Ionic liquid-wrapped MXene film with bowl-like structures for highly integrated micro-supercapacitor array with ultrahigh output voltage

Recent researches in the development of in-plane micro-supercapacitor (MSC) have been dedicated to advancing its energy density in a finite storage area. However, the low ion-accessible surface area of plane electrode material has been the bottleneck limiting the energy output of MSC. Herein, we design a stable ionic liquid (IL)-MXene microemulsion system in virtue of tween-20 (TW20), gathering IL-TW20 microdroplets around MXene nanosheets. The microemulsion can adhere on the current collector and form the dense MXene-TW20-IL film. The IL as spacer and electrolyte is retained in the interlamination of MXene with the elimination of the TW20 during heat treatment, which enlarges the ion-accessible surface area of the MXene electrode. Thus, the MSC based on the flexible MXene-IL film exhibits a high areal capacitance (44.6 mF·cm⁻²), a high areal and volumetric energy density (50.7 μW·h·cm⁻² and 39 mW·h·cm⁻³), surpassing most of the reported MXene-based MSCs. And the MSC unit can be arbitrarily integrated in terms of various energy and voltage requirements. For instance, the integrated array with thirty MSC units in series realizes a high voltage output of 90 V, widening the range of application in next-generation microelectronic devices.