Functionalized choline chloride ionic liquid, preparation method thereof and use in electrochemical energy storage device

Abstract

The present invention discloses a process for preparing a functionalized choline chloride ionic liquid as defined in formula (I), and thereof use in an electrochemical energy storage device, as an electrolyte solution or an additive for a lithium ion battery and a supercapacitor. The ionic liquid electrolyte material has better biocompatibility, flame retardance, high ionic conductivity, low viscosity, and wide electrochemical window. ##STR00001## wherein R.sup.1 is selected from the group consisting of: (CH.sub.2═CH—(CH.sub.2).sub.n)—, CN(CH.sub.2).sub.n—, or R.sup.2.sub.3Si—; R.sup.2 is selected from CH.sub.3—(CH.sub.2).sub.m—, n is an integer selected from 1 to 3, m is an integer selected from 0 to 2; or one of R.sup.2 is (CH.sub.3).sub.3Si—O—. Anion A in Formula I is selected from the group consisting of: Cl.sup.−, Br.sup.−, I.sup.−, BF.sub.4.sup.−, NO.sub.3.sup.−, SO.sub.4.sup.2−, CF.sub.3COO.sup.−, CF.sub.3SO.sub.3.sup.−, (CF.sub.3SO.sub.2).sub.2N.sup.−, PF.sub.6.sup.−, BF.sub.2C.sub.2O.sub.4.sup.−, or B(C.sub.2O.sub.4).sub.2.sup.−.

Claims

1. A functionalized choline chloride ionic liquid having the following formula I: ##STR00005## wherein R.sup.1 is (CH.sub.2═CH—(CH.sub.2).sub.n)—, CN(CH.sub.2).sub.n—, or R.sup.2.sub.3Si—; R.sup.2 is CH.sub.3—(CH.sub.2).sub.m— or (CH.sub.3).sub.3Si—O—; A is Cl.sup.−, Br.sup.−, I.sup.−, BF.sub.4.sup.−, NO.sub.3.sup.−, SO.sub.4.sup.2−, CF.sub.3COO.sup.−, CF.sub.3SO.sub.3.sup.−, (CF.sub.3SO.sub.2).sub.2N.sup.−, PF.sub.6.sup.−, BF.sub.2C.sub.2O.sub.4.sup.−, or B(C.sub.2O.sub.4).sub.2.sup.−; n is an integer selected from 1 to 3, m is an integer selected from 0 to 2, and one of R.sup.2 is (CH.sub.3).sub.3Si—O—.

2. A process for preparing the functionalized choline chloride ionic liquid according to claim 1, wherein the process comprises the steps of: under a condition of cooling in ice bath, reacting choline chloride with an equi-molar amount of sodium hydroxide in an acetonitrile as solvent at room temperature for 20 minutes, and adding drop-wise 1.1 times molar amount of halogenated alkane thereto, followed by reacting under reflux for 8 hours; or reacting choline chloride with an equi-molar amount of organosilicon reagent under reflux for 16 hours; removing solid by filtering after completion of the reaction, removing solvent by rotary evaporation, and subsequently using dichloromethane and diethyl ether as solvents for recrystallization to obtain the functionalized choline chloride ionic liquid; dissolving the functionalized choline chloride tonic liquid and an equi-molar amount of alkali metal or alkaline earth metal salt in water or other solvents for anion exchange, stirring the reaction for 4 to 6 hours, followed by extracting the product after the ion exchange by using the dichloromethane as a solvent, removing the solvent, and drying to yield the target ion liquid.

3. A process for preparing the functionalized choline chloride room-temperature ionic liquid according to claim 1, wherein the process comprises the steps of: at room temperature, dissolving choline chloride and an equi-molar amount of alkali metal or alkaline earth metal salt in water or other solvents for anion exchange, and reacting under stirring for 4 to 6 hours, followed by using dichloromethane or other solvents for extraction, and removing solvent to obtain a choline chloride ionic liquid obtained from the anion exchange, reacting the choline chloride ionic liquid obtained from the anion exchange with an organosilicon reagent under refluxing for 16 hours, and concentrated under vacuum to remove residual low boiling-point substances to yield the target ionic liquid.

