Electrolyte-mediated dense integration of graphene-MXene films for high volumetric capacitance flexible supercapacitors

High conductivity two-dimensional (2D) materials have been proved to be potential electrode materials for flexible supercapacitors because of its outstanding chemical and physical properties. However, electrodes based on 2D materials always suffer from limited electrolyte-accessible surface due to the restacking of the 2D sheets, hindering the full utilization of their surface area. In this regard, an electrolyte-mediated method is used to integrate dense structure reduced graphene oxide/MXene (RGM)-electrolyte composite films. In such composite films, reduced graphene oxide (RGO) and MXene sheets are controllable assembly in compact layered structure with electrolyte filled between the layers. The electrolyte layer between RGO and MXene sheets forms continuous ion transport channels in the composite films. Therefore, the RGM-electrolyte composite films can be used directly as self-supporting electrodes for supercapacitors without additional conductive agents and binders. As a result, the composite films demonstrate enhanced volumetric specific capacity, improved volumetric energy density and higher power density compared with both pure RGO electrode and porous composite electrode prepared by traditional methods. Specifically, when the mass ratio of MXene is 30%, the electrode delivers a volumetric specific capacity of 454.9 F·cm−3 with a high energy density of 39.4 Wh·L−1. More importantly, supercapacitors based on the composite films exhibit good flexibility electrochemical performance. The investigation provides a new approach to synthesize dense structure films based on 2D materials for application in high volumetric capacitance flexible supercapacitors.