PVDF (Polyvinylidene Fluoride) diaphragm with high ionic conductivity as well as preparation method and application of PVDF diaphragm

Abstract

The invention belongs to the technical field of battery diaphragms, and particularly relates to a PVDF diaphragm with high ionic conductivity and a preparation method and application thereof.The preparation method includes the steps that 1-vinyl imidazole and phosphotungstic acid are subjected to a grafting reaction to prepare a modifier, then the modifier and polyvinylidene fluoride (PVDF) are blended to prepare mixed slurry, and the modified PVDF diaphragm is prepared through coating and drying processes. The long side chain of 1-vinyl imidazole is utilized to construct a continuous ion transmission channel, the ion adsorption and conduction advantages of phosphotungstic acid high-crystallinity polyacid crystals are combined, the ionic conductivity of the diaphragm is increased to 2.4 mS / cm or above through the synergism of 1-vinyl imidazole and phosphotungstic acid high-crystallinity polyacid crystals, and meanwhile, the diaphragm has excellent mechanical properties and electrolyte wettability. The prepared diaphragm is suitable for various secondary batteries, the charge-discharge efficiency and the cycle stability of the battery can be remarkably improved, and the application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a PVDF separator with high ionic conductivity, its preparation method, and its application. Background Technology

[0002] Rechargeable batteries, as core energy storage devices in the new energy field, are widely used in new energy vehicles, portable electronic devices, energy storage power stations, and other fields. The separator, as a key component of a rechargeable battery, primarily functions to separate the positive and negative electrodes to prevent short circuits, while also providing a transport channel for electrolyte ions. The performance of the separator directly affects the battery's ionic conductivity, charge / discharge efficiency, cycle life, and safety.

[0003] Polyvinylidene fluoride (PVDF) is a commonly used substrate for battery separators due to its excellent chemical stability, mechanical strength, and resistance to electrolyte corrosion. However, the regular molecular chain structure and weak polarity of pure PVDF result in low ionic conductivity (typically below 1 mS / cm) and poor electrolyte wettability, limiting its application in high-performance batteries. To improve the ion transport performance of PVDF separators, existing technologies mainly optimize them through blending modification, surface coating, and the introduction of functional groups.

[0004] Existing technologies employ blending inorganic nanoparticles (such as titanium dioxide and alumina) with PVDF, which can improve the mechanical properties and thermal stability of the separator, but the improvement in ionic conductivity is limited. Alternatively, grafting hydrophilic monomers can improve the wettability of PVDF, but the introduction of long side chains can easily lead to a decrease in the mechanical properties of the separator. In addition, polyacid compounds, due to their unique crystal structure and high ionic conductivity potential, have been attempted for modification of battery materials. However, how to effectively combine polyacids with PVDF while synergistically improving ionic conductivity and mechanical properties remains a pressing technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a PVDF membrane with high ionic conductivity, its preparation method and application. It modifies PVDF by grafting with 1-vinylimidazolium and phosphotungstic acid, and uses long side chain groups to construct ion transport channels. Combined with the ion conduction advantages of highly crystalline polyacid crystals, the ionic conductivity of the PVDF membrane is significantly improved, while maintaining good mechanical properties and electrolyte wettability.

[0006] The objective of this invention is achieved through the following technical solution: This invention provides a PVDF membrane material with high ionic conductivity. The membrane material is composed of a modifier prepared by grafting 1-vinylimidazolium with phosphotungstic acid and a polyvinylidene fluoride (PVDF) matrix. The ionic conductivity of the membrane material is ≥2.4 mS / cm, and the electrolyte contact angle is ≤45°.

[0007] Furthermore, the tensile strength of the diaphragm material is ≥0.8MPa, and the compressive strength is ≥1.0MPa.

[0008] Furthermore, the porosity of the membrane material is 48% to 60%.

[0009] Furthermore, the modifier is obtained by grafting phosphotungstic acid with 1-vinylimidazolium, 4,4'-dimethyl-2,2'-bipyridine, and cuprous bromide as reactants via free radical polymerization.

[0010] Furthermore, the raw materials for preparing the modifier, by mass, include 180-220 parts of 1-vinylimidazole, 5 parts of 4,4'-dimethyl-2,2'-bipyridine, and 2 parts of cuprous bromide.

