CN109627227B - Piperidine type ionic liquid and preparation method and application thereof - Google Patents
Piperidine type ionic liquid and preparation method and application thereof Download PDFInfo
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- C07D295/00—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms
- C07D295/02—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms containing only hydrogen and carbon atoms in addition to the ring hetero elements
- C07D295/037—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms containing only hydrogen and carbon atoms in addition to the ring hetero elements with quaternary ring nitrogen atoms
Abstract
The invention discloses a preparation method of piperidine ionic liquid, which comprises the following steps: adding bromopropane into ethyl acetate, adding N-methylpiperidine, reacting for 8-48h, leaching the solid phase with acetone, and performing rotary evaporation to obtain an intermediate product; and (3) adding the intermediate product into water for dissolving, adding lithium trifluoromethanesulfonimide, extracting and separating, washing an organic phase with water, and performing rotary evaporation and drying to obtain the product. Also discloses a piperidine ionic liquid prepared by the method. Simultaneously discloses the application of the piperidine ionic liquid as a lithium ion battery electrolyte component. The preparation method is carried out at normal temperature, and has the advantages of high yield, economy and simple operation. The piperidine ionic liquid has the advantages of high purity, low water content, low viscosity, high conductivity and wide electrochemical window. The piperidine ionic liquid prepared by the method is used as an electrolyte component to be applied to lithium ion battery electrolyte, and has better non-flammability and chemical stability and lower electrochemical impedance.
Description
Technical Field
The invention relates to the technical field of ionic liquid, and particularly relates to piperidine type ionic liquid and a preparation method and application thereof.
Background
The ionic liquid has the performances of wide electrochemical window, high thermal stability and chemical stability, almost no volatilization and the like, has small pollution to the environment, and can be used as an electrolyte component to be applied to a lithium ion battery, particularly a lithium cobaltate battery, so that the safety performance of the battery can be improved, and the pollution to the environment can be reduced.
N-methyl-N-propyl-piperidine-bis (trifluoromethyl) sulfonimide (abbreviated as PI)13TFSI, the same below) is a common ionic liquid, belonging to the piperidine type. Ionic liquid PI (polyimide) from Zhao Jia Men at Liaoshi university13The application of TFSI in lithium secondary battery and the conductivity measurement of binary system thereof disclose a method for synthesizing ionic liquid by two steps: (1) reacting N-methylpiperidine with 1-bromopropane at 80 ℃ in a nitrogen atmosphere, cooling and crystallizing to obtain light yellow crystals, washing the light yellow crystals for 3 times by using ethyl acetate/acetonitrile with the volume ratio of 3:1, and recrystallizing to obtain an intermediate N-propyl-N-methyl bromide (PI for short)13Br，The same applies below); (2) subjecting the intermediate PI13Br and lithium trifluoromethanesulfonate (L iTFSI, the same below) react at normal temperature, the lower organic phase is washed repeatedly with deionized water to remove bromide ion, and colorless transparent product ionic liquid PI is obtained13TFSI, and finally dried under vacuum at 353K for 48 h. The method for preparing the ionic liquid PI13TFSI yield up to 90%, water content of product 500ppm, binary system prepared with ethanol, ionic liquid PI 1 mol/L at 298K13The conductivity of TFS is 1.77 ms/cm; at PI13Under the condition that the mass ratio of TFSI to organic solvent propylene carbonate (PC for short, the same below) is 3:2, the flame does not burn within 5s of a combustion test. However, in the mass ratio PI13PC =1:1, combustion test 2s burns; the research belongs to a laboratory pilot scale stage, and the impedance of a lithium ion secondary battery assembled by a product is higher and is more than 50 ohms; in addition, the reaction yield is low, the product purity is low, the test conditions are harsh, and the industrial production is limited by using toxic and harmful substances such as acetonitrile and the like.
Disclosure of Invention
The invention aims to provide a preparation method of piperidine ionic liquid, which has high product purity, high yield, economy and simple operation and overcomes the defects of the prior art.
Another object of the present invention is to provide a piperidine type ionic liquid having high purity, low water content, low viscosity, high conductivity, and a wide electrochemical window, which overcomes the above-mentioned disadvantages of the prior art.
Another objective of the present invention is to provide an application of the piperidine type ionic liquid prepared by the above method as an electrolyte component in an electrolyte of a lithium ion battery, in view of the above-mentioned deficiencies of the prior art. Compared with the traditional piperidine ionic liquid, the piperidine ionic liquid prepared by the method is applied to lithium ion battery electrolyte, and has better incombustibility, chemical stability and lower electrochemical impedance.
