Résumé
A MnO 2 -MXene composite material is reported, in which MnO 2 particles have been grown onto Ti 3 C 2 MXene flakes. Thanks to its interconnected structure, it can not only boost the low electrical conductivity of MnO 2 , but also suppress the restacking of MXene flakes. As an electrode material in a three-electrode cell, the composite showed greater capacitance and improved stability performance than raw MnO 2 in both KOH and Na 2 SO 4 aqueous electrolytes. Equipped with MnO 2 –MXene composite material as positive and activated carbon as negative, an asymmetric device using Na 2 SO 4 as electrolyte displayed an energy density of 20 Wh kg −1 at 500 W kg −1 power density. On the other hand, the device operated in KOH electrolyte showed an energy density of 17 Wh kg −1 at 400 W kg −1 , and 11 Wh kg −1 at 8 kW kg −1 .