Acid-Free and Synergistic Extraction of Li and Mn from Spent Lithium-Ion Batteries and Direct Resynthesis of Lithium Manganate Cathode Material

This study proposes a novel acid-free leaching method based on controlled (NH 4 ) 2 SO 4 roasting, which achieves efficient and selective co-extraction of Li and Mn while enriching Ni and Co in the oxide residue, thereby reducing the complexity of downstream transition-metal separation. The phase transformation pathway from complex sulfate intermediates (LiNH 4 SO 4, Li 2 TM(SO 4 ) 2 ) to final Li 2 SO 4, MnSO 4, NiO, and CoO is elucidated, revealing a thermodynamically driven ion-exchange mechanism that directs Li and Mn into the sulfate phase while stabilizing Ni and Co as divalent oxides. Under optimized conditions (550 °C, n [(NH 4 ) 2 SO 4 ]: n [2Li + Mn] = 1.2, 180 min), the water leaching efficiencies of Li and Mn reach 99.75% and 92.4%, respectively, while the co-dissolution rates of Co and Ni are only 6.4% and 0.55%. The resulting leachate directly yields a trace Ni/Co-doped lithium manganate cathode material (LiMn 1.89 Co 0.09 Ni 0.02 O 4 ) with an initial discharge capacity of 105.0 mAh/g. Techno-economic analysis indicates that this strategy achieves a 40.3% reduction in carbon emissions, offering both economic and environmental benefits. This study transforms the conventional selective Li extraction into synergistic Li–Mn co-extraction and establishes a short-process recycling and regeneration route from spent NCM to LiMn 2 O 4, providing a new paradigm for the precise separation and high-value regeneration of critical battery metals.