A nanofiber separator and a preparation method and application thereof

Abstract

The application discloses a nanofiber diaphragm and a preparation method and application thereof. The diaphragm has a thickness of 80-200 mu m, comprises a diaphragm and an inorganic ceramic material coated on the surface of the diaphragm, and the diaphragm contains a porous organic cage. The good solution processability and compatibility of the porous organic cage with the polymer provide a strong condition for the dispersion of the porous organic cage in the polymer, promote the hybridization of the porous organic cage and the polymer at a molecular level, and obtain a porous organic cage hybrid nanofiber diaphragm. The electrospinning porous organic cage hybrid nanofiber diaphragm has high porosity, electrolyte absorption rate and hydrophilicity, can combine a large number of water molecules, is favorable for reducing corrosion of a zinc negative electrode in contact with an aqueous electrolyte, has extremely high mechanical strength, can induce uniform deposition of zinc ions, and inhibits growth of zinc dendrites; the inorganic ceramic coating prevents the diaphragm from being punctured, improves the electrochemical performance and cycle life of an aqueous zinc ion battery, and has great application potential in the field of diaphragms for aqueous zinc ion batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of nanofiber diaphragm and its preparation method and application, belong to battery material field. BACKGROUND

[0002] In recent years, zinc ion battery has broad prospects in large-scale energy storage and intelligent wearable fields due to its high discharge capacity, good cycle performance, fast charge and discharge, low cost, easy processing, environmental friendliness, high ion conductivity and safety. However, during the charging and discharging process, the uneven deposition and dissolution of zinc ions on the surface of the metal zinc electrode will form rough and irregular dendrites on the surface of the metal zinc. Once the zinc dendrites with ultra-high Young's modulus (108 GPa) are formed, the zinc dendrites will pierce the diaphragm, causing the positive and negative electrodes in the battery to directly contact, resulting in short circuit of the battery, thereby hindering the excellent performance and actual industrialization of zinc ion battery. At present, the growth of zinc dendrites is one of the most difficult to overcome shortcomings in aqueous zinc ion battery.

[0003] So far, a large number of studies have been used to inhibit dendrite formation and protect zinc anode, such as by introducing a coating on the surface of the negative electrode or adjusting the electrolyte-electrode interface to provide physical protection; adding electrolyte additives or developing new electrolyte salts to coordinate ion transport, homogenize the interface electric field, and induce zinc deposition, etc. However, there are relatively few studies on stabilizing zinc ion battery by using battery diaphragm.

[0004] It is known that the diaphragm, as a component of the battery, not only allows ion transmission, but also avoids direct contact between the positive and negative electrodes. Therefore, the performance of the diaphragm has an important influence on the overall performance of the zinc ion battery, so designing and controlling the structure and performance of the diaphragm is expected to solve the problem of zinc dendrite formation during the operation of the zinc ion battery. At present, zinc ion battery mainly uses several hundred microns thick glass fiber (GF) diaphragm because of its good compatibility with aqueous electrolyte and high ion conductivity. Unfortunately, its poor mechanical properties and large pore size make it easy to be pierced by dendrites, leading to short circuit of the battery. SUMMARY

[0005] The present application uses porous organic cage and polymer material blending, combined with inorganic ceramic coating on the surface of the diaphragm, to prepare a porous organic cage hybrid nanofiber diaphragm. The good solution processability and compatibility of the porous organic cage with the polymer provide a strong condition for its dispersion in the polymer; the inorganic ceramic coating improves the mechanical strength of the diaphragm and the ability to resist dendrite puncture.

[0006] According to one aspect of the present application, a nanofiber diaphragm is provided, the thickness of the nanofiber diaphragm is 80-200 μm;

[0007] The nanofiber separator comprises a separator and a film coated on the surface of the separator;

[0008] The separator contains a porous organic cage;

[0009] The film coated on the surface of the separator contains an inorganic ceramic material.

