Closed-pore lithium battery diaphragm with high ionic conductivity and preparation method thereof
By filling modified polyethylene oxide derivatives into the PE base film, the problems of slow pore closure response and insufficient ionic conductivity of the PE separator are solved, and the rapid pore closure and high ionic conductivity of the lithium battery at high temperature are achieved, thereby improving the safety and performance of the battery.
Patent Information
- Application Number
- CN202510859377.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-25
- Publication Date
- 2025-09-26
AI Technical Summary
The existing PE separator has a slow closed-pore response in lithium batteries, cannot prevent heat accumulation in time and affects ionic conductivity, and cannot meet the requirements of high-performance lithium batteries.
Modified polyethylene oxide derivatives are filled in the pore structure of the PE-based membrane. By introducing N-isopropylacrylamide segments, fluorine-containing groups and thiourea groups, the modified polyethylene oxide derivatives promote rapid pore closure of the membrane at high temperatures and maintain high ionic conductivity.
The membrane achieves rapid pore closure at high temperatures, maintains high ionic conductivity and structural stability, and improves battery safety and performance.
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of battery separators, and in particular to a closed-cell lithium battery separator with high ionic conductivity and a preparation method thereof. Background Art
[0002] In lithium-ion batteries, the separator plays a key role in isolating the positive and negative electrodes, preventing short circuits, and allowing lithium ions to pass through. Polyethylene (PE) separators are one of the most widely used separators for lithium-ion batteries. However, existing PE separators have significant shortcomings in addressing battery thermal runaway. Their closed-cell response is slow, failing to prevent further heat accumulation within the battery. Furthermore, the closed-cell process often impairs ionic conductivity, impacting battery performance.
[0003] Although some studies have attempted to improve the performance of PE separators by introducing water-soluble, ion-conducting polymers during the aqueous coating process, these methods still have limitations in increasing the closure rate and maintaining high ionic conductivity, and cannot meet the strict requirements of high-performance lithium batteries for separators. Summary of the Invention
[0004] The purpose of the present invention is to provide a closed-cell lithium battery separator with high ionic conductivity and a preparation method thereof, and to solve the following technical problems:
[0005] How to achieve rapid thermal closure of PE separators while maintaining high ionic conductivity.
[0006] The purpose of the present invention can be achieved through the following technical solutions:
[0007] In a first aspect, the present invention discloses a closed-cell lithium battery separator with high ionic conductivity, comprising a PE-based membrane, wherein the pore structure of the PE-based membrane is filled with a modified polyethylene oxide derivative, wherein the modified polyethylene oxide derivative contains an N-isopropylacrylamide segment, a fluorine-containing group, and a thiourea group.
[0008] Furthermore, the preparation method of the modified polyethylene oxide derivative comprises the following steps:
[0009] Step 1. Polyethylene oxide (PEO) and N-isopropylacrylamide (NIPAM) are dissolved in an organic solvent at a molar ratio of (10-50):1, an initiator is added, and the mixture is reacted at 60-80° C. for 2-6 hours under nitrogen protection to obtain a reaction solution A. During the reaction, N-isopropylacrylamide is grafted onto the polyethylene oxide through a polymerization reaction to form PEO-NIPAM.
[0010] Step 2: Add 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM) to reaction solution A, add a catalyst, and react at 70-90° C. for 3-8 hours to obtain reaction solution B. During the reaction, the functional groups in 1-butyl-3-methylimidazolium hexafluorophosphate are grafted onto the molecular chain of PEO-NIPAM to form PEO-NIPAM-BMIM.
[0011] Step 3: add isothiocyanate to reaction solution B, add a catalyst, react at 70-80° C. for 2 h, precipitate, filter, wash, and dry to obtain a modified polyethylene oxide derivative.
[0012] Preferably, in step 1, the molar ratio of polyethylene oxide to N-isopropylacrylamide is 30:1.
[0013] Preferably, in step 1, the reaction temperature is 70° C. and the reaction time is 4 h.
[0014] Preferably, in step 2, the reaction temperature is 80° C. and the reaction time is 5 h.
[0015] Preferably, in step 3, the reaction temperature is 75° C. and the reaction time is 1.5 h.
[0016] Furthermore, in step 1, the initiator is any one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate, or a mixture of any multiple thereof in any proportion.
[0017] Preferably, in step 1, the initiator is azobisisobutyronitrile.
[0018] Furthermore, in step 1, the ratio of the mass of the polyethylene oxide to the N-isopropylacrylamide and the volume of the organic solvent is 1 g:(10-15) mL.
