Recycling of spent lithium nickel cobalt manganese oxides via a low-temperature ammonium sulfation roasting approach

A low-cost and environmentally friendly recycling approach can recover strategical elements from end-of-life lithium-ion batteries (LIBs), which is important to mitigate the resource scarcity and environmental footprint. This paper aims to develop a low-temperature pyro-metallurgical way to recycle spent LiNi0.6Co0.2Mn0.2O2 (NCM622). Unlike the traditional pyro-process generating liquid alloys and slags at above 1000 °C, the (NH4)2SO4 roasting approach operates at 350 °C and converts NCM622 to water-soluble sulfates with a sulfation rate of over 98.5%. The effects of operating temperature, mass ratio of (NH4)2SO4 and NCM, atmospheres, and duration of roasting on the sulfation are systematically studied. The sulfation reactions are thermodynamically spontaneous, and the rate of roasting is governed by the operating temperature. A temperature higher than 300 °C is required to enable the rapid roasting kinetics associated with the assistance of liquid phases. At last, a closed-loop recycling approach is approved by the excellent electrochemical performances of the regenerated NCM622 prepared by recovered sulfates. This paper provides a low-temperature sulfation approach to chemically breaking down the crystal structure of lithium metal oxides and simultaneously generating water-soluble sulfates without using any acid and reducing agent.