WO2013142994A1 - Redox-active ionic liquids - Google Patents

Abstract

The use of a redox-active ionic liquid as an additive in an electrolyte of a secondary battery or supercapacitor, the redox-active ionic liquid comprising a redox shuttle linked to an ionic liquid is provided. Further, there is also provided such redox-active ionic liquids and electrolytes comprising such redox-active ionic liquids. There is also provided a method of manufacturing such redox-active ionic liquid electrolyte additives as well as methods of increasing the solubility of a redox shuttle in an electrolyte, manufacturing an electrolyte, manufacturing a battery or supercapacitor, increasing the stability of an electrolyte, improving the safety of a battery or supercapacitor, and reducing the risks of overcharge or overdischarge of a battery or supercapacitor.

Description

REDOX-ACTIVE IONIC LIQUIDS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit, under 35 U.S.C. § 1 19(e), of U.S. provisional application Serial No. 61/617,958, filed on March 30, 2012.

FIELD OF THE INVENTION

[001] The present invention relates to redox-active ionic liquids. More specifically, the present invention is concerned with redox-active ionic liquids for use as electrolyte additives in secondary batteries and supercapacitors.

BACKGROUND OF THE INVENTION

[002] Currently, lithium-ion batteries (LIB) are the power supply of choice for portable electronic devices because they store more energy per volume than any other portable rechargeable battery available. LIB are considered the best battery option for the next generation of hybrid and electric vehicles (HEV and EV) and are currently used in EV developed by major car manufacturers (such as the GM Volt and Nissan Leaf). Current lithium-ion cells contain, simplistically, two active electrodes separated by a polymeric separator, surrounded by a liquid organic electrolyte solution.

[003] The active electrode materials of LIBs, in their charged state, have been shown to partake, when abused, in exothermic reactions at elevated temperatures. Temperatures in excess of 700°C have been measured and many cases of fires have been reported. The major thermal instability within LIB is due to the release of oxygen from the cathode at elevated temperature that initiates the ignition of the combustible liquid organic electrolyte. This reaction can be described via autocatalytic kinetics and results in a rapid temperature rise, followed closely with the explosion of the cell.

[004] One major problem of Li-ion batteries is the difficulty of internally preventing the battery from going into an abuse situation. Ideally, EV manufacturers would prefer to ensure that their batteries are completely prevented from entering an abuse situation. An example of an abuse situation is overcharge where the electrodes and electrolyte may be degraded leading to excessive heat generation and temperature increase as well as a decrease in battery performance. The probability of overcharge situations increases when individual cells are placed in a battery pack as one needs to ensure that every cell has an identical capacity. As an example, the battery pack of the Tesla roadster contains over 6000 individual lithium-ion cells in 11 modules. The manufacturer must ensure that every one of the about 600 cells per module is exactly the same capacity (balanced). If not, cells with inferior capacity will be overcharged (or overdischarged) during charging (or discharge) causing premature cell degradation. This will accelerate the replacement of the battery pack and will increase the probability of a safety event occurring within the unbalanced cell. Commonly available electrolytes cannot prevent the above reactions from occurring upon overcharge, and they will also aggravate the outcomes due to their flammability and high volatility. Preventing overcharging therefore becomes vital for a safe battery operation, especially when an inferior (or absent) battery management system is used. In an attempt to cure this problem, battery developers are turning towards complex engineering solutions such as regulating electronics and cooling systems. Numerous technologies have indeed been suggested, including the use of thermal fuses and self-resetting devices. These solutions typically add to the cost and complexities of the battery module, discouraging its use in possible low cost mass market applications. Some of the other methods to avoid problems with unbalanced cells include the use of redox-active chemical moieties ("redox shuttles") as additives into the electrolyte and/or redox-active polymers incorporated within the separator of the battery.

[005] Redox shuttles provide an oxidizable and reducible charge-transporting species that can repeatedly transport charge between the negative and positive electrodes once the potential reaches a desired value. They are typically dissolved in the electrolyte of the cell and operate by oxidizing (reducing) at a potential about 0.4 volts above (or below) the maximum (minimum) voltage of the cell. The dissolved oxidized (reduced) species then migrate to the other electrode and get reduced (oxidized) to regenerate the shuttle and repeat the cycle. The shuttle essentially provides an internal shunt for the cell. A major stumbling block towards the successful deployment of redox shuttles is the fact that their solubility within liquid organic electrolytes is limited to about 0.1 mol/L. This concentration limits the maximum current that can be passed via the shuttle since one molecule can only transfer one electron at a time and the maximum rate at which the shuttle can be used to prevent overcharge (overdischarge) depends on its concentration. Also, when a shuttle is in operation, as no electrical work is being performed, the cell generates heat. This heat must be dissipated, especially in EV applications where the current could be large giving rise to larger temperature increases and possible decay of the electrodes and electrolyte at these temperatures. Finally, the shuttle must be stable at the potential of each operating electrode.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided:

1. The use of a redox-active ionic liquid as an additive in an electrolyte of a secondary battery or of a supercapacitor, the redox-active ionic liquid comprising a redox shuttle linked to an ionic liquid.

2. The use of item 1 , wherein the redox shuttle is linked to a cation of the ionic liquid.

3. The use of item 1 , wherein the redox shuttle is linked to an anion of the ionic liquid.

4. The use of any one of items 1 to 3, wherein the redox-active ionic liquid is of formula RS-LK-IL, wherein RS is the redox shuttle, LK is a bond or a linker, and IL is the ionic liquid.

5. The use of item 4, wherein LK is -alkylene-, -COO-alkylene-, -CO-alkylene-, -O-alkylene-, -N-alkylene-, or -S-alkylene-.

6. The use of item 5, wherein LK is -CH2- or -CH2CH2- .

7. The use of any one of items 1 to 6, wherein the redox shuttle is ferrocene, or a ferrocene derivative, a dihydrophenazine, a metallocene, a dimethoxybenzene derivative, a thiantlurene derivative, 2,5-di-ferf- butyl-1 ,4-dimethoxybenzene (DDB), a phenothiazine derivative, 2,2,6,6-tetramethylpiperinyloxide (TEMPO), 2-(pentafluorophenyl)-tetrafluoro-1 ,3,2-benzodioxaborole (PFPTFBB), or an organometallic complex between a metal center and a ligand. The use of item 7, wherein the redox shuttle is:

wherein R is H, N0₂, S0₃H, F or CI, R_a is H or F, R_b is H or tert-butyl , L is SCN, CN or CO, Mi is Fe, Ru, Os, Co, Rh or lr and M₂ is Fe.

The use of item 8, wherein the redox shuttle is :

wherein R_a is H and M2 is Fe.

The use of item 8, wherein the redox shuttle is :

wherein Rb is H or tert-butyl.

The use of any one of items 1 to 10, wherein the ionic liquid comprises a imidazolium, pyridinium, pyrazolium, triazolium, thiazolium, oxazolium, pyridazinium, pyrimidinium, pyrazinium, pyrrolidinium, piperidinium, phosphonium, or quaternary ammonium cation with an accompanying anion.

The use of item 1 1 , wherein the ionic liquid is:

wherein R' is an alkyl, such as CH3, C4H9, CsHi₇ or C12H25, A- is an anion, such as TFSI, BF4, P0F6 CF3SO3, and Cat⁺ is an imidazolium cation, such as 1 -butyl-3-methylimidazolium, a pyridinium cation, quaternary ammonium cation, a pyrrolidinium cation or a piperidinium cation.

The use of item 12, wherein the ionic liquid is:

wherein R' is CH3, C4H9, CsHi₇ or C12H25, and A- is bistriflimide or PF6^".

The use of any one of items 1 to 13, wherein the redox-active ionic liquid is









10

wherein R, R_a, Rt>, L, Mi , M2, R', A-, and Cat⁺ are as defined in items 8 and 12. The use of item 1 , wherein the redox-active ionic liquid is:

The use any one of items 1 to 15, wherein the electrolyte comprises more than about 0.1 mmol/L of the redox-active ionic liquid.

The use of item 16, wherein the electrolyte comprises up to about 50% by volume of the redox-active ionic liquid based on the total volume of the electrolyte and redox-active ionic liquid.

The use of item 17, wherein the electrolyte comprises between about 1 and about 5% of the redox- active ionic liquid.

The use of any one of items 1 to 18, wherein the electrolyte is the electrolyte of a battery.

The use of item 18, wherein the battery is a lithium-ion battery.

The use of any one of items 1 to 18, wherein the electrolyte is the electrolyte of a capacitor.

A redox-active ionic liquid as defined in any one of items 1 to 21.

A redox-active ionic liquid as defined in any one of items 1 to 21 , the redox-active ionic liquid being for use as an additive in an electrolyte of a secondary battery or of a supercapacitor.

An electrolyte additive comprising a redox-active ionic liquid as defined in any one of items 1 to 21. An electrolyte comprising a redox-active ionic liquid as defined in any one of items 1 to 21.

The electrolyte of item 25, comprising more than about 0.1 mmol/L of the redox-active ionic liquid. The electrolyte of item 26, comprising up to about 50% by volume of the redox-active ionic liquid based on the total volume of the electrolyte and redox-active ionic liquid.

The electrolyte of item 27, comprising between about 1 and about 5% of the redox-active ionic liquid. The electrolyte of any one of items 25 to 28, being a secondary battery electrolyte.

The electrolyte of item 29, being a lithium-ion battery electrolyte.

The electrolyte of any one of items 25 to 28, being a supercapacitor electrolyte.

A secondary battery or supercapacitor comprising an electrolyte comprising a redox-active ionic liquid electrolyte additive as defined in any one of items 1 to 21. 33. A method of manufacturing a redox-active ionic liquid electrolyte additive as defined in any one of items 1 to 21 , the method comprising linking a redox shuttle to an ionic liquid.

34. A method of increasing the solubility of a redox shuttle in an electrolyte, the method comprising linking the redox shuttle to an ionic liquid, thereby producing a redox-active ionic liquid as defined in any one of items 1 to 21.

35. A method of manufacturing an electrolyte, the method comprising adding a redox-active ionic liquid as defined in any one of items 1 to 21 to a conventional electrolyte.

36. A method of manufacturing a battery or supercapacitor comprising an electrolyte, the method comprising adding a redox-active ionic liquid as defined in any one of items 1 to 21 to the electrolyte.

37. A method of increasing the stability of an electrolyte, the method comprising add adding a redox-active ionic liquid as defined in any one of items 1 to 21 to the electrolyte.

38. A method of improving the safety of a battery or supercapacitor comprising an electrolyte, the method comprising add adding a redox-active ionic liquid as defined in any one of items 1 to 21 to the electrolyte.

39. A method of reducing the risks of overcharge or overdischarge of a battery or supercapacitor comprising an electrolyte, the method comprising add adding a redox-active ionic liquid as defined in any one of items 1 to 21 to the electrolyte.

40. A method of increasing the amount of a redox shuttle that can be added to an electrolyte without precipitation, the method comprising linking the redox shuttle to an ionic liquid, thereby producing a redox-active ionic liquid as defined above.

41. The method of any one of items 33 to 39, wherein the electrolyte comprises more than about 0.1 mmol/L of the redox-active ionic liquid.

42. The method of item 40, wherein the electrolyte comprises up to about 50% by volume of the redox- active ionic liquid based on the total volume of the electrolyte and redox-active ionic liquid.

43. The method of item 41 , wherein the electrolyte comprises between about 1 and about 5% of the redox- active ionic liquid.

44. The method of any one of items 33 to 42, wherein the electrolyte is a secondary battery electrolyte.

45. The method of item 43, wherein the electrolyte is a lithium-ion battery electrolyte.

46. The method of any one of items 33 to 42, wherein the electrolyte is a supercapacitor electrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

[006] In the appended drawings:

[007] Figure 1 shows the overcharge protection mechanism of a redox shuttle;

[008] Figure 2 shows the synthesis of the compounds of Example 1 ; [009] Figure 3 shows the cyclic voltammogram of a 50% solution of compound 1 in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0010] Figure 4 shows cyclic voltammograms of 1 x 10² mol L ¹ of compound 1 in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0011] Figure 5 is a plot of peak current versus square root of scan rate for the anodic (diamonds) and cathodic (squares) currents;

[0012] Figure 6 is an Arrhenius plot for the solutions of compound 1 in varying amounts of EC/DEC (1 :2) with and without LiTFSI (measurements were done at an interval of 5 °C from 25 to 75 °C. The R² obtained from the fittings range from 0.9878 to 0.9988);

[0013] Figure 7 is a charging curve for a Li/Li4Ti₅0 2 cell in EC/DEC, pure and modified with 10% Fc-MlmTFSI at C/10 (contains 1.5 M LiTFSI);

[0014] Figure 8 shows successive charge/discharge curves (C/10) for Li/Li₄Ti₅0i2 cells using EC/DEC (1.5 M LiTFSI) electrolyte, (a) pure and (b) modified with 10% Fc-MlmTFSI;

[0015] Figure 9 shows the capacity curves (C/10) for Li/Li₄Ti₅0i2 cells using EC/DEC (1.5 M LiTFSI) electrolyte either pure (solid line) or modified with 10% Fc-MlmTFSI (broken lines) (The parameters were set to a full charge followed by a 100% overcharge and a cut-off at 4V.);

[0016] Figure 10 is a charging curve for Li/V₂0₅ cell in EC/DEC, pure and modified with 10% Fc-MlmTFSI at C/10 (contains 1.5 M LiTFSI);

[0017] Figure 11 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 50% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0018] Figure 12 is a cyclic voltammogram of 50% ionic liquid in EC/DEC (1 :2 v/v) (no LiTFSI);

[0019] Figure 13 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 50% ionic liquid in EC/DEC (1 :2 v/v) (no LiTFSI);

[0020] Figure 14 is a cyclic voltammogram of 10% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0021] Figure 15 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 10% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0022] Figure 16 is a cyclic voltammogram of 1 % solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0023] Figure 17 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 1 % solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0024] Figure 18 is a cyclic voltammogram of 0.34% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[0025] Figure 19 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 0.34% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v);

[0026] Figure 20 shows the TGA curve for the ferrocenyl(methyl)imidazolium-TFSI redox ionic liquid in pure form; [0027] Figure 21 is an Arrhenius plots for the FcEBIm TFSI in EC/DEC 1 :2 with presence or not of LiTFSI (measurements were done at an interval of 5 °C from 25 to 75 °C);

[0028] Figure 22 shows A) cyclic voltammograms obtained using different concentration of FcEBIm TFSI (1 , 10 and 50%) in EC/DEC 1 :2 with presence or not of LiTFSI (the scan rate was 100 mV s-1 ) and B) cyclic voltammograms obtained using a 10% solution of FcEBIm TFSI in EC/DEC 1 :2 with 1.5 M LiTFSI (the scan rates were 25, 50, 100, 150, 200, 500, 1000, 2000, 5000 and 10000 mV s ¹);

[0029] Figure 23 shows the synthesis of compound 1 of Example 3;

[0030] Figure 24 shows the synthesis of compounds 2 and 3 of Example 3;

[0031] Figure shows the DSC of compound 1 of Example 3;

[0032] Figure 26 shows the DSC of compound 2 of Example 3;

[0033] Figure 27 shows the DSC of compound 3 of Example 3;

[0034] Figure 28 shows the TGA of compound 1 of Example 3;

[0035] Figure 39 shows the TGA of compound 2 of Example 3;

[0036] Figure 30 shows the TGA of compound 3 of Example 3;

[0037] Figure 31 shows the TGA of compound 4 of Example 3;

[0038] Figure 32 shows the cyclic voltammogram of compounds 1 -3 of Example 3 (1 mM in EC:DEC + 1.5 M LiTFSI, 100 mV/s);

[0039] Figure 33 shows the cyclic voltammogram of compound 1 of Example 3 showing the formation of a new compound upon cycling (Inset shows the stable behaviour of compound 2. Conditions: 10 mM in EC:DEC + 1.5 M LiTFSI, 100 mV/s));

[0040] Figure 34 shows the cyclic voltammogram of compound 1 of Example 3 (1 mM) in EC:DEC + 1.5 M LiTFSI at different scan rates;

[0041] Figure 35 shows the cyclic voltammogram of compound 2 of Example 3 (1 mM) in EC:DEC + 1.5 M LiTFSI at different scan rates;

[0042] Figure 36 shows the cyclic voltammogram of compound 3 of Example 3 (1 mM) in EC:DEC + 1.5 M LiTFSI at different scan rates;

[0043] Figure 37 shows the cyclic voltammogram of compound 4 of Example 3 (1 mM) in EC:DEC + 1.5 M LiTFSI at different scan rates;

[0044] Figure 38 is a plot of current maximum against square root of scan rate for compounds 1 -4 of Example

3;

[0045] Figure 39 shows the cyclic voltammogram of compound 1 of Example 3 (1 M in 1.5 M LiTFSI in EC:DEC); [0046] Figure 40 shows the cyclic voltammogram of compound 2 of Example 3 (0.7 M in 0.7M LiTFSI EC:DEC);

[0047] Figure 41 shows the cyclic voltammogram of compound 2 of Example 3 (1 M in 0.7 M LiTFSI EC:DEC);

[0048] Figure 42 shows the cyclic voltammogram of compound 3 of Example 3 (0.1 M in 0.5 MLiPF₆ EC:DEC);

[0049] Figure 43 shows the cycling profile of 0.7 M of compound 2 of Example 3 in 0.7 M LiTFSI;

[0050] Figure 44 shows the cycling profile of 1 M of compound 2 of Example 3 in 0.7 M LiTFSI;

[0051] Figure 45 shows the cycling profile of 0.1 M of compound 3 of Example 3 in 0.5 M LiPF6 (10 first cycles in A and 34 cycles in B); and

[0052] Figure 46 shows the cycling profile of 0.1 M compound 4 of Example 3 (in 0.5 M LiPF6 in EC:DEC:PC:DMC).

