A gel polymer electrolyte with vertically oriented pores and its preparation method and application

Abstract

The present invention belongs to the field of polymer electrolyte preparation, and discloses a gel polymer electrolyte with vertically oriented channels, a preparation method thereof, and an application thereof. The present invention adopts a freeze casting technique (ice template method) to prepare a polymer matrix with vertically oriented channels, and then sequentially modifies the interior of the oriented channels with polydopamine, silicon dioxide, and ionic liquid, and finally soaks in a liquid electrolyte to obtain a gel polymer electrolyte with vertically oriented channels. The film thickness of the polymer electrolyte is 30 microns to 300 microns, which can greatly eliminate the safety hazards caused by liquid electrolyte leakage, shorten the transmission path of ions in the battery cycle, accelerate the ion migration speed, overcome the concentration polarization phenomenon, and improve the ion conductivity and migration number. It can be widely used in lithium ion batteries, thereby improving the cycle performance of lithium metal batteries.

Description

Technical Field

[0001] The invention belongs to the field of polymer electrolyte preparation, and in particular relates to a gel polymer electrolyte with vertically oriented pores and a preparation method and application thereof. Background Art

[0002] The rapid development of electric vehicles and portable electronics has put greater pressure on the battery industry to develop high energy density and safe devices. Rechargeable solid-state batteries are at the forefront of storage devices for future applications. Lithium metal batteries have an ultra-high theoretical specific capacity (3860 mAh g -1 ) and the lowest redox potential (-3.04 V), it is considered to be an alternative to lithium-ion batteries. However, due to the high reactivity of lithium metal, traditional liquid electrolytes are prone to react with it to form an unstable solid electrolyte (SEI) layer, which produces defects on the surface of lithium metal and forms a locally concentrated lithium ion flux, which in turn causes lithium ions to deposit at the tip and form lithium dendrites. The growth of lithium dendrites can pierce the diaphragm and cause a short circuit between the positive and negative electrodes, which can easily cause safety accidents. In addition, the uncontrollable growth of lithium dendrites can also form dead lithium, resulting in increased battery interface resistance and reduced coulombic efficiency, which significantly affects the cycle performance of lithium metal batteries. Compared with liquid electrolytes used in traditional commercial rechargeable batteries, solid electrolytes have the advantages of a wide electrochemical window, no flammability or leakage risk, and good thermal stability. In addition, many reports have shown that solid electrolytes can prevent the growth of lithium or other metal dendrites, thereby achieving the "holy grail" of high energy density metal batteries. Despite the obvious advantages of solid electrolytes, limited room temperature ionic conductivity leads to low capacity utilization and poor rate performance. Solid electrolytes face other challenges, including slow ion transport at the electrode / electrolyte interface and mechanical and chemical instabilities during cycling.

[0003] Gel polymer electrolytes (GPEs) are a type of electrolyte system composed of a polymer matrix and an electrolyte. They have some properties of solids, such as a certain geometric shape, strength, elasticity and yield value, and have the advantages of high ionic conductivity of liquid electrolytes. In addition, the formation of gel polymer electrolytes can effectively solve the safety hazards caused by leakage of liquid electrolytes. However, since the polymer chains are in an irregular and curved state in the polymer electrolyte matrix, the conduction path of lithium ions in the electrolyte is disordered conduction along the polymer chains, which reduces the conduction efficiency of lithium ions and also affects the electrochemical performance of lithium batteries. On the other hand, most polymer electrolytes are dual ion conductors, and both lithium ions and anions in the electrolyte can move freely. Since the migration rate of lithium ions is smaller than that of anions, it is easy to form concentration polarization near the electrode, which hinders the conduction of lithium ions, resulting in a low lithium ion migration number (0.2~0.3) of the polymer electrolyte. A low ion migration number can reduce the cycle performance of lithium batteries, and this effect is particularly significant when charging and discharging at high current density.

[0004] Therefore, the key to developing high-performance lithium metal batteries is to rationally design and prepare gel polymer electrolyte materials with short lithium ion conduction paths, high ionic conductivity and ion migration numbers. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies of the prior art and provide a gel polymer electrolyte with vertically oriented pores and a preparation method and application thereof, which specifically adopts the following technical solutions:

[0006] According to a first aspect of the present invention, a gel polymer electrolyte with vertically oriented pores is provided, which is composed of a polymer matrix, an ionic liquid and a liquid electrolyte; the polymer matrix has an internal pore structure with vertical orientation.

