CN116315065B - Preparation method of electrolyte and application of electrolyte in lithium ion battery - Google Patents
Preparation method of electrolyte and application of electrolyte in lithium ion battery Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention relates to the technical field of lithium batteries, in particular to a preparation method of electrolyte and application thereof in lithium ion batteries, wherein an inorganic ion conductor, an ionic liquid and a modified metal organic framework are introduced to construct a solid electrolyte with high ionic conductivity and high mechanical modulus, and when the solid electrolyte is applied to the lithium ion batteries, the service life and the multiple cycle safety of the batteries can be improved; the ether-ester substituted difunctional ionic liquid is synthesized, and ether and methyl are introduced on the basis of the ionic liquid, so that the viscosity reduction and capacity increase effects are achieved; the concentration of the current carrier is increased by regulating and controlling the concentration of lithium salt; meanwhile, a modified metal organic framework with a lithium ion selection function is added to obtain a composite solid electrolyte with excellent performance; in MoO by in situ growth method 3 The surface of the nanorod grows a copper-based metal framework, and then a polyoxometalate having excellent thermal and oxidation stability is introduced to improve the stability of the metal framework.
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a preparation method of electrolyte and application of the electrolyte in a lithium ion battery.
Background
With the progress of technology, lithium metal is used as a secondary battery, and the secondary battery has a higher working voltage, energy density and longer cycle life, so that the secondary battery is a battery with development prospect. The conventional lithium ion battery uses a large amount of flammable organic solvents as electrolyte, and has good ionic conductivity, but has inherent problems of flammability, easy leakage, easy volatilization and the like, so that potential safety hazards exist in battery production application, and consumers put forward higher demands on the safety of the lithium ion battery along with the wide application of the lithium ion battery in the fields of portable electronic equipment, electric automobiles and the like.
In addition, in the traditional lithium ion battery, lithium ions are unevenly distributed on the surface of lithium metal, dendritic lithium dendrites are easily formed in the deposition or stripping process, and the cycle life of the battery is attenuated and even short-circuited. Therefore, research into solid electrolytes that are nonflammable, have good mechanical properties, and have excellent encapsulation properties is a hot spot in this field.
Disclosure of Invention
The invention aims to provide a preparation method of electrolyte and application of the electrolyte in a lithium ion battery, so as to solve the problems in the background art.
In order to solve the technical problems, the invention provides the following technical scheme:
a method for preparing an electrolyte, comprising the steps of:
mixing lithium salt, 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bis (trifluoromethanesulfonyl) imide ionic liquid, a modified metal organic framework and N-methylpyrrolidone, ultrasonically stirring for 8-10h to obtain slurry, dripping the slurry on a substrate, and heating in vacuum to obtain a solid electrolyte.
Compared with the traditional organic electrolyte, the solid electrolyte prepared by the invention has the characteristics of good heat resistance, high chemical stability and the like, and the inherent mechanical modulus of the solid electrolyte can effectively inhibit the penetration of lithium dendrites. The solid electrolyte prepared by the invention belongs to an organic polymer electrolyte, and has the advantages of easy processing, strong plasticity and the like compared with an inorganic solid electrolyte, and can be compatible with deformation in the electrode cycle process.
And the existing organic solid electrolyte in the market has low room temperature ionic conductivity and mechanical property because of high crystallinity, so that the application range of the solid electrolyte is limited. In the invention, the inorganic ion conductor, the ionic liquid and the organic metal frame are introduced to construct the solid electrolyte with high ionic conductivity and high mechanical modulus, so that the service life and the multiple cycle safety of the battery can be improved when the solid electrolyte is applied to the lithium ion battery.
Further, the base material is one of a lithium sheet and a steel sheet; the working conditions of vacuum heating are as follows: maintaining at 75-80deg.C for 10-12 hr.
Further, the lithium salt is one of lithium hexafluorophosphate, lithium difluorooxalato borate and lithium difluorosulfimide.