The technical scheme adopted by the invention for solving a technical problem is to provide a preparation method of piperidine ionic liquid, which is characterized by comprising the following steps:
adding bromopropane into ethyl acetate, stirring, adding N-methylpiperidine, reacting for 8-48h, performing solid-liquid separation, leaching the separated solid phase with acetone, leaching, and performing rotary evaporation to obtain an intermediate product, wherein the addition amount of the bromopropane is (1.1-27.5) mol/L based on the volume of the ethyl acetate, and the molar ratio of the addition amount of the N-methylpiperidine to the bromopropane is 1 (1.01-1.17);
step two, adding the intermediate product into water to dissolve, adding lithium trifluoromethanesulfonylimide, stirring, extracting by an organic solvent, washing an organic phase for a plurality of times by water after liquid separation until no halogen ions exist, washing, and finally carrying out rotary evaporation and drying on the obtained organic phase to obtain a product, wherein the adding amount of the intermediate product is 0.1-1.0g/m L in terms of the volume of water, the mass ratio of the adding amount of the lithium trifluoromethanesulfonylimide to the intermediate product is (1.1-1.5): 1, the organic solvent is one or more of dichloromethane, ethyl acetate and n-hexane and is mixed at any ratio, and AgNO ions with no ions are adopted3/HNO3And (6) detecting.
Preferably, the elution is carried out 1 to 5 times, the dosage of each time of the acetone is (0.3 to 1.7) m L/g based on the mass of the solid phase, and the dosage of each time of the elution is (0.1 to 1) s/m L based on the dosage of the acetone.
Preferably, the drying in the second step comprises the following steps:
s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and carrying out vacuum drying for 6-24h at 110 ℃ to obtain a primary dried product;
s2.2: adding a molecular sieve into the primary dried product, and standing for more than 6 hours;
s2.3: sampling for moisture analysis, and repeating S2.2 when the moisture content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
Preferably, the first step adopts ultrasonic strengthening with the frequency of 30-60KHz in the reaction process.
Preferably, the second step is reinforced by microwaves in the reaction process.
Preferably, in the step one, the N-methylpiperidine is added dropwise at a dropping rate of 1.1 to 9.9 g/min.
Preferably, in the first step, the solid-liquid separation method is suction filtration, the rotary evaporation condition is vacuum evaporation at 80 ℃ for 5-8h, and the addition amount of bromopropane is (5.3-5.7) mol/L based on the volume of the ethyl acetate.
Preferably, the cleaning in the step two is as follows: adding water into the organic phase, stirring, separating liquid, and taking the organic phase; the addition amount of the water is 10-50% of the volume of the organic phase.
Preferably, in the second step, the adding amount of the intermediate product is (0.47-0.53) g/m L calculated by the volume of water, the mass ratio of the adding amount of the lithium trifluoromethanesulfonylimide to the intermediate product is (1.27-1.33): 1, the organic solvent is dichloromethane, and the rotary evaporation condition is that the vacuum pumping is carried out at 80 ℃ for 4-8 h.
The technical scheme adopted for solving the other technical problem is to provide the piperidine ionic liquid prepared by the method.
The invention solves another technical problem by adopting the technical scheme that the application of the piperidine ionic liquid as an electrolyte component in the lithium ion battery electrolyte is provided, and the application is characterized in that:
preferably, the lithium ion battery is a lithium ion battery using lithium cobaltate as a positive electrode material.
The preparation method of the piperidine ionic liquid provided by the invention has the following beneficial effects:
1. in the first step, acetone is adopted for leaching, ethyl acetate/acetonitrile is not used for washing, and as N-methylpiperidine and bromoethane are dissolved in acetone, but ionic liquid is insoluble, and the acetone has small molecular size and good volatility, a small amount of N-methylpiperidine and bromoethane wrapped between crystals can be well removed by the acetone, so that impurities such as N-methylpiperidine, bromoethane and the like in an intermediate product are greatly reduced; in addition, acetone has good volatility and is not easy to remain in the intermediate product.
2. Step one, heating is not carried out in the reaction process, so that various side reactions and oxidative denaturation of products and raw materials can be prevented to a great extent; because the reaction is not carried out under the protection of nitrogen atmosphere because of no heating, the cost is also reduced.
