Ionic liquids for energy storage systems

Abstract

The present invention provides ionic liquids of Formula (1) which have a wide electrochemical stability window (ESW).

Description

[0001] Full specification

[0002] Full specification shall include:

[0003] (Prior art - Problem and defect in prior art - full description of the invention

[0004] - how to use invention)

[0005] IONIC LIQUIDS FOR ENERGY STORAGE SYSTEMS

[0006] FIELD OF INVENTION

[0007] The present invention relates to ionic liquids, more particularly, but not exclusively, to ionic liquids for energy storage systems.

[0008] BACKGROUND TO THE INVENTION

[0009] Ionic liquids (ILs) are known to be compounds that have relatively low melting points and which liquids consist of ions (anions and / or cations).

[0010] Ionic liquids have many potential applications, amongst others, certain ILs may be suitable for use as electrolytes in energy storage systems. However, the degree of stability of said electrolytes, specifically its thermal and electrochemical stability, may pose a barrier to its use in energy storage systems such as supercapacitors and / or batteries. High thermal stability and a wide electrochemical stability window (ESW) typically are required. The ESW dictates the design space and theoretical operating voltage limits of an energy storage systems. A safe operating voltage would be within the ESW limits.

[0011] It is known in the art that electrolytes for energy storage systems have shown some development, specifically in the operating voltage it provides. The progress can be set out as follows:

[0012] Aqueous electrolyte (electrolyte containing water) has a low thermodynamic operating voltage of 1 .23 V (limited by hydrogen and oxygen evolution);

[0013] Water-in-salt electrolyte could suppress the hydrogen evolution and electrode oxidation, resulting in an operating voltage of up to 2.3 V;

[0014] Organic solvent as electrolyte can have an operating voltage of approximately 2.7 V and an operating temperature up to 65 °C. However, organic solvent is typically flammable;

[0015] Ionic liquids are typically non-flammable, and some reports have suggested that ionic liquids, as an electrolyte, may have an electrochemical stability window of 4.1 V to 6.1 V (DeVos et al. , 2014).

[0016] The commonly used ionic liquids, however, show limited success. The presence of hydrogen atoms on the [3-position of the positively charged hetero-atom of these ILs, promote the Hoffmann rearrangement (referred to in this case as the Hoffmann degradation). This results in low thermal and electrochemical stability.

[0017] Ionic liquids based on cations such as imidazolium, pyrrolidinium, piperidinium, tetraalkylammonium and pyridinium, combined with various anions (acetate, bromide, nitrate, and chloride) are known in the art. However, because of the Hoffmann degradation, these ILs have low thermal and electrochemical stability.

[0018] Furthermore, literature reports some ILs with one methyl substituent on the [3- position of the piperidinium cation in combination with bis(tr if luoromethanesulfonyl)imide. However, those ionic liquids have a low thermal stability and a narrow electrochemical stability.

[0019] OBJECT OF THE INVENTION

[0020] It is accordingly an object of the present invention to provide ionic liquids for energy storage systems to address the issues identified above, at least to some extent, or which may provide a useful alternative to existing technologies.

[0021] SUMMARY OF THE INVENTION

[0022] In accordance with the invention, there is provided ionic liquids ( I Ls) , which have high thermal stability and a wide electrochemical stability window (ESW). Specifically, Bis(2-ethylhexyl)ammonium based ionic liquids are provided. Typically, the ILs are suitable for use in energy storage systems. However, application of ILs is not limited to energy storage devices. Other suitable applications may include the use of ILs in surface or air treating compositions for consumer products and / or industrial products (surface or air treating compositions).

[0023] In one embodiment, provided herein is acompound / ionic liquid of Formula (1 ), wherein Ri to Re represent:

[0024] - hydrogen;

[0025] - a straight-chain or branched aliphatic hydrocarbon with 1 to 10 carbon atoms;

[0026] - an alkyl or aryl of 1 to 20 carbon atoms;

[0027] - C2 to C25 linear or branched aliphatic hydrocarbon having interruption by one or more heteroatoms, such as, oxygen, nitrogen or sulfur;

