Lithium–sulfur (Li–S) rechargeable batteries have been expected to be lightweight energy storage devices with the highest gravimetric energy density at the single-cell level reaching up to 695 Wh/kg-cell (a low rate of 0.005C, only in the first discharge). Sulfurized polyacrylonitrile (SPAN) is one of the sulfur-based active materials, which allows more freedom in the Li–S cell design because it shows no undesirable reactions with electrolyte solutions. An original Li–S pouch cell construction (ADEKA’s Lithium–Sulfur/Pouch Cell : ALIS-PC), the world's lightest rechargeable battery cell was designed by combining the SPAN cathode and state-of-the-art technologies. As a result, the highest gravimetric energy densities of 713 and 761 Wh/kg-cell after some charge-and-discharge cycles, which were based on the total mass of all cell components, were achieved with successful operating at 0.1 and 0.05C-rates, respectively, which significantly exceeded those of commercial lithium-ion and developed next-generation rechargeable batteries.