Highly cross-linked carbon sponge enables room-temperature long-life semi-liquid Na/polysulfide battery

Sodium/sulfur (Na/S) batteries are actively studied due to their low cost and potential energy density. Improvements have been achieved in the room temperature Na/S batteries during the last decades, however still with low practical capacity and unstable cycling performance. We hereby report a semi-liquid Na/polysulfide (Na/PS) cell with unique microscale intertwined carbon/polymer sponges to alleviate sulfur loss during cycling. The as-prepared highly cross-linked structure not only facilitates mass transfer but provides functional reservoir to entrap polysulfides. The Na/PS batteries with low electrolyte/sulfur (E/S) ratio (∼4.05 μL/mg) retain 375 mA h/g capacity after 200 cycles. More importantly, the interlinked sponge with high sulfur loading (e.g. 1.9 mg/cm2) restricts the decay rate of open-circuit voltage to only 0.04‰ per hour, which overcomes the severe self-discharge behavior observed in many Na/S cells. The highly cross-linked sponge therefore is an efficient approach to addressing the notorious challenges of Na/PS batteries.