Difunctional polymer electrolyte membrane and preparation method and application thereof

Abstract

The invention belongs to the technical field of new energy batteries, and particularly relates to a difunctional polymer electrolyte membrane as well as a preparation method and application thereof.According to the preparation method, a polymer electrolyte membrane containing a plasticizer is prepared through combination of a non-solvent induced phase separation method and a photocuring method, and in the presence of the plasticizer, the polymer electrolyte membrane containing the plasticizer can be prepared into the difunctional polymer electrolyte membrane. The characteristics of two different functional polymers are combined, and a porous structure and a macromolecular cross-linked structure are produced through preparation, so that the electrolyte membrane has relatively high ionic conductivity and mechanical property, and the cycle performance and dendritic crystal resistance of a solid-state battery can be improved after the electrolyte membrane is applied to the solid-state battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and in particular relates to a bifunctional polymer electrolyte membrane and a preparation method and application thereof. Background Art

[0002] Compared with traditional liquid electrolyte batteries, the advantages of solid-state batteries are higher energy density, better safety performance and longer service life. Solid-state batteries generally use solid electrolytes instead of carbonate liquid electrolytes. Solid electrolytes can be divided into polymer electrolytes and inorganic electrolytes. Inorganic electrolytes have poor processing performance and difficult production processes due to their own properties. Polymer electrolytes have been widely studied due to their excellent processing performance, but their low ionic conductivity at room temperature limits their practical application. Usually, some studies will add some liquids or plasticizers during the preparation of polymer electrolyte membranes, which can improve the ionic conductivity of the electrolyte membrane. However, the added ingredients will reduce the content of polymer in the system, resulting in poor mechanical properties of the electrolyte membrane and cannot be used in practice. Therefore, how to prepare polymer electrolyte membranes with both high ionic conductivity and good mechanical properties has become a difficult research point.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] To address the shortcomings and drawbacks of existing technologies, the present invention provides a bifunctional polymer electrolyte membrane, its preparation method, and its application. By combining two polymers with different functions using non-solvent-induced phase separation (NIPS) and ultraviolet (UV) curing, the performance of the electrolyte membrane is improved, resulting in both high ionic conductivity and good mechanical properties.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, a method for preparing a bifunctional polymer electrolyte membrane is characterized by comprising the following steps:

[0007] S1: adding a first polymer, a lithium salt, and a plasticizer to a first solvent, and stirring at high speed to fully dissolve the first polymer and the lithium salt to obtain a mixed solution;

[0008] S2: adding the second polymer monomer and the photoinitiator to the mixed solution and stirring evenly to obtain a polymer electrolyte precursor solution;

[0009] S3: applying a knife to the polymer electrolyte precursor solution to form a film to obtain a first wet film;

[0010] S4: subjecting the first wet film to a UV cross-linking treatment to obtain a second wet film;

[0011] S5: immersing the second wet film in a second solvent and performing a coagulation bath treatment to obtain a third wet film;

[0012] S6: Drying the third wet membrane to obtain a bifunctional polymer electrolyte membrane.

[0013] Furthermore, 2. the first polymer includes one or at least two of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, polyacrylonitrile, and polyacrylate;

[0014] And / or, the lithium salt includes one or at least two of lithium bis(trifluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, and lithium dioxalatoborate;

[0015] And / or, the plasticizer is one or at least two of imidazole ionic liquid, piperidine ionic liquid, pyrrole ionic liquid, and pyridine ionic liquid;

[0016] and / or, the first solvent is one or at least two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone;

[0017] And / or, the second polymer monomer includes one or at least two of polyacrylate monomers and polyether monomers;

[0018] And / or, the photoinitiator includes one or at least two of an acylphosphine oxide photoinitiator, a thioxanthone photoinitiator, and a diketone photoinitiator;

[0019] And / or, the second solvent comprises a mixture of one or more of deionized water, ethanol, and tetrachloromethane;

[0020] and / or, the weight ratio of the first polymer, lithium salt, plasticizer, first solvent, second polymer monomer, and photoinitiator is 5-15:1.5-4.5:3-9:40-80:2-6:0.02-0.3;

[0021] And / or, the carrier for the blade coating film is a polytetrafluoroethylene plate, a glass plate or a PET plate.

