Using green deep eutectic solvents for targeted regeneration to improve the cycle life of spent lithium iron phosphate batteries

Abstract

The rapid growth of lithium iron phosphate (LFP) batteries used in electric vehicles and energy storage systems has necessitated the development of sustainable and efficient recycling strategies to address impending end-of-life management challenges. Conventional pyrometallurgical and hydrometallurgical methods often require high energy consumption, cause environmental pollution, and suffer from economic inefficiency. In this study, a green deep eutectic solvent (DES) system, composed of lithium chloride, urea, and ascorbic acid, was developed for the direct regeneration of degraded LFP cathodes. Through integrated experimental and theoretical approaches, the regeneration mechanism was elucidated, wherein a reductive environment was provided for the conversion of Fe³⁺ to Fe²⁺, and highly efficient Li⁺ replenishment into vacant sites was achieved. The regenerated cathode material was shown to exhibit a high specific capacity of 163.5 mA h g⁻¹ at 0.1C and excellent cycling stability, with 92.6% capacity retention after 300 cycles at 1C. With significantly reduced energy consumption and economic cost compared to conventional hydrometallurgical and pyrometallurgical routes, this DES-based regeneration method presents a highly promising and sustainable pathway for resource recovery from spent lithium-ion batteries.