ZnNiCo oxide/three-dimensional graphene electrode performance in propylene carbonate- and water-based Li-ion hybrid supercapacitors

ZnNiCo oxide (ZNCO)-decorated three-dimensional graphene (3DG) was synthesized using a hydrothermal process, and applied as the electrode material in water- and propylene carbonate (PC)-based Li-ion hybrid supercapacitor (LIHSC). The properties of the prepared composite (i.e., 3DG@ZNCO) were compared with those of pristine 3DG hydrogel (3DGH) and ZNCO, prepared separately using the same conditions. ZNCO particles formed in 3DG@ZNCO showed a smaller particle size than the pristine ZNCO, and their simultaneous growth with 3DGH resulted in a higher interlayer spacing in 3DG@ZNCO than 3DGH. 3DG@ZNCO provided considerably higher specific capacitance, cycling performance, and lower charge resistance than the individual pristine comprising components in both water- and PC-based LiClO4 electrolytes. However, higher differences were observed when PC-based LiClO4 electrolyte was used, and 3DG@ZNCO exhibited the specific capacitance of 62.5 F.g−1 at 40 mV.s−1, which was higher than that obtained in the water-based LiClO4 electrolyte. This was confirmed by the highest Li+ diffusion coefficient of 2.83 × 10−15 cm2.s−1 recorded for 3DG@ZNCO in PC. The 3DG@ZNCO-based LIHSC containing PC exhibited a significantly higher energy density of 81.2 Wh.kg−1 and power density of 5976 W.kg−1, which were about 228.7% and 225.3% higher than those obtained for the water-based LIHSC (i.e., 24.7 Wh.kg−1 at 1837 W.kg−1).