[0019] Preferably, the organic solvent is dimethyl sulfoxide.
[0020] Preferably, in step 1, the mass ratio of the polyethylene oxide to the N-isopropylacrylamide to the volume of the organic solvent is 1 g:12 mL.
[0021] Furthermore, in step 2, the molar ratio of the reaction product in the reaction solution A to 1-butyl-3-methylimidazolium hexafluorophosphate is 1:(0.1-0.5).
[0022] Preferably, in step 2, the molar ratio of the reaction product in the reaction solution A to 1-butyl-3-methylimidazolium hexafluorophosphate is 1:0.3.
[0023] Furthermore, in step 2, the catalyst is any one of benzoyl peroxide, di-tert-butyl peroxide, and tert-butyl perbenzoate, or a mixture of any multiple thereof in any proportion.
[0024] Preferably, in step 2, the catalyst is benzoyl peroxide.
[0025] Furthermore, in step 3, the molar ratio of the reaction product to the isothiocyanate in the reaction solution B is 1:(0.2-0.6).
[0026] Preferably, in step 3, the molar ratio of the reaction product to the isothiocyanate in the reaction solution B is 1:0.4.
[0027] Furthermore, in step 3, the catalyst is any one of dibutyltin dilaurate, stannous octoate, dibutyltin diacetate, and dibutyltin didodecylsulfide, or a mixture of any two or more thereof.
[0028] Preferably, in step 3, the catalyst is dibutyltin dilaurate.
[0029] Based on this, a preferred method for preparing a modified polyethylene oxide derivative is obtained, comprising the following steps:
[0030] Step 1: Dissolve 3 mol of polyethylene oxide and 0.1 mol of N-isopropylacrylamide in dimethyl sulfoxide, add azobisisobutyronitrile, and react at 70° C. for 4 h under nitrogen protection to obtain a reaction solution A containing PEO-NIPAM;
[0031] Step 2: directly add 0.9 mol of 1-butyl-3-methylimidazolium hexafluorophosphate to the reaction solution A, add benzoyl peroxide, and react at 80° C. for 5 h to obtain a reaction solution B containing PEO-NIPAM-BM IM;
[0032] Step 3: directly add 1.2 mol of isothiocyanate and dibutyltin dilaurate to the reaction solution B, react at 70-80° C. for 2 h, precipitate, filter, wash, and dry to obtain a modified polyethylene oxide derivative.
[0033] In a second aspect, the present invention further discloses a method for preparing the closed-cell lithium battery separator with high ionic conductivity as described above, comprising the following steps:
[0034] S1. dissolving the modified polyethylene oxide derivative in water to form a coating solution with a mass fraction of 10-12%;
[0035] S2. The coating liquid is evenly coated on the PE base film with a coating thickness of 1-2 μm. After vacuum drying, a closed-cell lithium battery separator with high ionic conductivity is obtained.
[0036] Preferably, in step S1, the mass fraction of the coating liquid is 10-12%.
[0037] Furthermore, in step S2, the thickness of the PE base film is 12-20 μm.
[0038] Furthermore, in step S2, the vacuum drying is carried out at a temperature of 75-90°C and for a time of 1.5-2.5 hours.
[0039] Preferably, in step S2, the vacuum drying temperature is 85° C. and the time is 2 h.
[0040] Beneficial effects of the present invention:
[0041] (1) The closed-cell lithium battery separator with high ionic conductivity of the present invention is filled with a modified polyethylene oxide derivative, which introduces an N-isopropylacrylamide segment, a fluorine-containing group and a thiourea group. The N-isopropylacrylamide segment has a low critical solution temperature. When the temperature rises to near the critical solution temperature, its molecular chain undergoes a conformational transition from extension to curling. In the application of lithium battery separators, this temperature responsiveness can be combined with the thermal runaway process of the battery. At normal operating temperature, the N-isopropylacrylamide segment stretches, providing a good transmission channel for lithium ions and ensuring high ionic conductivity. When the battery temperature rises to 130°C, the N-isopropylacrylamide segment quickly curls up, interacts with the polyethylene oxide main chain, and promotes the rapid closure of the separator pores.
[0042] (2) The fluorinated groups in the modified polyethylene oxide derivatives are obtained by introducing 1-butyl-3-methylimidazolium hexafluorophosphate. 1-butyl-3-methylimidazolium hexafluorophosphate is an ionic liquid with excellent ion conductivity and thermal stability, which can significantly improve the ionic conductivity of the diaphragm. At the same time, the interaction between the functionalized groups and the polyethylene oxide main chain can enhance the structural stability of the diaphragm, help maintain the integrity of the diaphragm at high temperatures, and prevent the diaphragm from rupture due to thermal expansion. This improves its electrical conductivity and strength properties.
