Lithium–Oxygen batteries

Rechargeable Li–O2 batteries have gathered enormous attention in the research community for having amongst the highest theoretical energy storage. Realizing the promise, even in part, in practice could produce a device that stores significantly more energy than other rechargeable batteries. Fundamental understanding of the reaction mechanisms is now realized to be key to overcome many challenges. We give a critical overview of the current understanding of the chemistry underpinning the Li–O2 cell with focus on the cathode and give a perspective on the most important research needs. Since performance and reversibility are often grossly misunderstood, we put emphasis on realistic performances to be achieved by Li–O2 cells and on means to identify reversibility. Parasitic chemistry is the foremost barrier for reversible cycling and now realized to be predominantly caused by singlet oxygen rather than by the previously thought superoxide or peroxide. This finding profoundly affects any other area of research from reaction mechanisms, to electrolytes and catalysts and dominates future research needs.