Modeling of Li-Air Batteries with Dual Electrolyte

Li-air batteries with organic electrolyte at the anode and aqueous electrolyte at the cathode (dual electrolyte systems) are modeled using the mass transport and drift-diffusion equations of the electrolyte during the discharge of the cells. Two regimes of operation are analyzed: (1) when the concentration of the electrolyte is smaller than the concentration of saturation of Li + OH in water, and (2) when the electrolyte concentration reaches saturation and the reaction product is deposited at the cathode. Numerical simulations are performed to evaluate the dependence of the specific capacity, energy and power densities on the geometrical and material parameters during the two regimes of operation. It is shown that the energy density and specific capacity can be improved by increasing the solubility and the diffusion coefficient of oxygen in the cathode, but they are not much affected by adding a uniformly distributed catalyst in the cathode. The power density can be increased by 10% by increasing the solubility factor, the oxygen diffusion coefficient, or the reaction rate. The limiting factors for the low power density of these batteries are the low values of the oxygen diffusion coefficient in the cathode and the relatively high separator/anode and separator/cathode interface resistances.