When the solid electrolyte for the traditional lithium ion battery is circularly charged and discharged, the volume of the crystal can be seriously expanded or contracted, and the safety of the battery is further influenced. The invention introduces the difunctional ionic liquid as the electrolyte component, which can inhibit the side reaction of the battery, thereby improving the safety of the battery. However, since the ionic liquid generally has high viscosity characteristics and can lead to the reduction of battery capacity and cycle stability, the ionic liquid and the organic solvent are generally mixed to prepare a liquid electrolyte in the prior art;
the invention synthesizes the ether-ester substituted difunctional ionic liquid, introduces ether and methyl on the basis of the ionic liquid to achieve the effects of viscosity reduction and capacity increase, and then cooperates with the modified metal organic framework with multiple active sites to improve the ionic conductivity and mechanical modulus of lithium ions, so that the dimensional stability of the ionic liquid can be maintained under repeated cyclic charge and discharge, thereby improving the safety of the battery.
Further, the preparation of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethanesulfonimide ionic liquid comprises the following steps:
1) Mixing 2-methylimidazole, absolute ethyl alcohol and 2-bromoethyl methyl ether, transferring into a hydrothermal kettle, preserving heat for 42-45h at 135-140 ℃, extracting with diethyl ether, adding triethylamine into the lower solution after extraction, mixing, preserving heat for 12-14h at 125-130 ℃, filtering, distilling under reduced pressure, drying to obtain 1-ethylmethyl ether-2-methylimidazole salt, adding methyl chloroacetate and acetonitrile under nitrogen atmosphere, mixing, heating to 55-60 ℃, preserving heat for 20-22h, and distilling under reduced pressure to obtain 1-methoxyethyl-2-methyl-3-3-methyl acetate methylimidazole bromide;
2) Mixing dichloromethane and 1-methoxyethyl-2-methyl-3-3-methyl acetate imidazole bromide, adding lithium bistrifluoromethylsulfonyl imide, ultrasonically stirring for 2-4 hours, filtering, washing with deionized water, filtering, decompressing, distilling, and drying to obtain 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bistrifluoromethylsulfonyl imide salt.
Further, the molar ratio of 2-methylimidazole, 2-bromoethyl methyl ether and triethylamine is 1:1:1, a step of; the molar ratio of the 1-methoxyethyl-2-methyl-3-3-methyl acetate imidazole bromide to the lithium bistrifluoromethylsulfonyl imide is 1:1.
further, the electrolyte comprises the following components in parts by weight: 1-3 parts of lithium salt, 0.1 part of 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bis (trifluoromethyl) sulfonyl imide ionic liquid, 0.1-0.2 part of modified metal organic framework and 5-10 parts of N-methylpyrrolidone; the mass ratio of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoro methanesulfonimide ionic liquid to the modified metal organic framework is 0.1: (0.1-0.2).
The functional ionic liquid prepared by the invention not only maintains the mechanical property of the polymer, but also inherits the characteristics of high ionic conductivity, incombustibility, thermal stability and the like of the ionic liquid. However, after the ionic group is fixed on the polymer chain, the viscosity of the polyionic liquid is increased, so that the conductivity is influenced, and therefore, the concentration of carriers is increased by regulating and controlling the concentration of lithium salt; meanwhile, a modified metal organic framework with a lithium ion selection function is added to obtain the composite solid electrolyte with excellent performance. Compared with pure polyion liquid solid electrolyte added in the non-modified metal organic frame, the room temperature ion conductivity of the composite solid electrolyte is greatly improved.
Further, the preparation method of the modified metal organic framework comprises the following steps:
(1) Mixing nitric acid with deionized water, adding ammonium molybdate tetrahydrate, ultrasonic treating for 10-20min, transferring into a reaction kettle, maintaining at 195-200deg.C for 16-18 hr, cooling, centrifuging, washing with deionized water and ethanol for 3-5 times, and drying to obtain MoO 3 A nanorod;
(2) MoO is carried out 3 Mixing the nanorods, polyvinylpyrrolidone and methanol, performing ultrasonic dispersion for 20-30min, adding copper nitrate, stirring for 1-2h, adding a mixed solution of trimesic acid and methanol, stirring for 10-20min, adding a mixed solution of polytungstate and deionized water, stirring for 10-20min, performing centrifugal separation, and drying to obtain the modified metal organic frame.