DETAILED DESCRIPTION OF THE INVENTION

Redox-Active Ionic Liquid for use as an Additive in an Electrolyte of a Secondary Battery or of a Supercapacitor

[0053] Turning now to the invention in more details, there is provided a redox-active ionic liquid for use as an additive in an electrolyte of a secondary battery or of a supercapacitor.

[0054] A battery is a device that converts chemical energy directly to electrical energy. A secondary battery is a battery that can be recharged; that is, it can have its chemical reactions reversed by supplying electrical energy to the cell, restoring its original composition. Many types of secondary batteries are known including: Lead-acid, Nickel-cadmium, Zinc-manganese, Nickel-hydrogen, Nickel-metal hydride, Nickel-zinc, Lithium air, Lithium-ion, Lithium-ion polymer, Lithium sulfur, Sodium-ion, Zinc bromide, Vanadium redox, Sodium-sulfur, and Silver-oxide batteries. A battery (rechargeable or not) consists of a number of cells; each cell consisting of two electrodes (anode and cathode) separated by a conductive electrolyte containing anions and cations. The electrolyte is a substance containing free ions and that is electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible. Examples of electrolytes in various types of secondary batteries include KOH dissolved in water, LiPF6 dissolved in an organic solvent, LiTFSI dissolved in PEO (polyethylene oxide), and (among many others) V2O5 in H2SO4.

[0055] The redox-active ionic liquid of the invention can be used in any electrolyte of any secondary battery.

[0056] Lithium-ion batteries are a type of secondary battery. They contain, simplistically, two active electrodes separated by a polymeric separator, surrounded by a liquid organic electrolyte solution. The electrolytes currently in use in commercial Li-ion batteries are based on mixtures of propylene (PC), ethylene (EC), diethyl (DEC), ethylmethyl (EMC), and dimethyl (DMC) carbonates (or a combination thereof) as solvent, with a soluble lithium salt (such as LiPF6, L1BF4, LIBOB or a combination thereof), and various additives to improve the lifetime of the battery and its safety. While these solvents possess the dielectric constants and viscosities required to dissolve appreciable amounts of Li salts and to transport them rapidly, they generally are flammable, volatile and subject to oxidation at high potentials.

[0057] A supercapacitor is a device that stores energy as a charge in an electric double layer, at the interface between an electrolyte and a high surface area conductor. A supercapacitor is composed of two electrodes (typically made of porous activated carbon) deposited on current collectors, most of the times identical. These electrodes are immersed in an electrolyte and are separated by a porous insulating membrane. The electrolyte can be aqueous-based: for instance a water solution of potassium hydroxide (KOH) or sulphuric acid (H2SO4), or organic-based: acetonitrile, propylene carbonate, ethylene carbonate, diethyl carbonate. Commercial devices only use acetonitrile or propylene carbonate or mixtures of the two. Alkylammonium salts of tetrafluoroborate or hexafluorophosphate are dissolved in the above solvents. When a voltage is applied between the electrodes, negative ions from the electrolyte flow to the positive electrode. In the same time, positive ions from the electrolyte flow to the negative electrodes. An electric double layer is created at each electrode/electrolyte interface. The separator prevents any electrical contact between the two conductive electrodes but does not prevent the exchange of ions.

[0058] The redox-active ionic liquid of the invention can be used in any electrolyte of any supercapacitor.

[0059] The redox-active ionic liquid of the invention comprises a redox shuttle linked to an ionic liquid. The inventors have indeed found that modifying a redox shuttle to attach thereto an ionic liquid allowed producing redox-active ionic liquids.

[0060] These redox-active ionic liquids have further been found to be useful as additives in the electrolytes of batteries and supercapacitors. Generally, the presence of the redox-active ionic liquids does not negatively impact the properties of the electrolyte to which the redox-active ionic liquids are added and once in it, the redox- active ionic liquids act both as an ionic liquid and a redox shuttle. Also, generally, the incorporation of the redox shuttle moiety onto the ionic liquid structure has no negative impact of the transport properties. In some cases, it may even increase the oxidation potential of the redox shuttle.

[0061] In embodiments, these redox-active ionic liquid present several other advantages. For example, the redox-active ionic liquids can have low vapor pressure and be non-flammable. They can therefore reduce the volatility, increase the flash point, and/or reduce the flammability of the electrolyte (i.e. increase the thermal stability of the electrolyte). The incorporation of the redox shuttle moiety onto the ionic liquid structure generally increases the decomposition temperature of the redox shuttle. This may reduce safety risks, in particular the risk of explosion. It could thus reduce the costs associated with expensive electronics and other mechanical safety devices used to prevent such occurrences.

[0062] Another advantage is that the attachment of the ionic liquid allows, in embodiments, to increase, often greatly increase, the solubility of the redox shuttle in the electrolyte. There is indeed a recognized and long-felt need in the art for redox shuttle with increased solubility. This is because the overcharge protection afforded by any redox shuttle depends on the number of redox molecules dissolved in the electrolyte. There must be enough of these molecules to transport all of the excess electrons during charging conditions (rapid or slow charging). Therefore, the redox-active ionic liquids of the invention should have increased usefulness at high charge (discharge) rates, since they can transfer more charge. All of this can contribute to prolonging the life span of the battery and supercapacitor (in particular the electrolyte) at high rates of charge. This is especially important under fast charging conditions, envisioned for EV for example, where the goal is to recharge the large battery as quickly as possible.

[0063] Finally, it should be noted that the various component of the redox-active ionic liquid can be modified to tailor the exact properties of the redox-active ionic liquid for its intended end use.

[0064] In the redox-active ionic liquids of the invention, the redox shuttle and the ionic liquid may be linked directly or indirectly. In embodiments, the link is achieved through covalent bonds, where the redox shuttle and the ionic liquid are covalently attached directly to one another or are attached through a linker. In embodiments, the redox-active ionic liquid is of formula RS-LK-IL, wherein RS is the redox shuttle, LK is either a bond or a linker, and IL is the ionic liquid. The linker may be -alkylene-, -COO-alkylene-, -CO-alkylene-, -O-alkylene-, -N- alkylene-, or -S-alkylene-, wherein the alkylene group may comprise between 1 and 12 carbon atoms, preferably between 1 and 6 carbons atoms, more preferably between 1 and 3 carbon atoms. In embodiments, LK is -CH2- or -CH₂CH₂- .

[0065] A redox shuttle is a molecule added to an electrolyte to prevent overcharge and/or over-discharge. In some cases, for example lithium-ions batteries, overcharge and/or over-discharge can lead to chemical and electrochemical reactions within the battery, causing rapid temperature rise, self-accelerating reactions, and even explosion. In supercapacitors, this can lead to electrode material deterioration and losses in charge storage ability.

[0066] In a battery or a supercapacitor, the redox shuttle molecule is to be reversibly oxidized and reduced at a defined potential slightly higher (or lower) than the charge (or discharge) potential of the cell. Therefore, under normal conditions the shuttle has no function, but if the cell is over-oxidized (or over-reduced), the redox shuttle becomes oxidized (or reduced) receiving the excess charge; this new oxidized (or reduced) species then migrates to the opposite electrode and regenerates the redox shuttle to its initial state. This prevents the overcharging (or over discharging) of the battery or supercapacitor since the excess charge is used to drive the redox shuttle and not to overcharge (overdischarge) of the material. This mechanism is shown in Figure 1 in the case of a battery being overcharged. On the overcharged cathode surface, the redox shuttle molecule (S) is oxidized to its (radical) cation form (S+), which, via diffusion across the cell electrolyte, would be reduced back to its original or reduced state on the surface of the anode. The reduced form would then diffuse back to the cathode and oxidize again. This "oxidation-diffusion-reduction-diffusion" cycle is then repeated.

[0067] As stated above, an ideal redox shuttle should have an oxidation or reduction potential slightly (for instance about 0.3 or 0.4 V) above or below the charge or discharge potential (respectively) of the cell. This allows the cell to be normally charged before the shuttle molecule begins to function. Given the above, the skilled person will easily be able to choose which of the redox-active ionic liquid of the invention can be used in a given battery or supercapacitor.

[0068] In addition, the potential of the redox shuttle should ideally not exceed the electrochemical window of the electrolyte. Otherwise, the electrolyte could be oxidized when used.

[0069] The redox shuttle that is part of the redox-active ionic liquid of the invention can be any redox shuttle known in the art. It may also be any derivative of these redox shuttles.

[0070] In embodiments, the redox-shuttle may include those described in:

• US 7,585,590,

• US 7,615,312,

• US 7,615,317,

• US 7,648,801 ,

• US 7,81 1 ,710,

• US 2009/0286162,

• US 2010/0104950,

• Dahn, et al., The Electrochemical Society Interface · Winter 2005, page 27,

• Redox shuttles for safer lithium-ion batteries, Zonghai Chen, Yan Qin, and Khalil Amine in Electrochimica Acta, Volume 54, Issue 24, 1 October 2009, Pages 5605-5613, and

• Redox Shuttle Additives for Lithium-Ion Battery, Lu Zhang, Zhengcheng Zhang and Khalil Amine Chapter 7 in Lithium Ion Batteries - New Developments, llias Belharouak Editor, InTech, February 2012, and in references cited therein (all of these documents being herein incorporated by reference), as well as derivatives thereof.

[0071] Non-limiting examples of redox shuttles include ferrocene and ferrocene derivatives, dihydrophenazine systems, metallocenes, dimethoxybenzene derivatives, thiantlurene derivatives, 2 ,5 -d i -ie/t-b uty I - 1 ,4- dimethoxybenzene (DDB), phenothiazine derivatives, 2,2,6,6-tetramethylpiperinyloxide (TEMPO), 2- (pentafluorophenyl)-tetrafluoro-l ,3,2-benzodioxaborole (PFPTFBB), and organometallic complexes between a metal center and a ligand (non-limiting examples of which including acetylacetone, ortho-phenantrolines, and bipyridines.

[0072] Non-limiting examples of derivatives of the above includes molecules where substituents or side chains, non-limiting examples of which are alkyi chains, alkyi ethers, carboxylic groups, alkyi esters, alkyi sulfonyls, have been added.

[0073] In embodiments, the redox shuttle is:

, wherein R is H, N0₂, SO3H, F or CI, R_a is H or F, R_b is H or tert-butyl , L is SCN, CN or CO, Mi is Fe, Ru, Os, Co, Rh or Ir and M₂ is Fe.

[0074] In embodiments, the redox shuttle is:

, wherein M2 is Fe, and R_a is H.

[0075] In other embodiments, the redox shuttle is :

, wherein Rb is H or tert-butyl.

[0076] Herein, "ionic liquid" (IL) per se refers to a salt (comprising anion(s) and cation(s)) that is molten at low temperature, for example below about 100°C, below about 50°C, preferably at room temperature.

[0077] However, it should be noted that redox-active ionic liquids comprising the redox shuttle linked to the ionic liquid will have melting points different from that of their corresponding ionic liquids. As such, the redox- active ionic liquids may be molten at relatively low temperature, for example below about 200°C, below about 150°C, below about 100°C, below about 50°C, preferably at room temperature.

[0078] In the redox-active ionic liquid of the invention, the redox-shuttle can be linked to the cation or to the anion of the ionic liquid. In embodiments, the redox-shuttle is linked to the cation.

[0079] There are many classes of ionic liquids. Among them, substituted imidazolium-based salts have multiple applications. Depending on their anion, aprotic ionic liquids can have high conductivity, low vapor pressure, high thermal stability and/or a large window electrochemical. The ionic liquid that is part of the redox-active ionic liquid of the invention can be any ionic liquid. It may also be any derivative of these ionic liquids.

[0080] Several room-temperature ionic liquids, including the imidazoliums, have been suggested for use as the electrolyte of batteries or supercapacitors. Therefore, in embodiments, the ionic liquid that is part of the redox- active ionic liquid of the invention can be any ionic liquid known in the art to be useful as an electrolyte for batteries or supercapacitors. It may also be any derivative of these ionic liquids.

[0081] In embodiments, the ionic liquid may those described in: • Ionic liquids as electrolytes for Li-ion batteries— An overview of electrochemical studies, Andrzej Lewandowski and Agnieszka Swiderska-Mocek, Journal of Power Sources, Volume 194, Issue 2, 1 December 2009, Pages 601-609, and

• Ionic-liquid materials for the electrochemical challenges of the future, Michel Armand, Frank Endres, Douglas R. MacFarlane, Hiroyuki Ohno & Bruno Scrosati, Nature Materials 8, 621 - 629 (2009), and in the references cited therein (all these documents being herein incorporated by reference), as well as derivatives thereof.

[0082] In embodiments, the ionic liquid comprises cation with an accompanying anion, the cation comprising a nitrogen-containing ring with one or more optional side chains. In embodiments, the ionic liquid comprises an imidazolium, pyridinium, pyrazolium, triazolium, thiazolium, oxazolium, pyridazinium, pyrimidinium, pyrazinium, pyrrolidinium, piperidinium, phosphonium, or quaternary ammonium cation (including derivatives thereof) with an accompanying anion.

[0083] Non-limiting examples of derivatives of ionic liquids includes cations where substituents or side chains have been added and/or one or more heteroatoms, such as O, have been inserted in the ring. Side chains can include alkyl, alkoxy, and alkoxylakyl chains.

[0084] In some embodiments, the cation is N-methyl-N-alkyl-pyrrolidinium, N-methyl-N-alkyl-pyridinium, N- methyl-N-alkylpiperidinium, N-methyl-N-alkyl-imidazolium, N-methyl-N-alkyl-phosphonium, N-methyl-N-alkyl- ammonium, N-methyl-N-alkyl-guanidinium, or N-methyl-N-alkyl-isouronium.

[0085] A wide range of anions can be employed with the above cations, from simple halides to inorganic anions such as tetrafluoroborate and hexafluorophosphate and to large organic anions like bistriflimide (bis(trifluoromethane)sulfonimide, TFSI), triflate (trifluoromethanesulfonate, CF3SO3 ) or tosylate. Non- halogenated organic anions, such as formate, alkylsulfate, alkylphosphate or glycolate, can also be used. In some embodiments, the anions of the ion liquid are thus inorganic. In other embodiments they are organic. In one embodiment, the anion is an imide. Imide anions have large electron derealization and low melting temperature. Thus, in some embodiments, the anion is bis(trifluoro methane sulfonyl)imide or bis(perfluoro ethyl sulfonyl) imide. In some embodiments, the anion is an amide, which includes, but is not limited to, bis(trifluoro methane sulfonyl) amide. In other embodiments, the anion is trifluoromethanesulfonate, hexafluorophosphate (PF₆ ), tetrafluoroborate (BF₄ ), or tetraperchlorate (CIO4 ).