[0010] The inorganic ceramic material is selected from at least one of silicon dioxide, titanium dioxide, layered double hydroxide, boehmite, aluminum oxide, graphene.

[0011] According to another aspect of the present application, a preparation method of the above-mentioned nanofiber separator is provided, characterized in that,

[0012] comprising the following steps:

[0013] The porous organic cage, the polymer and the polar solvent are mixed to obtain a spinning solution, electrospinning is performed to obtain a separator, a coating containing an inorganic ceramic material, polytetrafluoroethylene and N,N-dimethylformamide is coated on the surface of the separator, and a forming treatment is performed to obtain the nanofiber separator.

[0014] The porous organic cage is selected from at least one of CC1, CC2, CC3, CC4, CC16, CC18;

[0015] The polymer is selected from at least one of polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, polycaprolactone;

[0016] The polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran;

[0017] In the spinning solution, the concentration of the polymer is 8-20wt%;

[0018] In the spinning solution, the mass of the porous organic cage is 5-30wt% of the mass of the polymer.

[0019] The voltage of the electrospinning is 15-30kv;

[0020] The extrusion speed is 1.5-3ml / h;

[0021] The receiving distance is 8-25cm.

[0022] In the coating, the addition amount of the polytetrafluoroethylene is 5-15wt% of the inorganic ceramic material;

[0023] In the coating, the addition amount of the inorganic ceramic material is 10-40wt% of the N,N-dimethylformamide.

[0024] The forming treatment includes hot rolling and hot pressing;

[0025] The temperature of the hot rolling is 60-120℃;

[0026] The temperature of the hot pressing is 80-120℃;

[0027] The pressure of the hot pressing is 5-15MPa;

[0028] The time of the hot pressing is 3-10min.

[0029] Specifically,

[0030] (1) Preparation of electrospinning solution: add polymer into polar solvent, stir and dissolve; dissolve porous organic cage into polar solvent; mix the above two solutions uniformly to obtain electrospinning solution with a certain concentration.

[0031] (2) Electrospinning separator: add the above electrospinning solution into a syringe, and perform electrospinning under appropriate voltage, receiving distance and extrusion speed to collect the composite membrane. Place the collected composite membrane in a vacuum drying box for normal temperature and reduced pressure treatment until no solvent residue is left to obtain the electrospinning separator.

[0032] (3) Surface coating of the separator: add inorganic ceramic material and polytetrafluoroethylene into N,N-dimethylformamide solution, ball mill and disperse uniformly, and then coat on both sides of the electrospinning separator, vacuum dry at 80℃ for 24h to obtain ceramic coated electrospinning separator.

[0033] (4) Post-treatment forming: after the above ceramic coated electrospinning separator is subjected to five times of hot rolling and once hot pressing, the electrospinning porous organic cage hybrid nanofiber separator is obtained.

[0034] According to another aspect of the present application, the application provides the use of the above-mentioned nanofiber separator for aqueous zinc ion battery.

[0035] The electrospinning porous organic cage hybrid nanofiber separator has higher porosity, electrolyte absorption rate and hydrophilicity, can combine a large number of water molecules, is beneficial to reduce the corrosion of zinc negative electrode in contact with aqueous electrolyte; and has extremely high mechanical strength, can induce uniform deposition of zinc ions, thereby effectively inhibiting the growth of zinc dendrites; the separator coating layer protects the separator from being pierced by dendrites, and overall improves the electrochemical performance and cycle life of the aqueous zinc ion battery.

[0036] Compared with the prior art, the electrospinning porous organic cage hybrid nanofiber separator provided by the present application has the following advantages:

[0037] (1) The porous organic cage is introduced into the polymer blend in the application. The good solution processability and compatibility of the porous organic cage with the polymer provide strong conditions for its dispersion in the polymer, promoting the hybridization of the porous organic cage and the polymer at the molecular level, thereby obtaining a porous organic cage hybrid nanofiber separator.

