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PIMs May Be the Cup of Choice for Lithium-Sulfur Batteries

posted Dec 3, 2015, 3:50 PM by Frederick Schuchardt   [ updated Dec 3, 2015, 4:02 PM ]

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. This substantially smaller pore size provides highly selective control over the ions transported through the membrane. Smaller ions, like lithium and sodium are allowed to pass through the membrane while larger polysulfides are blocked. When integrated into lithium-sulfur cells, PIM membranes proved 500 times more effective at blocking the unwanted crossover of polysulfide ions than conventional membranes.
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