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

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.