Ionic Liquid-Based Electrolytes for Energy Storage Devices: A Brief Review on Their Limits and Applications

Abstract

Since the ability of ionic liquid (IL) was demonstrated to act as a solvent or an electrolyte, IL-based electrolytes have been widely used as a potential candidate for renewable energy storage devices, like lithium ion batteries (LIBs) and supercapacitors (SCs). In this review, we aimed to present the state-of-the-art of IL-based electrolytes electrochemical, cycling, and physicochemical properties, which are crucial for LIBs and SCs. ILs can also be regarded as designer solvents to replace the more flammable organic carbonates and improve the green credentials and performance of energy storage devices, especially LIBs and SCs. This review affords an outline of the progress of ILs in energy-related applications and provides essential ideas on the emerging challenges and openings that may motivate the scientific communities to move towards IL-based energy devices. Finally, the challenges in design of the new type of ILs structures for energy and environmental applications are also highlighted.Polymers 2020, 12, 918 2 of 37 and structural stability of the ionic species are extremely crucial and responsible for the efficient outputs in energy storage devices. In the light of this fact, high current (i.e., automotive applications) operating devices are required to have storage devices that have higher power density and faster ion transport properties. Previous studies have suggested that one of the most favorable approaches to simultaneously progress the safety, along with energy and power densities, is the incorporation of ILs into the electrolyte system [11].In past decades, room temperature ionic liquids (RTILs) have been acknowledged with noteworthy attention due to their excellent miscellaneous properties, such as thermal and chemical stability, tunable structure over the wide range of operating temperature, a broad electrochemical stability window, high ionic conductivity in the range of 10 −3 -10 −2 S cm −1 at room temperature, and non-flammability as a potential candidate for EES devices, such as LIBs [12], electric double-layer SCs [13][14][15], proton exchange membrane fuel cells, and solar cells [16][17][18][19]. Using ILs as an alternative to organic electrolytes has the advantage of improving the ions' mobility, as well as eliminating the hazards associated within the organic electrolytes. Additionally, ILs often have comparable zero or negligible vapor pressure at normal temperatures due to their high thermal stability. Because of the above statements, ILs are widely used as solvents or electrolytes for energy storage applications in recent times [7,18,[20][21][22][23][24][25][26][27].Typically, ILs are organic salts, also defined as molten salts, which have a lower melting point (<100 • C) with a wide degree of variation. Moreover, they are comprised of organic cations, such as an pyridinium (PY) [28], imidazolium (Im) [29][30][31][32], pyrrolidinium (PYR) [33][34][35][36], ammonium [37], and sulfonium [38], derivatives joined inorganic or organic anions, such as BF 4 − [39,40], PF 6 − [30], triflate (...

UV-Cured Poly(Siloxane-Urethane)-Based Polymer Composite Materials for Lithium Ion Batteries—The Effect of Modification with Ionic Liquids

“…However, in most of these works, flammable solvents were used, including mainly ethylene carbonate (EC), propylene carbonate (PC), or a standard flammable 1/2 v/v mixture of EC with dimethyl carbonate (DMC) referred to as EC/DMC in this paper. Therefore, following earlier studies [16,17], the possibility of replacing these flammable solvents in crosslinked (usually UV-cured) polymer systems designed for lithium ion batteries with non-flammable ILs was investigated more deeply [18][19][20][21][22][23][24][25][26][27]. Specifically, application of the concept of single-ion conducting polymer electrolytes by synthesizing a polyurethane based on PEO and specifically designed IL monomer seemed to be quite promising [24].…”

Redox-active electrolyte-based MnWO4//AC asymmetric supercapacitors

“…Increasing environmental pollution and depletion of traditional energy resources has aroused extensive attention on energy storage and energy conversion devices [1]. Especially, electrochemical energy storage devices are projected to be a vital part of electronic portable devices, electric vehicles, and airplanes [2,3].…”

“…Among all the energy storage systems, supercapacitors (SCs) are the most promising candidates for the above-mentioned applications because they deliver relatively high power, fast charging, good cyclic stability, and low maintenance cost [4][5][6]. However, SCs possess very low energy density in comparison to fuel cells and batteries [2,3]. The energy density of SCs can be further enhanced by developing asymmetric supercapacitors (AS) where one electrode stores the charges by faradaic redox reactions and the other one stores the charges based on the electrical double layer capacitance (EDLC) mechanism [3].…”

Recent Advances in Nanostructured Transition Metal Carbide- and Nitride-Based Cathode Electrocatalysts for Li–O2 Batteries (LOBs): A Brief Review

“…Graphene and its composites have thus been broadly utilized in energy storage and conversion devices, but, due to the mono-layer thickness of graphite, they offer only a limited range of applications. On the other hand, graphene analogues, including 2D layered transition metal oxides, phosphides, sulfides, and selenides, have been considered capable candidates for use in energy storage devices because of their ultrathin nature and planar topology [ 16 ]. However, due to their low working potential, poor specific capacity, weak cyclability, and high-temperature synthesis, these compounds have yet to be commercialized.…”