A battery separator is an ion-permeable membrane installed between the anode and cathode of the battery to separate the electrodes to prevent short circuits. For Li-S batteries, it is vital that Li⁺-ions can pass, but intermediate reaction products where lithium is chemically bound to sulfur (so-called lithium polysulfides, Li₂S_x) are blocked at the cathode side. 

The goal of the 3S Battery project is to develop highly effective membranes as separators with tailored functionalities using advanced nanostructures and/or coatings to mitigate the issues caused by polysulfide migration and dendrite formation. The defined separator should act as a selective medium that effectively suppresses the polysulfides migration while facilitating the Li⁺ ion transport with uniform distribution. Functional coatings will also reactivate the trapped sulfur to increase cathode efficiency. 

The developed separators are expected to enable Li-S batteries to  achieve high performance as indicated by the project’s key performance indicators (KPI), including high cycle stability of >2000 cycles, corresponding to a capacity decay of ~0.01% per cycle, with an initial discharge capacity of ~1300 mAh g-1  at a 0.1 C.