Among the decommissioned lithium iron phosphate batteries, the batteries that do not have the value of cascading use and the batteries after the cascade use will eventually enter the dismantling and recycling stage. The difference between lithium iron phosphate battery and ternary material battery is that it does not contain heavy metals, and the recovery is mainly Li, P, Fe. The added value of the recovered products is low, and it is necessary to develop a low-cost recovery route. There are mainly two recycling methods: fire method and wet method.
Fire recovery process
The traditional fire method is generally to burn the electrode pieces at a high temperature to burn off the carbon and organic matter in the electrode fragments. The remaining ash that cannot be burned is finally screened to obtain a fine powder material containing metals and metal oxides. The process is simple, but the treatment process is long, and the comprehensive recovery rate of valuable metals is low. The improved fire recovery technology is to remove the organic binder by calcination to separate the lithium iron phosphate powder from the aluminum foil to obtain the lithium iron phosphate material, and then add an appropriate amount of raw materials to obtain the required lithium, iron, and phosphorus Molar ratio, the new lithium iron phosphate is synthesized by high temperature solid phase method. According to cost estimates, the improved pyrotechnical dry recycling of waste lithium iron phosphate batteries can achieve profitability, but the newly prepared lithium iron phosphate according to this recycling process has many impurities and unstable performance.
Wet recovery process
Wet recovery is mainly to dissolve the metal ions in the lithium iron phosphate battery through acid-base solutions, and further use precipitation, adsorption and other methods to extract the dissolved metal ions in the form of oxides, salts, etc., most of the reaction process uses H2SO4, NaOH and H2O2 and other reagents. The wet recycling process is simple, the equipment requirements are not high, and it is suitable for industrial-scale production. It is the most studied by scholars, and it is also the mainstream domestic waste lithium-ion battery treatment route.
The wet recycling of lithium iron phosphate batteries focuses on recycling the positive electrode. When using a wet process to recover lithium iron phosphate cathodes, the aluminum foil current collector must first be separated from the cathode active material. One of the methods is to use lye to dissolve the current collector, and the active material does not react with the lye, and the active material can be obtained by filtration. The second method is to dissolve the binder PVDF with an organic solvent to separate the lithium iron phosphate cathode material from the aluminum foil, the aluminum foil is reused, the active material can be subjected to subsequent treatment, and the organic solvent can be distilled to realize its recycling. Compared with the two methods, the second is more environmentally friendly and safer. One type of recovery of lithium iron phosphate in the positive electrode is to generate lithium carbonate. This kind of recycling method has low cost and is adopted by most lithium iron phosphate recycling companies, but the main component of lithium iron phosphate (content 95%) is not recycled, resulting in a waste of resources.
The ideal wet recycling method is to convert the waste lithium iron phosphate cathode material into lithium salt and iron phosphate to realize the recovery of all elements of Li, Fe, and P. In order for lithium iron phosphate to become lithium salt and iron phosphate, it is necessary to oxidize ferrous iron to trivalent iron, and then use acid leaching or alkaline leaching to extract the lithium. Some scholars use oxidation calcination to separate aluminum flakes and lithium iron phosphate, and then leaching and separating with sulfuric acid to obtain crude iron phosphate. The solution is impurity-removed and sodium carbonate is used to precipitate lithium carbonate; the filtrate is evaporated and crystallized to obtain anhydrous sodium sulfate as a by-product for sale; The crude iron phosphate is further refined to obtain battery-grade iron phosphate, which can be used for the preparation of lithium iron phosphate materials. The process has been relatively mature after years of research.