Preparation method, product and application of polymer electrolyte membrane

Abstract

The invention relates to the technical field of polymer electrolyte membranes, in particular to a preparation method, a product and application of a polymer electrolyte membrane. The preparation method comprises the following steps: dissolving Br-PEO-Br, copper bromide, N, N, N, N, N-pentamethyldiethylenetriamine, a monomer and ascorbic acid in a solvent, and carrying out a polymerization reaction after circulation of freezing, vacuumizing and unfreezing for three times; precipitating in a poor solvent after the polymerization reaction is finished, and washing and drying the obtained precipitate to obtain a modified PEO material; and uniformly mixing the modified PEO material with a lithium salt and an ionic liquid, and carrying out hot press molding to obtain the polymer electrolyte membrane. The polymer electrolyte membrane disclosed by the invention has relatively high conductivity, the ionic conductivity at room temperature is greater than 10 <-3 > S / cm, and meanwhile, the polymer electrolyte membrane has the characteristics of good processing performance and excellent mechanical performance of a polymer.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer electrolyte membranes, and particularly to a preparation method, product and application of a polymer electrolyte membrane. Background Art

[0002] Lithium-ion batteries have been widely used in many fields such as consumer electronics, electric vehicles, energy storage systems, industrial applications, aerospace and medical devices due to their advantages of high energy density, long cycle life, low self-discharge rate and no memory effect. With the continuous progress of technology, the performance and safety of lithium-ion batteries will be further improved, and their application scope will also continue to expand.

[0003] Liquid electrolyte is a key medium for lithium-ion batteries to transport ions. Its main function is to provide a transport channel for lithium ions during the charge and discharge process of the battery and ensure the reversibility of chemical reactions. In lithium-ion batteries, liquid electrolyte usually consists of lithium salt, organic solvent and other additives. Liquid electrolyte usually has a high ionic conductivity, can support the fast charge and discharge of the battery, and it can well wet the electrode material to ensure sufficient contact between the electrode and the electrolyte, thereby improving the overall performance of the battery. At present, the production process of liquid electrolyte is relatively mature, the production cost is low, it is suitable for large-scale commercial applications and has achieved certain results. However, liquid electrolyte usually contains flammable organic solvents, which are prone to decomposition at high temperature or short circuit, release gas and cause the battery to expand, and then trigger fire and explosion. In addition, the commonly used organic solvents have a high freezing point, the viscosity becomes larger at low temperature, and may even solidify, hindering the migration of lithium ions and resulting in a decrease in ionic conductivity. At low temperature, the deposition rate of lithium ions on the negative electrode surface accelerates, and it is easier to form lithium dendrites. The growth of lithium dendrites will not only reduce the cycle life of the battery, but also may cause the battery to short circuit and trigger safety problems. These problems restrict the application of lithium-ion batteries in specific places and the development of new batteries.

[0004] Developing high-performance solid electrolytes is an important method to improve the safety of lithium-ion batteries. Solid electrolyte is a solid ionic conductor electrolyte, which can be divided into inorganic solid ceramic electrolyte and organic solid polymer electrolyte according to different chemical compositions. Inorganic solid ceramic electrolyte usually has characteristics such as high ionic conductivity, good chemical stability, good thermal stability and high safety, but its brittleness, poor mechanical properties and high cost also limit its further development.

[0005] Polymer electrolytes have the advantages of good mechanical properties, good film-forming properties, good viscoelasticity and stability, effectively overcoming problems such as easy leakage and poor safety of liquid electrolytes, and making up for problems such as poor mechanical properties and poor film-forming properties of inorganic solid ceramic electrolytes, meeting the development trend of new energy. However, the ionic conductivity of polymer electrolytes is relatively low at room temperature, and usually needs to be heated to above 60 °C to achieve a higher conductivity. To make polymer electrolytes enter commercial use, further improvement and enhancement are still required. Summary of the Invention

[0006] Based on the above, the present invention provides a preparation method, product and application of a polymer electrolyte membrane with high ionic conductivity.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention is a preparation method of a polymer electrolyte membrane, including the following steps:

[0009] Dissolve Br-PEO-Br, copper bromide, N,N,N,N,N-pentamethyldiethylenetriamine (PMDETA), monomer and ascorbic acid in a solvent, and carry out a polymerization reaction (ATRP polymerization method) after 3 cycles of "freezing - vacuum pumping - thawing"; after the polymerization reaction is completed, precipitate in a poor solvent, and the obtained precipitate is washed and dried to obtain a modified PEO material;

[0010] Mix the modified PEO material with a lithium salt and an ionic liquid and hot press to form the polymer electrolyte membrane.