[0038] (2) The porous organic cage is rich in nano-cage structure, providing a channel for ion transmission; the introduction of the porous organic cage improves the mechanical strength of the separator, and the inorganic ceramic coating further improves the mechanical strength and the ability to resist dendrite penetration of the separator.

[0039] (3) The electrospun porous organic cage hybrid nanofiber separator has higher porosity, electrolyte absorption rate and hydrophilicity, can combine a large number of water molecules, is conducive to reducing the corrosion of zinc negative electrode in contact with aqueous electrolyte; and has extremely high mechanical strength, which can induce uniform deposition of zinc ions, thereby effectively inhibiting the growth of zinc dendrites; the inorganic ceramic coating prevents the separator from being pierced by dendrites, thereby improving the overall electrochemical performance and cycle life of the aqueous zinc ion battery, and has great application potential in the field of aqueous zinc ion battery separators. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Figure 1 is a scanning electron microscope image of the electrospun porous organic cage hybrid nanofiber separator in Example 1 of the application, with a scale of 100 nm.

[0041] Figure 2 Figure 2 is a scanning electron microscope image of the electrospun nanofiber separator in Comparative Example 1 of the application, with a scale of 100 nm.

[0042] Figure 3 Figure 3 is a scanning electron microscope image of the commercial electrospun PAN nanofiber separator in Comparative Example 2 of the application, with a scale of 100 nm.

[0043] Figure 4a Figures 4, 5, 6 and 7 are polarization long cycle curves of the zinc-zinc batteries assembled with the separators in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the application at 5 mA / cm 2 DETAILED DESCRIPTION

[0044] The application will be described in detail below with reference to the examples, but the application is not limited to the following examples.

[0045] Example 1

[0046] (1) Preparation of electrospinning solution: 1.17 g of polyacrylonitrile was added to 8 g of N,N-dimethylformamide and stirred to dissolve; 0.12 g of porous organic cage CC3 was dissolved in 2 g of N,N-dimethylformamide; the above two solutions were mixed uniformly to obtain an electrospinning solution. ​

[0047] (2) Electrospun diaphragm: The above electrospinning solution was added to a syringe, and electrospinning was carried out under the conditions of 20kV voltage, receiving distance of 15cm, and extrusion speed of 2ml / h. The collected composite membrane was placed in a vacuum drying oven and treated under reduced pressure at room temperature until no solvent residue was left, thus obtaining the electrospun diaphragm.

[0048] (3) Surface coating of diaphragm: 1g of inorganic ceramic material silicon dioxide and 0.1g of polyvinylidene fluoride were added to 5g of N,N-dimethylformamide solution, ball milled and dispersed evenly, and then coated on both sides of the electrospun diaphragm. The diaphragm was vacuum dried at 80℃ for 24h to obtain ceramic-coated electrospun diaphragm.

[0049] (4) Post-processing and molding: The above-mentioned ceramic-coated electrospun diaphragm is subjected to five hot rolling processes (in sequence: 80℃, roll gap 260μm; 80℃, roll gap 230μm; 100℃, roll gap 200μm; 120℃, roll gap 180μm; 80℃, roll gap 160μm) and hot pressing at 100℃ and 10MPa for 5 minutes to obtain an electrospun porous organic cage hybrid nanofiber diaphragm.

[0050] Figure 1 This is a scanning electron microscope (SEM) image of the electrospun porous organic cage hybrid nanofiber membrane from Example 1 of this application, at a scale of 100 nm. Figure 1 It is evident that the nanofibers are uniform in size and the membrane has a high porosity. The surface of the fiber filaments has uniformly distributed protrusions, indicating that the porous organic cage is uniformly dispersed in the polymer.

[0051] Comparative Example 1

[0052] Compared with Example 1, except that the porous organic cage CC3 was not introduced, the other steps were exactly the same, and the electrospun nanofiber membrane with a thickness of 75 μm was finally obtained.

