PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries and its preparation method
By using PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane in lithium batteries, the problems of low conductivity and insufficient mechanical properties of traditional electrolytes are solved, and the high energy density and safety of lithium batteries are achieved.
Patent Information
- Application Number
- CN202311427060.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-31
- Publication Date
- 2025-06-24
- Estimated Expiration
- 2043-10-31
AI Technical Summary
The low room temperature conductivity and poor mechanical properties of traditional PVDF-HFP-based gel polymer electrolytes limit their application in lithium batteries.
The PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane is used to form semi-interpenetrating network polymers through a specific structural design, combining materials such as PEGDA and PEGMEMA to improve the retention ability and mechanical properties of ionic liquids.
The ionic conductivity and mechanical properties of the gel polymer electrolyte membrane for lithium batteries have been significantly improved, ensuring the high energy density and safety of lithium batteries.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention belongs to the field of polymer electrolytes, and relates to a gel polymer electrolyte membrane, and particularly to a PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries and a preparation method thereof. Background Art
[0002] Due to problems such as resource scarcity of fossil fuels and the "greenhouse effect" caused during their use, energy storage technologies such as solar energy and wind energy have become research hotspots. Lithium metal batteries are considered the holy grail among various energy storage technologies due to their theoretical specific capacity about ten times higher than that of graphite anodes, extremely low redox potential, and low density. However, when using ordinary commercial liquid electrolytes, due to the uneven distribution of current density during the cycling process, lithium dendrites formed and grown on the lithium anode will pierce the separator, ultimately leading to battery short-circuit. On the other hand, the heat released by the side reaction between lithium dendrites and liquid electrolytes will also pose a fire hazard. To address these challenges, considerable efforts have been made to explore safe and stable electrolytes compatible with lithium metal. Solid electrolytes are the most promising candidate materials for achieving high-energy-density safe lithium metal batteries.
[0003] Among various solid electrolytes, gel polymer electrolytes combine the advantages of traditional liquid electrolytes and all-solid-state polymer electrolytes, showing high ionic conductivity, eliminating the risk of liquid leakage, and improving the thermal stability of lithium metal batteries. Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) has a low glass transition temperature, high dielectric constant, wide electrochemical window, and excellent mechanical properties, and is the most promising polymer matrix. However, for traditional PVDF-HFP-based gel polymer electrolytes, due to the influence of the addition of materials such as lithium salts, plasticizers, and flame retardants, they have disadvantages such as low conductivity at room temperature and poor mechanical properties, which limit their application and development. Therefore, how to improve the ionic conductivity and mechanical properties of gel polymer electrolytes is an urgent problem to be solved currently. Summary of the Invention
[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries.
[0005] To achieve the above purpose, the technical solution adopted by the present invention is: A PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries, and its structure is shown in the following formula:
[0006]
[0007] Another object of the present invention is to provide a method for preparing the above PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane, and the main steps are as follows:
[0008] (1) First, dissolve N-methylimidazole and bromoethane in organic solvents respectively. After mixing evenly, slowly drop the bromoethane solution into the N-methylimidazole solution at a speed of 1 ml / S. At 60 °C, react fully for 24 h, wash repeatedly 3 times, and perform rotary evaporation to remove the organic solvent.
[0009] Among them, the molar ratio of N-methylimidazole to bromoethane is 1:1, and the organic solvent is ethyl acetate.
[0010] (2) Dissolve the product of step (1) and lithium bis(trifluoromethanesulfonyl)imide in deionized water according to a ratio, stir at room temperature for 24 h. After the reaction is complete, add an organic solvent for layering and extraction. Rotate and evaporate the obtained lower-layer solution to obtain a room-temperature liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][TFSI]) ionic liquid.
[0011] Among them, the molar ratio of the product of step (1) to lithium bis(trifluoromethanesulfonyl)imide is 1:1, and the organic solvent is dichloromethane.
