Rechargeable Sodium Solid‐State Battery Enabled by In Situ Formed Na–K Interphase

Abstract Solid‐state metal batteries have displayed great advantages in the domain of electrochemical energy storage owing to their remarkably improved energy density and safety. However, the practical application of solid‐state batteries (SSBs) is still greatly impeded by unfavorable interface stability and terrible low temperature performance. In this work, a local targeting anchor strategy is developed to realize an impressively long cycling life for a NASICON‐based solid‐state sodium metal battery at 0 °C. With the electrochemical migration of K + from the cathode side to the anode side, a spontaneous generated liquid Na–K interphase can stabilize the ceramic electrolyte/metallic Na anode interface, and address the issues of sluggish kinetics at the interface together with metal dendrite deposition. In addition, the capability of K + conduction in NASICON is also theoretically and experimentally validated. Of particular note, a K 2 MnFe(CN) 6 cathode paired with a Na 3 Zr 2 Si 2 PO 12 ceramic electrolyte and metallic Na anode, enable the long‐term cycling and excellent rate capability of all‐solid‐state sodium batteries at 0 °C. Without the purposely designed matrix host for a liquid Na–K interphase, this work opens up a new route for the design of high energy density SSBs.