Li-air batteries: A classic example of limitations owing to solubilities

A review is presented of the present state-of-the-art of Li-air cells and batteries. We examine the properties of this unique system in terms of the effects of solubilities of reactants and products in both nonaqueous (aprotic) and aqueous electrolyte solutions. Definite trends are observed, such as increasing cell-specific energy and capacity as both the oxygen solubility increases and viscosity decreases in organic solvents, but quantitative analyses are limited owing to the complex relations between solubility, solution viscosity, oxygen diffusion, and electrolytic conductivity. Adding to this complex relation is the dependence of the nature of the carbon-based air cathode (surface area and pore volume) upon practical specific capacities, which can be realized with Li-air cells that far exceed the specific energies and capacities of all present commercial metal-air and Li-ion cells and batteries.