Recovery of LiCoO₂ from Spent Lithium-Ion Batteries through a Low-Temperature Ammonium Chloride Roasting Approach: Thermodynamics and Reaction Mechanisms

Abstract

An ammonium chloride roasting approach can convert lithium metal oxides to water-soluble lithium and transition metal chlorides at 300 °C, promising an energy-efficient and environmentally benign way to recover end-of-life lithium-ion batteries. Unlike conventional chlorination processes, the roasting of LiCoO2 using NH4Cl as both reducing and chlorination agents is complex, and thus more efforts such as thermodynamics and the underlying mechanism are required to be understood. This paper aims to study the chlorination process by comprehensive thermodynamic analysis and a variety of control experiments such as operating temperature, gas atmosphere, NH4Cl/LiCoO2 mass ratios, and the way of mixing feedstocks. It is found that the chlorination of LiCoO2 is governed by a solid-to-solid reaction mechanism based on thermodynamics, thermal analysis, and roasting products. Finally, the regenerated LiCoO2 delivers a specific capacity of over 139.8 mAh g–1 at 0.5C with a capacity retention rate of 99% after 100 cycles. Overall, the chlorination process can be engineered by adjusting the temperatures, pressure, and contact area between NH4Cl and LiCoO2 to further reduce the energy consumption and thereby increase the utilization of NH4Cl and chlorination efficiencies.