Selective Electrodeposition of Cobalt from Lithium–Ion Battery Cathodes via Speciation Control and Surface-Modified Porous Electrodes

Abstract

Electrochemical separations have emerged as cost-effective and sustainable pathways for battery recycling. To address the challenge of cobalt–nickel separation from lithium nickel manganese cobalt oxide (NMC) cathodes in spent batteries, we present a synergistic strategy that integrates ion speciation control with surface modification of nanoporous membrane electrodes to drive Co-selective electrodeposition. Introducing the chelating agent ethylenediaminetetraacetic acid (EDTA) to a Co–Ni solution converts most Ni2+ cations into NiEDTA2– anions while leaving the majority of Co as Co2+ cations. Continuum modeling reveals that selective complexation of Ni2+ ions in the bulk solution enhances the local concentration of electroactive Co2+ over Ni2+ near the electrode, which coupled with the intrinsically faster charge-transfer kinetics of Co electrodeposition yields highly Co-rich deposits. Coating the nanoporous polycarbonate membrane with the negative polyelectrolyte poly(styrenesulfonate) (PSS) is seen to further enhance the Co/Ni atomic ratio in the deposits, which our continuum model indicates is due to the PSS surface chemistry rather than its charge, which preferentially enriches Co2+ over Ni2+ in the pore channels. The combined effect of speciation and PSS surface chemistry allows electrodeposition of Co-rich nanorods/tubes in a Co-Ni-EDTA mixture solution with a peak Co/Ni atomic ratio close to 40. Furthermore, the proposed system could recover cobalt from commercial NMC cathodes with a metal-based purity of 98.8% through two sequential deposition steps. This strategy highlights the potential of combining speciation chemistry with electrokinetic control to enhance the selectivity in electrochemical metal recovery.