CN102227034B - A kind of lithium-air battery hybrid ionic liquid electrolyte and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium-air battery mixed type ionic liquid electrolyte and its preparation method, which belongs to the electrolyte preparation technology field. The electrolyte can be obtained by mixing dialkyl pyridines hexafluorophosphate ionic liquid, organic lithium salt with hexafluorophosphoric acid double core annular quaternary ammonium salt under the protective atmosphere of argon, stirring in the vacuum environment and vacuum drying. The electrolyte has the advantages of wide electrochemistry window, high conductivity, small internal resistance and excellent hydrophobicity. The specific capacitance and charge and discharge frequency can be improved by the lithium-air battery produced by the electrolyte, so that the electrolyte has strong practicality and enables large-scale industrial production.

Description

A kind of lithium-air battery hybrid ionic liquid electrolyte and preparation method thereof

technical field

The invention belongs to the technical field of electrolyte preparation, and in particular relates to a mixed ionic liquid electrolyte for a lithium-air battery and a preparation method thereof.

Background technique

With its excellent physical and chemical properties, ionic liquids, as ideal "green" solvents, new reaction media and "soft" functional materials, have become one of the most active frontier research fields of green chemistry with interdisciplinary fields. The excellent electrochemical properties of ionic liquids make them have extremely high application potential in the field of electrochemical research. Lithium-air batteries have become an energy conversion system that has attracted much attention due to their high theoretical specific capacity, specific energy, and environmental friendliness. Its cathode active material _O2 can be obtained directly from the surrounding air. At the same time, due to the high theoretical specific capacity (3862mAh/g) of Li, the theoretical specific energy of lithium-air batteries can reach 11,140Wh/kg, which is higher than the current theoretical specific energy. All conventional power systems are more than 10 times that of current high-performance lithium-ion batteries. The main factors that determine the performance of lithium-air batteries are electrolytes and electrodes, and ionic liquids have the advantages of wide electrochemical window, non-volatile, easy storage and recycling, etc. The application of new ionic liquids in the research of electrolytes for lithium-air batteries has become a current trend. It is a frontier of interdisciplinary research, and related research is in the ascendant.

For the organic electrolyte system, the organic solvent is used in the preparation, and the organic solvent will cause the corrosion of the negative electrode lithium due to the water content, resulting in a decrease in the specific capacity and charge-discharge efficiency of the lithium-air battery. Solid electrolytes and gel electrolytes have good reliability and no electrolyte leakage, high specific energy, and wide cycle voltage, but most solid electrolytes have low conductivity and solubility at room temperature. The mixed ionic liquid electrolyte has many excellent properties, such as ionic liquids can prepare hydrophobic ionic liquids through the design of anions and cations to ease the reaction between water and lithium metal in the air, and dinuclear cyclic ammonium salt of hexafluorophosphate The thermal stability of the electrolyte can prevent the battery capacity drop caused by the volatilization of the electrolyte during the working process, etc., which are enough to make it have the potential to be an electrolyte for lithium-air batteries.

Contents of the invention

The object of the present invention is to provide a mixed ionic liquid electrolyte.

The object of the present invention is also to provide a method for preparing a mixed ionic liquid electrolyte.

The object of the present invention is also to provide an application of a mixed ionic liquid electrolyte in a lithium-air battery.

A mixed ionic liquid electrolyte is composed of dialkylpyridine hexafluorophosphate ionic liquid, organic lithium salt and hexafluorophosphate dinuclear cyclic ammonium salt.

The dialkylpyridine hexafluorophosphate ionic liquid is 1-methyl-3-butylpyridine hexafluorophosphate ionic liquid or 1-ethyl-3-ethylpyridine hexafluorophosphate ionic liquid; organic lithium The salt is lithium hexafluorophosphate, lithium perchlorate or lithium tetrafluoroborate; the dinuclear cyclic ammonium salt of hexafluorophosphate is N, N'-1-ethyl-4-butyl triethylene diammonium hexafluorophosphate or N, N '-1-Ethyl-4-ethyltriethylenediammonium hexafluorophosphate.

