Selective Lithium Recovery from Spent Lithium Iron Phosphate Batteries Used in Solar Energy Storage

The growing adoption of lithium iron phosphate (LiFePO4, LFP) batteries in renewable energy storage systems is expected to generate substantial volumes of end-of-life batteries, presenting both waste-management challenges and opportunities for critical-mineral recovery. Although lithium recovery from spent LFP batteries has been widely investigated, many hydrometallurgical processes employ strong inorganic acids, external heating, and finely ground feed material. Comparatively few studies have specifically examined selective lithium recovery from end-of-life LFP batteries used in stationary solar-energy-storage systems. This study investigated the selective recovery of lithium from spent solar-energy-storage LFP batteries using an acetic acid–hydrogen peroxide leaching system. Cathode active material (CAM) recovered from spent batteries was characterized and subjected to scouting and OFAT optimization experiments. The optimized conditions comprised 100% stoichiometric acetic acid addition, 275% stoichiometric H2O2 addition, an initial ambient temperature, a pulp density of 20% (w/w) solids, a residence time of 1 h, and unmilled CAM with 85% (w/w) passing 850 µm. Three independent confirmatory experiments achieved mean leaching efficiencies of 95.382 ± 0.109% for Li, 0.089 ± 0.008% for Fe, and 0.009 ± 0.002% for P. XRD analysis identified heterosite (FePO4) as the dominant crystalline phase in the residue, with semi-quantitative analysis indicating an approximate phase proportion of 96%, supporting the selective delithiation of the LFP structure. The process produced a lithium-rich leachate and an FePO4-rich residue under mild operating conditions without external heating or additional grinding. These findings demonstrate the potential of the acetic–H2O2 system for the selective hydrometallurgical recovery of lithium from spent LFP batteries.