Optimizing Ion Pathway in Titanium Carbide MXene for Practical High-Rate Supercapacitor

The lengthened ion pathway in restacked 2D materials greatly limits the electrochemical performance of practically dense film electrodes (mass loading >10 mg cm). Typical strategies such as the insertion of nanomaterials and 3D-structure design is expected to reduce the volumetric capacitance of TiCT electrodes, diminishing the dominating advantage of TiCT over other electrode materials. Here, a novel, facile, and controllable HSO oxidation method is developed for alleviating the restacking issue of TiCT film with few electrochemically inactive side-products such as TiO. A hierarchical ion path “highway” in TiCT film is fabricated with porous structure, atomic-level increased interlayer spacing, and reduced flake size (through probe-sonication). As a result, ultra-high rate performance is obtained with high volumetric capacitance. For a ≈1.1 µm thick TiCT film, capacitance retention of 64% is obtained (208 F g/756 F cm) when the scan rate is increased from 5 to 10,000 mV s. Even at higher mass loadings exceeding 12 mg cm (48 µm thickness), the rate capability is still comparable to unoptimized TiCT electrodes with low mass loading (1 mg cm). Consequently, a high areal capacitance of ≈3.2 F cm is achieved for pathway-optimized thick TiCT film, which is of great significance for practical applications.