[0028] - a branched aliphatic hydrocarbon with 2 to 20 carbon atoms linear or terminally functionalized by Cl, Br, F, I, NH, OH, NH2, NHCH3 or SH; or an ether of the type R’-(O-CH2)n-R”, wherein at least one of the following is true: i. R’ is a linear or branched hydrocarbon of 2 to 20 carbon atoms ; ii. R” is a linear or branched hydrocarbon of 2 to 20 carbon atoms ; and / or ill. wherein n is from 1 to 20; and wherein R1 of the cationic components consist of ether of the type R’-(O-CH2)n-R”, wherein at least one of the following is true: i. R’ is a linear or branched hydrocarbon of 2 to 20 carbon atoms. ii. R” is a linear or branched hydrocarbon of 2 to 20 carbon atoms; and / or ill. wherein n is from 1 to 20. In Formula (1 ), the [X] may represent at least one anion selected from the group of anions consisting of : N(CN)2_; BF4- ; ClCk- ; PFe- ; (CF3)2PF_; (CFs^PFs- ; (CF3)4PF2_; (CF3)5PF- ; (CF3)6P- ; (CF2SO3 )2 ; (CF2CF2SO3 )2; (CFsSC^N- ; CF3CF2(CF3)2CO- ; (SF5)3C_; (CF3SO2)3C- ; [O(CF3)2C2(CF3)2O]2PO_; CF3(CF2)7SO3_, and mixtures thereof.

[0029] The compound / ionic liquid of Formula (1 ) may provide athermal stability above 500 °C.

[0030] Furthermore, the compound / ionic liquid of Formula (1 ) may provide an electrochemical stability window which is greater than 5 V.

[0031] In another embodiment of the invention, an energy storage system may include the ionic liquid of claim 1 . The energy storage system may be selected from the group consisting of , but not limited to, supercapacitors and batteries.

[0032] Also provided is a method of producing the compound / ionic liquid of Formula (1 ), including the steps of :

[0033] - providing a starting material, selected from the group including bis(2- ethylhexyl) amine;

[0034] - adding the starting material to a reactant solution consisting of af irst reactant and a solvent, to form a reaction mixture, wherein the solvent may be selected from the group including acetonitrile, and the first reactant is selected from the group including potassium carbonate or iodomethane;

[0035] - stirring the reaction mixture at room temperature for one hour;

[0036] - adding iodomethane / methyl iodide to the reaction mixture; heating the reaction mixture at 40 °C for 48 hours - 72 hours;

[0037] - filtering the reaction mixture;

[0038] - evaporating the solvent;

[0039] - obtaining a solid;

[0040] - washing the solid with diethyl ether to remove unreacted starting material;

[0041] - obtaining a product, wherein the product may include, but is not limited to, Bis(2-ethylhexyl)dimethylammonium iodide or Bis(2- ethylhexyl)methylammonium iodide; and

[0042] - drying the product for 45 hours at 50 °C - 55 °C.

[0043] The method may further include the steps of:

[0044] - making a solution of the product in water;

[0045] - adding a second reactant to the product solution, to form an ion exchange solution, wherein the second reactant is selected from the group including lithium bis(trifluromethanesulfonyl) imide, lithium bis(flurosulfonyl)imide or sodium dicyanamide;

[0046] - stirring the ion exchange solution at room temperature for24 hours;

[0047] - forming two layers, a bottom IL layer and a top waste layer, wherein the top layer is decanted;

[0048] - washing the bottom IL layer with deionized water;

[0049] - evaporating excess water;

[0050] - drying the IL at 55 °C for 48 hours; and

[0051] - storing the IL in an argon filled glove box.

[0052] BRIEF DESCRIPTION OF TH E DRAWINGS

[0053] The invention will now be described further by way of non -limiting examples with reference to the accompanying drawings wherein: Figure 1 is a schematic representation of avoltammogram showing the limits and safe operating potentials for electrochemical systems;

[0054] Figure 2 shows a cyclic voltammogram of synthesized IL A1 according to the invention, at 298.15 K (25 °C);

[0055] Figure 3 shows a cyclic voltammogram of synthesized IL A1 according to the invention, at 313.15 K (40 °C);

[0056] Figure 4 shows a cyclic voltammogram of synthesized IL A1 according to the invention, at 333.15 K (60 °C); and

[0057] Figure 5 shows a cyclic voltammogram of synthesized IL A1 according to the invention, at 353.15 K (80 °C).

