Bistacked Titanium Carbide (MXene) Anodes for Hybrid Sodium-Ion Capacitors

Two-dimensional transition-metal carbides (MXenes) have shown great promise as electrode materials for high-rate pseudocapacitive energy storage. In this study, we report on the fabrication of bistacked two-dimensional titanium carbide electrodes which are free of binder, conductive additives, and current-collector. This MXene electrode is capable of reversible electrochemical storage of sodium ions with good cycling stability and rate capability. A prototype hybrid Na-ion capacitor was assembled by combining the bistacked MXene anode with an activated carbon cathode, which showed an energy density of 39 Wh/kg (including the total weight of bistacked MXene and activated carbon, 6 mg/cm(2)) at 1C rate and maintained up to 60% of its performance at a 60C rate, in the operating voltage window of 3.4 V. This study opens new avenues for developing self-standing binder and additive-free MXene electrodes for metal-ion batteries and capacitors.