Asymmetric coatings for lablet supercaps Y3 WP5: RUBa, UOG

MnO2-MnO2 symmetric supercapacitors were extended to asymmetric materials to improve the working voltage and capacitance. 

Several materials were investigated for use with the MnO2 system. Fe3O4 (as proposed in [1]) showed a large voltage window however there were problems with the fabrication process and unwanted Fe particles precipitating on the lablets. 

A polypyrrole (Ppy) alternative [2] was investigated with greatly improved results for deposition onto lablets. Figures 1 A and B show the cyclic voltammograms of the MnO2-Ppy asymmetric supercap at increasing voltage windows and also good stability over 200 cycles. C shows the precise alternating deposition of MnO2 and Ppy on the power lines of the supercaps. 

Figure 1. Asymmetric coatings with MnO2 and Ppy for lablet supercar. A,B Cyclic voltammograms showing expanded potential range. C. Coatings applied asymmetrically to interdigital structures on CMOS2 lablets.

The final deposition finish of the films was also improved using reduced graphene oxide (RGO) as an additive to the Ppy [3]. Finally Ppy was also added to the MnO2 supercapacitor to increase longevity of the material and increase conductivity. The new Ppy/MnO2-Ppy-RGO asymmetric supercapacitor system was found to show lower capacitance when combined with Na2SO4 as the electrolyte. These new asymmetric films have an estimated capacitance of around 400 F/m2 which is in the same region as the MnO2-MnO2 symmetric supercapacitors, however the new materials have a greater working voltage, up to 1.4 V. 

The final optimised system replaced the 1 M Na2SO4 electrolyte with 1 M KNO3 for the final fabrication conditions. (publication pending)

[1] Brousse T and Bélanger D 2003 A Hybrid Fe[sub 3]O[sub 4]-MnO[sub 2] Capacitor in Mild Aqueous Electrolyte Electrochemical and Solid-State Letters 6(11) A244-5.

[2] Khomenko V, et al. 2005 High-voltage asymmetric supercapacitors operating in aqueous electrolyte Applied Physics A 82(4) 567-573.

[3] Wang C, et al. 2014 High-voltage and high-rate symmetric supercapacitor based on MnO2-polypyrrole hybrid nano film.  Nanotechnology 25 305401-305410.

Highlight in Y3: WP6, RUBa,c

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