[0007] The polymer electrolyte prepared by the present invention is a thin film with a thickness of 30 microns to 300 microns. The gel polymer electrolyte has vertically oriented pores inside. Compared with the prior art, on the one hand, the vertically oriented gel polymer electrolyte greatly eliminates the potential safety hazards to the battery caused by leakage of liquid electrolytes; on the other hand, the vertically oriented pores can shorten the transmission path of ions in the battery cycle and accelerate the ion migration speed. At the same time, the ionic liquid modified inside the pores can accelerate the dissociation of lithium salts in the electrolyte through electrostatic action, overcome the concentration polarization phenomenon, improve the ion conductivity and migration number, and ultimately improve the cycle performance of the lithium metal battery.

[0008] Preferably, the polymer matrix is ​​at least one of polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), and polyethylene oxide. The polymer matrix membrane is obtained by freeze casting technology (ice template method), and its internal pores are vertically oriented. With high molecular polymer as the matrix, its excellent heat resistance can significantly improve the safety performance of the electrolyte under extreme conditions, and can significantly expand the operating temperature of lithium-ion batteries.

[0009] Preferably, the ionic liquid is at least one of 1-methyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride, 1-ethyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride, and 1-propyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride. Ionic liquids are liquids at room temperature and have the characteristics of being environmentally friendly and easy to recycle. Compared with traditional organic solvents, ionic liquids generally have the following characteristics: (1) low vapor pressure and low volatility; (2) low flammability and good safety; (3) good thermal stability; (4) wide electrochemical stability window. Imidazole ionic liquids have the advantages of low viscosity and high conductivity and are the first type of ionic liquids to be valued and studied. Their combination with conventional organic electrolytes can improve the relevant properties of ionic liquid electrolytes, improve the effective transport of electrolytes, thereby improving the conductivity and migration number of electrolyte membranes, and improving the cycle performance of lithium metal batteries.

[0010] Preferably, the liquid electrolyte is composed of a lithium salt and a solvent. More preferably, the lithium salt is lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate) or lithium oxalatodifluoroborate; and the solvent is at least one of ethylene carbonate, diethyl carbonate, 1,3-pentane oxide, dimethyl carbonate, ethylene glycol dimethyl ether and propylene carbonate.

[0011] More preferably, the concentration of the liquid electrolyte is 0.1 mol L -1 -2 mol L -1 .

[0012] According to a second aspect of the present invention, there is also provided a method for preparing the above-mentioned gel polymer electrolyte, comprising the following steps:

[0013] 1) The polymer is mixed evenly with a first solvent having a mass fraction of 5 wt% to 15 wt% and heated at -150 o C-0 o C conditions; after the solution is frozen into a solid film, washing and drying are performed to obtain a polymer film with vertically oriented pores; the first solvent is at least one of N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide;

[0014] 2) placing the polymer film obtained in step 1) in an alkaline buffer solution containing dopamine hydrochloride and shaking for 24 h to 72 h to obtain a polydopamine-modified polymer film; adding the polydopamine-modified polymer film to a mixed solution of tetraethyl orthosilicate, ammonia water and ethanol at 25 o C -50 o C, react for 12 h-48 h, wash and dry to obtain a silica-modified polymer film;

[0015] 3) The silica-modified polymer membrane obtained in step 2), the ionic liquid and the second solvent were mixed uniformly and heated at 60 o C-120 o C, reacting for 12 h-100 h, washing, drying, and then mixing evenly with lithium salt to obtain an ionic liquid modified polymer membrane; the second solvent is at least one of ethanol, toluene, ether, acetone, ethyl acetate, n-pentane, and cyclohexane;

[0016] 4) placing the polymer membrane modified with the ionic liquid obtained in step 3) into a liquid electrolyte to obtain a gel polymer electrolyte with vertically oriented pores.

