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Metal–oxygen batteries have been growing rapidly as an energy storage technology in light of their high specific energy density. However, waste metal–oxygen batteries will raise many environmental issues; therefore, the recycling and reusing of the spent metal–oxygen batteries has attracted great attention. Herein, we report the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese–oxygen battery (MOB). Trace amounts of PTIO result in the discharge capacity of MOB increase to 2588 mAh g−1 and enhance the formation of manganese dioxide (MnO2) with toroidal appearance and high crystallinity on the cathode. After being used, the dismantled MnO2/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled free-standing MnO2/CNT electrode demonstrates an exceptional specific capacitance (253.86 F g−1) at a current density of 0.5 A g−1 in a 0.5 M Na2SO4 electrolyte. Moreover, we prepare an asymmetric supercapacitor fabricated with the recycled MnO2/CNT electrode and activated carbon (AC), which exhibits excellent energy density (32.00 Wh kg−1 at 413.70 W kg−1) with 78.26% retention over 6000 cycles. This work provides a promising strategy to derive high-quality and high-value MnO2/CNT electrode materials from the spent MOBs. It's the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese-oxygen battery (MOB). The recycled manganese dioxide (MnO2)/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled MnO2/CNT electrode shows the toroidal appearance and high crystallinity. Furthermore, the asymmetric supercapacitor fabricated with the MnO2/CNT free-standing electrode displays high specific capacitance, superior energy density, and good cyclic ability. [ABSTRACT FROM AUTHOR]

Here, germanium (Ge) nanofilm as the high-capacity electrode was deposited on the three-dimensional porous nickel foam substrate by radio frequency sputtering. Then, cyclized-polyacrylonitrile (PAN) was coated on the surface of Ge nanofilm to get the excellent rate capability and cycle stability owing to the poor cycle life of the as-prepared Ge nanofilm. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy were employed to analyze the microstructure and morphology of the Ge/cyclized-PAN electrodes. The Ge/cyclized-PAN manifests excellent electrochemical performance with high specific capacity and good cycling stability due to the unique structural features. At the charge-discharge rate of 0.1, 0.2, 0.5, 1, 2, and 5 C over a voltage window of 0.01-1.0 V, the discharge capacities of the composite are 731, 722, 701, 676, 621, and 566 mAh g, respectively. The specific capacity retention is up to 98 % with less capacity fading after 100 cycles at 1 C. [ABSTRACT FROM AUTHOR]