Recycling of nickel metal from spent nickel-manganese-cobalt (NMC) cathode batteries using H3PO4–H2C2O4 solution combination as an efficient leaching agent

Nickel-manganese-cobalt (NMC) is a type of cathode material widely used in lithium-ion batteries (LiBs). It performs well on high energy density and thermal stability, but after several charged-discharged cycles, its capacity significantly degrades and becomes waste. Leaching methods with strong inorganic acids are widely used to prevent the release of valuable metals into the environment. Still, these methods must be effectively achieved regarding the low selectivity of specific metals and environmental emissions. This study presents a selective leaching treatment for Ni metals extraction with the organic acid combination of H₃PO₄–H₂C₂O₄ as a leaching agent. The research started with preparation, including discharge, dismantling, calcination steps, leaching, and precipitation. Ni, Mn, and Co leaching efficiency can reach up to 99.90 %, 3.29 %, and 43.65 %, respectively. The leaching experiment shows that a combination system contributes to obtaining excellent selectivity towards Ni metals compared to the others. The optimum conditions for selectively recovering Ni metals were an H₃PO₄–H₂C₂O₄ volume ratio of 8:2 and a liquid-solid ratio of 25 mL/g, leaching at 60 °C for 1.5 h. The thermodynamics and kinetics of the leaching reactions were analyzed to determine the feasibility of leaching three metals. Leachate, which is Ni-saturated from cathode powder, was added with Cyanex272 to facilitate the precipitation of Ni₃(PO₄)₂ with a yield of up to 40 %. This study presents a potential "waste-to-wealth" approach to lead the efficient and environmental recycling of spent NMC cathode LIBs.