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Cell voltage versus electrode potential range in aqueous supercapacitors

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ABSTRACT

Supercapacitors with aqueous electrolytes and nanostructured composite electrodes are attractive because of their high charging-discharging speed, long cycle life, low environmental impact and wide commercial affordability. However, the energy capacity of aqueous supercapacitors is limited by the electrochemical window of water. In this paper, a recently reported engineering strategy is further developed and demonstrated to correlate the maximum charging voltage of a supercapacitor with the capacitive potential ranges and the capacitance ratio of the two electrodes. Beyond the maximum charging voltage, a supercapacitor may still operate, but at the expense of a reduced cycle life. In addition, it is shown that the supercapacitor performance is strongly affected by the initial and zero charge potentials of the electrodes. Further, the differences are highlighted and elaborated between freshly prepared, aged under open circuit conditions, and cycled electrodes of composites of conducting polymers and carbon nanotubes. The first voltammetric charging-discharging cycle has an electrode conditioning effect to change the electrodes from their initial potentials to the potential of zero voltage, and reduce the irreversibility.

No MeSH data available.


Effect of operating voltage on charge-discharge cycle stability.The 2nd and 500th cyclic voltammograms of PAN-CNT symmetrical supercapacitors with the maximum charging voltage (MCV) of (a) 0.65 V and (b) 0.68 V. Voltage scan rate: 10 mV s−1.
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f5: Effect of operating voltage on charge-discharge cycle stability.The 2nd and 500th cyclic voltammograms of PAN-CNT symmetrical supercapacitors with the maximum charging voltage (MCV) of (a) 0.65 V and (b) 0.68 V. Voltage scan rate: 10 mV s−1.

Mentions: The CVs in Figs. 3 and 4 commonly exhibit an increase of current near the high voltage end of the scanned voltage window, indicating some irreversible processes. They provide a reference of the MCV for the construction and safe operation of supercapacitors with different electrode selections. In Fig. 5, the PAN-CNT symmetrical supercapacitor showed initially capacitive CVs at the MCV of 0.65 and 0.68 V. The energy capacity was 9% higher in the latter case. However, after 500 continuous charge-discharge cycles, the current decay was more severe at the MCV of 0.68 V. The capacitance retention was calculated as 81.2% and 77.4% at the MCV of 0.65 and 0.68 V respectively. Thus, there is a trade-off between the MCV and the cycle life of a supercapacitor. This seemingly simple but important fact has rarely been reported in the literature1722. It suggests that in order to maximise the cycle life, a supercapacitor should not operate at an inappropriately high voltage.


Cell voltage versus electrode potential range in aqueous supercapacitors
Effect of operating voltage on charge-discharge cycle stability.The 2nd and 500th cyclic voltammograms of PAN-CNT symmetrical supercapacitors with the maximum charging voltage (MCV) of (a) 0.65 V and (b) 0.68 V. Voltage scan rate: 10 mV s−1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384324&req=5

f5: Effect of operating voltage on charge-discharge cycle stability.The 2nd and 500th cyclic voltammograms of PAN-CNT symmetrical supercapacitors with the maximum charging voltage (MCV) of (a) 0.65 V and (b) 0.68 V. Voltage scan rate: 10 mV s−1.
Mentions: The CVs in Figs. 3 and 4 commonly exhibit an increase of current near the high voltage end of the scanned voltage window, indicating some irreversible processes. They provide a reference of the MCV for the construction and safe operation of supercapacitors with different electrode selections. In Fig. 5, the PAN-CNT symmetrical supercapacitor showed initially capacitive CVs at the MCV of 0.65 and 0.68 V. The energy capacity was 9% higher in the latter case. However, after 500 continuous charge-discharge cycles, the current decay was more severe at the MCV of 0.68 V. The capacitance retention was calculated as 81.2% and 77.4% at the MCV of 0.65 and 0.68 V respectively. Thus, there is a trade-off between the MCV and the cycle life of a supercapacitor. This seemingly simple but important fact has rarely been reported in the literature1722. It suggests that in order to maximise the cycle life, a supercapacitor should not operate at an inappropriately high voltage.

View Article: PubMed Central - PubMed

ABSTRACT

Supercapacitors with aqueous electrolytes and nanostructured composite electrodes are attractive because of their high charging-discharging speed, long cycle life, low environmental impact and wide commercial affordability. However, the energy capacity of aqueous supercapacitors is limited by the electrochemical window of water. In this paper, a recently reported engineering strategy is further developed and demonstrated to correlate the maximum charging voltage of a supercapacitor with the capacitive potential ranges and the capacitance ratio of the two electrodes. Beyond the maximum charging voltage, a supercapacitor may still operate, but at the expense of a reduced cycle life. In addition, it is shown that the supercapacitor performance is strongly affected by the initial and zero charge potentials of the electrodes. Further, the differences are highlighted and elaborated between freshly prepared, aged under open circuit conditions, and cycled electrodes of composites of conducting polymers and carbon nanotubes. The first voltammetric charging-discharging cycle has an electrode conditioning effect to change the electrodes from their initial potentials to the potential of zero voltage, and reduce the irreversibility.

No MeSH data available.