The dialkylpyridine hexafluorophosphate ionic liquid is 1-methyl-3-butylpyridine hexafluorophosphate ionic liquid; the organic lithium salt is lithium hexafluorophosphate; 1-methyl-3-butylpyridine hexafluorophosphate The molar ratios of the salt ionic liquid, lithium hexafluorophosphate and dinuclear cyclic ammonium salt of hexafluorophosphate are 5:4:1, 5:3:2, 4:4:2, 3:5:2, 4:5:1.

A method for preparing a mixed ionic liquid electrolyte. Firstly, a dialkylpyridine-based hexafluorophosphate ionic liquid and a hexafluorophosphate dinuclear cyclic ammonium salt are prepared, and then the dialkylpyridine-based hexafluorophosphate Fluorophosphate ionic liquid is mixed with organolithium salt and hexafluorophosphate dinuclear cyclic ammonium salt, uniformly stirred for 36 hours in a vacuum environment, and then vacuum dried for 24 hours to obtain the product.

The preparation method of the dialkylpyridine hexafluorophosphate ionic liquid is:

Step 1: Add 100-500ml of N-picoline and the corresponding volume of n-bromobutane with a molar ratio slightly greater than 1 into a 2000ml single-necked flask, or add 100-500ml of N-ethylpyridine and a corresponding volume with a molar ratio slightly greater than 1 Add the corresponding volume of bromoethane into a 2000ml single-necked flask, reflux in an oil bath at a temperature of 100°C, and after reflux for 36 hours, cool down and crystallize;

Step 2: Suction filtration of the crystals obtained in Step 1;

Step 3: Add 60-300ml of acetonitrile and 120-600ml of ethyl acetate to the crystals obtained by suction filtration in Step 2, heat in an oil bath at 80°C, and reflux for 20 minutes. After the white precipitate is completely dissolved, filter while it is hot, and cool down to crystallize;

Step 4: Repeat the operations of Step 2 and Step 3 for 2 to 3 times to obtain white crystals, namely intermediates;

Step 5: Take 43.8-219.0 grams of the intermediate obtained in Step 4, put it into a 1000ml beaker, add 100-500ml of deionized water and stir to fully dissolve it;

Step 6: Take 32.6-163.0 grams of ammonium hexafluorophosphate, add it to the beaker described in step 5, and stir at room temperature for 4 hours;

Step 7: Wash the reaction solution obtained in Step 6 with 20-100 ml of deionized water and ether twice respectively, and remove the water layer;

Step 8: Vacuum-dry the solution obtained in Step 7 at 80° C. for 32 hours to obtain a dialkylpyridine hexafluorophosphate ionic liquid.

The preparation method of the dinuclear cyclic ammonium salt of hexafluorophosphate is:

Step 1: Preparation of N, N'-1-ethyl-4-butyl triethylene diammonium halide salt, add C ₂ H ₅ Br dropwise to the methanol solution of triethylene diammonium, heat to reflux, and reduce pressure Unreacted raw materials were removed by distillation to obtain monosubstituted N-1-yl triethylene diammonium bromide salt;

Step 2: Prepare a solution of monosubstituted N-1-yl triethylene diammonium bromide salt and C ₄ H ₉ Br or C ₂ H ₅ Br with a molar ratio slightly greater than 1:1, and continue heating to reflux to prepare N,N '-1-Ethyl-4-butyl triethylene diammonium bromide salt or N, N'-1-ethyl-4 ethyl triethylene diammonium bromide salt;

Step 3: Dissolve the prepared N,N'-1,4-diethyltriethylenediammonium bromide salt or N,N'-1-ethyl-4ethyltriethylenediammonium bromide salt in a small amount of water , added to equimolar mass of hexafluorophosphoric acid aqueous solution for ion exchange, after vacuum distillation and recrystallization to obtain dinuclear cyclic ammonium salt of hexafluorophosphate, then dissolve the crude salt in an appropriate solvent, add a decolorizing agent and heat Reflux, after the reaction is completed, filter the material while it is hot, and crystallize after static precipitation to obtain the finished product dinuclear cyclic ammonium hexafluorophosphate.

