Non-flammable Ionic Liquid Research Articles

Innovations and strategies for optimizing lithium-ion battery performance: From material advancements to system management

This paper explores the multifaceted advancements in lithium-ion battery (LIB) technology, focusing on material innovations and engineering strategies aimed at optimizing performance, safety, and efficiency. We delve into the development of advanced cathode materials like lithium nickel manganese cobalt oxide (NMC) and lithium iron phosphate (LFP), highlighting their contributions to enhancing energy density and safety. The investigation extends to silicon-based anode materials, underscoring their potential to significantly increase energy storage capacity despite challenges related to volume expansion. Furthermore, we discuss electrolyte optimization techniques that promise to improve battery safety through the use of non-flammable ionic liquids and solid-state electrolytes. Engineering strategies, including microstructure design of electrodes and thermal management systems, are analyzed for their role in improving electrochemical performance and extending battery lifespan. Smart battery management systems (BMS) are also examined for their ability to optimize battery usage through real-time monitoring and predictive analytics. Through a comprehensive review and quantitative analysis, this study presents a cohesive overview of current trends and future directions in LIB technology.

Locally Concentrated Ionic Liquid Electrolytes for Lithium-Metal Batteries.

Non-flammable ionic liquid electrolytes (ILEs) are well-known candidates for safer and long-lifespan lithium metal batteries (LMBs). However, the high viscosity and insufficient Li+ transport limit their practical application. Recently, non-solvating and low-viscosity co-solvents diluting ILEs without affecting the local Li+ solvation structure are employed to solve these problems. The diluted electrolytes, i.e., locally concentrated ionic liquid electrolytes (LCILEs), exhibiting lower viscosity, faster Li+ transport, and enhanced compatibility toward lithium metal anodes, are feasible options for the next-generation high-energy-density LMBs. Herein, the progress of the recently developed LCILEs are summarised, including their physicochemical properties, solution structures, and applications in LMBs with a variety of high-energy cathode materials. Lastly, a perspective on the future research directions of LCILEs to further understanding and achieve improved cell performances is outlined.

A Nonflammable High-Voltage 4.7 V Anode-Free Lithium Battery.

Anode-free lithium-metal batteries employ in situ lithium-plated current collectors as negative electrodes to afford optimal mass and volumetric energy densities. The main challenges to such batteries include their poor cycling stability and the safety issues of the flammable organic electrolytes. Here, a high-voltage 4.7V anode-free lithium-metal battery is reported,which usesa Cu foil coated with a layer (≈950nm) of silicon-polyacrylonitrile (Si-PAN, 25.5µg cm-2 ) as the negative electrode, a high-voltage cobalt-free LiNi0.5 Mn1.5 O4 (LNMO) as the positive electrode and a safe, nonflammable ionic liquid electrolyte composed of 4.5m lithium bis(fluorosulfonyl)imide (LiFSI) salt in N-methyl-N-propyl pyrrolidiniumbis(fluorosulfonyl)imide (Py13 FSI) with 1 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as additive. The Si-PAN coating is found to seed the growth of lithium during charging, and reversibly expand/shrink during lithium plating/stripping over battery cycling. The wide-voltage-window electrolyte containing a high concentration of FSI- and TFSI- facilitates the formation of stable solid-electrolyte interphase, affording a 4.7V anode-free Cu@Si-PAN/LiNi0.5 Mn1.5 O4 battery with a reversible specific capacity of ≈120 mAh g-1 and high cycling stability (80% capacity retention after 120 cycles). These results represent the first anode-free Li battery with a high 4.7V discharge voltage and high safety.

Stability of FeF3-Based Sodium-Ion Batteries in Nonflammable Ionic Liquid Electrolytes at Room and Elevated Temperatures.

