Lawrence Berkeley National Laboratory

Here, we lay the design rules for linking microporous polymer membrane architecture and pore chemistry to membrane stability, conductivity, and transport selectivity in aqueous electrolytes over a broad range of pH. We tie these attributes to prospects for crossover-free electrochemical cell operation. These guiding principles are applied to two emerging cell chemistries for grid batteries: specifically, Zn–TEMPO-4-sulfate and Zn–K4Fe(CN)6 cells. Key to our success is the placement of ionizable amidoxime functionalities, which are stable at high pH, within the pores of microporous ladder polymer membranes, yielding a family of charge-neutral and cation exchange membranes at low and high pH, respectively—which we call AquaPIMs. Their notably high conductivity (up to 21.5 mS cm−1 in 5.0 M aqueous KOH) and high transport selectivity (up to 104 reduction in active-material permeability through the membrane) suggest exciting opportunities for battery development, even beyond those presently demonstrated.