Hydrogen Reduction of LiCoO2 Cathode Material: Thermodynamic Analysis, Microstructure, and Mechanisms

Hydrogen is an alternative reductant to replace carbon for the production of metals. Reduction by hydrogen has advantages compared to carbothermic reduction, such as faster reaction rate and cleaner by-product (water vapor). This study investigated the application of hydrogen reduction for recycling and recovering cobalt and lithium from Li-ion battery cathode material (LiCoO2). The study consisted of thermodynamic simulations of the reactions and microstructure evolution analysis from experimental work to propose mechanisms of the reduction process. The thermodynamic assessment predicted that metallic Co could be generated from 400 degrees C and was stable up to 1200 degrees C, but strongly dependent on the molar amount of H-2. The final experimental reduction products of lithium and cobalt were found to vary and consisted of Li2O, LiOH, Li2O2 and Co, CoO, Co3O4, respectively. The experimental work revealed that the overall reduction mechanism is uniquely characterized by the reduction temperature. The temperature range of 800 degrees C to 900 degrees C offered more benefit as Co could be generated as a larger mass indicating a more progressive reduction. The data and information obtained can help optimize the parameters in the recycling of Li-ion batteries.