, -SO3- ⁺Cat, or wherein R' is an alkyl, for example Ch , C4H9, CeHi? or C12H25, A- is an anion, for example bistriflimide, BF4-, PF6^" or CF3SO3^", and Cat⁺ is an imidazolium cation, for example 1-butyl-3-methylimidazolium, a pyridinium cation, a quaternary ammonium cation, a pyrrolidinium cation or a piperidinium cation.

[0087] In embodiments, the ionic liquid is

, wherein R' is -CH3, -C4H9, -CsH or -C12H25, preferably -CH3, and A- is bistriflimide or PF6^".

[0088] In embodiments, the redox-active ionic liquid of the invention is











, wherein n is 0, 3, 7 or 1 1 ,

[0090] As explained above, the redox-active ionic liquid is to be used as an additive in an electrolyte of a secondary battery or of a supercapacitor. As such, the redox-active ionic liquid will be mixed with the electrolyte, in which it should be miscible. Generally, the redox-active ionic liquids of the invention are miscible (if liquid at room temperature) or soluble (if solid) with organic solvents over a wide range of concentration. The maximum amount of redox-active ionic liquid added to the electrolyte will depend on the desired properties of the battery or supercapacitor. An excess of redox-active ionic liquid may be defined as the concentration at which the conductivity and/or viscosity of the electrolyte is decreased below a desired minimum level. The minimum amount of redox-active ionic liquid added to the electrolyte will depend on the magnitude of protection desired. This will in turn depend on the end use of the battery or capacitor and the nature of its electrolyte and electrodes. In embodiments, the electrolyte may comprise more than about 0.1 mmol/L of the redox-active ionic liquid, for example, more than about 1 , 10, or 100 mmol/L, an up to about 1 mol/L. In embodiments, the electrolyte comprises between about 1 and about 5% of the redox-active ionic liquid. Other Aspects of the Invention

[0091] The present invention also relates to a redox-active ionic liquid as defined above per se. In particular embodiments, the invention relates to such redox-active ionic liquids for use as additives in electrolytes of secondary batteries, such as lithium-ion batteries, or supercapacitors as described above.

[0092] The present invention also relates to an electrolyte additive, this additive comprising a redox-active ionic liquid as defined above.

[0093] The present invention also relates to an electrolyte comprising a redox-active ionic liquid as defined above.

[0094] The present invention also relates to a method of manufacturing a redox-active ionic liquid electrolyte additive as defined above, the method comprising linking a redox shuttle to an ionic liquid.

[0095] The present invention also relates to a method of increasing the solubility of a redox shuttle in an electrolyte, the method comprising linking the redox shuttle to an ionic liquid, thereby producing a redox-active ionic liquid as defined above. More specifically, the present invention relates to a method of increasing the amount of a redox shuttle that can be added to an electrolyte without precipitation, the method comprising linking the redox shuttle to an ionic liquid, thereby producing a redox-active ionic liquid as defined above. In cases where the redox-active ionic liquid produced is solid at room temperature, the increase amount is due to the increased solubility of the redox-active ionic liquid in the electrolyte. In cases where the redox-active ionic liquid produced is liquid at room temperature, the increase amount is due to the miscibility of the redox-active ionic liquid in the electrolyte.

[0096] The present invention also relates to:

• a method of manufacturing an electrolyte;

• a method of manufacturing a battery or supercapacitor comprising an electrolyte;

• a method of increasing the stability of an electrolyte;

• a method of improving the safety of a battery or supercapacitor comprising an electrolyte;

• a method of reducing the risks of overcharge or overdischarge of a battery or supercapacitor comprising an electrolyte;

the method comprising adding a redox-active ionic liquid as defined above to the electrolyte.

[0097] In all these various aspect of the invention, the electrolyte is an electrolyte as described above in respect of the use of the redox-active ionic liquid. In particular, the electrolyte can be a secondary battery electrolyte, such as a lithium-ion battery electrolyte, or a supercapacitor electrolyte.

[0098] In addition, the quantity of redox-active ionic liquid in the electrolyte is as described above in respect of the use of the redox-active ionic liquid. In particular, the electrolyte may comprises more than about 0.1 mmol/L of the redox-active ionic liquid, for example, more than about 1 , 10, or 100 mmol/L or more than about 1 mol/L, for example between about 1 and about 5% of the redox-active ionic liquid. Definitions and Clarifications

[0099] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[00100] The terms "comprising", "having", "including", and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted.

[00101] Herein, the term "about" has its ordinary meaning. For example, it may means plus or minus 10% of the numerical value thus qualified.

[00102] Herein, the term "alkyl" refers to branched or linear radicals of formula -C_nH2n+i . Similarly, the terms "alkylene" refers to branched or linear radicals of formula -C_nH2n-. In embodiments, n may range from 1 to 12.

[00103] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[00104] Recitation of ranges of values or classes of compounds herein are merely intended to serve as a shorthand method of referring individually to each separate value or compound falling within the range or class, unless otherwise indicated herein, and each separate value or compound is incorporated into the specification as if it were individually recited herein. All subsets of values or compounds within the ranges or classes are also incorporated into the specification as if they were individually recited herein.

[00105] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

[00106] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.

[00107] No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[00108] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENT

[00109] The present invention is illustrated in further details by the following non-limiting examples.

Example 1

[00110] An electroactive ionic liquid (IL), 1 -ferrocenylmethyl)-3-methylimidazolium- b^'\s(trifluoromethanesulfonyl)arr\0e (TFSI) was synthesised and its electrochemical properties investigated when diluted with ethylene carbonate/diethyl carbonate (EC/DEC) solvent at various ratios. Cyclic voltammetry data were gathered to determine the redox potential, diffusion coefficient and heterogeneous rate constants of the electroactive imidazolium TFSI ionic liquid in solutions. The properties of these solutions as electrolytes in lithium batteries were studied in test cells with metallic Li anodes and L^TisO^, V2O5 and LiFeP04 cathodes. The efficiency of electroactive ionic liquid, at least added as an additive to existing solvents, is clearly demonstrated hereinafter. Its use presents the benefit of increasing the concentration of the redox moiety in the electrolyte.

[00111] First, a methylimidazolium functionalised with ferrocenemethyl (Fc-Mlm, 1 shown below) with the bis(trifluoromethanesulfonyl)amide TFSI) anion was prepared.

[00112] The ionic conductivity, viscosity, and electrochemical behaviour using cyclic voltammetry of Compound 1 were studied. Used in its pure form, the Fc-Mlm TFSI electroactive IL would contain approximately 2.9 M of redox moieties (calculated from density and MW). It was found that the redox ILs can be added as an additive to EC/DEC (1 :2) with a Li salt dissolved without compromising the viscosity and conductivity of the electrolyte. Such mixtures of Fc-Mlm TFSI and EC/DEC were then incorporated in coin cells based on Li4Ti₅0i2 and V2O5 cathodes to demonstrate their ability to protect the electrode against overcharge.

Experimental

Synthesis

[00113] (Dimethylaminomethyl)ferrocene, iodomethane, /V,/V-carbonyldiimidazole, silver nitrate, bis(trifluoromethane)sulfonimide, lithium salt sodium hydroxide, magnesium sulphate, and sodium sulphate were purchased from Aldrich. Methanol, diethyl ether, dichloromethane and phosphoric acid were purchased from Fisher, and acetonitrile was purchased from EMD. All were used without further purification.

[00114] ¹H and ¹³C Nuclear magnetic resonance spectra were recorded either on a Bruker AMX300 or Avance 500 using CDCI3 or deuterated DMSO as the solvent. Electrospray ionisation mass spectrometry were performed by the Centre regional de spectroscopie de masse de I'Universite de Montreal.

[00115] The synthesis of ferrocenyl(methyl)imidazolium bis(trifluoromethanesulfonyl)amide (Fc-Mlm TFSI: 1) was carried out according to the scheme shown in Figure 2. The first reaction was an SN2 displacement of the trimethylamine iodide (3) with a primary alcohol to give ferrocenemethanol (4). This reaction was achieved by refluxing (ferrocenylmethyl)trimethyl ammonium iodide in sodium hydroxide solution. The second step of the modified procedure was the reaction of 4 with Λ/,Λ/'-carbonyldiimidazole to give the desired (ferrocenylmethyl) imidazole (5). Quaternization of 5 with iodomethane to form 6 was refluxed in acetonitrile for 24 h to improve yields. Conversion of the iodide salt 6 to the final product 1 was possible but the work-up with water to remove all traces of iodide from the ionic liquid gave a product in low yield and hence an extra step was introduced. Ferrocenyl(methyl)imidazolium iodide 6 was reacted with silver nitrate in acetonitrile, the resulting silver iodide precipitate was filtered off and the new nitrate salt 7 was collected under reduced pressure. The metathesis reaction of 7 with an aqueous solution of lithium bis(trifluromethanesulfonyl)amide gave 1 .

Trimethylferrocenyl(methyl)ammonium iodide 3

[001 16] 8.00 g (32.91 mmol) of 2 was dissolved in 2 ml of methanol, 2.05 ml (32.91 mmol) of iodomethane was added dropwise to the solution. The mixture was heated to 75°C for 15 minutes. The resulting crude precipitate was filtered off and washed with portions of ether until the ether portions were colourless. Yield: 11.15 g (28.96 mmol, 88%). Orange powder,. ¹H-NMR (CDCI₃, δ, ppm): 3.28 (s, 9H, 3 CH₃); 4.27 -4.55 (m, 9H, Fc); 4.88 (t, J = 1.7 Hz, 2H, CH₂).

Ferrocenemethanol 4

[001 17] 1 1.15 g (28.96 mmol) of 3 was dissolved in 120 ml 1 M NaOH solution and refluxed for 3 h. The resulting mass was cooled and extracted with five 100 ml portions of ether. The combined organic layers were washed with five portions of H2O, dried with MgSC>4 and evaporated to dryness on a rotary evaporator. Yield: 4.94g (22.88 mmol, 79%). Orange crystals, ¹ H-NMR (DMSO-d₆, δ, ppm): 4.09 (t, J = 1.7 Hz, 2H, Cp_Subst); 4.13 (m, 5H, Cpunsubst); 4.18 (t, J = 1.7 Hz, 2H, Cp_Subst); 4.21 (s, 1 H, 2H, CH₂); 4.71 (t, J = 5.6 Hz, 1 H, OH).

Ferrocenyl(methyl)imidazole 5

[001 18] 4.94 g (22.88 mmol) of 4 and 3.71 g (22.88 mmol) of Λ/, Λ/ -carbonydii midazole were dissolved in CH2CI2 and refluxed for 3 hours. The resulting mass was cooled, 50 ml of ether was added and extracted with 20% phosphoric acid solution (4 x 50 ml). The aqueous phase was alkalised to pH 5 with NaOH solution and then extracted with four portions of CH2CI2, dried with Na2S04 and evaporated to dryness on a rotary evaporator. Yield: 3.65 g (13.73 mmol, 60%). Yellow crysyals,. ¹ H-NMR (CDCI₃, δ, ppm): 4.154.19 (m, 9H, Fc); 4.87 (s, 2H, CH₂); 6.93 (s, 1 H, imidazole); 7.05 (s, 1 H, imidazole), 7.51 (s, 1 H, imidazole).

Ferrocenyl(methyl)imidazolium iodide 6

[001 19] 3.65 g (13.73 mmol) of 5 was dissolved in 20 ml of CH₃N, 0.86 ml (13.81 mmol) of iodomethane was added dropwise to the solution. The mixture was refluxed for 24 h. The resulting mixture was evaporated to dryness and washed with small portions of ether until the ether fractions were colourless. Yield: 5.21 g (12.77 mmol, 93%). Yellow solid,. ¹H-NMR (DMSO-de, δ, ppm): 3.82 (s, 3H, CH₃); 4.24 (m, 7H, Cp_Subst and Cp_Unsubst); 4.44 (t, J = 1.9 Hz, 2H, Cp_Subst); 5.17 (s, 2H, CH₂); 7.66 (t, J = 1.7 Hz, 1 H, imidazole); 7.75 (t, J = 1.8 Hz, 1 H, imidazole); 9.08 (s, 1 H, imidazole).

Ferrocenyl(methyl)imidazolium nitrate 7

[00120] 5.21 g (12.77 mmol) of 6 and 2.17 (12.77 mmol) of silver nitrate were dissolved in CH₃N and stirred for 30 minutes. The resulting precipitate was filtered off and the solution was collected and evaporated to dryness on a rotary evaporator. Yield: 4.16 g (12.13 mmol, 95%). Yellow-green solid,. ¹H-NMR (DMSO-de, δ, ppm): 3.81 (s, 3H, CH₃); 4.23 (m, 7H, Cp_Subst and Cp_Unsubst); 4.43 (t, J = 1.9 Hz, 2H, Cp_Subst); 5.15 (s, 2H, CH₂); 7.65 (t, J = 1.7 Hz, 1 H, imidazole); 7.75 (t, J = 1.8 Hz, 1 H, imidazole); 9.08 (s, 1 H, imidazole). ¹³C-NMR (DMSO-de, δ, ppm): 35.62 (CH₃); 48.12 (CH₂); 68.57 (Cp_Unsubst); 68.71 (Cp_Subst); 68.79 (Cp_Subst); 80.83 (Cp_Subst); 121.87, 123.46, 135.76 (imidazole).

Ferrocenyl(methyl)imidazolium bis(trifluoromethanesulfonyl)amide 1

[00121] An aqueous solution of LiTFSI (5.22 g, 18.20 mmol, 1.5 equivalents) was added drop wise to an aqueous solution of 7 (4.16 g, 12.13 mmol) and the solution was stirred for 2 h at room temperature and left overnight to allow a red-orange liquid to separate from the aqueous phase. The mixture was extracted with CH2CI2 and the organic layer washed with five portions of H2O and dried over MgSC The solvent was then evaporated under reduced pressure and the product vacuum-dried at 80°C for 24 h. Yield: 5.20 g (5.70 mmol, 47%). Orange liquid,. ¹H-NMR (DMSO-de, δ, ppm): 3.82 (s, 3H, CH₃); 4.24 (m, 7H, Cp_Subst and Cp_Unsubst); 4.43 (t, J = 1.8 Hz, 2H, Cpsubst); 5.16 (s, 2H, CH₂); 7.64 (t, J = 1.5 Hz, 1 H, imidazole); 7.73 (t, J = 1.8 Hz, 1 H, imidazole); 9.06 (s, 1 H, imidazole). ¹³C-NMR (DMSO-d₆, δ, ppm): 35.75 (CH₃); 48.28 (CH₂); 68.69 (Cp_Unsubst); 68.85 (Cp_Subst); 68.91 (Cpsubst); 80.89 (Cp_Subst); 120.74 (CF₃); 121.99, 123.58, 135.85 (imidazole). HRMS (ESI) m/z [M]⁺ calcd for Ci5Hi₇FeN₂ 281.07357; found 281.07444; [M]- calcd for C2F6NO4S2 calcd 279.91784; found 279.91699.

[00122] The synthesis of ruthenocenyl(methyl)imidazolium bis(trifluoromethanesulfonyl)amide was prepared in the same manner as the ferrocenyl version except dimethylaminomethylruthenocene was first synthesised by the electrophilic addition of the imminium ion generated in situ from W,W,W,W-tetramethylammoniumethane to ruthenocene, before the subsequent reactions followed. The synthesis of ruthenocenyl(methyl)imidazolium hexaflurorophosphate followed the same procedure as the bis(trifluoromethanesulfonyl)amide version except with addition of silver nitrate was replaced with silver hexafluorophosphate to give directly the desired product.

ThermoQravimetric analysis

[00123] Thermogravimetric analysis was performed on a TGA 2950 TA Instruments, measurements were performed under nitrogen from room temperature to 600 °C.

Electrochemical Measurements

[00124] Cyclic voltammetry measurements were performed in a heart-shaped electrochemical cell using a potentiostat from Princeton Applied Research (model PARSTAT 2273). The electrodes were platinum, platinum wire and silver wire as the working, counter and reference electrodes, respectively. The solutions were degassed with nitrogen for 15 minutes prior to measurements. All measurements are referenced against the E of the Fc/Fc⁺ redox couple.