Iron trifluoride (FeF3), a conversion-type cathode for sodium-ion batteries (SIBs), is based on cheap and abundant Fe and provides high theoretical capacity. However, the applications of FeF3-based SIBs have been hindered by their low-capacity utilization and poor cycling stability. Herein, we report greatly enhanced performance of FeF3 in multiple types of ionic liquid (IL) electrolytes at both room temperature (RT) and elevated temperatures. The Pyr1,4FSI electrolyte demonstrated the best cycling stability with an unprecedented decay rate of only ∼0.023% per cycle after the initial stabilization and an average coulombic efficiency of ∼99.5% for over 1000 cycles at RT. The Pyr1,3FSI electrolyte demonstrated the best cycling stability with a capacity decay rate of only ∼0.25% per cycle at 60 °C. Cells using Pyr1,3FSI and EMIMFSI electrolytes also showed promising cycling stability with capacity decay rates of ∼0.039% and ∼0.030% per cycle over 1000 cycles, respectively. A protective and ionically conductive cathode electrolyte interphase (CEI) layer is formed during cycling in ILs, diminishing side reactions that commonly lead to gassing and excessive CEI growth in organic electrolytes, especially at elevated temperatures. Furthermore, the increased ionic conductivity and decreased viscosity of ILs at elevated temperatures help attain higher accessible capacity. The application of ILs sheds light on designing a protective CEI for its use in stable SIBs.

Organic Crystalline Solid Electrolytes with High Mg-Ion Conductivity Composed of Nonflammable Ionic Liquid Analogs and Mg(TFSA)2

The development of solid electrolytes with Mg-ion conductivity at room temperature is an important issue to achieve all-solid magnesium batteries. We focus on organic ionic crystals with Mg-ion conduction paths in addition to nonflammable and nonvolatile features as an innovative candidate of solid electrolytes with Mg-ion conductivity. Herein, we show the development of novel organic ionic crystals, [N(CH3)4-n(CH2CH3)n][Mg{N(SO2CF3)2}3] (n = 0 or 2), using analogs of ionic liquids, [N(CH3)4][N(SO2CF3)2] (N1111TFSA) and [N(CH3)2(CH2CH3)2][N(SO2CF3)2] (N1122TFSA), and magnesium salt, Mg{N(SO2CF3)2}2 (Mg(TFSA)2). We also report the crystal structures of the obtained crystals and the high Mg-ion conductivity of 10-4 S cm-1 under mild conditions of 80 °C in the solid state. These results indicate that organic ionic crystals with ion conduction paths have significant potential as safe solid electrolytes and provide insights into developing innovative Mg-ion conductors.

Dual-anion ionic liquid electrolyte enables stable Ni-rich cathodes in lithium-metal batteries

<h2>Summary</h2> High-energy-density lithium-metal batteries face the challenge of developing functional electrolytes enabling both the stabilization of the lithium-metal negative electrode and high-voltage positive electrodes (> 4 V versus Li⁺/Li). Herein, a low-volatility and non-flammable ionic liquid electrolyte (ILE) incorporating two anions, bis(fluorosulfonyl) imide (FSI) and bis(trifluoromethanesulfonyl)imide (TFSI), is successfully applied to overcome this challenge, employing the high-energy, low-Co, and Ni-rich positive-electrode material, LiNi_0.88Co_0.09Mn_0.03O₂ (NCM88), in Li-metal batteries. With this specific electrolyte, the cathode exhibits remarkable electrochemical performance, achieving an initial specific capacity of 214 mAh g⁻¹ and outstanding capacity retention of 88% over 1,000 cycles. More importantly, this electrolyte enables an average Coulombic efficiency of 99.94%. The excellent compatibility of the dual-anion ILE with both the lithium metal (50 μm) and the high-voltage positive-electrode material enables the realization of Li-metal cells achieving specific energies of more than 560 Wh kg⁻¹ based on their combined active material masses.

Electrochemical and Physical Properties of Imidazolium Chloride Ionic Liquids with Pyrrolidinium or Piperidinium Cation Addition and Their Application in Dual‐Ion Batteries

Herein, nonflammable ionic liquid (IL) electrolytes are prepared for dual‐ion batteries (DIBs) by mixing 1‐methyl‐1‐propylpyrrolidinium chloride (P13Cl) or 1‐butyl‐1‐methylpiperidinium chloride (PP14Cl) with 1,2‐dimethyl‐3‐propylimidazolium chloride (DMPICl)/aluminum chloride (AlCl3) to form mixed IL electrolytes. Then, viscosity, ionic conductivity, thermal stability, and electrochemical limits measurements are recorded to reveal the fundamental properties of the mixed IL electrolytes for DIBs, which are not reported previously. As compared with DMPICl/AlCl3 (=1 in mole ratio) electrolyte, using electrolyte with addition of P13Cl or PP14Cl (e.g., 0.63 mole to replace DMPICl), the DIB with graphite electrodes show better electrochemical stability. With the addition of 0.63 P13Cl, the Coulombic efficiency of the DIB reaches up to 96.7% (≈91% for DMPICl/AlCl3); however, specific capacity loss should be considered. In general, ideas for designing higher energy density electrochemical energy storage devices are provided.

