title: Polysulfide-Blocking Microporous Polymer Membrane Tailored for Hybrid Li-Sulfur Flow Batteries.
abstract: Redox flow batteries (RFBs) present unique opportunities for multi-hour electrochemical energy storage (EES) at low cost. Too often, the barrier for implementing them in large-scale EES is the unfettered migration of redox active species across the membrane, which shortens battery life and reduces Coulombic efficiency. To advance RFBs for reliable EES, a new paradigm for controlling membrane transport selectivity is needed. We show here that size- and ion-selective transport can be achieved using membranes fabricated from polymers of intrinsic microporosity (PIMs). As a proof-of-concept demonstration, a first-generation PIM membrane dramatically reduced polysulfide crossover (and shuttling at the anode) in lithium-sulfur batteries, even when sulfur cathodes were prepared as flowable energy-dense fluids. The design of our membrane platform was informed by molecular dynamics simulations of the solvated structures of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) vs lithiated polysulfides (Li2Sx, where x = 8, 6, and 4) in glyme-based electrolytes of different oligomer length. These simulations suggested polymer films with pore dimensions less than 1.2-1.7 nm might incur the desired ion-selectivity. Indeed, the polysulfide blocking ability of the PIM-1 membrane (∼0.8 nm pores) was improved 500-fold over mesoporous Celgard separators (∼17 nm pores). As a result, significantly improved battery performance was demonstrated, even in the absence of LiNO3 anode-protecting additives.
authors.affiliation: The Joint Center for Energy Storage Research , 1 Cyclotron Road, Berkeley, California 94720, United States.|The Molecular Foundry, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.|Department of Chemical and Biomolecular Engineering, University of California , Berkeley, California 94720, United States.
authors.forename: Changyi
authors.initials: C
authors.lastname: Li
authors.affiliation: The Joint Center for Energy Storage Research , 1 Cyclotron Road, Berkeley, California 94720, United States.|The Molecular Foundry, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Ashleigh L
authors.initials: AL
authors.lastname: Ward
authors.affiliation: The Joint Center for Energy Storage Research , 1 Cyclotron Road, Berkeley, California 94720, United States.|The Molecular Foundry, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.|Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Sean E
authors.initials: SE
authors.lastname: Doris
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Tod A
authors.initials: TA
authors.lastname: Pascal
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: David
authors.initials: D
authors.lastname: Prendergast
authors.affiliation: The Joint Center for Energy Storage Research , 1 Cyclotron Road, Berkeley, California 94720, United States.|The Molecular Foundry, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Helms
keywords: Polymers of intrinsic microporosity; electrochemical energy storage; ion-selective membrane; lithium−sulfur battery; redox flow battery; size-selective membrane