Poreless Separator and Electrolyte Additive for Lithium–Sulfur Batteries with High Areal Energy Densities

Abstract Despite the attractive theoretical capacity of sulfur over 1600 mA h g⁻¹, lithium–sulfur (Li–S) batteries suffer from insufficient cycle lives mainly due to fatal polysulfide dissolution. This chronic drawback becomes amplified at high areal capacities, especially close to commercial levels (i.e., >3 mA h cm⁻²). Here, we introduce an integrated approach of adopting poreless urea–urethane copolymer (spandex) separator and cesium nitrate (CsNO₃) electrolyte additive. The spandex separator prevents soluble polysulfides from reaching Li metal anode and also suppresses Li dendrite growth via its intrinsic wet adhesion. When combined with a sulfur–carbon composite cathode, the cell based on the spandex separator and the electrolyte additive delivers a high areal capacity of 4 mA h cm⁻² with decent cycling performance, such as 79.2 % capacity retention after 200 cycles with respect to the capacity in the second cycle.