“Water in salt/ionic liquid” electrolyte for 2.8 V aqueous lithium-ion capacitor

Development of high-voltage electrolytes with non-flammability is significantly important for future energy storage devices. Aqueous electrolytes are inherently non-flammable, easy to handle, and their electrochemical stability windows (ESWs) can be considerably expanded by increasing electrolyte concentrations. However, further breakthroughs of their ESWs encounter bottlenecks because of the limited salt solubility, leading to that most of the high-energy anode materials can hardly function reversibly in aqueous electrolytes. Here, by introducing a non-flammable ionic liquid as co-solvent in a lithium salt/water system, we develop a “water in salt/ionic liquid” (WiSIL) electrolyte with extremely low water content. In such WiSIL electrolyte, commercial niobium pentoxide (Nb2O5) material can operate at a low potential (−1.6 V versus Ag/AgCl) and contribute its full capacity. Consequently, the resultant Nb2O5-based aqueous lithium-ion capacitor is able to operate at a high voltage of 2.8 V along with long cycling stability over 3000 cycles, and displays comparable energy and power performance (51.9 Wh kg−1 at 0.37 kW kg−1 and 16.4 Wh kg−1 at 4.9 kW kg−1) to those using non-aqueous electrolytes but with improved safety performance and manufacturing efficiency.

High-Safety and High-Energy-Density Lithium Metal Batteries in a Novel Ionic-Liquid Electrolyte.

Rechargeable lithium metal batteries are next generation energy storage devices with high energy density, but face challenges in achieving high energy density, high safety, and long cycle life. Here, lithium metal batteries in a novel nonflammable ionic-liquid (IL) electrolyte composed of 1-ethyl-3-methylimidazolium (EMIm) cations and high-concentration bis(fluorosulfonyl)imide (FSI) anions, with sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) as a key additive are reported. The Na ion participates in the formation of hybrid passivation interphases and contributes to dendrite-free Li deposition and reversible cathode electrochemistry. The electrolyte of low viscosity allows practically useful cathode mass loading up to ≈16 mg cm-2 . Li anodes paired with lithium cobalt oxide (LiCoO2 ) and lithium nickel cobalt manganese oxide (LiNi0.8 Co0.1 Mn0.1 O2 , NCM 811) cathodes exhibit 99.6-99.9% Coulombic efficiencies, high discharge voltages up to 4.4 V, high specific capacity and energy density up to ≈199 mAh g-1 and ≈765 Wh kg-1 respectively, with impressive cycling performances over up to 1200 cycles. Highly stable passivation interphases formed on both electrodes in the novel IL electrolyte are the key to highly reversible lithium metal batteries, especially for Li-NMC 811 full batteries.

Magnesium Storage Performance and Mechanism of 2D-Ultrathin Nanosheet-Assembled Spinel MgIn2 S4 Cathode for High-Temperature Mg Batteries.

Magnesium batteries have the potential to be a next generation battery with large capability and high safety, owing to the high abundance, great volumetric energy density, and reversible dendrite-free capability of Mg anodes. However, the lack of a stable high-voltage electrolyte, and the sluggish Mg-ion diffusion in lattices and through interfaces limit the practical uses of Mg batteries. Herein, a spinel MgIn2 S4 microflower-like material assembled by 2D-ultrathin (≈5.0 nm) nanosheets is reported and first used as a cathode material for high-temperature Mg batteries with an ionic liquid electrolyte. The nonflammable ionic liquid electrolyte ensure the safety under high temperatures. As prepared MgIn2 S4 exhibits wide-temperature-range adaptability (50-150 °C), ultrahigh capacity (≈500 mAh g-1 under 1.2 V vs Mg/Mg2+ ), fast Mg2+ diffusibility (≈2.0 × 10-8 cm2 s-1 ), and excellent cyclability (without capacity decay after 450 cycles). These excellent electrochemical properties are due to the fast kinetics of magnesium by the 2D nanosheets spinel structure and safe high-temperature operation environment. From ex situ X-ray diffraction and transmission electron microscopy measurements, a conversion reaction of the Mg2+ storage mechanism is found. The excellent performance and superior security make it promising in high-temperature batteries for practical applications.

