Unraveling Cation Intercalation Mechanism in MXene for Enhanced Supercapacitor Performance

MXenes are two-dimensional materials with high electrical conductivity, adjustable composition, and tunable surface terminations, endowing them with significant potential for supercapacitors (SCs). However, during etching preparation, the susceptibility to interlayer restacking and the attachment of inactive -F terminations reduce their capacitances and rate performance. To resolve these issues, electrochemistry-driven cation intercalation (ECI) followed by calcination is proposed to widen their interlayer spacing and modify surface chemistry simultaneously. Results show that the Mn-modified Ti 3 C 2 T z exhibits an exceptionally high volumetric capacitance (1655.5 F cm − 3 at 1 mV s − 1 , 1.5 times higher than that of pristine Ti 3 C 2 T z ) and excellent rate performance (72.3% retention from 1 to 50 A g − 1 ) due to the unblocked interlayers and the increased -O terminations. Density Functional Theory (DFT) results reveal that the intercalated Mn 2+ displayed the largest formation energy difference, manifesting a great driving force to form active -O terminations, which is crucial for improving electrochemical performance. Kinetic analysis reveals that the intercalated Mn 2+ increases the termination-related capacitances (pseudocapacitance and diffusion-controlled capacitance) significantly. The asymmetric SCs assembled with Mn-intercalated Ti 3 C 2 T z and nitrogen-doped activated carbon, show the combination of high energy densities at high powers (38.2 Wh L − 1 at 30.1 kW L − 1 ). The findings clarify how metal cation intercalation affects MXene performance, providing insights for advancing MXene-based electrodes in energy storage applications.