[0011] Another technical solution of the present invention is a polymer electrolyte membrane prepared according to the above preparation method.

[0012] Another technical solution of the present invention is a battery, including a positive electrode, a negative electrode and the above polymer electrolyte membrane.

[0013] The present invention discloses the following technical effects:

[0014] (1) The modified PEO material prepared by the present invention is a BAB-type block copolymer, where PEO serves as the soft segment, improving the flexibility of the polymer electrolyte membrane. At the same time, PEO can form a complex with the lithium salt to promote the conduction of lithium ions; the rigid monomer serves as the hard segment, which can improve the strength of the polymer electrolyte membrane, thereby enhancing the safety of the battery. In addition, the block structure can effectively disrupt the regularity of the PEO molecular chain, reduce the crystallinity of PEO, and further enhance the conduction of lithium ions.

[0015] (2) Ionic liquids have the advantages of low volatility, good thermal stability, good chemical stability, and high ionic conductivity. When used in polymer electrolyte membranes, they can effectively improve the ionic conductivity of the membranes. In addition, ionic liquids have a certain plasticizing effect on the modified PEO material, which is beneficial to the conduction of lithium ions.

[0016] (3) The raw material PEO used in the present invention is rich in output, wide in source, and green and non-toxic. Its high flexibility, good interfacial compatibility, and processability make it have broad application prospects in the field of lithium-ion batteries, especially in the field of solid-state batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 It is the room-temperature AC impedance spectrum diagram of the polymer electrolyte membrane (PS-PEO-PS electrolyte membrane) prepared in Example 1 of the present invention.

[0019] Figure 2 It is the room-temperature AC impedance spectrum diagram of the polymer electrolyte membrane prepared in Comparative Example 2 of the present invention.

[0020] Figure 3 It is the DSC comparison diagram of the polymer PS-PEO-PS prepared in Example 1 of the present invention and the polymer PEO used in Comparative Example 1.

[0021] Figure 4 It is the comparison diagram of the ionic conductivity of the polymer electrolyte membranes prepared in Example 1 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0024] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0025] Without departing from the scope or spirit of this invention, various modifications and variations can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0026] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0027] One of the technical solutions of this invention, a method for preparing a polymer electrolyte membrane, comprises the following steps:

[0028] Dissolve Br-PEO-Br, copper bromide, N,N,N,N,N-pentamethyldiethylenetriamine (PMDETA), monomer and ascorbic acid in a solvent, and carry out a polymerization reaction after 3 cycles of "freezing - vacuum pumping - thawing"; after the polymerization reaction is completed, precipitate in a poor solvent, and the obtained precipitate is washed and dried to obtain a modified PEO material;

[0029] Mix the modified PEO material with a lithium salt and an ionic liquid and then hot-press to form the polymer electrolyte membrane.

[0030] In a preferred embodiment of this invention, the molar ratio of Br-PEO-Br, copper bromide, N,N,N,N,N-pentamethyldiethylenetriamine, monomer, and ascorbic acid is 1:(0.01 - 1):(0.5 - 2):(20 - 200):(0.5 - 2);

[0031] The monomer is one of styrene, methyl methacrylate, sodium p-styrenesulfonate, and acrylonitrile;

[0032] The mass ratio of Br-PEO-Br to the solvent is (1 - 10):1;

[0033] The solvent is one of tetrahydrofuran, dimethyl sulfoxide, and N,N-dimethylformamide.

[0034] The "freezing - vacuum pumping - thawing" is carried out through a double - row tube. The freezing is carried out in liquid nitrogen, then the vacuum is pumped for 5 min by an oil pump, and the thawing is carried out in a water bath at 50 °C.

[0035] In a preferred embodiment of the present invention, the polymerization reaction is specifically carried out at 70 - 90 °C for 8 - 24 h under a nitrogen atmosphere; the poor solvent is ether or methyl tert - butyl ether.

[0036] In a preferred embodiment of the present invention, the mass ratio of the modified PEO material, lithium salt and ionic liquid is 1:(0.2 - 0.5):(0.5 - 1);

[0037] The lithium salt is one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate;

[0038] The ionic liquid is one of 1 - ethyl - 3 - methylimidazolium dicyanamide, 1 - butyl - 3 - methylimidazolium hexafluorophosphate, 1 - ethyl - 3 - methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0039] In a preferred embodiment of the present invention, the temperature of the hot - pressing molding is 70 - 100 °C, the pressure is 10 - 30 MPa, and the time is 3 - 5 min.