[0043] (3) The thiourea groups in the modified polyethylene oxide derivatives form moderate hydrogen bonds with water molecules or themselves at room temperature. At a high temperature of 130 °C, water evaporates or migrates, and a stronger and denser hydrogen bond network is formed between the thiourea groups, resulting in physical cross-linking of the PEO chains, a sudden increase in viscosity, and further promoting closed cells. DETAILED DESCRIPTION
[0044] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.
[0045] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.
[0046] Preparation Example 1
[0047] The modified polyethylene oxide derivatives are prepared by following the steps below:
[0048] Step 1. In a stirrer, 132 g (3 mol) of polyethylene oxide and 11.316 g (0.1 mol) of N-isopropylacrylamide were dissolved in 1720 mL of dimethyl sulfoxide, azobisisobutyronitrile was added, and the mixture was reacted at 70° C. for 4 h under nitrogen protection to obtain reaction solution A;
[0049] Step 2: directly add 266.6 g (0.9 mol) of 1-butyl-3-methylimidazolium hexafluorophosphate to the reaction solution A, add 2.12 g of benzoyl peroxide, and react at 80° C. for 5 h to obtain reaction solution B;
[0050] Step 3: directly add 60.11 g (1.2 mol) of isothiocyanate and 0.95 g of dibutyltin dilaurate to the reaction solution B, and react at 75° C. for 2 h to obtain a reaction solution C;
[0051] Step 4: The reaction solution C was precipitated for 2 hours and then filtered using a funnel. The filter material was repeatedly washed with ether and then placed in a vacuum drying oven and dried at 60° C. for 5 hours to obtain a modified polyethylene oxide derivative.
[0052] Preparation Example 2
[0053] The modified polyethylene oxide derivatives are prepared by following the steps below:
[0054] Step 1. In a stirrer, 44 g (1 mol) of polyethylene oxide and 11.316 g (0.1 mol) of N-isopropylacrylamide were dissolved in 664 mL of dimethyl sulfoxide, azobisisobutyronitrile was added, and the mixture was reacted at 70° C. for 3 h under nitrogen protection to obtain reaction solution A;
[0055] Step 2: directly add 29.62 g (0.1 mol) of 1-butyl-3-methylimidazolium hexafluorophosphate to the reaction solution A, add 1.42 g of benzoyl peroxide, and react at 80° C. for 3.5 h to obtain a reaction solution B;
[0056] Step 3: directly add 11.82 g (0.2 mol) of isothiocyanate and 0.59 g of dibutyltin dilaurate to the reaction solution B, and react at 70° C. for 2 h to obtain a reaction solution C;
[0057] Step 4: The reaction solution C was precipitated for 2 hours and then filtered using a funnel. The filter material was repeatedly washed with ether and then placed in a vacuum drying oven and dried at 60° C. for 5 hours to obtain a modified polyethylene oxide derivative.
[0058] Preparation Example 3
[0059] The modified polyethylene oxide derivatives are prepared by following the steps below:
[0060] Step 1. In a stirrer, 220 g (5 mol) of polyethylene oxide and 11.316 g (0.1 mol) of N-isopropylacrylamide were dissolved in 2776 mL of dimethyl sulfoxide, azobisisobutyronitrile was added, and the mixture was reacted at 70° C. for 6 h under nitrogen protection to obtain reaction solution A;
[0061] Step 2: directly add 740 g (2.5 mol) of 1-butyl-3-methylimidazolium hexafluorophosphate to the reaction solution A, add 3.41 g of benzoyl peroxide, and react at 80° C. for 5 h to obtain a reaction solution B;
[0062] Step 3: directly adding 177.3 g (3 mol) of isothiocyanate to the reaction solution B, adding 2.49 g of dibutyltin dilaurate, and reacting at 75° C. for 2 h to obtain a reaction solution C;
[0063] Step 4: The reaction solution C was precipitated for 2 hours and then filtered using a funnel. The filter material was repeatedly washed with ether and then placed in a vacuum drying oven and dried at 60° C. for 5 hours to obtain a modified polyethylene oxide derivative.
[0064] Comparative Preparation Example 1
[0065] The preparation of the modified polyethylene oxide derivative is different from that of Preparation Example 1 only in that step 2 is eliminated, and the other steps and conditions remain the same, ultimately obtaining the modified polyethylene oxide derivative.
