Identifying a Stable Counter/Reference Electrode for the Study of Aprotic Na–O2 Batteries

Abstract

The aprotic Na–O2 battery has attracted significant interest over the past few years because of its high theoretical specific energy and uncompromised round-trip efficiency. So far, most of the Na–O2 studies, using a cell configuration of Na metal anode, aprotic Na+ electrolyte and porous O2 cathode, focus on the O2 reactions in the cathode, which, however, could be complicated by the use of Na metal anode. This is because both the electrolyte and O2 (from cathode) can react with the Na metal anode and some of the side reaction products could cross over to the cathode and interfere with the O2 reactions occurring therein. Toward a better understanding of the O2 electrochemistry in aprotic Na–O2 batteries, it is essential to set up a clean electrochemical system, i.e., using counter/reference electrodes that react with neither electrolyte nor O2. In this report, Na3V2(PO4)3/NaV2(PO4)3 couple having a formal potential of 3.35 V vs. Na/Na+, reacts with neither electrolyte nor O2 during its multiple cycles of intercalation/deintercalation process, and therefore has been identified to be a stable counter/reference electrode for the study of O2 electrochemistry in aprotic Na–O2 batteries.