[0022] Furthermore, the molecular weight of the second polymer monomer is 200-1000.

[0023] Furthermore, in step S4, the wavelength of the ultraviolet cross-linking treatment is 365 nm; and / or the time of the ultraviolet cross-linking treatment is T1, 5 min < T1 < 60 min.

[0024] Furthermore, in step S5, the time of the coagulation bath treatment is T2, 0min<T2<30min.

[0025] Furthermore, in step S6, the drying temperature is 60-100°C; and / or the drying time is T3, 8h<T3<24h.

[0026] Furthermore, the bifunctional polymer electrolyte membrane has a thickness of 5 to 100 μm.

[0027] In a second aspect, a bifunctional polymer electrolyte membrane is prepared by the preparation method described in the first aspect.

[0028] Furthermore, the bifunctional polymer electrolyte membrane has a porous structure and an ionic conductivity greater than 10 at room temperature. -4 S / cm, while tensile strength>6MPa.

[0029] In a third aspect, a solid-state battery comprises the bifunctional polymer electrolyte membrane prepared by the preparation method of the first aspect or the bifunctional polymer electrolyte membrane of the second aspect.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] 1. The preparation method of the present invention combines a non-solvent-induced phase separation method with a photocuring method to prepare a polymer electrolyte membrane (electrolyte membrane) containing a plasticizer. In the presence of a plasticizer, the characteristics of two different functional polymers are combined to produce a porous structure and a high molecular cross-linked structure, thereby achieving an electrolyte membrane with high ionic conductivity and mechanical properties. When used in solid-state batteries, it can improve the cycling performance and anti-dendrite ability of solid-state batteries.

[0032] Specifically, during the preparation of the electrolyte membrane, the present invention directly adds a plasticizer to the first polymer, which is then directly mixed with the second polymer monomer. Using a photocuring method, the second polymer monomer polymerizes from small molecules to form a high-molecular cross-linked structure, which improves the mechanical properties of the electrolyte membrane. Furthermore, the second polymer monomer interacts with the first polymer and lithium salt, further enhancing the lithium ion transport rate and tensile strength of the electrolyte membrane. Subsequently, a coagulation bath treatment is performed at room temperature to form a porous structure on the surface and inside the polymer electrolyte membrane, which improves the lithium ion transport performance of the electrolyte membrane.

[0033] 2. The preparation method of the present invention further varies the porous structure formed on the surface and inside of the polymer electrolyte membrane by varying the coagulation bath treatment time, ultimately affecting the mechanical properties and lithium ion transport of the electrolyte membrane. Controlling the coagulation bath treatment time to less than 30 minutes not only ensures the mechanical properties of the electrolyte membrane but also facilitates lithium ion transport.

[0034] 3. The polymer electrolyte membrane of the present invention contains a plasticizer (liquid) with high ionic conductivity and good mechanical properties. The ionic conductivity at room temperature can be greater than 10 -4 S / cm, and the tensile strength is greater than 6MPa, the cycle performance is excellent, the lithium symmetric battery has a long cycle number, and has a certain anti-dendrite effect.

[0035] In addition, the polymer electrolyte membrane of the present invention can replace the diaphragm and electrolyte, simplifying the assembly process of the battery. The preparation process is relatively short and can be adapted to current production equipment, and is expected to be mass-produced on a large scale. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0037] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0038] In a first aspect, the present invention provides a method for preparing a bifunctional polymer electrolyte membrane, comprising the following steps:

[0039] S1: adding a first polymer, a lithium salt, and a plasticizer to a first solvent, and stirring at high speed to fully dissolve the first polymer and the lithium salt to obtain a mixed solution;

[0040] S2: adding the second polymer monomer and the photoinitiator to the mixed solution obtained above, stirring evenly to obtain a polymer electrolyte precursor solution;

[0041] S3: Scaling the polymer electrolyte precursor solution into a film to obtain a first wet film;

[0042] S4: After the first wet film is placed at room temperature for a certain period of time, it is subjected to UV cross-linking treatment for a time period of T1 to obtain a second wet film;

[0043] S5: immersing the second wet film in a second solvent and performing a coagulation bath treatment for a time period of T2 to obtain a third wet film;

[0044] S6: Drying the third wet film for a time period of T3 to finally obtain a bifunctional polymer electrolyte membrane.

