Ultrastable Sodium/Potassium Metal Anode Enabled by a Multifunctional Interphase Layer with Enhanced Ion Transport Kinetics

Abstract Na (K) metal batteries (NMB and KMB) have gained tremendous attention as large‐scale energy storage systems because of their high specific capacity, low working potential, and natural abundance. However, severe Na dendrite growth hinders the practical application of Na (K) anode. Here, a multifunctional interphase layer consisting of fast‐ion conductive Na–Bi (K–Bi) alloy and sodiophilic (potassiophilic) Na₃VO₄ (K₃VO₄) phases, which i derived from a spontaneous reaction (denoted as BVO@Na or BVO@K), is proposed and prepared. The designed electrode exhibits enhanced ion transport kinetics and homogenous Na (K) deposition behavior, and finally achieving dendrite‐free Na (K) growth. Accordingly, the BVO@Na displays a high Na plating/stripping reversibility of 960 h at 1.0 mA cm⁻², 1.0 mAh cm⁻², and the BVO@K electrode can be operated a cycle lifespan of 870 h under 1.0 mA cm⁻², 2.0 mAh cm⁻² in symmetric cells. In BVO@Na||Na₃V₂(PO₄)₃ full battery, it shows remarkable cycling stability (91% of capacity retention after 1900 cycles) and a high energy density of 281 Wh kg⁻¹ at a power density of 16.2 kW kg⁻¹. The findings lend credence to the prospect of the multifunctional interface layer contributing to the design of a protective layer for alkali metal anodes.