Recycling of Spent Lithium-ion Batteries via Hydrothermal Process

Abstract

Hydrothermal treatment has demonstrated great potential in regeneration and terminal recycling spent LIB cathode materials. On the one hand, hydrothermal regeneration is a hydrothermal reaction that uses a lithium-containing solution (especially LiOH) at elevated temperatures and pressures to replenish the missing Li in degraded cathode materials, which are subsequently treated by roasting to accomplish the phase repair.Compared with solid-state sintering regeneration, hydrothermal regeneration offers several advantages including the elimination of the need to pre-analyze Li loss in degraded cathodes, the ability to simultaneously regenerate degraded cathodes with various Li/Co ratios, and a constant Li/Co ratio in the regenerated particles even after a short annealing process. Moreover, this method uses water as a reaction medium and reduces energy consumption by eliminating the need for dehydration, accelerates reaction rates by acting as a medium, reactant and catalyst, and prevents secondary pollution under a sealed environment. On the other hand, hydrothermal leaching has been used for selective extraction of critical metals such as Li from spent LIB cathode materials. By using the subcritical water reaction combined with organic acids (e.g., citric acid) or weak acid systems, the efficient extraction of critical metals such as Li, Co, Ni, and Mn can be achieved. Thus, this review discussed the spent LIBs recycling technologies to highlight the superiority of hydrothermal regeneration and recovery technologies. Furthermore, research advances and future challenges in hydrothermal relithiation for direct regeneration and hydrothermal leaching for metals recovery are concluded to promote the hydrothermal recycling technologies towards sustainable applications.