In MoO by in situ growth method 3 The copper-based metal frame grows on the surface of the nano rod, then the polyoxometallate with excellent thermal and oxidation stability is introduced to improve the thermal stability of the metal frame, and the modified metal-organic frame can improve specific capacity through conversion reaction and MoO 3 The introduction of the nanorods enhances the conductivity of the material, buffering the volume expansion of the metal compound during charging and discharging. When applied to lithium ion batteries, the lithium ion batteries remarkably improve the cycle stability and the rate capability.
Further, moO 3 The mass ratio of the nanorod to the polyvinylpyrrolidone to the copper nitrate to the trimesic acid is 0.3:1:2:1.6; the mass ratio of the trimesic acid to the polytungstate is 8:1.
further, the preparation of the polytungstate comprises the following steps: mixing sodium tungstate and deionized water, adding phosphoric acid and hydrogen peroxide, heating under reflux for 1-2h, cooling, adding potassium chloride, stirring for 30-50min, filtering, cooling in ice water mixed bath, recrystallizing, filtering, and drying to obtain poly-tungstate.
Further, the application of the electrolyte in the lithium ion battery is that the prepared electrolyte is used for preparing the lithium ion battery.
The beneficial effects are that:
according to the invention, the inorganic ion conductor, the ionic liquid and the modified metal organic framework are introduced to construct the solid electrolyte with high ionic conductivity and high mechanical modulus, so that the service life and the multiple cycle safety of the battery can be improved when the solid electrolyte is applied to the lithium ion battery.
According to the invention, the ether-ester substituted difunctional ionic liquid is synthesized, the ether and methyl are introduced on the basis of the ionic liquid, so that the viscosity reduction and capacity increase effects are achieved, and then the ionic conductivity and mechanical modulus of lithium ions are synergistically improved by the ionic liquid and the modified metal-organic framework with multiple active sites, so that the dimensional stability of the ionic liquid can be maintained under repeated cyclic charge and discharge, and the safety of a battery is improved.
The functional ionic liquid prepared by the invention not only maintains the mechanical property of the polymer, but also inherits the characteristics of high ionic conductivity, incombustibility, thermal stability and the like of the ionic liquid. However, after the ionic group is fixed on the polymer chain, the viscosity of the polyionic liquid is increased, so that the conductivity is influenced, and therefore, the concentration of carriers is increased by regulating and controlling the concentration of lithium salt; meanwhile, a modified metal organic framework with a lithium ion selection function is added to obtain the composite solid electrolyte with excellent performance. Compared with pure polyion liquid solid electrolyte added in the non-modified metal organic frame, the room temperature ion conductivity of the composite solid electrolyte is greatly improved.
In MoO by in situ growth method 3 The copper-based metal frame grows on the surface of the nano rod, then the polyoxometallate with excellent thermal and oxidation stability is introduced to improve the thermal stability of the metal frame, and the modified metal-organic frame can improve specific capacity through conversion reaction and can be communicatedOver MoO 3 The introduction of the nanorods enhances the conductivity of the material, buffering the volume expansion of the metal compound during charging and discharging. When applied to lithium ion batteries, the lithium ion batteries remarkably improve the cycle stability and the rate capability.
