Discharge Voltage and Maximum Power Density of Li-Air Batteries with Dual Electrolyte

Abstract

A new analytical model is developed and a closed-form expression for the discharge voltage and power density of Li-air batteries with mixed electrolyte is derived. Li-air batteries with mixed/dual electrolyte possess the unique advantage of having soluble reaction products at low electrolyte concentrations during discharge. This makes it possible to eliminate some limitation factors by using them as flow batteries. Oxygen diffusion, Butler-Volmer kinetics at the cathode/anode, the resistance of the separator, aqueous electrolyte, solid-electrolyte insulating layer at anode, and the finite conductivity of the electron conductive medium are taken into account. It is shown that the maximum power density depends not only on the internal resistances but also on the oxygen pressure, solubility, and diffusivity in the electrolyte. Results are shown for Li-air batteries with aqueous/basic electrolyte in the cathode but the model can be extended to other metal-air batteries by appropriately adjusting the material constants and geometrical proportions.