Direct regeneration method and application of waste lithium iron phosphate positive electrode
By repairing the structure of waste lithium iron phosphate cathode materials through pre-annealing and polar amino acids, a continuous lithium transport channel is formed, solving the problem of LFP/FP coexistence structure and realizing the preparation of efficient and low-cost recycled materials with excellent electrochemical performance and long-term cycle stability.
Patent Information
- Application Number
- CN202511401464.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-28
- Publication Date
- 2026-01-16
AI Technical Summary
In existing technologies, waste lithium iron phosphate cathode materials exhibit a coexisting LFP/FP two-phase structure during long-term cycling, which affects lithium-ion transport and results in poor long-term stability of recycled materials. Furthermore, existing recycling methods are energy-intensive and costly, making it difficult to achieve efficient regeneration.
By removing structural strain through pre-annealing, the aluminum sheet is removed and then mixed with a lithium source and polar amino acids. After wet ball milling, drying, tableting, and curing annealing, a continuous lithium transport channel is formed, the crystal structure is repaired, and the conversion of LFP/FP to LFP is achieved.
The regenerated lithium iron phosphate cathode material has excellent electrochemical performance, high initial capacity, good long-term cycle stability, short process flow, low cost, and is suitable for recycling batteries of different capacities.
Smart Images
Figure CN121355441A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method and application for the direct regeneration of waste lithium iron phosphate cathodes. Background Technology
[0002] The goals of carbon neutrality and carbon peaking have driven the rapid development of clean energy. Lithium-ion batteries, as a new energy device, have been widely used in electronic devices, mobile communications, and energy storage since their inception. Lithium iron phosphate (LiFePO4, LFP), as one of the mainstream cathode materials for lithium-ion batteries, has rapidly gained a significant position in energy storage and power batteries since its initial proposal in 1996, thanks to its unique performance advantages. Compared to traditional lithium cobalt oxide (LiCoO2) and ternary materials (such as NCM / NCA), LFP has advantages such as high safety, long cycle life, and low cost, thus gaining widespread use. However, the cycle life of lithium-ion batteries is only 8-10 years. It is foreseeable that a large number of batteries will be retired in the future. These scrapped batteries contain valuable metal resources (cobalt, nickel, lithium, etc.), and direct landfilling will pollute the environment. Therefore, developing green and efficient recycling technologies is of great significance.
[0003] Currently, commonly used methods for recycling waste batteries include pyrometallurgy and hydrometallurgy. Pyrometallurgy is a traditional metal recycling method that involves high-temperature treatment of various waste materials, using high-temperature chemical reactions to alter their physical and chemical states, thereby extracting valuable metals. Hydrometallurgy involves dissolving metals in various solutions, followed by separation and purification to obtain metal compounds. Both pyrometallurgy and hydrometallurgy aim to disrupt crystal structures and extract metal elements, often requiring large amounts of energy and chemical substances. They are complex processes, costly, and run counter to the principles of sustainable development. Existing improvements, such as methods for repairing and regenerating waste lithium iron phosphate cathode materials through reduction, often suffer from poor long-term stability of the repaired lithium iron phosphate material. For example, patent application 2024111409129 discloses a method for recycling and regenerating waste lithium iron phosphate cathode materials, specifically disclosing that lithium, iron, and phosphorus are added to the lithium iron phosphate / carbon powder, a reducing agent is added and mixed to obtain a mixture, which is then calcined to obtain recycled lithium iron phosphate material. This method is based on supplementing the missing elements in the waste lithium iron phosphate cathode sheet and then repairing it through reduction. However, the regenerated material does not have long-term cycle stability. In the process of realizing this invention, the inventors discovered that the prior art has at least the following problems: LFP has an olivine-shaped structure and is an important cathode material in lithium-ion batteries because of its characteristic of reversibly inserting and extracting lithium ions. During charging, LFP undergoes delithiation and is converted into FePO4(FP). During discharge, it is restored to the initial phase structure through lithium intercalation. However, in long-term cycle batteries, FP cannot be completely restored to LFP. There is a coexistence of LFP / FP two-phase structure in waste lithium iron phosphate cathode materials. The existence of this structure affects lithium transport and hinders the diffusion of lithium ions during the regeneration of cathode materials.
