Separating the effects of the electrolyte and solid electrolyte interphase on alkali metal ion transfer resistance in non-graphitizable carbon

Non-graphitizable carbon has attracted much attention because it ideally has a larger alkali metal ion capacity than graphite. The behavior of alkali metal ions at the non-graphitizable carbon/electrolyte interface has not been clarified. In this work, the influence of electrolyte and solid electrolyte interface (SEI) on the alkali metal ion transfer resistance to non-graphitizable carbon was investigated separately. In lithium-ion transfer reaction, the resistance value was significantly small, independent of either electrolyte or SEI. On the other hand, the sodium-ion transfer reaction showed a much larger difference depending on SEI than electrolyte, and SEI derived from fluoroethylene carbonate (FEC) had a larger resistance. FEC-based SEI had large amount of NaF. The results of this study revealed that it is important to construct an optional SEI to reduce the sodium-ion transfer resistance to non-graphitizable carbon.