A hybrid ionic liquid electrolyte is used in a lithium-air battery, and the lithium-air battery includes a lithium negative electrode, an electrolyte, an air positive electrode, and a sealed casing.

Beneficial effects of the present invention: the electrolyte of the present invention has the advantages of wide electrochemical window, high electrical conductivity, small internal resistance, etc., and has excellent hydrophobicity. Adding dinuclear cyclic ammonium salt of hexafluorophosphate can make use of its thermal stability To prevent the decrease in battery capacity caused by the volatilization of the electrolyte during the working process, the lithium-air battery made of the electrolyte improves the specific capacity and charge-discharge times of the battery, has strong practicability, and can be mass-produced industrially.

Detailed ways

The present invention will be further described below with specific examples.

Example 1 Preparation of Dialkylpyridine Hexafluorophosphate Ionic Liquid

Step 1: Add 100-500ml of N-picoline and the corresponding volume of n-bromobutane with a molar ratio slightly greater than 1 into a 2000ml single-necked flask, or add 100-500ml of N-ethylpyridine and a corresponding volume with a molar ratio slightly greater than 1 Add the corresponding volume of bromoethane into a 2000ml single-necked flask, reflux in an oil bath at a temperature of 100°C, and after reflux for 36 hours, cool down and crystallize;

Step 2: Suction filtration of the crystals obtained in Step 1;

Step 3: Add 60-300ml of acetonitrile and 120-600ml of ethyl acetate to the crystals obtained by suction filtration in Step 2, heat in an oil bath at 80°C, and reflux for 20 minutes. After the white precipitate is completely dissolved, filter while it is hot, and cool down to crystallize;

Step 4: Repeat the operations of Step 2 and Step 3 for 2 to 3 times to obtain white crystals, namely intermediates;

Step 5: Take 43.8-219.0 grams of the intermediate obtained in Step 4, put it into a 1000ml beaker, add 100-500ml of deionized water and stir to fully dissolve it;

Step 6: Take 32.6-163.0 grams of ammonium hexafluorophosphate, add it to the beaker described in step 5, and stir at room temperature for 4 hours;

Step 7: Wash the reaction solution obtained in Step 6 with 20-100 ml of deionized water and ether twice respectively, and remove the water layer;

Step 8: Vacuum-dry the solution obtained in Step 7 at 80° C. for 32 hours to obtain a dialkylpyridine hexafluorophosphate ionic liquid.

The preparation of embodiment 2 hexafluorophosphate dinuclear cyclic ammonium salt

Step 1: Preparation of N, N'-1-ethyl-4-butyl triethylene diammonium halide salt, add C ₂ H ₅ Br dropwise to the methanol solution of triethylene diammonium, heat to reflux, and reduce pressure Unreacted raw materials were removed by distillation to obtain monosubstituted N-1-yl triethylene diammonium bromide salt;

Step 2: Prepare a solution of monosubstituted N-1-yl triethylene diammonium bromide salt and C ₄ H ₉ Br or C ₂ H ₅ Br with a molar ratio slightly greater than 1:1, and continue heating to reflux to prepare N,N '-1-Ethyl-4-butyl triethylene diammonium bromide salt or N, N'-1-ethyl-4 ethyl triethylene diammonium bromide salt;

Step 3: Dissolve the prepared N,N'-1,4-diethyltriethylenediammonium bromide salt or N,N'-1-ethyl-4ethyltriethylenediammonium bromide salt in a small amount of water , was added to an aqueous solution of hexafluorophosphoric acid of equimolar mass, ion-exchanged, dinuclear cyclic ammonium hexafluorophosphate was obtained after recrystallization by distillation under reduced pressure, then the crude salt was dissolved in a suitable solvent, a decolorizing agent was added and heated Reflux, after the reaction is completed, filter the material while it is hot, and crystallize after static precipitation to obtain the finished product dinuclear cyclic ammonium hexafluorophosphate.

