2D titanium carbide (Ti3C2TxMXene) showed good capacitance in both organic and neat ionic liquid electrolytes, but its charge storage mechanism is still not fully understood. Here, electrochemical characteristics of Ti3C2Tx electrode were studied in neat EMI-TFSI electrolyte. A capacitive behavior was observed within a large electrochemical potential range (from −1.5 to 1.5 V vs. Ag). Intercalation and de-intercalation of EMI+ cations and/or TFSI− anions were investigated by in-situ X-ray diffraction. Interlayer spacing of Ti3C2Tx flakes decreases during positive polarization, which can be ascribed to either electrostatic attraction effect between intercalated TFSI− anions and positively charged Ti3C2Tx nanosheets or steric effect caused by de-intercalation of EMI+ cations. The expansion of interlayer spacing when polarized to negative potentials is explained by steric effect of cation intercalation.