Detailed Description
The following will clearly and completely describe the technical solutions in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
A method for preparing an electrolyte, comprising the steps of:
mixing 1g of lithium salt, 0.1g of 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethanesulfonimide ionic liquid, 0.1g of modified metal organic framework and 5 mLN-methylpyrrolidone, ultrasonically stirring for 8 hours to obtain slurry, dripping the slurry on a substrate, and heating in vacuum to obtain a solid electrolyte;
the base material is a lithium sheet; the working conditions of vacuum heating are as follows: maintaining at 80 ℃ for 10 hours;
the lithium salt is lithium hexafluorophosphate;
the preparation method of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bis (trifluoromethanesulfonyl) imide ionic liquid comprises the following steps:
1) Mixing 4.11g of 2-methylimidazole, 20mL of absolute ethyl alcohol and 7.3g of 2-bromoethyl methyl ether, transferring into a hydrothermal kettle, preserving heat at 135 ℃ for 45 hours, extracting with diethyl ether, adding 5.06g of triethylamine into the extracted lower solution, mixing, preserving heat at 125 ℃ for 14 hours, filtering, distilling under reduced pressure, drying to obtain 1-ethylmethyl ether-2-methylimidazole salt, adding 4.72g of methyl chloroacetate and 7.5mL of acetonitrile under nitrogen atmosphere, mixing, heating to 55 ℃ for 22 hours, and distilling under reduced pressure to obtain 1-methoxyethyl-2-methyl-3-3-methyl acetate methylimidazole bromide;
2) Mixing 5mL of dichloromethane and 9.96g of 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bromide, adding 10.05g of lithium bistrifluoromethylsulfonyl imide, stirring for 2-4h by ultrasonic, filtering, washing with deionized water, filtering, distilling under reduced pressure, and drying to obtain 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bistrifluoromethylsulfonyl imide salt;
the preparation method of the modified metal organic framework comprises the following steps:
(1) Mixing 14mL of nitric acid with 66mL of deionized water, adding 2.8g of ammonium molybdate tetrahydrate, performing ultrasonic treatment for 10min, transferring into a reaction kettle, maintaining at 195 ℃ for 18h, cooling, performing centrifugal separation, washing with deionized water and ethanol for 3 times in sequence, and drying to obtain MoO 3 A nanorod;
(2) Will be 0.3g MoO 3 Mixing the nanorods, 1g of polyvinylpyrrolidone and 80mL of methanol, performing ultrasonic dispersion for 20min, adding 2g of copper nitrate, stirring for 1h, adding a mixed solution of 1.6g of trimesic acid and 90mL of methanol, stirring for 10min, adding a mixed solution of 0.2g of polytungstate and 10mL of deionized water, stirring for 10min, performing centrifugal separation, and drying to obtain a modified metal organic frame;
the preparation of the polytungstate comprises the following steps: 10g of sodium tungstate and 35mL of deionized water are mixed, 15mL of 85% phosphoric acid and 1mL of hydrogen peroxide are added, reflux heating is carried out for 1h, 10g of potassium chloride is added after cooling, stirring is carried out for 30min, suction filtration is carried out, cooling is carried out in an ice water mixed bath, recrystallization, filtration and drying are carried out, and thus the polytungstate is obtained.
