Built-in anionic equilibrium for atom-economic recycling of spent lithium-ion batteries

Abstract

Recycling spent lithium-ion batteries (LIBs) is crucial to address environmental and global sustainability issues. Wet chemical extraction of valuable metals is currently the most practical disposal technology, but it is challenging due to excessive chemical consumption and concomitant secondary pollution. In this study, a built-in anionic equilibrium strategy was proposed to recycle spent LiFePO₄ (sLFP) cathodes with high atom economy. The selective extraction of lithium and phosphorus was successfully achieved in deionized water under oxygen pressure by the anionic equilibrium between OH⁻ produced by oxygen reduction and PO₄³⁻ released from sLFP. The formed LiFePO₄OH phase limited the lithium leaching efficiency to 65.6%, so the trapped lithium was further extracted by rebuilding the anionic equilibrium after adding phosphoric acid with a low H₃PO₄/Li molar ratio. The degraded LiFePO₄ evolved into a fusiform Fe₅(PO₄)₄(OH)₃·2H₂O crystal, and 90.19% of lithium and 19.88% of phosphorus in sLFP can be recovered as Li₃PO₄ products. This built-in anionic equilibrium mechanism contributes to reduce chemical consumption and high-saline wastewater, thus providing a sustainable hydrometallurgical recycling route for spent lithium-ion batteries.