Ionic Conductivity

[00125] The conductivity of the ionic liquid and its solutions were measured by electrochemical impedance spectroscopy using the PARSTAT 2273 and a low-volume Orion conductivity cell (model 018012) with two platinised Pt electrodes, σ was calculated from the resistance (R_s) determined as the intersection of the curve obtained with the real axis (Ζι¾) of the Nyquist plot obtained by scanning from 1 to 10⁶ Hz around the open circuit potential and with a perturbation amplitude of 10.0 mV rms. A thermocouple was placed in direct contact with the ionic liquid (or solutions) in the cell to accurately determine its temperature (±0.1 °C). Viscosity

[00126] Viscosity was measured with a Cambridge Applied System VL-4100 apparatus using pistons with range 0.5 to 10 cP and 10 to 200 cP. All measurements were performed at 25 °C.

Coin cell tests

[00127] Electrochemical evaluation of the redox ionic liquid samples in coin cell batteries was performed. Initially the Li4Ti₅0i2 cathode material (Sud Chemie) was combined with 10% of a conductive carbon (Super S, Timcal) and 10 wt% polyvinylidene difluoride (5 wt% in n-methyl pyrrolidone (NMP)). An extra portion of NMP was added to the mixture to form slurry, which was then mixed several hours in a Turbula shaker. The slurry was then coated on a piece of carbon-coated Al foil. The electrodes were then dried overnight at 80 °C under dry air. The next day, 13 mm diameter disks were punched for cell assembly in standard 2032 coin-cell hardware (Hohsen) with a single lithium-metal foil for both counter and reference electrodes. Then, the whole electrode set (coin-cell hardware and punched-electrode disks) was dried overnight at 70 °C under vacuum. Cells were assembled in an argon filled glove box using 1.5M LiTFSI in ethylene carbonate/diethyl carbonate (1 :2 v/v) electrolyte (UBE). For the redox ionic liquid, a known portion of the samples was added to the 1.5M LiTFSI electrolyte. Electrochemical evaluations were performed with an Arbin battery tester. The cells were cycled at constant current at 30 °C from 4 V to 1.2 V for Li₄Ti₅0i₂ at a rate of ~C/10.

Results

Electrochemical Characterization

[00128] Figure 3 shows the cyclic voltammogram of a 50% solution of 1 dissolved in an electrolyte of 1.5 M LiTFSI in ethylene carbonate / diethyl carbonate (EC/DEC) at both 100 and 10 mV s ¹ scan rates. The voltammogram shows the reversible nature of the pendant ferrocenyl redox group in the ionic liquid with an Ei/2^0X = +0.18 V vs. Fc/Fc⁺ at 100 mV S^"1 and Ei_/2°^x = +0.1 1 V vs. Fc/Fc⁺ at 10 mV s-¹.

[00129] Figure 3 also shows the potential of the redox process with reference to lithium, Ei/2^0X = +3.39 V vs. Li/Li⁺ at 100 mV s ¹ and Ei/2^0X = +3.32 V vs. Li/Li⁺ at 10 mV s ¹ The voltammogram also shows that due to the high concentration of the ionic liquid, the peak separation (ΔΕ_ρ3-_ρο = 1.21 , and 0.82 V at 100, and 10 mV s ¹ , respectively), indicates that the viscous nature of the solution influences the electrode kinetics. To explore the effect of the lithium salt on the oxidation potential of the solution, cyclic voltammogram measurements were also performed in a 50% solution without LiTFSI (see Table 1 and FIGS 10 and 1 1 ). In this case the anodic peak (+0.79 V) at 100 mV s ¹ is nearly the same as the solution with LiTFSI (+0.76 V) but the reverse back to the neutral ferrocene group is higher in potential (-0.44, and -0.13 V, for solutions with and without LiTFSI, respectively). As seen in the viscosity measurements (see below), the lithium salt increases the viscosity of the solution and therefore the energy required to return an electron back to the neutral species. As a consequence, the Ei/2^0X for the 50% solution without LiTFSI is higher (Ei/2^0X = +0.18, and +0.46 V, for solutions with and without LiTFSI, respectively). [00130] To examine the effect of the percentage of ionic liquid in solution has on the electrochemical properties, 10%, 1% and 0.34% (which corresponds to 1 x 10² mol L ¹) solutions were prepared and analysed. By decreasing the concentration to a 10% solution, the difference in peak to peak separation decreases greatly (AEpa-pc = 0.40, and 0.21 V at 100, and 10 mV s ¹, respectively). This effect is again seen in reducing the concentration further to a 1% solution with ΔΕ_Ρ values of 0.17, and 0.13 V for 100, and 10 mV s ¹, respectively. Note that the difference in ΔΕ_Ρ values between the two scan rates also decreases with lower concentrations. Interestingly, the 0.34% solution actually has a higher oxidation half wave than all the solutions and is of lowest concentration of ionic liquid in solution. At this concentration, the oxidation waves are almost identical at either scan rate.

[00131] The onset of oxidation limit is measured at the start of a new irreversible wave (see FIGS 10 to 18) and is the last stable point in the electrochemical window and as expected this value decreases as the concentration of ionic liquid in solution decreases. The exception to this is the 50% solution that contains no LiTFSI. Without the supporting electrolyte, the resistance of the solution is much greater and therefore expectedly reaches the end of its potential window at a lower voltage. In the reduction analysis of the solutions, a quasi-reversible peak is evident in all cases except that of the solution without the lithium salt. It is likely therefore that this is reduction is from lithium, perhaps a reaction with moisture or oxygen in the solution. However, these values are not constant on each solution or follow a pattern. The reduction limit, measured as the onset of an irreversible wave after the quasi-reversible wave follows the opposite pattern to the oxidation limit in that it increases to a more negative potential with less ionic liquid. A summary of these data can be seen in Table 1.

Table 1. Summary of cyclic voltammetry data of ionic liquid solutions.

Ratio of Concentration of El/2°^X El/2°^X Oxidation Reduction

Ionic Liquid LiTFSI (100 mV s-¹) (10 mV s-¹) Limit Limit

/ % / mol L-¹ / V / V / V / V

+0.18 +0.1 1

50 1.5 +2.04 -2.30

(+0.77/-0.44) (+0.52/-0.30)

+0.46 +0.49

50 0 +0.98 -2.30

(+0.79 / -0.13) (+0.70 / +0.27)

+0.10 +0.08

10 1.5 +1.78 -2.40

(+0.30/-0.10) (+0.18/-0.03)

+0.02 -0.03

1 1.5 +1.62 -2.46

(+0.07/-0.10) (+0.04/-0.09)

+0.20 +0.19

0.34^a 1.5 +1.44 -2.71

(+0.25/+0.15) (+0.23/+0.15)

a Ratio corresponds to 1 x 10 ² mol L ¹.

[00132] The diffusion coefficient and heterogeneous rate transfer constant was calculated for the redox-active ionic liquid using the 1 x 10 ² mol L ¹ solution. A series of CVs at varying scan rates (from 0.025 to 50 V s ¹) with iR compensation were performed and are shown in Figure 4. The diffusion coefficient, a factor in the determination of the maximum current that the redox shuttle can carry, was calculated for both the reduced (DR) and oxidised (Do) forms of the redox shuttle from the gradient of peak current (i_p) against the square root of the scan rate (Figure 5) through the Randles-Sevcik equation (Bard, A. J.; Faulkner, L. R. Electrochemical Methods Fundamentals and Applications; Second ed.; John Wiley & Sons, Inc., 2001 ):

where n is the number of electrons, in this case one, F is the Faraday constant, A is the electrode area, C is the concentration, R is the gas constant, T is the temperature, v \s the scan rate and D is the diffusion coefficient. The diffusion coefficients calculated were 6.57 x 10 ⁷ and 6.16 x 10 ⁷ cm² s ¹, for the reduced and the oxidised forms, respectively. Although the diffusion coefficient is not as high as other redox shuttles used for Li-ion battery safety, the greater concentration of our redox shuttle that can be dissolved in solution compensates for this. The ratio of DO/DR is 0.93; this value is close to 1 and shows that the diffusion expectedly follows Arrhenius-type behaviour.

[00133] The solution had a viscosity of 4.69 x 10 ³ Pa-s. [00134] The heterogeneous rate transfer constant (k_s) was determined using peak-to-peak separation (Δρ) using Nicholson's method,³¹ which relates Δρ with a kinetic parameter ψ, which in turn allows the heterogeneous rate transfer to be calculated from the following equation (Nicholson, R. S. Analytical Chemistry 1965, 37, 1351 ):

Ψ ^KD° ^~RY

k =

r (2) where y = (Do / DR)^1/2 and a = 0.5. The value of a is nearly independent for reversible reactions. At low scan rates, the peak separations are small. At these values, the electron transfer is Nernstian and not controlled by the electrode reaction kinetics. At scan rates of 2 V s ¹ and higher, the peak separation was used to calculate k_s from equation 2. The average k_s calculated for five scan rates is 0.013 cm s ¹.

Ionic Conductivity.

[00135] The ionic conductivity of the pure and solutions of the ionic liquid were measured along with the conductivity of an EC/DEC (1 :2) with 1.5 M LiTFSI as a blank to investigate the effect the inclusion of the redox shuttle has. The specific conductivity (σ) was calculated from the resistance of the solution (R_s) using equation 3, where K is the cell constant. R_S was calculated from the intersection of the curve on the real axis (Z_re) of the Nyquist plots using electrochemical impedance spectroscopy.

K

(t = —

^R= (3)

[00136] Measurements were acquired from 10⁶ to 10¹ Hz around an open circuit potential with perturbation amplitude of 10.0 mV rms from 25 to 75 °C. The activation energy for conductivity (E_SA) for each solution was calculated from equation 4, where the formula in parenthesis is the slope obtained from the Arrhenius plots shown in Fi ure 6.

[00137] All data are summarised in Table 2. As the viscosity of a liquid greatly influences conductivity, the lowest recorded value is expectedly the neat 100% solution of the ionic liquid with values of 0.10 and 2.17 mS cnr¹ at 25 and 75 °C, respectively. The addition of the large ferrocene group reduces the conductivity 100 fold compared to the non-redox ionic liquid, EMI-TFSI (Ishikawa, M.; Sugimoto, T.; Kikuta, M.; Ishiko, E.; Kono, M. Journal of Power Sources 2006, 162, 658.). The blank, an EC/DEC (1 :2) + 1.5 M LITFSI solution, has a conductivity of 6.02 and 13.18 mS cnr¹ at 25 and 75 °C, respectively. A 50% solution in EC/DEC (1 :2) has a conductivity at 25°C of 4.03 mS cnr¹, at 75°C the conductivity measured (12.17 mS cnr¹) is almost as high as the blank solution. The addition of the lithium salt to the 50% solution produces a much more viscous solution resulting in a diminished conductivity, over 60% loss at 25°C and 45% loss at 75°C compared to the solution without the salt. At lower concentrations, the conductivity of EC/DEC + LiTFSI solution can be kept as high as the blank up to 10% of ionic liquid in the solution. It is this solution that we particularly propose be used as the electrolyte in Li-ion batteries. Although the conductivity of the solution is lower than the blank, it is still in the same order of magnitude. Further, more concentrated solutions could also be beneficial for over-charge protection. After 10%, the interaction between the lithium salt and the ionic liquid occurs to a greater extent; increasing the viscosity (see below) and hence lowering the measured conductivity of the solution.

[00138] The activation energy of the conductivity of these solutions follows similar trend as seen for the differences in conductivity. The 100% ionic liquid measurement requires the greatest activation energy for conductivity (53.1 kJ mol^"1); the 50% solution in EC/DEC is a third of this value (18.1 kJ moM), while the addition of the lithium salt as discussed above increases the viscosity and therefore the energy required is greater with an E_aa of 25.8 kJ mol^"1. As the use of ionic liquid as an additive to the electrolyte produces a less viscous solution, the energy required is lowered (10% (14.7 kJmol^"1) and 1 % (13.8 kJ mol^"1)). The blank solution expectedly produces the lowest value with an activation energy of 13.6 kJ mol^"1. The anomaly in this series of measurements is the 0.34% solution which produces an E_sa for conductivity from the Arrhenius plot of 19.1 kJ mol^"1. This discrepancy is unusual as generally there is a strong correlation between ionic conductivity and activation energy: typically, it is found that higher conductivity is associated with lower activation energies,³⁵ and the 0.34% solution has the highest recorded conductivities at 25°C and 75°C.

Table 2. Summary of Ionic conductivity data of ionic liquid and blank solutions.

/ mS cm^"1 / mS cm^"1 / kJ mol-¹

EC / DEC + LiTFSI 6.02 13.18 13.6

100% 0.10 2.17 53.1

50% (no LiTFSI) 4.03 12.17 18.1

50% + LiTFSI 1.46 6.47 25.8

10% + LiTFSI 5.48 13.00 14.7

1 % + LiTFSI 6.18 12.97 13.8

0.34%^a + LiTFSI 6.22 13.86 19.1

³ Percentage corresponds to 1 x 10² mol L ¹.

Viscosity.

[00139] The viscosities of the five ionic solutions and the blank EC/DEC + 1.5 M LiTFSI were measured to support the conclusions of the electrochemical and conductivity analysis. All data are reported in Table 3. The 100% solution was too viscous for measurement. The viscosity follows the same trend seen in the conductivity were addition of LiTFSI to a 50% solution of the ionic liquid in a carbonate solution increases the viscosity greatly, 86.59 cP with and 1 1.57 cP without LiTFSI. Reducing the amount of ionic liquid to 10% (7.07 cP), 1 % (6.40 cP) and finally to 0.34% (4.69 cP) decreases the viscosity value measured. Table 3. Summary of viscosity data for the ionic liquid solutions.

n. at 25°C / cP

EC / DEC + LiTFSI 4.52

100% -

50% (no LiTFSI) 11.57

50% + LiTFSI 86.59

10% + LiTFSI 7.07

1 % + LiTFSI 6.40

0.34%^a + LiTFSI 4.69

a Percentage corresponds to 1 x 10² mol L ¹.

Evaluation in Lithium Cells.

[00140] The Fc-Mlm TFSI - EC/DEC mixture with 10 % redox ionic liquid was selected for the coin cell tests. The solution at this particular ratio presents the highest concentration of ionic liquid and an ionic conductivity and a viscosity reasonably close to that obtained for the EC/DEC electrolyte with 1.5 M LiTFSI.

[00141] Figure 7 shows a typical charging curve for Li/Li4Ti₅0i2. Up to 163 mAh/g, normal charging is observed with a stable cell voltage of 1.6 V. When reaching a capacity of 163 mAh/g, the cell is fully charged. To simulate overcharging conditions, the charger is programmed to apply constant current for twice the required amount of time to fully charge the battery. The sudden increase in cell voltage above 163 mAh/g shows that the cell is undergoing overcharging. The overcharge cut-off voltage is 4V vs Li/Li+. In the presence of EC/DEC electrolyte with the Fc-Mlm redox ionic liquid shuttle, the potential stabilizes at a plateau at 3.35 V. This plateau is due to the oxidation of the redox shuttle. The oxidized redox shuttle can then migrate through the separator and get reduced on the surface of the anode. This endless cycle permits a stabilization of the charge voltage at the redox shuttle oxidation potential and eliminates the exposure of the cell to a voltage higher than 3.35V during overcharge.

[00142] Figure 8 shows the charge/discharge cycles, starting with a full charge, followed by a 100% overcharge for a Li/Li4Ti₅0i2 coin cell at a C/10 rate, using the unmodified electrolyte in (a) and the electrolyte containing 10% of Fc-Mlm TFSI in (b). The overcharging situation appears very clearly for the cell without redox shuttle added (Fig. 4b) where the voltage increases sharply up to the 4 V cut-off after the charging plateau at 1.6 V of the Li4TisOi2 material. Adding the redox ionic liquid in the electrolyte prevents reaching the cut-off voltage of 4V. Rather, a plateau is observed at -3.36 V, corresponding to the onset potential for the oxidation of the ferrocene moiety on the ionic liquid. This plateau was stable for the full duration of the first 10-hour overcharging cycle, but upon further cycling there is a clear drifting to higher voltage in the following cycles. The increase in voltage during these overcharging periods suggests that the redox shuttle becomes less available for oxidation over time. Such instability was not observed for ferrocene redox shuttle¹⁷' ¹⁸, and could be ascribed to the slower heterogeneous electron exchange rate of the Fc-Mlm (see above).