[0017] The present invention adopts the freezing casting technology (ice template method) to prepare a polymer matrix with vertically oriented pores, and then sequentially modifies polydopamine, silicon dioxide, and ionic liquid inside the oriented pores, and finally immerses the liquid electrolyte to prepare a gel polymer electrolyte with vertically oriented pores. At present, this method of using ionic liquid to modify the pores with vertically oriented structures to improve the electrochemical performance of gel polymer electrolytes has not been reported.

[0018] In addition, the ice template method is used to form vertical oriented channels inside the polymer matrix, which will greatly shorten the lithium ion transmission distance, reduce the obstacles to ion conduction, and effectively improve the ionic conductivity of the gel electrolyte. Grafting polydopamine and silica to the oriented channels can provide a basis for the modification of ionic liquids. The hydroxyl groups on the surface of silica can undergo condensation reactions with the ionic liquids to fix the ionic liquids in the internal channels. The surface-modified ionic liquids can accelerate the dissociation of lithium salts through interaction with lithium salt anions. At the same time, fixing the anions in the channels can effectively increase the lithium ion migration number of the electrolyte, thereby effectively improving the cycle stability of lithium-ion batteries. It can also increase the porosity and liquid absorption rate of the gel polymer electrolyte. At the same time, the liquid electrolyte can be stored in the ordered channels to reduce the risk of electrolyte leakage and improve the safety performance of lithium-ion batteries.

[0019] Preferably, the concentration of the alkaline buffer solution of dopamine hydrochloride in step 2) is 0.1 mg mL -1 -10 mg mL -1 .

[0020] Preferably, in step 2), the mass ratio of tetraethyl orthosilicate to ethanol is (10 wt%-40 wt%): (60 wt%-90 wt%).

[0021] Preferably, in step 3), the amount of ionic liquid added is 50 wt%-200 wt% of the mass of the silica-modified polymer membrane.

[0022] According to the third aspect of the present invention, there is also provided application of the above-mentioned gel polymer electrolyte having vertically oriented pores in a lithium ion battery.

[0023] The beneficial effects of the present invention are as follows: the present invention adopts the freezing casting technology (ice template method) to prepare a polymer matrix with vertically oriented pores, and then sequentially modifies polydopamine, silicon dioxide, and ionic liquid inside the oriented pores, and finally immerses the polymer electrolyte in a liquid electrolyte to obtain a gel polymer electrolyte with vertically oriented pores. The film thickness of the polymer electrolyte prepared by the present invention is 30 microns to 300 microns, which can greatly eliminate the potential safety hazards of liquid electrolytes to batteries due to leakage, and can also shorten the transmission path of ions in the battery cycle and accelerate the ion migration speed. At the same time, the ionic liquid modified inside the pores can accelerate the dissociation of lithium salts in the electrolyte through electrostatic action, overcome the concentration polarization phenomenon, and improve the ion conductivity and migration number. It can be widely used in lithium ion batteries, thereby improving the cycle performance of lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Shown is a schematic diagram of the preparation of a gel polymer electrolyte with vertically oriented pores;

[0025] Figure 2 Shown is a physical picture of a polymer film with vertically oriented pores prepared in Example 1;

[0026] Figure 3 Shown is a physical picture of the ionic liquid modified polymer membrane with vertically oriented pores prepared in Example 1;

[0027] Figure 4 Shown is a scanning electron microscope image of the ionic liquid modified polymer membrane with vertically oriented pores prepared in Example 1;

[0028] Figure 5 It is a comparison chart of the high temperature resistance experiment of the polymer membrane with vertically oriented pores in Example 1 and the commercial diaphragm;

[0029] Figure 6 The figure shows the change of ionic conductivity of the gel polymer electrolyte with vertically oriented pores in Example 1 with temperature;

[0030] Figure 7 Shown is a test graph of the ion migration number of a gel polymer electrolyte having vertically oriented pores;

[0031] Figure 8 Shown is a cycle performance test diagram of a lithium-ion battery assembled using the gel polymer electrolyte with vertically oriented pores prepared in Example 1. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments and drawings to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, scheme and effect of the present invention. It should be noted that the embodiments and features in the embodiments of this application can be combined with each other without conflict.

