Among the retired lithium iron phosphate batteries
, the batteries that do not have echelon utilization value and the batteries after echelon utilization will eventually enter the stage of disassembly and recycling. 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 recovered products is low, so it is necessary to develop a low-cost recovery route. There are mainly two recovery methods: fire method and wet method.
Fire recovery process
The traditional fire recovery method is generally to burn the electrode pieces at high temperature to burn the carbon and organic matter in the electrode fragments. The remaining ash that cannot be burned is finally screened to obtain fine powder 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 the organic binder by calcination, 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 molar ratio of lithium, iron and phosphorus, and synthesize a new lithium iron phosphate by high-temperature solid-state method. According to the cost calculation, the improved fire dry recovery of lithium iron phosphate waste battery can achieve profit, but the newly prepared lithium iron phosphate according to this recovery process has many impurities and unstable performance.
Wet recovery process
Wet recovery is mainly to dissolve the metal ions in lithium iron phosphate battery through acid-base solution, and further extract the dissolved metal ions in the form of oxides and salts by precipitation and adsorption. H2SO4, NaOH, H2O2 and other reagents are mostly used in the reaction process. The wet recovery process is simple and the equipment requirements are not high. It is suitable for industrial large-scale production. It is not only the most studied by scholars, but also the mainstream treatment route of waste lithium-ion batteries in China.
The main method of wet recovery of lithium iron phosphate battery is to recover the cathode. When the lithium iron phosphate cathode is recovered by wet process, the aluminum foil collector must be separated from the cathode active material. One of the methods is to use alkali solution to dissolve the collector, and the active substance does not react with alkali solution. The active substance can be obtained by filtration. The second method is to dissolve the binder PVDF with organic solvent to separate the lithium iron phosphate cathode material from the aluminum foil. The aluminum foil can be reused. The active material can be treated later, and the organic solvent can be distilled to realize its recycling. Compared with the two methods, the second method is more environmentally friendly and safe. One way to recover lithium iron phosphate from cathode is to generate lithium carbonate. This recycling method has low cost and is adopted by most lithium iron phosphate recycling enterprises, but the main component of lithium 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 ferrous phosphate cathode material into lithium salt and iron phosphate to realize the full element recovery of Li, Fe and P. In order to turn lithium ferrous phosphate into lithium salt and iron phosphate, ferrous oxide needs to be oxidized into ferric iron, and lithium is leached by acid leaching or alkali leaching. Some scholars separated aluminum sheet and lithium iron phosphate by oxidative calcination, and then leached and separated it by sulfuric acid to obtain crude iron phosphate. The solution was precipitated into lithium carbonate with sodium carbonate; The filtrate is evaporated and crystallized to obtain anhydrous sodium sulfate, which is sold as a by-product; 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. After years of research, the process has been relatively mature.