Retired lithium iron phosphate batteries that lack secondary use value, as well as batteries that have already undergone secondary use, must eventually enter the dismantling and recycling stage. Unlike ternary lithium batteries, lithium iron phosphate batteries do not contain heavy metals; the main recyclables are Li, P, and Fe. The added value of the recycled products is relatively low, necessitating the development of low-cost recycling routes. The main recycling methods are pyrometallurgical and hydrometallurgical processes.
I. Pyrometallurgical Recovery Process
Traditional pyrometallurgical recycling typically involves high-temperature incineration of electrode sheets to burn off carbon and organic matter in the electrode fragments. The remaining ash, which cannot be burned off, is then screened to obtain a fine powder containing metals and metal oxides. This method is simple, but the processing time is long, and the overall recovery rate of valuable metals is low. The improved pyrometallurgical recycling technology removes organic binders through calcination, separating lithium iron phosphate powder from aluminum foil to obtain lithium iron phosphate material. Then, appropriate raw materials are added to achieve the desired lithium, iron, and phosphorus molar ratio, and new lithium iron phosphate is synthesized via a high-temperature solid-state method. Cost calculations indicate that the improved dry pyrometallurgical recycling of spent lithium iron phosphate batteries can be profitable; however, the newly prepared lithium iron phosphate produced using this recycling process has many impurities and unstable performance.
II. Wet recovery process
Wet recycling primarily involves dissolving metal ions in lithium iron phosphate batteries using acid or alkaline solutions, and then extracting the dissolved metal ions as oxides or salts through precipitation and adsorption. Reagents such as H₂SO₄, NaOH, and H₂O₂ are commonly used in the reaction process. Wet recycling is a simple process with low equipment requirements, suitable for large-scale industrial production, and is the most studied method and the mainstream waste lithium-ion battery treatment route in China.
The wet recycling of lithium iron phosphate (LFP) batteries primarily focuses on recovering the positive electrode. When using a wet process to recover the LFP positive electrode, the aluminum foil current collector must first be separated from the positive electrode active material. One method is to dissolve the current collector with an alkaline solution, while the active material does not react with the alkaline solution and can be obtained through filtration. Another method is to dissolve the PVDF binder with an organic solvent, causing the LFP positive electrode material to separate from the aluminum foil. The aluminum foil can be reused, the active material can be further processed, and the organic solvent can be distilled for recycling. Compared to the first method, the second is more environmentally friendly and safer. Another method for recovering lithium iron phosphate from the positive electrode is to generate lithium carbonate. This recycling method is lower in cost and is adopted by most LFP recycling companies, but the main component of LFP (95% content) is not recovered, resulting in resource waste.
A more ideal wet recycling method involves converting waste lithium iron phosphate cathode materials into lithium salts and iron phosphate, achieving full elemental recovery of Li, Fe, and P. To convert lithium iron phosphate into lithium salts and iron phosphate, ferrous iron needs to be oxidized to ferric iron, followed by acid or alkaline leaching to extract lithium. Some researchers have used oxidative calcination to separate aluminum flakes and lithium iron phosphate, followed by sulfuric acid leaching and separation to obtain crude iron phosphate. The solution is then purified by sodium carbonate precipitation to form lithium carbonate; the filtrate is evaporated and crystallized to obtain anhydrous sodium sulfate, which is sold as a byproduct; the crude iron phosphate is further refined to obtain battery-grade iron phosphate, which can be used in the preparation of lithium iron phosphate materials. This process has been relatively mature after years of research.
