Study on carbonate ester and ether-based electrolytes and hard carbon anodes interfaces for sodium-ion batteries

The hard carbon (HC) is the key anode materials for sodium ion batteries. While the electrolyte and interface from carbonate-based and ether-based electrolytes on the HC has not been deeply analysed. Herein, by combining the theory calculation with experiments analysis of Fourier transform infrared spectroscopy, we successfully construct accurate Na⁺-solvents models that the oxidation resistance stability of Na⁺[EC₂/EMC/DMC][PF₆⁻] complexes are better than that of Na⁺[DIGLYME₄][CF₃SO₃⁻] sheaths. And also, the reduction resistance stability of the ether-based electrolyte is better than that of ester-based electrolyte. It is also demonstrated that the ether-based electrolytes generate dense, thin and fast Na-ions transport SEI on the HC particles at the initial stage of the electrochemical cycle, and the organics fill the gaps between inorganics in carbonated ester-based electrolytes, effectively preventing electrolyte decomposition and permeation in the long cycling process by CV, TEM, EIS, AFM, ToF-SIMS and XPS analysis. It is also found that the ratio of organic to inorganic components in DIGLYME-based electrolyte is greater than in EC/DMC/EMC-based electrolyte after cycling, which may affect the electrochemical performance of cells.