All-solid-state electrochemical capacitors using MnO2 electrode/SiO2–Nafion electrolyte composite prepared by the sol–gel process

Abstract

Electrode–electrolyte composites of MnO2 active material, acetylene black (AB), and SiO2–Nafion solid electrolyte were prepared using the sol–gel process to form good solid–solid interfaces. The composites were obtained by the addition of MnO2 and AB into a sol of hydrolyzed tetraethoxysilane with Nafion, and successive solidification of the precursor sol. Scanning electron microscope and energy dispersive X-ray spectroscopy measurements show that good solid–solid interface is formed between electrodes and solid electrolytes in the composites. All-solid-state hybrid capacitors were fabricated using the composites or the hand-grinding mixture of MnO2, AB and SiO2–Nafion powder as positive electrodes, activated carbon powder as a negative electrode, and phosphosilicate gel as a solid electrolyte. The all-solid-state hybrid capacitors using the composites exhibit larger capacitances and better rate performance than the capacitors using the electrode prepared by hand-mixing of powders. Specific discharge capacitances of the capacitor with the composite are 85 F g−1 for the one with the composite electrode and 48 F g−1 for the one with the hand-mixed electrode, at 1 mA cm−2. Moreover, the all-solid-state capacitors using the composite electrode can be operated at temperatures between −30 °C and 60 °C.