4. A method for using the functionalized choline chloride ionic liquid according to claim 1, comprising using the functionalized choline chloride ionic liquid as an electrolyte material or additive for an electrochemical energy storage device.

5. A method for using the functionalized choline chloride ionic liquid according to claim 1 as an electrolyte material or additive for an electrochemical energy storage device, comprising using the functionalized choline chloride ionic liquid as a quaternary ammonium salt-type ionic liquid electrolyte material, which is used as an electrolyte material or additive for an lithium-ion battery or supercapacitor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a linear sweep voltammetry plot of 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide;

(2) FIG. 2 illustrates cyclic performance of a lithium titanate lithium metal battery in which 0.8 M lithium bis(trifluoromethylsulfonyl)imide in 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide ionic liquid as an electrolyte (.square-solid. indicates a specific capacity, and .Math. indicates a Coulombic efficiency);

(3) FIG. 3 illustrates cyclic performance of a graphite half-cell in which 0.8 M lithium bis(trifluoromethylsulfonyl)imide in 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide ionic liquid with 10% vinylene carbonate as an additive as an electrolyte (.square-solid. indicates a specific discharge capacity, and .Math. indicates a specific charge capacity);

(4) FIG. 4 illustrates cyclic performance of a lithium iron phosphate lithium metal battery in which 0.8 M 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide ionic liquid of bis(trifluoromethylsulfonyl)imide lithium with 10% vinylene carbonate as an additive as an electrolyte (.square-solid. indicates a specific capacity, and .Math. indicates a Coulombic efficiency);

(5) FIG. 5 is a linear sweep voltammetry plot of 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide;

(6) FIG. 6 is a graph illustrating the variation of the conductivity of 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide with temperature;

(7) FIG. 7 illustrates cyclic voltammetry performance of a supercapacitor formed from 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide;

(8) FIG. 8 illustrates cyclic voltammetry performance of a supercapacitor formed from 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide added with AN;

(9) FIG. 9 is a charge and discharge curve of a supercapacitor formed from 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide added with 90% AN;

(10) FIG. 10 illustrates great current charge and discharge performance of a supercapacitor formed from 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide added with 90% AN.

DETAILED DESCRIPTION

(11) The present invention is further described with reference to specific embodiments.

(12) However, such embodiments construe no limitation to the protection scope of the present invention.

Example 1: Synthesis of 2-allyloxyethyl trimethyl ammonium chloride salt

(13) Under the condition of cooling in ice bath, 0.5 mol of choline chloride was reacted with an equi-molar amount of sodium hydroxide in an acetonitrile solvent at room temperature for 20 minutes, and then 0.55 mol of allyl bromide was added drop-wise thereto. The resulting reaction mixture was reacted under reflux for 8 hours. After the reaction is completed, the resulting reaction product was filtered to remove the solid, and treated via rotary evaporation to remove solvent. The residue was recrystallized from the solvents of dichloromethane and diethyl ether to obtain 2-allyloxyethyl trimethyl ammonium chloride salt: .sup.1H NMR (CDCl.sub.3): σ 3.47 (m, 9H, +N(CH.sub.3).sub.3), 3.90, 3.94 (dd, 4H, OCH.sub.2CH.sub.2O), 4.02 (m, 2H, CH.sub.2═CH—CH.sub.2—O), 5.23 (ddq, 2H, CH.sub.2═CH—CH.sub.2—O), 5.84 (ddt, 1H, CH.sub.2═CH—CH.sub.2—O); .sup.13C NMR (CDCl.sub.3): σ 54.61, 63.98, 65.68, 72.21, 118.43, 133.27.

