Research progress on the alkaline-system selective recycling technology in spent lithium-ion batteries

Due to the issue of raw material depletion, lithium-ion batteries are becoming less value-added. In addition, the highly toxic organic electrolytes contained in them cause serious harm to humans and the environment. That is why the effective recovery of spent lithium-ion batteries is of great importance for the development and sustainable use of lithium-ion batteries. Currently, recovery of metals present in spent lithium-ion batteries mainly relies on hydrometallurgical extraction: The main metals are extracted through acid or alkali media followed by recovery of metal compounds through further processing or the resynthesis of high-performance materials. Among them, acid leaching is a short and highly efficient process; however, this process dissolves all the metal ions in the solution, making it difficult to subsequently separate and purify the valuable metals. Contrarily, the hydroxide of impure metal in lithium-ion batteries shows low solubility, whereas lithium, nickel, and cobalt have high solubility, allowing for the formation of complexes with ammonia ions that can exist in alkali solution in large quantities. Thus, alkaline leaching has better selective leaching of metals in electrode materials due to the high solubility of lithium, nickel, and cobalt ammonia complexes and has a more efficient and cleaner recovery process, which is of outstanding importance in the industry. Most research was mainly focused on various acid recovery systems and scales, and the research progress on the alkaline recovery process was insufficient. Here, based on the industrial research status of alkali leaching recovery, four alkali leaching recovery systems, which include the ammonia leaching-reductant-hot working system, ammonia leaching-reductant-electrodeposition system, ammonia leaching-reductant-lithium adsorption system, and ammonia leaching-reductant-oxidation separation system, were reviewed along with their principles and advantages. Finally, a brief summary of the recovery methods for spent lithium-ion batteries was expressed.