[0012] (3) Dissolve a certain proportion of PVDF-HFP and lithium bis(trifluoromethanesulfonyl)imide in an organic solvent, stir at 50 °C for 4 h until PVDF-HFP is completely dissolved and mixed evenly, then stir at room temperature for 10 min and wait for the solution to cool to room temperature.
[0013] Among them, the mass ratio of PVDF-HFP to lithium bis(trifluoromethanesulfonyl)imide is 5:2 to 6, and the organic solvent is acetone.
[0014] (4) Uniformly mix a certain proportion of [EMIm][TFSI], polyethylene glycol diacrylate (PEGDA), and polyethylene glycol methyl ether methacrylate (PEGMEMA), and then add a certain amount of photoinitiator, and stir at room temperature until evenly mixed.
[0015] Among them, the mass ratio of [EMIm][TFSI], PEGDA, and PEGMEMA is 10:1:4 to 10:4:1, and the photoinitiator benzoin ethyl ether accounts for 0.6% of the total mass of the monomers.
[0016] (5) Add the product of step (4) to the product of step (3), stir for 5 min, then drop it onto a clean polytetrafluoroethylene mold, and place the polytetrafluoroethylene mold under an ultraviolet lamp for irradiation for 30 minutes to obtain the corresponding gel polymer electrolyte membrane.
[0017] The mass ratio of the product in step (4) to the product in step (3) is 9:7 to 11.
[0018] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:
[0019] (1) The ionic liquid of the present invention is not easy to volatilize and has little environmental pollution, and is considered a green reagent, which will be widely used in future energy, environment and other aspects.
[0020] (2) The abundant ether oxygen (EO) chains in PEGDA and PEGMEMA can efficiently dissociate lithium salts and promote the migration of lithium ions, providing guarantee for the high ionic conductivity of the ionic liquid gel polymer electrolyte membrane. The semi-interpenetrating network composed of the linear polymer PVDF-HFP and the network polymer (polymerization of PEGDA and PEGMEMA) reduces the crystallinity of PVDF-HFP and enhances the interaction between the polymer matrix and the ionic liquid, thereby retaining the ionic liquid in the matrix, providing good mechanical properties for the ionic liquid gel polymer electrolyte while ensuring excellent ionic conductivity. Description of the Drawings
[0021] Figure 1 It is a test chart of the mechanical properties of the dielectric film in Example 2.
[0022] Figure 2 It is a graph showing the change of ionic conductivity of the dielectric film in Example 2 with temperature.
[0023] Figure 3 It is a scanning electron microscope image of the network skeleton of the dielectric film in Example 2 after ethanol etching.
[0024] Figure 4 It is a test chart of the cycle performance of the LiFePO4 battery assembled in Example 2. Detailed Embodiments
[0025] The present invention will be further described below in conjunction with embodiments, but is not limited thereto.
[0026] The present invention is based on a PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane, and its structure is shown as follows:
[0027]
[0028] Through specific structural design, a semi-interpenetrating network polymer is formed, overcoming the problems of low ionic conductivity and mechanical strength in traditional PVDF-HFP-based gel polymer electrolytes
[0029] Example 1
[0030] (1) First, dissolve 3 g of N-methylimidazole and 3.98 g of bromoethane in 35 ml of ethyl acetate respectively. After mixing evenly, slowly drop the latter solution into the former solution at a rate of 1 ml / S. After reacting fully at 60 °C for 24 h, wash it repeatedly with ethyl acetate for 3 times, and then perform rotary evaporation to remove ethyl acetate.
[0031] (2) Dissolve 3 g of the product in step (1) and 4.5 g of lithium bis(trifluoromethanesulfonyl)imide in 70 ml of deionized water, stir at room temperature for 24 h. After the reaction is complete, add dichloromethane for layering and extraction. Rotate evaporate the obtained lower-layer solution to obtain the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][TFSI]) ionic liquid which is liquid at room temperature.
