Ultrahigh gravimetric and volumetric capacitance in Ti3C2Tx MXene negative electrode enabled by surface modification and in-situ intercalation

Two-dimensional titanium carbide (MXene) has attracted significant attentions in supercapacitors owing to its high metallic conductivity and excellent chemical properties. However, the inherent restacking issue and –F surface termination severely limit the energy storage. Here, an effective strategy to construct high-performance Ti3C2Tx MXene (A-Ti3C2Tx/PANI) based on the synergistic effect of modified surface termination, expanded interlayer spacing and three-dimensional structure is reported. Benefiting from the interconnected structure, enhanced electrochemical activity and efficient ion/electron transport layer, the prepared negative electrode demonstrates an outstanding specific capacitance of 652.3 F g−1 at 1 A g−1 (∼3 times of the pristine MXene), an impressive rate capability with 81% capacitance retention at 50 A g−1, and excellent cycling stability with above 99% capacitance retention after 10, 000 cycles. In addition, a symmetric supercapacitor is fabricated using A-Ti3C2Tx/PANI, and it delivers a high energy density of 20.3 Wh kg−1. Furthermore, the prepared free-stranding film electrode based on A-Ti3C2Tx/PANI shows a high volumetric capacitance of 2368 F cm−3. The improved gravimetric and volumetric capacitances surpass almost all the reported MXene-based electrodes. This study demonstrates a new strategy to enhance the electrochemical performance of Ti3C2Tx electrode and could be a universal way applicable to other MXenes.