Redox-Mediated Upcycling of Mixed Spent LiFePO4 and LiMn2O4 into High-Voltage LiFexMn1–xPO4 Cathodes without External Reagents

The continuous accumulation of spent LiFePO4 (S-LFP) and LiMn2O4 (S-LMO) cathodes demands efficient and sustainable recycling strategies, as conventional hydrometallurgical processes rely heavily on external redox agents, increasing the cost and environmental burden. This study proposes an innovative synergistic leaching process that enables the upcycling of mixed spent LFP and LMO into high-voltage LiFexMn1–xPO4 (LFMP) without any additional redox agents. We established a multireaction feedback system centered on self-redox in a sulfuric acid medium through the design of multiple sets of experiments for verification, achieving highly efficient leaching of Li (99.5%), Mn (99.2%), and Fe (99.6%) under optimized conditions (H2SO4–metal molar ratio of 2, liquid–solid ratio of 5, temperature of 30 °C, and time of 120 min). The leachate was subsequently converted to an Fe–Mn–P composite precursor and then upcycled into LFMP. The regenerated LiFe0.4Mn0.6PO4 cathode delivers a remarkable energy density of 557.67 Wh kg–1 at 0.2 C, significantly surpassing that of commercial LFP and LMO. Electrochemical analysis confirmed that the diffusion capability of Li+ within the Mn reaction region is critical for the unlocking of energy density for LFMP electrodes. Economic and environmental assessments further confirmed the superior profitability (2.24 $ kg–1) and reduced greenhouse gas emissions of this synergistic upcycling route, demonstrating its potential as a sustainable and economically viable strategy for recycling multisource spent cathodes into new-generation high-energy-density materials.