Revisit Electrolyte Chemistry of Hard Carbon in Ether for Na Storage

Hard carbons (HCs) as an anode material in sodium ion batteries present enhanced electrochemical performances in ether-based electrolytes, giving them potential for use in practical applications. However, the underlying mechanism behind the excellent performances is still in question. Here, ex situ nuclear magnetic resonance, gas chromatography–mass spectrometry, and high-resolution transmission electron microscopy were used to clarify the insightful chemistry of ether- and ester-based electrolytes in terms of the solid–electrolyte interphase (SEI) on hard carbons. The results confirm the marked electrolyte decomposition and the formation of a SEI film in EC/DEC but no SEI film in the case of diglyme. In situ electrochemical quartz crystal microbalance and molecular dynamics support that ether molecules have likely been co-intercalated into hard carbons. To our knowledge, these results are reported for the first time. It might be very useful for the rational design of advanced electrode materials based on HCs in the future.