Beyond Divalent Copper: A Redox Couple for Sodium Ion Battery Cathode Materials

, and canwithstand a thousand cycles, maintaining 61% of its original capacity. We demonstrate that copper can enable not only high voltage,but also excellent stability. This work opens up a new avenue of oxide design for high energy, cost effective battery systems.© The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative CommonsAttribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/),which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in anyway and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0041505eel]All rights reserved.Manuscript submitted February 4, 2015; revised manuscript received March 4, 2015. Published March 19, 2015.