[00143] Figure 9 shows the specific capacity curves for the same experiments to further detail the effect of the addition of Fc-Mlm on the charge storage. The curves obtained with the unmodified electrolyte (solid line) shows reversibility and a maximum specific capacity of 163 mAh/g, before reaching the overcharging point. When the Fc-Mlm is added, a 6% loss in capacity is observed after the first cycle, but tends to stabilize as the third cycle coincides with the second. While these results show the possibility of using an electroactive ionic liquid to prevent Li-ion battery cathode from overcharging, improving the stability and modifying the ionic liquid with redox moieties with higher oxidation potential will be required to apply these electrolytes in current or future commercial battery systems. We are currently studying new moieties that present improved stability and electrochemical performance.

[00144] The redox shuttle effect is also observed with a higher voltage V2O5 cathode. Figure 10 shows a charging curve for Li/V₂0₅ cell in EC/DEC, pure and modified with 10% Fc-MlmTFSI at C/10 (contains 1.5 M LiTFSI). Figure 9 shows that after being fully charged, the cell without the redox shuttle charges to 4V, while the addition of the redox shuttle shows a plateau in charge voltage again at 3.35V, as aboved with Li4Ti5012.

[00145] FIG 1 1 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 50% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[00146] FIG 12 is a cyclic voltammogram of 50% ionic liquid in EC/DEC (1 :2 v/v) (no LiTFSI).

[00147] FIG 13 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 50% ionic liquid in EC/DEC (1 :2 v/v) (no LiTFSI).

[00148] FIG 14 is a cyclic voltammogram of 10% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[00149] FIG 15 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 10% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[00150] FIG 16 is a cyclic voltammogram of 1 % solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[00151] FIG 17 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 1% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[00152] FIG 18 is a cyclic voltammogram of 0.34% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[00153] FIG 19 shows cyclic voltammograms of (a) oxidation and (b) reduction limits of 0.34% solution in 1.5 M LiTFSI in EC/DEC (1 :2 v/v).

[00154] The redox ionic liquid (1) presents a melting point of 47 °C, but remained in the liquid phase at room temperature in a supercooled state which is commonly found in ionic liquids.

[00155] The thermal stability of the redox ionic liquid (1) in its pure form was evaluated by TGA. The analysis (see Fig. 20) showed a decomposition onset at 207°C which is more than 200°C lower than the value reported for 1-butyl-3-methylimidazolium-TFSI. The decomposition of the ferrocenyl(methyl)imidazolium at lower temperature is likely to occur because of the electron withdrawing effect of the ferrocene on the Fc-Emi bond.

Conclusions

[00156] The electrochemical properties of mixtures of the redox ionic liquid 1 -ferrocenyl(methyl)-3- methylimidazolium TFSI with carbonate solvents were studied to evaluate their use as electrolytes in lithium-ion batteries, and the use of redox IL is reported. Having a redox shuttle that is an ionic liquid allows a much higher concentration of redox moieties in the electrolyte compared to a dissolving a redox salt as presented previously in the literature. This increased concentration is due to the miscibility of the carbonates solvents and imidazolium- based IL over the entire molar fraction range. Higher concentrations of redox species within the electrolyte lead to the capability of shuttling more electrons through the overcharge condition and thus a RIL could be used to improve overcharge protection, especially at high rates of charge. This may lead to the introduction of devices capable to recharge their lithium-ion batteries at faster rates leading to consumers waiting less time for their portable equipment to recharge. Cyclic voltammetry results show that the viscous nature of the solution influences the electrode kinetics with the oxidation potential of the pendant ferrocenyl group changing depending on the concentration. The diffusion coefficient and heterogeneous rate transfer constant for this redox ionic liquid have been calculated for the first time in carbonate solvents and these values are in between those of acetonitrile and EMI-TFSI were the difference can be attributed to the different viscosities of each solvent.

Example 2

[00157] Herein, the preparation of three redox ionic liquids (RILs) based on 1 -(ferrocenyl)3-butylimidazolium TFSI (FcEBIm TFSI), 1 -(ferrocenyl)3-octylimidazolium TFSI (FcEOlm TFSI) and 1 -(ferrocenyl)3- dodecenylimidazolium TFSI (FcEDIm TFSI) is presented. The characterization of ferrocenylalkylimidazolium salts was done with conductivity measurement and cyclic voltammetry measurement. The solutions used had different concentration of RIL (100, 50, 10, 1 %) in EC/DEC 1 :2 (Ethylene cabonate/Diethylene carbonate) solution with presence of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[00158] The redox molten salts used were:

n=0: FcEMIm TFSI;

n=3: FcEBIm TFSI;

n=7: FcEOlm TFSI; and n=1 1 : FcEDIm TFSI.

Experimental

Synthesis

Preparation ofN,N-dimethylaminomethylferrocene methiodide (1)

[00159] To a cooled solution of 6,00 g (23,24 mMol) of Ν,Ν-dimethylaminomethylferrocene in 1 ,54 ml (51 mMol) of absolute methanol corresponding to 2 molar equivalents was added dropwise a solution of 1 ,54 ml (24,74 mMol) methyl iodide. The solution was heated to 75°C during 10 minutes. The brown solid was crushed and was then washed on filter paper with ether until the washings were colorless. The resulting precipitate was dried under vacuum and there was obtained 8,01 g of the product 1 (yield: 86%). NMR ¹H (300 MHz,CdCI₃) δ (ppm) : 4,886 (S,2H); 4,561 (S,2H); 4,327 (S,2H); 4,293 (S,5H); 3,297 (S,9H)

Preparation of hydroxymethylferrocene (2)

[00160] To a solution of 1.71 g (1 ,07 M) of sodium hydroxide in 40 ml of distilled water was dissolved 4,01 g (10,387 mMol) of Ν,Ν-Dimethylaminomethylferrocene methiodide. The mixture was heated to 135°C during 3 hours. After cooling to room temperature, the compound was extracted with 4 x 100 ml of ether and organic layer was combined. The volume of the ethereal solution was divided by two and was washed with 5 x 200 ml of distilled water for each half. The solution was dried over magnesium sulfate and after filtering, the solvent was removed. The resulting compound was a yellow powder and there was obtained 1 ,28 g of the product 2 (yield: 57%) NMR ¹H (300 MHz,CdCI₃) δ (ppm) : 4,217-4,101 (M,11 H); 1 ,5 (S,1 H)

Preparation of N-(Ferrocenylmethyl)imidazole (3)

[00161] In 13 ml of dichloromethane, 2,48 g (1 1 ,478 mMol) of hydroxymethylferrocene and 1 ,94 g (1 1 ,964 mMol) of 1 , 1 '-carbonyldiimidazole corresponding to equal molar equivalent were dissolved. The mixture was heated to 65°C during 3 hours. After cooling to room temperature, 100 ml of ether was added to the mixture and the ethereal solution was washed with 4 x 100 ml of phosphoric acid 20% (50 ml phosphoric acid in 150 ml distilled water). The volume was divided by two and was added 350 ml of basic solution of sodium hydroxide 2M (16 g sodium hydroxide in 200 ml distilled water) for each half until pH around 5. For each half, the compound was extracted with 4 x 100 ml of dichloromethane until aqueous layer has become whitish. The solution was concentrated under vacuum and the concentrated solution was dried over sodium sulfate. After filtering, the solvent was removed. There was obtained 1 ,73 g (yield: 56%) of product 3. NMR ¹H (300 MHz,CdCI₃) δ (ppm) : 7.55 (S,1 H); 7,12 (S,2H); 4.844 (S,2H); 4,163-4.135 (M,9H).

Preparation of 1-(Ferrocenylmethyl)-3-alkylimidazolilium bromide

[00162] In 10 ml acetonitrile, 1 ,00 g (3,744 mMol) of N-(Ferrocenylmethyl)imidazole was dissolved and a equal molar equivalent of 1 -bromoalkane was added to the mixture. The solution was heated to 50°C during 15 hours. The solvent was removed and was washed several times with ether. The brown oil was recrystallized with dichloromethane/hexane. [FcEBIm Br] NMR ¹H (300 MHz, CdCI₃) δ (ppm) : 10.4(S,1 H); 7,25 (S,2H); 5,4 (S,2H); 4,4 (S,2H); 4,354,15 (M,9H); 1.90 (Q,2H); 1 ,3(Q,2H); 0,9 (T,3H). [FcEOlm Br] NMR ¹H (300MHz, DMSO-de) δ (ρριτι): 9.243 (S,1 H); 7.771 (S,2H); 5,147 (S,2H); 4,41 1 (S,2H); 4,221 -4,206 (M,9H); 1.740 (Q,2H); 1 ,207 (S,10H); 0,825 (T,3H). [FcEDIm Br] NMR ¹ H (300 MHz, DMSO-d₆) δ (ppm): 9.243 (S,1 H); 7.771 (S,2H); 5,147 (S,2H); 4,41 1 (S,2H); 4,221 -4,206 (M,9H); 1.740 (Q,2H); 1 ,207 (S,18H); 0,825 (T,3H).

Preparation of 1-(Ferrocenylmethyl)-3-alkylimidazolilium bis(trifluoromethane-sulfonyl)imide

[00163] In a minimum milli-Q water, 1 -(Ferrocenylmethyl)-3-alkylimidazolilium bromide was dissolve and if necessary, the solution was heated to 90°C until all was dissolve. After, the mixture was added dropwise a solution of 1 ,2 molar equivalents of lithium bis(trifluoromethanesulfonyl)imide in a minimum milli-Q water. During 2 hours, the combined solution was exposed to ultrasound and was let rest during 12 hours. The water excess was carefully removed and ionic liquid was dissolve in dichloromethane. The brown solution was washed 3 times with milli-Q water. The solution was dried over magnesium sulfate and after filtering, the solvent was removed. There was obtained brown oil. [FcEBIm TFSI] NMR ¹ H (300 MHz, DMSO-d₆) δ (ppm): 9.243 (S, 1 H); 7.771 (S,2H); 5,147 (S,2H); 4,41 1 (S, 2H); 4,2214,206 (M,9H); 1.740 (Q,2H); 1 ,207 (Q,2H); 0,825 (T,3H). NMR ¹³C (125 MHz, DMSO-de) δ (ppm) : 135,97; 122,76 ; 121 ,26 ; 1 18,70 ; 81 ,48 ; 69,20 ; 49,11 ; 48,85 ; 31 ,75 ; 19,27 ; 13,68 ppm. (ESI) m/z: [M*⁺](C18H23FeN2): 323,1215 et [M*-](C2F6N04S2): 279,9178. [FcEOlm TFSI] NMR ¹ H (300 MHz, DMSO-de) δ (ppm): 9.243 (S,1 H); 7.771 (S,2H); 5,147 (S,2H); 4,411 (S, 2H); 4,221 -4,206 (M,9H); 1.740 (Q,2H); 1 ,207 (S,10H); 0,825 (T,3H). NMR ¹³C (125 MHz, DMSO-de) δ (ppm): 135,81 ; 122,82 ; 121 ,24 ; 1 18,66 ; 81 ,34 ; 69,32 ; 49,34 ; 48,84 ; 31 ,51 ; 29,68 ; 28,93 ; 28,78 ; 28,68 ; 25,94 ; 22,51 ; 14,28. (ESI) m/z: [M*⁺](C22H31 FeN2): 377,1887 et [M*-](C2F6N04S2): 279,9180. [FcEDIm TFSI] NMR ¹ H (300 MHz, DMSO-de) δ (ρρηι): 9.243 (S,1 H); 7.771 (S,2H); 5,147 (S,2H); 4,411 (S, 2H); 4,221 -4,206 (M,9H); 1.740 (Q,2H); 1 ,207 (S,18H); 0,825 (T,3H). NMR ¹³C (125 MHz, DMSO-de) δ (ppm): 135,88 ; 122,92 ; 121 ,26 ; 1 18,70 ; 81 ,48 ; 69,16 ; 49,1 1 ; 48,85 ; 31 ,76 ; 29,45 ; 29,35 ; 29,27 ; 29,18 ; 28,78 ; 25,96 ; 22,55 ; 22,55 ; 14,37. (ESI) m/z: [M*⁺](C26H39FeN2): 433.2516 et [M*-](C2F6N04S2): 279,9176.

Measurement of conductivity

[00164] See Example 1 above

Cyclic Voltammetry and diffusion coefficient

[00165] See Example 1 above

Results

Table 4: Measurement of pure RIL conductivity and Activation Energy

Conductivity at 25°C Conductivity at 75°C Activation Energy

Ionic liquid

(S cm-¹) (S cm-¹) (kJ moM)

FcEMIm TFSI 1 ,04E-4 2,17E-3 53,12

FcEBIm TFSI 9,88E-5 1 ,64E-3 48,94

FcEOlm TFSI 6,59E-5 1.08E-3 48,48 FcEDIm TFSI 4.32E-5 7,87E 50,22

Table 5: Measurement of molar conductivity of RIL in EC/DEC 1:2 (v/v)

LiTFSI A_m at 25°C A_m at 25°C Am at 25°C A_m at 25°C

Ratio of IL

Concentration FcEMIm TFSI FcEBIm TFSI FcEOlm TFSI FcEDIm TFSI

C%1

(M) (S m² mol-¹) (S m² mol-¹) (S m² mol-¹) (S m² mol-¹)

50 0 2J4E-4 3,12E 2,38E 1 J6E-4

Table 6: Measurement of diffusion coefficient for oxidation and reduction of RIL (FcEMIm TFSI, FcEBIm TFSI, FcEOlm TFSI and FcEDIm TFSI)

Diffusion coefficient Diffusion Coefficient

for oxidation R₀ (cm² s^-1) for reduction R_r (cm² s^-1)

Ratio LiTFSI

FcEMIm FcEBIm FcEOlm FcEDIm FcEMIm FcEBIm FcEOlm FcEDIm of IL Concentration

TFSI TFSI TFSI TFSI TFSI TFSI TFSI TFSI

(%) (M)

50 0 - 4,26E-8 1.38E-8 1.48E-8 1.70E-9 4.75E-8 3.73E-9 1.35E-8

50 1 ,5 1.36E-9 1.40E-8 5,05E-9 1.63E-9 2.14E-9 5.76E-9 3,83E-8 1.54E-9

10 1 ,5 3.14E-8 2,02E-7 2.19E-7 8.73E-8 2,88E-8 1.20E-7 1.67E-7 7,40E-8

1 1 ,5 2,33E-7 2,06E-6 2,41 E-6 4.75E-7 2.75E-7 1.54E-6 1.78E-6 3,92E-7

Table 7: Measurement of standard potential according to the ferrocene oxidation and the oxidation limit ionic liquid Ratio of IL (%) LiTFSI concentration (M) El/2°*(V) AEpa-pc(V) Ox limit (V)

50 0 0,46 0,92 0,98

50 1,5 0,18 1,21 2,04

FcEMIm TFSI

10 1,5 0,10 0,40 1,78

1 1,5 0,02 0,17 1,62

50 0 0,814 1,030 3,087

50 1,5 0,617 1,126 2,723

FcEBIm TFSI

10 1,5 0,516 0,408 2,354

1 1,5 0,432 0,155 1,687

50 0 0,869 1,435 3,493

50 1,5 0,678 1,730 2,689

FcEOlm TFSI

10 1,5 0,538 0,550 2,063

1 1,5 0,445 0,197 1,923

50 0 0,514 1,189 3,204

50 1,5 0,224 1,934 2,149

FcEDIm TFSI

10 1,5 0,141 0,406 1,828

1 1,5 0,066 0,122 1,302

[00166] Figure 21 is an Arrhenius plots for the FcEBIm TFSI in EC/DEC 1:2 with presence or not of LiTFSI (measurements were done at an interval of 5 °C from 25 to 75 °C).

[00167] Figure 22 shows A) Cyclic voltammograms obtained using different concentration of FcEBIm TFSI (1, 10 and 50%) in EC/DEC 1:2 with presence or not of LiTFSI (the scan rate was 100 mV s-1) and B) Cyclic voltammograms obtained using a 10% solution of FcEBIm TFSI in EC/DEC 1:2 with 1,5 M LiTFSI (the scan rates were 25, 50, 100, 150, 200, 500, 1000, 2000, 5000 and 10000 mV s-1).

[00168] As can be seen above, increasing the scan rate results in an increase in the peaks current as expected for a diffusion-limited system. The current values were measured for each of the cyclic voltammograms and plotted against v^1/2 to calculate the diffusion coefficients from the Randles-Sevcik equation. The increase in peak splitting observed with an augmentation of the scan rate (for values up to 2 V/s) is mostly due to the uncompensated resistance of the cell setup (IR drop). Above 2 V/s the peak splitting is due to a combination of the IR drop and kinetic limitations.

