In the retired lithium iron phosphate batteries, the batteries that do not have the value of step utilization and the batteries after step utilization will eventually be dismantled and recycled. 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 and Fe. The added value of the recovery product is low, so a low-cost recovery route needs to be developed. There are two main methods of recovery: fire method and wet method.
Fire recovery process
The traditional fire-recovery method is to incinerate the electrodes at high temperature, burning off the carbon and organic matter in the electrode fragments. The remaining ash that cannot be burned is eventually screened to produce fine powdery materials containing metals and metal oxides. The process is simple, but the treatment process is long, and the comprehensive recovery of valuable metals is low. The improved fire-recovery technology is to remove organic binder by calcination, separate lithium iron phosphate powder from aluminum foil sheet to obtain lithium iron phosphate material, and then add appropriate raw materials to obtain the required mole ratio of lithium, iron and phosphorus, and synthesize new lithium iron phosphate by high-temperature solid-phase method. According to the cost calculation, the waste lithium iron phosphate battery can be recycled by the improved fire and dry method, but the new lithium iron phosphate prepared by this recovery process has many impurities and unstable performance.
Wet recovery process
Wet recovery is mainly through acid and alkali solution to dissolve metal ions in lithium iron phosphate battery, further use precipitation, adsorption and other ways to extract the dissolved metal ions in the form of oxides, salts and other forms, most of the reaction process using H2SO4, NaOH, H2O2 and other reagents. Wet recovery process is simple, equipment requirements are not high, suitable for industrial large-scale production, is the most studied by scholars, is also the mainstream waste lithium ion battery treatment route in China.
The recovery of lithium iron phosphate battery is mainly positive electrode. When recovering the positive electrode of lithium iron phosphate by wet process, the aluminum foil collector should be separated from the active substance of the positive electrode first. One of the methods is to use lye solution to dissolve fluid collection, and the active substance does not react with the lye, can be filtered to obtain the active substance. The second method is to use organic solvent to dissolve the binder PVDF, so that lithium iron phosphate anode material and aluminum foil separated, aluminum foil reuse, active substances can be subsequent treatment, organic solvent can be treated by distillation, to achieve its recycling. Compared with the two methods, the second method is more environmentally safe. The recovery of lithium iron phosphate in the positive electrode is the formation of lithium carbonate. This recovery method has low cost and is adopted by most lithium iron phosphate recycling enterprises, but the main component of lithium iron phosphate iron phosphate (95%) has not been recycled, resulting in a waste of resources.
The ideal wet recovery method is to convert waste lithium ferrous phosphate cathode material into lithium salt and iron phosphate to realize the recovery of Li, Fe and P. If lithium ferrous phosphate wants to become lithium salt and iron phosphate, it is necessary to oxidize ferrous to trivalent iron, and use acid leaching or alkali leaching to leach lithium. Some scholars separated aluminum sheets and lithium iron phosphate by oxidation calcination, and then obtained crude iron phosphate by sulfuric acid leaching and separation. Sodium carbonate was used to precipitate lithium carbonate in solution removal. Evaporation crystallization of the filtrate to obtain anhydrous sodium sulfate products sold as by-products; 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. The technology has been relatively mature after years of research.