[0045] The preparation method of the present invention combines a non-solvent-induced phase separation method with a photocuring method to produce a polymer electrolyte membrane (electrolyte membrane) containing a plasticizer. In the presence of the plasticizer, the characteristics of two different functional polymers are combined to produce a porous structure and a high-molecular cross-linked structure, achieving an electrolyte membrane with both high ionic conductivity and mechanical properties. When used in solid-state batteries, it can improve the cycling performance and anti-dendrite ability of solid-state batteries.

[0046] Specifically, during the preparation of the electrolyte membrane, the present invention directly adds a plasticizer to the first polymer, which is then directly mixed with another polymer monomer (a second polymer monomer). The second polymer monomer is polymerized from small molecules to form a high-molecular cross-linked structure through photocuring, which improves the mechanical properties of the electrolyte membrane. Furthermore, the second polymer monomer interacts with the other polymer (the first polymer) and the lithium salt, which further enhances the lithium ion transport rate and tensile strength of the electrolyte membrane. Subsequently, a coagulation bath treatment is performed to replace and remove the first solvent with the second solvent at room temperature, thereby forming a porous structure on the surface and inside the polymer electrolyte membrane, which can promote the lithium ion transport performance of the electrolyte membrane. Furthermore, unlike drying pore formation (in which the solvent or pore-forming agent evaporates), the coagulation bath treatment easily forms gradient pores or finger-shaped pores and more easily improves air permeability.

[0047] The electrolyte membrane prepared by the method of the present invention can have an ion conductivity greater than 10 at room temperature. -4 S / cm, and the tensile strength is greater than 6MPa, the cycle performance is excellent, the lithium symmetric battery has a long cycle number, and has a certain anti-dendrite effect.

[0048] In addition, the electrolyte membrane prepared by the present invention can replace the diaphragm and electrolyte, simplifying the assembly process of the battery. The preparation process is relatively short and can be adapted to current production equipment, and is expected to be mass-produced on a large scale.

[0049] As an optional embodiment of the preparation method of the present invention, the first polymer includes one or at least two of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), polyacrylonitrile (PAN), and polyacrylate (PMMA).

[0050] As an optional embodiment of the preparation method of the present invention, the lithium salt includes one or at least two of lithium bistrifluorosulfonyl imide (LiTFSI), lithium bisfluorosulfonyl imide (LiFSI), lithium difluorooxalatoborate (LiDFOB), and lithium dioxalatoborate (LiBOB); and / or the plasticizer is one or at least two of imidazole ionic liquids, piperidine ionic liquids, pyrrole ionic liquids, and pyridine ionic liquids; and / or the first solvent is one or at least two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone.

[0051] In the present invention, the plasticizer can be selected from existing ones according to the above-mentioned range. For example, the imidazole ionic liquid can be selected from: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) and the like; the piperidine ionic liquid can be selected from: N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide salt (PP13TFSI) and the like; the pyrrole ionic liquid can be selected from: N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt (BMPTF2N) and the like; the pyridine ionic liquid can be selected from: N-butylpyridine trifluoromethanesulfonyl salt (BuPyPF6) and the like.

[0052] The plasticizer used in the present invention is relatively stable and will not react chemically with the solvent. The plasticizer itself has good thermal stability and a decomposition temperature above 300°C. Therefore, the dry content will not change at a certain temperature, which does not affect the improvement of the ionic conductivity of the electrolyte membrane.

[0053] As an optional embodiment of the preparation method of the present invention, the second polymer monomer includes one or at least two of a polyacrylate monomer and a polyether monomer. Furthermore, the preferred molecular weight of the monomer is 200 to 1000, typically but not limited to 250, 300, 400, 500, 600, 700, 800, 900, 950, etc.; and / or, the photoinitiator is one or at least two of an acylphosphine oxide photoinitiator, a thioxanthone photoinitiator, and a diketone photoinitiator.