3. Most of water in the synthesized ionic liquid is removed by vacuum rotary evaporation of an organic phase at 80 ℃, the ionic liquid is placed in a vacuum drying oven containing phosphorus pentoxide for vacuum drying to remove residual water, and finally a molecular sieve is added to remove trace water, so that various water removal modes are comprehensively utilized, the water content in the product is ensured to be less than 10ppm under the condition of controlling oxidation and denaturation, and the cost is well controlled.
4. In the first step, ultrasonic wave reinforcement is adopted, the ultrasonic wave can form a local high-temperature high-pressure microenvironment in the reaction system by means of ultrasonic cavitation, the ultrasonic wave enables mixing and heat transfer to be more effective for the formed solid product, conversion is promoted, and the vibration stirring of the ultrasonic wave can assist in improving the reaction rate and the yield.
5. In the second step, microwave reinforcement is adopted, and the direction of various polar molecules in a reaction system is continuously changed in a rapidly changing electromagnetic field, so that the molecules are subjected to frictional heating, the reaction rate is increased, and the yield is further increased.
6. The process does not heat, reacts in the air, improves the conversion rate by increasing the reaction time, is suitable for industrial production, and has the yield of the ionic liquid reaching more than 97 percent under a small test strip in a laboratory; under the condition of large-scale production (single yield of 50-1000 Kg), the yield is still kept above 95%, and the leaching process replaces the heating reflux process, so that the process steps are greatly simplified, the production efficiency is improved, the working hours and the energy consumption are reduced, and the production cost is reduced.
The piperidine ionic liquid prepared by the method provided by the invention has the following beneficial effects:
1. the product has high purity and less impurities; the purification of the ionic liquid is very difficult, the cost is high, and side reactions are easy to occur.
2. The water content of the product is extremely low and is below 10ppm, and the water content is greatly reduced compared with 500ppm disclosed by the literature, which is very important for the application of the ionic liquid as an electrolyte component in the lithium ion battery, and the stability of the electrochemical performance of the lithium ion battery can be improved.
3. The synthesized ionic liquid has the advantages of low viscosity of 160mPs, high conductivity and electrochemical window as high as 5.5V, and is suitable for being used as a lithium ion battery electrolyte component.
The piperidine type ionic liquid provided by the invention has the following beneficial effects when being applied as an electrolyte component in a lithium ion battery electrolyte:
1. the synthesized ionic liquid takes EC/DEC mixed liquid with the volume ratio of 1:1 as a solvent, lithium ion battery electrolyte with the mass ratio of the ionic liquid to the solvent of 1:1 is prepared, and a combustion experiment is carried out, so that the ionic liquid is ignited for 2s, does not combust afterwards, and shows good and stable electrochemical performance.
2. The synthesized ionic liquid is used as the electrolyte component of the lithium ion battery and assembled into the lithium ion battery in the form of a button half battery, the impedance of the battery is reduced, and particularly, the impedance of the lithium ion battery taking lithium cobaltate as the anode is reduced more obviously.
Drawings
FIG. 1 is a graph showing the results of hydrogen nuclear magnetic resonance spectroscopy characterization of the ionic liquid prepared in example 1.
FIG. 2 is a graph showing the results of cyclic voltammetry tests on the ionic liquid prepared in example 1.
FIG. 3 is a chromatogram of an intermediate product to be prepared in comparative example 1 by the method of Zhao Jia Men paper of Liaoning university.
FIG. 4 is a chromatogram of an intermediate product to be produced by the method of example 1 of the present invention in comparative example 1.
Fig. 5 is a graph showing the results of the ac impedance test of the four ionic liquids in comparative example 3.
Detailed Description
The following are specific embodiments of the present invention and are further described with reference to the drawings, but the present invention is not limited to these embodiments.
Example 1
Step one, adding 1.1mol of bromopropane into 200m L ethyl acetate, stirring at 20 ℃, slowly dropwise adding 1mol of N-methylpiperidine at a dropping speed of 5.5g/min, stirring for reaction for 12h, performing suction filtration, leaching the separated solid phase with acetone, performing rotary evaporation at 80 ℃ for 6.5h after leaching to obtain an intermediate product, wherein the acetone leaching conditions are that leaching is performed for 3 times, the dosage of acetone is 0.8m L/g per time based on the mass of the solid phase, and the leaching time is 0.55s/m L per time based on the dosage of acetone.
Step two, weighing 100g of the intermediate product, adding the intermediate product into 200m L of water for dissolving, adding 130g of lithium trifluoromethanesulfonimide, stirring for 1h, extracting with 400m L of organic solvent, washing an organic phase for 5 times with water after liquid separation until no halogen ions are generated, washing, and finally obtaining an ionic liquid product by performing rotary evaporation on the organic phase after vacuum pumping at 80 ℃ for 6h and drying, wherein the organic solvent is dichloromethane, and AgNO is adopted as the halogen ions3/HNO3And (6) detecting.
