Dendrite-free lithium metal and sodium metal batteries

Lithium and sodium metal batteries (LMBs, SMBs) with high theoretical capacities and high energy densities have attracted tremendous attention as a new class of energy storage devices. However, these metal batteries usually suffer from uneven metal plating/stripping behavior, continuous side reactions between lithium/sodium metal and electrolyte as well as uncontrollable dendrite growth, seriously hampering their practical applications. To address the abovementioned issues, multi-level strategies have been explored. Studies reveal a few potential solutions: namely, to reduce the local current density of anodes, to form flexible solid-electrolyte interface (SEI) films, to increase the number of metal ion transfer paths, and to improve the shear modulus of electrolytes. This review is aimed to summarize recent advances in rational design of dendrite-free LMBs and SMBs by means of modulation of metal anodes, optimization of electrolytes and modification of separators. The original design concepts, synthesis approaches and their effects on electrochemical performance of metal batteries are discussed. The challenges encountered for future development of dendrite-free LMBs and SMBs are proposed. It is hoped that this review will provide new insights into their technological development and real-world applications.