[0054] In the present invention, the second polymer monomer can be selected from existing monomers within the aforementioned range. For example, polyacrylate monomers include polyethylene glycol diacrylate (PEGDA), pentaerythritol triacrylate (PETA), and trimethylolpropane triacrylate (TMPTA); polyether monomers include polyethylene glycol monomethyl ether and allyl polyoxyethylene ether. The preferred molecular weight of the monomer is 200 to 1000 because a higher molecular weight increases the viscosity, which increases the viscosity of the first wet film, hindering subsequent pore formation in the coagulation bath and affecting the pore formation rate and the formation of the membrane's porous structure.

[0055] For the photoinitiator, the aforementioned types can be selected. Specifically, the acylphosphine oxide type photoinitiator can be selected from: 2,4,6-trimethylbenzamide-diphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; the thioxanthone type photoinitiator can be selected from: isopropylthioxanthone, etc.; the diketone type photoinitiator can be selected from: benzophenone, etc.

[0056] As an optional embodiment of the preparation method of the present invention, in step S4, the wavelength of the ultraviolet cross-linking treatment is 365 nm, and / or 5 min<T1<60 min.

[0057] In the above technical solution, photocuring is used to crosslink small polymer monomers into a high-molecular structure. This structure interacts with another polymer and lithium salt, which helps improve the lithium ion transfer rate and the tensile strength of the electrolyte membrane. Typical, but not limiting, options for T1 include 6 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 55 minutes.

[0058] As an optional embodiment of the preparation method of the present invention, the second solvent includes a mixture of one or more of deionized water, ethanol, and tetrachloromethane.

[0059] As an optional embodiment of the preparation method of the present invention, in step S5, 0 min<T2<30 min.

[0060] In the above technical solution, different coagulation bath treatment times result in different porous structures formed on the surface and inside of the polymer electrolyte membrane. The optimal coagulation bath treatment time is less than 30 minutes, which can not only ensure the mechanical properties of the electrolyte membrane, but also facilitate lithium ion transmission. Generally, the coagulation bath treatment time will not exceed 10 minutes to avoid the possibility that more lithium salts will dissolve in the second solvent during the coagulation bath process, resulting in a decrease in the ionic conductivity and electrochemical performance of the subsequently formed electrolyte membrane. T2 can typically but not limitatively be selected from 5s, 10s, 0.5min, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, 15min, 20min, 25min, etc.

[0061] As an optional embodiment of the preparation method of the present invention, in step S6, the drying temperature of the oven is 60-100°C (such as 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, etc.), and / or 8h<T3<24h, and T3 can typically but not limitatively be 9h, 11h, 13h, 15h, 17h, 19h, 21h, 23h, etc.

[0062] As an optional embodiment of the preparation method of the present invention, the thickness of the bifunctional polymer electrolyte membrane is 5 to 100 μm (such as 6 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 95 μm, etc.).

[0063] As an optional embodiment of the preparation method of the present invention, the weight ratio of the first polymer, lithium salt, plasticizer, first solvent, second polymer monomer, and photoinitiator is 5-15:1.5-4.5:3-9:40-80:2-6:0.02-0.3;

[0064] And / or, the carrier for the blade coating film is a polytetrafluoroethylene plate, a glass plate or a PET plate.

[0065] In the above technical solution, the weight ratio of the first polymer, lithium salt, plasticizer, first solvent, second polymer monomer, and photoinitiator is controlled to be 5-15:1.5-4.5:3-9:40-80:2-6:0.02-0.3, that is, under the same weight ratio, the weight ratio of the first polymer is controlled to be 5-15, typically but not limited to 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, etc.; the weight ratio of the lithium salt is controlled to be 1.5-4.5, typically but not limited to 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9, 3.1, 3.3, 3.5, 3.7, 3.9, 4.1, 4.3, 4.5, etc.; the weight ratio of the plasticizer is controlled to be 3-9, typically but not limited to 3, 3.5, 4 , 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, etc.; the mass parts of the first solvent are controlled to be 40 to 80, typically but not limited to 40, 45, 50, 55, 60, 65, 70, 75, 80, etc.; the mass parts of the second polymer monomer are controlled to be 2 to 6, typically but not limited to 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, etc.; the mass fraction of the photoinitiator is controlled to be 0.02-0.3, typically but not limited to 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, etc.