Example 3

[00169] Three new redox-active ionic salts have been synthesised based on 1 ,4-dimethoxybenzene (1 ) and 2,5- di-tert-1 ,4-dimethoxybenzene (2 and 3). These imidazolium salts are the first organic redox-active groups to be incorporated into an ionic liquid structure. There are no negative effects on the transport properties from incorporating 2,5-di-tert-1 ,4-dimethoxybenzene into an electroactive imidazolium salt. The thermal stability and oxidation potential have been increased.

[00170] Herein, we report the first synthesis of three new redox-active imidazolium salts, compounds 1-3, based on the known redox-active groups 1 ,4-dimethoxybenzene and 2,5-di-tert-1 ,4-dimethoxybenzene (4), respectively.

[00171] This last molecule, is a stable, high potential redox shuttle with known application in lithium-ion batteries. It has been shown to be fully reversible when oxidised and can cycle more than 200 times, due to the two bulky tert-butyl arms protecting the radical cation and preventing it from dimerising and subsequently polymerising when oxidised, as sometimes observed with 1 ,4-dimethoxybenzene.

[00172] Compound 1 is an ionic liquid in which an ethyl-methyl-imidazolium (EMI) cation is directly connected to a methoxyphenoxy group. Bis(trifluoromethanesulfonyl)amide (TFSI) was chosen as the anion as when combined with the imidazolium cation, it makes a well-known and characterised ionic liquid, EMI-TFSI.

[00173] Compounds 2 and 3 are both imidazolium salts with the only difference between being the anion, TFSI, and hexafluorophosphate (PF6), respectively. The cation in both examples is propyl-methyl-imidazolium, this time linked to a 2,5-di-tert-butyl-dimethoxyphenoxy group.

Synthesis

[00174] Ionic Liquid 1 was synthesised in four steps, as depicted in the scheme shown in Figure 23. Compound 6 was synthesised from the etherification of 4-methoxyphenol (5) with 2-chloroethanol in 80% yield. The corresponding alcohol was brominated to give compound 7 in 78% yield. Reaction of 7 with 1 -methylimidazole affords the imidazolium bromide salt, 8 in 82% yield. Conversion of the bromide counter ion to TFSI was achieved from a metathesis reaction of 8 with lithium bis(trifluromethanesulfonyl)amide in an aqueous solution to give the desired product 1.

[00175] Redox-active imidazolium salts 2 and 3 were synthesised in a similar fashion, as shown in Scheme 2 in Figure 24, using 3-bromo-propanol in the etherification step to provide 10 in 56% yield. As before, bromination to 11 was performed with carbon tetrabromide (82% yield) which was then reacted with 1 -methylimidazole to give imidazolium bromide salt, 12 in 73% yield. The TFSI salt (2) was synthesised from a metathesis reaction of 12 with lithium bis(trifluoromethanesulfonyl)amide in methanol in 67% yield. Methanol was used as the solvent rather than water as compound 11 is insoluble in aqueous media. The PF6 salt (3) was obtained from the reaction of 12 with silver hexaflurorophosphate in acetonitrile, the resulting silver bromide precipitate was filtered and the desired salt 3 was collected under reduced pressure in 75% yield. Compounds 1-3 were vacuum-dried at 80°C for 24 h.

[00176] 2,5-di-tert-butyl-4-methoxyphenol was purchased from Frontier Scientific. 2,5-di-tert-1 ,4- dimethoxybenzene was purchased from 3M. Dichloromethane, hexanes, methanol, and ether were purchased from Fisher. All other chemicals and solvents were purchased from Sigma-Aldrich. All were used without further purification.

2-(4-methoxyphenoxy)ethanol (6)

6

[00177] 10.0 g 4-methoxyphenol (5) (80.61 mmol) and 41.85 cm³ 2-chloroethanol (50.22 g) were dissolved in 10% sodium hydroxide solution (300 cm³) and the mixture was stirred at room temperature for 24 h. The solution was extracted with 5 x 100 cm³ dichloromethane. The organic extract was washed with water (5 x 200 cm³), dried with MgSC and evaporated to dryness on a rotary evaporator. The white powder was recrystallised from 10% sodium hydroxide solution. . Yield: 10.77 g (64.08 mmol, 80%). White crystals, m.p. 67-68 °C. IR (v, cm ¹): 3302, 2936, 1509, 1443, 1379, 1230, 11 17, 1090, 1053, 1033, 922, 892, 827, 728. ¹H-NMR (CDCI₃-d₆, δ, ppm): 2.07 (s, 1 H, OH); 3.72 (s, 3H, OCH₃); 3.94 (t, J = 4.5 Hz, 2H, CH₂); 4.04 (t, J = 4.5 Hz, 2H, CH₂); 6.84 (s, 2H, 2 x Ar-H); 6.86 (s, 2H, 2 x Ar-H). ¹³C-NMR (CDCI₃, δ, ppm): 55.84 (OCH₃); 61.71 (CH₂); 69.93 (CH₂); 114.78 (2 x Ar C); 1 15.65 (2 x Ar C); 152.82 (Ar C); 154.19 (Ar C). HRMS (ESI) m/z [M+H]⁺ calcd for C₉Hi₃0₃ 169.08592; found 169.08547. Anal. Calcd for C₉Hi₂0₃: C, 64.27; H, 10.7.19. Found: C, 64.09; H, 7.27. 1-(2-bromoethoxy}-4-methoxybenzene (7)

7

[00178] 23.4 g of carbon tetrabromide was slowly added to a cold solution (0 °C) of 9.96 g (59.26 mmol) of 6 and 18.58 g triphenylphosphine in 180 cm³ anhydrous acetonitrile with stirring. The reaction mixture was stirred for 4 h at room temperature under argon and then poured into an ice-cold 300 cm³ solution of methanol-water (3:2). The precipitate was filtered and washed with methanol-water (3:2) and recrystallized from methanol. Yield: 10.69 g (46.26 mmol, 78%). White crystals, m.p. 49-50 °C. IR (v, cm ¹): 1509, 1463, 1428, 1279, 1227, 11 1 1 , 1030, 879, 822, 723. ¹H-NMR (CDCI₃-d₆, δ, ppm): 3.61 (t, J = 6.3 Hz, 2H, CH₂); 3.77 (s, 3H, OCH₃); 4.24 (t, J = 6.3 Hz, 2H, CH₂); 6.84 (s, 2H, 2 x Ar-H); 6.86 (s, 2H, 2 x Ar-H). ¹³C-NMR (CDCI₃, δ, ppm): 29.48 (CH₂); 55.86 (OCH₃); 68.95 (CH₂); 114.87 (2 x Ar C); 1 16.23 (2 x Ar C); 152.33 (Ar C); 154.54 (Ar C). HRMS (ESI) m/z [M*Ag]⁺ calcd for C₉Hn0₂AgBr 336.89879; found 336.89795. Anal. Calcd for C₉Hn0₂Br: C, 46.78; H, 4.80. Found: C, 46.80; H, 4.78.

1-(2-(4-methoxyphenoxy)ethyl)-3-methyl-1H-imidazol-3-ium bromide (8)

[00179] 8.36 g of 7 (40.50 mmol) and 3.34 g of 1 -methylimidazole were dissolved in 50 cm³ anhydrous acetonitrile and refluxed overnight under argon. The resulting mixture was evaporated to dryness and washed with small portions of ether. Yield: 10.34 g (33.14 mmol, 82%). Pale-yellow liquid, T_g = -44.0 °C. IR (v, cm ¹): 1567, 1509, 1467, 1293, 1226, 1 171 , 11 12, 1061 , 1031 , 914, 831 , 738, 655, 623. ¹ H-NMR (DMSO, δ, ppm): 3.65 (s, 3H, OCH₃); 3.88 (s, 3H, CH₃); 4.28 (t, J = 4.9 Hz, 2H, CH₂); 4.57 (t, J = 4.8 Hz, 2H, CH₂); 6.86 (s, 2H, 2 x Ar- H); 6.88 (s, 2H, 2 x Ar-H); 7.74 (s, 1 H, Imidazolium H); 7.83 (s, 1 H, Imidazolium H); 9.24 (s, 1 H, Imidazolium H). ¹³C-NMR (DMSO, δ, ppm): 35.82 (CH₂); 48.58 (CH₂); 55.40 (OCH₃); 66.35 (CH₂); 114.64 (2 x Ar C); 1 15.71 (2 x Ar C); 122.77 (Imidazolium C); 123.52 (Imidazolium C); 137.03 (Imidazolium C); 151.66 (Ar C); 153.87 (Ar C). HRMS (ESI) m/z [M]⁺ calcd for Ci₃Hi₇0₂N₂ 233.12845; found 233.12865. 1-(2-(4-methoxyphenoxy}ethyl}-3-methyl-1H-imidazol-3-ium bis((trifluoromethyl}sulfonyl}amide (1)

[00180] An aqueous solution of lithium bis(trifluromethanesulfonyl)amide (13.06 g, 45.50 mmol, 1.5 equivalents) was added dropwise to an aqueous solution of 8 (9.50 g, 30.33 mmol) and the solution was stirred for 2 h at room temperature and left over-night to allow a colourless liquid to separate from the aqueous phase. The mixture was extracted with dichloromethane and the organic layer washed with five portions of water and dried over MgSCv The solvent was then evaporated under reduced pressure and the product vacuum-dried at 80°C for 24 h. Yield: 7.66 g (14.92 mmol, 49%). Colourless liquid, T_g = -62.4 X, density 1.68 g cm ³. IR (v, cm ¹): 1512, 1351 , 1 181 , 1 136, 1055, 831 , 791 , 741 , 654, 614, 570, 515. ¹H-NMR (DMSO, δ, ppm): 3.69 (s, 3H, OCH₃); 3.87 (s, 3H, CH₃); 4.28 (t, J = 4.8 Hz, 2H, CH₂); 4.56 (t, J = 4.8 Hz, 2H, CH₂); 6.87 (s, 2H, 2 x Ar-H); 6.88 (s, 2H, 2 x Ar-H); 7.71 (s, 1 H, Imidazolium H); 7.80 (s, 1 H, Imidazolium H); 9.16 (s, 1 H, Imidazolium H). ¹³C-NMR (DMSO, δ, ppm): 35.80 (CH₂); 48.58 (CH₂); 55.37 (OCH₃); 66.31 (CH₂); 114.63 (2 x Ar C); 1 15.69 (2 x Ar C); 121.62 (CF₃) 122.80 (Imidazolium C); 123.53 (Imidazolium C); 137.02 (Imidazolium C); 151.66 (Ar C); 153.89 (Ar C). HRMS (ESI) m/z [M]⁺ calcd for Ci₃Hi₇0₂N₂ 233.12845; found 233.12852; [M]- calcd for C₂F₆N0₄S₂ calcd 279.91784; found 279.91881. Anal. Calcd for Ci₅Hi₇06N₃F₆S₂: C, 35.09; H, 3.34; N, 8.18; S, 12.49 Found: C, 35.04; H, 3.24; N, 8.15; S, 12.50.

3-(2, 5-Di-tert-butyl-4-methoxy-phenoxy)-pro an-1-ol (10)

10

[00181] 17.0 g 2,5-di-tert-butyl-4-methoxyphenol (9) (71.94 mmol) and 29.9 g of tetrabutylammonium bromide in 70 cm³ anhydrous dimethylformamide was added slowly to a stirred solution of 3.74 g sodium hydride (60% in mineral oil) under argon and the mixture was stirred at room temperature for 1 hour until the evolution of H₂ gas ceased. The solution was cooled to 0 °C and 7.5 cm³ 3-bromo-propanol (1 1.53 g, 82.96 mmol) in 30 cm³ dimethylformamide was added slowly over a period of 15 minutes. The reaction mixture was stirred at room temperature for 40 h and then poured into 750 cm³ ice-cold water. The precipitate was filtered and washed with water and then redissolved in 250 cm³ dichloromethane. The organic solution was washed with water (3 x 250 cm³), dried with MgSC t and evaporated to dryness on a rotary evaporator. The brown powder (15.15 g) was chromatographed on silica gel (ethyl acetate-hexanes 3:7) and the pure fractions were recrystallized from acetonitrile. Yield: 1 1.9 g (40.42 mmol, 56%). White crystals, m.p. 96-97 °C. IR (v, cm ¹): 3281 , 2958, 1510, 1466, 1398, 1377, 1209, 1128, 1074, 1040, 933, 864, 781. ¹H-NMR (CDCI₃-d₆, δ, ppm): 1.37 (s, 9H, t-Bu); 1.39 (s, 9H, t-Bu); 1.72 (s, 1 H, OH); 2.10 (q, J = 6.1 Hz, 2H, CH₂); 3.82 (s, 3H, OCH₃); 3.93 (t, J = 6.2 Hz, 2H, CH₂); 4.12 (t, J = 5.9 Hz, 2H, CH₂); 6.85 (s, 1 H, Ar-H); 6.86 (s, 1 H, Ar-H). ¹³C-NMR (CDCI₃, δ, ppm): 29.92 (3 x CH₃); 30.07 (3 x CH₃); 32.75 (CH₂); 34.72 (C); 34.75 (C); 56.05 (OCH₃); 60.75 (CH₂); 66.07 (CH₂); 1 1 1.92 (Ar C); 1 12.24 (Ar C); 136.26 (Ar C); 136.49 (Ar C); 151.17 (Ar C); 151.18 (Ar C). HRMS (ESI) m/z [M]⁺ calcd for CisH₃₀O₃ 294.21895; found 294.21984. Anal. Calcd for Ci₈H₃₀O₃: C, 73.43; H, 10.27. Found: C, 73.21 ; H, 10.39.

1-(3-bromopropoxy)-2,5-di-tert-butyl-4-methoxybenzene (11)

11

[00182] 14.1 g of carbon tetrabromide was slowly added to a cold solution (0 °C) of 10.5 g (35.66 mmol) of 10 and 1 1.19 g triphenylphosphine in 100 cm³ anhydrous acetonitrile with stirring. The reaction mixture was stirred for 4 h at room temperature under argon and the poured into an ice-cold 200 cm³ solution of methanol-water (3:2). The precipitate was filtered and washed with methanol-water (3:2) and recrystallized from methanol. Yield: 10.47 g (29.31 mmol, 82%). White crystals, m.p. 60-61 X. IR (v, cm ¹): 2955, 1509, 1469, 1397, 1376, 1254, 1204, 1 129, 1041 , 863, 780. ¹H-NMR (DMSO, δ, ppm): 1.31 (s, 9H, f-Bu); 1.33 (s, 9H, f-Bu); 2.28 (q, J = 6.2 Hz, 2H, CH₂); 3.71 (t, J = 6.6 Hz, 2H, CH₂); 3.76 (s, 3H, OCH₃); 4.06 (t, J = 5.9 Hz, 2H, CH₂); 6.79 (s, 1 H, Ar-H); 6.81 (s, 1 H, Ar-H). ¹³C-NMR (DMSO, δ, ppm): 29.58 (3 x CH₃); 29.69 (3 x CH₃); 31.54 (CH₂); 32.29 (CH₂); 34.19 (C); 34.21 (C); 55.74 (OCH₃); 65.66 (CH₂); 11 1.54 (2 x Ar C); 135.29 (Ar C); 135.44 (Ar C); 150.32 (Ar C); 151.50 (Ar C). HRMS (ESI) m/z [M]⁺ calcd for Ci₈H₂₉0₂Br 356.13454; found 356.13369. Anal. Calcd for Ci₈H₂₉0₂Br: C, 60.50; H, 8.18. Found: C, 60.83; H, 8.48.

