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 nonaqueous (organic) electrolyte. It is shown that 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. It is shown that, in order 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 will enhance the current and power density of the cell but will not increase significantly the specific capacity and energy density. It is also shown that the specific capacity and energy density can be increased by suppressing the reaction rate at the oxygen-entrance interface in order 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.