All-Solid High-Performance Asymmetric Supercapacitor Based on Yolk–Shell NiMoO4/V2CTx@Reduced Graphene Oxide and Hierarchical Bamboo-Shaped MoO2@Fe2O3/N-Doped Carbon

The development of high-performance electrochemical energy storage systems is highly desirable for portable and wearable electronic devices. In this study, we proposed a new method to prepare a yolk–shell NiMoO4/V2CTx@reduced graphene oxide (rGO) composite material using a room-temperature ionic liquid (RTIL)-assisted hydrothermal method. NiMoO4 was incorporated into the V2CTx MXene layer in the presence of the RTIL 1-butyl-3-methylimidazole tetrafluoroborate ([Bmim]BF4). rGO was coated on the NiMoO4/V2CTx yolk under electrostatic forces. [Bmim]BF4 effectively prevents the overoxidation of V2CTx MXene during the hydrothermal synthesis of NiMoO4 and reduces its surface energy, which makes the NiMoO4/V2CTx@rGO composite highly stable. This alternating arrangement facilitates the rapid diffusion and transport of electrolyte ions, resulting in excellent electrochemical performance of the NiMoO4/V2CTx@rGO composites. Bamboo-shaped MoO2@Fe2O3/N-doped carbon (NC) was used as a negative electrode material to assemble a solid asymmetric supercapacitor (ASC) with NiMoO4/V2CTx@rGO (NiMoO4/V2CTx@rGO//MoO2@Fe2O3/NC). The ASC possesses a high energy density of 56.1 W h kg–1 at 800 W kg–1. The capacitance retention rate remains as high as 90.7% after 5000 cycles, demonstrating that the proposed material has promising performance for supercapacitor applications.