Highly stable and ultrafast electrode reaction of graphite for sodium ion batteries

Sodium ion battery is a potential sustainable energy storage system due to its abundance and low cost. To date, some Na-storage anode materials have achieved long life span, but the rate performance still remains insufficient. Herein, we show that in some linear ether-based electrolytes, graphite can not only render unprecedented cyclability (∼6000 cycles), but also exhibit ultrahigh rate capability (up to 10 A g −1 ), along with a reversible capacity of ∼110 mAh g −1 . By combining electrochemical measurements and structural analysis (e.g. in situ Raman and ex situ XRD measurements), we reveal that graphite undergoes a stage-evolution mechanism induced by the insertion of solvated sodium ions . Furthermore, kinetic studies have shown that this process accompanies with an intercalation pseudocapacitive behavior, which should be responsible for the obtained superior electrode properties.