LiO2: Cryosynthesis and Chemical/Electrochemical Reactivities

The reduction of O 2 o solid Li 2 O 2 , via the intermediates O 2 - and LiO 2 , is the desired discharge reaction at the positive electrode of the aprotic Li-O 2 batteries. In practice, a plethora of byproducts are identified together with Li 2 O 2 and have been assigned to the side reactions between the reduced oxygen species (O 2 - , LiO 2 , and Li 2 O 2 ) and the battery components (the cathode and electrolyte). Understanding the reactivity of these reduced oxygen species is critical for the development of stable battery components and thus high cycle life. O 2 - and Li 2 O 2 are readily available, and their reactivities have been studied in depth both experimentally and theoretically. However, little is known about LiO 2 , which readily decomposes to Li 2 O 2 and is thus unavailable under usual laboratory conditions. Here we report the synthesis and reactivity of LiO 2 in liquid NH 3 at cryogenic temperatures and conclude that LiO 2 is the most reactive oxygen species in Li-O 2 batteries.