The preparation of embodiment 3 mixed type ionic liquid electrolyte

(1) Under an argon protective atmosphere, mix 1-methyl-3-butylpyridine hexafluorophosphate ionic liquid with lithium hexafluorophosphate and N, N'-1-ethyl-4-butyltriethylene diammonium hexafluoro Phosphate mixed, the molar ratio of 1-methyl-3-butylpyridine hexafluorophosphate ionic liquid, lithium hexafluorophosphate and N,N'-1-ethyl-4-butyl triethylene diammonium hexafluorophosphate is 5 : 4:1, 5:3:2, 4:4:2, 3:5:2 or 4:5:1, uniformly stirred for 36 hours in a vacuum environment, and then dried in a vacuum for 24 hours to obtain the final product.

(2) Under an argon protective atmosphere, mix 1-methyl-3-butylpyridine hexafluorophosphate ionic liquid with lithium hexafluorophosphate and N, N'-1-ethyl-4-ethyltriethylenediammonium hexafluoro Phosphate mixture, the molar ratio of 1-methyl-3-butylpyridine hexafluorophosphate ionic liquid, lithium hexafluorophosphate and N,N'-1-ethyl-4-ethyltriethylene diammonium hexafluorophosphate is 5 : 4:1, 5:3:2, 4:4:2, 3:5:2 or 4:5:1, uniformly stirred for 36 hours in a vacuum environment, and then dried in a vacuum for 24 hours to obtain the final product.

(3) Under an argon protective atmosphere, mix 1-ethyl-3-ethylpyridine hexafluorophosphate ionic liquid with lithium perchlorate and N,N'-1-ethyl-4-ethyltriethylenedi Mix ammonium hexafluorophosphate, stir evenly under vacuum for 36 hours, and then dry in vacuum for 24 hours to obtain the product.

(4) Under an argon protective atmosphere, mix 1-ethyl-3-ethylpyridine hexafluorophosphate ionic liquid with lithium tetrafluoroborate and N,N'-1-ethyl-4-ethyltriethylenedi Mix ammonium hexafluorophosphate, stir evenly under vacuum for 36 hours, and then dry in vacuum for 24 hours to obtain the product.

(5) Under an argon protective atmosphere, mix 1-ethyl-3-ethylpyridine hexafluorophosphate ionic liquid with lithium tetrafluoroborate and N,N'-1-ethyl-4-butyltriethylenedi Mix ammonium hexafluorophosphate, stir evenly under vacuum for 36 hours, and then dry in vacuum for 24 hours to obtain the product.

(6) Under an argon protective atmosphere, mix 1-methyl-3-butylpyridine hexafluorophosphate ionic liquid with lithium perchlorate and N, N'-1-ethyl-4-butyltriethylenedi Mix ammonium hexafluorophosphate, stir evenly under vacuum for 36 hours, and then dry in vacuum for 24 hours to obtain the product.

Embodiment 4 Assembly of lithium-air battery

The mixed ionic liquid electrolyte described in Example 3 is placed between the lithium negative electrode and the air positive electrode, and assembled into a lithium-air battery through a sealed case.

Claims (5)

1. a mixed type ionic liquid electrolyte, is characterized in that, this electrolyte is comprised of dialkyl group pyridines hexafluorophosphate ionic liquid, organic lithium salt and hexafluorophosphoric acid double-core ring-type quaternary ammonium salt;

Described dialkyl group pyridines hexafluorophosphate ionic liquid is 1-methyl-3-butyl-pyridinium hexafluorophosphate ionic liquid, described organic lithium salt is lithium hexafluoro phosphate, and the mol ratio of described 1-methyl-3-butyl-pyridinium hexafluorophosphate ionic liquid, lithium hexafluoro phosphate and hexafluorophosphoric acid double-core ring-type quaternary ammonium salt is 5:4:1,5:3:2,4:4:2,3:5:2,4:5:1.

