Insights on the mechanism of Na-ion storage in expanded graphite anode

Currently, Na-ion battery (NIB) has become one of the most potential alternatives for Li-ion batteries due to the safety and low cost. As a promising anode for Na-ion storage, expanded graphite has attracted considerable attention. However, the sodiation-desodiation process is still unclear. In our work, we obtain expanded graphite through slight modified Hummer's method and subsequent thermal treatment, which exhibits excellent cycling stability. Even at a high current density of 1 A g⁻¹, our expanded graphite still remains a high reversible capacity of 100 mA h g⁻¹ after 2600 cycles. Furthermore, we also investigate the electrochemical mechanism of our expanded graphite for Na-ion storage by operando Raman technique, which illuminate the electrochemical reaction during different sodiation-desodiation processes.