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

Abstract

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 ≈1.1 µm 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 µm 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 ≈3.2 F cm−2 is achieved for pathway-optimized thick Ti3C2Tx film, which is of great significance for practical applications.