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, holding promise for supercapacitors (SCs). However, 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 unclog the interlayers and modify surface chemistry simultaneously. It is found that Mn-modified Ti3C2Tz MXene exhibits exceptional volumetric capacitance (1655.5 F cm−3 at 1 mV s−1, 1.5 times higher than that of pristine Ti3C2Tz) and excellent rate performance (72.3 % retention from 1 A g−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 Mn2+ 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 Mn2+ increases the termination-related capacitances (pseudocapacitance and diffusion-controlled capacitance) significantly. Symmetric and asymmetric SCs demonstrate high energy densities at high powers, showing the advance of the Mn-intercalated Ti3C2Tz. The findings clarify how metal cation intercalation affects MXene performance, providing insights for designing MXene-based electrodes in energy storage applications.