Defect-tailored graphite recovery from spent LIBs using natural deep eutectic solvents

Abstract The impurities and structural cracks within spent graphite (SG) in lithium-ion battery anodes hamper lithium-ion intercalation and extraction after successive charge-discharge operations, thereby yielding poor lithium storage behavior. Herein, low-viscosity natural deep eutectic solvent (NDES) composed of citric acid (CA) and betaine hydrochloride was employed to remove the organic impurities in SG via a one-step benign process involving hydrogen bonds and electrostatic interactions at mild conditions of 80 °C for only 30 min. After NDES leaching under optimal conditions (molar ratio of CA to betaine hydrochloride = 3:1, 80 °C, 30 min), the as-obtained sample (denoted as BG-3) exhibited an extremely clean surface, moderately enlarged interlayer distance, and more structural defects at the edge of graphite lamellae. These features facilitated lithium-ion intercalation and withdrawal, bestowing BG-3 with remarkable activity in lithium-ion battery (LIB) recycling. For instance, BG-3 delivered a capacity of 438.6 mAh g −1 at a current density of 0.1 A g −1 . Its capacity retention reached 97.9%, accompanied by a Coulombic efficiency of 99.1%, upon completing 100 cycles. A molecular dynamics simulation was employed to illuminate the regeneration mechanism for anode graphite from a theoretical perspective. It revealed that NDES exhibits lower binding energy with all contaminants compared to graphite, which is favorable for NDES to eliminate impurities from graphite surfaces. This study unveils a method of recycling SG from retired LIBs by a short eco-friendly process, providing a competitive blueprint to address the shortage of battery-grade anode graphite and to achieve carbon neutrality.