Graphite-based dual-ion batteries (DIBs), which involve the intercalation of anions into the carbon layers, are promising for high-power applications. Many researchers inevitably choose ethyl methyl carbonate (EMC) as the electrolyte, as they observe superior electrochemical performances compared to other solvents. Here, we clarify the underlying reason why EMC is better. Specifically, EMC forms a thinner layer of cathode electrolyte interface on the graphite surface with fewer Li-F and ROCO2Li species than that with dimethyl carbonate and diethyl carbonate. EMC electrolyte reduces charge-transfer resistance, polarization, and self-discharge of graphite electrodes. It also enhances Coulombic efficiency, cycle, and rate performances. 90% of the available capacity can be obtained even at 12 C (1200 mA g-1). Our work also emphasizes the importance of electrolyte and electrolyte interface on future developments of DIBs.