Dismantling and recycling of lithium iron phosphate batteries

Among the decommissioned lithium iron phosphate batteries, the batteries that do not have the value of cascade utilization and the batteries after cascade utilization will eventually enter the stage of dismantling and recycling. Lithium iron phosphate batteries are different from ternary material batteries in that they do not contain heavy metals and are mainly recovered from Li, P, and Fe. The added value of recovered products is low, and it is necessary to develop low-cost recovery routes. There are mainly two recycling methods: fire method and wet method.
Fire recovery process:
The traditional pyrotechnic recycling generally involves incinerating the electrode sheets at high temperature to burn off the carbon and organic matter in the electrode fragments, and the remaining ash that cannot be burned is finally screened to obtain fine powder materials containing metals and metal oxides. The process of this method 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, separate the lithium iron phosphate powder from the aluminum foil, and obtain the lithium iron phosphate material, and then add an appropriate amount of raw materials to it to obtain the required molar ratio of lithium, iron, and phosphorus, and synthesize new lithium iron phosphate through a high-temperature solid-phase method. According to cost calculations, the improved fire-dry recycling of lithium iron phosphate waste batteries can achieve profitability, but the newly prepared lithium iron phosphate by this recycling process has many impurities and unstable performance.
Wet recycling process:
Wet recovery is mainly to dissolve metal ions in lithium iron phosphate batteries through acid-base solution, and further use precipitation, adsorption and other methods to extract the dissolved metal ions in the form of oxides and salts. Most of the reaction process uses reagents such as H2SO4, NaOH and H2O2. 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 is also the mainstream domestic waste lithium-ion battery treatment route.
The wet recycling of lithium iron phosphate batteries is mainly to recover the cathode. When the lithium iron phosphate cathode is recycled by a wet process, the aluminum foil current collector must be separated from the cathode active material first. One of the methods is to use lye to dissolve the current collector, and the active substance does not react with the lye, and the active substance can be obtained by filtration. The second method is to dissolve the binder PVDF with an organic solvent, so that the lithium iron phosphate cathode material is separated from the aluminum foil, and the aluminum foil can be reused. The active material can be processed later, and the organic solvent can be distilled to realize its recycling. Compared with the two methods, the second one is more environmentally friendly and safe. The recovery of lithium iron phosphate in the positive electrode is to generate lithium carbonate. This recycling method is low in cost and has been adopted by most lithium iron phosphate recycling companies, but the main component of lithium iron phosphate, iron phosphate (content 95%), has not been recycled, resulting in a waste of resources.
The ideal wet recovery method is to convert the waste lithium iron phosphate cathode material into lithium salt and iron phosphate, so as to realize the full element recovery of Li, Fe, and P. In order to turn lithium ferrous phosphate into lithium salt and ferric phosphate, ferrous iron needs to be oxidized to ferric iron, and lithium is leached out by acid leaching or alkali leaching. Some scholars use oxidative calcination to separate aluminum flakes and lithium iron phosphate, and then leaching and separating with sulfuric acid to obtain crude iron phosphate, and remove impurities from the solution with sodium carbonate to precipitate into lithium carbonate; the filtrate is evaporated and crystallized to obtain anhydrous sodium sulfate for sale as a by-product; crude iron phosphate is further refined to obtain battery-grade iron phosphate, which can be used in the preparation of lithium iron phosphate materials. The process has been relatively mature after years of research.