Membranes based on PIMs feature subnanometer-sized pores that allow smaller ions such as LiTFSI to pass through while blocking larger polysulfide ions (Li2Sx). This selectivity prevents unwanted crossovers that reduce battery lifetimes and performance.
Renewable sources of energy including solar and wind are fast gaining ground on fossil fuels, in part because of their sustainability and environmental benefits. A major issue, however, has been finding efficient ways to store the energy that renewables generate for use when the demand for energy is high. Lithium-sulfur batteries, which store electrical energy by transferring electrons to or from a sulfur electrode are well poised to provide high-density, long-term and low-cost electrochemical energy storage. The potential of lithium-sulfur batteries, has yet to be fully realized, however, due to the uncontrolled migration of soluble sulfur species through the membrane that separates the electrodes. This crossover of polysulfides reduces battery efficiency and lifetime. Berkeley Lab researchers have found a solution to the polysulfide crossover problem with the development of a membrane made from polymers of intrinsic microporosity (PIMs). PIMs feature pore sizes of less than one nanometer in diameter, compared to the 17 nanometer pore size of typical membrane separators.
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