Solid electrolyte interphase manipulation towards highly stable hard carbon anodes for sodium ion batteries

Electrolytes and interfacial chemistry with controllable properties are critical to improve the cycling stability and rate capability of hard carbons in sodium-ion batteries. Here a simple but effective strategy was developed to construct a sustainable solid electrolyte interphase (SEI) film on hard carbon anodes by introducing a small amount of ester additives as SEI film formation agents into an ether-based electrolyte. The involvement of the ester molecule into the sodium ion solvation structure promotes its reduction to produce more organic polymeric components. Combining the high ionic conductivity of ether-based electrolytes, such SEI film can effectively protect hard carbon electrodes from structural changes, and thus, demonstrating an extraordinary cycling performance with a remarkable capacity of 211 mAh g−1 after 2000 cycles at a high rate of 1 A g−1, corresponding to a quite high capacity retention of 95.6%. The scalable leverage developed in this work highlights the promise of electrolyte screening and interfacial composition control for more efficient battery chemistries.