[0004] This invention provides a method for regenerating spent lithium iron phosphate cathode materials that enables efficient lithium-ion transport, which is one of the key approaches to achieving the recycling and regeneration of retired batteries. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to provide a method and application for direct regeneration of waste lithium iron phosphate cathodes, which addresses the shortcomings of the prior art. This method can effectively promote the conversion of LFP / FP in waste lithium iron phosphate cathode materials into LFP. The regenerated lithium iron phosphate cathode has excellent electrochemical performance, and the corresponding battery has significantly improved initial capacity and can operate stably in 300 long cycles.
[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:
[0007] On the one hand, a method for direct regeneration of waste lithium iron phosphate cathodes is provided, including:
[0008] Waste lithium iron phosphate batteries are discharged and disassembled to obtain lithium iron phosphate positive electrode sheets. The electrolyte is removed to obtain pretreated lithium iron phosphate positive electrode sheets.
[0009] After pre-annealing, the aluminum sheet of the pretreated lithium iron phosphate cathode is removed and then ground to obtain a powdered cathode active material.
[0010] The powdered positive electrode active material, lithium source, and polar amino acid are mixed, wet ball milled, dried, pressed into tablets, and cured and annealed to obtain regenerated lithium iron phosphate positive electrode material.
[0011] On the other hand, a lithium-ion battery cathode material prepared by the above-mentioned method of direct regeneration of waste lithium iron phosphate cathode is provided.
[0012] On the other hand, a lithium-ion battery assembled from the above-mentioned lithium-ion battery cathode material is provided.
[0013] Compared with the prior art, the present invention has the following advantages:
[0014] 1. The lithium iron phosphate cathode material obtained by the direct regeneration method of the waste lithium iron phosphate cathode of the present invention exhibits excellent electrochemical performance in electrochemical reactions, and has the structural characteristics of high initial capacity and stable operation in 300 long cycles.
[0015] 2. The method for direct regeneration of waste lithium iron phosphate cathodes of the present invention has a short process flow and low production cost, which can greatly shorten the recycling process of retired batteries. It is applicable to the recycling of batteries of different capacities and has good economic and environmental benefits.
[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the process for direct regeneration of waste lithium iron phosphate cathode in Example 1;
[0018] Figure 2 The images show the XRD patterns of the waste positive electrode sheet (S-LFP), the pre-annealed positive electrode sheet (P-LFP), and the recycled lithium iron phosphate positive electrode material (R-LFP) from Example 1.
[0019] Figure 3 This is a comparison of the XRD curves of the waste positive electrode (S-LFP) in Example 1 and the XRD curves after structural refinement.
[0020] Figure 4 The initial charge-discharge curves of the S-LFP and R-LFP coin cells of Example 1 at 0.1C are shown.
[0021] Figure 5This is a schematic diagram of the rate performance test results of S-LFP and R-LFP coin cells in Example 1.
[0022] Figure 6 A schematic diagram showing the effect of different serine addition amounts on the electrochemical performance of regenerated LFP. Detailed Implementation
[0023] The technical solution will now be clearly and completely described with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.
[0024] In the following description, the term "and / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural.
[0025] In the following description, the terms “including,” “containing,” “having,” and “containing” are open-ended terms, meaning that they include but are not limited to.
[0026] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.
[0027] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0028] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0029] The technical principle employed in this invention is as follows: It creatively proposes a method for regenerating waste battery cathodes by first removing the LFP / FP two-phase coexistence structure from waste lithium iron phosphate cathode sheets and then performing solidification regeneration. Based on the principle of topological chemical reaction to repair crystal structures, the method includes removing the electrolyte from the disassembled lithium iron phosphate cathode sheets and then pre-annealing them, followed by removing the aluminum sheets and then pulverizing them. Subsequently, lithium replenishment and polar amino acid modification are carried out simultaneously to achieve direct regeneration. This regeneration method includes a preparatory stage to eliminate structural strain in the waste lithium iron phosphate cathode sheets. The regenerated lithium iron phosphate cathode sheets obtained in this way have excellent electrochemical performance.
