Upcycling the Lithium Extraction By-products from Spent Lithium-ion Batteries into High-voltage Polyanionic LiMnxFe1-xPO4

Abstract

Lithium iron phosphate (LiFePO4, LFP) and lithium manganese oxide (LiMn2O4, LMO) batteries dominate the energy storage market due to their superior safety, thermal stability, and cost-effectiveness compared to nickel-cobalt-manganese (NCM) oxide-based systems. However, the imminent retirement of these batteries necessitates sustainable recycling methods. Conventional hydrometallurgical and pyrometallurgical processes hold a dominant position in the present lithium recovery industry, but generate low-value by-products such as FePO4 and MnO2, majority of which are discarded, causing issues of resources waste and environment pollution. Herein, we propose a upcycling protocol to transform these FePO4 and MnO2 residues into LiMnxFe1-xPO4, a promising cathode material renowned for its high operating voltage, enhanced energy density, and structural robustness. Specifically, the recovered FePO4 and MnO2 were mixed with lithium and carbon sources in designed molar ratios and then subjected to solid-state reaction at high temperatures to produce LiMnxFe1-xPO4. The synthesized LiMn0.3Fe0.7PO4/C cathode material with a homogeneous carbon coating exhibits remarkable electrochemical performance with a large specific capacity of 164.44 mAh·g-1 at 0.1 C, high rate capability (121.73 mAh·g-1 at 10 C) and great cycling stability (97.46% capacity retention after 500 cycles at 1 C). Notably, the regenerated cathode material after Mn doping delivers about 20% greater energy density than the regenerated LFP. This work establishes a scalable and eco-efficient methodology for closed-loop battery recycling, successfully addressing critical challenges in resource utilization and high-value material synthesis for advanced energy storage systems.