Advances in K-Q (Q = S, Se and SexSy) batteries

Metal-sulfur batteries are advanced energy storage systems featuring intriguingly high theoretical capacity and high energy density. Spurred on by the failures in commercializing Li-S and Na-S batteries, K-Q (Q = S, Se, and SexSy) batteries have entered the sights of researchers because of the low redox potential and natural abundance of element K and its synergistic reaction with S or Se. Unfortunately, the current K-Q battery still suffers from several drawbacks, such as drastic volume change, shuttling phenomenon, relatively low reactivity, and dendrite growth. To help to push forward progress of the K-Q battery, here in this review, we first introduce the operation principle and the fundamental challenges faced by the current K-Q batteries, followed by a comprehensive review of effective strategies that have been developed, including engineering of the electrode structure and optimization of the battery composition. Discussions of the mechanism are also included to deepen the understanding of such battery systems. Finally, we discuss the perspectives and challenges for practical application of K-Q batteries. We hope the insights provided in this review can shed light on this new yet rapidly developing field and offer guidance for the development of future high-performance K-Q batteries.