[0033] Example 1

[0034] A gel polymer electrolyte having vertically oriented pores, wherein the preparation method comprises the following steps (the preparation schematic diagram of the gel polymer electrolyte having vertically oriented pores is as shown in FIG. Figure 1 shown):

[0035] 1) Mix 1 g of PVDF powder with 10 g of dimethyl sulfoxide and stir to obtain a uniform solution. Pour the obtained solution onto a copper plate and place the copper plate at -150 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained. The appearance of the PVDF polymer film is as follows Figure 2 shown.

[0036] 2) The obtained polymer membrane was placed in an alkaline buffer solution (25 mL, pH = 8.5) containing 50 mg of dopamine hydrochloride, and the reaction was shaken for 72 h. The membrane was taken out and washed several times with ethanol and deionized water alternately to obtain a polydopamine-modified polymer membrane PDA@PVDF. A mixture of 60 mL of ethanol, 20 mL of water, 2 mL of ammonia water, and 12 mL of tetraethyl orthosilicate was added to a round-bottom flask and stirred. PDA@PVDF was added and stirred at 25 o The reaction was carried out at 40 °C for 48 h, and the polymer membrane after the reaction was washed with deionized water and ethanol to obtain a silica-modified polymer membrane SiO2@PVDF.

[0037] 3) Mix 0.5 g SiO2@PVDF with 1.0 g 1-methyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride and ethanol at 80 °C. oThe reaction was stirred at 40 °C for 24 h, and the polymer membrane was washed with ethanol and deionized water and dried to obtain the ionic liquid modified polymer membrane IL@PVDF. The obtained ionic liquid modified membrane was placed in a lithium bis(trifluoromethanesulfonyl)imide solution and stirred for lithiation, and then dried.

[0038] 4) Mix 5 mL of 1,3-dioxolane and ethylene glycol dimethyl ether, place in a reagent bottle, add 2.87 g of lithium bis(trifluoromethanesulfonyl imide), stir evenly to obtain a liquid electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with vertically oriented pores.

[0039] The thickness of the polymer electrolyte membrane prepared in this example is about 130 microns. Figure 3 The cross-sectional scanning electron microscope image is shown in Figure 4 As shown in the cross-sectional scanning electron micrograph, the polymer membrane has vertically oriented pores of uniform size, which can provide an orderly transmission path for the migration of lithium ions.

[0040] Example 2

[0041] A gel polymer electrolyte having vertically oriented pores, the preparation method of which comprises the following steps:

[0042] 1) Mix 1.2 g PVDF powder with 15 g N,N-dimethylformamide and stir to obtain a uniform solution. Pour the obtained solution onto a copper plate and place the copper plate at 0 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained.

[0043] 2) The obtained polymer membrane was placed in an alkaline buffer solution (25 mL, pH = 8.5) containing 2.5 mg of dopamine hydrochloride, and the reaction was shaken for 24 h. The membrane was taken out and washed alternately with ethanol and deionized water several times to obtain a polydopamine-modified polymer membrane PDA@PVDF. A mixture of 30 mL of ethanol, 20 mL of water, 2 mL of ammonia water, and 12 mL of tetraethyl orthosilicate was added to a round-bottom flask and stirred. PDA@PVDF was added and stirred at 40 o The reaction was carried out at 40 °C for 12 h, and the polymer membrane after the reaction was washed with deionized water and ethanol to obtain a silica-modified polymer membrane SiO2@PVDF.

[0044] 3) Mix 0.5 g SiO2@PVDF, 0.5 g 1-ethyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride and ethanol at 60 °C. oThe reaction was stirred at 40 °C for 120 h, and the polymer membrane was washed with ethanol and deionized water and dried to obtain an ionic liquid-modified polymer membrane IL@PVDF. The obtained ionic liquid-modified membrane was placed in a lithium hexafluorophosphate solution and stirred for lithiation, and then dried.

[0045] 4) Mix 5 mL of dimethyl carbonate and ethylene carbonate, place in a reagent bottle, add 1.52 g of lithium hexafluorophosphate, stir evenly to obtain a liquid electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with vertically oriented pores.

[0046] The thickness of the polymer electrolyte membrane prepared in this example is about 250 microns.

