Developing Polymer Semi-Solid-State Gel Electrolyte with High-Performance Aqueous Zn-Mn Battery-Type Hybrid Capacitor Device for MnO2–MWCNT Cathode

Abstract

In recent years, energy storage devices have had a lower energy density for supercapacitor devices. Fortunately, certain drawbacks limit the liquid-based battery-type aqueous zinc-ion hybrid capacitor electrodes. For this reason, zinc–manganese (Zn-Mn)-based zinc-ion hybrid supercapacitors (ZIHSCs) have been designed using a manganese-dioxide-functionalized carbon nanotube (MnO2–f-MWCNT) battery-type cathode in a semi-solid gel–free-standing film electrolyte. Herein, as-prepared MnO2–MWCNTs are synthesized and assembled for nanostructured cathode composite materials by a facile hydrothermal technique. In this work, MnO2 nanorods with f-MWCNTs are applied to the electrode, resulting in a semi-solid-state gel film electrolyte realized by assembling the Zn-Mn hybrid capacitor. The materials’ physical–chemical conformation and their unique characteristics, crystalline structures, and different morphologies are studied through XRD, FE-SEM, FE-TEM, and XPS analysis. In this work, the design of major-source MnO2-based materials for positive and battery-type zinc metal anode approaches, along with the electrochemical properties of MnO2–MWCNT//Zn hybrid charge storage mechanisms, are evaluated. The coin-cell-type ZIHSC investigation of cyclic voltammetric (CV) curves and lower constant current charge/discharge (GCD) and electrochemical impedance (EIS) methods is also carried out. In addition, the maximum specific capacitance values, 339.98 mAh/g and 203.52 mAh/g, were observed for MnO2–MWCNT//Zn and MnO2//Zn at 0.2 mA/g, respectively. Finally, the higher cycling stability of MnO2−f-MWCNT of a 94.15% capacity retention after 15,000 cycles was evaluated and compared to MnO2//Zn of 73.05% retention in ZIHSC device applications. The assessment of electrochemical MnO2 cathode-based Zn-Mn ZIHSC performance is applicable for future aqueous electrical energy storage devices.