[0040] After the hot - pressing molding, it further includes the step of transferring the hot - pressing molding die to the cold - pressing area and cold - pressing it to room temperature, and the pressure in the cold - pressing area is 10 - 30 MPa.

[0041] In a preferred embodiment of the present invention, the preparation method of the Br - PEO - Br includes the following steps:

[0042] Dissolve polyethylene oxide (PEO) and triethylamine in solvent A, then add 2 - bromoisobutyryl bromide for reaction, then precipitate in a poor solvent, and the obtained precipitate is washed and dried to obtain the Br - PEO - Br.

[0043] In a preferred embodiment of the present invention, the molecular weight of the polyethylene oxide is 10000 - 100000 g / mol;

[0044] The molar ratio of the polyethylene oxide, triethylamine and 2 - bromoisobutyryl bromide is 1:(2 - 10):(2 - 10);

[0045] The mass ratio of the polyethylene oxide to the solvent A is 1:(1 - 10);

[0046] The solvent A is one of dichloromethane, chloroform, tetrahydrofuran;

[0047] The poor solvent is ether or methyl tert - butyl ether;

[0048] The temperature of the reaction is room temperature and the time is 18 - 36 h.

[0049] When adding 2 - bromoisobutyryl bromide, the temperature of the solution is adjusted to 0 °C. The addition method of 2 - bromoisobutyryl bromide is dropwise addition.

[0050] The second technical solution of the present invention is a polymer electrolyte membrane prepared by the above - mentioned preparation method.

[0051] This polymer electrolyte membrane has a relatively high conductivity, and the room - temperature ionic conductivity is greater than 10 -3 S / cm, and at the same time retains the characteristics of good polymer processability and excellent mechanical properties.

[0052] The third technical solution of the present invention is a battery, which includes a positive electrode, a negative electrode, and the above - mentioned polymer electrolyte membrane.

[0053] In a preferred embodiment of the present invention, the positive electrode is LiFePO4; the negative electrode is metallic lithium.

[0054] The positive electrode material is prepared by the following steps: by mass percentage, 80% LiFePO4, 9% SUPER P, 1% carbon nanotubes, and 10% PVDF are added to N - methylpyrrolidone and stirred evenly. The obtained slurry is coated on an aluminum foil and vacuum - dried to obtain a positive electrode sheet.

[0055] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art. The reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been made public.

[0056] The technical solutions provided by the present invention will be described in detail below with reference to the examples, but they should not be construed as limiting the protection scope of the present invention.

[0057] Example 1

[0058] 1. Dissolve 40 g of PEO (molecular weight 20000 g / mol) in 200 mL of dichloromethane, add 0.8095 g of triethylamine, slowly dropwise add 1.8393 g of 2 - bromoisobutyryl bromide at 0 °C, the dropping time is 20 min, and then raise the temperature to 25 °C and continue stirring for 24 h for the reaction. After the reaction is completed, pour the solution into an excessive amount of cold ether for precipitation, obtain a white product and wash it three times, and then vacuum - dry it at 40 °C to obtain Br - PEO - Br.

[0059] 2. Dissolve 10 g of the above-mentioned Br-PEO-Br in N,N-dimethylformamide, and successively add 0.0022 g of CuBr2, 0.0866 g of PMDETA, 30 g of styrene, and 0.8806 g of ascorbic acid. Subsequently, perform the "freezing - vacuum pumping - thawing" cycle three times in liquid nitrogen, and place it under nitrogen protection and react at 80 °C for 12 h. After the reaction is completed, pour the solution into an excess of cold diethyl ether for precipitation, wash the product three times, and then dry it under vacuum at 40 °C to obtain PS-PEO-PS.

[0060] 3. Mix the prepared PS-PEO-PS, lithium bis(trifluoromethanesulfonyl)imide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide evenly in a mass ratio of 1:0.25:1, and place them in a stainless-steel mold with a radius of 3 cm. Place the mold on a hot press, hot press at 80 °C for 5 min, with a pressure of 25 MPa. After the hot pressing is completed, transfer the mold to the cold pressing area and cold press it to room temperature with a pressure of 25 MPa to obtain a PS-PEO-PS electrolyte membrane.

