Deep Eutectic Solvents Based on N-Methylacetamide and a Lithium Salt as Electrolytes at Elevated Temperature for Activated Carbon-Based Supercapacitors

Azepanium-based ionic liquids as green electrolytes for high voltage supercapacitors

This work provides a first-time-study of Azepanium-based ionic liquids (ILs) as electrolyte components for electrochemical double layer capacitors (EDLCs). Herein, two Azepanium-based ILs, namely N-methyl, N-butyl-azepanium bis(trifluoromethanesulfonyl)imide (Azp(14)TFSI) and N-methyl, N-hexyl-azepanium bis(trifluoromethanesulfonyl)imide (Azp(16)TFSI) were compared with the established IL N-butyl, N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr(14)TFSI) in terms of viscosity, conductivity, thermal stability and electrochemical behavior in EDLC systems. The ILs' operative potentials were found to be comparable, leading to operative voltages up to 3.5 V without significant electrolyte degradation. 

Mixtures of azepanium based ionic liquids and propylene carbonate as high voltage electrolytes for supercapacitors

This work provides a study of mixtures of the azepanium-based ionic liquid (IL) N-methyl, N-butyl-azepanium bis[(trifluoromethane) sulfonyl]imide (Azp₁₄TFSI) and propylene carbonate (PC) as electrolyte components in electrochemical double layer capacitors (EDLCs). The considered mixtures' properties were then compared to the properties of mixtures of N-butyl, N-methylpyrrolidinium bis[(trifluoromethane) sulfonyl]imide (Pyr₁₄TFSI) and PC in terms of viscosity, conductivity and electrochemical behavior. The mixtures' operative potentials were found to be comparable to each other, leading to operative voltages as high as 3.5 V, while retaining the low viscosities and high conductivities of PC based EDLC electrolytes.

The use of binary mixtures of 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide and aliphatic nitrile solvents as electrolyte for supercapacitors

Abstract The development of high voltage electrolytes is one of the key aspects for increasing both energy and power density of electrochemical double layer capacitors (EDLCs). The usage of blends of ionic liquids and organic solvents has been considered as a feasible strategy since these electrolytes combine high usable voltages and good transport properties at the same time. In this work, the ionic liquid 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide ([Pyrr14][TFSI]) was mixed with two nitrile-based organic solvents, namely butyronitrile and adiponitrile, and the resulting blends were investigated regarding their usage in electrochemical double layer capacitors. Both blends have a high electrochemical stability, which was confirmed by prolonged float tests at 3.2 V, as well as, good transport properties. In fact, the butyronitrile blend reaches a conductivity of 17.14 mS·cm−1 and a viscosity of 2.46 mPa·s at 20 °C, which is better than the state-of-the-art electrolyte (1 mol·dm−3 of tetraethylammonium tetrafluoroborate in propylene carbonate).

Energy storage in electrochemical capacitors: designing functional materials to improve device performance

Electrochemical capacitors, also known as supercapacitors, are becoming increasingly important components in energy storage, although their widespread use has not been attained due to a high cost/ performance ratio. Fundamental research is contributing to lowered costs through the engineering of new materials. Currently the most viable materials used in electrochemical capacitors are biomassderived and polymer-derived activated carbons, although other carbon materials are useful research tools. Metal oxides could result in a step change for electrochemical capacitor technology and is an exciting area of research. The selection of an appropriate electrolyte and electrode structure is fundamental in determining device performance. Although there are still many uncertainties in understanding the underlying mechanisms involved in electrochemical capacitors, genuine progress continues to be made. It is argued that a large, collaborative international research programme is necessary to fully develop the potential of electrochemical capacitors.

Comparative study on performances of trimethyl-sulfonium and trimethyl-ammonium based ionic liquids in molecular solvents as electrolyte for electrochemical double layer capacitors

The present work reports a comparative study on the performances of two bis[(trifluoromethyl)sulfonyl]imide-based protic (PIL) and aprotic (AIL) ionic liquids, namely, trimethyl-ammonium bis[(trifluoromethyl)sulfonyl]imide ([HN][TFSI], PIL) and trimethyl-sulfonium bis[(trifluoromethyl) sulfonyl]imide ([S][TFSI], AIL), as mixtures with three molecular solvents: gamma butyrolactone (?-BL), propylene carbonate (PC), and acetonitrile (ACN) as electrolytes for supercapacitor applications. After an analysis of their transport properties as a function of temperature, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge measurements were conducted at 25 and -30 C to investigate the performance of these mixtures as electrolytes for supercapacitors using activated carbon as the electrode material. Surprisingly, for each solvent investigated, no significant differences were observed between the electrolytes based on the PIL and AIL in their electrochemical performance due to the presence or the absence of the labile proton. Furthermore, good specific capacitances were observed in the case of ?-BL-based electrolytes even at low temperature. Capacitances up to 131 and 80 F·g are observed for the case of the [S][TFSI] + ?-BL mixture at 25 and -30 C, respectively. This latter result is very promising particularly for the formulation of new environmentally friendly electrolytes within energy storage systems even at low temperatures. © 2013 American Chemical Society.