Example 2: Synthesis of 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt

(14) 0.4 mol of 2-allyloxyethyl trimethyl ammonium chloride salt (the product obtained in Example 1) and an equi-molar amount of lithium bis(trifluoromethylsulfonyl)imide were dissolved in water for anion exchange, and mechanically stirred for 4 to 6 hours. Subsequently, the product obtained from the anion exchange was extracted by using the dichloromethane solvent, concentrated to remove the solvent. The residue was dried to obtain the target 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt ionic liquid: .sup.1H NMR (CDCl.sub.3): σ 3.19 (m, 9H, +N(CH.sub.3).sub.3), 3.58, 3.86 (m, 4H, OCH.sub.2CH.sub.2O), 4.05 (m, 2H, CH.sub.2═CH—CH.sub.2—O), 5.28 (ddq, 2H, CH.sub.2═CH—CH.sub.2—O), 5.85 (m, 1H, CH.sub.2═CH—CH.sub.2—O); .sup.13C NMR (CDCl.sub.3): σ 54.65, 63.50, 66.20, 72.31, 118.70, 132.97.

Example 3: Synthesis of choline bis(trifluoromethylsulfonyl)imide salt

(15) At room temperature, 0.5 mol of choline chloride and an equi-molar amount of lithium bis(trifluoromethylsulfonyl)imide were dissolved in water for ion exchange, and mechanically stirred for 4 to 6 hours. The resulting reaction product was then extracted with dichloromethane, and then treated to remove the solvent to yield the choline bis(trifluoromethylsulfonyl)imide salt obtained from the anion exchange: .sup.1H NMR (300 MHz, CDCl.sub.3): δ 6 3.16 (s, 9H, +N(CH.sub.3).sub.3), 3.40 (s, 1H, OH), 3.45 (s, 2H, CH.sub.2O), 4.03 (s, 2H, CH.sub.2N+); .sup.13C NMR (300 MHz, CDCl.sub.3): 54.06, 56.21, 67.66, 119.75.

Example 4: Synthesis of 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt

(16) 0.4 mol of hexamethyl disilazane was added drop-wise into 0.4 mol of choline bis(trifluoromethylsulfonyl)imide salt (the product obtained in Example 3) and reacted under reflux for 16 hours. The resulting reaction product was evaporated under vacuum to remove residual low boiling-point substances to obtain the target 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt ionic liquid: .sup.1H NMR (300 MHz, CDCl.sub.3): δ 0.16 (s, 9H, Si(CH.sub.3).sub.3), 3.22 (s, 9H, +N(CH.sub.3).sub.3), 3.50 (s, 2H, CH.sub.2O), 4.00 (s, 2H, CH.sub.2N+); .sup.13C NMR (75 MHz, CDCl.sub.3): −1.04, 54.55, 56.81, 67.86, 119.87.

Example 5: Synthesis of 2-allyloxyethyl trimethyl ammonium bis(oxalate)borate salt

(17) 2-allyloxyethyl trimethyl ammonium bis(oxalate)borate salt was synthesized by using the process similar to that disclosed in Example 2. 0.4 mol of 2-allyloxyethyl trimethyl ammonium chloride salt (the product obtained in Example 1) and an equi-molar amount of lithium bis(oxalate)borate were dissolved in water for anion exchange, and the resulting solution was mechanically stirred for 4 to 6 hours. Subsequently, the product obtained from the anion exchange was extracted by using dichloromethane, removed the solvent. The residue was dried to obtain the target 2-allyloxyethyl trimethyl ammonium bis(oxalate)borate salt ionic liquid: .sup.1H NMR (CDCl.sub.3): σ 3.44 (m, 9H, +N(CH.sub.3).sub.3), 3.89, 3.91 (m, 4H, OCH.sub.2CH.sub.2O), 4.04 (m, 2H, CH.sub.2═CH—CH.sub.2—O), 5.28 (ddq, 2H, CH.sub.2═CH—CH.sub.2—O), 5.87 (m, 1H, CH.sub.2═CH—CH.sub.2—O); .sup.13C NMR (CDCl.sub.3): σ 54.67, 63.63, 66.92, 72.37, 118.85, 132.01, 158.89.