[0058] DETAILED DESCRIPTION OF THE INVENTION

[0059] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood in the art. It must be noted that the singular form includes the plural unless the context clearly indicates otherwise. For example, a reference to “the compound” includes aplurality of such compounds. Furthermore, a dash (“-”) that is not between two letters or symbols is used to indicate a point of attachment for a substituent.

[0060] Compounds

[0061] In accordance with the invention, there is provided ionic liquids which have high thermal stability and a wide electrochemical stability window (ESW).

[0062] As illustrated in Figure 1 , when the ESW of a compound is deduced using voltammetry, recorded current peaks, and positive and negative limits, signify the potentials at which the electrolyte degrades and / or becomes unstable due to undesired side-reactions. The widerthe ESW, the wider the design space to achieve a high operating potential in batteries or supercapacitors.

[0063] In this invention, the extent of the Hofmann degradation is minimized by introducing substituents on the [3-position of the positively charged hetero-atom. The presence of bigger substituents on the [3-position creates steric hindrance for the available hydrogen atoms on the [3-position, which reduces the possibility of the Hofmann degradation, and increases the thermal and electrochemical stability.

[0064] In one embodiment, provided herein is acompound (ionic liquid) of Formula (1 ), wherein Ri to Re represent:

[0065] - hydrogen;

[0066] - a straight-chain or branched aliphatic hydrocarbon with 1 to 10 carbon atoms;

[0067] - an alkyl or aryl of 1 to 20 carbon atoms;

[0068] - C2 to C25 linear or branched aliphatic hydrocarbon having interruption by one or more heteroatoms, such as, oxygen, nitrogen or sulfur;

[0069] - a branched aliphatic hydrocarbon with 2 to 20 carbon atoms linear or terminally functionalized by Cl, Br, F, I, NH, OH, NH2, NHCH3 or SH; or an ether of the type R’-(O-CH2)n-R”, wherein at least one of the following is true: i. R’ is a linear or branched hydrocarbon of 2 to 20 carbon atoms ; ii. R” is a linear or branched hydrocarbon of 2 to 20 carbon atoms; and / or ill. wherein n is from 1 to 20; and wherein R1 of the cationic components consist of ether of the type R’-(O-CH2)n-R”, wherein at least one of the following is true: i. R’ is a linear or branched hydrocarbon of 2 to 20 carbon atoms. ii. R” is a linear or branched hydrocarbon of 2 to 20 carbon atoms; and / or ill. wherein n is from 1 to 20.

[0070] In Formula (1 ), the [X] represents at least one anion selected from the group of anions consisting of : N(CN)2_; BF4- ; ClCk- ; PFe- ; (CF3)2PF_; (CFs^PFs- ; (CF3)4PF2_; (CF3)5PF- ; (CF3)6P- ; (CF2SO3 )2 ; (CF2CF2SO3 )2; (CFsSC^N- ; CF3CF2(CF3)2CO- ; (SF5)3C_; (CF3SO2)3C- ; [O(CF3)2C2(CF3)2O]2PO_; CF3(CF2)7SO3_, and mixtures thereof .

[0071] The compound / ionic liquid of Formula (1 ) has a thermal stability above 500 °C.

[0072] Furthermore, the compound / ionic liquid of Formula (1 ) has an electrochemical stability window (ESW) which is greater than / at least 5 V, as will be shown in the examples below.

[0073] In another embodiment of the invention, an energy storage system includes the ionic liquid of Formula (1 ) as an electrolyte. The energy storage system is selected from the group consisting of, but not limited to, supercapacitors and batteries. Synthesis

[0074] The compounds of the disclosure may be prepared using methods disclosed herein. Routine modifications thereof will be apparent given the disclosure herein and methodswell known in the art. Conventional and well-known methods may be used in addition to the teachings herein. The synthesis of typical co mpounds of Formula (1 ), e.g., compounds having structures described by one or more of Formula (1), or other formulas or compounds disclosed herein, may be accomplished as described in the following examples. However, the current invention is not limited to that.

