Two-Dimensional Titanium Carbide MXene as a Capacitor-Type Electrode for Rechargeable Aqueous Li-Ion and Na-Ion Capacitor Batteries

To bridge the gap of the alkali-metal-ion (Li or Na) batteries and supercapacitors, hybrid devices called capacitor batteries are being designed, which are adaptive for large-scale energy-storage systems. Two-dimensional transition-metal carbide materials (MXene) with high electronic conductivities have become capable electrode materials for supercapacitors. Herein, Ti3C2Tx synthesized by selectively etching the Al layer from the Ti3AlC2 presents a remarkable electrochemical performance as an electrode material for the supercapacitor with Li2SO4 or Na-2 SO4 aqueous electrolyte. It displays a capacitance of 243 Fg(-1) at a low current density of 100 mAg(-1) with a capacitance retention of 95% in the Li2SO4 electrolyte, and a capacitance of 150 Fg(-1) at a low current density of 200 mAg(-1) with a capacitance retention of 95% in the Na2SO4 electrolyte, which shows its potential application for capacitor batteries. Moreover, the LiMn2O4//Ti3C2Tx Li-ion capacitor battery and MnO2//Ti3C2Tx Na-ion capacitor battery are designed and assembled for the first time. Such rechargeable aqueous capacitor batteries display capable capacities, remarkable rate abilities, and excellent cycling performances, which further demonstrates that Ti3C2Tx is an outstanding capacitor- type electrode material for capacitor batteries.