[0032] (3) Dissolve 0.5 g of PVDF-HFP and 0.4 g of lithium bis(trifluoromethanesulfonyl)imide in 8 ml of acetone, stir at 50 °C for 4 h until PVDF-HFP is completely dissolved and mixed evenly, then stir at room temperature for 10 min until the solution cools down to room temperature.
[0033] (4) Uniformly mix 1 g of the product in step (2), 0.1 g of polyethylene glycol diacrylate (PEGDA), and 0.4 g of methoxypolyethylene glycol methacrylate (PEGMEMA), and then add 0.003 g of benzoin ethyl ether, stir at room temperature until evenly mixed.
[0034] (5) Add all the product in step (4) to the product in step (3), stir for 5 min, then drop it onto a clean and flat polytetrafluoroethylene mold, and then place the polytetrafluoroethylene mold under an ultraviolet lamp for irradiation for 30 minutes to obtain the corresponding gel polymer electrolyte membrane.
[0035] Measure the conductivity and mechanical properties of the above gel polymer electrolyte membrane. The ionic conductivity at room temperature is measured to be 0.58×10 -3 S / cm, and the tensile strength is 0.86 MPa. At the same time, to detect the application of the gel polymer electrolyte membrane in lithium metal batteries, punch the above gel polymer electrolyte membrane into a disk with a diameter of 19 mm and assemble it with a positive electrode (lithium iron phosphate electrode sheet) and a negative electrode (lithium metal sheet) into a 2025 type button battery. Perform charge-discharge cycle performance tests at room temperature. The initial discharge specific capacity of the battery is measured to be 97 mAh·g -1 .
[0036] Example 2
[0037] This example provides a PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries and its preparation method. It is basically the same as Example 1, except that PEGDA is 0.2 g and PEGMEMA is 0.3 g in step (4). The ionic conductivity of the gel polymer electrolyte membrane at room temperature is measured to be 1.05×10 -3 S / cm, and the tensile strength is 0.56 MPa. To detect the application of the gel polymer electrolyte membrane in a lithium metal battery, the above gel polymer electrolyte membrane is punched into a disk with a diameter of 19 mm and assembled into a 2025-type button battery. The charge-discharge cycle performance is tested at room temperature. At a 0.1C rate, the initial discharge specific capacity of the battery is measured to be 150 mAh·g -1 .
[0038] Example 3
[0039] This example provides a PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries and its preparation method. It is basically the same as Example 1, except that PEGDA is 0.3 g and PEGMEMA is 0.2 g in step (4). The ionic conductivity of the gel polymer electrolyte membrane at room temperature is measured to be 0.90×10 -3 S / cm, and the tensile strength is 0.64 MPa. To detect the application of the gel polymer electrolyte membrane in a lithium metal battery, the above gel polymer electrolyte membrane is punched into a disk with a diameter of 19 mm and assembled into a 2025-type button battery. The charge-discharge cycle performance is tested at room temperature. At a 0.1C rate, the initial discharge specific capacity of the battery is measured to be 121 mAh·g -1 .
[0040] Example 4
[0041] This example provides a PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries and its preparation method. It is basically the same as Example 1, except that PEGDA is 0.4 g and PEGMEMA is 0.1 g in step (4). The ionic conductivity of the gel polymer electrolyte membrane at room temperature is measured to be 0.73×10 -3 S / cm, and the tensile strength is 0.79 MPa. To detect the application of the gel polymer electrolyte membrane in a lithium metal battery, the above gel polymer electrolyte membrane is punched into a disk with a diameter of 19 mm and assembled into a 2025-type button battery. The charge-discharge cycle performance is tested at room temperature. At a 0.1C rate, the initial discharge specific capacity of the battery is measured to be 103 mAh·g -1 .