[0066] In a second aspect, a bifunctional polymer electrolyte membrane is prepared using the above-mentioned preparation method.

[0067] In a third aspect, a solid-state battery comprises the above-mentioned bifunctional polymer electrolyte membrane.

[0068] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are intended to illustrate the present invention only and should not be construed as limiting the scope of the present invention. If specific conditions are not specified in the examples, conventional conditions were used. Reagents or instruments used without manufacturer's indication are conventional products that can be purchased through normal channels.

[0069] Example 1

[0070] A polymer electrolyte membrane, the preparation method of which comprises the following steps:

[0071] S1: 10 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, molecular weight 455000) was added to 50 g of the first solvent N-methylpyrrolidone and stirred for more than 12 h to fully dissolve the polymer. Then, 3 g of lithium salt LiTFSI and 6 g of imidazole ionic liquid EMIMTFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) purchased from Shanghai Chengjie Chemical Co., Ltd., product number LM1024) were added and magnetically stirred to obtain a mixed solution;

[0072] S2: 4 g of polyethylene glycol diacrylate (PEGDA, molecular weight 600) and 80 mg of photoinitiator 2,4,6-trimethylbenzamide-diphenylphosphine oxide (TPO) were added to the above mixed solution and stirred to obtain a polymer electrolyte precursor solution;

[0073] S3: Apply the polymer electrolyte precursor solution to the glass plate with a four-sided coating applicator at a coating height of 100 μm to obtain a first wet film;

[0074] S4: The first wet film is placed at room temperature for 12 hours, and then cross-linked with an ultraviolet lamp with a wavelength of 365 nm for 10 minutes to obtain a second wet film;

[0075] S5: Soak the glass plate containing the second wet film in deionized water for a coagulation bath treatment for 1 minute. Use dust-free paper to absorb excess deionized water around the glass plate to obtain a third wet film.

[0076] S6: The third wet film was placed in an oven at 80° C. and dried for 18 h to finally obtain a bifunctional polymer electrolyte membrane with a thickness of about 30 μm.

[0077] Example 2

[0078] This embodiment is basically the same as embodiment 1, with the only difference being:

[0079] In S5, a coagulation bath treatment is performed for 3 minutes.

[0080] Example 3

[0081] This embodiment is basically the same as embodiment 1, with the only difference being:

[0082] In S5, a coagulation bath treatment is performed for 5 minutes.

[0083] Example 4

[0084] This embodiment is basically the same as embodiment 1, with the only difference being:

[0085] In S5, a coagulation bath treatment is performed for 8 minutes.

[0086] Example 5

[0087] This embodiment is basically the same as embodiment 1, with the only difference being:

[0088] In S5, a coagulation bath treatment is performed for 10 minutes.

[0089] Example 6

[0090] This embodiment is basically the same as embodiment 3, with the only difference being:

[0091] In S2, PEGDA was replaced with pentaerythritol triacrylate (PETA, molecular weight 298).

[0092] Example 7

[0093] This embodiment is basically the same as embodiment 1, with the only difference being:

[0094] The lithium salt LiTFSI in S1 was replaced with LiFSI, and the imidazole ionic liquid EMIMTFSI was replaced with the piperidine ionic liquid PP13TFSI (N-methyl-N-propylpiperidinium bistrifluoromethanesulfonyl imide salt, purchased from Shanghai Chengjie Chemical Co., Ltd., product number PD1003).

