Ultrahigh Areal Capacitance of Flexible MXene Electrodes: Electrostatic and Steric Effects of Terminations

Two-dimensional (2D) Ti3C2Tx MXene has shown great potential in the energy storage field, and its performance strongly depends on the intercalation of cations. Therefore, engineering its interlayer ion channels is the key to enhance the electrochemical performance of Ti3C2Tx, but it is challenging due to the restacking nature of 2D materials. Herein, an original strategy for in situ introduction of large-size and electrostatic −SO4 termination is developed to engineer Ti3C2Tx MXene interlayer channels. The chemical binding and steric effect of −SO4 termination ensure a stable and expanded interlayer ion channel. The electrostatic effect of −SO4 benefits electrolyte ion infiltration. Consequently, the capacitance of Ti3C2Tx is increased by approximately 66 and 143% compared to those synthesized by common methods. The Ti3C2Tx electrode exhibits a high areal capacitance of 1399.0 mF cm–2 at 1 mV s–1, excellent rate capability, and ultralong cycle life without capacitance loss after 17,200 cycles. The all-solid-state supercapacitor (ASSS) based on the Ti3C2Tx delivers an ultrahigh areal capacitance of 391.5 mF cm–2, which reaches the state-of-the-art level. Moreover, the ASSS shows excellent flexibility and wearable potential. The established strategy blazes a new trail to improve the capacitance performance of MXenes.