Some possible approaches for improving the energy density of Li-air batteries

A physics-based model is proposed for the simulation of Li-air batteries. The model is carefully calibrated against published data and is used to simulate standard Li-air batteries with a nonaqueous (organic) electrolyte. The specific capacity is mainly limited by the oxygen diffusion length, which is a function of the oxygen diffusivity in the electrolyte and the discharge current density. Various approaches to increase the specific capacity of the cathode electrode and the energy density of Li-air batteries are discussed. To increase the specific capacity and energy density, it is more efficient to use a nonuniform catalyst that enhances the reaction rate only at the separator-cathode interface than a catalyst uniformly distributed. Using uniformly distributed catalysts enhances the current and power density of the cell but does not increase significantly the specific capacity and energy density. The specific capacity and energy density can be increased by suppressing the reaction rate at the oxygen-entrance interface to delay the pinch-off of the conduction channel in this region. Other possibilities to enhance the energy density such as using solvents with high oxygen solubility and diffusivity and partly wetted electrodes are discussed.