Physicochemical Investigation of Adiponitrile-Based Electrolytes for Electrical Double Layer Capacitor

Sandwich nanoarchitecture of LiV3O8/graphene multilayer nanomembranes via layer-by-layer self-assembly for long-cycle-life lithium-ion battery cathodes

A lack of suitable high-performance cathode materials has become the major barrier to their applications in future advanced communication equipment and electric vehicle power systems. In this paper, we have developed a layer-by-layer self-assembly approach for fabricating a novel sandwich nanoarchitecture of multilayered LiV₃O₈ nanoparticle/graphene nanosheet (M-nLVO/GN) hybrid electrodes for potential use in high performance lithium ion batteries by using a porous Ni foam as a substrate. The prepared sandwich nanoarchitecture of M-nLVO/GN hybrid electrodes exhibited high performance as a cathode material for lithium-ion batteries, such as high reversible specific capacity (235 mA h g^-1 at a current density of 0.3 A g^-1), high coulombic efficiency (over 98%), fast rate capability (up to a current density of 10 A g^-1), and superior capacity retention during cycling (90% capacity retention with a current density of 0.3 A g^-1 after 300 cycles). Very significantly, this novel insight into the design and synthesis of sandwich nanoarchitecture would extend their application to various electrochemical energy storage devices, such as fuel cells and supercapacitors.

Carbons, Ionic Liquids, and Quinones for Electrochemical Capacitors

Carbons are the main electrode materials used in supercapacitors, which are electrochemical energy storage devices with high power densities and long cycling lifetimes. However, increasing their energy density capacity will improve their potential for commercial implementation.
In this regard, the use of high surface area carbons and high voltage electrolytes are well known strategies to increase the attainable energy density, and lately ionic liquids have been explored as promising alternatives to current state of the art acetonitrile-based electrolytes. Also, in terms of safety and sustainability ionic liquids are attractive electrolyte materials for supercapacitors. In addition, it has been shown that the matching of the carbon pore size with the electrolyte ion size further increases the attainable electrochemical double layer (ECDL) capacitance and energy density.
The use of pseudocapacitive reactions can significantly increase the attainable energy density, and quinonic-based materials offer a potentially sustainable and cost effective research avenue for both the electrode and the electrolyte.
This perspective will provide an overview of the current state of the art research on supercapacitors based on combinations of carbons, ionic liquids and quinonic compounds, highlighting performances and challenges and discussing possible future research avenues. In this regard, current interest is mainly focused on strategies which may ultimately lead to commercially competitive sustainable high performance supercapacitors for different applications including those requiring mechanical flexibility and biocompatibility.

Effect of the Electrolyte Formulation on the Performances of Edlc and Li-Ion Batteries

One of the most important components in electrochemical storage devices (batteries and supercapacitors) is undoubtedly the electrolyte. The basic function of any electrolyte in these systems is the transport of ions between the positive and negative electrodes. In addition, electrochemical reactions occurring at each electrode/electrolyte interface are the origin of the current generated by storage devices. In other words, performances (capacity, power, efficiency and energy) of electrochemical storage devices are strongly related to the electrolyte properties, as well as, to the affinity for the electrolyte to selected electrode materials. Indeed, the formulation of electrolyte presenting good properties, such as high ionic conductivity and low viscosity, is then required to enhance the charge transfer reaction at electrode/electrolyte interface (e.g. charge accumulation in the case of Electrochemical Double Layer Capacitor, EDLC). For practical and safety considerations, the formulation of novel electrolytes presenting a low vapor pressure, a large liquid range temperature, a good thermal and chemical stabilities is also required.