[0053] Figure 2 This is a scanning electron microscope (SEM) image of the electrospun nanofiber membrane in Comparative Example 1 of this application, at a scale of 100 nm. As can be seen from the image, the nanofibers are uniform in size and the membrane exhibits high porosity, consistent with... Figure 1 In comparison, the surface of the fiber is smoother.

[0054] Comparative Example 2

[0055] Comparative Example 2 is a commercially available electrospun PAN nanofiber membrane with a thickness of 75 μm.

[0056] Figure 3 This is a scanning electron microscope (SEM) image of the commercially available electrospun PAN nanofiber membrane from Comparative Example 2 of this application, at a scale of 100 nm. As can be seen from the image, the nanofibers are uniform in size and the membrane exhibits high porosity. Figure 1In contrast, the fiber filament surface is relatively smooth.

[0057] Comparative Example 3

[0058] Comparative Example 3 is a commercial glass cellulose membrane, thickness 220 μm.

[0059] Figure 4a , b, c, d are the polarization long cycle curves of the separators in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 in zinc-zinc batteries at 5 mA / cm 2 .

[0060] The separators in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were cut into round pieces, soaked in 1 M zinc sulfate for 1 minute, and the excess water on the surface was absorbed, and zinc-zinc batteries were assembled, and the polarization stability of the zinc-zinc batteries was tested at a current density of 5 mA / cm 2 . The results are shown in Figure 4. The battery in Example 1 can be stably cycled for more than 2400 hours, the battery in Comparative Example 1 short-circuits after 900 hours of cycling, the battery in Comparative Example 2 short-circuits after 900 hours of cycling, and the battery in Comparative Example 3 short-circuits after 350 hours of cycling.

[0061] It can be seen that the stability of the electrospun nanofiber membrane and the commercial electrospun PAN membrane in the aqueous zinc ion battery in the present application is much higher than that of the commercial glass cellulose membrane, and the stability of the electrospun porous organic cage hybrid nanofiber separator in Example 1 is significantly improved. This is mainly due to

[0062] The good solution processability and compatibility of the porous organic cage with the polymer provide a strong condition for its dispersion in the polymer, promoting the hybridization of the porous organic cage and the polymer at the molecular level; and its rich nanocage structure provides a channel for ion transport; the introduction of the porous organic cage improves the mechanical strength of the separator, and the inorganic ceramic coating further improves the mechanical strength and the ability to resist dendrite penetration of the separator; at the same time, the electrospun porous organic cage hybrid nanofiber separator has higher porosity, electrolyte absorption rate and hydrophilicity, can combine a large number of water molecules, and is conducive to reducing the corrosion of the zinc negative electrode in contact with the aqueous electrolyte. The electrospun porous organic cage hybrid nanofiber separator has a high zinc ion transference number, the electrolyte is uniformly infiltrated, and the high mechanical strength improves the ability to resist zinc dendrites, thus showing higher stability.

[0063] Example 2

[0064] (1) Preparation of electrospinning solution: 1.0 g of polyacrylonitrile and 0.5 g of polyurethane were added to 10 g of dimethyl sulfoxide and stirred to dissolve; 0.5 g of porous organic cage CC1 was dissolved in 5 g of N,N-dimethylformamide; the two solutions were mixed uniformly to obtain an electrospinning solution.

[0065] (2) Electrospinning of the separator: The electrospinning solution was added to a syringe and electrospinning was performed under the conditions of a voltage of 25 kV, a receiving distance of 10 cm, and an extrusion speed of 1.5 ml / h. The collected composite membrane was placed in a vacuum drying oven and treated at room temperature under reduced pressure until no solvent residue was left, to obtain an electrospun separator.

[0066] (3) Surface coating of the separator: 1.5 g of the inorganic ceramic material boehmite and 0.1 g of polytetrafluoroethylene were added to a 5 g solution of N,N-dimethylformamide, and ball-milling was performed to uniformly disperse the mixture. The mixture was then coated on both sides of the electrospun separator, and vacuum drying was performed at 80°C for 24 h, to obtain a ceramic-coated electrospun separator.

