Towards economically feasible recycling of spent LiFePO4 black mass: a thermodynamic-assisted targeted delithiation strategy

Abstract

The recycling of spent LiFePO₄ batteries is hindered by economic inefficiencies, primarily due to poor selectivity during lithium recovery. Here, we introduce a thermodynamic-assisted electrochemical delithiation strategy to achieve high-purity lithium extraction. By refining the thermodynamic models of the Li–Fe–P–H₂O system, we delineate a precise operational window (pH 4.0–5.2 and an oxidation potential of 0.15–0.4 V) that favors Li⁺ removal while stabilizing the FePO₄ framework, as verified by in situ electrochemical quartz crystal microbalance measurements. Crucially, we uncover that trace yet persistent iron dissolution originates from a proton-coupled reaction that forms an unstable HFePO₄ intermediate, a previously overlooked mechanism that redefines the stability limits of the material in aqueous media. This study establishes a targeted, energy-efficient recycling pathway and provides fundamental insights into ion-exchange dynamics in olivine-type cathodes.