Determining Realistic Electrochemical Stability Windows of Electrolytes for Electrical Double‐Layer Capacitors

Water-in-salt electrolytes (WISEs) have attracted widespread attention due to their non-flammability, environmental friendliness, and wider electrochemical stability window than conventional dilute aqueous electrolytes. When applied in the electrochemical energy storage (EES) devices, WISEs can offer many advantages such as high-level safety, manufacturing efficiency, as well as, superior electrochemical performances. Therefore, there is an urgent need for a timely and comprehensive summary of WISEs and their EES applications. In this review, the physicochemical and electrochemical properties of the WISEs are first introduced. Then, the research progresses of the WISEs using different metal salts and their analogues are summarized. Next, the current research progresses of WISEs applied in different EES devices (e.g., batteries and supercapacitors) as well as the insights into challenging and future perspectives are systematically discussed.

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“…Therefore, it is necessary to search salts used as WISEs with low molecular weight and low density. [ 112–114 ]…”

Section: Discussionmentioning

confidence: 99%

The Applications of Water‐in‐Salt Electrolytes in Electrochemical Energy Storage Devices

Liang

Hou

Dou

et al. 2020

Adv Funct Materials

153

116

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“…In most cases, the ESW of an electrolyte measured on metal electrodes is larger than that on porous carbon electrodes, which is probably due to that porous carbon exhibits much larger surface area and abundant catalytic sites. [154,157] On the other hand, to achieve high capacitance of SCs, theoretically it is beneficial to choose electrolytes contain only bare ions, such as ILs, without using solvents because the formed solvation shells around ions increase ion sizes. [149] The absence of solvents is expected to make a larger number of ions be adsorbed on the surface of electrode materials.…”

Section: Theoretical Aspects Into Electrolytesmentioning

confidence: 99%

“…Therefore, the ESW measured by experimental methods, such as CV and linear sweep voltammetry, is a reflection of combined features with both kinetics and thermodynamics taken into account. [ 150,154,155 ] The excess potential of the practical ESW (Δ E ) than the thermodynamic ESW (Δ E 0 ) is termed as overpotential (η):

Δ E = Δ E_{0} + η

…”

Section: Electrolytesmentioning

confidence: 99%

“…Moreover, an electrolyte may exhibit different practical ESWs when different electrodes are used. [ 154,156 ] Therefore, it is necessary to mention the electrodes used when describing ESW. In most cases, the ESW of an electrolyte measured on metal electrodes is larger than that on porous carbon electrodes, which is probably due to that porous carbon exhibits much larger surface area and abundant catalytic sites.…”

Section: Electrolytesmentioning

confidence: 99%

Section: Electrolytesmentioning

confidence: 99%

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Perspective on High‐Energy Carbon‐Based Supercapacitors

Dou

Park

2020

Energy & Environ Materials

166

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Supercapacitors based on carbon materials have advantages such as high power density, fast charging/discharging capability, and long lifetime stability, playing a vital role in the field of electrochemical energy storage technologies. To further expand the practical applications of carbon-based supercapacitors, their energy density, which is essentially determined by the specific capacitance and operating voltage, should be improved. This review provides fundamental knowledge on achieving high energy density of supercapacitors. We first address the relationship of the features of carbon materials, such as the surface area, pore size distribution, and surface functional groups, with their electrochemical performances, such as the gravimetric and volumetric capacitance, surface pseudocapacitance, and operating voltage. Then, we discuss the properties of electrolytes from nonaqueous and aqueous to hybrid one from the thermodynamic and kinetic aspects, and present their effects on capacitance and operating voltage. Finally, we illustrate different cell design strategies and their basic principles for increasing operating voltage. We also highlight the recent advances related to these fields and provide our insight into high-energy supercapacitors.

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Comparative Internal Pressure Evolution at Interfaces of Activated Carbon for Supercapacitors Containing Electrolytes Based on Linear and Cyclic Ammonium Tetrafluoroborate Salts in Acetonitrile

Nikiforidis

Phadke

Anouti

2022

Adv Materials Inter

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EDLC), where the prevalent mechanism entails non-Faradaic charge storage at the interface between a high surface area material and a liquid electrolyte. These energy storage devices are intriguing due to their high power density (10 kW kg −1 ), rapid response time (1 s), cycle-life (10 5 cycles) and safety. [1] Nanoporous carbon materials are commonly used in EDLCs. Their porous structures act as a bulk buffering reservoir for any medium, curtailing the ion transport resistance to the interior surface of the pores. [2] Increased pore accessibility caters to a larger number of cations to populate the electrode's double layer, leading to specific capacitances of the order of 200 F g −1 , as is for the case of activated carbon. [3] The latter is widely used in these energy storage devices as it is inexpensive, i.e., the carbonization process originates from wood, coal, and nutshell and is easily prepared compared with other porous materials such as templated carbons and carbide-derived carbons. With a specific surface area of ≈2000 m 2 g −1 , it can provide ≈30 mAh g −1 V −1 counter to 150 mAh g −1 V −1 for standard battery electrodes. [4,5] Typically, the electrochemical window of EDLCs is lower than that of batteries (e.g., 4.3 V for nickel manganese oxidegraphite battery). Thus, as the energy stored is proportional to the square root of the voltage (E EDLC = ½ C × V 2 ; C denotes capacitance and V voltage), their energy density is hindered, i.e., E LIB = 3-30 × E EDLC . It should be noted that E EDLC hinges on the nature of the double layer, that is, the specific Helmholtz compact layer geometry, the size of electrolyte cations and anions, their degree of solvation, and the orientation of the electrolyte solvent dipoles in the imposed electric field. [6] Accordingly, organic electrolytes are an attractive choice as they can reach operating voltages as high as 3.5 V. Acetonitrile (ACN) is a representative dipolar aprotic solvent that boasts operating temperatures at sub-zero range (T melting ACN = −45 °C), fluidity (η = 0.345 mPa s −1 at 25 °C), a large operating voltage window (>3.0 V), [7] low internal resistance, facile ionic adsorption within the pores of carbon-based electrodes and electrochemical stability due to its low viscosity and high dielectric constant (e = 38) In this study, the real-time increase in pressure of the accumulated gases at the electrode/electrolyte interface serves as a safety criterion for four conductive electrolytes comprising acetonitrile (ACN) and organic salts. They include tetrafluoroborate as an anion and cyclic 1,1-dimethylpyrrolidinium (Pyr11 + ), spiro-(1,1′)-bipyrrolidinium (SBP + ), acyclic methyl triethyl ammonium (Et 3 MeN + ) or standard tetraethylammonium (Et 4 N + ) as cations. The main focus lies on the SPBF 4 /ACN system. While the concentrated Pyr11BF 4 /ACN exhibits a minimal pressure evolution (≈25 Pa) under ambient conditions at 3.0 V, its electrochemical stability is inferior to SPBF 4 at high operating voltage. The electrolytes with acyclic tetrafluoroborate s...

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Determining Realistic Electrochemical Stability Windows of Electrolytes for Electrical Double‐Layer Capacitors

Cited by 45 publications

References 75 publications

The Applications of Water‐in‐Salt Electrolytes in Electrochemical Energy Storage Devices

The Applications of Water‐in‐Salt Electrolytes in Electrochemical Energy Storage Devices

Perspective on High‐Energy Carbon‐Based Supercapacitors

Comparative Internal Pressure Evolution at Interfaces of Activated Carbon for Supercapacitors Containing Electrolytes Based on Linear and Cyclic Ammonium Tetrafluoroborate Salts in Acetonitrile

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