[0075] The following is a list of abbreviations and acronyms used throughout the application:

[0076] °C degrees Celsius pL microliter

[0077] Ag silver

[0078] AgCI silver chloride

[0079] CV cyclic voltammetry

[0080] DCN dicyanamide

[0081] DEHA bis(2-ethylhexyl)dimethylammonium

[0082] DEHA[I] bis(2-ethylhexyl)dimethylammonium iodide

[0083] DEM HA Bis(2-ethylhexyl)methylammonium

[0084] DEMHA[I] Bis(2-ethylhexyl)methylammonium iodide

[0085] Ea oxidation potential

[0086] Ec reduction potential ESW electrochemical stability window

[0087] FSI bis(f lurosulfonyl) imide g grams

[0088] IL ionic liquid

[0089] K kelvin mL milliliter mmol millimol mV millivolt mV / s millivolt per second ppm parts per million

[0090] Pt platinum

[0091] TFSI bis(trifluromethanesulfonyl) imide

[0092] V volt

[0093] In respect of the synthesis of the ILs, provided is a method of producing the ionic liquid(s) of Formula (1 ), including the steps of:

[0094] - providing a starting material, selected from the group including bis(2- ethylhexyl) amine;

[0095] - adding the starting material to a reactant solution consisting of af irst reactant and a solvent, to form a reaction mixture, wherein the solvent may be selected from the group including acetonitrile, and the first reactant is selected from the group including potassium carbonate or iodomethane;

[0096] - stirring the reaction mixture at room temperature for one hour; adding iodomethane / methyl iodide to the reaction mixture (only if not done so in the step above); heating the reaction mixture at 40 °C for 48 hours - 72 hours;

[0097] - filtering the reaction mixture;

[0098] - evaporating the solvent;

[0099] - obtaining a solid;

[0100] - washing the solid with diethyl ether to remove unreacted starting material;

[0101] - obtaining a product, wherein the product may include, but is not limited to, Bis(2-ethylhexyl)dimethylammonium iodide or Bis(2- ethylhexyl)methylammonium iodide; and

[0102] - drying the product for 45 hours at 50 °C - 55 °C.

[0103] Depending on the IL which is to be obtained, the method further includes the steps of :

[0104] - making a solution of the above product in water;

[0105] - adding a second reactant to the product solution, to form an ion exchange solution, wherein the second reactant is selected from the group including lithium bis(trifluromethanesulfonyl) imide, lithium bis(flurosulfonyl)imide or sodium dicyanamide;

[0106] - stirring the ion exchange solution at room temperature for24 hours;

[0107] - forming two layers, a bottom IL layer and a top waste layer, wherein the top layer is decanted;

[0108] - washing the bottom IL layer with deionized water;

[0109] - evaporating excess water;

[0110] - drying the IL at 55 °C for 48 hours; and

[0111] - storing the IL in an argon filled glove box.

[0112] Example 1 : Ionic Liquid 1 In this embodiment, the procedure for synthesizing [DEHA][TFSI], represented by the structural formula A1 , will be described.

[0113] Step 1 : Synthesis of Bis(2-ethylhexyl)dimethylammonium iodide ([DEHA][I])

[0114] To a solution of potassium carbonate [K2CO3] (7 g, 51 .76 mmol) in acetonitrile (25 mL) in a round bottom flask, bis(2-ethylhexyl) amine (5g, 20.70 mmol) was added and stirred at room temperature for 1 hour using a magnetic stirrer, lodomethane, or methyl iodide, [CH3I] (5.87 g, 41 .41 mmol) was added to the solution and heated to 40 °C using an oil bath for 48 hours. The reaction mixture was filtered using filter paper to remove the K2CO3 and the acetonitrile was removed using a rotary evaporator. The pale solid obtained was washed with diethyl ether to remove the unreacted starting material and the product was further dried in a vacuum oven for 48 hours at 55 °C. Bis(2-ethylhexyl)dimethylammonium iodide was obtained in a 76 % yield as a pale-yellow solid.

[0115] Step 2: Synthesis of Bis(2-ethylhexyl)dimethylammonium bis(trifluromethanesulfonyl) imide ([DEHA][TFSI])

[0116] To a solution of Bis(2-ethylhexyl)dimethylammonium iodide (10 g, 26.2 mmol) in water, lithium bis(trifluromethanesulfonyl) imide (7.52 g, 26.2 mmol) was added and stirred for 24 hours using a magnetic stirrer at room temperature. Two layers were formed. The upper water layer was decanted, and the lower ionic liquids layer was washed with fresh deionized water until the washing water give no precipitate. With aqueous silver nitrate solution, the excess water removed using a rotary evaporator. The ionic liquids obtained was further dried in a Schlenk line (vacuum gas manifold) at 55 °C for 48 hours to remove the traces of water. The dried ionic liquid was stored in an argon filled glove box with a water and oxygen content of 0.1 ppm. Bis(2- ethylhexyl)dimethylammonium bis(trifluromethanesulfonyl) imide was obtained as a pale-yellow liquid with a 90 % yield.

