Operando Tracking of Resistance, Thickness, and Mass of Ti₃C₂T_x MXene in Water‐in‐Salt Electrolyte

Abstract MXenes are among the fastest‐growing families of 2D materials, promising for high‐rate, high‐energy energy storage applications due to their high electronic and ionic conductivity, large surface area, and reversible surface redox ability. The Ti₃C₂T_x MXene shows a capacitive charge storage mechanism in diluted aqueous LiCl electrolyte while achieving abnormal redox‐like features in the water‐in‐salt LiCl electrolyte. Herein, various operando techniques are used to investigate changes in resistance, mass, and electrode thickness of Ti₃C₂T_x during cycling in salt‐in‐water and water‐in‐salt LiCl electrolytes. Significant resistance variations due to interlayer space changes are recorded in the water‐in‐salt LiCl electrolyte. In both electrolytes, conductivity variations attributed to charge carrier density changes or varied inter‐sheet electron hopping barriers are detected in the capacitive areas, where no thickness variations are observed. Overall, combining those operando techniques enhances the understanding of charge storage mechanisms and facilitates the development of MXene‐based energy storage devices.