Toward Reliable Values of Electrochemical Stability Limits for Electrolytes

Xu, Ke; Ding, Sheng; Jow, T. Richard

doi:10.1149/1.1392609

Cited by 280 publications

(286 citation statements)

References 18 publications

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“…While the onset of reduction occurs at approximately −2.5 V (see Figure 6B), the most commonly used J cut-off value of 1.0 mA/cm 2 predicts for all highly porous carbons unreasonably small cathodic limits in the range of −0.5 to −1.0 V. This is readily explained by the large capacitive current at these high-surface area electrodes. 3,24,38 This problem was also observed by Jow and coworkers, who recommended an alternative method for assessing the electrochemical electrolyte stability at electrodes with high surface areas. 21,24 They proposed an approach according to which the limit of electrochemical electrolyte stability is defined by the voltage at which the faradaic current associated with electrolyte decomposition reaches one ninth of the capacitive current (i.e., 10% of the total current, also referred to as 1/R cut-off ; see Figure 3 in Ref.…”

Section: Resultsmentioning

confidence: 71%

Unbiased Quantification of the Electrochemical Stability Limits of Electrolytes and Ionic Liquids

Mousavi

Dittmer

Wilson

et al. 2015

J. Electrochem. Soc.

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The electrochemical window is the potential range in which an electrolyte/solvent system does not get reduced or oxidized. Usually, voltammograms are measured, and the potentials at which specific current densities are reached are identified as the electrochemical limits. We measured electrochemical limits of several electrolytes-including ionic liquids-and show that this approach has disadvantages that can be overcome by an alternate approach of defining electrochemical limits. The choice of the cutoff current density, J cut-off , is arbitrary and strongly affects the determined electrochemical windows, which are strongly influenced by electrolyte mass transport. Moreover, the J cut-off method does not provide an accurate estimate of the electrochemical window at electrodes with high surface areas, where the capacitive currents are large. We propose a method that requires no definition of J cut-off . This method minimizes electrolyte mass transport effects, gives realistic electrochemical stability limits at high surface area electrodes, and is less affected by experimental parameters such as the scan rate. The method is based on linear fits of the current-voltage curve at potentials below and above the onset of electrolyte decomposition. The potential at which the two linear fits intersect is defined as the electrolyte electrochemical limit. Electrolytes and solvents are essential for the proper function of a variety of electrochemical devices, such as batteries and supercapacitors. The voltage polarization in these devices can cause electrochemical degradation of the electrolyte and solvent, resulting in device malfunction. This can be avoided by constraining the working range of the device to the electrochemical window limited by the electrolyte and solvent, i.e., the potential range in which they are chemically stable and do not get reduced or oxidized.1,2 Due to their localized charges, the inherently ionic electrolytes often have a lower electrochemical stability than neutral solvent molecules, and therefore frequently limit the device working range.2 There has been extensive research on modifying the structure of electrolytes to improve their electrochemical stability, and thus expanding their working range. [3][4][5][6][7] The determination of the electrochemical window of electrolytes is not well defined. Generally a current-voltage polarization curve is measured, starting at a voltage at which the electrolyte is electrochemically stable, followed by increasing or decreasing the potential to observe the anodic or cathodic decompositions, respectively. The potential at which a specific current density, J, is reached is defined as the cathodic or anodic limit of the electrolyte. This approach has several disadvantages, as noted by several researchers.3-5 Firstly, since the choice of the cut-off current density is arbitrary, different standards have been applied in the literature. Cut-off current densities, J cut-off , in the range of 0.01 to 5.0 mA/cm 2 were reported, 3,7-20 resulting in electrochemical ...

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Section: Resultsmentioning

confidence: 71%

Unbiased Quantification of the Electrochemical Stability Limits of Electrolytes and Ionic Liquids

Mousavi

Dittmer

Wilson

et al. 2015

J. Electrochem. Soc.

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“…Several flaws in using this method to determine the operating voltage of devices have been raised, and alternative approaches explored. [46][47][48][49] As the ESW tends to be asymmetric with respect to the open circuit potential of symmetric EDLCs, the operating potential that can be used without appreciable electrolyte decomposition is often substantially lower than the full ESW. 20 Operating potentials for the symmetric cells used in this work were identified using symmetrical two electrode cells in a manner similar to that employed in previous investigations.…”

Section: Electrochemical Stability Of Ionic Liquidsmentioning

confidence: 99%

Ionic liquid based EDLCs: influence of carbon porosity on electrochemical performance