[0066] Comparative Preparation Example 2
[0067] The preparation of the modified polyethylene oxide derivative is different from that of Preparation Example 1 only in that step 3 is eliminated, and the other steps and conditions remain the same, and the modified polyethylene oxide derivative is finally obtained.
[0068] Example 1
[0069] To prepare a closed-cell lithium battery separator with high ionic conductivity, follow the steps below:
[0070] S1. Dissolve 11 g of the modified polyethylene oxide derivative prepared in Preparation Example 1 in 89 g of water to form a coating solution;
[0071] S2. Use a diaphragm coater to evenly coat the coating liquid on a PE base film with a length of 6 cm, a width of 4 cm, and a thickness of 15 μm, with a coating thickness of 1.5 μm. Then place it in a vacuum dryer and dry it at 85°C for 2 hours to obtain a closed-cell lithium battery diaphragm with high ionic conductivity.
[0072] Example 2
[0073] To prepare a closed-cell lithium battery separator with high ionic conductivity, follow the steps below:
[0074] S1. Dissolve 10 g of the modified polyethylene oxide derivative prepared in Preparation Example 1 in 90 g of water to form a coating solution;
[0075] S2. Use a diaphragm coater to evenly coat the coating liquid on a PE base film with a length of 6 cm, a width of 4 cm, and a thickness of 15 μm, with a coating thickness of 1.5 μm. Then place it in a vacuum dryer and dry it at 85°C for 2 hours to obtain a closed-cell lithium battery diaphragm with high ionic conductivity.
[0076] Example 3
[0077] To prepare a closed-cell lithium battery separator with high ionic conductivity, follow the steps below:
[0078] S1. Dissolve 12 g of the modified polyethylene oxide derivative obtained in Preparation Example 1 in 88 g of water to form a coating liquid;
[0079] S2. Use a diaphragm coater to evenly coat the coating liquid on a PE base film with a length of 6 cm, a width of 4 cm, and a thickness of 15 μm, with a coating thickness of 1.5 μm. Then place it in a vacuum dryer and dry it at 85°C for 2 hours to obtain a closed-cell lithium battery diaphragm with high ionic conductivity.
[0080] Example 4
[0081] To prepare a closed-cell lithium battery separator with high ionic conductivity, follow the steps below:
[0082] S1. Dissolve 11 g of the modified polyethylene oxide derivative prepared in Preparation Example 2 in 89 g of water to form a coating solution;
[0083] S2. Use a diaphragm coater to evenly coat the coating liquid on the PE base film with a coating thickness of 1.5 μm, and then place it in a vacuum dryer and dry it at 85° C. for 2 hours to obtain a closed-cell lithium battery diaphragm with high ionic conductivity.
[0084] Example 5
[0085] To prepare a closed-cell lithium battery separator with high ionic conductivity, follow the steps below:
[0086] S1. Dissolve 11 g of the modified polyethylene oxide derivative prepared in Preparation Example 3 in 89 g of water to form a coating solution;
[0087] S2. Use a diaphragm coater to evenly coat the coating liquid on the PE base film with a coating thickness of 1.5 μm, and then place it in a vacuum dryer and dry it at 85° C. for 2 hours to obtain a closed-cell lithium battery diaphragm with high ionic conductivity.
[0088] Comparative Example 1
[0089] A closed-cell lithium battery separator was prepared. Compared with Example 1, the only difference was that the modified polyethylene oxide derivative prepared in Preparation Example 1 was replaced by the modified polyethylene oxide derivative prepared in Comparative Preparation Example 1, and the other steps and conditions remained the same, and finally a closed-cell lithium battery separator with high ionic conductivity was obtained.
[0090] Comparative Example 2
[0091] A closed-cell lithium battery separator was prepared. Compared with Example 1, the only difference was that the modified polyethylene oxide derivative prepared in Preparation Example 1 was replaced by the modified polyethylene oxide derivative prepared in Comparative Preparation Example 2, and the other steps and conditions remained the same, and finally a closed-cell lithium battery separator with high ionic conductivity was obtained.
[0092] Comparative Example 3
[0093] A closed-cell lithium battery separator was prepared. Compared with Example 1, the only difference was that the modified polyethylene oxide derivative obtained in Preparation Example 1 was replaced by polyethylene oxide, and the other steps and conditions remained the same, and finally a closed-cell lithium battery separator with high ionic conductivity was obtained.
