Innovative discontinuous-SEI constructed in ether-based electrolyte to maximize the capacity of hard carbon anode

Compared with graphite, the lower sodiation potential and larger discharge capacity of hard carbon (HC) makes it the most promising anode material for sodium-ion battery. Utilizing ether-based electrolyte rather than conventional carbonate-based electrolyte, HC achieves superior electrochemical performance. Nevertheless, the mechanism by which ether-based electrolyte improves the properties of HC is still controversial, primarily focusing on whether it forms solid electrolyte interphase (SEI) film. In this work, according to the sodium storage mechanisms in HC at low voltage (<0.1 V), including Na+-diglyme co-interaction into the carbon layer (SEI forbidden) and desolvated Na+ insertion in the irregular carbon holes (SEI required), the NaPF6 concentration in ether-based electrolyte was regulated, so as to construct a discontinuous-SEI on the surface of the HC anode, which significantly enhances the electrochemical performances of HC. Specifically, with 0.2 M NaPF6 ether-based electrolyte, HC deliverers a discharge capacity of 459.7 mA h g−1 at 0.1 C and stays at 357.2 mA h g−1 after 500 cycles at 1 C, which is substantially higher than that of higher/lower salt concentration electrolytes.