The drying in the second step comprises the following steps: s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and performing vacuum drying for 12 hours at 110 ℃ to obtain a primary dried product; s2.2: adding a molecular sieve into the primary dried product, and standing for more than 24 hours; s2.3: sampling, measuring the water content by using a Karl Fischer moisture tester, and repeating S2.2 when the water content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
The cleaning in the second step is as follows: adding water into the organic phase, stirring for 10min, separating liquid, and taking the organic phase; the amount of water added was 20% by volume of the organic phase.
Nuclear magnetic resonance hydrogen spectrum characterization of the prepared ionic liquid: the Bruker AVANCE III 500MHz nuclear magnetic resonance spectrometer is adopted for testing, the result is shown in figure 1, and the ionic liquid of the prepared product is proved to be PI13And (4) TFSI. No impurity peak appears in the nuclear magnetic resonance spectrogram of the test result, which shows that the synthesized ionic liquid has no impurities and high purity.
The synthesized ionic liquid has low viscosity of 160mPs, and is prepared into a binary system with ethanol, and the conductivity of the ionic liquid is 1.92ms/cm when the ionic liquid is measured at the temperature of 298K and is 1 mol/L.
Cyclic voltammetry testing of the prepared ionic liquid: by adopting a CHI660D electrochemical workstation, taking a Cu disc electrode as a working electrode, a Pt sheet electrode as a counter electrode and an Ag wire as a reference electrode, and sweeping at a speed of 50mV/s, the ionic liquid is added into a self-made electrolytic cell, and the result is shown in figure 2. The result shows that the electrochemical window of the ionic liquid product is larger than 5.5V, and the ionic liquid product can be used as a component of electrolyte in a lithium ion battery. Good chemical stability can be maintained during battery operation.
Example 2
The first step is that 1.1mol of bromopropane is added into 200m L ethyl acetate, stirring is carried out at the temperature of 20 ℃, 1mol of N-methylpiperidine is slowly dripped, the dripping speed is 5.5g/min, stirring and reacting are carried out for 8h, ultrasonic strengthening with the frequency of 45KHZ is adopted in the reaction process, suction filtration is carried out, the separated solid phase is leached by acetone, after leaching, vacuum pumping is carried out at the temperature of 80 ℃ for 6.5h, an intermediate product is obtained, the acetone leaching conditions are that leaching is carried out for 3 times, the dosage of acetone is 0.8m L/g per time, the dosage of acetone is 0.55s/m L per time.
Step two, weighing 100g of the intermediate product, adding the intermediate product into 200m L of water for dissolving, adding 130g of lithium trifluoromethanesulfonimide, stirring for 1h, adopting microwave for reinforcement in the stirring reaction process, extracting with 400m L of organic solvent, washing an organic phase for 5 times with water after liquid separation until no halogen ions are generated, and obtaining a product ionic liquid by vacuumizing and rotary steaming the organic phase for 6h at 80 ℃ and drying after washing, wherein the organic solvent is dichloromethane, and the no ions are AgNO3/HNO3And (6) detecting.
The drying in the second step comprises the following steps: s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and performing vacuum drying for 12 hours at 110 ℃ to obtain a primary dried product; s2.2: adding a molecular sieve into the primary dried product, and standing for more than 24 hours; s2.3: sampling, measuring the water content by using a Karl Fischer moisture tester, and repeating S2.2 when the water content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
The cleaning in the second step is as follows: adding water into the organic phase, stirring for 10min, separating liquid, and taking the organic phase; the amount of water added was 20% by volume of the organic phase.
In order to reduce the impurities in the product ionic liquid, on the one hand we distilled all the solvents used in steps one and two, the alkane was washed with sulphuric acid and with Na2CO3Neutralizing the solution and finally distilling; the salt in the reaction process is removed by water washing, the product is extracted by dichloromethane, and the ratio of water to dichloromethane (the optimal ratio is 1: 2) is adjusted so as to improve the yield and purity of the product.
L iPF is prepared by taking EC/DEC mixed solution with the volume ratio of 1:1 as a solvent for the ionic liquid prepared by the method6The lithium ion battery is assembled into a button half-battery form by electrolyte with the concentration of 0.8 mol/L and the concentration of ionic liquid of 0.2 mol/L, the positive electrode material of the button battery is lithium cobaltate, lithium iron phosphate, lithium nickelate, lithium manganate, ternary or multi-element material, the specific capacity of the lithium ion battery is not obviously changed, the impedance is reduced, and the cycle performance is stable.
