Activating Li2S as the Lithium-Containing Cathode in Lithium-Sulfur Batteries

Lithium-sulfur batteries are considered a possible next-generation energy-storage solution, but their commercial viability is still in question because of several technical challenges, including the use of a highly reactive lithium anode. Using Li2S as the cathode to couple with Li-free anodes presents a feasible approach to circumvent the safety issue of lithium. Unfortunately, Li2S is largely electrochemically inert and needs a high activation potential during the initial oxidation. Here, we provide an overview of recent progress on electrochemically activating Li2S as a lithium-containing cathode for lithium-sulfur batteries. We first discuss the origin of its large charging overpotential and current understanding of its activation process. This is then followed by an up-to-date account of different strategies to activate Li2S and promote its electrochemical performance by engineering the electrode material, the cathode catalyst, or the electrolyte. Finally, a short perspective is offered about the possible future directions of this exciting field.