Example 2
A method for preparing an electrolyte, comprising the steps of:
mixing 2g of lithium salt, 0.1g of 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethanesulfonimide ionic liquid, 0.15g of modified metal organic framework and 8 mLN-methylpyrrolidone, ultrasonically stirring for 9h to obtain slurry, dripping the slurry on a substrate, and heating in vacuum to obtain a solid electrolyte;
the base material is a lithium sheet; the working conditions of vacuum heating are as follows: maintaining at 78 ℃ for 11h;
the lithium salt is lithium difluoro oxalate borate;
the preparation method of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bis (trifluoromethanesulfonyl) imide ionic liquid comprises the following steps:
1) Mixing 4.11g of 2-methylimidazole, 20mL of absolute ethyl alcohol and 7.3g of 2-bromoethyl methyl ether, transferring into a hydrothermal kettle, preserving heat at 138 ℃ for 43h, extracting with diethyl ether, adding 5.06g of triethylamine into the lower solution after extraction, mixing, preserving heat at 123 ℃ for 13h, filtering, distilling under reduced pressure, drying to obtain 1-ethylmethyl ether-2-methylimidazole salt, adding 4.72g of methyl chloroacetate and 7.5mL of acetonitrile under nitrogen atmosphere, mixing, heating to 58 ℃ for 21h, and distilling under reduced pressure to obtain 1-methoxyethyl-2-methyl-3-3-methyl acetate methylimidazole bromide;
2) Mixing 5mL of dichloromethane and 9.96g of 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bromide, adding 10.05g of lithium bistrifluoromethylsulfonyl imide, stirring for 3h by ultrasound, filtering, washing with deionized water, filtering, distilling under reduced pressure, and drying to obtain 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bistrifluoromethylsulfonyl imide salt;
the preparation method of the modified metal organic framework comprises the following steps:
(1) Mixing 14mL of nitric acid with 66mL of deionized water, adding 2.8g of ammonium molybdate tetrahydrate, performing ultrasonic treatment for 15min, transferring into a reaction kettle, maintaining at 198 ℃ for 17h, cooling, performing centrifugal separation, washing with deionized water and ethanol for 4 times in sequence, and drying to obtain MoO 3 A nanorod;
(2) Will be 0.3g MoO 3 Mixing the nanorods, 1g of polyvinylpyrrolidone and 80mL of methanol, performing ultrasonic dispersion for 25min, adding 2g of copper nitrate, stirring for 1.5h, adding a mixed solution of 1.6g of trimesic acid and 90mL of methanol, stirring for 15min, adding a mixed solution of 0.2g of polytungstate and 10mL of deionized water, stirring for 15min, performing centrifugal separation, and drying to obtain a modified metal organic frame;
the preparation of the polytungstate comprises the following steps: 10g of sodium tungstate and 35mL of deionized water are mixed, 15mL of 85% phosphoric acid and 1mL of hydrogen peroxide are added, reflux heating is carried out for 1.5h, 10g of potassium chloride is added after cooling, stirring is carried out for 40min, suction filtration is carried out, cooling is carried out in an ice water mixed bath, recrystallization, filtration and drying are carried out, and thus the polytungstate is obtained.
Example 3
A method for preparing an electrolyte, comprising the steps of:
3g of lithium salt, 0.1g of 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethanesulfonimide ionic liquid, 0.2g of modified metal organic framework and 10 mLN-methyl pyrrolidone are mixed, ultrasonic stirring is carried out for 10 hours to obtain slurry, the slurry is dripped on a substrate, and vacuum heating is carried out to obtain a solid electrolyte;
the base material is a lithium sheet; the working conditions of vacuum heating are as follows: maintaining at 75 ℃ for 12 hours;
the lithium salt is lithium bis (fluorosulfonyl) imide;
the preparation method of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bis (trifluoromethanesulfonyl) imide ionic liquid comprises the following steps:
1) Mixing 4.11g of 2-methylimidazole, 20mL of absolute ethyl alcohol and 7.3g of 2-bromoethyl methyl ether, transferring into a hydrothermal kettle, preserving heat at 140 ℃ for 42h, extracting with diethyl ether, adding 5.06g of triethylamine into the extracted lower solution, mixing, preserving heat at 130 ℃ for 12h, filtering, distilling under reduced pressure, drying to obtain 1-ethylmethyl ether-2-methylimidazole salt, adding 4.72g of methyl chloroacetate and 7.5mL of acetonitrile under nitrogen atmosphere, mixing, heating to 60 ℃ for 20h, and distilling under reduced pressure to obtain 1-methoxyethyl-2-methyl-3-3-methyl acetate methylimidazole bromide;
2) 5mL of dichloromethane and 9.96g and 35mmol of 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bromide are mixed, 10.05g and 35mmol of lithium bistrifluoromethylsulfonyl imide are added, ultrasonic stirring is carried out for 4 hours, filtration is carried out, deionized water is used for washing, filtration, reduced pressure distillation and drying are carried out, and 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bistrifluoromethylsulfonyl imide salt is obtained;
