Chalcogen cathode and its conversion electrochemistry in rechargeable Li/Na batteries

Chalcogen elements, such as sulfur (S), selenium (Se), tellurium (Te) and the interchalcogen compounds, have been studied extensively as cathode materials for the next-generation rechargeable lithium/sodium (Li/Na) batteries. The high energy output of the Li/Na-chalcogen battery originates from the two-electron conversion reaction between chalcogen cathode and alkali metal anode, through which both electrodes are able to deliver high theoretical capacities. The reaction also leads to parasitic reactions that deteriorate the chemical environment in the battery, and different cathode-anode combinations show their own features. In this article, we intend to discuss the fundamental conversion electrochemistry between chalcogen elements and alkali metals and its potential influence, either positive or negative, on the performance of batteries. The strategies to improve the conversion electrochemistry of chalcogen cathode are also reviewed to offer insights into the reasonable design of rechargeable Li/Na-chalcogen batteries.