1028
Expanding the Potential Window of Aqueous Hybrid Supercapacitors with Electrostatically Sprayed Manganese Oxide Composite Cathodes

Sunday, 13 May 2018: 11:20
Room 205 (Washington State Convention Center)
R. Agrawal, A. Rabiei Baboukani, and C. Wang (Florida International University)
Electrochemical capacitors or “supercapacitors” are a class of electrochemical energy storage devices that bridge the gap between conventional capacitors and rechargeable batteries. Despite their high power handling, their low specific energy densities limit their application in fields that require simultaneous supply of high power and high energy. In the wake of improving the energy density of supercapacitors, the concept of utilizing redox and double layer mechanisms within one system has garnered significant attention in recent years. Such systems typically referred to as asymmetric or hybrid capacitors benefit from the kinetics and cycle life of the double layer material and the high capacitance of the redox material. In this work, electrostatic spray deposition (ESD) derived manganese oxide (MnOx) films were employed as the redox component for the hybrid cell. Three compositions of MnOx were evaluated for the optimal electrochemical characteristics with different amounts of carbon nanotube (CNT) additive. The composition with 10% CNT (MnOx-CNT 9-1) exhibited superior electrochemical performance as compared to both the pristine MnOx and MnOx films with 20% CNT (MnOx-CNT 8-2). The MnOx-CNT 9-1 electrode exhibited a high specific capacitance of 281 Fg-1 in addition to excellent rate handling and high capacitance retention over long term cycling. Upon verifying the viability of the ESD derived MnOx-CNT 9-1 films as electrochemical electrodes, the latter were used in an asymmetric capacitor configuration comprising activated carbon (AC) counter electrodes. The hybrid capacitor with the AC electrode with a mass 2.6 times as that of the MnOx-CNT 9-1 electrode exhibited optimal energy-power trade-off with high rate capability as compared to the other asymmetric capacitors, as well as the symmetric AC//AC and MnOx-CNT 9-1// MnOx-CNT 9-1 systems. The optimized asymmetric capacitor exhibited a maximal energy of 30.3 Whkg-1 and a maximal power density of 4 kWkg-1; the excellent electrochemical characteristics of the optimized hybrid capacitor are ascribed to the wider cell voltage of 2V as well as the high gravimetric capacitance of the ESD based MnOx-CNT composite cathode.