the preparation method of the modified metal organic framework comprises the following steps:
(1) Mixing 14mL of nitric acid with 66mL of deionized water, adding 2.8g of ammonium molybdate tetrahydrate, performing ultrasonic treatment for 20min, transferring into a reaction kettle, maintaining at 200 ℃ for 16h, cooling, performing centrifugal separation, washing with deionized water and ethanol for 5 times in sequence, and drying to obtain MoO 3 A nanorod;
(2) Will be 0.3g MoO 3 Mixing nanorods, 1g polyvinylpyrrolidone and 80mL methanol, performing ultrasonic dispersion for 30min, adding 2g copper nitrate, and stirring2h, adding a mixed solution of 1.6g of trimesic acid and 90mL of methanol, stirring for 20min, adding a mixed solution of 0.2g of polytungstate and 10mL of deionized water, stirring for 20min, centrifugally separating, and drying to obtain a modified metal-organic frame;
the preparation of the polytungstate comprises the following steps: 10g of sodium tungstate and 35mL of deionized water are mixed, 15mL of 85% phosphoric acid and 1mL of hydrogen peroxide are added, reflux heating is carried out for 2h, 10g of potassium chloride is added after cooling, stirring is carried out for 50min, suction filtration is carried out, cooling is carried out in an ice water mixed bath, recrystallization, filtration and drying are carried out, and thus the polytungstate is obtained.
Comparative example 1
Using example 3 as a control, no 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethanesulfonimide ionic liquid was prepared, and the other procedures were normal.
Comparative example 2
Using example 3 as a control, no MoO was prepared in the preparation of the modified metal organic framework 3 The nanorods and other working procedures are normal.
Comparative example 3
With example 3 as a control group, no polytungstate was prepared in the preparation of the modified metal organic framework, and the other procedures were normal.
Comparative example 4
Using example 3 as a control, the modified metal organic framework was prepared without adding a polytungstate and MoO 3 The nanorods and other working procedures are normal.
Comparative example 5
Taking example 3 as a control group, the mass ratio of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethanesulfonimide ionic liquid to the modified metal organic framework is 0.1:0.08, and other working procedures are normal.
Comparative example 6
Taking example 3 as a control group, the mass ratio of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethanesulfonimide ionic liquid to the modified metal organic framework is 0.1:0.22, and other working procedures are normal.
The raw materials are as follows:
n-methylpyrrolidone M813015, 2-methylimidazole M813135, lithium hexafluorophosphate L822100, lithium difluoroborate L875429, triethylamine T818774, methyl chloroacetate M813092, ammonium molybdate tetrahydrate a915090, polyvinylpyrrolidone P816206, copper nitrate C838621, trimesic acid T819407, sodium tungstate S817652: shanghai Miclin Biochemical technologies Co., ltd; lithium sheet (0.6 mm): emerging Bei Nuote battery materials limited; lithium bis (fluorosulfonyl) imide 171611-11-3: (alpha) Henan Wei Bosch chemical industry Co., ltd; 2-bromoethyl methyl ether 6482-24-2: hubei huge science and technology limited company; hydrogen peroxide, potassium chloride, absolute ethanol, diethyl ether, acetonitrile, dichloromethane, nitric acid, methanol, phosphoric acid, analytically pure: national drug group reagent.
Performance test:
solid electrolyte ionic conductivity test: the solid electrolyte was sandwiched between two stainless steel plate electrodes and tested by an electrochemical workstation (CHI-660 e) at a temperature range of 5-60 c, a frequency range of 0.01-106Hz, and an amplitude of 5 mV: ion conductivity σ=l/(R) b S), wherein Rb is the volume resistance (Ω) and l is the thickness (cm); s is the effective contact area (cm) between the electrolyte and the stainless steel plate 2 )；
The solid electrolytes prepared in examples and comparative examples were assembled into lithium ion batteries:
firstly, preparing a lithium iron phosphate anode material: mixing 0.8g of lithium iron phosphate powder, 0.1g of conductive carbon black and 0.1g of polytetrafluoroethylene powder, grinding for 30min in a mortar, adding 10 mLN-methylpyrrolidone, and stirring for 8h to obtain slurry; coating the slurry on a pre-cleaned copper foil current collector by using a 150 mu m film coater, drying, and preparing a wafer with the thickness of 12mm for standby, wherein the wafer is used as an anode;
and (3) sequentially assembling the positive electrode shell, the positive electrode material, the solid electrolyte, the lithium sheet, the elastic sheet and the negative electrode shell, then moving to a sealing machine, applying 50MPa pressure for sealing, and using the solid electrolyte as a diaphragm in the battery and electrolyte to obtain the lithium ion battery.
