Potassium Pyrosulfate-Assisted Roasting and Water Leaching for Selectively Li and Fe Recycling from Spent LiFePO4 Batteries

Abstract

In the era of extensive deployment of LiFePO₄ batteries in energy storage and electric vehicle domains, the recycling of lithium from spent LiFePO₄ (SLFP) batteries has emerged as a focus, which helps in alleviating environmental pollution and resource shortages. Traditional recycling techniques, encompassing pyrometallurgical and hydrometallurgical methods, are often marred by low selectivity and extraction efficiency. Herein, an eco-friendly and low-consumption recycling strategy involving potassium pyrosulfate (K₂S₂O₇)-assisted low-temperature roasting and subsequent water leaching has been developed for selectively recycling Fe and Li from SLFP batteries. The proposed strategy, compared to the conventional inorganic acid leaching method, mitigates the environmental hazards caused by acidic wastewater generation and reduces the costs associated with wastewater treatment. Investigations of thermal performance characterization and thermodynamic calculation analyses have revealed that K₂S₂O₇ plays a pivotal role in extracting lithium from the Fe–P–O framework, converting lithium into a soluble sulfate variant and iron into insoluble compounds. This process culminates in the segregation of a lithium-rich leachate and an iron-enriched residue, which are further processed to synthesize Li₂CO₃ and FePO₄. The effects on Li leaching of the mass ratio of K₂S₂O₇ to SLFP, roasting time, roasting temperature, and water leaching time are systematically studied and 95.87% Li was leached in water under optimal conditions. In addition, the feasibility of the strategy was further illustrated by the regeneration of LiFePO₄ produced by the recycled Li₂CO₃ and FePO₄. Overall, this recovery strategy stands out for its effective lithium-iron segregation, environmental sustainability, and economic viability, which provide some inspiration for high-efficiency and environmentally friendly recovery metal from spent lithium-ion batteries.