[0094] The performance tests of the closed-cell lithium battery separators prepared in Examples 1-5 and Comparative Examples 1-3 were performed using the following method:
[0095] Pore closure response time test: The diaphragm was tested using a thermomechanical analyzer (TMA) to record the time when the pores of the diaphragm began to close during the heating process.
[0096] Ionic conductivity test: The separator was assembled into a symmetrical battery, and the electrochemical impedance spectroscopy (EIS) was used to test the ionic conductivity of the separator at different temperatures.
[0097] Mechanical strength test: A tensile testing machine is used to perform a tensile test on the diaphragm to measure the tensile strength and elongation at break of the diaphragm.
[0098] The test results are listed in Table 1, which is as follows:
[0099] Table 1
[0100] Closed cell response time / s(130℃) <![CDATA[Ionic conductivity / 10 -3 S / cm (25 °C)]]> Tensile strength / MPa Example 1 55 1.8 25.6 Example 2 58 1.9 24.5 Example 3 58 1.9 24.6 Example 4 57 2.0 24.8 Example 5 59 2.0 24.5 Comparative Example 1 78 2.9 27.9 Comparative Example 2 85 2.8 28.5 Comparative Example 3 99 3.1 29.7
[0101] By analyzing the data in Table 1, it can be seen that compared with Comparative Examples 1-3, the high ionic conductivity closed-cell lithium battery separators of Examples 1-5 have a significantly faster response time at 130°C, and at the same time, their conductivity and strength properties are significantly better.
[0102] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.
Claims
1. A closed-cell lithium battery separator with high ionic conductivity, comprising a PE base film, characterized in that: The pore structure of the PE-based membrane is filled with a modified polyethylene oxide derivative, which contains an N-isopropylacrylamide segment, a fluorine-containing group and a thiourea group.
2. The closed-cell lithium battery separator with high ionic conductivity according to claim 1, characterized in that: The preparation method of the modified polyethylene oxide derivative comprises the following steps: Step 1: dissolving polyethylene oxide and N-isopropylacrylamide in an organic solvent at a molar ratio of (10-50):1, adding an initiator, and reacting at 60-80° C. for 2-6 hours under nitrogen protection to obtain a reaction solution A; Step 2: Add 1-butyl-3-methylimidazolium hexafluorophosphate to reaction solution A, add a catalyst, and react at 70-90° C. for 3-8 hours to obtain reaction solution B; Step 3: add isothiocyanate to reaction solution B, add a catalyst, react at 70-80° C. for 2 h, precipitate, filter, wash, and dry to obtain a modified polyethylene oxide derivative.
3. The closed-cell lithium battery separator with high ionic conductivity according to claim 2, characterized in that: In step 1, the initiator is any one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate, or a mixture of any multiple thereof in any proportion.
4. The closed-cell lithium battery separator with high ionic conductivity according to claim 2, characterized in that: In step 1, the mass ratio of the polyethylene oxide to the N-isopropylacrylamide to the volume of the organic solvent is 1 g:(10-15) mL.
5. The closed-cell lithium battery separator with high ionic conductivity according to claim 2, characterized in that: In step 2, the molar ratio of the reaction product to 1-butyl-3-methylimidazolium hexafluorophosphate in the reaction solution A is 1:(0.1-0.5).
6. The closed-cell lithium battery separator with high ionic conductivity according to claim 2, characterized in that: In step 2, the catalyst is any one of benzoyl peroxide, di-tert-butyl peroxide, and tert-butyl perbenzoate, or a mixture of any multiple thereof in any proportion.
7. The closed-cell lithium battery separator with high ionic conductivity according to claim 2, characterized in that: In step 3, the molar ratio of the reaction product to the isothiocyanate in the reaction solution B is 1:(0.2-0.6).
8. The closed-cell lithium battery separator with high ionic conductivity according to claim 2, characterized in that: In step 3, the catalyst is any one of dibutyltin dilaurate, stannous octoate, dibutyltin diacetate, and dibutyltin didodecylsulfide, or a mixture of any two or more thereof.
9. A method for preparing a closed-cell lithium battery separator with high ionic conductivity according to any one of claims 1 to 8, characterized in that: The steps include: S1. dissolving the modified polyethylene oxide derivative in water to form a coating solution with a mass fraction of 10-12%; S2. The coating liquid is evenly coated on the PE base film with a coating thickness of 1-2 μm. After vacuum drying, a closed-cell lithium battery separator with high ionic conductivity is obtained.
10. The method for preparing a closed-cell lithium battery separator with high ionic conductivity according to claim 9, characterized in that: In step S2, the vacuum drying is carried out at a temperature of 75-90°C and for a time of 1.5-2.5 hours.