Investigations on Discharge Pretreatment of Spent Lithium-Ion Battery: A Review

With the widespread application of lithium-ion batteries (LIBs) in electric vehicles (EVs), the resource recycling of LIBs has received extensive attention and study. Discharge is a small but important subprocess in the spent LIB recycling. Safe and effective discharge can ensure that there are no safety hazards such as fire and explosion in the subsequent recycling. This paper introduces the safe discharge cutoff voltage (SDCV) and voltage rebound (VR), reviews the research progress of conventional physical (energy-saving feedback discharge (ESFD) and physical load discharge (PLD)), chemical (with organic and/or inorganic electrolyte solutions (ESs) as the discharge media), unconventional physical and/or chemical discharge methods, and nondischarge technology (high-temperature incineration, low temperature freezing, and inert gas protection technology). It provides a comprehensive evaluation of diverse discharge pretreatment strategies from multiple dimensions, including discharge efficiency, corrosion behavior, battery types, solution types and concentrations. Finally, their advantages and disadvantages in the applications are discussed, and the research and optimization of spent LIB discharge technology in the future are prospected to achieve safe, efficient, and green recycling of spent LIBs.