Pressure-Engineered Ti 3 C 2 T x MXene with Enhanced Conductivity and Accelerated Reaction Kinetics of Lithium Storage.

We studied the structure-function relationship of compressed Ti 3 C 2 T x MXene using high-pressure in situ synchrotron radiation, impedance spectroscopy, Hall effect measurements, and first-principles calculations. With increasing pressure, the conductivity of Ti 3 C 2 T x MXene increases along with its continued lattice shrinkage. A pressure range of 0.4-2.2 GPa exhibits a sharp decrease in resistance, which decreases by more than one order of magnitude from 3.3 × 10 4 to 1.4 × 10 3 Ω. A pressure range of 2.2-6.6 GPa exhibits a steady resistance with a slight decrease of 0.2%. As the pressure drops to atmospheric conditions, the resistance increases slightly to 4.2 × 10 3 Ω. This is accompanied by a transformation of the semiconductor into metal. An irreversible increase in conductivity is observed owing to an increase in the electron concentration and a decrease in the grain-boundary potential barrier. Furthermore, abundant Ti 3 C 2 T x undergoing prepressure treatments (0.4, 2.0, and 4.0 GPa) was first prepared using a double-anvil hydraulic press. The recycled samples retain an accordion-like layered structure with slight lattice shrinkage while the voids between the sheets contract considerably, increasing the density. Correspondingly, electrochemical results show a pressure threshold of 2.0 GPa based on the rapid quenching from the hydraulic press. This weakens the electric polarization in redox reactions and increases the ionic transport rate for the formation of a Ti 3 C 2 T x anode owing to pressure improving the conductivity and interlaminar densification. Our study shows a new, simple, and universal way to regulate various MXenes and also promotes the application of MXene-based materials in energy storage and related fields.