[0030] On the one hand, a method for direct regeneration of waste lithium iron phosphate cathodes is provided, including:
[0031] Waste lithium iron phosphate batteries are discharged and disassembled to obtain lithium iron phosphate positive electrode sheets. The electrolyte is removed to obtain pretreated lithium iron phosphate positive electrode sheets.
[0032] After pre-annealing, the aluminum sheet of the pretreated lithium iron phosphate cathode is removed and then ground to obtain a powdered cathode active material.
[0033] The powdered positive electrode active material, lithium source, and polar amino acid are mixed, wet ball milled, dried, pressed into tablets, and cured and annealed to obtain regenerated lithium iron phosphate positive electrode material.
[0034] In some embodiments, the removal of the electrolyte is carried out by immersing the lithium iron phosphate cathode in dimethyl carbonate.
[0035] In some embodiments, the pre-annealing includes: heating to 300–500°C at a heating rate of 2–5°C / min under an inert atmosphere, holding at that temperature for 1–4 hours, and then naturally cooling to room temperature. In some embodiments, the inert atmosphere is nitrogen or argon. The pre-annealing equipment can be a tube furnace or a box furnace.
[0036] By pre-annealing the disassembled lithium iron phosphate (LFP) cathode sheets before removing the aluminum foil to eliminate structural strain, the inventors discovered during their research that pre-annealing the disassembled LFP cathode sheets under an inert atmosphere promotes the transformation of FePO4 (FP phase) in the LFP cathode sheets into the Fe2P2O7 phase with smaller cell parameters, releasing residual stress and repairing the failed LFP structure. This effectively reduces the impact of the coexistence of LFP / FP phases in waste LFP cathode materials on lithium transport, forming a continuous and unobstructed lithium transport channel, thus providing favorable conditions for subsequent direct lithium regeneration. Simultaneously, pre-annealing also effectively promotes the removal of PVDF and the separation of the cathode active material from the aluminum foil.
[0037] By holding the material at 300–500°C for 1–4 hours and then allowing it to cool naturally to room temperature in the furnace, it is possible to prevent the material from coming into contact with air and generating impurities during the process of cooling from high temperature to room temperature.
[0038] In some embodiments, the amount of the powdered positive electrode active material is a mol, and the molecular formula is Li. x FePO4 (where x < 1), the amount of lithium in the lithium source is b mol, b / a = (1 ~ 1.05) - x. By adding a lithium source, the structural formula of the powdered positive electrode active material is changed from Li x FePO4 was replenished to Li 1.0～1.05 FePO4, in this invention, Li x The x-value in FePO4 is 0.8–0.9, and the molecular weight of the powdered positive electrode active material is approximately 157.
[0039] In some embodiments, the mass ratio of the powdered positive electrode active material to the polar amino acid is 2:(0.05-0.2); in some preferred embodiments, the mass ratio of the powdered positive electrode active material to the polar amino acid is 2:(0.1-0.2). In some more preferred embodiments, the mass ratio of the powdered positive electrode active material to the polar amino acid is 2:0.1.
[0040] Using pre-annealed powdered positive electrode active material as the regeneration source, regeneration is achieved through a solid-phase reaction involving lithium source and polar amino acids, including wet ball milling, drying, pressing, and curing annealing. By utilizing the reducing properties of polar amino acids and their ability to provide a nitrogen doping source, Li-Fe antisite defects are eliminated and a surface N-doped C protective layer is formed. In particular, when the mass ratio of powdered positive electrode active material to polar amino acids is 2:0.1, the regeneration of lithium iron phosphate positive electrode material can be achieved more efficiently, resulting in batteries with high initial capacity and long-term cycle stability.
