Outline of Li–S Battery Project

In this project, Li–S batteries have been investigated by a team comprising 12 principal investigators. In particular, we focused on developing Li–S batteries with sparingly solvating electrolytes for cathode active materials. Prior to the start of our project, the dissolution of the discharge products of sulfur (lithium polysulfides: Li2Sx, x = 8 ~ 2) was considered to be inevitable, which resulted in a decrease in the amount of cathode active materials and served as a redox shuttle. We thermodynamically suppressed the dissolution of Li2Sx by the development of two different materials. One of these are the sparingly solvating electrolytes, which have intrinsically low solubility toward Li2Sx. The other materials are the microporous carbon substrates in which sulfur is encapsulated, where the direct contact between electrolyte solvent and Li2Sx is not possible and therefore, Li2Sx cannot be dissolved into electrolyte. We set a target performance for two different Li–S battery systems. One is the Li–S battery using metallic lithium anode, where the target performance is 300 Wh/kg for energy density. The other includes graphite/Si–Li2S battery using Li2S cathode, where the target performance is 200 Wh/kg for energy density. In this part, the state-of-the-art of our project is briefly interpreted.