Preparation And Characerization Of (Co,Ba)-Doped MnO₂ Thin-Film Electrode

Cathode MnO2 thin films doped with Baand Co were prepared by using spin-coating. Effects of concentrations of Mn2+, Ba2+ and Co2+ in spin-coating solution, dosage of adulterants of Ba and Co, spin-rate, spin-time, and anneal temperature on resistivity were studied.First, the preparation process of pure MnO2 film was studied. The results showed that the solution containing 0.4 M Mn2+ is suitable for the spin coating process. The appropriate parameters for preparating the films are heating temperature from room temperature to 150℃at 12℃/min and kept for 0.5h at 150℃, and ramping to 700℃at 12℃/min held at 700℃for 2h, then down to room temperature, spin-coating (3000r/s,30s) and thermal decomposition were also used to produce MnO2 film precursor, and the pure MnO2 films exhibit low resistivity (-0.0932Ω·cm). Then, the Ba and Co amount doped were adjusted. When annealing temperature is higher than 650℃, stable hollandite structure can be formed and when the doped amount of Ba and Co were 2mol% and 15mol%, stable hollandite structure (Ba1.4Co0.2Mn8O16) and its resistivity reached the lowest point (0.2Ω·cm) after treating at 700℃. Lower resistivity means lower equivalent series resistance(ESR) in circuit, and also means higher output power of capacitors. The film has good structure stability and retains its perfect crystallinity even after steam treatment at 1000℃. This test indicates its high thermal stability and perhaps the films can be further used under high temperature and high pressure. At last, these films were tested by means of Cyclic Voltammetry. When Co amount is 2mol%, the capacitance is much higher as 95.8F/g at scanning rate of 20mV/s. With the increases of Co dopant amount further, the capacitance decreased to some extent. When Co amount is 2mol% and scanning speed is 20mV/s, the capacitance of films treated after 550℃is up to 107.3F/g.