[0047] Example 3

[0048] A gel polymer electrolyte having vertically oriented pores, the preparation method of which comprises the following steps:

[0049] 1) Mix 2 g of PEO powder with 20 g of dimethyl sulfoxide and stir to obtain a uniform solution. Pour the obtained solution onto a copper plate and place the copper plate at -100 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained.

[0050] 2) The obtained polymer film was placed in an alkaline buffer solution (25 mL, pH = 8.5) containing 100 mg dopamine hydrochloride, and the reaction was shaken for 48 h. The film was taken out and washed alternately with ethanol and deionized water several times to obtain a polydopamine-modified polymer film PDA@PEO. A mixture of 90 mL ethanol, 20 mL water, 2 mL ammonia water, and 12 mL tetraethyl orthosilicate was added to a round-bottom flask and stirred. PDA@PEO was added and stirred at 30 o The reaction was carried out at 40 °C for 36 h, and the polymer membrane after the reaction was washed with deionized water and ethanol to obtain a silica-modified polymer membrane SiO2@PEO.

[0051] 3) Mix 1.0 g SiO2@PEO with 0.5 g 1-methyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride and ethanol at 120 °C. o The reaction was stirred at 40 °C for 12 h, and the polymer membrane was washed with ethanol and deionized water and dried to obtain the ionic liquid modified polymer membrane IL@PEO. The obtained ionic liquid modified membrane was placed in a bis(trifluoromethanesulfonyl)imide lithium salt aqueous solution and stirred for lithiation, and then dried.

[0052] 4) Mix 5 mL of 1,3-dioxolane and ethylene glycol dimethyl ether, place in a reagent bottle, add 5.74 g of lithium bis(trifluoromethylsulfonyl)imide, stir evenly to obtain a liquid electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with vertically oriented pores.

[0053] The thickness of the polymer electrolyte membrane prepared in this example is about 100 microns.

[0054] Example 4

[0055] A gel polymer electrolyte having vertically oriented pores, the preparation method of which comprises the following steps:

[0056] 1) Mix 0.6 g PVDF-HFP powder with 10 g dimethyl sulfoxide and stir to obtain a uniform solution. Pour the obtained solution onto a copper plate and place the copper plate at -100 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained.

[0057] 2) The obtained polymer membrane was placed in an alkaline buffer solution (25 mL, pH = 8.5) containing 120 mg of dopamine hydrochloride, and the reaction was shaken for 40 h. The membrane was taken out and washed alternately with ethanol and deionized water several times to obtain a polydopamine-modified polymer membrane PDA@PVDF-HFP. A mixture of 120 mL of ethanol, 20 mL of water, 2 mL of ammonia water, and 12 mL of tetraethyl orthosilicate was added to a round-bottom flask and stirred. PDA@PVDF-HFP was added and stirred at 40 o The reaction was carried out at 40 °C for 48 h, and the polymer membrane after the reaction was washed with deionized water and ethanol to obtain a silica-modified polymer membrane SiO2@PVDF-HFP.

[0058] 3) Mix 1.0 g SiO2@PVDF-HFP with 1.5 g 1-propyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride and ethanol at 50 °C. o The reaction was stirred at 40 °C for 30 h, and the polymer membrane was washed with ethanol and deionized water and dried to obtain the ionic liquid modified polymer membrane IL@PVDF-HFP. The obtained ionic liquid modified membrane was placed in a lithium hexafluorophosphate solution and stirred for lithiation, and then dried.

[0059] 4) Mix 5 mL of dimethyl carbonate and ethylene carbonate, place in a reagent bottle, add 1.52 g of lithium hexafluorophosphate, stir evenly, and obtain a lithium-containing electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with vertically oriented pores.

[0060] The thickness of the polymer electrolyte membrane prepared in this example is about 30 microns.

[0061] Example 5

[0062] A gel polymer electrolyte having vertically oriented pores, the preparation method of which comprises the following steps:

[0063] 1) Mix 1.4 g of PEO powder with 20 g of N,N-dimethylformamide and stir to obtain a uniform solution. Pour the obtained solution onto a copper plate and place the copper plate at -120 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained.

