A comparative study of activated carbon-based symmetric supercapacitors in Li2SO4 and KOH aqueous electrolytes

Abstract

In this work, we have prepared activated carbon (AC)-based symmetric supercapacitor (SC) using Li 2 SO 4 aqueous electrolyte instead of H 2 SO 4 and KOH and obtained a device with an improved cell voltage window (CVW) of 0−1.6 V from 0 to 1.0 V. The SC using KOH electrolyte is also fabricated for comparison. The electrochemical characteristics of SCs such as cyclic voltammetry (CV), galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS) and cycle stability are investigated systematically. The possible redox reactions of electrodes that occurred in Li 2 SO 4 and KOH electrolytes that restrict the CVWs are discussed. The results indicate that in the case of Li 2 SO 4 , the AC electrode can deliver a specific capacitance of 210 Fg −1 at a current density of 0.1 Ag −1 , and the energy density of capacitor can be as high as 16.9 Wh kg −1 at 200 Wkg −1 (based on the total mass of active electrode materials), 80% higher than that in the case of KOH.

Electrochemical Capacitors Based on Carbon Electrodes in Aqueous Electrolytes

“…The potential window of the carbon/Na 2 SO 4 system is roughly twice that in the traditional KOH and H 2 SO 4 electrolytes [17,[69][70][71]. Such enhancement has been attributed either to the high overpotential for dihydrogen evolution at the negative electrode [79] or to the strong solvation of cations and anions [19].…”

“…Despite all the aforementioned advantages of aqueous electrolyte, a major disadvantage of water, when considering Equations 8.6 and 8.7, is its low thermodynamic stability and consequently low reachable cell potential of 1.23 V [68]. In practice, it is even less than 1.00 V in symmetric carbon-based SCs with H 2 SO 4 and KOH aqueous electrolytes [17,[69][70][71][72], whereas AC/AC capacitors in organic medium can be cycled at 2.7-2.8 V [73]. Hence, most of the industrial EDLCs available in the market are based on organic electrolyte, for example, tetraethylammonium tetrafluoroborate in AN.…”

“…Even though the thermodynamic stability of water is 1.23 V, the cell potential of symmetric carbon-based SCs with H 2 SO 4 and KOH aqueous electrolytes is generally less than 1.00 V [17,[69][70][71][72], because the potential range of the individual electrodes is not controlled, and one of them might operate out of the stability limits. Consequently, for a long time, it has been accepted that the energy density of capacitors in aqueous electrolyte is much lower than in organic electrolyte.…”

“…Notwithstanding, aqueous electrolytes based on neutral sulfates lately revealed potentialities for developing high-energy density AC/AC ECs, with cell potential reaching values as high as 1.6 V in 0.5 mol l −1 Na 2 SO 4 (around 12% capacitance fading after 8000-10 000 galvanostatic cycles at 1 A g −1 ) [17,18] and 2 V when using 1 mol l −1 Li 2 SO 4 [19]. The Ragone plots of AC/AC ECs in Li 2 SO 4 and KOH aqueous electrolytes (Figure 8.7) show that the energy density in Li 2 SO 4 is enhanced by 80% as compared with KOH [70]. At 25 s time constant, the energy and power density in Li 2 SO 4 are 12.3 Wh kg −1 and 1.6 kW g −1 against 7.2 Wh kg −1 and 1.0 kW g −1 , respectively, in KOH.…”

Tra Bac Activated Carbon Used as Electrode Material in Aqueous Supercapacitor

“…Although, the high concentration of salt solution can enlarge the potential window due to the increase of over potential to H + reduction or O 2 oxidation reaction. Sun et al [13] reported the enlargement of oxidation potential of EDLC up to 1.6 V in 1 M Li 2 SO 4 solution. Therefore, in our work, the operational potential in Li 2 SO 4 and Na 2 SO 4 solution was cut at 1 V and the concentration was 1 M to avoid the corrosion of stainless steel current collector and the decomposition of electrolyte at its surface.…”