2. the preparation method of a kind of mixed type ionic liquid electrolyte as claimed in claim 1; it is characterized in that; at first prepare dialkyl group pyridines hexafluorophosphate ionic liquid and hexafluorophosphoric acid double-core ring-type quaternary ammonium salt; then under argon shield atmosphere; dialkyl group pyridines hexafluorophosphate ionic liquid is mixed with organic lithium salt and hexafluorophosphoric acid double-core ring-type quaternary ammonium salt; uniform stirring 36h under vacuum environment, by vacuumize 24h, obtain.

3. a kind of preparation method of mixed type ionic liquid electrolyte according to claim 2, is characterized in that, the preparation method of described dialkyl group pyridines hexafluorophosphate ionic liquid is:

Step 1: 100～500ml N-picoline and mol ratio are slightly larger than to 1 respective volume bromination of n-butane and join in 2000ml single port flask, perhaps 100～500ml N-ethylpyridine and mol ratio being slightly larger than to 1 respective volume bromic ether joins in 2000ml single port flask, in 100 ℃ of lower oil baths of temperature, reflux, after backflow 36h, decrease temperature crystalline;

Step 2: the prepared crystallization of step 1 is carried out to suction filtration;

Step 3: add 60～300ml acetonitrile and 120～600ml ethyl acetate in the crystal obtained to the step 2 suction filtration, heat under 80 ℃ of oil baths, backflow 20min, treat that white precipitate dissolves fully, filters while hot decrease temperature crystalline;

Step 4: obtain white crystal after the operation of repeating step two and step 3 2～3 times, i.e. intermediate;

Step 5: get intermediate 43.8～219.0 grams that step 4 makes, be put in the 1000ml beaker, add 100～500ml deionized water and stirring that it is fully dissolved;

Step 6: get ammonium hexafluorophosphate 32.6～163.0 grams, add in the described beaker of step 5, stir 4 hours under room temperature;

Step 7: the reactant liquor obtained through step 6 by deionized water and each washed twice of ether for 20～100ml, is removed water layer respectively;

Step 8: the solution that step 7 is obtained, 80 ℃ of vacuum dryings 32 hours, obtains dialkyl group pyridines hexafluorophosphate ionic liquid.

4. a kind of preparation method of mixed type ionic liquid electrolyte according to claim 2, is characterized in that, the preparation method of described hexafluorophosphoric acid double-core ring-type quaternary ammonium salt is:

Step 1: N, the preparation of N '-1-ethyl-4-butyl triethylene diammonium halogeno salt, by C ₂h ₅br is added drop-wise in the methanol solution of triethylene diammonium, adds hot reflux, and unreacted raw material is removed in decompression distillation, makes monosubstituted N-1-base triethylene diammonium bromo salt;

Step 2: the C that monosubstituted N-1-base triethylene diammonium bromo salt and mol ratio is slightly larger than to 1:1 ₄h ₉br or C ₂h ₅the Br wiring solution-forming, continue to add hot reflux, preparation N, N '-1-ethyl-4 butyl triethylene diammonium bromo salt or N, N '-1-ethyl-4 ethyl triethylene diammonium bromo salt;

Step 3: by the N made, N ’ – 1,4 – diethyl triethylene diammonium bromine salt or N, N '-1-ethyl-4 ethyl triethylene diammonium bromo salt is dissolved in a small amount of water, join etc. in the hexafluorophosphoric acid aqueous solution of molal weight, carry out ion-exchange, obtain hexafluorophosphoric acid double-core ring-type quaternary ammonium salt after the decompression distillation recrystallization, then crude salt is dissolved in appropriate solvent, add decolorizer and add hot reflux, after reaction finishes, material is filtered while hot, static crystallization, obtain the hexafluorophosphoric acid double-core ring-type quaternary ammonium salt of finished product.

5. the application of the described mixed type ionic liquid electrolyte of claim 1, is characterized in that, this electrolyte is for lithium-air battery, and lithium-air battery comprises cathode of lithium, electrolyte, air positive pole and seal casinghousing.