[0064] 2) The obtained polymer film was placed in an alkaline buffer solution (25 mL, pH = 8.5) containing 200 mg dopamine hydrochloride, and the reaction was shaken for 36 h. The film was taken out and washed alternately with ethanol and deionized water several times to obtain a polydopamine-modified polymer film PDA@PEO. A mixture of 90 mL ethanol, 20 mL water, 2 mL ammonia water, and 12 mL tetraethyl orthosilicate was added to a round-bottom flask and stirred. PDA@PEO was added and stirred at 50 o The reaction was carried out at 40 °C for 36 h, and the polymer membrane after the reaction was washed with deionized water and ethanol to obtain a silica-modified polymer membrane SiO2@PEO.

[0065] 3) Mix 0.5 g SiO2@PVDF-HFP with 0.25 g 1-ethyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride and ethanol at 65 °C. o The reaction was stirred at 40 °C for 36 h, and the polymer membrane was washed with ethanol and deionized water and dried to obtain the ionic liquid modified polymer membrane IL@PVDF-HFP. The obtained ionic liquid modified membrane was placed in a lithium bis(oxalatoborate) solution and stirred for lithiation, and then dried.

[0066] 4) Take 5 mL of ethylene carbonate and diethyl carbonate, mix them, put them in a reagent bottle, add 2.56 g of lithium bis(oxalatoborate), stir evenly, and obtain a liquid electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with vertically oriented pores.

[0067] The thickness of the polymer electrolyte membrane prepared in this example is about 250 microns.

[0068] Example 6

[0069] A gel polymer electrolyte having vertically oriented pores, the preparation method of which comprises the following steps:

[0070] 1) Mix 0.8 g PVDF powder and 10 g N-methylpyrrolidone and stir to obtain a uniform solution. Pour the obtained solution onto a copper plate and place the copper plate at -50 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained.

[0071] 2) The obtained polymer membrane was placed in an alkaline buffer solution (25 mL, pH = 8.5) containing 200 mg dopamine hydrochloride, and the reaction was shaken for 72 h. The membrane was taken out and washed alternately with ethanol and deionized water several times to obtain a polydopamine-modified polymer membrane PDA@PVDF. A mixture of 60 mL ethanol, 20 mL water, 2 mL ammonia water, and 12 mL tetraethyl orthosilicate was added to a round-bottom flask and stirred. PDA@PVDF was added and stirred at 40 o C for 24 h, and the polymer membrane after the reaction was washed with deionized water and ethanol to obtain a silica-modified polymer membrane SiO2@PVDF.

[0072] 3) Mix 2.0 g SiO2@PVDF, 2.0 g 1-methyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride and ethanol at 65 °C. o The reaction was stirred at 40 °C for 50 h, and the polymer membrane was washed with ethanol and deionized water and dried to obtain an ionic liquid-modified polymer membrane IL@PVDF. The obtained ionic liquid-modified membrane was placed in a lithium bis(oxalatoborate) solution and stirred for lithiation, and then dried.

[0073] 4) Mix 5 mL of 1,3-dioxolane and ethylene glycol dimethyl ether, place in a reagent bottle, add 3.84 g of lithium dioxalate borate, stir evenly, and obtain a liquid electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with vertically oriented pores. The thickness of the polymer electrolyte membrane prepared in this example is about 200 microns.

[0074] Example 7

[0075] A gel polymer electrolyte having vertically oriented pores, the preparation method of which comprises the following steps:

[0076] 1) Mix 3 g of PVDF-HFP powder with 20 g of dimethyl sulfoxide and stir to obtain a uniform solution. Pour the obtained solution dropwise onto a copper plate and place the copper plate at -10 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained.

[0077] 2) The obtained polymer membrane was placed in an alkaline buffer solution (25 mL, pH = 8.5) containing 250 mg of dopamine hydrochloride, and the reaction was shaken for 48 h. The membrane was taken out and washed alternately with ethanol and deionized water several times to obtain a polydopamine-modified polymer membrane PVDF-HFP. A mixture of 90 mL of ethanol, 20 mL of water, 2 mL of ammonia water, and 12 mL of tetraethyl orthosilicate was added to a round-bottom flask and stirred. PDA@PVDF-HFP was added and stirred at 25 o The reaction was carried out at 40 °C for 48 h, and the polymer membrane after the reaction was washed with deionized water and ethanol to obtain a silica-modified polymer membrane SiO2@PVDF-HFP.

