Stabilizing electrode-electrolyte interface via crown ether-containing selective coating for dendrite-free Na-K anode-based solid-state sodium batteries

Abstract

Sodium-potassium (Na-K) alloy is considered a promising anode material due to its liquid characteristics at room temperature. However, unstable interfaces and disastrous ion exchange between Na-K alloy anodes and solid-state Na electrolytes (SSNEs) have hindered further applications of solid-state Na batteries (SSNBs) based on Na-K anodes. In this work, a specially designed Na+/K+ selective gel coating with 15-crown 5-ether (15C5) is constructed on the beta-alumina solid electrolyte (BASE) to achieve a good match with Na-K anodes. The coordination of 15C5 with Na+ forms Na+-permeable complexes and affects the electrolyte solvation structure in the gel coating, resulting in the formation of solid electrolyte interfaces (SEIs) that lack K+ channels and are organically rich, which effectively inhibit the ion exchange and stabilize the interface. Benefitting from the selective coating, the cycling lifetime of the Na-K|Gel-BASE-Gel|Na-K symmetric cell reaches over 1000 h, and the Na-K|Gel-BASE-Gel|Na3V2(PO4)3 full cell exhibits great long-cycle stability and excellent rate performance at room temperature. This work extends the application of Na-K anodes and provides a suggestion for achieving high-performance SSNBs at room temperature.