The initial capacity and the capacity after 500 cycles of stable cycling of the battery were tested at 25℃and at a current density of 3C (room temperature 25 ℃):
TABLE 1
According to the invention, the inorganic ion conductor, the ionic liquid and the modified metal organic framework are introduced to construct the solid electrolyte with high ionic conductivity and high mechanical modulus, so that the service life and the multiple cycle safety of the battery can be improved when the solid electrolyte is applied to the lithium ion battery.
As can be seen from comparison of example 3 and comparative example 1, the ether-ester substituted difunctional ionic liquid is synthesized, ether and methyl are introduced on the basis of the ionic liquid to achieve the effects of viscosity reduction and capacity increase, and then the ionic conductivity and mechanical modulus of lithium ions are synergistically improved by the ionic liquid and the modified metal organic framework with multiple active sites, so that the dimensional stability of the ionic liquid can be maintained under repeated charge and discharge cycles, and the safety of a battery is improved.
As can be seen from a comparison of example 3 with comparative example 2, comparative example 3 and comparative example 4, the in situ growth method was used for MoO 3 The copper-based metal frame grows on the surface of the nano rod, then the polyoxometallate with excellent thermal and oxidation stability is introduced to improve the thermal stability of the metal frame, and the modified metal-organic frame can improve specific capacity through conversion reaction and MoO 3 The introduction of the nanorods enhances the conductivity of the material, buffering the volume expansion of the metal compound during charging and discharging. When applied to lithium ion batteries, the lithium ion batteries remarkably improve the cycle stability and the rate capability.
As can be seen from comparison of example 3 with comparative example 5 and comparative example 6, the functionalized ionic liquid prepared by the invention not only maintains the mechanical properties of the polymer, but also inherits the characteristics of high ionic conductivity, incombustibility, thermal stability and the like of the ionic liquid. However, after the ionic group is fixed on the polymer chain, the viscosity of the polyionic liquid is increased, so that the conductivity is influenced, and therefore, the concentration of carriers is increased by regulating and controlling the concentration of lithium salt; meanwhile, the modified metal organic frame with the lithium ion selection function is added, and the composite solid electrolyte with excellent performance is obtained by controlling the mass ratio of the modified metal organic frame to the functionalized ionic liquid, so that compared with the pure polyionic liquid solid electrolyte without the modified metal organic frame, the room-temperature ionic conductivity of the composite solid electrolyte is greatly improved.