[0078] 3) Mix 0.5 g SiO2@PVDF with 1.0 g 1-ethyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride and ethanol at 80 °C. o The reaction was stirred at 40 °C for 36 h, and the polymer membrane was washed with ethanol and deionized water and dried to obtain the ionic liquid modified polymer membrane IL@PVDF-HFP. The obtained ionic liquid modified membrane was placed in a lithium oxalate difluoroborate solution and stirred for lithiation, and then dried.

[0079] 4) Mix 5 mL of ethylene carbonate and diethyl carbonate, place in a reagent bottle, add 2.87 g of lithium oxalate difluoroborate, stir evenly, and obtain a liquid electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with vertically oriented pores, and the membrane thickness is about 100 microns.

[0080] Example 8

[0081] In this embodiment, the prepared polymer electrolyte is subjected to a high temperature resistance test, a conductivity variation test with temperature, and an ion migration number test. High temperature resistance test: mainly evaluates the high temperature resistance by observing the shrinkage of the membrane at an increased temperature; conductivity variation test with temperature: ion conductivity is tested by assembling SS|electrolyte membrane|SS battery; ion migration number test: ion migration number is tested by assembling Li|electrolyte membrane|Li battery.

[0082] like Figure 5 (The first row from left to right is 30 o C. 50 o C. 80 o C, the second row from left to right is 110 o C. 150 o C. 200 o C) shows that the prepared IL@PVDF membrane o C still maintains its original shape. Compared with IL@PVDF membrane, commercial separatorso C begins to shrink at 200 o C, which indicates that the polymer film prepared by this method has good thermal stability.

[0083] like Figure 6 As shown in the graph of the conductivity of the obtained polymer electrolyte changing with temperature, its ionic conductivity at room temperature can reach 3.8 × 10 -3 S cm -1 In comparison, the conductivity of the gel polymer electrolyte without pores and the one without pore modification at room temperature is 3.3 × 10 -4 S cm -1 and 3.1 × 10 -3 S cm -1 (See Example 1 and Comparative Example 2), indicating that the ionic liquid-modified gel polymer electrolyte with vertically oriented pores has higher ionic conductivity. Figure 7 This is the ion migration number test graph of the gel polymer electrolyte prepared in this embodiment. The migration number of IL@GPE is 0.72 calculated by it graph and AC impedance, which is significantly higher than the ion migration number of ordinary dual-ion electrolytes (generally less than 0.3). This is mainly due to the fact that the modified ionic liquid can fix the lithium salt anions through interaction, thereby increasing the ion migration number of the electrolyte. A higher ion migration number helps to weaken the concentration polarization effect and improve the cycle performance of lithium-ion batteries.

[0084] Example 9

[0085] This example tests the cycle performance of a lithium-ion battery assembled with the polymer electrolyte prepared in Example 1.

[0086] The gel polymer electrolyte prepared in Example 1 was assembled into a Li|IL@GPE|LFP lithium metal battery for charge and discharge tests. It was found that after 200 cycles at 0.5 C, the discharge capacity retention rate of the battery was still 99.37% ( Figure 8 ), indicating that the lithium metal battery assembled with the gel polymer electrolyte has excellent cycling performance.

[0087] Comparative Example 1

[0088] A non-porous gel polymer electrolyte, the preparation method of which comprises the following steps (compared with Example 1, the non-porous gel polymer electrolyte is prepared by changing the experimental steps and conditions):

[0089] 1) Mix 1 g of PVDF powder with 10 g of dimethyl sulfoxide and stir to obtain a uniform solution. Add the solution dropwise onto the glass and place it at 100 o C oven for 24 h to obtain a pore-free polymer membrane.

[0090] 2) Mix 5 mL of 1,3-dioxolane and ethylene glycol dimethyl ether, place in a reagent bottle, add 2.87 g of lithium bis(trifluoromethanesulfonyl)imide, stir evenly, and obtain a liquid electrolyte. Soak the non-porous polymer membrane in the electrolyte to obtain a non-porous gel polymer electrolyte.