A high surface area N-doped holey graphene aerogel with low charge transfer resistance as high performance electrode of non-flammable thermostable supercapacitors

The high quality carbonaceous material with high surface area and low charge transfer resistance is vital for assembling the advanced supercapacitor. Herein, a novel kind of N-doped holey graphene aerogel (NHGA) is prepared. The NHGA has high specific BET surface area of 446 m2 g−1 and low charge transfer resistance of 0.4 Ω. A large specific capacity of 318.3 F g−1 is obtained at 0.5 A g−1 in a three-electrode configuration in 6 M KOH electrolyte, indicating the high capacity characteristic. As to the NHGA based symmetrical supercapacitor, the specific capacity of 96.0 F g−1 can be achieved at 200 A g−1, presenting its robust rate property. After 10,000 cycles at 2 A g−1, the specific capacity is 262.5 F g−1 with the capacity retention of 98.4%, showing its excellent cyclic stability. Notably, the energy density of 60.3 Wh kg−1 superior to that of the related typical reported supercapacitors, is obtained at the power density of 0.9 kW kg−1 in a non-flammable ionic liquid EMIMTFSI-80 electrolyte, which is effective from 20 to 100 °C. Thus, the advanced electrochemical property of NHGA is distinctly valuable for the supercapacitor utilization especially in the extremely conditions such as fire safety and/or high temperature.

A Large-Sized Reduced Graphene Oxide with Low Charge-Transfer Resistance as a High-Performance Electrode for a Nonflammable High-Temperature Stable Ionic-Liquid-Based Supercapacitor.

Large-sized reduced graphene oxide prepared was prepared by combined microwave intermittent heating and an extraction process (e.g., 900 W for 10 min (MRG-900-10)) with a lateral size of several micrometers and a thickness of 4-6 monosheets . The MRG-900-10 has a high C/O molar ratio (5.89) and a sp2 C content of 69.0 %, which leads to a fast electronic transmission in the sample. In addition, MRG-900-10 possesses a large specific surface area of 568.2 m2 g-1 , which increases the contact surface area between the active material and the electrolyte, thus enhancing the electron and ion transport in the interfaces when used as the electrode material in supercapacitors. MRG-900-10 possesses a low charge-transfer resistance (≈0.36 Ω). Used as the electrode material for a supercapacitor in 6 m KOH aqueous electrolyte, MRG-900-10 produces a high specific capacity of 327.6 F g-1 at the current density of 0.5 A g-1 . A specific capacity of 248.3 F g-1 was obtained at a high current density of 100 A g-1 , which indicated its high-rate ability. The initial capacity of 92 % can be maintained after 40 000 cycles at 5 A g-1 , which indicated its high cycling stability. As for the MRG-900-10 symmetric supercapacitors, the energy densities of 11.0 and 36.2 Wh kg-1 were obtained in 6 m KOH aqueous and 1 m tetraethylammonium tetrafluoroborate ([TEA]BF4 )/acetonitrile (ACN) electrolytes, respectively. Importantly, a high energy density of 68.6 Wh kg-1 was achieved in the nonflammable ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethane)sulfonimide ([EMIM][TFSI])/ACN (80 vol % [EMIM][TFSI]), and the supercapacitor was effective from room temperature to 100 °C.

Synthesis and physicochemical characterization of room temperature ionic liquids and their application in sodium ion batteries.

Sodium ion batteries (SIBs) based on IL electrolytes have attracted great attention, particularly in large-scale energy storage systems for renewable energy due to the abundance of sodium and the excellent safety resulting from the use of non-flammable ionic liquid (IL) electrolytes. In this article, a series of 15 functionalized room temperature ionic liquids (RTILs) suitable as electrolytes is presented. Special emphasis was laid on the purity of the synthesized RTILs and a consistent and uniform characterization of their physicochemical properties. Evaluation of the viscosity, conductivity, and thermal and electrochemical stabilities resulted in clear structure-property relationships, rendering the ether functionalized RTILs most promising for application in SIBs. Electrochemical investigations of the ether functionalized IL electrolytes in SIB half cells (Na0.6Mn0.9Co0.1O2 as cathode material) proved their compatibility with a SIB system. Stable cycling performance was achieved with the piperidinium based RTIL IL 6 outperforming the organic electrolyte by far with a retention of 81% after 350 cycles. These results show the suitability of RTILs to enhance the performance of SIB systems and serve as a basis for the design of high performance IL electrolytes.

