Improving the Stability of Supercapacitors at High Voltages and High Temperatures by the Implementation of Ethyl Isopropyl Sulfone as Electrolyte Solvent

Abstract

promising technologies. [1] EDLCs display high power densities and extremely high lifetime which makes them the technology of choice for a variety of applications requiring a fast and continuous delivery of energy. However, as the energy density of these devices is rather limited (5-8 Wh kg −1 ), their use is currently limited to applications that require a relatively low amount of energy. [2] As indicated by several studies, an increase in energy density would lead to a drastic increase in the number of possible applications for EDLCs. [3] Furthermore, it would enable the use of these devices as replacement for established battery systems in fields where high power is required. [4] This latter application is particularly interesting because nowadays the use of batteries in high-power applications is typically leading to increased cell degradation and, consequently, to increased cost due to early system failure. For this reason, in the available electric vehicles, EDLCs are often applied as a support to reduce the load on the main battery system during rapid acceleration and power uptake by regenerative braking. It has been shown that this hybrid energy storage solution results in improved performance while extending the lifetime of the battery system. [5] Nonetheless, further improvements are urgently needed to extend the battery life even more.For these reasons, current research focuses on the development of EDLCs with improved energy density. To reach this goal, the electrode capacitance needs to be maximized and, at the same time, the operating voltage of these systems needs to be significantly increased. While commercially available devices are limited to operating voltages of up to 3.0 V, an increase to 3.2 V or more would increase the energy density significantly. The operating voltage of EDLCs is mainly determined by the onset of electrolyte decomposition at the electrode surface. [6] The state-of-the-art electrolytes consist of solutions containing ammonium-based conducting salt, e.g. tetraethylammonium tetrafluoroborate (TEABF 4 ), dissolved in acetonitrile (ACN). [7] These electrolytes display high conductivity but guarantee high stability only if used in devices with a maximum voltage of 3 V. [8] With the aim to overcome this limitation and realize high-voltage EDLCs, a variety of novel solvents, salts, and ionic liquids have been investigated in the last years. [9] Although Two of the main weaknesses of modern electric double-layer capacitors are the rather limited ranges of operating voltage and temperature in which these devices do not suffer from the occurrence of irreversible decomposition processes. These parameters are strongly interconnected and lowering the operating voltage when increasing the temperature is unavoidable, so as to protect the electric double-layer capacitor from damage. With the aim to maintain the operating voltage as high as possible at elevated temperatures, in this study, the application of ethyl isopropyl sulfone as an electrolyte solvent for electric double-layer ...

The Many Deaths of Supercapacitors: Degradation, Aging, and Performance Fading

“…[80] Köps et al investigated using EiPS in EDLCs at high voltages and temperatures. [81] By investigating the aged electrolyte by GC-MS and the aged electrodes by XRD and XPS, the authors propose several degradation mechanisms that coincide well with the previously mentioned works. GC-MS analysis of the aged electrolyte revealed that no soluble decomposition products originating from the solvent were formed.…”

“…While resulting in pore blocking and thus capacitance‐reducing effects, this layer drastically increased the electrochemical long‐term stability. [ 81 ]…”

“…While resulting in pore blocking and thus capacitance-reducing effects, this layer drastically increased the electrochemical long-term stability. [81] In summary, primary failure mechanisms of EiPS-based EDLCs are the evolution of volatile decomposition products (ethane, propane) and the deposition of insoluble decomposition products on the positive and negative electrodes.…”

Ion Bridging by Carbon Dioxide Facilitates Electrochemical Energy Storage at Charged Carbon–Ionic–Liquid Interfaces

“…[ 30 ] The inhibited hydrolysis of the acidic C2‐H position in the [EMIM] + cation or the fluorinated [BF 4 ] − anion on the hydrophilic NDSTC interface thus contributes to reduced electrolyte decomposition and improved floating stability. [ 27 ] The cycling test of the NDSTC‐IL+CO 2 device (Figure S9c–e, Supporting Information) performed at 10 A g −1 for 10 000 cycles ends with a capacitance retention over 93.2% and a coulombic efficiency close to 100%, which is higher than that of 89.4% observed for the NDSTC‐IL device. This result highlights improved cycling stability with lower contact‐ and diffusion‐resistance, and thus lower thermal stress in NDSTC‐IL+CO 2 device during fast processes.…”

“…After balancing between the high‐energy demand and the voltage stability for practical application, the voltage window of NDSTC‐IL+CO 2 device is further expanding to3.4 V (Figure S6, Supporting Information). [ 27 ] The GCPL profiles exhibit a comparable coulombic efficiency over 98.5% and a specific capacitance of 198 F g −1 at a low current density of 0.5 A g −1 , indicating that no significant side reactions are induced with higher voltages. Accordingly, the NDSTC‐IL+CO 2 electrode delivers a specific energy of 63.4 Wh kg −1 at 75.6 W kg −1 , along with a power density of 7363 W kg −1 at 53.5 Wh kg −1 within a voltage window of 3.0 V (Figure S5b, Supporting Information).…”