Air Electrodes for Aqueous Lithium Air Batteries

Abstract

The aqueous rechargeable lithium battery such as the one developed by EDF and its partners, uses an aqueous electrolyte as opposed to the anhydrous lithium air concept which uses an organic electrolyte. Typical electrolytes used are saturated aqueous solutions of lithium hydroxide or lithium chloride. Since the negative electrode (lithium metal) is not stable in aqueous media, it needs to be separated from the positive aqueous compartment by using a watertight, lithium–ion conducting, separator such as a Lisicon ceramic membrane [1]. This separator is therefore the interface between the negative compartment and the aqueous electrolyte. The negative compartment needs to be hermetically sealed from the external environment, that is, both from the air and the aqueous electrolyte. The air electrode provides the other interface, between the aqueous electrolyte and the external environment. It must therefore be open to allow oxygen from the air to access the positive electrode. The air electrode not only needs to be sufficiently porous for the air to penetrate the electrode from outside the cell, but it also needs to act as a barrier to contain the aqueous electrolyte inside the cell, and prevent it from leaking through the electrode. This compromise between water tightness and porosity to air is typically obtained by the addition of a hydrophobic agent such as PTFE.