[0011] The present invention also provides a method for preparing the PVDF membrane material with high ionic conductivity, comprising the following steps: (1) Add 1-vinylimidazole, 4,4'-dimethyl-2,2'-bipyridine and cuprous bromide to pure water, pass in an inert gas and then seal and stir to react, to obtain slurry 1; (2) Add PVDF powder to dimethylformamide DMF or alkali / DMF mixed solution, heat and stir until PVDF is completely dissolved to obtain PVDF slurry; (3) After mixing slurry 1 with PVDF slurry and reacting, add phosphotungstic acid and stir evenly to obtain a mixed slurry; coat the mixed slurry onto the surface of the base membrane, and after drying, obtain a modified PVDF membrane on the base membrane.

[0012] Furthermore, the reaction temperature in step (1) is 80~100℃ and the reaction time is 8~10h; the heating temperature in step (2) is 60~80℃; the reaction time of slurry 1 and PVDF slurry in step (3) is 2~4h and the drying temperature is 60~80℃.

[0013] Furthermore, in step (3), the coating thickness of the mixed slurry on the base film is 10~25μm, and the drying time is 10min.

[0014] The present invention also provides an application of the PVDF membrane material with high ionic conductivity described above in a secondary battery, wherein the PVDF membrane material is used as an electrolyte membrane in the secondary battery.

[0015] Furthermore, the secondary battery is a zinc-air battery, a zinc-ion battery, a lithium-ion battery, or a sodium-ion battery; when the PVDF separator material is used in a zinc-air battery, the battery's open-circuit voltage is ≥1.46V, and its power density is ≥248.8mW / cm³. 2 Stable cycle duration ≥300h.

[0016] The beneficial effects of this invention are as follows: This invention prepares a modifier through a grafting reaction of 1-vinylimidazole and phosphotungstic acid. The long side chain groups of 1-vinylimidazole can construct continuous ion transport channels in the PVDF matrix, while the highly crystalline polyacid crystal structure of phosphotungstic acid provides abundant ion adsorption sites and enhances ion conduction. The synergistic effect of the two increases the ionic conductivity of the PVDF membrane to over 2.4 mS / cm, which is far superior to the industry standard of less than 1 mS / cm for pure PVDF membranes. Compared with single-component modification schemes, the synergistic modification effect of this invention is significant, with the ionic conductivity increasing by 50% compared to the control group without 1-vinylimidazole and by 33% compared to the control group without phosphotungstic acid, completely solving the core problem of insufficient ion transport efficiency of traditional PVDF membranes.

[0017] The modified PVDF separator prepared by this invention has a uniformly dispersed mesoporous structure, which can significantly increase the contact area between the separator and the electrolyte. The electrolyte contact angle can reach as low as 23.6°, which is far superior to the industry standard of 45°. It has excellent electrolyte affinity and rapid wetting ability. At the same time, the modifier has good compatibility with the PVDF matrix. While optimizing ion transport and wetting performance, the mechanical properties of the separator are not sacrificed. The tensile strength of the obtained separator can reach 0.8 MPa and the compressive strength can reach 1.01 MPa, which is more than 30% higher than the control group modified by a single component. It also has excellent resistance to deformation and structural stability, which can effectively avoid the risk of internal short circuit caused by separator damage during battery cycling.

[0018] The modified PVDF separator prepared by this invention is suitable for various secondary battery systems such as zinc-air batteries, zinc-ion batteries, lithium-ion batteries, and sodium-ion batteries. When used as a separator for zinc-air batteries, it can enable the battery to achieve a high open-circuit voltage of 1.46V and a flow rate of 248.8mW / cm². 2 It boasts high power density and stable cycle performance for up to 300 hours; when used in Zn / / Zn symmetric batteries, the battery charge and discharge voltage is stable with no significant fluctuations, and the cycle life can reach more than 100 hours. All performance characteristics are far superior to conventional glass fiber separators, which can effectively improve the charge and discharge efficiency, rate performance and long-term cycle stability of secondary batteries, and fully meet the needs of high-performance energy storage devices.

[0019] The preparation process of this invention adopts conventional solution blending, coating and drying processes, without the need for complex special equipment and harsh reaction conditions. The core reactions are all carried out under normal pressure, the reaction temperature range is mild and controllable, and the process parameters are highly stable. The raw materials used are all commercially available chemical raw materials, the production cost is low, the batch consistency is easy to control, and there is no need for complex post-processing procedures, which has mature conditions for large-scale industrial promotion and application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a scanning electron microscope (SEM) image of the modified PVDF membrane of Example 1 of the present invention; Figure 2 This is a graph showing the ionic conductivity of the modified PVDF membrane in Example 1 of the present invention. Figure 3 The stability test diagram of the assembled zinc-air battery half-cell when the modified PVDF separator of Example 1 of the present invention is used as the separator of the zinc-air battery. Figure 4 The diagram shows the open-circuit voltage, power density, and cycle stability of the assembled zinc-air battery when the modified PVDF separator of Embodiment 1 of the present invention is used as the separator of the zinc-air battery. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] The present invention will be further illustrated below through examples.