[0117] Example 2: Ionic Liquid 2 In this embodiment, the procedure for synthesizing Bis(2-ethylhexyl)dimethylammonium bis(f lurosulfonyl) imide ([DEHA][FSI]), represented bythe structural formula A2, will be described.

[0118] The ionic liquid Bis(2-ethylhexyl)dimethylammonium bis(f lurosulfonyl) imide ([DEHA][FSI]) was synthesized from bis(2-ethylhexyl)dimethylammonium iodide, [DEHA][I] (10 g, 26.2 mmol) and lithium bis(flurosulfonyl)imide (4.91 g, 26.2 mmol) as per the procedure described in step 2 of the example 1 above. Bis(2-ethylhexyl)dimethylammonium bis(flurosulfonyl) imide was obtained as a pale-yellow liquid with a yield of 87%.

[0119] Example 3: Ionic Liquid 3

[0120] In this embodiment, the procedure for synthesizing Bis(2-ethylhexyl)dimethylammonium dicyanamide ([DEHA][DCN]), represented by the structural formula A3, will be described.

[0121] A3

[0122] Bis(2-ethylhexyl)dimethylammonium dicyanamide ([DEHA][DCN]) was synthesized from Bis(2- ethylhexyl)dimethylammonium iodide, [DEH A] [ I] (10 g, 26.2 mmol) and sodium dicyanamide (2.33 g, 26.2 mmol) as per the procedure described in the step 2 of example 1 above. Bis(2- ethylhexyl)dimethylammonium dicyanamide was obtained as a brown liquid with a yield of 84 %. Example 4: Ionic Liquid 4

[0123] In this embodiment, the procedure for synthesizing Bis(2-ethylhexyl)methylammonium iodide ([DEMHA][I]), represented by the structural formula A4, will be described.

[0124] A4

[0125] Bis(2-ethylhexyl)methylammonium iodide was synthesized by the reaction of bis(2- ethylhexyl)amine (5 g, 20.70 mmol) with iodomethane, or methyl iodide, [CHsI] (2.93 g, 20.7 mmol) in acetonitrile (20 mL). The reaction mixture was heated at 40 °C for 72 hours in a round bottom flask equipped with a reflux condenser using amagnetic stirrer. After the reaction was completed, the solvent was removed using a rotary evaporator. The solid obtained was washed with diethyl ether (3 x 20 mL). The remaining solvent was removed using rotary evaporator and furtherdried in a vacuum oven at 50 °C for 48 hours. Bis(2-ethylhexyl)methylammonium iodide was obtained as a dark yellow solid in a 89 % yield.

[0126] Example 5: Ionic Liquid 5

[0127] In this embodiment, the procedure for synthesizing Bis(2-ethylhexyl)methylammonium bis(trif luromethylsulfonyl) imide ([DEMHA][TFSI]), represented by the structural formula A5, will be described.

[0128] AS

[0129] Bis(2-ethylhexyl)methylammonium iodide was synthesized by the reaction of bis(2-ethylhexyl) amine (5 g, 6.20 mmol) and iodomethane, or methyl iodide, [CHsI] (2.93 g, 6.20 mmol) in acetonitrile (15 mL) as per the procedure described for step 1 of example 1 above.

[0130] Bis(2-ethylhexyl)methylammonium bis(trif luromethylsulfonyl) imide was synthesized by the ion exchange reaction of the Bis(2-ethylhexyl)methylammonium iodide (7 g, 18.44 mmol) with lithium bis(tr if luromethylsulfonyl) imide (5.29 g, 18.44 mmol) as per the procedure mentioned in step 2 of example 1 above. Bis(2-ethylhexyl)methylammonium bis(trif luromethylsulfonyl) imide was obtained in a 76% yield.

[0131] Electrochemical stability window (ESW) measurements

[0132] The ESW of the developed ILs were measured using an electrochemical measurement know as cyclic voltammetry (CV).

