Cations‐Intercalated Two‐Dimensional Titanium Carbonitride (Ti ₃ CNT _x ) MXene for High‐Performance Supercapacitors

ABSTRACT The development of high‐performance cation‐intercalated‐based electrochemical energy storage devices (EESDs), exhibiting high pseudocapacitance and long cycle life, demands for a rational, cost‐effective, and promising electrode materials. Two‐dimensional (2D) titanium carbonitride (Ti ₃ CNT _x ) MXene is emerging as a key member of the MXene family for electrode applications in EESDs due to its high electrical conductivity and rich surface chemistry. Here in, we investigated the method to reduce sheet restacking and to significantly improve the aggregated structure of Ti ₃ CNT _x MXenes, which leads to higher gravimetric capacitance by hydrophilic cations (Li ⁺ , Na ⁺ , Mg ^{2 +} ) and hydrophobic cation (K ⁺ ) intercalation. In potassium ions‐intercalated Ti ₃ CNT _x MXene (K ⁺ ‐Ti ₃ CNT _x ), the hydrophobic nature of K ⁺ inevitably enhances the number of redox‐active sites, resulting in improved environmental stability and superior electrochemical performance through a pillaring effect, emerging as a high‐performance anode material for advanced potassium‐ion storage devices. Notably, the engineered K ⁺ ‐Ti ₃ CNT _x exhibited a high charge storage capacity of 1003 F g ⁻¹ , which represents an almost threefold increase compared to delaminated Ti ₃ CNT _x (d‐Ti ₃ CNT _x ), outperforming the already reported conventional supercapacitors. Moreover, the AC //K ⁺ ‐Ti ₃ CNT _x device exhibits an excellent energy density of 37 W h kg ⁻¹ and remarkable long‐term cycling stability of 95%, coupled with a Coulombic efficiency greater than 99% over 10 000 cycles.