[0028] Example 1 This embodiment provides a PVDF membrane with high ionic conductivity, and its preparation steps are as follows: Step (1): Preparation of 1-vinylimidazolium slurry: 1.88 g of 1-vinylimidazolium, 93.0 mg of 4,4'-dimethyl-2,2'-bipyridine and 93.0 mg of cuprous bromide were added to 15 mL of pure water. Argon gas was then introduced and the mixture was sealed and stirred for 10 hours to obtain slurry 1. Step (2): Preparation of PVDF slurry: Add 5g of PVDF powder to 25mL of alkali / DMF (volume ratio 1:1) mixed solution, stir at 60℃ for 30 minutes until PVDF is completely dissolved to obtain PVDF slurry; Step (3): Add the slurry 1 obtained in step (1) to the PVDF slurry obtained in step (2), and while magnetically stirring at 60°C, add 2g of phosphotungstic acid, and then magnetically stir for 30 minutes to obtain a mixed slurry; Step (4): The mixed slurry obtained in step (3) is coated on the base membrane with a coating thickness of 20 μm. Then the base membrane is placed in a vacuum oven and dried at 60°C for 10 minutes to obtain the modified PVDF membrane of this embodiment.

[0029] Example 2 This embodiment provides a PVDF membrane with high ionic conductivity, and its preparation steps are as follows: Step (1): Preparation of 1-vinylimidazol slurry: 1.69 g of 1-vinylimidazol, 93.0 mg of 4,4'-dimethyl-2,2'-bipyridine and 93.0 mg of cuprous bromide were added to 15 mL of pure water, and then argon gas was introduced and the mixture was sealed and stirred for 10 hours to obtain slurry 1; Step (2): Preparation of PVDF slurry: Add 5g of PVDF powder to 25mL of alkali / DMF (volume ratio 1:1) mixed solution, stir at 60℃ for 30 minutes until PVDF is completely dissolved to obtain PVDF slurry; Step (3): Add the slurry 1 obtained in step (1) to the PVDF slurry obtained in step (2), and while magnetically stirring at 60°C, add 2g of phosphotungstic acid, and then magnetically stir for 30 minutes to obtain a mixed slurry; Step (4): The mixed slurry obtained in step (3) is coated on the base membrane with a coating thickness of 20 μm. Then the base membrane is placed in a vacuum oven and dried at 60°C for 10 minutes to obtain the modified PVDF membrane of this embodiment.

[0030] Example 3 This embodiment provides a PVDF membrane with high ionic conductivity, and its preparation steps are as follows: Step (1): Preparation of 1-vinylimidazol slurry: 2.07 g of 1-vinylimidazol, 93.0 mg of 4,4'-dimethyl-2,2'-bipyridine and 93.0 mg of cuprous bromide were added to 15 mL of pure water. Argon gas was then introduced and the mixture was sealed and stirred for 10 hours to obtain slurry 1. Step (2): Preparation of PVDF slurry: Add 5g of PVDF powder to 25mL of alkali / DMF (volume ratio 1:1) mixed solution, stir at 60℃ for 30 minutes until PVDF is completely dissolved to obtain PVDF slurry; Step (3): Add the slurry 1 obtained in step (1) to the PVDF slurry obtained in step (2), and while magnetically stirring at 60°C, add 2g of phosphotungstic acid, and then magnetically stir for 30 minutes to obtain a mixed slurry; Step (4): The mixed slurry obtained in step (3) is coated on the base membrane with a coating thickness of 20 μm. Then the base membrane is placed in a vacuum oven and dried at 60°C for 10 minutes to obtain the modified PVDF membrane of this embodiment.

[0031] Comparative Example 1 This comparative example provides a PVDF membrane whose preparation steps differ from those of Example 1 only in that 1-vinylimidazolium slurry is not added during the preparation process, while the other raw materials, process parameters, and operating steps are the same as those of Example 1.

[0032] Comparative Example 2 This comparative example provides a PVDF membrane whose preparation steps differ from those of Example 1 only in that phosphotungstic acid is not added during the preparation process, while the other raw materials, process parameters, and operating steps are the same as those of Example 1.

[0033] Experimental Example 1 The modified PVDF membranes obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to various performance tests, and the test results are shown in Table 1.

