The selective separation of Ni, Co, and Mn from spent lithium-ion batteries remains difficult because these ions often show similar solubility and coordination behaviour in conventional leaching media. Herein, we design a sequence of solvent-controlled coordination environments to amplify these otherwise subtle differences while retaining solvent regenerability. Li is first extracted in a low-water formic acid medium, where lithium formate is highly soluble but transition-metal formates are poorly soluble. The remaining Ni, Co, and Mn formates are then transferred into an anhydrous choline chloride/formic acid deep eutectic solvent (DES). In this chloride/formate medium, ligand competition differentiates the transition metals: Ni2+ favours a mixed Cl−/HCOO− octahedral coordination structure and is retained as a low-solubility solid, whereas Co2+ and Mn2+ are stabilized as chloride-rich tetrahedral complexes in the DES. Ethanol addition subsequently weakens this chloride-dominated solvation environment, enabling Co/Mn precipitation, followed by pH-controlled sulfide chemistry for their separation. By progressively engineering distinct coordination environments, this strategy enables the efficient recovery of Li, Ni, Co, and Mn from NCM cathodes while maintaining complete solvent regenerability. The work demonstrates how solvent coordination design can translate intrinsic metal–ligand preferences into practical separation selectivity, establishing a general strategy for closed-loop recycling of spent lithium-ion batteries.