[0041] By combining pre-annealing treatment with solid-state regeneration of pre-annealed powdered positive electrode active material with lithium source and polar amino acids, the failed LFP is repaired through pre-annealing, promoting the opening of lithium transport channels. The generated Fe2P2O7 can provide more active sites to facilitate subsequent topological reactions. At the same time, the Fe-O bond energy is weakened, and subsequent direct regeneration simultaneously achieves efficient Li replenishment and elimination of Li-Fe antisite defects, giving the regenerated material excellent electrochemical performance.
[0042] In some embodiments, the lithium source is lithium carbonate, and the polar amino acid is L-serine.
[0043] In some embodiments, the wet ball milling is performed in anhydrous ethanol. In some preferred embodiments, the wet ball milling speed is 500 r / min, and the milling time is 4–5 h.
[0044] In some embodiments, the drying is performed under vacuum at 60°C for 6–8 hours; and / or, the tableting pressure is 8 tons.
[0045] In some embodiments, the curing annealing includes: at 2-5°C for 1 minute... -1 Heat to 350℃ at a heating rate and hold for 2 hours; then heat at 5–10℃ per minute. -1 Heat to 700℃ at the specified heating rate and hold for 6 hours.
[0046] On the other hand, a lithium-ion battery cathode material prepared by the above-mentioned method of direct regeneration of waste lithium iron phosphate cathode is provided.
[0047] On the other hand, a lithium-ion battery assembled from the above-mentioned lithium-ion battery cathode material is provided.
[0048] Prior to the application for this invention, a series of experiments were conducted. Some of the experimental results are listed below to provide a more detailed description of the invention. The following is a detailed description in conjunction with the embodiments.
[0049] Example 1
[0050] This embodiment provides a method for direct regeneration of waste lithium iron phosphate cathodes, the process of which is illustrated below. Figure 1 As shown, it includes the following steps:
[0051] Pretreatment and pre-annealing:
[0052] Step 1: Soak the waste lithium iron phosphate batteries in a 0.5M NaCl solution for 48 hours to release residual charge, and then let them air dry in a fume hood; the waste lithium iron phosphate batteries are from Hunan Desay Battery Co., Ltd.
[0053] Step 2: Manually disassemble the battery, separating the positive electrode (S-LFP), separator, and negative electrode. Quickly immerse the positive electrode in DMC to remove the surface electrolyte, and then dry it in a fume hood. The Li / Fe molar ratio in the disassembled positive electrode is 0.85.
[0054] Step 3: Place the dried positive electrode sheet in a tube furnace and heat it to 300℃ at a heating rate of 5℃ / min under argon protection. Hold the temperature for 2 hours and allow it to cool naturally to obtain the pre-annealed positive electrode sheet (P-LFP).
[0055] Step 4: Manually separate the positive electrode active material and aluminum foil, and grind the positive electrode active material into powder;
[0056] Lithium iron phosphate regeneration:
[0057] Step 5: Place 2g of powdered positive electrode active material in a ball mill jar, add 0.068g of Li2CO3 and 0.1g (5%) of L-serine, and then add 2mL of anhydrous ethanol as a solvent. Ball mill at 500r / min for 5 hours.
[0058] Step 6: Place the ball-milled sample in a 60℃ forced-air drying oven and dry for 8 hours;
[0059] Step 7: Place the dried material into a tablet press, set the pressure of the tablet press to 8 tons, maintain for 1 minute, and obtain a tablet material;
[0060] Step 8: Place the sheet material in a ceramic boat and then place it in a tube furnace for annealing under argon atmosphere. The temperature program during annealing is set to 2℃ / min. -1 Heat to 350℃ at a heating rate, hold for 2 hours, then heat at 10℃ / min. -1 Heat to 700℃ at the specified heating rate and hold for 6 hours.
[0061] Step 9: Allow the material to cool naturally to obtain the regenerated lithium iron phosphate cathode material (R-LFP).
