Selective Sulfidation and Electrowinning of Nickel and Cobalt for Lithium Ion Battery Recycling

Abstract

Processes for recycling lithium ion batteries (LIB), in particular complex chemistries such as those containing nickel-manganese-cobalt oxide (NMC) cathodes, are hindered by tradeoffs between capital cost, process sustainability, and materials recovery. Most metal separations in primary and secondary production of critical elements rely on anion exchange chemistries. Herein, we explore the application of a novel oxide-sulfide anion exchange methodology to facilitate LIB recycling. Beginning with selective sulfidation of NMC cathode oxides, we demonstrate that lithium may be stabilized as a sulfate, manganese as an oxysulfide, and nickel and cobalt as sulfides from the mixed metal feed, potentially facilitating isolation of lithium via leaching and nickel-cobalt via flotation. Following, we explore molten sulfide electrolysis as a method of process intensification, combining separation and reduction into a single unit operation for difficult to separate metals such as cobalt and nickel. We demonstrate selective reduction of cobalt from mixed nickel-cobalt sulfide, as produced in selective sulfidation of waste NMC cathodes, using a barium-lanthanum sulfide supporting electrolyte. Our preliminary results suggest that selective sulfidation as a pretreatment for selective molten sulfide electrolysis is a promising avenue for separation of critical elements from complicated materials feeds, such as those found in lithium ion battery recycling streams.