  The lithium-air (Li-O$_2$) battery has received enormous attention as a
possible alternative to current state-of-the-art rechargeable Li-ion batteries
given their high theoretical specific energy. However, the maximum discharge
capacity in nonaqueous Li-O$_2$ batteries is limited to a small fraction of its
theoretical value due to the insulating nature of lithium peroxide,
Li$_2$O$_2$, the battery$'$s primary discharge product. In this work, we show
that the inclusion of trace amounts of electrolyte additives, such as H$_2$O,
significantly improve the capacity of the Li-O$_2$ battery. These additives
trigger a solution-based growth mechanism due to their solvating properties,
thereby circumventing the Li$_2$O$_2$ conductivity limitation. Experimental
observations and a growth model imply that this solution mechanism is
responsible for Li$_2$ toroid formation. We present a general formalism
describing an additive$'$s tendency to trigger the solution process, providing
a rational design route for electrolytes that afford larger Li-air battery
capacities.
