Opening MXene Ion Transport Channels by Intercalating PANI Nanoparticles from the Self-Assembly Approach for High Volumetric and Areal Energy Density Supercapacitors

Two-dimensional (2D) MXene materials have attracted great attention as advanced energy storage devices. A Ti3C2 MXene film can be used as a high-performance electrode material for flexible supercapacitors owing to its high specific capacitance, excellent conductivity, and remarkable flexibility. Unfortunately, self-stacking of MXene nanosheets makes them hard to balance the volumetric and areal capacitance performance. Herein, high conductive polyaniline nanoparticles (PANI NPs, ∼10 nm) are proposed as intercalators to regulate the MXene nanosheet interlayer by the self-assembly method. Interlayered PANI NPs not only restrain MXene self-stacking but also enable more ion transport routes, and conductive PANI NPs filled in MXene interlayer are in the form of nanoparticles that can build interconnected conductive channels. Meanwhile, PANI NPs slightly changes the thickness of the MX/PANI NPs hybrid film, thus bringing a high volumetric capacitance. As a result, the freestanding MX/PANI NPs-10% electrode displays an excellent areal capacitance of 1885 mF cm–2 (377 F g–1), meanwhile maintains a high volumetric capacitance of 873 F cm–3 even when the load of MXene reaches 5 mg cm–2. Moreover, the symmetric supercapacitor assembled by MX/PANI NPs hybrid film demonstrates high areal energy density (90.3 μWh cm–2) and volumetric energy density (20.9 Wh L–1) compared to MXene-based symmetric supercapacitors reported in the literature. This rational design balancing areal and volumetric energy densities provides another approach for solving the inherent problems of MXene and further exploiting MXene materials toward application in advanced energy storage devices.