[0091] Comparative Example 2

[0092] A gel polymer electrolyte with unmodified pores, the preparation method of which comprises the following steps (compared with Example 1, the gel polymer electrolyte with unmodified pores is prepared by changing the experimental steps and conditions):

[0093] 1) Mix 1 g of PVDF powder with 10 g of dimethyl sulfoxide and stir to obtain a uniform solution. Pour the obtained solution onto a copper plate and place the copper plate at -150 o After the solution is frozen into a solid film on the copper plate, the film is transferred to ice ethanol to extract the solvent, and after drying, a polymer film with vertically oriented pores is obtained.

[0094] 2) Mix 5 mL of 1,3-dioxolane and ethylene glycol dimethyl ether, place in a reagent bottle, add 2.87 g of lithium bis(trifluoromethanesulfonyl)imide, stir evenly to obtain a liquid electrolyte. Soak the polymer membrane in the electrolyte to obtain a gel polymer electrolyte with unmodified pores.

[0095] In summary, the electrochemical and mechanical properties of the gel polymer electrolyte prepared in the present invention are greatly improved, and it has a high ion migration number, electrical conductivity, and thermal stability, which can provide a new method for preparing a new gel polymer electrolyte.

[0096] The above is only a preferred embodiment of the present invention. The present invention is not limited to the above implementation. As long as the technical effect of the present invention is achieved by the same means, it should belong to the protection scope of the present invention. Within the protection scope of the present invention, its technical scheme and / or implementation method can have various modifications and changes.

Claims

1. A gel polymer electrolyte having vertically oriented pores, characterized in that: The gel polymer electrolyte is composed of a polymer matrix, an ionic liquid and a liquid electrolyte; The polymer matrix is ​​at least one of polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), and polyethylene oxide. The polymer matrix is ​​formed into a polymer matrix membrane by an ice template method. The polymer matrix membrane has an internal pore vertically oriented structure, and the oriented pores are sequentially modified with polydopamine, silicon dioxide, and ionic liquid; The ionic liquid is at least one of 1-methyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride, 1-ethyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride, and 1-propyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride; The liquid electrolyte consists of a lithium salt and a solvent; The preparation method comprises the following steps: 1) uniformly mixing a polymer with a first solvent having a mass fraction of 5 wt%-15 wt%, and freezing the mixture at -150°C-0°C; after the solution is frozen into a solid film, washing and drying the mixture to obtain a polymer film having vertically oriented pores; the first solvent is at least one of N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide; 2) placing the polymer film obtained in step 1) in an alkaline buffer solution containing dopamine hydrochloride, shaking for 24 h-72 h to obtain a polydopamine-modified polymer film; adding the polydopamine-modified polymer film to a mixed solution of tetraethyl orthosilicate, ammonia water, and ethanol, reacting at 25° C.-50° C. for 12 h-48 h, washing, and drying to obtain a silica-modified polymer film; 3) the silica-modified polymer membrane obtained in step 2), the ionic liquid and the second solvent are mixed uniformly, reacted at 60°C-120°C for 12 h-100 h, washed and dried, and then mixed uniformly with lithium salt to obtain an ionic liquid-modified polymer membrane; the second solvent is at least one of ethanol, toluene, ether, acetone, ethyl acetate, n-pentane and cyclohexane; 4) placing the polymer membrane modified with the ionic liquid obtained in step 3) into a liquid electrolyte to obtain a gel polymer electrolyte with vertically oriented pores.

2. The gel polymer electrolyte according to claim 1, characterized in that The concentration of the liquid electrolyte is 0.1 mol L -1 -2 mol L -1 .

3. The gel polymer electrolyte according to claim 1, characterized in that The concentration of the dopamine hydrochloride alkaline buffer solution in step 2) is 0.1 mg mL -1 -10 mg mL -1 .

4. The gel polymer electrolyte according to claim 1, characterized in that: In step 2), the mass ratio of the tetraethyl orthosilicate to the ethanol is (10 wt%-40 wt%): (60 wt%-90 wt%).

5. The gel polymer electrolyte according to claim 1, characterized in that: In step 3), the amount of the ionic liquid added is 50 wt%-200 wt% of the mass of the silica-modified polymer membrane.

6. Use of the gel polymer electrolyte with vertically oriented pores as claimed in claim 1 in lithium ion batteries.

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