This lecture will be focused on the effect of the electrolyte formulation on the performances of electrochemical storage devices (Li-ion batteries and supercapacitors). During which, a summary of the physical, thermal and electrochemical data obtained by our group, recently, on the formulation of novel electrolyte-based on the mixture of an ionic liquid (such as EmimNTf2 and Pyr14NTf2) and carbonate or dinitrile solvents will be presented and commented. The impact of the electrolyte formulation on the storage performances of EDLC and Li-ion batteries will be also discussed to further understand the relationship between electrolyte formulation and electrochemical performances. This talk will also be an opportunity to further discuss around the effects of additives (SEI builder: fluoroethylene carbonate and vinylene carbonate), ionic liquids, structure and nature of lithium salt (LiTFSI vs LiPF6) on the cyclability of negative electrode to then enhance the electrolyte formulation. For that, our recent results on TiSnSb and graphite negative electrodes will be presented and discussed, for example 1,2.

1-C. Marino, A. Darwiche1, N. Dupré, H.A. Wilhelm, B. Lestriez, H. Martinez, R. Dedryvère, W. Zhang, F. Ghamouss, D. Lemordant, L. Monconduit “ Study of the Electrode/Electrolyte Interface on Cycling of a Conversion Type Electrode Material in Li Batteries” J. Phys.chem. C, 2013, 117, 19302-19313

2- Mouad Dahbi, Fouad Ghamouss, Mérièm Anouti, Daniel Lemordant, François Tran-Van “Electrochemical lithiation and compatibility of graphite anode using glutaronitrile/dimethyl carbonate mixtures containing LiTFSI as electrolyte” 2013, 43, 4, 375-385.

Binary Mixtures of 1-Butyl-1-Methylpyrrolidinium Bis{(trifluoromethyl)Sulfonyl}Imide and Aliphatic Nitrile Solvents As Electrolyte for Electrochemical Double Layer Capacitors (Invited).

Electrochemical double layer capacitors (EDLCs), also known as supercapacitors, are promising energy storage devices, especially when considering high power applications [1]. EDLCs can be charged and discharged within seconds [1], feature high power (10 kW·kg-1) and an excellent cycle life (>500,000 cycles). All these properties are a result of the energy storage process of EDLCs, which relies on storing energy by charge separation instead of chemical redox reactions, as utilized in battery systems. Upon charging, double layers are forming at the electrode/electrolyte interface consisting of the electrolyte’s ions and electric charges at the electrode surface.In state-of-the-art EDLC systems activated carbons (AC) are used as active materials and tetraethylammonium tetrafluoroborate ([Et4N][BF4]) dissolved in organic solvents like propylene carbonate (PC) or acetonitrile (ACN) are commonly used as the electrolyte [2]. These combinations of materials allow operative voltages up to 2.7 V - 2.8 V and an energy in the order of 5 Wh·kg-1[3]. The energy of EDLCs is dependent on the square of the operative voltage, thus increasing the usable operative voltage has a strong effect on the delivered energy of the device [1]. Due to their high electrochemical stability, ionic liquids (ILs) were thoroughly investigated as electrolytes for EDLCs, as well as, batteries, enabling high operating voltages as high as 3.2 V - 3.5 V for the former [2]. While their unique ionic structure allows the usage of neat ILs as electrolyte in EDLCs, ILs suffer from low conductivity and high viscosity increasing the intrinsic resistance and, as a result, a lower power output of the device. In order to overcome this issue, the usage of blends of ionic liquids and organic solvents has been considered a feasible strategy as they combine high usable voltages, while still retaining good transport properties at the same time.In our recent work the ionic liquid 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide ([Pyrr14][TFSI]) was combined with two nitrile-based organic solvents, namely butyronitrile (BTN) and adiponitrile (ADN), and the resulting blends were investing regarding their usage in electrochemical double layer capacitors [4,5]. Firstly, the physicochemical properties were investigated, showing good transport properties for both blends, which are similar to the state-of-the-art combination of [Et4N][BF4] in PC. Secondly, the electrochemical properties for EDLC application were studied in depth revealing a high electrochemical stability with a maximum operative voltage as high as 3.7 V. In full cells these high voltage organic solvent based electrolytes have a good performance in terms of capacitance and an acceptable equivalent series resistance at cut-off voltages of 3.2 and 3.5 V. However, long term stability tests by float testing revealed stability issues when using a maximum voltage of 3.5 V for prolonged time, whereas at 3.2 V no such issues are observed (Fig. 1).Considering the obtained results, the usage of ADN and BTN blends with [Pyrr14][TFSI] in EDLCs appears to be an interesting alternative to state-of-the-art organic solvent based electrolytes, allowing the usage of higher maximum operative voltages while having similar transport properties to 1 mol∙dm-3 [Et4N][BF4] in PC at the same time.