Example 3
The first step is that 0.22mol of bromopropane is added into 200m L ethyl acetate, stirring is carried out at 20 ℃, 0.218mol of N-methylpiperidine is slowly dropped, the dropping speed is 1.1g/min, stirring and reacting are carried out for 8h, ultrasonic strengthening with the frequency of 30KHz is adopted in the reaction process, suction filtration is carried out, the solid phase obtained by separation is leached by acetone, vacuum pumping is carried out after leaching for 5h at the temperature of 80 ℃, an intermediate product is obtained, the acetone leaching conditions are that leaching is carried out for 1 time, the dosage of acetone is 0.3m L/g according to the mass of the solid phase, and the leaching time is 0.1s/m L according to the dosage of acetone.
Weighing 20g of the intermediate product, adding the intermediate product into 200m L of water for dissolving, adding 22g of lithium trifluoromethanesulfonimide, stirring for 1h, adopting microwave for reinforcement in the stirring reaction process, extracting with 400m L of organic solvent, washing an organic phase for 5 times with water after liquid separation until no halogen ions are generated, and performing rotary evaporation on the organic phase obtained after washing at the temperature of 80 ℃ for 4h by vacuumizing and drying to obtain the ionic liquid product, wherein the organic solvent is ethyl acetate, and the no halogen ions are AgNO3/HNO3And (6) detecting.
The drying in the second step comprises the following steps: s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and performing vacuum drying for 6 hours at 110 ℃ to obtain a primary dried product; s2.2: adding a molecular sieve into the primary dried product, and standing for more than 6 hours; s2.3: sampling, measuring the water content by using a Karl Fischer moisture tester, and repeating S2.2 when the water content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
The cleaning in the second step is as follows: adding water into the organic phase, stirring for 10min, separating liquid, and taking the organic phase; the amount of water added was 10% by volume of the organic phase.
Example 4
Step one, adding 5.5mol of bromopropane into 200m L ethyl acetate, stirring at 20 ℃, slowly dropwise adding 4.701mol of N-methylpiperidine at a dropping speed of 9.9g/min, stirring for reacting for 48h, adopting 60KHz ultrasonic wave for reinforcement in the reaction process, filtering, leaching the separated solid phase with acetone, vacuumizing at 80 ℃ and carrying out rotary evaporation for 8h after leaching to obtain an intermediate product, wherein the acetone leaching conditions are that leaching is carried out for 5 times, the dosage of acetone is 1.7m L/g per time based on the mass of the solid phase, and the leaching time is 1s/m L per time.
Weighing 200g of the intermediate product, adding 200m of the intermediate product into L m of water for dissolution, adding 300g of lithium trifluoromethanesulfonimide, stirring for 1h, adopting microwave for reinforcement in the stirring reaction process, extracting with 400m of L organic solvent, washing an organic phase for 5 times with water after liquid separation until no halogen ions are generated, and performing rotary evaporation on the organic phase obtained finally after washing at the temperature of 80 ℃ for 8h by vacuumizing and drying to obtain the ionic liquid product, wherein the organic solvent is n-hexane and the halogen ions are AgNO3/HNO3And (6) detecting.
The drying in the second step comprises the following steps: s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and carrying out vacuum drying for 24h at 110 ℃ to obtain a primary dried product; s2.2: adding a molecular sieve into the primary dried product, and standing for more than 12 hours; s2.3: sampling, measuring the water content by using a Karl Fischer moisture tester, and repeating S2.2 when the water content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
The cleaning in the second step is as follows: adding water into the organic phase, stirring for 10min, separating liquid, and taking the organic phase; the amount of water added was 50% by volume of the organic phase.
Example 5
The first step is that 1.06mol of bromopropane is added into 200m L ethyl acetate, stirring is carried out at 20 ℃, 1mol of N-methylpiperidine is slowly dripped, the dripping speed is 5.5g/min, stirring and reacting are carried out for 8h, ultrasonic strengthening with the frequency of 45KHz is adopted in the reaction process, suction filtration is carried out, the separated solid phase is leached by acetone, after leaching, vacuum pumping is carried out at the temperature of 80 ℃ and rotary evaporation is carried out for 6.5h, an intermediate product is obtained, the acetone leaching conditions are that leaching is carried out for 3 times, the dosage of acetone for each time is 0.8m L/g calculated by the mass of the solid phase, and the leaching time for each time is 0.55s/m L.