[0133] Specifically, cyclic voltammetry was performed using amicrocell setup (TSC 70 closed measuring cell from rhd instruments), apotentiostat (AutoLab PGSTAT302N, Metrohm) and workstation. The closed measuring cell has an airtight compartment, insulated from the atmosphere. The microcell setup has a 70 pL platinum (Pt) crucible as a counter electrode and four separately connectable Pt wire ends as working electrodes. Theexposed working electrode diameter to the IL electrolytes is 0.25 mm. A silver chloride (AgCI) coated silver (Ag) wire, in direct contact with the ILs being measured, was used as a quasi-reference for all measurements. For each test, approximately 100 pL of IL was used in the microcell. CV scans were done at a scan rate of 50 mV / s. Accurate temperature control was ensured in the microcell using a Peltier element for active heating / cooling of the compartment via potentiostat software.

[0134] The temperatures on the cell stand were verified to be consistent with set points by means of a thermal camera. The CV scans were performed at temperatures of 298.15 K (25 °C), 313.15 K (40 °C), 333.15 K (60 °C) and 353.15 K (80 °C), respectively, at standard pressure.

[0135] To allow the recording of steady-state voltametric responses, the last of 4 CV cycles for each scan was selected for analyses. The values of the electrochemical stability limits (Ea and Ec, the anodic and cathodic limits) were determined using a practical, numerically consistent method described by Mousavi et. al. (Mousavi et al., 2015). In the method, both stability limits are estimated as potentials at the intersection of two tangents, one crossing the non-faradaic plateau of the CV and the other through anodic / cathodic faradaic current rise towards vertex potentials, i.e., the potential limits of the scan (where the sweep direction is reversed) .

[0136] The resulting electrochemical characteristics of IL A1 is shown in Figure 2-5.

[0137] Figure 2 shows the CV results (voltammogram) of IL A1 at a temperature of 298.15 K (25 °C). The reduction potential (Ec) and oxidation potential (Ea) of IL A1 were -2.84 V and 3.13 V, respectively. Therefore, the electrochemical stability window at 298.15 K was calculated to be 5.97 V.

[0138] Figure 3 shows the CV results of IL A1 at a temperature of 313.15 K (40 °C). At this temperature, the electrochemical stability window was calculated as 6.07 V.

[0139] Figure 4 shows the CV results of IL A1 at a temperature of 333.15 K (60 °C). At this temperature, the electrochemical stability window was calculated as 6.1 1 V.

[0140] The electrochemical stability of IL A1 reduced to 5.42 V at 353.15 K (80 °C), shown in Figure 5.

[0141] In conclusion, the IL A1 shows a wide ESW, i.e., above 6.1 V, at 60 °C and has an ESW of more than 5.4 V at an elevated temperature.

[0142] The results of the largest ESW obtained for the currently synthesized IL A1 according to the invention is shown in Table 1 below.

[0143] Table 1

[0144] It will be appreciated that various alternative embodiments are also possible in accordance with the present invention. For example, applications of ILs are not limited to energy storage devices. Other suitable applications include the use of ILs in surface or air treating compositions for consumer products and / or industrial products (surface or air treating compositions). Furthermore, it will be understood that some advantages of the present invention may be attained by selecting some of the features of the present invention without utilizing other features. Accordingly, those skilled in the art will recognize that modifications and adaptations to the present invention may be possible or desirable in certain circumstances and may form part of the present invention.

