Discharge Pathways and Deactivation Mechanisms of Retired Lithium-Ion Batteries

Discharge is an essential step during the recycling of retired lithium-ion batteries. However, state-of-the-art discharge methods are inefficient and/or contribute to pollution, as the reaction mechanisms underlying different discharge pathways remain poorly understood. To explore reliable, safe, and rapid discharge methods, this research systematically investigated the effects of three discharge pathways, namely, water electrolysis, electrolyte leakage, and short-circuit exothermic discharge, on lithium-ion migration and safety. Moreover, the relationship between the discharge pathways and deactivation mechanisms is clarified. As a consequence, a rapid and safe discharge strategy for retired lithium-ion batteries is developed through a reversed physical short-circuit with which the lithium-ion migration velocity achieves 610.07 mg/h and the energy consumption is reduced by 54.24% compared with traditional physical discharge. The causes of deactivation can be identified including electrolyte decomposition, crystal structure failure in cathode materials, copper foil oxidation of current collectors, and the formation of cracks on the the cathode and anode plates. This study identifies an intrinsically safe and efficient discharge pathway, thereby addressing the issues of low efficiency, pollution, and incomplete discharge associated with current methods and ensuring safe and efficient recycling of retired lithium-ion batteries.