[0034] Table 1. Performance Data Comparison between Examples and Comparative Examples

[0035] Analysis of the above test results shows that the contact angle of Example 1 is 23.6°, indicating that it has excellent hydrophilicity; the tensile strength and compressive strength of Example 1 are 0.8MPa and 1.01MPa, respectively, and the elongation and compressive strength are 106.3% and 103.6%, respectively. Its overall performance is better than that of Examples 2-3 and Comparative Examples 1-2.

[0036] The modified PVDF membrane obtained in Example 1 was characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown, the membrane surface is smooth and has a uniformly dispersed mesoporous structure, which is more conducive to membrane wetting and accelerates electron / ion transfer.

[0037] The modified PVDF separator obtained in Example 1 was subjected to ionic conductivity testing in a Zn / / Zn symmetric cell, and the results are as follows: Figure 2 As shown, the membrane ionic conductivity of Example 1 is 2.4 mS / cm, demonstrating its excellent ion transport performance; simultaneously, the cycle performance of this symmetrical battery was tested, and the results are as follows. Figure 3 As shown, the battery charge and discharge voltage remains stable with almost no change, and the cycle life is at least 100 hours, which is significantly better than the battery assembled with glass fiber separator.

[0038] The modified PVDF membrane obtained in Example 1 was used as the membrane in a zinc-air battery assembly to create a full cell, and its electrochemical performance was tested. The results are as follows: Figure 4 As shown: This zinc-air battery exhibits a high open-circuit voltage of 1.46V and a power density of 248.8mW / cm². 2 Its high power density and stable cycle performance of up to 300 hours are far superior to zinc-air batteries assembled with glass fiber separators.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A PVDF membrane material with high ionic conductivity, characterized in that, The membrane material is a modifier prepared by grafting 1-vinylimidazolium with phosphotungstic acid, and is composited with a polyvinylidene fluoride (PVDF) matrix; the ionic conductivity of the membrane material is ≥2.4 mS / cm, and the electrolyte contact angle is ≤45°.

2. The PVDF membrane material according to claim 1, characterized in that, The tensile strength of the diaphragm material is ≥0.8MPa, and the compressive strength is ≥1.0MPa.

3. The PVDF membrane material according to claim 1 or 2, characterized in that, The porosity of the diaphragm material is 48%~60%.

4. The PVDF membrane material according to any one of claims 1-3, characterized in that, The modifier is obtained by grafting phosphotungstic acid with 1-vinylimidazolium, 4,4'-dimethyl-2,2'-bipyridine, and cuprous bromide as reactants via free radical polymerization.

5. The PVDF membrane material according to claim 4, characterized in that, The raw materials for preparing the modifier, by mass, include 180-220 parts of 1-vinylimidazole, 5 parts of 4,4'-dimethyl-2,2'-bipyridine, and 2 parts of cuprous bromide.

6. A method for preparing a PVDF membrane material with high ionic conductivity as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Add 1-vinylimidazole, 4,4'-dimethyl-2,2'-bipyridine and cuprous bromide to pure water, pass in an inert gas and then seal and stir to react, to obtain slurry 1; (2) Add PVDF powder to dimethylformamide DMF or alkali / DMF mixed solution, heat and stir until PVDF is completely dissolved to obtain PVDF slurry; (3) After mixing slurry 1 with PVDF slurry and reacting, add phosphotungstic acid and stir evenly to obtain a mixed slurry; coat the mixed slurry onto the surface of the base membrane, and after drying, obtain a modified PVDF membrane on the base membrane.

7. The preparation method according to claim 6, characterized in that, The reaction temperature in step (1) is 80~100℃ and the reaction time is 8~10h; the heating temperature in step (2) is 60~80℃; the reaction time of slurry 1 and PVDF slurry in step (3) is 2~4h and the drying temperature is 60~80℃.

8. The preparation method according to claim 6 or 7, characterized in that, The coating thickness of the mixed slurry on the base film in step (3) is 10~25μm, and the drying time is 10min.

9. The application of the PVDF membrane material with high ionic conductivity as described in any one of claims 1-5 in a secondary battery, characterized in that, The PVDF membrane material is used as the electrolyte membrane for secondary batteries.

10. The application according to claim 9, characterized in that, The secondary battery is a zinc-air battery, a zinc-ion battery, a lithium-ion battery, or a sodium-ion battery; when the PVDF separator material is used in a zinc-air battery, the battery's open-circuit voltage is ≥1.46V, and its power density is ≥248.8mW / cm². 2 Stable cycle duration ≥300h.

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