Na Reactivity toward Carbonate-Based Electrolytes: The Effect of FEC as Additive

Na-ion batteries have regained attention because they offer sustainability advantages over the Li-ion technology, hence their interest for massive electrochemical storage. Although the Na-ion electrochemistry is analogous to that of the Li-ion concept, there are a few notable differences such as the stability of carbonated-based electrolytes toward the Li or Na metal anodes. Herein we report on the positive effect of FEC as electrolyte additive on the efficiency of Na-half cells which unfortunately comes with a side effect involving the sudden onset of polarization during discharge at unpredictable capacity values. We show that these anomalies, associated to an inefficient plating-stripping at the sodium metal anode, do not appear in full Na-ion cells. Therefore, FEC-based electrolytes are not the panacea and alternative additives must be sought to enable building of reliable half cells with metal anodes. (C) The Author(s) 2016. Published by ECS. All rights reserved.