Exploring and Understanding the Roles of Li2Sn and the Strategies to beyond Present Li-S Batteries

Li-S batteries have long been at the pinnacle in the realm of high-energy Li-metal batteries. Although valuable progress has been made in the last few years, there is not yet any report with stable theoretical capacity output due to the complexity of electrode conversion reactions during battery operation, which is the intrinsic bottleneck to realize the full potential of Li-S batteries for practical application. In this Review, we take a mechanism-oriented view into Li-S batteries. The principles, strategies, and in-operando characterization techniques to understand the effects of Li2Sn in sulfur cathode and Li anode are summarized to elucidate the surface electrochemical and chemical reactions on electrodes. New insights are also prospected to design Li-S batteries and to satisfy the high expectation in the future, including the requirement to design advanced sulfur cathode and Li anode, various Li-S battery construction strategies, and novel characterization ways to investigate single electrode and whole cell.