Advances on Na-K liquid alloy-based batteries

Sodium-potassium (Na-K) liquid alloys attract increasing research attention, as an ideal alternative of Li metal for metal-based batteries, attributing to their high abundance, low redox potential, high capacity, and dendrite-free properties. In addition, the liquid and self-healing features of Na-K alloys endow good electrode/electrolyte interfacial contact. The recent advances on the Na-K liquid alloy-based batteries (NKBs) are reviewed herein. The anode designs for immobilization of the liquid alloy are introduced. The influences of the electrolyte and cathode materials on the battery performances are discussed. In addition, considering the co-existence of both K+ and Na+ in the electrolyte, the working mechanisms of the NKBs are elaborated. We also show that despite the improvement, challenges of the NKBs remain. The compatibility between Na-K liquid alloy and electrolyte, as well as disputed working mechanisms, request detailed surface analyses of the liquid alloy and local element distribution evolution in the battery. This review would shed light on the fundamental understanding of Na-K alloy electrochemistry and the development of dendrite-free metal-based energy storage systems with high energy density.