the lithium supplementing and repairing method for the spent lithium iron phosphate cathode material based on 2,5-thiophenediyl diborate tetralithium salt is characterized in that, In step three, the high-temperature calcination comprises: holding at 200-450℃ for 2-4 h, then increasing the temperature to 500-900℃ and holding for 6-12 h.
7. The method according to claim 3, wherein the lithium supplementing and repairing method for the spent lithium iron phosphate cathode material based on 2,5-thiophenediyl diborate tetralithium salt is characterized in that, In step three, the temperature is increased at a rate of 2-20℃ / min under an argon atmosphere.