We propose and demonstrate the direct application of immiscible aqueous/organic interfaces in lithium–air and lithium–copper batteries. Therefore, the two half-reactions are separated in their respectively favourable electrolytic environments without using any other membranes. In order to prevent water and oxygen from interrupting the reaction in organic phases, we add poly(methyl methacrylate) (PMMA) to propylene carbonate (PC) and investigate its concentration effects using Pt ultramicroelectrodes (UMEs). Pt UMEs provide us the sensitive measure of water contamination as well as the diffusion property of oxygen in the polymer electrolytes. By studying the discharge profiles under various electrolytic conditions, we demonstrate that these batteries are of longer discharge time and higher specific capacity when the polymer electrolyte contains about 10 to 20% of PMMA.