There has been much interest in rechargeable aprotic lithium-oxygen (Li-O₂) batteries because their energy density can be significantly higher than that of the conventional Li-ion batteries. However, many challenges remain for Li-O₂ batteries before they can become a reality.  Understanding the growth and nucleation mechanisms of the discharge product is one of the keys to addressing these challenges because it controls the resulting morphology and composition of the discharge product. The efficiency and reversibility are dependent on the type of morphology and composition that is formed during discharge. In this paper experimental and computational results will be reported that have shed light on the growth and nucleation mechanism in Li-O₂ batteries. Specifically, the role of lithium superoxide (LiO₂) in the nucleation and growth mechanism during discharge and how to suppress the disproportionation reaction of LiO₂ to lithium peroxide (Li₂O₂) will be discussed. The implications of these new results for reducing charge overpotentials in Li-O₂ batteries and in the design of new cathode materials will be discussed.