Structural Design of Cathodes for Li-S Batteries

Battery technologies involving Li-S chemistries have been touted as one of the most promising next generation systems. The theoretical capacity of sulfur is nearly an order of magnitude higher than current Li-ion battery insertion cathodes and when coupled with a Li metal anode, Li-S batteries promise specific energies nearly five-fold higher. However, this assertion only holds if sulfur cathodes could be designed in the same manner as cathodes for Li-ion batteries. Here, the recent efforts to engineer high capacity, thick, sulfur-based cathodes are explored. Various works are compared in terms of capacity, areal mass loading, and fraction of conductive additive, which are the critical parameters dictating the potential for a device to achieve a specific energy higher than current Li-ion batteries (i.e., >200 Wh kg^-1). While an inferior specific energy is projected in the majority of cases, several promising strategies have the potential to achieve >500 Wh kg^-1. The challenges associated with the limited cycle-life of these systems due to both the polysulfide shuttle phenomenon and the rapid degradation of the Li metal anode that is experienced at the current densities required to charge high specific energy batteries in a reasonable timeframe are also discussed. Lithium-sulfur batteries promise significant improvements to specific energy over traditional Li-ion batteries. Various cathode design strategies are analyzed in terms of their potential to achieve high practical specific energy, power, and cycle-life. The most promising routes to success and the most significant challenges hindering adoption of Li-S batteries are highlighted.