Unconventional Deep Eutectic Solvents: Aqueous Salt Hydrates

Neoteric solvents for sustainable chemical processes are continuously sought nowadays. Deep eutectic solvents (DES), i.e., liquids that are mixtures of two components that have freezing points considerably below the melting points of these components, constitute a possible solution for this search. Mixtures of certain congruently melting salt hydrates with water have freezing points considerably below the melting points of ice and of the salt hydrate. They should be considered as DES for applications in which their properties could be useful, namely their being “green” and nonflammable ionic liquids at very low temperatures. The eutectic points and eutectic temperature distances of such salt hydrate DES, calculated from literature data, are tabulated, and some illustrative phase diagrams are shown. Physical properties of the aqueous salt hydrate DES that are relevant to their possible applications are reported, and they compare favorably with those of conventional DES. The Brunauer–Emmett–Teller modeling ...

Prospective Symbiosis of Green Chemistry and Energetic Materials

A global increase in environmental pollution demands the development of new "cleaner" chemical processes. Among urgent improvements, the replacement of traditional hydrocarbon-derived toxic organic solvents with neoteric solvents less harmful for the environment is one of the most vital issues. As a result of the favorable combination of their unique properties, ionic liquids (ILs), dense gases, and supercritical fluids (SCFs) have gained considerable attention as suitable green chemistry media for the preparation and modification of important chemical compounds and materials. In particular, they have a significant potential in a specific and very important area of research associated with the manufacture and processing of high-energy materials (HEMs). These large-scale manufacturing processes, in which hazardous chemicals and extreme conditions are used, produce a huge amount of hard-to-dispose-of waste. Furthermore, they are risky to staff, and any improvements that would reduce the fire and explosion risks of the corresponding processes are highly desirable. In this Review, useful applications of almost nonflammable ILs, dense gases, and SCFs (first of all, CO2 ) for nitration and other reactions used for manufacturing HEMs are considered. Recent advances in the field of energetic (oxygen-balanced and hypergolic) ILs are summarized. Significant attention is paid to the SCF-based micronization techniques, which improve the energetic performance of HEMs through an efficient control of the morphology and particle size distribution of the HEM fine particles, and to useful applications of SCFs in HEM processing that makes them less hazardous.

Pilot Electrodeposition of Aluminium for Microelectronics, Aerospace and Automotive Applications

Ionic liquids are salts which have per definition a melting point below 100 ° C. They are non-flammable and have a high thermal stability as well as a very low vapor pressure. Many ionic liquids are characterized by a wide electrochemical window of up to seven volts, which in principle also allows the deposition of metals with high reduction potentials. Since most ionic liquids are aprotic solvents, this results in another important advantage over aqueous electroplating systems: the lack of hydrogen evolution and the corresponding hydrogen embrittlement of the deposited metal layer.Due to its high reduction potential, aluminum cannot be deposited from aqueous solutions in pure state. However, there are very interesting applications for aluminum coatings in the area of corrosion protection or in the design sector. For example, in the (automotive) design area, chromium coatings can be replaced by shiny aluminum layers. Even in the electronics industry, homogeneous aluminum coatings on different substrates open up new possibilities for increased efficiency, e.g. copper printed circuit board tracks are replaced by corresponding aluminum ones with similar conductivity. This saves, among other things, costs for raw materials and reduces the weight of the component, which can be a significant advantage in this industry. A galvanic coating with aluminum from non-flammable ionic liquids is therefore promising from the technical point of view.In a European joint project, the automated aluminum deposition from ionic liquids on plastic and metal substrates for the automotive industry and turbine construction could now be successfully demonstrated in a pilot plant. The talk presents our current research results on the development and the scaling up of aluminum deposition from ionic liquids for applications in automotive engineering as well as in the field of microelectronics on circuit boards and Si wafers. We will report on the high requirements that the electrolytes place on plant design and components, the influence of additives or impurities such as water on the quality of the aluminum deposition. In addition, the influence of the post-treatment of the so produced aluminum layers will be presented. A life-cycle analysis of the electrolyte is presented for the economic and ecological consideration of this aluminum deposition process.