2014

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Electrochemical double layer capacitors (EDLCs) are a category of supercapacitors; devices that store charge at the interface between electrodes and an electrolyte. Currently available commercial devices have a limited operating potential that restricts their energy and power densities. Ionic liquids (ILs) are a promising alternative electrolyte as they generally exhibit greater electrochemical stabilities and lower volatility. This work investigates the electrochemical performance of EDLCs using ILs that combine the bis(trifluoromethanesulfonyl)imide anion with sulfonium and ammonium based cations. Different activated carbon materials were employed to also investigate the influence of varying pore size on electrochemical performance. Electrochemical impedance spectroscopy (EIS) and constant current cycling at different rates were used to assess resistance and specific capacitance. In general, greater specific capacitances and lower resistances were found with the sulfonium based ILs studied, and this was attributed to their smaller cation volume. Comparing electrochemical stabilities indicated that significantly higher operating potentials are possible with the ammonium based ILs. The marginally smaller sulfonium cation performed better with the carbon exhibiting the largest pore width, whereas peak performance of the larger sulfonium cation was associated with a narrower pore size. Considerable differences between the performance of the ammonium based ILs were observed and attributed to differences not only in cation size but also due to the inclusion of a methoxyethyl group. The improved performance of the ether bond containing IL was ascribed to electron donation from the oxygen atom influencing the charge density of the cation and facilitating cation–cation interactions.

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“…The practical EDLC electrodes, however, suffer from a self-discharge at the charged state that is caused by leakage currents. [1][2][3][4][5] This nonideally polarized behavior should thus be minimized to improve the charge-discharge efficiency and reliability of commercial cells.The leakage current appearing in EDLC electrodes can be analyzed using ac impedance spectroscopy. When impedance data are analyzed using the conventional Nyquist plot, the vertical line in the low-frequency region that is observed for ideally polarized electrodes becomes inclined with an increase in the leakage current.…”

mentioning

confidence: 99%

Complex Capacitance Analysis on Leakage Current Appearing in Electric Double-layer Capacitor Carbon Electrode

Jang

Yoon

et al. 2005

J. Electrochem. Soc.

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Complex capacitance analysis was done on the porous carbon electrode-electrolyte interface, where a minor leakage current is involved in addition to the dominant capacitor charging current. Based on the transmission line model, imaginary capacitance profiles ͑C im vs. log f͒ were theoretically derived for a cylindrical pore and multiple pore systems of nonuniform pore geometry. The parallel RC circuit was assumed for the interfacial impedance, where R is the charge-transfer resistance for leakage current and C the double-layer capacitance. The theoretical derivation illustrated that the resistive tail relevant to the leakage current appears in addition to the capacitive peak, which was in accordance with the experimental data taken on the porous carbon electrode. The electric double-layer capacitor ͑EDLC͒ parameters such as the extent of leakage current, total capacitance, and rate capability were visually estimated from the imaginary capacitance profiles. The more quantitative EDLC parameters were obtained by a nonlinear fitting to the experimental data. Electric double-layer capacitor ͑EDLC͒ utilizes the double layer formed at the electrode-electrolyte interface, where electric charges are stored on the electrode surface and ions of counter charge are arranged in the electrolyte side. The most demanding feature for EDLC electrodes is the ideally polarized behavior over a wide potential range. The practical EDLC electrodes, however, suffer from a self-discharge at the charged state that is caused by leakage currents. [1][2][3][4][5] This nonideally polarized behavior should thus be minimized to improve the charge-discharge efficiency and reliability of commercial cells.The leakage current appearing in EDLC electrodes can be analyzed using ac impedance spectroscopy. When impedance data are analyzed using the conventional Nyquist plot, the vertical line in the low-frequency region that is observed for ideally polarized electrodes becomes inclined with an increase in the leakage current. [6][7][8] The extent of leakage current can thus be estimated from the degree of inclination. The problem here, however, is that the inclination is also observed even in ideally polarized electrodes when they have a nonuniform pore geometry that is common in most practical porous EDLC electrodes. [9][10][11][12] In theory, the differentiation between the leakage current and nonuniform pore geometry for the cause of inclination is possible when the measurement is made at very low frequencies. In the extremely low-frequency region, ideally polarized electrodes with nonuniform pore geometry give a vertical line on the Nyquist plot, whereas the leakage current is visualized as a semicircle whose diameter reflects the charge-transfer resistance for leakage reaction. In practice, however, it is difficult to obtain data at such a low frequency due to an instrumental limitation and extremely long measuring time.In this work, the complex capacitance analysis is done on the leakage current involved in porous carbon electrode. From the imagi...

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Toward Reliable Values of Electrochemical Stability Limits for Electrolytes

Cited by 280 publications

References 18 publications

Unbiased Quantification of the Electrochemical Stability Limits of Electrolytes and Ionic Liquids

Unbiased Quantification of the Electrochemical Stability Limits of Electrolytes and Ionic Liquids

Ionic liquid based EDLCs: influence of carbon porosity on electrochemical performance

Complex Capacitance Analysis on Leakage Current Appearing in Electric Double-layer Capacitor Carbon Electrode

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