Engineered Mn3O4–NiSe2 Heterostructure for High-Performance Battery-Type Positrode in All-Solid-State Hybrid Supercapacitors

To develop highly efficient electrode materials for hybrid supercapacitors, in this study, a hetero oxide-selenide positrode material system, Mn₃O₄–NiSe₂, has been developed through a sluggish precipitation followed by an anion exchange strategy. The Mn₃O₄–NiSe₂ exhibits a distinctive Tyndall effect, high specific surface area (89 m² g^–1), and more redox active sites (8.5 × 10¹⁸ @ 10 mV s^–1), which are responsible for the material’s surface wettability, bulk accessibility, and redox activity. The electrochemical studies reveal high kinetic reversibility, enhanced charge storage (primarily diffusion-controlled with minor surface contributions), low charge transfer resistance (0.09 Ω), equivalent series resistance (0.7 Ω), relaxation time (30 ms), and a typical Warburg response indicative of low ion diffusion resistance. The 1.7 V Mn₃O₄–NiSe₂||N-rGO all-solid-state hybrid supercapacitor (ASSHSC), utilizing N-rGO as the negatrode and PVA-KOH polymer as the solid electrolyte separator, demonstrates high-rate charge storage efficiency, low equivalent series resistance (0.9 Ω) as well as charge transfer resistance (0.2 Ω) during its operation. The device delivers high power and energy densities of 7200 W kg^–1 and 33 Wh kg^–1, respectively, and an excellent cyclic capacitance retention of 98.7% after 14,500 cycles. The superior charge storage performance is attributed to the Se and O vacancy/excess-induced electronic conductivity of Mn₃O₄–NiSe₂, physicoelectrochemical compatibility between Mn₃O₄–NiSe₂ and N-rGO and lowly resisted electrolyte-ion mobility during the electrochemical processes. The reported research protocol can be tailored according to the unique requirements and properties to develop various associated material–electrolyte systems for applications in contemporary electrochemical energy storage systems.