[0095] Comparative Example 1

[0096] A polymer electrolyte membrane, the preparation method of which comprises the following steps:

[0097] S1: 10 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, molecular weight 455000) was added to 50 g of the first solvent N-methylpyrrolidone and stirred for more than 12 h to fully dissolve the polymer. Then, 3 g of lithium salt LiTFSI and 6 g of imidazole ionic liquid EMIMTFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) purchased from Shanghai Chengjie Chemical Co., Ltd., product number LM1024) were added and magnetically stirred to obtain a mixed solution;

[0098] S2: 4 g of polyethylene glycol diacrylate (PEGDA) and 80 mg of photoinitiator 2,4,6-trimethylbenzamide-diphenylphosphine oxide (TPO) were added to the above mixed solution and stirred to obtain a polymer electrolyte precursor solution;

[0099] S3: Apply the polymer electrolyte precursor solution to the glass plate with a four-sided coating applicator at a coating height of 100 μm to obtain a first wet film;

[0100] S4: The first wet film is placed at room temperature for 12 hours, and then cross-linked with an ultraviolet lamp with a wavelength of 365 nm for 10 minutes to obtain a second wet film;

[0101] S5: The second wet film was placed in an oven at 80° C. and dried for 18 h to finally obtain a bifunctional polymer electrolyte membrane with a thickness of about 30 μm.

[0102] That is, the only difference between this comparative example and Example 1 is that there is no coagulation bath treatment step.

[0103] Comparative Example 2

[0104] A polymer electrolyte membrane, the preparation method of which comprises the following steps:

[0105] S1: 10 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, molecular weight 455000) was added to 50 g of the first solvent N-methylpyrrolidone and stirred for more than 12 h to fully dissolve the polymer. Then, 3 g of lithium salt LiTFSI and 6 g of imidazole ionic liquid EMIMTFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) purchased from Shanghai Chengjie Chemical Co., Ltd., product number LM1024) were added and magnetically stirred to obtain a mixed solution;

[0106] S2: Add 4 g of polyethylene glycol diacrylate (PEGDA, molecular weight 600) to the above mixed solution and stir evenly to obtain a polymer electrolyte precursor solution;

[0107] S3: Apply the polymer electrolyte precursor solution to the glass plate with a four-sided coating applicator at a coating height of 100 μm to obtain a first wet film;

[0108] S4: The first wet film is placed at room temperature for 12 hours, then immersed in deionized water for a coagulation bath treatment for 1 minute, and excess deionized water around the glass plate is absorbed with dust-free paper to obtain a second wet film;

[0109] S5: The second wet film was placed in an oven at 80° C. and dried for 18 h to finally obtain a bifunctional polymer electrolyte membrane with a thickness of about 30 μm.

[0110] That is, the only difference between this comparative example and Example 1 is that no photoinitiator and UV cross-linking treatment step are used.

[0111] Comparative Example 3

[0112] A polymer electrolyte membrane, the preparation method of which comprises the following steps:

[0113] S1: 14 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, molecular weight 455000) was added to 50 g of solvent N-methylpyrrolidone and stirred for more than 12 h to fully dissolve the polymer. Then, 3 g of lithium salt LiTFSI and 6 g of imidazole ionic liquid EMIMTFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) purchased from Shanghai Chengjie Chemical Co., Ltd., product number LM1024) were added and magnetically stirred to obtain a mixed solution;

[0114] S2: The mixed solution was scraped onto a glass plate with a four-sided coating applicator at a scraping height of 100 μm to obtain a first wet film;

[0115] S3: Soak the glass plate containing the first wet film in deionized water for a coagulation bath treatment for 1 minute. Use dust-free paper to absorb excess deionized water around the glass plate to obtain a second wet film.

[0116] S4: The second wet film was placed in an oven at 80° C. and dried for 18 h to finally obtain a polymer electrolyte membrane with a thickness of about 30 μm.

[0117] That is, the only difference between this comparative example and Example 1 is that PVDF-HFP is used to replace the second polymer, that is, there is no second polymer monomer and UV cross-linking treatment step.

