Transition-Metal-Substituted Nanoporous Manganese Ferrites Mn_0.95M_0.05Fe₂O₄ (M: Co, Cu, and Zn) as Electrode Materials for High-Performance Supercapacitors in Redox-Active Nonaqueous Electrolytes

Transition-metal-substituted manganese ferrites, Mn0.95M0.05Fe2O4 (M: Co, Cu, and Zn), synthesized by the combustion method exhibit a single-phase cubic spinel structure. A maximum specific surface area (SABET) of 125 m2 g-1 and a controlled pore size distribution (1.0 and 3.6 nm) and pore volume (0.17 cm3 g-1) were estimated for Mn0.95Zn0.05Fe2O4. All of these ferrites are used as active electrode materials for electrochemical supercapacitor applications. The best specific capacitance (Csp) and areal capacitance (Car) in nonaqueous electrolytes, i.e., 0.1 M lithium perchlorate/propylene carbonate (LiClO4/PC), were estimated for Mn0.95Zn0.05Fe2O4. Further, in order to understand the effect of redox additive electrolytes, the Csp and Car for Mn0.95Zn0.05Fe2O4 were measured in 0.1 M lithium perchlorate/propylene carbonate/tetraethylammonium tetrafluoroborate/ potassium iodide (LiClO4/PC/TEA-BF4/KI) along with non-redox-active electrolytes (LiClO4/PC). The electrodes were fabricated using Mn0.95Zn0.05Fe2O4 with optimized mass and exhibited high Csp and Car of 829 F g-1 and 1277 mF cm-2, respectively, in a redox-active electrolyte as compared to lower values of 452 F g-1 and 696 mF cm-2, respectively, at 1 mV s-1, in a non-redox-active electrolyte. A symmetric pouch cell supercapacitor device (SPCSDR) fabricated using Mn0.95Zn0.05Fe2O4 with a redox-active electrolyte (LiClO4/PC/TEA-BF4/KI) provides high energy (E) and power (P) densities of 77.5 W h kg-1 and 900 W kg-1, respectively, at 0.5 A g-1. The SPCSDR has demonstrated stability up to 8000 charge-discharge cycles with an initial Csp retention of -,80% and high Coulombic efficiencies of -,97-100%, at 2 A g-1.