Flow through negatively charged, nanoporous membranes separates Li+ and K+ due to induced electromigration

Abstract

Flow through negatively charged nanopores separates Li⁺ and K⁺ with selectivities of up to 70 and Li⁺ passages from 20% to above 100%. Remarkably, both the Li⁺/K⁺ selectivity and Li⁺ passage initially increase with flow rate, breaking the permeability/selectivity trade-off. Modelling demonstrates that flow through the membranes creates electric fields that retard transport of cations. Selectivity increases with flow rate because the K⁺ electromigration velocity exceeds its convective velocity, but for Li⁺ electromigration is weaker than convection. Modelling also shows the importance of controlling concentration polarization. With further work, related separations might provide highly pure Li salts for battery manufacturing.