Weighing 94g of the intermediate product, adding the intermediate product into 200m L of water for dissolving, adding 119.38g of lithium trifluoromethanesulfonimide, stirring for 1h, adopting microwave for reinforcement in the stirring reaction process, extracting with 400m L of organic solvent, washing an organic phase for 5 times with water after liquid separation until no halogen ions are generated, and obtaining a product ionic liquid by performing rotary evaporation on the organic phase obtained after washing at a vacuum pumping temperature of 80 ℃ for 6h and drying, wherein the organic solvent is a dichloromethane and ethyl acetate mixed solution with a volume ratio of 1:1, and AgNO is adopted for the halogen-free ions3/HNO3And (6) detecting.
The drying in the second step comprises the following steps: s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and performing vacuum drying for 12 hours at 110 ℃ to obtain a primary dried product; s2.2: adding a molecular sieve into the primary dried product, and standing for more than 24 hours; s2.3: sampling, measuring the water content by using a Karl Fischer moisture tester, and repeating S2.2 when the water content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
The cleaning in the second step is as follows: adding water into the organic phase, stirring for 10min, separating liquid, and taking the organic phase; the amount of water added was 20% by volume of the organic phase.
Example 6
The first step is that 1.14mol of bromopropane is added into 200m L ethyl acetate, stirring is carried out at 20 ℃, 1mol of N-methylpiperidine is slowly dripped, the dripping speed is 5.5g/min, stirring and reacting are carried out for 8h, ultrasonic strengthening with the frequency of 45KHz is adopted in the reaction process, suction filtration is carried out, the separated solid phase is leached by acetone, after leaching, vacuum pumping is carried out at the temperature of 80 ℃ for rotary evaporation for 6.5h, an intermediate product is obtained, the acetone leaching conditions are that leaching is carried out for 3 times, the dosage of acetone for each time is 0.8m L/g calculated by the mass of the solid phase, and the leaching time for each time is 0.55s/m L calculated by the.
Weighing 106g of the intermediate product, adding the intermediate product into 200m L of water for dissolving, adding 140.98g of lithium trifluoromethanesulfonimide, stirring for 1h, adopting microwave for reinforcement in the stirring reaction process, extracting with 400m L of organic solvent, washing an organic phase for 5 times with water after liquid separation until no halogen ions are generated, and obtaining a product ionic liquid by performing rotary evaporation on the organic phase obtained finally after washing at the temperature of 80 ℃ for 6h through vacuumizing and drying, wherein the organic solvent is a mixed solution of dichloromethane, ethyl acetate and n-hexane with the volume ratio of 1:1:1, and AgNO is adopted as the halogen-free ions3/HNO3And (6) detecting.
The drying in the second step comprises the following steps: s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and performing vacuum drying for 12 hours at 110 ℃ to obtain a primary dried product; s2.2: adding a molecular sieve into the primary dried product, and standing for more than 24 hours; s2.3: sampling, measuring the water content by using a Karl Fischer moisture tester, and repeating S2.2 when the water content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
The cleaning in the second step is as follows: adding water into the organic phase, stirring for 10min, separating liquid, and taking the organic phase; the amount of water added was 20% by volume of the organic phase.
Comparative example 1
Respectively adopting ionic liquid PI of Zhao Jia Men at Liaoning faculty university13Application of TFSI in lithium secondary batteries and conductivity measurement of binary system thereof, two ionic liquids were prepared in a two-step process (the finally synthesized ionic liquid was named sample # 1, the same below) as in the preparation process of example 1 of the present invention (the finally synthesized ionic liquid was named sample # 2, the same below). The first step of the two methodsThe prepared intermediate products were tested by using Thermo FisherScientific DSQ single quadrupole mass spectrometer, respectively, and the results are shown in fig. 3-4. The results show that the purity of the intermediate product prepared by the method of the embodiment 1 of the invention reaches more than 98 percent, which is obviously higher than that of the ionic liquid prepared by the method disclosed in the master academic paper of Zhao Jia Men, Liaoning faculty university, which is attributed to the following reasons: the obtained intermediate is leached by acetone without being washed by ethyl acetate/acetonitrile, and because N-methylpiperidine and bromoethane are dissolved in acetone, but ionic liquid is insoluble, and the molecular size of the acetone is small and the volatility is good, a small amount of N-methylpiperidine and bromoethane wrapped between crystals can be well removed by the acetone, so that impurities such as N-methylpiperidine, bromoethane and the like in the intermediate are greatly reduced; in addition, acetone itself has good volatility and is not easily left in the intermediate product.