Lithium Battery Using High Conducting Emifsi-Doped Solid Polymer Electrolytes Process Under the Electric Field

Lithium-ion battery holds great promises for future energy storage purpose. However, traditional Lithium-ion battery uses liquid organic electrolytes which is flammable and leads to safety problems. In this work, we present a highly ion conducting membrane which is discovered by doping a nonvolatile conducting medium, ionic liquids (ILs) in solid polymer electrolytes (SPEs) prepared under external electric field(EF) poling. The poling created aligned morphology in PVDF-HFP and PMMA blending system yield the long-range ordered but nearly totally amorphous domains where nonflammable ionic liquids is inter-dispersed to display unusually high Li+ transport with room temperature conductivity reaching over 10-3S/cm. The highest conductivity of 7.53x10-3 S/cm is observed for polymer electrolyte containing PMMA/PVDF-HFP (50/50 wt%, eV8E2L). The alignment by the external electric field not only altered the interaction between polymer components which suppressed PVDF-HPF crystallinity in the SPEs, it also improves mechanical strength of the membrane .The coin cell (R2032) using eV8E2L as the SPEs and LiFePO4 cathode shows fair half-cell performance and durable cycle stability. Under 0.1C-rate the half-cell displayed consistent discharge capacity of 140 mAh/g , without apparent capacity decay. Figure 1

A Long-Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution.

In this paper, we report an advanced long-life lithium ion battery, employing a Pyr14 TFSI-LiTFSI non-flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn-C) nanocomposite anode, and a layered LiNi1/3 Co1/3 Mn1/3 O2 (NMC) cathode. The IL-based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel-Tammann-Fulcher (VTF) trend. Lithium half-cells employing the Sn-C anode and NMC cathode in the Pyr14 TFSI-LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn-C electrodes are combined into a cathode-limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g(-1) and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL-based lithium ion cells are suitable batteries for application in electric vehicles.

Addressing Fundamental Problems in Capacitive Energy Storage

The rapidly growing demand for capacitive energy storage systems for applications such as self-powered micro and nanosystems, portable electronic devices, and large-scale stationary applications has inspired much research in an effort to develop devices that can provide high power and energy densities. The important factors affecting the performance of electrochemical capacitors (ECs) are the intrinsic properties of electrode materials and electrolytes, as well as the properties of their interfaces. There is no perfect electrode material and no ideal electrolyte that can meet the performance goal for every application. Therefore, a rational design of these materials is crucial for rapid advancement and widespread implementation of ECs. A large variety of nanostructured carbon materials are available nowadays that can be used as electrode materials.1 Zero- and one-dimensional nanoparticles, such as onion-like carbon and nanotubes, can provide a high power due to fast ion sorption/desorption on their outer surfaces.2 Two-dimensional graphene has been receiving an increasing attention due to its higher charge-discharge rates compared to porous carbons and high volumetric energy density. Three-dimensional porous activated, carbide-derived and templated carbon networks, having a high surface area and porosity in the subnanometer or a few-nanometers range, can provide high energy density if the pore size is matched with the electrolyte ion size.3 While aqueous electrolytes, such as sodium sulfate, are the safest and least expensive, they have a limited voltage window. Organic electrolytes are the most commonly used ones in commercial devices. Non-flammable ionic liquids are attracting an increasing attention due to their low vapor pressure leading to a safe operation in the range from -50°C to at least 100°C and a larger voltage window resulting in a higher energy density compared to other electrolytes.4 Further advances in development of materials and understanding charged solid-electrolyte interfaces are expected to lead to a wider use of capacitive energy storage at the scales ranging from microelectronics to automobiles and electrical grid.5,6 This talk will summarize some of the research efforts at Fluid Interface Reactions, Structure and Transport (FIRST) center towards understanding the effects of the structure of the electrode materials and properties of the electrode/electrolyte interfaces on the capacitive energy storage in ECs. References (1) Simon, P.; Gogotsi, Y. Capacitive Energy Storage in Nanostructured Carbon Electrolyte Systems. Acc. Chem. Res. 2012, 46, 1094–1103. (2) McDonough, J.; Gogotsi, Y. Carbon Onions: Synthesis and Electrochemical Applications. Electrochem. Soc. Interface 2013, 12, 61–66. (3) Presser, V.; Heon, M.; Gogotsi, Y. Carbide-Derived Carbons - From Porous Networks to Nanotubes and Graphene. Adv. Funct. Mater. 2011, 21, 810–833. (4) Van Aken, K. L.; Beidaghi, M.; Gogotsi, Y. Formulation of Ionic-Liquid Electrolyte to Expand the Voltage Window of Supercapacitors. Angew. Chemie 2015, 127, 4888–4891. (5) Presser, V.; Dennison, C. R.; Campos, J.; Knehr, K. W.; Kumbur, E. C.; Gogotsi, Y. The Electrochemical Flow Capacitor: A New Concept for Rapid Energy Storage and Recovery. Adv. Energy Mater. 2012, 2, 895–902. (6) Beidaghi, M.; Gogotsi, Y. Capacitive Energy Storage in Micro-Scale Devices: Recent Advances in Design and Fabrication of Micro-Supercapacitors. Energy Environ. Sci. 2014, 7, 867.

