Recycling Spent LiMn2O4 and Resynthesizing Olivine-Type Cathode via Sulfating–Roasting and Al Doping for Enhanced Stability

Abstract Restricted by complex processes, high energy consumption, and poor economic traits, the recycling of LiMn2O4 (LMO) is facing serious challenges. Focusing on these challenges, an upcycling strategy of low-value spent LMO converted into high-value LiMnxFe1–xPO4 (LMFP) is proposed. Supported by the sulfating–roasting–water leaching process, spent LMO could be efficiently converted into soluble Li2SO4 and insoluble Mn3O4, which achieved 99.6% Li leached and avoided Mn leaching (<0.4%), successfully preparing high-purity Li2CO3 products. Additionally, the prepared Li2CO3 and Mn3O4 could be utilized as raw materials to fabricate LMFP, and optimized samples with a tailored Mn/Fe ratio (6:4) exhibit excellent rate capability and reversibility. Applied as the cathode, the initial discharge capacity reaches 148.5 mAh g–1 at 0.1C, with 87.35% capacity retention after 500 cycles at 1.0C, and 107.6 mAh g–1 even at 10C. Furthermore, the potential impact of Al impurity in practical recycling is investigated. Moderate Al doping (0.2 wt % as LMFP/C-0.2A) significantly enhances the long-cycle stability and Li+ diffusion kinetics, delivering a high discharge capacity of 125.2 mAh g–1 at 10C, with capacity retention of 83.05% after 1000 cycles at 5C. This paper reveals the potential value of LMFP material regeneration and provides an economically viable strategy for the upcycling of low-value spent LMO materials.