[0042] The reason for this phenomenon is that in the ionic liquid gel polymer electrolyte, the increase in the crosslinker content helps to form more network polymers, reduce the crystallinity of PVDF-HFP, and lock more ionic liquids, which is beneficial to ion transport and the improvement of ion mobility. However, excessive crosslinking will lead to an increase in the crosslinking density of the network polymer and an increase in the resistance of the three-dimensional network, which instead inhibits ion transport and inevitably leads to a decrease in ionic conductivity, accompanied by an increase in mechanical properties. On the other hand, ion transport in the ionic liquid gel polymer electrolyte mainly occurs in the ionic liquid phase. The PEGMEMA comb structure and the hydrophilic linear poly-PEG chain are both beneficial to improving the liquid retention ability of the ionic liquid gel polymer. However, a high content of linear PEG chain segments will induce the crystallization of ionic liquids, and Li + ion migration mainly occurs in the amorphous region. Therefore, when the content of PEGMEMA is too high, ionic liquid crystallization will occur, resulting in a decrease in the ionic conductivity of the gel polymer membrane and an increase in mechanical properties. In summary, only the optimal ratio of PEGDA and PEGMEMA can form a flexible and mechanically stable ionic liquid gel polymer with good electrochemical properties.
[0043] Example 5
[0044] This example provides a PVDF-HFP semi-interpenetrating network-based ionic liquid gel polymer electrolyte membrane and its preparation method, which is basically the same as Example 2, except that the lithium bis(trifluoromethanesulfonyl)imide in step (3) is 0.2 g. The ionic conductivity of the gel polymer electrolyte membrane at room temperature is measured to be 0.68×10 -3 S / cm -1 , the tensile strength is 0.63 MPa. To detect the application of the gel polymer electrolyte membrane in a lithium metal battery, the above gel polymer electrolyte membrane is punched into a disc with a diameter of 19 mm and assembled into a 2025-type button battery. The charge-discharge cycle performance is tested at room temperature. At a 0.1C rate, the initial discharge specific capacity of the battery is measured to be 101 mAh·g -1 .
[0045] Example 6
[0046] This example provides a PVDF-HFP semi-interpenetrating network-based ionic liquid gel polymer electrolyte membrane and its preparation method, which is basically the same as Example 2, except that the lithium bis(trifluoromethanesulfonyl)imide in step (3) is 0.6 g. The ionic conductivity of the gel polymer electrolyte membrane at room temperature is measured to be 1.10×10 -3 S / cm -1, the tensile strength is 0.23 MPa. To test the application of the gel polymer electrolyte membrane in lithium metal batteries, the above gel polymer electrolyte membrane was punched into a disc with a diameter of 19 mm and assembled into a 2025-type button battery. The charge-discharge cycle performance was tested at room temperature, and the initial discharge specific capacity of the battery was measured to be 64 mAh·g -1 .
[0047] Comparative Example 1
[0048] This example provides a PVDF-HFP-based ionic liquid gel polymer solid electrolyte and its preparation method. 0.5 g of PVDF-HFP, 0.5 g of [EMIm][TFSI], and 0.4 g of LiTFSI were dissolved in 16 ml of NMP solution. The obtained solution was cast on the surface of a glass plate and vacuum-dried at 60 °C for 24 hours to obtain a gel polymer electrolyte membrane. The conductivity of the polymer electrolyte membrane at room temperature was measured to be 0.98×10 -4 S / cm, and the tensile strength was 0.02 MPa. To test the application of the gel polymer electrolyte membrane in lithium metal batteries, it was assembled into a disc with a diameter of 19 mm and assembled with a positive electrode (lithium iron phosphate electrode sheet) and a negative electrode (lithium metal sheet) into a 2025-type button battery. The charge-discharge cycle performance was tested at room temperature, and the initial discharge specific capacity of the battery was measured to be 83 mAh·g-1 at a 0.1C rate.
[0049] Comparative Example 2
[0050] This example provides a PVDF-HFP-based ionic liquid gel polymer electrolyte membrane and its preparation method, which is basically the same as Example 2, except that the amount of PEGDA in step (4) is 0 g and the amount of PEGMEMA is 0.5 g. The ionic conductivity of the gel polymer electrolyte membrane at room temperature was measured to be 0.49×10 -3 S / cm, and the tensile strength was 0.97 MPa. To test the application of the gel polymer electrolyte membrane in lithium metal batteries, the above gel polymer electrolyte membrane was punched into a disc with a diameter of 19 mm and assembled into a 2025-type button battery. The charge-discharge cycle performance was tested at room temperature, and the initial discharge specific capacity of the battery was measured to be 95 mAh·g -1 .
