A Bipolar Pulsed Electrodeposition Method to Selectively Separate Cobalt and Nickel from Spent Lithium-Ion Battery (LIB) Cathodes

Growing demand for electric vehicles has intensified the need for sustainable recovery of critical metals from end-of-life lithium-ion batteries (LIBs). A specific challenge is the separation of Ni and Co due to nearly identical coordination chemistry and redox potentials. Here, we report a bipolar pulsed electrodeposition strategy in reline deep eutectic solvent (DES) that enables selective separation of Ni and Co without the use of aqueous acids or organic extractants. Spectroscopic analyses reveal that Ni2+ and Co2+ exist predominantly as tetrahedral [NiCl4]2- and [CoCl4]2- complexes in reline, while cyclic voltammetry shows distinct redox kinetics that can be temporally modulated through alternating cathodic and anodic pulses. This dynamic control drives preferential Ni deposition and rapid Co stripping, producing progressively Ni-enriched films with tunable morphologies. COMSOL simulations reproduce the periodic current response and confirm that selectivity arises from kinetic asymmetry rather than equilibrium speciation. These findings establish the use of bipolar pulsed electrodeposition for targeted separation of Ni and Co, offering a green perspective for green electrochemical metal recovery and circular battery resource management.