[0118] Comparative Example 4

[0119] A polymer electrolyte membrane, the preparation method of which comprises the following steps:

[0120] S1: 14 g of polyethylene glycol diacrylate (PEGDA, molecular weight 600) and 280 mg of photoinitiator 2,4,6-trimethylbenzamide-diphenylphosphine oxide (TPO) were added to 50 g of solvent N-methylpyrrolidone and stirred for more than 12 h to fully dissolve the polymer. Then, 3 g of lithium salt LiTFSI and 6 g of imidazole ionic liquid EMIMTFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) purchased from Shanghai Chengjie Chemical Co., Ltd., product number LM1024) were added and magnetically stirred to obtain a mixed solution;

[0121] S2: The mixed solution was scraped onto a glass plate with a four-sided coating applicator at a scraping height of 100 μm to obtain a first wet film;

[0122] S3: The first wet film is placed at room temperature for 12 hours, and then cross-linked with an ultraviolet lamp with a wavelength of 365 nm for 10 minutes to obtain a second wet film;

[0123] S4: Immerse the glass plate containing the second wet film in deionized water for a coagulation bath treatment for 1 minute, and absorb excess deionized water around the glass plate with dust-free paper to obtain a third wet film;

[0124] S5: The third wet film was placed in an oven at 80° C. and dried for 18 h to finally obtain a polymer electrolyte membrane with a thickness of about 30 μm.

[0125] That is, the only difference between this comparative example and Example 1 is that PEGDA is used instead of the first polymer PVDF-HFP.

[0126] Experimental example

[0127] The mechanical properties and electrochemical properties of the polymer electrolyte membranes provided in various embodiments and comparative examples were tested.

[0128] The test method is as follows:

[0129] (1) Ionic conductivity σ: The impedance spectrum of the blocked cell composed of stainless steel sheet | polymer electrolyte membrane | stainless steel sheet was measured using an electrochemical workstation at 25°C and a test frequency of 10 6 The ionic conductivity is calculated as σ = L / (R*S), where L is the thickness of the electrolyte membrane, R is the impedance, and S is the effective contact area.

[0130] (2) Capacity and long cycle test: Using lithium iron phosphate (lithium iron phosphate: PVDF: SP mass ratio = 8:1:1) as the positive electrode and lithium sheet as the negative electrode, a lithium iron phosphate | polymer electrolyte membrane | lithium sheet button cell was assembled and the capacity retention and cycle tests were performed on a blue electric test system with a cycle rate of 0.5C and a temperature of 25°C.

[0131] (3) Lithium symmetrical battery cycle test: Assemble lithium sheet | polymer electrolyte membrane | lithium sheet symmetrical battery and perform cycle test on the blue electric test system with a current density of 0.5 mA / cm 2 , the temperature is 25℃.

[0132] (4) Mechanical properties test: The polymer electrolyte membranes prepared in the examples and comparative examples were used as samples for testing. Each group of samples was cut into strips with a width of 20 mm and a length of 150 mm. The initial distance between the clamps of the electronic tensile testing machine was set to 100 mm. The two ends of the test strips along the length direction were placed in the upper and lower ends of the clamps in sequence, and the clamps were clamped. During the test, the strips and the clamps were ensured to be in the same vertical direction and there was no obvious tensile deformation. After preparation, tensile testing was carried out at a rate of 50 mm / min. Each group of samples was tested three times and the average value was taken to calculate the elongation at break. The formula is as follows:

[0133] Elongation at break = [(L1-L0) / L0] × 100%

[0134] Among them, L1 is the gauge length after fracture (mm), L0 is the initial gauge length (mm), and the initial gauge length is set to 100 mm in this test.

[0135] The test data is shown in the following table:

[0136]

[0137]

[0138] As shown in Examples 1-5, a 5-minute coagulation bath treatment can produce a polymer electrolyte membrane with both high ionic conductivity and good mechanical properties. As the coagulation bath time increases, the ionic conductivity of the electrolyte membrane gradually decreases, which may be related to the dissolution of the lithium salt in the non-solvent.

[0139] Comparative Example 1 and Example 1 demonstrate that a coagulation bath facilitates the formation of a porous structure in the electrolyte membrane, thereby promoting lithium ion transport and improving the membrane's ionic conductivity. Furthermore, the coagulation bath pore formation in Example 1, compared to the solvent evaporation pore formation in Comparative Example 1, yields an electrolyte membrane with superior mechanical properties.

[0140] It can be seen from Comparative Example 2 and Example 1 that the photocuring method triggers the formation of an internal cross-linked structure of small polymer monomer molecules, thereby further improving the mechanical properties of the electrolyte membrane.

