Strategies Toward Stable Nonaqueous Alkali Metal-O2 Batteries
Alkali metal-O 2 batteries, by coupling high-capacity alkali metal anodes with gaseous oxygen, possess extremely high gravimetric energy density that is comparable to gasoline and are potential energy storage technologies beyond lithium-ion batteries. The development of alkali metal-O 2 batteries has achieved great progress in recent years, from materials to prototype devices and on fundamental mechanisms. The stability of alkali metal-O 2 batteries is still poor, however, leading to a huge gap between laboratory research and commercial applications. A series of parasitic reactions result in the instability, which occur during electrochemical discharging and charging. The ubiquitous active oxygen species attack both the organic electrolyte and the carbon cathode, triggering various parasitic reactions. Meanwhile, dendrite growth and volume expansion upon repeated plating/stripping and O 2 crossover severely limit the reversibility of alkali metal anodes. Here, an overview of the strategies against these issues is given to improve the stability of nonaqueous alkali metal-O 2 batteries, which is discussed from three aspects: air cathodes, alkali metal anodes, and aprotic electrolytes. Furthermore, perspectives for future research of stable alkali metal-O 2 batteries are outlined.