Deep Eutectic Solvents for High‐Temperature Electrochemical Capacitors

Abstract

An invited contribution to the Marcin Opałło FestschriftThis article provides an overview of a deep eutectic mixture based on the application of lithium nitrate (V) and acetamide as an electrolyte in a carbon-based electrochemical capacitor. This type of electrolyte is intended to be applied in devices designed for operation under critical conditions (e. g., extreme temperatures). In contrast to water-and common organic-based formulations, the proposed electrolyte ensures good device performance at 100 °C. To describe the chemistry of the proposed mixture, infrared and Raman spectroscopy, differ-ential scanning calorimetry, and gas chromatography with mass spectrometry were used. Electrochemical analysis includes the verification of system ageing, self-discharge monitoring, leakage current measuring, and fundamental testing related to determining the specific capacitance or maximum voltage. Additionally, comprehensive analysis of the lithium nitrate salt and organic solvent addition to the operating system was carried out, including the replacement of lithium ions with sodium or potassium.

Ag(e)ing and Degradation of Supercapacitors: Causes, Mechanisms, Models and Countermeasures

“…Deep eutectic solvents (DES) have been proposed for supercapacitors operating at elevated temperatures [ 1 ]. Because one component (in [ 1 ], it was acetamide) may evaporate, precipitation of the other component (LiNO 3 ) may occur, yielding faster ageing because of the detrimental effects of solid deposition on porous electrode performance as discussed above.…”

“…Deep eutectic solvents (DES) have been proposed for supercapacitors operating at elevated temperatures [ 1 ]. Because one component (in [ 1 ], it was acetamide) may evaporate, precipitation of the other component (LiNO 3 ) may occur, yielding faster ageing because of the detrimental effects of solid deposition on porous electrode performance as discussed above. A DES based on lithium bis(fluorosulfonyl)imide and formamide as the electrolyte in an EDC-device showed gas evolution at excessive cell voltages, which was in part electrochemically reversible [ 165 ].…”

“…Although there does not appear to be a standard, it seems that a capacitance loss of 20% compared with the initial value and an increase of the ESR by 100% are the failure criteria that describe a device as worn out. The statement in [ 1 ] suggesting that the 80% criterion was set in the IEC 62391-1 standard attributed to [ 2 ] is misleading; the authors in the latter communication refer to this standard only because it describes the procedure of measuring the capacitance without proving any further criterion. Despite the claims praising the exceptional stability, i.e., constancy of said parameters, they tend to change over time and use, i.e., calendar ageing in terms of time passed and cyclic ageing in terms of run charge/discharge cycles can be noticed [ 3 ].…”

Recent Advances in the Synthesis of Inorganic Materials Using Environmentally Friendly Media

“…This family of DES is known as LADES (Lewis Acid DES)) [ 129 ], compared to the more common “BADES” (with Brønsted acids, such as choline chloride + oxalic acid). According to the Abbot classification, LADES belong to Type I, II, or IV DES (such as, for instance, ChCl:2ZnCl 2 , ChCl:2CrCl 3 ·6H 2 O, ZnCl 2 :urea 1:3.5 (or:4) melts), as do several amide-nitrate eutectics [ 130 ] (such as LiNO 3 :acetamide 22:78 eutectic, which was recently described as a valuable medium for electrochemical capacitors [ 131 ]) and the DES mixture already described (silver triflate:acetamide [ 79 ]), while Type III DES can form only BADES. The existence of these non-conventional melts was quite recently discussed regarding the preparation or modification of inorganic nanoparticles.…”

Natural Eutectic Mixtures of Sodium Salt and Fatty Acids as Electrolytes for Supercapacitors

“…14 Until now, the study of Na-based ESs as electrolytes for SCs has not been extensively investigated. Some of the studied systems include NaNO 3 with acetamide 15 and N-methylacetamide, 16 NaFSI and NaFTSI, or NaTFSICN 17 with N-methylacetamide and formamide. 18 Despite the promising results, voltage windows above 2 V 16 and specific capacitance above 100 F/ g in activated carbon (AC), 18 these studies lack life-cycling tests and do not address the ES safety issues.…”