[0062] Example 2
[0063] This embodiment provides a method for direct regeneration of waste lithium iron phosphate cathodes, which is the same as in Embodiment 1, except that in step three, the temperature is raised to 400°C and held for 2 hours.
[0064] Example 3
[0065] This embodiment provides a method for direct regeneration of waste lithium iron phosphate cathodes, which is the same as in Embodiment 1, except that in step three, the temperature is raised to 500°C and held for 2 hours.
[0066] Example 4
[0067] This embodiment provides a method for direct regeneration of waste lithium iron phosphate cathodes, which is the same as in Embodiment 1, except that L-serine is not added in step five.
[0068] Example 5
[0069] This embodiment provides a method for direct regeneration of waste lithium iron phosphate cathodes, which is the same as in Embodiment 1, except that in step five, 0.2g (10%) of L-serine is added.
[0070] Performance Evaluation
[0071] Figure 2 The XRD patterns of waste lithium iron phosphate cathode material (S-LFP), pre-annealed lithium iron phosphate cathode material (P-LFP), and recycled lithium iron phosphate cathode material (R-LFP) from Example 1 are shown below. Figure 2It is evident that characteristic peaks belonging to FePO4 (FP phase) are present in the waste cathode sheet (S-LFP). Figure 3 This is a comparison of the XRD curves of the waste positive electrode sheet (S-LFP) from Example 1 and the XRD curves after structural refinement. Phase 1: LiFePO4 (Pnma space group): α=β=γ=90°, percentage: 82.4%. Phase 2: FePO4 (Pnma space group): α=β=γ=90°, accounting for 17.6%, from Figure 3 As can be seen from Table 1, in the waste positive electrode (S-LFP), the c-axis unit cell parameter of LFP is... The unit cell parameters of the FP phase are Differences in unit cell parameters cause structural expansion along the crystallographic c-axis, resulting in compressive strain on the crystal planes containing the a-axis and b-axis, leading to lattice distortion. This, in turn, triggers the continuous accumulation of internal stress in the cathode material, causing the Fe-O bond length to shorten, the FeO6 octahedral volume to shrink, and structural collapse to occur. The combined effects of lattice distortion and structural collapse result in the shrinkage of the lithium transport channel cross-section, impairing continuous transport and affecting the direct regeneration of the cathode material and efficient lithium transport. The pre-annealed cathode sheet (P-LFP) spectrum shows characteristic peaks belonging to the Fe2P2O7 phase, while the characteristic peaks belonging to FePO4 (FP phase) disappear, indicating that this invention achieves the transformation of the FP phase into the Fe2P2O7 phase through pre-annealing.
[0072] Table 1 shows the phase space group distribution of waste cathode sheets (S-LFP).
[0073]
[0074] The electrochemical performance of the material synthesized in Example 1 was characterized using a CR2032 coin cell. The method included: first, mixing the positive electrode material, conductive agent acetylene black, and PVDF in a mass ratio of 8:1:1, then adding an appropriate amount of N-methylpyrrolidone as a solvent, mixing thoroughly to obtain a slurry, coating it on aluminum foil, drying it under vacuum at 90°C for 12 hours, cutting out circular pieces with a diameter of 12 mm using a cutting machine, and compacting them under 20 MPa to obtain the positive electrode sheet of the coin cell. Figure 4 The initial charge-discharge curves of the S-LFP and R-LFP coin cells of Example 1 at 0.1C are shown. The negative electrode is a lithium sheet, the separator is polypropylene (model 2500), and the electrolyte is 1M lithium hexafluorophosphate dissolved in a mixed solvent of diethyl carbonate, dimethyl carbonate, and ethylene carbonate in a volume ratio of 1:1:1. Figure 4 It can be seen that the charge and discharge capacity of R-LFP is significantly improved compared to S-LFP. Figure 5The rate performance diagram also proves the good electrochemical performance of R-LFP, and the performance of the cathode material obtained by the regeneration method of this invention meets the relevant industry standards.