The foregoing description is only a preferred embodiment of the present invention, and the present invention is not limited thereto, but it is to be understood that modifications and equivalents of some of the technical features described in the foregoing embodiments may be made by those skilled in the art, although the present invention has been described in detail with reference to the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A preparation method of electrolyte is characterized in that: the method comprises the following steps:
mixing lithium salt, 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoromethylsulfonimide ionic liquid, a modified metal organic framework and N-methylpyrrolidone, ultrasonically stirring for 8-10 hours to obtain slurry, dripping the slurry on a substrate, and heating in vacuum to obtain a solid electrolyte;
the preparation method of the modified metal organic framework comprises the following steps:
(1) Mixing nitric acid with deionized water, adding ammonium molybdate tetrahydrate, ultrasonic treating for 10-20min, transferring into a reaction kettle, maintaining at 195-200deg.C for 16-18 hr, cooling, centrifuging, washing with deionized water and ethanol for 3-5 times, and drying to obtain MoO 3 A nanorod;
(2) MoO is carried out 3 Mixing the nanorods, polyvinylpyrrolidone and methanol, performing ultrasonic dispersion for 20-30min, adding copper nitrate, stirring for 1-2h, adding a mixed solution of trimesic acid and methanol, stirring for 10-20min, adding a mixed solution of polytungstate and deionized water, stirring for 10-20min, performing centrifugal separation, and drying to obtain a modified metal organic frame;
in the preparation of the modified metal organic frameworks, the MoO 3 The mass ratio of the nanorod to the polyvinylpyrrolidone to the copper nitrate to the trimesic acid is 0.3:1:2:1.6; the benzene tricarballylThe mass ratio of formic acid to polytungstate is 8:1, a step of;
the preparation of the polytungstate comprises the following steps: mixing sodium tungstate and deionized water, adding phosphoric acid and hydrogen peroxide, heating under reflux for 1-2h, cooling, adding potassium chloride, stirring for 30-50min, filtering, cooling in ice water mixed bath, recrystallizing, filtering, and drying to obtain poly-tungstate.
2. The method for preparing an electrolyte according to claim 1, wherein: the base material is one of lithium sheets and steel sheets; the working conditions of vacuum heating are as follows: maintaining at 75-80deg.C for 10-12 hr.
3. The method for preparing an electrolyte according to claim 1, wherein: the lithium salt is one of lithium difluorooxalate borate, lithium difluorosulfimide and lithium hexafluorophosphate.
4. The method for preparing an electrolyte according to claim 1, wherein: the electrolyte comprises the following components in parts by weight: 1-3 parts of lithium salt, 0.1 part of 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bis (trifluoromethyl) sulfonyl imide ionic liquid, 0.1-0.2 part of modified metal organic framework and 5-10 parts of N-methylpyrrolidone; the mass ratio of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bistrifluoro methanesulfonimide ionic liquid to the modified metal organic framework is 0.1: (0.1-0.2).
5. The method for preparing an electrolyte according to claim 1, wherein: the preparation method of the 1-ethylmethoxy-2-methyl-3-methyl acetate imidazole bis (trifluoromethanesulfonyl) imide ionic liquid comprises the following steps:
1) Mixing 2-methylimidazole, absolute ethyl alcohol and 2-bromoethyl methyl ether, transferring into a hydrothermal kettle, preserving heat for 42-45h at 135-140 ℃, extracting with diethyl ether, adding triethylamine into the lower solution after extraction, mixing, preserving heat for 12-14h at 125-130 ℃, filtering, distilling under reduced pressure, drying to obtain 1-ethylmethyl ether-2-methylimidazole salt, adding methyl chloroacetate and acetonitrile under nitrogen atmosphere, mixing, heating to 55-60 ℃, preserving heat for 20-22h, and distilling under reduced pressure to obtain 1-methoxyethyl-2-methyl-3-3-methyl acetate methylimidazole bromide;
2) Mixing dichloromethane and 1-methoxyethyl-2-methyl-3-3-methyl acetate imidazole bromide, adding lithium bistrifluoromethylsulfonyl imide, ultrasonically stirring for 2-4 hours, filtering, washing with deionized water, filtering, decompressing, distilling, and drying to obtain 1-methoxyethyl-2-methyl-3-methyl acetate imidazole bistrifluoromethylsulfonyl imide salt.
6. The method for preparing an electrolyte according to claim 5, wherein: the molar ratio of the 2-methylimidazole to the 2-bromoethyl methyl ether to the triethylamine is 1:1:1, a step of; the molar ratio of the 1-methoxyethyl-2-methyl-3-3-methyl acetate imidazole bromide to the lithium bistrifluoromethylsulfonyl imide is 1:1.
7. use of an electrolyte prepared by the method according to any one of claims 1-6 in a lithium ion battery, characterized in that: and the prepared electrolyte is used for preparing a lithium ion battery.
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