Example 6: Synthesis of 2-allyloxyethyl trimethyl ammonium bis(fluorooxalate)borate salt

(18) 2-allyloxyethyl trimethyl ammonium bis(fluorooxalate)borate salt was synthesized by using the process similar to that disclosed in Example 2. 0.4 mol of 2-allyloxyethyl trimethyl ammonium chloride salt (the product obtained in Example 1) and an equi-molar amount of lithium bis(fluorooxalate)borate were dissolved in water for anion exchange, and the resulting solution was mechanically stirred for 4 to 6 hours. Subsequently, the product obtained from the anion exchange was extracted by using the dichloromethane solvent, concentrated to remove the solvent. The residue was dried to obtain the target 2-allyloxyethyl trimethyl ammonium bis(fluorooxalate)borate salt: .sup.1H NMR (CDCl.sub.3) ionic liquid: σ 3.38 (m, 9H, +N(CH.sub.3).sub.3), 3.80, 3.89 (m, 4H, OCH.sub.2CH.sub.2O), 4.03 (m, 2H, CH.sub.2═CH—CH.sub.2—O), 5.27 (ddq, 2H, CH.sub.2═CH—CH.sub.2—O), 5.87 (m, 1H, CH.sub.2═CH—CH.sub.2—O); .sup.13C NMR (CDCl.sub.3): σ 54.64, 63.67, 66.72, 72.22, 118.67, 133.05, 160.28.

Example 7: Synthesis of 2-cyanopropyloxyethyl trimethyl ammonium chloride salt

(19) 2-cyanopropyloxyethyl trimethyl ammonium chloride salt was synthesized by using the process similar to that disclosed in Example 1. Under the condition of cooling in ice bath, 0.5 ml of choline chloride was reacted with 0.5 mol of sodium hydroxide in an acetonitrile solvent at room temperature for 20 minutes, and then 0.55 mol of cyanopropyl bromide was added drop-wise thereto. The resulting reaction mixture was reacted under reflux for 8 hours. The resulting reaction product was treated via rotary evaporation to remove solvent. The residue was recrystallized from the solvents of methanol and diethyl ether to obtain 2-cyanopropyloxyethyl trimethyl ammonium chloride salt: .sup.1H NMR (CDCl.sub.3): σ 3.40 (m, 9H, +N(CH.sub.3).sub.3), 3.88, 3.94 (dd, 4H, OCH.sub.2CH.sub.2O), 3.68 (m, 2H, CNCH.sub.2—CH.sub.2—O), 2.72 (m, 2H, CN—CH.sub.2—CH.sub.2—O).

Description of Electrochemical Energy Storage Performance

Example 8: Performance of 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt

(20) The electrochemical energy storage performance of the functionalized choline chloride room-temperature ionic liquid according to the present invention is described by using 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt (the product obtained in Example 2) as an example.

(21) The measurement of the electrochemical window of 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt employs a three-electrode glass battery system, wherein Pt wire was used as an operating electrode, Li wire was used as a counter electrode, and the other Li wire was used as a reference electrode. The obtained linear sweep voltammetry plot was as illustrated in FIG. 1, wherein the electrochemical window was 0.5 to 5.2 V, better than that of an imidazoles ionic liquid (which generally has an electrochemical window of 4 V, A. Lewandowski, Journal of Power Sources 194 (2009) 601-609).

(22) 0.8 M lithium bis(trifluoromethylsulfonyl)imide was added into 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt to obtain an electrolyte solution without additive. The cyclic performance of a lithium metal battery using the obtained electrolyte solution and lithium titanate as the cathode was as illustrated in FIG. 2. The circulation was stable and the capacity was maintained at 145 mAh/g, with no attenuation.