[0061] 4. Cut the electrolyte membrane into circular membrane pieces with a diameter of 16 mm, use a CR2032 coin cell assembly, and assemble a stainless-steel symmetric battery (both the positive and negative electrodes of the stainless-steel symmetric battery are replaced by stainless-steel gaskets, and the size of the stainless-steel gasket: diameter 15.8 mm, thickness 1.0 mm) in a glove box filled with argon. After the assembled coin cell stands for 8 h, perform electrochemical tests.

[0062] 5. Cut the electrolyte membrane into circular membrane pieces with a diameter of 16 mm, use a CR2032 coin cell assembly, and assemble a battery (LiFePO4 / PS-PEO-PS / Li, that is, a solid-state lithium metal battery) in a glove box filled with argon. This battery uses metallic lithium as the negative electrode and LiFePO4 as the positive electrode. After the assembled coin cell stands for 8 h, perform cycling tests.

[0063] After the assembled coin cell stands for 8 h, perform electrochemical tests.

[0064] Figure 1 It is the room-temperature alternating current impedance spectrogram of the PS-PEO-PS electrolyte membrane prepared in Example 1. As can be seen from Figure 1 it, the room-temperature ionic conductivity of the PS-PEO-PS electrolyte membrane is greater than 10 -3 S / cm.

[0065] Example 2

[0066] The difference from Example 1 is only that 30 g of styrene in step 2 is replaced by 30 g of acrylonitrile; the remaining steps and parameters are the same as those in Example 1.

[0067] Comparative Example 1

[0068] 1. Mix PEO (molecular weight 20,000 g / mol), lithium bis(trifluoromethanesulfonyl)imide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide evenly in a mass ratio of 1:0.25:1, and place the mixture in a stainless-steel mold with a radius of 3 cm. Place the mold on a hot press, hot press at 80 °C for 5 min under a pressure of 25 MPa. After the hot pressing is completed, transfer the mold to the cold pressing area and cold press it to room temperature under a pressure of 25 MPa to obtain a PEO electrolyte membrane.

[0069] 2. Cut the electrolyte membrane into circular membrane pieces with a diameter of 16 mm, use a CR2032 coin cell assembly, and assemble a stainless-steel symmetric cell (the cell composition is the same as that in Example 1) in a glove box filled with argon. After the assembled coin cell is left standing for 8 h, perform electrochemical tests.

[0070] 3. Cut the electrolyte membrane into circular membrane pieces with a diameter of 16 mm, use a CR2032 coin cell assembly, and assemble a cell (LiFePO4 / PS-PEO-PS / Li) in a glove box filled with argon. This cell uses metallic lithium as the negative electrode and LiFePO4 as the positive electrode. After the assembled coin cell is left standing for 8 h, perform cycling tests. (The cell composition is the same as that in Example 1)

[0071] Comparative Example 2 (Cycling tests are not performed in Comparative Example 2 because the ionic conductivity is too low to be measured)

[0072] The difference from Example 1 is only that the addition of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in Step 3 is omitted; the remaining steps and parameters are the same as those in Example 1.

[0073] Perform the same electrochemical tests on the electrolyte membrane prepared in Comparative Example 2 as in Example 1, and the results are as Figure 2 shown.

[0074] Figure 2 is the room-temperature alternating current impedance spectrum diagram of the electrolyte membrane prepared in Comparative Example 2. As can be seen from Figure 2 it, the room-temperature ionic conductivity of the electrolyte membrane prepared in Comparative Example 2 is 8.47×10 -7 S / cm, which is much smaller than the room-temperature ionic conductivity of Example 1. The addition of an ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) significantly improves the ionic conductivity of the polymer electrolyte membrane. By adding an ionic liquid, the defect of poor ionic conductivity of the polymer electrolyte is effectively improved.

[0075] Figure 3 is the DSC comparison diagram of PEO in Comparative Example 1 and PS-PEO-PS in Example 1. As can be seen from Figure 3As can be seen, the melting point of PEO is 64 °C and it has a relatively high crystallinity. By carrying out chemical reactions at the end groups of PEO, monomers with greater strength are introduced into PS-PEO-PS, effectively disrupting the regularity of the PE molecular chains, reducing the crystallinity of PEO, and at the same time reducing the melting point of PEO, which is beneficial to the migration of lithium ions in the polymer chains.