[0141] Comparative Example 3 and Example 1 show that the mechanical and electrochemical properties of the electrolyte membrane produced using only the first polymer are inferior to those using both polymers. This is because the small monomer molecules of the second polymer added in Example 1 form a cross-linked structure within the electrolyte membrane after photocuring, improving the mechanical properties of the entire membrane. Furthermore, their interaction with the first polymer and lithium salt contributes to an increase in the electrolyte membrane's lithium ion transport rate and further enhances its tensile strength.

[0142] Comparative Example 4 and Example 1 show that the performance of the electrolyte membrane obtained by polymerizing only the second polymer monomer is lower than that obtained by using both polymers. This is because the first polymer added in Example 1, after treatment in the coagulation bath, easily forms a porous internal structure, which facilitates lithium ion transport and improves the ionic conductivity of the membrane.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a bifunctional polymer electrolyte membrane, characterized in that: The following steps are involved: S1: adding a first polymer, a lithium salt, and a plasticizer to a first solvent, and stirring at high speed to fully dissolve the first polymer and the lithium salt to obtain a mixed solution; S2: adding the second polymer monomer and the photoinitiator to the mixed solution and stirring evenly to obtain a polymer electrolyte precursor solution; S3: applying a knife to the polymer electrolyte precursor solution to form a film to obtain a first wet film; S4: subjecting the first wet film to a UV cross-linking treatment to obtain a second wet film; S5: immersing the second wet film in a second solvent and performing a coagulation bath treatment to obtain a third wet film; S6: Drying the third wet membrane to obtain a bifunctional polymer electrolyte membrane.

2. The preparation method according to claim 1, wherein: The first polymer includes one or at least two of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, polyacrylonitrile, and polyacrylate; And / or, the lithium salt includes one or at least two of lithium bis(trifluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, and lithium dioxalatoborate; And / or, the plasticizer is one or at least two of imidazole ionic liquid, piperidine ionic liquid, pyrrole ionic liquid, and pyridine ionic liquid; and / or, the first solvent is one or at least two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone; And / or, the second polymer monomer includes one or at least two of polyacrylate monomers and polyether monomers; And / or, the photoinitiator includes one or at least two of an acylphosphine oxide photoinitiator, a thioxanthone photoinitiator, and a diketone photoinitiator; And / or, the second solvent comprises a mixture of one or more of deionized water, ethanol, and tetrachloromethane; And / or, the weight ratio of the first polymer, lithium salt, plasticizer, first solvent, second polymer monomer, and photoinitiator is 5 to 15: 1.5～4.5：3～9：40～80：2～6：0.02～0.3； And / or, the carrier for the blade coating film is a polytetrafluoroethylene plate, a glass plate or a PET plate.

3. The preparation method according to claim 2, wherein: The molecular weight of the second polymer monomer is 200-1000.

4. The preparation method according to claim 1, wherein: In step S4, the wavelength of the ultraviolet cross-linking treatment is 365 nm; and / or the time of the ultraviolet cross-linking treatment is T1, 5 min < T1 < 60 min.

5. The preparation method according to claim 1, wherein: In step S5, the time of the coagulation bath treatment is T2, 0 min<T2<30 min.

6. The preparation method according to claim 1, wherein: In step S6, the drying temperature is 60-100°C; and / or the drying time is T3, 8h<T3<24h.

7. The preparation method according to claim 1, wherein: The bifunctional polymer electrolyte membrane has a thickness of 5 to 100 μm.

8. A bifunctional polymer electrolyte membrane, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 7.

9. The bifunctional polymer electrolyte membrane according to claim 8, wherein: The bifunctional polymer electrolyte membrane has a porous structure and an ionic conductivity greater than 10 at room temperature. -4 S / cm, while tensile strength>6MPa.

10. A solid-state battery, characterized in that: The invention comprises a bifunctional polymer electrolyte membrane prepared by the preparation method according to any one of claims 1 to 7 or a bifunctional polymer electrolyte membrane according to any one of claims 8 to 9.

Images