Electrochemical-assisted triple oxidation strategy to efficiently extract lithium from spent LiFePO4

Abstract

High-efficiency lithium extraction from spent LiFePO4, while maintaining intact FePO4 crystalline structure and composition, is critically important for sustainable recycling of spent LiFePO4 batteries. Here we report an innovative electrochemical-assisted approach that employs a Ti4O7 electrode as the anode to activate peroxydisulfate (PDS), to enable efficient extraction of lithium from spent LiFePO4 dispersed in the electrolyte. The results indicate that the electrolysis performed under a voltage of 0.8 V, the leaching efficiency of lithium from LiFePO4 can reach ~99.8% within 20 min, and the amount of PDS used is only 0.85 times the theoretical value, simultaneously maintaining good crystalline structure and composition of FePO4 with ignorable dissolution of Fe and P elements. This superior performance can be attributed to the electrochemical assistance approach, which can stabilize the solution pH within the range of 2-6 suitable for Li+ extraction and stable existence of FePO4. More impotantly, electroactivation and the Fenton-like effect of Fe2+ activate PDS to generate active free radicals (SO4•⁻ and •OH) for oxidation, direct electrolyte (PDS) oxidation, and electrochemical oxidation on Ti4O7 electrode, forming a triple oxidation synergy to facilitate the transformation of Fe2+ to Fe3+ in LiFePO4 and thus efficiently release Li+ and form FePO4. The above has been confirmed by means of series of comparable experiments and spectroscopic measurement results. Both thermodynamic and kinetic studies have shown that this synergistic oxidation strategy is highly efficient, which would be helpful for scalable and eco-friendly recycle of spent LiFePO4 batteries.