Novel Insight into the Concept of Favorable Combination of Electrodes in High Voltage Supercapacitors: Toward Ultrahigh Volumetric Energy Density and Outstanding Rate Capability

Abstract

Most of the biomass-derived carbon-based supercapacitors using organic electrolytes exhibit very low energy density due to their low operating potential range between 2.7 and 3.0 V. A novel insight into the concept of the different porous architecture of electrode materials that is employed to extend a device's operating potential up to 3.4 V using TEABF₄ in acetonitrile, is reported. The combination of two high surface area activated carbons derived from abundant natural resources such as industrial waste cotton and wheat flour as sustainable and green carbon precursors is explored as an economical and efficient supercapacitor carbon electrode. Benefitting from the simultaneous achievement of the higher potential window (3.4 V) with higher volumetric capacitance (101 F cm^-3), the supercapacitor electrodes exhibit higher volumetric energy density (42.85 Wh L^-1). Bimodal pore size distribution of carbon with a tuned pore size and high specific surface area of the electrode can promote the fast transport of cations and anions. Hence, it exhibits a high rate capability even at 30 A g^-1. In addition, the electrodes remain stable during operation cell voltage at 3.4 V upon 15 000 charging-discharging cycles with 90% capacitance retention.

Keywords: carbons; high durability; supercapacitors; volumetric capacitance; volumetric energy density.

Figure 1

Overall concept of favorable combination of electrodes for high voltage supercapacitors.

Figure 2

Surface morphology of the supercapacitor carbons examined by SEM analysis: a) ACF, b) AWF, c) ACF electrode, d) AWF electrode, e,f) cross‐section of ACF and AWF electrodes, g,h) elemental mapping of cross‐section of ACF and AWF electrodes, i,j) EDAX analysis of ACF and AWF.

Figure 3

N₂ adsorption–desorption isotherm of ACF and AWF: a) BET isotherm, b) average pore size versus pore volume, c) cumulative surface area versus pore size, d) cumulative pore volume versus pore size.

Figure 4

Electrochemical performances of ACF, AWF and combination of supercapacitor electrodes: a–c) ACF, d–f) AWF, g–i) combination of supercapacitor electrodes.

Figure 5

EIS of supercapacitor electrodes: a) ACF, b) AWF, c) combination of ACF//AWF supercapacitor electrodes.

Figure 6

Electrochemical performances of combination of ACF//AWF supercapacitor electrodes. a) CV curves at 5 mV s^–1, b) CV curves with different scan rates (5–1000 mV s^–1), c) GCD, d) EIS.

Figure 7

The rate capability, energy and power densities of combination of ACF//AWF supercapacitor electrodes. a) Gravimetric capacitance at various current densities, b) volumetric capacitance at various current densities, c) gravimetric energy density versus power density, d) volumetric energy density versus power density.

Figure 8

Durability test of the supercapacitor electrodes. a) Cycling stability, b) holding test.