Langmuir, Vol.31, No.28, 7835-7843, 2015
Solid State Flexible Asymmetric Supercapacitor Based on Carbon Fiber Supported Hierarchical Co(OH)(x)CO3 and Ni(OH)(2)
Conducting flexible carbon fiber (CF) cloth was used as a substrate for the hydrothermal growth of nickel hydroxide (Ni(OH)(2)) and cobalt hydroxy carbonate [Co(OH)(x)CO3] with unique hierarchical flowery architecture and then was used as a flexible supercapacitor electrode. In a three-electrode configuration in 6 M KOH aqueous electrolyte, the CF Ni(OH)(2) and CF-Co(OH)(x)CO3 electrode showed the maximum specific capacitance of 789 F/g and 550 F/g, respectively, at 2A/g current accompanied by outstanding cycle stability by retaining 99.9% and 99.5% specific capacitance over 1500 consecutive charge discharge cycles at 5 A/g. However, the low cell voltage (0.4 V) restricted the respective specific energy to 4.38 and 3.05 Wh/kg at a specific power of 100 W/kg. To overcome the issue, two solid state flexible asymmetric supercapacitors were fabricated using the CF-Ni(OH)(2) and CF-Co(OH)(x)CO3 as the anode and sonochemically deposited CNT over carbon fiber as the cathode material in PVA-KOH gel electrolyte. The as-fabricated flexible supercapacitors CF Ni(OH)(2)//CF-CNT and CF-Co(OH)(x)CO3//CF-CNT were able to deliver high specific energy of 41.1 and 33.48 Wh/kg, respectively, at high specific power of 1.4 kW/kg accompanied by excellent cycle stability (retaining 98% and 97.6% specific capacitance, respectively, over 3000 charge discharge cycle at 5 A/g).