^ 3-(^,2,5-d/^'-terf-buf -4-me^oxyp ?enox rop )-3-me^ -W-/^'m/^'dazo/-3-/^'um bromide (12)

12

[00183] 9.6 g of 11 (26.88 mmol) and 2.22 g of 1 -methylimidazole were dissolved in 30 cm³ anhydrous acetonitrile and refluxed overnight under argon. The resulting mixture was evaporated to dryness and washed with small portions of ether. Yield: 8.64 g (19.65 mmol, 73%). White powder, m.p. 183-184 °C. IR (v, cm ¹): 2954, 1571 , 1512, 1465, 1210, 1168, 1 129, 1041 , 859, 818, 787, 620. ¹H-NMR (DMSO, δ, ppm): 1.30 (s, 9H, f-Bu); 1.32 (s, 9H, f-Bu); 2.32 (q, J = 6.5 Hz, 2H, CH₂); 3.75 (s, 3H, OCH₃); 3.86 (s, 3H, CH₃); 4.01 (t, J = 5.9 Hz, 2H, CH₂); 4.38 (t, J = 6.6 Hz, 2H, CH₂); 6.76 (s, 1 H, Ar-H); 6.80 (s, 1 H, Ar-H); 7.76 (s, 1 H, Imidazolium H); 7.86 (s, 1 H, Imidazolium H); 9.29 (s, 1 H, Imidazolium H). ¹³C-NMR (DMSO, δ, ppm): 29.58 (3 x CH₃); 29.78 (3 x CH₃); 34.17 (C); 34.19 (C); 35.15 (CH₂); 46.50 (CH₂); 55.74 (OCH₃); 65.20 (CH₂); 1 1 1.43 (Ar C); 1 12.04 (Ar C); 123.33 (Imidazolium C); 123.68 (Imidazolium C); 135.44 (Ar C); 135.51 (Ar C); 136.74 (Imidazolium C); 150.35 (Ar C); 151.63 (Ar C). HRMS (ESI) m/z [M]⁺ calcd for C₂₂H₃₅0₂N₂ 359.2693; found 359.27016. Anal. Calcd for C₂₂H₃₅0₂N₂Br: C, 60.13; H, 8.03; N, 6.37. Found: C, 60.11 ; H, 8.05; N, 6.34.

^ 3- 2,5-d/^'-terf-buf -4-me^oxyp ?enoxy)prop )-3-me^W-W-/^'m/^'dazo/-3-/^'um bis(trifluoromethanesulfonyl)amide

(21

2

[00184] 5.0 g (11.38 mmol) of 12 and 4.9 g (17.07 mmol, 1.5 equivalents) of lithium bis(trifluromethanesulfonyl)amide were dissolved in 40 cm³ of methanol and refluxed for 3 h. The resulting mixture was evaporated to dryness and redissolved in 100 cm³ dichloromethane. The organic solution was washed with water (5 x 100 cm³), dried with MgSC and the solvent was then evaporated under reduced pressure and the product vacuum-dried at 80°C for 24 h. Yield: 4.89 g (7.64 mmol, 67%). Off-white powder, m.p. 93-94 °C. IR (v, cm ¹): 2962, 1577, 1510, 1482, 1377, 1332, 1183, 1131 , 1049, 859, 789, 765, 740, 652, 623. ¹ H-NMR (DMSO, δ, ppm): 1.31 (s, 9H, f-Bu); 1.33 (s, 9H, f-Bu); 2.32 (q, J = 6.7 Hz, 2H, CH₂); 3.76 (s, 3H, OCH₃); 3.85 (s, 3H, CH₃); 4,01 (t, J = 6.2 Hz, 2H, CH₂); 4.36 (t, J = 7.3 Hz, 2H, CH₂); 6.76 (s, 1 H, Ar-H); 6.81 (s, 1 H, Ar-H); 7.72 (t, J = 1.6 Hz, 1 H, Imidazolium H); 7.82 (t, J = 1.7 Hz, 1 H, Imidazolium H); 9.18 (s, 1 H, Imidazolium H). ¹³C-NMR (DMSO, δ, ppm): 29.58 (3 x CH₃); 29.78 (3 x CH₃); 34.18 (C); 34.21 (C); 35.74 (CH₂); 46.55 (CH₂); 55.74 (OCH₃); 65.20 (CH₂); 11 1.46 (Ar C); 1 12.05 (Ar C); 121.61 (CF₃) 122.35 (Imidazolium C); 123.71 (Imidazolium C); 135.48 (Ar C); 135.55 (Ar C); 136.74 (Imidazolium C); 150.37 (Ar C); 151.67 (Ar C). HRMS (ESI) m/z [M]⁺ calcd for C₂₂H₃₅0₂N₂ 359.2693; found 359.27023; [M]- calcd for C₂F₆N0₄S₂ calcd 279.91784; found 279.91868. Anal. Calcd for C₂₄H₃₅06N₃F₆S₂: C, 45.06; H, 5.52; N, 6.57; S, 10.03. Found: C, 44.98; H, 5.59; N, 6.55; S, 10.13.

^ 3- 2,5-d/^'-terf-buf -4-me^oxyp ?enoxy)prop )-3-me^W-W-/^'m/^'dazo/-3-/^'um hexafluorophosphate (3)

3 [00185] 2.5 g (5.69 mmol) of 12 and 1.44 g (5.69 mmol) of silver hexafluorophosphate were dissolved in anhydrous acetonitrile and stirred for 2 h at room temperature. The resulting precipitate was filtered off and the solution was collected and evaporated to dryness on a rotary evaporator. The product was then vacuum-dried at 80°C for 24 h. Yield: 2.16 g (4.29 mmol, 75%). Light purple powder, m.p. 148-149 °C. IR (v, cm ¹): 2956, 2343, 1579, 1511 , 1468, 1378, 121 1 , 1 175, 1 127, 1055, 824, 623. ¹H-NMR (DMSO, δ, ppm): 1.31 (s, 9H, f-Bu); 1.33 (s, 9H, f-Bu); 2.32 (q, J = 6.6 Hz, 2H, CH₂); 3.76 (s, 3H, OCH₃); 3.85 (s, 3H, CH₃); 4,01 (t, J = 5.9 Hz, 2H, CH₂); 4.36 (t, J = 6.8 Hz, 2H, CH₂); 6.77 (s, 1 H, Ar-H); 6.81 (s, 1 H, Ar-H); 7.72 (s, 1 H, Imidazolium H); 7.82 (s, 1 H, Imidazolium H); 9.18 (s, 1 H, Imidazolium H). ¹³C-NMR (DMSO, δ, ppm): 29.58 (3 x CH₃); 29.78 (3 x CH₃); 34.17 (C); 34.19 (C); 35.15 (CH₂); 46.50 (CH₂); 55.74 (OCH₃); 65.20 (CH₂); 1 1 1.43 (Ar C); 1 12.04 (Ar C); 123.33 (Imidazolium C); 123.68 (Imidazolium C); 135.44 (Ar C); 135.51 (Ar C); 136.74 (Imidazolium C); 150.35 (Ar C); 151.63 (Ar C). HRMS (ESI) m/z [M]⁺ calcd for C₂₂H₃₅0₂N₂ 359.2693; found 359.26993; [M]- calcd for PF₆ calcd 144.96473; found 144.96439. Anal. Calcd for C₂₂H₃₅0₂N₂PF₆: C, 52.38; H, 6.99; N, 5.55. Found: C, 52.22; H, 7.12; N, 5.57.

Experimental

[00186] Melting points and crystallisation temperatures were obtained using a Perkin Elmer Jade DSC.

[00187] Glass transition temperatures were obtained on a TA Instruments Q1000 DSC.

[00188] Infrared spectra were taken on a Perkin Elmer Spectrum One FTIR.

[00189] ¹H and ¹³C Nuclear magnetic resonance spectra were recorded either on a Bruker AMX300, Avance 500 or Avance 700 using CDCI₃ or deuterated DMSO as the solvent.

[00190] Electrospray ionisation mass spectrometry were performed by the Centre regional de spectroscopie de masse de I'Universtite de Montreal.

[00191] Elemental analyses were performed by the Laboratoire d'analyse elementaire de I'Universite de Montreal.

[00192] Thermogravimetric analysis was performed on a TGA 2950 TA Instruments, measurements were performed under nitrogen from room temperature to 600 °C.

[00193] Cyclic voltammetry measurements were performed in a heart-shaped electrochemical cell using a BioLogic SP-50 potentiostat. The electrodes were platinum, platinum wire and silver wire as the working, counter and reference electrodes, respectively. The solutions were degassed with argon for 15 minutes prior to measurements. All measurements are referenced against the Ei/₂ of the Fc/Fc⁺ redox couple. Diffusion coefficients were calculated from the gradient of peak current (i_p) against the square root of the scan rate through the Randles-Sevcik equation:

(1) where n is the number of electrons, in this case one, F is the Faraday constant, A is the electrode area, C is the concentration, R is the gas constant, T is the temperature, v is the scan rate and D is the diffusion coefficient.

[00194] The heterogeneous rate transfer constant (k_s) was determined using peak-to-peak separation (Δ_Ρ) using Nicholson's method, which relates Δ_Ρ with a kinetic parameter ψ, which in turn allows the heterogeneous rate transfer to be calculated from the following equation:

1

II F V

Ψ

k _r =

k. = (2) where γ = (Do / DR)^1/2 and a = 0.5. The value of a is nearly independent for reversible reactions.

Results

[00195] The melting points and crystallisation temperatures of 2 and 3 (Fig. 26 and 27) are considerably high for imidazolium TFSI and PF₆ based structure compounds (T_m / T_c: 94.35 / 51 .30 °C and 149.37 / 1 19.78 °C, respectively, measured by differential scanning calorimetry). In comparison, EMI-TFSI has a melting point of around -21 °C, and EMI-PFe at 60°C. Compound 1 is an ionic liquid at room temperature with a Tg at -62.4X (Fig. 25). The addition of the bulky tert-butyl groups has clearly a large effect on the melting point, the aliphatic groups possibly providing additional symmetry or helping facilitate ττ-π stacking of the aromatic cores. The TFSI derivative has a lower melting point than the PF6 version, as the anion in this case is unable to hydrogen-bond and has a more delocalised charge.

[00196] Thermogravimetric analysis (TGA) was performed on compounds 1-4 (Fig. 28 to 31) from room temperature to 600 °C. Compound 1 is the most stable with an onset of degradation at 320 °C, the addition of the aliphatic tert-butyl groups lowers the onset to 250 °C for compound 2. The change of anion from TFSI to PF6 lowers the onset further; this time to 190 °C for 3, while 4 is the least stable, with an onset of degradation occurring at 60°C.

[00197] These TGA results show that the incorporation of 2,5-di-tert-1 ,4-dimethoxybenzene into an imidazolium salt increases the thermal stability by at least 130 °C.

[00198] The electrochemical properties of the newly synthesised compounds 1-3 were assessed by cyclic voltammetry (CV) using Pt working and counter electrodes and a pseudo Ag reference electrode in ethylene carbonate-diethyl carbonate (1 :2 v/v) with lithium TFSI as the supporting electrolyte (1 .5 M). This solution was selected to evaluate the electrochemistry of the redox ionic liquids in an electrolyte usable in Li-ion batteries. Fig. 32 shows the oxidation of all three compounds in 1 mM solutions, all three compounds oxidise to give a radical cation. All data are summarised in the table below.

/ V / cm² S^"1 / cm² S^"1 / cm s^-1

1 + 1.00^a 3.72 x 10-⁷

2 + 0.51 (+ 0.56 / + 0.45) 3.64 x 10 ⁷ 3.52 x 10⁷ 0.0049

3 + 0.51 (+ 0.56 / + 0.46) 5.21 x 10 5.08 x 10 0.0090

4 + 0.44 (+ 0.50 / + 0.37) 3.24 x 10 3.21 x 10 0.0049 ^a Quasi-reversible wave.

[00199] Compound 1 shows a quasi-reversible wave at +1.00 V, full reduction of the oxidised species in this case to the neutral compound is not possible as the radical cation formed from the oxidation reacts with another radical cation to give a dimer. At this concentration, dimerisation is not seen when multiple CV cycles are performed but at higher concentrations (10 mM) this phenomena can be observed upon the first ten cycles (see Fig 33). Indeed, Fig. 33 shows a decrease of the peaks at 0.98 and 1.13 V (compound 1), with new peaks appearing at 0.56 and 0.69 V (dimers of 1). Compounds 2 and 3 however do show full reversibility as the large tert-butyl groups protect the radical and prevent dimerization (inset of Fig. 33). Consequently though, the addition of the tert-butyl groups through a large inductive effect lowers the oxidation potential greatly, the anodic peaks of 2 and 3 are 0.34 V lower than 1. For comparison, we also measured the oxidation potential of 2,5-di-tert-1 ,4- dimethoxybenzene (4) in the same conditions. This compound also shows a reversible oxidation wave with Ei/2^0X = +0.44 V which is 0.07 V lower than the Ei/2^0X of 2 and 3 (+0.51 V for both). The difference in potential can be attributed to the imidazolium cation on the chain pulling electron density away from the core thus requiring more energy to remove an electron. To examine the effect the addition of the tert-butyl groups and the incorporation of the redox shuttle into an ionic liquid has on the transport properties, the diffusion coefficients (reduced, DR and oxidised, Do forms) of compounds 1-4 and the heterogeneous rate transfer (k_s) of compounds 2-4 were measured. Compound 1 does not show a reversible oxidation and therefore Do and k_s could not be calculated.

[00200] The diffusion coefficient was calculated from a series of oxidations at different scan rates (Fig. 34 to 38). The diffusion coefficients of the reduced forms are all in the same order of magnitude (x 10 ⁷ cm² s ¹), for the four compounds with the only difference being the PF6 salt (3) which has a higher diffusion coefficient in both the reduced and oxidised forms. The reason for the small increase can be explained by the PF6 salt experiencing less interaction with the electrolyte than the other imidazolium salts, which will encounter an association of multiple TFSI anions with a lithium cation.¹⁹ The ratio of DO/DR is 0.97 and 0.98 for 2 and 3, respectively; these values are really close to 1 thus showing that the oxidation process is fully reversible and the diffusion expectedly follows Arrhenius-type behaviour. The heterogeneous rate transfer constant (k_s) was determined using peak-to-peak separation (Δ_Ρ) according to Nicholson's method.²⁰ The scan rate experiment was carried out using iR compensation. At low scan rates, the electron transfer is Nernstian and not controlled by the electrode reaction kinetics. At scan rates of 2 V s ¹ and higher, the peak separations from these scan rates were used to calculate ks. Again, all data are summarised in the table above. As discussed above, compound 3 with less interaction to the electrolyte than 2, has predictably a higher k_s value (0.0090 and 0.0049 cm s ¹ , respectively). An interesting comparison is between compounds 2 and 4, the diffusion coefficient is marginally higher for 2 and the k_s are identical. This indicates that the incorporation of the redox shuttle into an imidazolium salt has no negative effect to the transport properties.

[00201] In conclusion, three new imidazolium salts, 1-3 which are based on 1 ,4-dimethoxybenzene and 2,5-di- tert-1 ,4-dimethoxybenzene redox-active groups linked to imidazolium cations to form salts with TFSI and PF6 anions were reported. Compound 1 has the highest oxidation but is irreversible; compounds 2 and 3 are fully reversible, the large tert-butyl groups prevents dimerisation but also lowers oxidation potential through a large inductive effect. The PF6 salt, 2 shows the higher diffusion coefficients and heterogeneous rate transfer of the three compounds. In comparison to 4, the incorporation of 2,5-di-tert-1 ,4-dimethoxybenzene onto a redox-active imidazolium salt improves the thermal stability, has no negative impact on the transport properties and even actually increases the oxidation potential.

Example 4

[00202] Compounds 1 -4 of Example 3 are further characterized below.

Cyclic Voltammetry

[00203] Cyclic Voltammetry (CV) measurements were performed for compounds 1 , 2 and 3 of Example 3 in ethylene carbonate (EC):diethyl carbonate (DEC) (1 :2 v/v) solvent.

[00204] CV of compound 1 (Fig. 39) was performed outside the glovebox using platinum working electrode, platinum wire counter electrode and silver pseudo reference. 1 M solution was prepared in a 1.5 M lithium bis(trifluromethanesulfonyl)amide (LiTFSI) solution. CV of 1 (Fig. 39) is referenced to ferrocene (Fc/Fc⁺), an additional x-axis versus lithium (Li/Li⁺) is provided for comparison. This ionic liquid has no protective tert-butyl arms and therefore polymerising when oxidised as seen with an irreversible wave in the CV.

[00205] Two solutions of ionic salt 2 were prepared, 0.7 and 1 M with 0.7 M LiTFSI, as the supporting electrolyte. These concentrations are greater than that possible by the commercially available 2,5-di-tert-1 ,4- dimethoxybenzene. The cyclic voltammograms of these two solutions, shown in Fig. 40 and 41 , were measured in an Argon-filled glovebox using platinum working electrode and two lithium foil electrodes as the counter and reference electrodes. The CVs show full reversible oxidation waves, the addition of the tert-butyl arms protect the molecule from coupling reactions. Detrimentally though, the large aliphatic groups through an inductive effect lower the oxidation potential. However, the oxidation potential of these solutions, ca. +3.9 V vs. Li/Li⁺ makes this ionic salt an ideal redox shuttle for the over-charge protection of lithium iron phosphate LiFePC t (LFP) cathode.