[0075] Figure 6 The effect of different serine addition amounts on the electrochemical performance of regenerated LFP was demonstrated (no L-serine added (Example 4), 5% added (Example 1), and 10% added L-serine added (Example 5) correspond to R-LFP-0% Ser, R-LFP, and R-LFP-10% Ser, respectively). The tests used the aforementioned coin half-cell as the sample. Figure 6 It can be seen that the battery with regenerated active material without L-serine loses 85.2% of its capacity after 50 cycles, while the regenerated active material with 5% L-serine retains 96.6% of its capacity after 300 cycles. The initial capacity of the regenerated active material with 10% L-serine is 112.17 mAh / g, which is significantly lower than that of the regenerated active material with 5% L-serine. Therefore, in the method of obtaining regenerated positive electrode active material of this invention, when the amount of L-serine added is 5%, the resulting regenerated positive electrode battery has the characteristics of high initial capacity and high long-cycle stability.
Claims
1. A method for direct regeneration of a spent lithium iron phosphate cathode, characterized in that, The application relates to a method for directly regenerating a waste lithium iron phosphate positive electrode. The waste lithium iron phosphate battery is discharged and disassembled to obtain a lithium iron phosphate positive electrode sheet, and electrolyte is removed to obtain a pretreated lithium iron phosphate positive electrode sheet. The pretreated lithium iron phosphate positive electrode sheet is pre-annealed, the aluminum sheet is peeled off, and the pretreated lithium iron phosphate positive electrode sheet is ground to obtain a powder positive electrode active material. The powder positive electrode active material, a lithium source and a polar amino acid are mixed, wet ball-milled, dried, tablet-pressed and solidified annealed to obtain a regenerated lithium iron phosphate positive electrode material.
2. The method for direct regeneration of a spent lithium iron phosphate cathode according to claim 1, characterized in that, The electrolyte is removed by immersing the lithium iron phosphate positive electrode sheet in dimethyl carbonate.
3. The method for direct regeneration of waste lithium iron phosphate cathodes according to claim 1, characterized in that, The pre-annealing comprises the following steps: under an inert atmosphere, the temperature is raised to 300-500 DEG C at a temperature raising rate of 2-5 DEG C / min, the temperature is kept for 1-4 h, and then the temperature is naturally cooled to room temperature. 4.The method of claim 1, wherein the method further comprises: adding a lithium source to the mixture of the spent lithium iron phosphate cathode and the solvent to form a mixture; and heating the mixture to a temperature of 300-400 ℃ for 1-3 hours to obtain a regenerated lithium iron phosphate cathode. The powdered positive electrode active material has a substance amount of a mol and a molecular formula of Li x FePO4, wherein the x < 1, the substance amount of lithium element in the lithium source is b mol, and b / a = (1 ~ 1.05) - x.
5. The method for direct regeneration of spent lithium iron phosphate cathode according to claim 1, characterized in that, The mass ratio of the powder positive electrode active material to the polar amino acid is 2:(0.05-0.2). 6.The method for direct regeneration of a waste lithium iron phosphate cathode according to claim 5, characterized in that, The mass ratio of the powder positive electrode active material to the polar amino acid is 2:(0.1-0.2).
7. The method for direct regeneration of spent lithium iron phosphate cathode according to claim 1, characterized in that, The solidification annealing comprises: heating to 350℃ at a heating rate of 2-5℃min -1 , holding for 2 hours; then heating to 700℃ at a heating rate of 5-10℃min -1 , holding for 6 hours. 8.The method for direct regeneration of a waste lithium iron phosphate cathode according to claim 1, characterized in that, The lithium source is lithium carbonate, and the polar amino acid is L-serine. 9.A lithium ion battery positive electrode material obtained by a method for directly regenerating a waste lithium iron phosphate positive electrode according to any one of claims 1-8. 10.A lithium ion battery obtained by assembling the lithium ion battery positive electrode material according to claim 9.