Two-Step Hydrothermal Synthesis of Ni₃(NO₃)₂(OH)₄@MnO₂ Heterojunction Supported α-MnO₂ Material on Foam Nickel for High-Performance Asymmetric Supercapacitors

Enhancing the performance of electrode materials is an effective strategy for increasing the energy density, power density, and lifespan of supercapacitors. In this study, a one-step hydrothermal method is employed to fabricate a large-sized interlaced lamellar structure with Ni3(NO3)2(OH)4@MnO2 (NNM-2) heterojunctions loaded onto nickel foam. Then, a uniform layer of α-MnO2 nanosheets is deposited to create a hierarchical structure of Ni3(NO3)2(OH)4@MnO2/α-MnO2 (NNMM-2) via a subsequent hydrothermal process. The interaction between various components, along with an increased number of active sites, significantly improves the electrochemical performance of the electrode material. Furthermore, the designed core–shell structure helps alleviate volume changes during charge and discharge cycles, thereby improving the stability of the material. Consequently, NNMM-2 demonstrates an impressive specific capacitance of 1261.3 F g–1 when measured at a current density of 1 A g–1. When employed as the positive electrode in an asymmetric supercapacitor that features activated carbon as the negative electrode, it demonstrates an energy density of 36.5 W h kg–1 at a power density of 471.7 W kg–1. After 7000 charge–discharge cycles, the capacity retention rate remains at 73% with a Coulombic efficiency of 99%, demonstrating excellent stability and capacitance retention capability. This research offers important perspectives on the creation of enhanced electrode materials for energy storage devices with superior performance.