Carbothermic reduction of LiCoO2 cathode material: Thermodynamic analysis, microstructure and mechanisms

Abstract

Carbothermic reduction using secondary carbon materials such as graphite anode provides an option for recycling critical elements in the spent Li-ion batteries. In this study, carbothermic reduction of battery cathode material LiCoO2 using graphite as reductant was systematically investigated. The study included thermodynamic evaluation using the FactSage™ thermochemical modelling, isothermal high-temperature experimentation at 700–1100 °C under argon atmosphere, and detailed microstructure evolution analysis to establish the mechanisms of the reduction. The products from the reduction experiments were found to be Li2CO3, Li2O, and Co, and these corresponded well with the thermodynamic assessments. The overall reduction mechanism was evaluated to start with LiCoO2 decomposition followed by the reduction of cobalt oxide to form metallic cobalt. The results also suggest that reduction occurs indirectly through reduction by CO(g). The information generated in the study are useful for improvement and parameter optimization for high temperature recycling of Li-ion batteries.