A Study of Copper as a Cathode Material for an Ambient Temperature Sodium Ion Battery

Abstract

The electrochemical behavior of copper was examined as a possible metal/metal(II) chloride cathode for a room temperature sodium battery in a nonaqueous melt comprised of methanesulfonyl chloride, aluminum chloride, and sodium chloride. Electrodes plated with a finite amount of copper showed a decrease in the amount of stored charge with increasing cycles, while solid copper electrodes showed a steady amount of oxidation and reduction. To keep the electrolyte buffered, the electrolyte contained excess NaCl in the form of a slurry. Results with a working electrode in NaCl slurry showed a Cu/Cu(II) coulombic efficiency (reduction/oxidation) of less than 100%, while a coulombic efficiency of 55% was observed for the electrode in the buffered slurry. On the other hand, a coulombic efficiency over 100% was observed for trials where the electrode surface was not submerged in the NaCl slurry resulting in a lower buffer capacity. This was probably due to local acidity change near the electrode surface caused by the decrease in chloride ions as the copper is oxidized to copper chloride. This local acidity may cause side reactions to take place that chemically participated in the oxidation. This was supported by results using an electrochemical quartz crystal nanobalance that show a greater increase in mass than expected from the amount of current passed during oxidation. © 2001 The Electrochemical Society. All rights reserved.