[0051] Comparative Example 3
[0052] This example provides a PVDF-HFP semi-interpenetrating network-based ionic liquid gel polymer electrolyte membrane and its preparation method, which is basically the same as Example 2, except that the amount of PEGDA in step (4) is 0.5 g and the amount of PEGMEMA is 0 g. The ionic conductivity of the gel polymer electrolyte membrane at room temperature was measured to be 0.38×10 -3 S / cm-1 , the tensile strength is 1.02 MPa. To detect the application of the gel polymer electrolyte membrane in lithium metal batteries, the above gel polymer electrolyte membrane was stamped into a disc with a diameter of 19 mm and assembled into a 2025-type button battery. The charge-discharge cycle performance was tested at room temperature, and the initial discharge specific capacity of the battery was measured to be 88 mAh·g -1 .
[0053] The above embodiments are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It is not intended to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.
Claims
1. A preparation method of a PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for a lithium battery, characterized in that, The preparation method is as follows: (1) First, dissolve N-methylimidazole and bromoethane in organic solvents respectively. After mixing evenly, slowly drip the bromoethane solution into the N-methylimidazole solution. React at 60 °C for 24 h, wash repeatedly 3 times, and perform rotary evaporation to remove the organic solvent; (2) Dissolve the product of step (1) and lithium bis(trifluoromethanesulfonyl)imide in deionized water according to a ratio, stir at room temperature for 24 h. After the reaction is complete, add an organic solvent for liquid separation and extraction. Rotary evaporate the obtained lower-layer solution to obtain 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][TFSI]) ionic liquid which is liquid at room temperature; (3) Dissolve PVDF-HFP and lithium bis(trifluoromethanesulfonyl)imide in an organic solvent, stir at 50 °C for 4 h until PVDF-HFP is completely dissolved and mixed evenly, then stir at room temperature for 10 min and wait for the solution to cool to room temperature; (4) Uniformly mix [EMIm][TFSI], polyethylene glycol diacrylate, and methoxypolyethylene glycol methacrylate, and then add a photoinitiator, stir at room temperature until evenly mixed; (5) Add the product of step (4) to the product of step (3), stir for 5 min, then drip it onto a clean polytetrafluoroethylene mold, and irradiate the polytetrafluoroethylene mold under an ultraviolet lamp for 30 minutes to obtain a gel polymer electrolyte membrane.
2. The preparation method of the PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries according to claim 1, characterized in that, In step (1), the molar ratio of N-methylimidazole to bromoethane is 1:1, and the organic solvent is ethyl acetate.
3. The preparation method of the PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries according to claim 1, characterized in that, In step (2), the molar ratio of the product of step (1) to lithium bis(trifluoromethanesulfonyl)imide is 1:1, and the organic solvent is dichloromethane.
4. The preparation method of the PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries according to claim 1, characterized in that, In step (3), the mass ratio of PVDF-HFP to lithium bis(trifluoromethanesulfonyl)imide is 5:2 - 6, and the organic solvent is acetone.
5. The preparation method of the PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries according to claim 1, characterized in that, In step (4), the mass ratio of [EMIm][TFSI], polyethylene glycol diacrylate, and methoxypolyethylene glycol methacrylate is 10:1:4 - 10:4:
1.
6. The preparation method of the PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries according to claim 1, characterized in that, In step (4), the photoinitiator is benzoin ethyl ether, and it accounts for 0.6% of the total mass of the monomers.
7. The preparation method of the PVDF-HFP-based semi-interpenetrating network ionic liquid gel polymer electrolyte membrane for lithium batteries according to claim 1, characterized in that, In step (5), the mass ratio of the product of step (4) to the product of step (3) is 9:7 - 11.