Dendrite-free and gasless potassium metal anodes assisted by the mechanical-electrochemical enhancing solid K-electrode and electrolyte interface

•For the most reducible potassium metal anode, this is the first attempt to regulate gas production by using NaNO3 as an electrolyte additive.•The mechanical-electrochemical interface in situ was constructed by introducing NaNO3, which reduced side reactions and relieved interface stress.•By introducing NaNO3, the potassium salt anion structure was designed to stabilize the electrolyte. With their high-energy density and low-price advantage, potassium (K) metal batteries have been considered the next generation of energy storage system. However, applications of K metal anode are always obstructed by severe side reactions and rapid growth of K dendrites upon cycles due to the fragile solid electrolyte interface (SEI). Herein, a novel mechanical-electrochemical stability enhancement interface is constructed through potassium salt anion structure design and in-situ ion exchange reaction, which enables SEI with reducing side reactions and relieving interface stress during cycling process. The batteries with the designed SEI could deliver excellent performances with a high average Coulombic Efficiency of 95.91 %, a critical current density of 7.5 mA cm−2 and a durable stability of more than 1350 h (0.1 mA cm−2). This work provides an effective strategy to construct a high-energy and stable K metal anode interface and will inspire the electrolyte design for other alkali metal batteries.