In recent years, metal-oxygen batteries, especially non-aqueous lithium-oxygen batteries (or Li-O₂ batteries), have drawn considerable research attention for future energy storage applications due to high theoretical specific energy densities. Compared to conventional lithium-oxygen batteries, potassium-oxygen (K-O₂) batteries are based on a reversible O₂/KO₂ redox chemistry, resulting in much better round-trip efficiencies (higher than 90%) without using electrocatalysts. While the reversibility of the cathode reactions is improved, the cycling performance of K-O₂ batteries is greatly limited by the K metal anode stability. The highly reducing K anode would react with electrolyte molecules and degrade seriously during cycling. Moreover, the oxygen crossover to the anode further accelerate the degradation process.  Here, we report our studies about the improved K metal anode stability in K-O₂ batteries with concentrated electrolytes. It is shown that in this class of electrolytes, a stable Solid Electrolyte Interface (SEI) layer is critical for protecting the K anode and suppressing the undesired side reactions. As a result, the metal anode cycling efficiency and the cycle life of K-O₂ batteries can be largely increased.