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 important for the 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), enabling efficient extraction of lithium from spent LiFePO₄ dispersed in the electrolyte. The results indicate that when the electrolysis is performed under a voltage of 3.8 V, the leaching efficiency of lithium from LiFePO₄ reaches ∼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 negligible 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 the stability of FePO₄. More importantly, 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 the Ti₄O₇ electrode, forming a triple oxidation synergy to facilitate the transformation of Fe²⁺ to Fe³⁺ in LiFePO₄, thus efficiently releasing Li⁺ and forming FePO₄. The above has been confirmed by means of a series of comparative experiments and spectroscopic measurement results. Both thermodynamic and kinetic studies have shown that this synergistic oxidation strategy is highly efficient, which will be helpful for the scalable and eco-friendly recycling of spent LiFePO₄ batteries.