Synergistic carbon-sulfur co-roasting driven sustainable and selective recovery of lithium from spent ternary lithium-ion batteries.

Spent lithium-ion batteries (LIBs) contain high-value strategic metals which are essential for the sustainable resource utilization and eco-environment conservation. Conventional recycling technologies usually involve complicated procedures, high energy consumption and hazardous gas emissions. Hence, a novel process based on "C/S synergistic roasting - water leaching" is put forward to selective and environment-friendly recovery of lithium from spent LIBs. The effects of the molar ratio of sodium sulfide hydrate (NaS) to LiNiCoMnO (NCM523), graphite content, roasting temperature and time on the selective leaching of lithium are firstly investigated, then these process parameters are optimized to further increase the selectivity and recycling efficiency of lithium from spent LIBs. It is found that the leaching efficiency of lithium can achieve 98.57 %, while those of nickel, cobalt and manganese are as low as 0.30 %, 0.25 % and 0.60 %, respectively under the following optimal conditions: the molar ratio of NaS to NCM523 of 1.5:1, 17.5 wt% graphite, 700 °C for 90 min. During the roasting process, lithium is released from the unstable layered crystal structure and then converted into water-soluble NaLiS at high temperature, while nickel, cobalt and manganese are converted into water-insoluble NiS, CoS, and MnO, respectively. Furthermore, lithium is preferentially recovered by facile water leaching, and the sulfur in NaS is combined with metals without toxic SO generation, achieving selective and cleaner recovery of lithium from spent NCM523 batteries.