Exclusive Solution Discharge in Li–O(2) Batteries?

[Image: see text] Capacity, rate performance, and cycle life of aprotic Li–O(2) batteries critically depend on reversible electrodeposition of Li(2)O(2). Current understanding states surface-adsorbed versus solvated LiO(2) controls Li(2)O(2) growth as surface film or as large particles. Herein, we show that Li(2)O(2) forms across a wide range of electrolytes, carbons, and current densities as particles via solution-mediated LiO(2) disproportionation, bringing into question the prevalence of any surface growth under practical conditions. We describe a unified O(2) reduction mechanism, which can explain all found capacity relations and Li(2)O(2) morphologies with exclusive solution discharge. Determining particle morphology and achievable capacities are species mobilities, true areal rate, and the degree of LiO(2) association in solution. Capacity is conclusively limited by mass transport through the tortuous Li(2)O(2) rather than electron transport through a passivating Li(2)O(2) film. Provided that species mobilities and surface growth are high, high capacities are also achieved with weakly solvating electrolytes, which were previously considered prototypical for low capacity via surface growth.