High Volumetric Capacitance and Mechanisms of Electrochemical Charge Storage in Two-Dimensional Ti₃C₂-Based Mxene

MXenes, a recently discovered large family of two-dimensional (2D) early transition metal carbides and carbonitrides, have shown much promise in electrochemical energy storage applications, such as battery and supercapacitor electrodes. Here we report on large volumetric capacitance and high rate capability of Ti 3 C 2 T x – the most studied MXene to date. Spontaneous intercalation of a variety of single- and multiply charged cations (such as Li + , Na + , K + , NH 4 + , Mg 2+ , and Al 3+ ) , together with highly reversible electrochemical insertion of the same cations, has been demonstrated for Ti 3 C 2 T x in aqueous electrolytes. Perfect capacitive behavior was observed for Ti 3 C 2 T x MXene even at quite high charge and discharge rates, contradicting to slow intercalation of ions in a specific potential range, which is usually observed in layered materials used in battery applications. In order to understand the mechanism of capacitive charge storage in MXenes, we performed characterization of the material using in-situ spectroscopy, X-ray diffraction and other techniques.