Aluminum Dissolution in the Aluminum Chloride 1-Ethyl-3-Methylimidazolium Chloride (AlCl3-EtMeImCl) Ionic Liquid

There is increasing interest in the use of chloroaluminate ionic liquids (ILs) as solvents for the electrodeposition of aluminum. This effort is to replace the electrochemical solvent currently used for the commercial plating of aluminum in the Siemens Sigal process, which is based on pyrophoric alkylaluminum fluoride compounds dissolved in toluene. Low melting chloroaluminate ILs such as AlCl3-1-ethyl-3-methylimidazolium chloride (AlCl3-EtMeImCl)1are popular choices for this application. Although reactive with moisture, these non-flammable ILs are otherwise relatively benign. BASF SE recently marketed a successful aluminum plating technology based on this ionic liquid. The plating of Al from organic salt based chloroaluminates must be carried out under Lewis acidic conditions (> 50 m/o AlCl3) so that the reducible species, Al2Cl7 -, is present in the IL 4Al2Cl7 - + 3e- ↔ Al + 7AlCl4 - (1) This requirement stems from the fact that the reduction potential of the coordinately saturated AlCl4 - ion is more negative than that for the organic cation. This factor prohibits Al plating in basic and neutral (£ 50 m/o AlCl3) ILs. However, Al2Cl7 - (AlCl3) can be introduced into these ILs by the anodization of Al in order to change the composition to > 50 m/o AlCl3. Furthermore, during Al plating from this IL, an aluminum anode must be present in an undivided cell to resupply Al2Cl7 -that is lost from the ionic solvent during the plating process. Although the electrodeposition of Al from organic salt-based chloroaluminates has been thoroughly investigated for more than 50 years, virtually nothing is known about this anode reaction, i.e., the reverse of Eq. 1. Recent work in our laboratory involving Al anodization in the related inorganic molten salt, LiAlBr4-NaAlCl4-KAlCl4 (3:5:2), determined that under certain conditions this process is complicated by passivation of the Al electrode with AlCl3(s). In the absence of passivation, this multistep reaction is itself relatively slow, proceeding under mixed kinetic/mass transfer control.2 In this presentation, we describe an investigation of the anodic dissolution of Al in AlCl3-EtMeImCl (> 50 m/o AlCl3) carried out with rotating disk electrode (RDE) voltammetry. Figure 1 shows current-time plots recorded during potential step experiments at an Al RDE. The anodization process becomes limited by passivation of the Al electrode as the rate of the anodization process is increased and/or the temperature is decreased. As expected, this phenomenon occurs more readily in ILs with greater Lewis acidity. At smaller overpotentials, where passivation can be avoided, Levich plots recorded at the Al RDE (Fig. 2) were non-linear, indicating that Al anodization proceeds under mixed control in this ionic solvent as well. The exchange current density, j 0, for the anodization reaction was determined as a function of the IL composition by using classical Tafel analysis (Fig. 3). The mechanism of the anode reaction, and its implication for high rate Al plating will be discussed. ACKNOWLEDGEMENT :This work was funded by the Strategic Environmental Research and Development Program (SERDP) through contract DE-AC05-00OR22725. 1. J. S. Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey, Inorg. Chem., 21, 1263 (1982). 2. C. Wang and C. L. Hussey, ECS Trans., 64, 257 (2014). Figure 1