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

Two-dimensional (2D) Ti 3 C 2 T x 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 Ti 3 C 2 T x, 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 −SO 4 termination is developed to engineer Ti 3 C 2 T x MXene interlayer channels. The chemical binding and steric effect of −SO 4 termination ensure a stable and expanded interlayer ion channel. The electrostatic effect of −SO 4 benefits electrolyte ion infiltration. Consequently, the capacitance of Ti 3 C 2 T x is increased by approximately 66 and 143% compared to those synthesized by common methods. The Ti 3 C 2 T x 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 Ti 3 C 2 T x 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.