In Searching for Electrolyte Compatible with NaMnO2 Cathode Material in Sodium Ion Battery

In the past few years, concerns over lithium reservoir depletion have driven researchers to go beyond lithium ion battery[1]. Sodium ion battery (SIB) has been considered as a promising candidate as sodium is highly abundant and widely distributed around the world. One of the challenges in state of the arts sodium ion battery is searching for cathode materials that can provide electrochemical performance comparable to lithium ion battery and electrolytes compatible with the related cathode materials. Among the reported cathode materials for SIB, O3 or O'3 type layered transition metal oxides are of great interest due to their high specific capacities[2]. In order to get a better understanding on these transition metal oxides, it is important to decouple the mixing transition metals and carry out a thorough investigation on the end member of the series. One of the end members, NaMnO2, has been reported with high specific capacity but shown low coulombic efficiency[3], which may be associated with electrolytes decomposition. Therefore, it is critical to search for a suitable electrolyte as well as additives. The influence of FEC (Fluoroethylene Carbonate) additive and some commonly used electrolytes in sodium ion battery were examined in NaMnO2/Na coin cells. For the cell using 1M NaClO4/PC as electrolyte, coulombic efficiency is relatively low at first but increases to 94% within ten cycles. While the coulombic efficiency of NaPF6/EC+DMC stays as low as 80% till 40 cycles. Apparently, the coulombic efficiency can be improved by adding FEC as additive in both electrolytes. The study regarding function mechanism for the FEC additive will be comprehensively understood by in-situ high energy X-ray diffraction and high precision electrochemical test, which could serves a good guide for the exploration of suitable electrolytes for high performance cathode materials of SIB. Figure 1