A Highly Flexible Supercapacitor Based on MnO₂/RGO Nanosheets and Bacterial Cellulose-Filled Gel Electrolyte

The flexible supercapacitors (SCs) of the conventional sandwich-type structure have poor flexibility due to the large thickness of the final entire device. Herein, we have fabricated a highly flexible asymmetric SC using manganese dioxide (MnO₂) and reduced graphene oxide (RGO) nanosheet-piled hydrogel films and a novel bacterial cellulose (BC)-filled polyacrylic acid sodium salt-Na₂SO₄ (BC/PAAS-Na₂SO₄) neutral gel electrolyte. Apart from being environmentally friendly, this BC/PAAS-Na₂SO₄ gel electrolyte has high viscosity and a sticky property, which enables it to combine two electrodes together. Meanwhile, the intertangling of the filled BC in the gel electrolyte hinders the decrease of the viscosity with temperature, and forms a separator to prevent the two electrodes from short-circuiting. Using these materials, the total thickness of the fabricated device does not exceed 120 μm. This SC device demonstrates high flexibility, where bending and even rolling have no obvious effect on the electrochemical performance. In addition, owing to the asymmetric configuration, the cell voltage of this flexible SC has been extended to 1.8 V, and the energy density can reach up to 11.7 Wh kg^-1 at the power density of 441 W kg^-1. This SC also exhibits a good cycling stability, with a capacitance retention of 85.5% over 5000 cycles.