Synthesis of the sandwich-type NiMn2O4@N-C@MnO2 core-shell nanostructured materials for the high-performance battery-supercapacitor hybrid devices

In this study, we successfully synthesized the sandwich-type NiMn2O4@N-C@MnO2 core-shell nanostructures. The NiMn2O4@N-C@MnO2 had a unique structure compared with the core-shell nanostructures previously reported. The microvillous nitrogen-doped carbon (NC) was considered as a highly conductive material, similar to a highway network, which facilitated the transport of electrons, improved the conductivity of core-shell nanomaterials, and acted as a buffer during the repeated charge-discharge cycles, thereby improving the overall stability of the nanomaterials. The introduction of N could increase the active sites for a redox reaction to a certain extent. Among all the prepared electrodes, NiMn2O4@N-C@MnO2-2 exhibited excellent performance. The NiMn2O4@N-C@MnO2-2//AC BSH device achieved an energy density of 34.29 W h kg−1 at a current density of 10 mA cm−2 when the power density was 946.75 W kg−1. In addition, the device retained 96.68 % of the initial specific capacitance after charge-discharge 30,000 cycles, which was better than most related studies previously reported. The excellent electrochemical performance of the device indicates that sandwich-type NiMn2O4@N-C@MnO2 core-shell nanomaterials have great application potential in the development of energy storage and conversion equipment.