(23) 0.8 M lithium bis(trifluoromethylsulfonyl)imide and 10% vinylene carbonate were added into 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt to obtain an electrolyte solution having an additive. The cyclic performance of the half-cell using the obtained electrolyte solution and graphite as the cathode is as illustrated in FIG. 3.

(24) 0.8 M lithium bis(trifluoromethylsulfonyl)imide and 10% vinylene carbonate were added into 2-allyloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt to obtain an electrolyte solution having an additive. The cyclic performance of a lithium metal battery using the obtained electrolyte solution and lithium iron phosphate as the cathode is as illustrated in FIG. 4.

Example 9: Performance of 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt

(25) The electrochemical energy storage performance of the functionalized choline chloride room-temperature ionic liquid according to the present invention is described by using 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide (the product obtained in Example 4) as an example.

(26) The measurement of the electrochemical window of 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt employs a three-electrode glass battery system, wherein Pt wire was used as an operating electrode, Li wire was used as a counter electrode, and the other Li wire was used as a reference electrode. The obtained linear sweep voltammetry plot of 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide was as illustrated in FIG. 5, wherein the electrochemical window thereof was 0 to 5.3 V. The reduction potential of the obtained battery is lower than that of an imidazoles ionic liquid (which is generally 1 V vs. Li/Li.sup.|), and the oxidation potential thereof is also higher than that of the imidazoles ionic liquid (which is generally 4 V vs. Li/Li.sup.|). In addition, since the reduction potential is 0 V, 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquid is applicable to a lithium metal battery and a high-voltage lithium metal battery.

(27) The measurement of the conductivity of 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide salt employs a battery system adopting a glass carbon electrode. Variations of the conductivity with the temperature are as illustrated in FIG. 6.

(28) The performance of an electrochemical supercapacitor formed from the functionalized choline chloride room-temperature ionic liquid according to the present invention is described by using 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide (the product obtained in Example 4) as an example.

(29) The inventors have investigated cyclic voltammetry performance of a symmetric supercapacitor formed from the active carbon electrode and an electrolyte solution of pure 2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide, under different cut-off voltages (from 1 to 5 V) at a scanning rate of 5 mV/s (as illustrated in FIG. 7). The electrolyte solution falls within the range of 1 to 4 V, and the cyclic voltammetry curve is presented as a symmetric rectangle, which indicates that the active carbon electrode has better reversibility, exhibiting better electric double-layer capacitor features.

(30) FIG. 8 illustrates impacts caused by addition of low viscosity AN to the cyclic voltammetry performance of the supercapacitor, wherein with the increase of the adding amount of AN (from 20% to 90%), the cyclic voltammetry curve presents as better rectangles. Therefore, capacitor performance is investigated by using a symmetric supercapacitor formed from the active carbon electrode and an electrolyte solution of the added AN having a volume fraction of 90%/2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide as an electrolyte.

(31) FIG. 9 is a constant-current charge/discharge curve of a symmetric supercapacitor formed from the active carbon electrode and an electrolyte solution of 90% AN/2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide as an electrolyte, at a current density of 0.2 A/g. Within a voltage range of from 0 to 3.5 V, the discharge curve of the active carbon electrode displays a linear variation, without obvious gassing phenomenon or damage. The voltage range is far higher than that of the commercial-use tetraethylammonium tetrafluoroborate (Et.sub.4NBF.sub.4)/PC electrolyte solution (from 0 to 2.7 V).

(32) FIG. 10 illustrates a rate capability of a symmetric supercapacitor formed from the active carbon electrode an electrolyte solution of 90% AN/2-trimethylsiloxyethyl trimethyl ammonium bis(trifluoromethylsulfonyl)imide as an electrolyte. When the current density is 0.2 A.Math.g.sup.−1, the specific capacitance of the active carbon electrode is 90 F.Math.g.sup.−1; and when the current density increases to 2 A.Math.g.sup.−1, the specific capacitance still reaches 70 F.Math.g.sup.−1, exhibiting better charge/discharge performance under great-current.