Two kinds of lithium ion battery electrolytes with the mass ratio of the ionic liquid to the solvent of 1:1 are prepared by taking EC/DEC mixed liquid with the volume ratio of 1:1 as the solvent of the two kinds of ionic liquid prepared by the two methods, as shown in Table 1.
A, B two electrolytes are subjected to a flammability test, and incombustibility of the two electrolytes is compared, wherein the method comprises the steps of taking 1cm of asbestos paper of × 6cm, dropwise adding the electrolytes on the front 1-2 cm of the asbestos paper by a dropper, enabling the electrolytes to fully infiltrate the asbestos paper, conducting a combustion test by using a flame of a liquefied petroleum gas lighter, lighting the flame of the lighter at the asbestos paper infiltrated by the electrolytes, keeping the lighting position at the same position, and counting by using a stopwatch.
Comparative example 2
By using a controlled variable method, using the experimental conditions of example 1 as basic experimental conditions (i.e., if no specific description is provided, the experimental conditions except for variables are the same as those of example 1), 11 intermediate products shown in table 2 were prepared by adjusting the solvent used for rinsing in step one and the reaction temperature in step one. The purity of the intermediate product was tested using a Thermo Fisher Scientific DSQ single quadrupole GC-MS.
The results show that the solvent used for rinsing in step one has a significant effect on improving the purity of the intermediate product, which is the highest when rinsing with acetone, due to the following: because N-methylpiperidine and bromoethane are dissolved in acetone, but ionic liquid is insoluble, and the molecular size of the acetone is small and the volatility is good, the acetone can well remove a small amount of N-methylpiperidine and bromoethane wrapped between crystals, thereby greatly reducing impurities such as N-methylpiperidine, bromoethane and the like in the intermediate product; in addition, acetone itself has good volatility and is not easily left in the intermediate product. The reaction temperature in the step one has obvious influence on improving the purity of the intermediate product, and when the temperature is below 30 ℃, the purity of the intermediate product is higher and reaches 98 percent; when the temperature is above 50 ℃, the purity of the intermediate product is reduced; this is due to: the raw materials used in the reaction in the first step are unstable in chemical properties, and can generate various side reactions when being heated slightly in the air, and the prior art needs to carry out the reaction under the protection of nitrogen atmosphere and strictly controls the conditions of reaction temperature, time and the like to realize higher yield and product purity; the method disclosed by the invention has the advantages that the reaction is carried out at normal temperature in the air atmosphere, the reaction time is prolonged, the higher conversion rate is realized, and meanwhile, the prepared intermediate product is purified by adopting an acetone leaching process, so that the preparation method is simplified, the cost is reduced, and the purity of the intermediate product is improved.
Comparative example 3
The same as in comparative examples 1 and 2Preparing L iPF with EC/DEC mixed solution with volume ratio of 1:1 as solvent from four final products of 1#, 2#, 5#, and 10# ionic liquids6The electrolyte with the concentration of 0.8 mol/L and the ionic liquid concentration of 0.2 mol/L is assembled into a lithium ion battery in the form of a button half battery, the anode material of the button battery adopts lithium cobaltate, the resistance of the battery prepared by four different ionic liquids is tested by adopting alternating current impedance, and the result is shown in figure 56~10-2Hz. The results show that: the impedances of the 1#, 2#, 5#, and 10# samples are about 40, 10, 30, and 20 ohms, respectively. The impedance of the battery prepared by the 2# ionic liquid is the smallest, which is attributed to: the four ionic liquids have different purities, and impurities contained in the four ionic liquids can affect the impedance of the lithium ion battery to a greater extent, wherein the higher the purity is, the smaller the impedance is.
Comparative example 4
By using a controlled variable method, taking the experimental conditions of example 2 as basic experimental conditions (i.e., if no special description is made, the experimental conditions except for variables are the same as those of example 2), and comparing the purity and yield of the final product ionic liquid by adjusting whether ultrasonic wave reinforcement is adopted in the reaction process of the first step and whether microwave reinforcement is adopted in the reaction process of the second step, as shown in table 3. The ionic liquid purity was tested using a Thermo Fisher Scientific DSQ single quadrupole GC-MS.