[00206] As hexafluorophosphate (PFe) is a more common anion in Li-ion battery electrolyte, an ionic salt with PF6 (compound 3) was synthesised. In a solution of 0.5 M LiPF6 in EC:DEC, a maximum concentration of 0.1 M of 3 was dissolved. However, this solution was still tested by CV and in coin cells. The CV (Fig. 42) again shows a reversible anodic wave ca. +3.9 V vs. Li/Li⁺. This imidazolium salt is also ideal for the protection of LFP.

Coin Cells

[00207] Coin cell cycling was carried out with lithium cells containing compounds 2 and 3 as electrolyte additives. CR-2032 coin cells were assembled in an Argon-filled glove box using a LiFePC t (LFP) cathode and lithium foil as anode. LFP cathodes were prepared by mixing 80% of pure active material LFP (Phostech Lithium), 10% conductive carbon (Super S, Timcal) and 10% polyvinylidene fluoride (PVDF) binder. Two standard electrolytes for Lithium-ion batteries were used; LiTFSI and LiPF6 both in EC:DEC (1 :2 v/v) solvent at different concentrations. Both concentrations of ionic salt 2 (0.7 and 1 M) and 0.1 M of compound 3 were tested. In order to compare with the commercial redox shuttle 4, a solution of 0.1 M ionic salt 4 in 0.5 M LiPF6 in ethylene carbonate : diethyl carbonate : propylene carbonate : dimethyl carbonate (EC:DEC:PC:DMC 1 :2:1 :2 v/v) was prepared and tested in coin cells. Cells were cycled between 2.5 and 4.2 V vs. Li/Li⁺. They were first charged to 4.2 V for 10 hours (C-rate = C/10), over-charged for an extra 10 hours (100% overcharged) then discharged for 10 hours to 2.5 V.

[00208] Figure 43 shows cycling profile of a cell containing 0.7 M compound 2 in 0.7 M LiTFSI electrolyte. The potential increases from the open circuit voltage to 3.5 V where the charge process takes place for 10 hours enabling a full charge of LiFePC t at a constant voltage. Then, the potential rises to reach the set cut off voltage (4.2 V). At this point, in a cell where no redox shuttle was added, the potential should drop until the discharge potential is reached and the cell starts discharging. Whereas, a cell protected by a redox shuttle will show a plateau indicating the redox shuttle's oxidation at its determined potential. Here, the redox shuttle's (compound 2) activity is shown at 4 V for the 1 ^st cycle and stabilises at 3.9 V over cycling as suggested by cyclic voltammograms shown above. During the four first cycles, the potential of the redox shuttle shows a trend to higher potential before demonstrating a flat potential plateau, which may be due to an activation process of the redox shuttle on the cathode surface. Because of an abrupt cut in power within the facility during testing, the 6^th cycle (Fig. 43) shows a potential drop that was resumed quickly after a return in power. Twenty cycles were completed and the cell continues cycling demonstrating the same performances offering a good protection of LFP during overcharge.

[00209] Figure 44 shows the cycling profile of 1 M of 2. At high concentration, compound 2 still provides a good overcharge protection for LFP. Interestingly, the redox-shuttle plateau is stabilised from the 2nd cycle indicating that more redox-shuttle was available to be oxidized. Also, the higher concentration of redox shuttle is expected to ensure protection of cells operating at higher rates of charge. The cell is not limited to the number of cycles shown.

[00210] Even at low concentration (0.1 M), compound 3 exhibits a performance equal to that of compound 2. Figure 45 shows cycling profile of a cell containing ionic salt 3 for which a redox shuttle plateau is stabilised after 3 cyles (Fig. 45A) suggesting that during first few cycles, on the cathode surface the redox shuttle molecules were progressively activated. Indeed, a different carbonates mixture is expected to increase the solubility of our ionic salt 2 and consequently improved operation ensuring a full overcharge protection from the 1 ^st charge cycle. Over 34 cycles have been performed (Fig. 45B) and the cell was still provides the same performance. For the same reason mentioned above, the 18^th cycle shows a potential drop due to an abrupt power cut in the testing facility.

[00211] To compare the commercially available redox shuttle with compounds 1-3, compound 4 was also tested in lithium cells (Fig. 46). Redox shuttles 1-3 provide a comparable overcharge protection as that provided by compound 4.

[00212] Although the present invention has been described herein above by way of specific embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.

REFERENCES

[00213] The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety. These documents include, but are not limited to, the following:

• Abraham, K. M.; Pasquariello, D. M.; Willstaedt, E. B. Journal of the Electrochemical Society 1990, 137, 1856.

• Armand, M.; Endres, F.; MacFarlane, D.R.; Ohno, H.; Scrosati, B. Nature Materials 8, 621 - 629 (2009)

• Balakrishnan, P. G.; Ramesh, R.; Kumar, T. P. Journal of Power Sources 2006, 155, 401.

• Balasubramanian, R.; Wang, W.; Murray, R. W. Journal of the American Chemical Society 2006, 128, 9994.

• R. Balasubramanian, W. Wang, R.W. Murray (2008) J. Phys. Chem. C 1 12(46): 18207-18216

• Bildstein, B.; Malaun, M.; Kopacka, H.; Ongania, K. H.; Wurst, K. Journal Of Organometallic Chemistry 1998, 552, 45.

• Chamiot et al (2009) Langmuir 25(3) 131 1 -1315

• Chen, Z. H.; Qin, Y.; Amine, K. Electrochimica Acta 2009, 54, 5605.

• Chen, J.; Buhrmester, C; Dahn, J. R. Electrochemical and Solid State Letters 2005, 8, A59.

• Dahn, et al., The Electrochemical Society Interface · Winter 2005, page 27.

• Fontaine, O.; Lagrost, C; Ghilane, J.; Martin, P.; Trippe, G.; Fave, C; Lacroix, J. C; Hapiot, P.;

Randriamahazaka, H. N. Journal of Electroanalytical Chemistry 2009, 632, 88.

• Gao, Y.; Twamley, B.; Shreeve, J. M. Inorganic Chemistry 2004, 43, 3406.

• Golovin, M. N.; Wilkinson, D. P.; Dudley, J. T.; Holonko, D.; Woo, S. Journal of the Electrochemical Society 1992, 139, 5.

• lonica-Bousquet CM. et al. Electrochemistry Communications 12 (2010) 636-639.

• Inagaki, T. & Mochida, T. (2010). Chem. Lett., 39, 572-573.

• Ishikawa, M.; Sugimoto, T.; Kikuta, M.; Ishiko, E.; Kono, M. Journal of Power Sources 2006, 162, 658.

• Lednicer, D.; Hauser, C. R. Org. Synth. Coll. 1973, 5, 434.

• Lewandowski, A.; and Swiderska-Mocek, A. Journal of Power Sources 194 (2009) 601-609.

• Lindsay, J. K.; Hauser, C. R. The Journal of Organic Chemistry 1957, 22, 355.

• Miao, W. J.; Ding, Z. F.; Bard, A. J. Journal of Physical Chemistry B 2002, 106, 1392.

• Miura, Y.; Shimizu, F.; Mochida, T. Inorganic Chemistry 2010, 49, 10032.

• Moshurchak, L. M.; Lamanna, W. M.; Bulinski, M.; Wang, R. L.; Garsuch, R. R.; Jiang, J. W.; Magnuson, D.; Triemert, M.; Dahn, J. R. Journal Of The Electrochemical Society 2009, 156, A309.

• Nyamori, V. O., M. Gumede, et al. (2010). J. Organomet. Chem. 695(8): 1 126-1 132 • Sharma, M.; Yashonath, S. Journal Of Chemical Physics 2008, 129. (19) Lednicer, D.; Hauser, C. R. Org. Synth. Coll. 1973, 5, 434.

• Simenel, A. A.; Morozova, E. A.; Kuzmenko, Y. V.; Snegur, L. V. Journal Of Organometallic Chemistry 2003, 665, 13.

• Taylor, A. W.; Licence, P.; Abbott, A. P. Physical Chemistry Chemical Physics 2011 , 13, 10147.

• Taylor, A. W.; Qiu, F. L; Hu, J. P.; Licence, P.; Walsh, D. A. Journal Of Physical Chemistry B 2008, 1 12, 13292.

• Thomas, J-L, Howarth J. and M.Kennedy A. (2002). Molecules 7: 861-866.

• Thomas, J-L, Howarth J., Hanlon K., McGuirk D. Tetrahedron Let. 2000, 41 , 413.

• Zhang, L.; Zhang, Z. C; Wu, H. M.; Amine, K. Energy & Environmental Science 2011 , 4, 2858.

• Zhang, L.; Zhang, Z. C; Amine, K. Chapter 7 Redox Shuttle Additives for Lithium-Ion Battery in Lithium Ion Batteries - New Developments, llias Belharouak Editor, InTech, February 2012.

• US 7.585.590.

• US 7.615.312.

• US 7.615.317.

• US 7.648.801.

• US 7.81 1.710.

• US 2009/0286162.

• US 2010/0104950.

Claims

CLAIMS:

1. The use of a redox-active ionic liquid as an additive in an electrolyte of a secondary battery or of a supercapacitor, the redox-active ionic liquid comprising a redox shuttle linked to an ionic liquid.

2. The use of claim 1 , wherein the redox shuttle is linked to a cation of the ionic liquid.

3. The use of claim 1 , wherein the redox shuttle is linked to an anion of the ionic liquid.

4. The use of any one of claims 1 to 3, wherein the redox-active ionic liquid is of formula RS-LK-IL, wherein RS is the redox shuttle, LK is a bond or a linker, and IL is the ionic liquid.

5. The use of claim 4, wherein LK is -alkylene-, -COO-alkylene-, -CO-alkylene-, -O-alkylene-, -N-alkylene-, or -S-alkylene-.

6. The use of claim 5, wherein LK is -CH2- or -CH2CH2- .

7. The use of any one of claims 1 to 6, wherein the redox shuttle is ferrocene, or a ferrocene derivative, a dihydrophenazine, a metallocene, a dimethoxybenzene derivative, a thiantlurene derivative, 2,5-di-ferf- butyl-1 ,4-dimethoxybenzene (DDB), a phenothiazine derivative, 2,2,6,6-tetramethylpiperinyloxide (TEMPO), 2-(pentafluorophenyl)-tetrafluoro-1 ,3,2-benzodioxaborole (PFPTFBB), or an organometallic complex between a metal center and a ligand.

8. The use of claim 7, wherein the redox shuttle is:

wherein R is H, N0₂, S0₃H, F or CI, R_a is H or F, R_b is H or tert-butyl , L is SCN, CN or CO, Mi is Fe, Ru, Os, Co, Rh or lr and M₂ is Fe.

9. The use of claim 8, wherein the redox shuttle is :

wherein R_a is H and M₂ is Fe.

10. The use of claim 8, wherein the redox shuttle is

wherein Rb is H or tert-butyl.

1 1. The use of any one of claims 1 to 10, wherein the ionic liquid comprises a imidazolium, pyridinium, pyrazolium, triazolium, thiazolium, oxazolium, pyridazinium, pyrimidinium, pyrazinium, pyrrolidinium, piperidinium, phosphonium, or quaternary ammonium cation with an accompanying anion.

12. The use of claim 11 , wherein the ionic liquid is:

wherein R' is an alkyl, such as CH3, C4H9, CsHi₇ or C12H25, A- is an anion, such as TFSI, BF4, P0F6 CF3SO3, and Cat⁺ is an imidazolium cation, such as 1 -butyl-3-methylimidazolium, a pyridinium cation, quaternary ammonium cation, a pyrrolidinium cation or a piperidinium cation.

13. The use of claim 12, wherein the ionic liquid is:

wherein R' is CH3, C4H9, CsHi₇ or C12H25, and A- is bistriflimide or PF6^".

14. The use of any one of claims 1 to 13, wherein the redox-active ionic liquid is:

66

67

68

69

wherein R, R_a, Rt>, L, Mi , M2, R', A-, and Cat⁺ are as defined in claims 8 and 12.

15. The use of claim 1 , wherein the redox-active ionic liquid is:

16. The use any one of claims 1 to 15, wherein the electrolyte comprises more than about 0.1 mmol/L of the redox-active ionic liquid.

17. The use of claim 16, wherein the electrolyte comprises up to about 50% by volume of the redox-active ionic liquid based on the total volume of the electrolyte and redox-active ionic liquid.

18. The use of claim 17, wherein the electrolyte comprises between about 1 and about 5% of the redox- active ionic liquid.

19. The use of any one of claims 1 to 18, wherein the electrolyte is the electrolyte of a battery.

20. The use of claim 18, wherein the battery is a lithium-ion battery.

21. The use of any one of claims 1 to 18, wherein the electrolyte is the electrolyte of a capacitor.

22. A redox-active ionic liquid as defined in any one of claims 1 to 21.

23. A redox-active ionic liquid as defined in any one of claims 1 to 21, the redox-active ionic liquid being for use as an additive in an electrolyte of a secondary battery or of a supercapacitor.

24. An electrolyte additive comprising a redox-active ionic liquid as defined in any one of claims 1 to 21.

25. An electrolyte comprising a redox-active ionic liquid as defined in any one of claims 1 to 21.

26. The electrolyte of claim 25, comprising more than about 0.1 mmol/L of the redox-active ionic liquid.

27. The electrolyte of claim 26, comprising up to about 50% by volume of the redox-active ionic liquid based on the total volume of the electrolyte and redox-active ionic liquid.

28. The electrolyte of claim 27, comprising between about 1 and about 5% of the redox-active ionic liquid.

29. The electrolyte of any one of claims 25 to 28, being a secondary battery electrolyte.

30. The electrolyte of claim 29, being a lithium-ion battery electrolyte.

31. The electrolyte of any one of claims 25 to 28, being a supercapacitor electrolyte.

32. A secondary battery or supercapacitor comprising an electrolyte comprising a redox-active ionic liquid electrolyte additive as defined in any one of claims 1 to 21.

33. A method of manufacturing a redox-active ionic liquid electrolyte additive as defined in any one of claims 1 to 21 , the method comprising linking a redox shuttle to an ionic liquid.

34. A method of increasing the solubility of a redox shuttle in an electrolyte, the method comprising linking the redox shuttle to an ionic liquid, thereby producing a redox-active ionic liquid as defined in any one of claims 1 to 21.

35. A method of manufacturing an electrolyte, the method comprising adding a redox-active ionic liquid as defined in any one of claims 1 to 21 to a conventional electrolyte.

36. A method of manufacturing a battery or supercapacitor comprising an electrolyte, the method comprising adding a redox-active ionic liquid as defined in any one of claims 1 to 21 to the electrolyte.

37. A method of increasing the stability of an electrolyte, the method comprising add adding a redox-active ionic liquid as defined in any one of claims 1 to 21 to the electrolyte.

38. A method of improving the safety of a battery or supercapacitor comprising an electrolyte, the method comprising add adding a redox-active ionic liquid as defined in any one of claims 1 to 21 to the electrolyte.

39. A method of reducing the risks of overcharge or overdischarge of a battery or supercapacitor comprising an electrolyte, the method comprising add adding a redox-active ionic liquid as defined in any one of claims 1 to 21 to the electrolyte.

40. A method of increasing the amount of a redox shuttle that can be added to an electrolyte without precipitation, the method comprising linking the redox shuttle to an ionic liquid, thereby producing a redox-active ionic liquid as defined above.

41. The method of any one of claims 33 to 39, wherein the electrolyte comprises more than about 0.1 mmol/L of the redox-active ionic liquid.

42. The method of claim 40, wherein the electrolyte comprises up to about 50% by volume of the redox- active ionic liquid based on the total volume of the electrolyte and redox-active ionic liquid.

43. The method of claim 41 , wherein the electrolyte comprises between about 1 and about 5% of the redox- active ionic liquid.

44. The method of any one of claims 33 to 42, wherein the electrolyte is a secondary battery electrolyte.

45. The method of claim 43, wherein the electrolyte is a lithium-ion battery electrolyte.

46. The method of any one of claims 33 to 42, wherein the electrolyte is a supercapacitor electrolyte.