Flexible solid-state symmetric supercapacitors based on MnO2 nanofilms with high rate capability and long cyclability

Flexible solid-state symmetric supercapacitor was fabricated using MnO2 nanofilms growing directly on carbon cloth as the electrodes and PVA/H3PO4 gel as the electrolyte/separator. The device can be operated at a stable cell-voltage up to 1.4 V, obviously larger than that of conventional solid-state symmetric supercapacitors (≤1 V). It exhibited excellent rate capability with a scan rate as high as 20 V s−1 and a long cyclability (∼60000 cycles) even under severe mechanical deformation. The charge storage mechanism at different scan rates was also quantitatively analyzed.