The results show that whether ultrasonic wave strengthening is adopted in the reaction process of the step one and whether microwave strengthening is adopted in the reaction process of the step two has no obvious influence on the purity of the finally prepared ionic liquid, but has great influence on the yield of the ionic liquid, which is attributed to that: (1) in the first step, ultrasonic wave reinforcement is adopted, the ultrasonic wave can form a local high-temperature high-pressure microenvironment in a reaction system by virtue of ultrasonic cavitation, the ultrasonic wave enables mixing and heat transfer to be more effective for the formed solid product, conversion is promoted, and the vibration stirring of the ultrasonic wave can assist in improving the reaction rate and the yield; (2) in the second step, microwave reinforcement is adopted, and the direction of various polar molecules in a reaction system is continuously changed in a rapidly changing electromagnetic field, so that the molecules are subjected to frictional heating, the reaction rate is increased, and the yield is further increased.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (7)
1. A preparation method of piperidine ionic liquid is characterized by comprising the following steps:
adding bromopropane into ethyl acetate, stirring, adding N-methylpiperidine, reacting for 8-48h at the temperature below 30 ℃, carrying out solid-liquid separation, leaching the separated solid phase with acetone, and carrying out rotary evaporation after leaching to obtain an intermediate product, wherein the addition amount of the bromopropane is (1.1-27.5) mol/L based on the volume of the ethyl acetate, and the molar ratio of the addition amount of the N-methylpiperidine to the bromopropane is 1 (1.01-1.17);
and step two, adding the intermediate product into water to dissolve, adding lithium trifluoromethanesulfonylimide, stirring, extracting by using an organic solvent, washing an organic phase for several times by using water after liquid separation until the organic phase is free of halogen ions, removing most of water from the organic phase obtained finally after washing through vacuum rotary evaporation at 80 ℃, then putting the organic phase into a vacuum drying oven containing phosphorus pentoxide to perform vacuum drying to remove residual water, finally adding a molecular sieve to remove trace water until the water content in the product is less than 10ppm, wherein the addition amount of the intermediate product is 0.1-1.0g/m L based on the volume of water, the mass ratio of the addition amount of the lithium trifluoromethanesulfonylimide to the intermediate product is (1.1-1.5): 1, and the organic solvent is one or a mixture of more of dichloromethane, ethyl acetate and n-hexane in any ratio.
2. The method for preparing the piperidine type ionic liquid according to claim 1, wherein:
and in the first step, the acetone is leached for 1 to 5 times, the dosage of the acetone is (0.3 to 1.7) m L/g in terms of the mass of the solid phase, and the leaching time is (0.1 to 1) s/m L in terms of the dosage of the acetone.
3. The method for preparing piperidine type ionic liquid according to claim 2, wherein the drying in step two comprises the following steps:
s2.1: putting the product obtained after rotary evaporation into a vacuum drying oven containing phosphorus pentoxide, and carrying out vacuum drying for 6-24h at 110 ℃ to obtain a primary dried product;
s2.2: adding a molecular sieve into the primary dried product, and standing for more than 6 hours;
s2.3: sampling for moisture analysis, and repeating S2.2 when the moisture content is more than 10 ppm; when the water content is not more than 10ppm, the final product is obtained.
4. The method for preparing a piperidine type ionic liquid according to claim 3, wherein:
step one, ultrasonic strengthening with the frequency of 30-60KHz is adopted in the reaction process.
5. The method for preparing the piperidine type ionic liquid according to claim 4, wherein:
and step two, microwave reinforcement is adopted in the reaction process.
6. The method for preparing the piperidine type ionic liquid according to claim 5, wherein:
in the first step, the N-methylpiperidine is added dropwise at the dropping speed of 1.1-9.9 g/min, the solid-liquid separation method is suction filtration, the rotary evaporation condition is vacuum pumping at the temperature of 80 ℃ for 5-8h, and the addition amount of bromopropane is (5.3-5.7) mol/L calculated by the volume of the ethyl acetate;
the cleaning in the second step is as follows: adding water into the organic phase, stirring, separating liquid, and taking the organic phase; the addition amount of the water is 10-50% of the volume of the organic phase.
7. The method for preparing the piperidine type ionic liquid according to claim 6, wherein:
in the second step, the adding amount of the intermediate product is (0.47-0.53) g/m L calculated by the volume of water, the mass ratio of the adding amount of the lithium trifluoromethanesulfonylimide to the intermediate product is (1.27-1.33): 1, the organic solvent is dichloromethane, and the rotary evaporation condition is that the intermediate product is subjected to rotary evaporation at 80 ℃ for 4-8h through vacuum pumping.
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