Claims

Claims1 . An ionic liquid of Formula (1),wherein Ri to Re represent: hydrogen; a straight-chain or branched aliphatic hydrocarbon with 1 to 10 carbon atoms bis(di alkyl) dialkylammonium, bis(di alkyl) alkylammonium, wherein the alkyl group is selected from the group including methyl, ethyl, propyl, butyl, pentyl chain;C2 to C25 linear or branched aliphatic hydrocarbon having interruption by one or more heteroatoms, including oxygen, nitrogen or sulfur; a branched aliphatic hydrocarbon with 2 to 20 carbon atoms linear or terminally functionalized by Cl, Br, F, I, NH, OH, NH2, NHCH3or SH; or an ether of the type R’-(O-CH2)n-R”, wherein at least one of the following is true: i. R’ is a linear or branched hydrocarbon of 2 to 20 carbon atoms; or ii. R” is a linear or branched hydrocarbon of 2 to 20 carbon atoms; and iii. wherein n is from 1 to 20; and wherein R1 of the cationic components consist of ether of the type R’-(O-CH2)n-R”, wherein at least one of the following is true: i. R’ is a linear or branched hydrocarbon of 2 to 20 carbon atoms; or ii. R” is a linear or branched hydrocarbon of 2 to 20 carbon atoms; and iii. wherein n is from 1 to 20;wherein [X] is at least one anion selected from the group of anions consisting of: N(CN)2_; BF4- ; CIO4 ; PF6- ; (CF3)2PF- ; (CF3)3PF3- ; (CF3)4PF2- ; (CF3)5PF- ; (CF3)6P’ ; (CF2SO3- )2; (CF2CF2SO3-)2; (CF3SO2)2N- ; CF3CF2(CF3)2CO- ; (SF5)3C- ; (CF3SO2)3C- ; [O(CF3)2C2(CF3)2O]2PO' ; CF3(CF2)7SO3' ; (FSO2)2N_; I; and mixtures thereof; and wherein the positively charged hetero-atom includes a substituent on the p- position of said hetero-atom, thereby creating steric hindrance for the available hydrogen atoms on the p-position, which increases thermal and electrochemical stability of the ionic liquid; and wherein the ionic liquid has an electrochemical stability window of at least 5 V.

2. The ionic liquid of claim 1 , wherein the substituent on the p-position of the hetero-atom is bis(2-ethylhexyl) group.

3. The ionic liquid of claim 1 , wherein the ionic liquid of Formula (1) is selected from the group including a bis(2-ethyl hexyl) methylammonium based ionic liquid.

4. The ionic liquid of claim 1 , wherein the ionic liquid of Formula (1) is further selected from the group including a bis(2-ethylhexyl) dimethylammonium based ionic liquid.

5. The ionic liquid of claim 1 , wherein the ionic liquid of Fomula (1) is represented by Formula (A1):

6. The ionic liquid of claim 5, wherein the ionic liquid has an electrochemical stability window of at least 6 V.

7. The ionic liquid of claim 1 , wherein the ionic liquid of Fomula (1) is further represented by Formula (A2):

8. The ionic liquid of claim 1 , wherein the ionic liquid of Fomula (1) is further represented by Formula (A3):

9. The ionic liquid of claim 1 , wherein the ionic liquid of Fomula (1) is further represented by Formula (A4):

10. The ionic liquid of claim 1 , wherein the ionic liquid of Fomula (1) is further represented by Formula (A5):AS11. The ionic liquid of claim 1 , wherein the ionic liquid has a thermal stability above 500 °C.

12. An energy storage system including the ionic liquid of claim 1 as an electrolyte.

13. The energy storage system of claim 12, selected from the group consisting of supercapacitors and batteries.

14. A method of producing the ionic liquid of claim 1 , including the steps of: providing a starting material, selected from the group including bis(2-ethylhexyl) amine; adding the starting material to a reactant solution consisting of a first reactant and a solvent, to form a reaction mixture, wherein the solvent may be selected from the group including acetonitrile, and the first reactant is selected from the group including potassium carbonate or iodomethane; stirring the reaction mixture at room temperature for one hour; adding iodomethane to the reaction mixture; heating the reaction mixture at 40 °C for 48 hours - 72 hours; filtering the reaction mixture; evaporating the solvent; obtaining a solid;- washing the solid with diethyl ether to remove unreacted starting material; obtaining a product, wherein the product is Bis(2-ethylhexyl)dimethylammonium iodide or Bis(2-ethylhexyl)methylammonium iodide; and drying the product for 45 hours at 50 °C - 55 °C.

15. The method of claim 14, including the further steps of: making a solution of the product of claim 13 in water; adding a second reactant to the product solution, to form an ion exchange solution, wherein the second reactant is selected from the group including lithium bis(trifluromethanesulfonyl) imide, lithium bis(flurosulfonyl)imide or sodium dicyanamide; stirring the ion exchange solution at room temperature for 24 hours; allowing the formation of two layers, a bottom IL layer and a top waste layer, wherein the top layer is decanted;- washing the bottom IL layer with deionized water; evaporating excess water; drying the I L at 55 °C for 48 hours; and storing the IL in an argon filled glove box.

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