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(-2)). Typical strategies such as the insertion of nanomaterials and 3D-structure design is expected to reduce the volumetric capacitance of Ti3C2Tx electrodes, diminishing the dominating advantage of Ti3C2Tx over other electrode materials. Here, a novel, facile, and controllable H2SO4 oxidation method is developed for alleviating the restacking issue of Ti3C2Tx film with few electrochemically inactive side-products such as TiO2. A hierarchical ion path "highway" in Ti3C2Tx 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 approximate to 1.1 mu m thick Ti3C2Tx film, capacitance retention of 64% is obtained (208 F g(-1)/756 F cm(-3)) when the scan rate is increased from 5 to 10,000 mV s(-1). Even at higher mass loadings exceeding 12 mg cm(-2) (48 mu m thickness), the rate capability is still comparable to unoptimized Ti3C2Tx electrodes with low mass loading (1 mg cm(-2)). Consequently, a high areal capacitance of approximate to 3.2 F cm(-2) is achieved for pathway-optimized thick Ti3C2Tx film, which is of great significance for practical applications.