Selective extraction of lithium from spent LiNixCoyMnzO2 cathode via in-situ conversion of ethylene glycol in subcritical water system

The resources scarcity and explosive growing demand of lithium have made the selective extraction of lithium from spent lithium-ion batteries (LIBs) more and more widely concerned. Yet the current lithium recovery routes still suffer the problems of complex process, low efficiency and unfriendly environment. In this study, a strategy of selective lithium extraction from spent LiNixCoyMnzO2 cathode with ethylene glycol (EG) in subcritical water system is proposed. The in-situ conversion pathway and lithium extraction mechanism in this new system are investigated in detail. Benefit from the reducibility of EG and the dynamic strengthening of the subcritical water system, more than 99% of lithium can be selectively extracted into the solution under the optimal conditions. The leaching kinetics show that the selective leaching process is controlled by chemical reactions and the leaching mechanism suggests that EG plays a dual role of reducing and donating protons in subcritical environment. Furthermore, the lithium-containing leachate can be applid to prepare Li2CO3 products with high purity, and the transition metals (Ni, Co, Mn) in the lithium extraction residue are recovered by acid leaching without adding reducing agent. This process puts forward a innovative idea for preferentially extracting lithium from spent LIBs and even lithium-containing wastes, which has the significant advantages of high efficiency, environmental protection and simplicity.