<p>The increasing demand for valuable materials and the enforcement of environmental regulations have made sustainable recycling solutions for spent lithium-ion batteries more necessary than ever. This study develops an integrated recycling route for spent lithium-ion batteries that combines thermal pretreatment, ultrasonic delamination, oxalic-acid hydrometallurgical leaching, and direct precipitation to selectively recover lithium. Under optimized conditions, lithium was selectively dissolved while cobalt, nickel, and manganese were retained in the solid phase as mixed metal oxalates. Lithium was ultimately recovered as high-purity Li₂CO₃ (97.2 pct), achieving an overall lithium recovery efficiency of approximately 80 pct. Unlike conventional methods, this technique achieves high-purity lithium carbonate without harsh acids or complex separation steps, offering a simplified, environmentally compatible pathway for lithium recovery from end-of-life lithium-ion batteries.</p>