Effect of the Electrolyte Alkaline Ions on the Electrochemical Performance of α-Ni(OH)2/Activated Carbon Composites in the Hybrid Supercapacitor Cell

Hybrid electrochemical supercapacitors supply a high energy density and reduced cycle stability. Herein, we provide new data on the effect of the Li+ and K+ ion from the aqueous alkaline electrolyte on the hybrid supercapacitor performance. The electrochemical cell is assembled by two dissimilar electrodes: AC versus alpha-Ni(OH)(2)/AC composite. Two types of alkaline electrolytes are used: individual KOH and mixed LiOH-KOH solutions. The performance of the composite electrodes is tested by galvanostatic and cyclic voltammetry experiments. The Li+ ions from the electrolyte display a positive effect on the discharge capacitance and the cycling stability of alpha-Ni(OH)(2)/AC. The improved performance is discussed on the basis of structure and morphology changes of the composite electrode after electrochemical testing that are probed by ex-situ X-ray Diffraction, Scanning Electron Microscopy and Atomic-force Microscopy. The results show that Li+ ions and H2O from the LiOH-KOH electrolyte are intercalated into alpha-Ni(OH)(2). The surface of the composite electrode becomes smoother in the mixed electrolyte. As a result, the alpha-Ni(OH)(2)/AC displays an improved performance in the mixed LiOH-KOH electrolyte than that in the individual KOH electrolyte.