Complexation-driven ion-exchange polymer inclusion membranes for separation of cobalt and nickel ions from lithium-ion via proton pumping

Abstract

Cobalt and nickel are vital components of lithium-ion battery (LIB) cathodes; their increasing demand requires efficient recovery from spent LIBs to foster a sustainable battery future. The limitations of current separation technologies necessitate the development of more cost-effective, efficient, and eco-friendly metal recovery methods. Herein, we developed a complexation-driven ion-exchange polymer inclusion membrane (IEPIM) by confining an ionic liquid (IL) and a protic extractant in a polymer host to separate cobalt and nickel ions from lithium ions. While past studies achieved selective separation of cobalt ions using basic extractants in aqueous chloride solutions, this study utilizes a protic extractant to achieve a multi-ion separation in aqueous solution. Our approach relies on proton pumping facilitated by the protic extractant, making the separation process effective while avoiding harmful organic solvents. The IEPIM made from 50% PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) as the polymer host, 30% Cyanex 301 (bis(2,4,4-trimethylpentyl) dithiophosphinic acid) as the protic extractant, and 20% [C₈mim][NTf₂] (1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) as the plasticizer, efficiently separates Co²⁺ and Ni²⁺ from Li⁺ in aqueous solution, with over 90% transport efficiency for Co²⁺ and 73% for Ni²⁺. The membrane maintained this efficiency through three cycles, indicating its stability. These results demonstrate that the IEPIM could be a viable alternative to conventional metal ion separation methods, offering an environmentally sustainable and cost-effective strategy for recycling critical metals from spent lithium-ion batteries with the potential for industrial application in separation technology.