[0076] Figure 4 Figure for comparing the ionic conductivities of the electrolyte membranes prepared in Comparative Example 1 and Example 1. From Figure 4 As can be seen, at each temperature, the ionic conductivity of the electrolyte membrane prepared in Example 1 is greater than that of the electrolyte membrane prepared in Comparative Example 1. This is because the polymer in Example 1 has a lower crystallinity and stronger ability to conduct lithium ions, which is consistent with the test results of DSC.

[0077] The charge-discharge cycle tests were carried out on the solid-state lithium metal batteries in Example 1, Example 2 and Comparative Example 1. At 25 °C, in the first step, charge at 0.1C to 4V and let it stand for 1 min; in the second step, discharge at 0.1C to 2.4V, record the discharge capacity and let it stand for 1 min; cycle the first step and the second step to test the cycle performance of the battery for 300 cycles. The results are summarized in Table 1.

[0078] Table 1

[0079]

[0080] As can be seen from Table 1, the ionic conductivities of Example 1 and Example 2 are both higher than that of Comparative Example 1, thanks to the reduction of the polymer crystallinity. During the cycling process, the battery with higher ionic conductivity shows better initial discharge capacity and better cycle stability.

[0081] The above-described embodiments are only descriptions of the preferred modes of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a polymer electrolyte membrane, characterized in that: The following steps are involved: Dissolving Br-PEO-Br, copper bromide, N,N,N,N,N-pentamethyldiethylenetriamine, monomers and ascorbic acid in a solvent, and subjecting the mixture to a polymerization reaction after three cycles of "freeze-vacuum-thaw"; after the polymerization reaction, precipitating the mixture in a poor solvent, washing the precipitate and drying the precipitate to obtain a modified PEO material; The modified PEO material is mixed with lithium salt and ionic liquid and then hot-pressed to obtain the polymer electrolyte membrane.

2. The method for preparing a polymer electrolyte membrane according to claim 1, characterized in that: The molar ratio of Br-PEO-Br, copper bromide, N,N,N,N,N-pentamethyldiethylenetriamine, monomer, and ascorbic acid is 1:(0.01-1):(0.5-2):(20-200):(0.5-2); The monomer is one of styrene, methyl methacrylate, sodium p-styrene sulfonate and acrylonitrile; The mass ratio of the Br-PEO-Br to the solvent is (1-10):1; The solvent is one of tetrahydrofuran, dimethyl sulfoxide and N,N-dimethylformamide.

3. The method for preparing a polymer electrolyte membrane according to claim 1, characterized in that: The polymerization reaction is specifically carried out under nitrogen atmosphere at 70-90° C. for 8-24 hours; the poor solvent is diethyl ether or methyl tert-butyl ether.

4. The method for preparing a polymer electrolyte membrane according to claim 1, characterized in that: The mass ratio of the modified PEO material to the lithium salt and the ionic liquid is 1:(0.2-0.5):(0.5-1); The lithium salt is one of lithium bis(trifluoromethanesulfonyl imide), lithium hexafluorophosphate, lithium bis(fluorosulfonyl imide) and lithium perchlorate; The ionic liquid is one of 1-ethyl-3-methylimidazolium dinitrile amine salt, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

5. The method for preparing a polymer electrolyte membrane according to claim 1, characterized in that: The temperature of the hot pressing molding is 70-100° C., the pressure is 10-30 MPa, and the time is 3-5 min.

6. The method for preparing a polymer electrolyte membrane according to claim 1, characterized in that: The preparation method of the Br-PEO-Br comprises the following steps: Polyethylene oxide and triethylamine are dissolved in solvent A, and then 2-bromoisobutyryl bromide is added to react, and then precipitated in a poor solvent. The obtained precipitate is washed and dried to obtain the Br-PEO-Br.

7. The method for preparing a polymer electrolyte membrane according to claim 6, characterized in that: The molecular weight of the polyethylene oxide is 10000-100000 g / mol; The molar ratio of the polyethylene oxide to triethylamine and 2-bromoisobutyryl bromide is 1:(2-10):(2-10); The mass ratio of the polyethylene oxide to the solvent A is 1:(1-10); The solvent A is one of dichloromethane, chloroform and tetrahydrofuran; The poor solvent is diethyl ether or methyl tert-butyl ether; The reaction temperature is room temperature and the reaction time is 18-36 hours.

8. The polymer electrolyte membrane prepared according to the preparation method according to any one of claims 1 to 7.

9. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode and the polymer electrolyte membrane according to claim 8.

10. The battery according to claim 9, characterized in that The positive electrode is LiFePO4; the negative electrode is metallic lithium.

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