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

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.