Rationally designed alloy phases for highly reversible alkali metal batteries

Alkali metal batteries (AMBs) have been recognized one of the most promising battery systems owing to the remarkable theoretical capacities and low redox potentials of alkali metals, enabling a high energy density of over 500 Wh kg−1. However, the problematic dendrite growth and huge volume variation during the iterative plating/stripping processes lead to inferior Coulombic efficiency, short lifespan, and even safety issues. Constructing metal alloy-based phases in the bulk or on the surface of alkali metals has been proved to be effective for improving the cyclic stability and longevity of AMBs. This review reports recent developments in the creation of alloy phases for reversible alkali metal plating/stripping. The fabrication methods of alkali metal-containing hosts and protective layers are also overviewed and compared. Finally, we discuss the challenges and potential directions of constructing alloy phases to prolong the lifespan and safety of AMBs.