[0067] (4) Post-treatment and molding: The ceramic-coated electrospun separator was subjected to five times of hot roller pressing (in the order of 80°C, a roll gap of 260 μm; 80°C, a roll gap of 230 μm; 100°C, a roll gap of 200 μm; 120°C, a roll gap of 180 μm; 80°C, a roll gap of 160 μm), and hot pressing at 120°C and 5 MPa for 3 min, to obtain an electrospun porous organic cage hybrid nanofiber separator.

[0068] Example 3

[0069] (1) Preparation of the electrospinning solution: 0.5 g of polytetrafluoroethylene and 0.8 g of polycaprolactone were added to 8 g of N,N-dimethylformamide, and stirring was performed to dissolve the mixture; 0.25 g of the porous organic cage CC2 was dissolved in 2 g of N,N-dimethylformamide; and the two solutions were mixed to obtain an electrospinning solution.

[0070] (2) Electrospinning of the separator: The electrospinning solution was added to a syringe and electrospinning was performed under the conditions of a voltage of 15 kV, a receiving distance of 25 cm, and an extrusion speed of 2.5 ml / h. The collected composite membrane was placed in a vacuum drying oven and treated at room temperature under reduced pressure until no solvent residue was left, to obtain an electrospun separator.

[0071] (3) Surface coating of the separator: 1.0 g of the inorganic ceramic material alumina, 0.2 g of graphene, and 0.1 g of polytetrafluoroethylene were added to a 5 g solution of N,N-dimethylformamide, and ball-milling was performed to uniformly disperse the mixture. The mixture was then coated on both sides of the electrospun separator, and vacuum drying was performed at 80°C for 24 h, to obtain a ceramic-coated electrospun separator.

[0072] (4) Post-treatment and molding: The ceramic-coated electrospun separator was subjected to five times of hot roller pressing (in the order of 80°C, a roll gap of 260 μm; 80°C, a roll gap of 230 μm; 100°C, a roll gap of 200 μm; 120°C, a roll gap of 180 μm; 80°C, a roll gap of 160 μm), and hot pressing at 80°C and 5 MPa for 10 min, to obtain an electrospun porous organic cage hybrid nanofiber separator.

[0073] Example 4

[0074] (1) Preparation of electrospinning solution: 1.0 g of polyacrylonitrile and 0.2 g of polyvinylidene fluoride were added to 7 g of dimethyl sulfoxide and stirred to dissolve; 0.3 g of porous organic cage CC18 was dissolved in 2 g of tetrahydrofuran; the above two solutions were mixed uniformly to obtain an electrospinning solution.

[0075] (2) Electrospinning of the separator: the above electrospinning solution was added to a syringe, and electrospinning was performed under the conditions of a voltage of 20 kV, a receiving distance of 15 cm, and an extrusion speed of 1.5 ml / h. The collected composite membrane was placed in a vacuum drying box for normal temperature and reduced pressure treatment until no solvent residue was left, to obtain an electrospinning separator.

[0076] (3) Surface coating of the separator: 0.5 g of inorganic ceramic material layered double hydroxide, 0.1 g of graphene, and 0.05 g of polyvinylidene fluoride were added to 5 g of N,N-dimethylformamide solution, which was uniformly ball-milled and dispersed, and then coated on both sides of the electrospinning separator, which was vacuum dried at 80°C for 24 h, to obtain a ceramic-coated electrospinning separator.

[0077] (4) Post-processing forming: the above ceramic-coated electrospinning separator was subjected to five times of hot roller pressing (80°C, 260 μm roll gap; 80°C, 230 μm roll gap; 100°C, 200 μm roll gap; 120°C, 180 μm roll gap; 80°C, 160 μm roll gap, respectively), and hot pressing at 100°C and 5 MPa for 10 min after forming, to obtain an electrospinning porous organic cage hybrid nanofiber separator.

[0078] Example 5

[0079] (1) Preparation of electrospinning solution: 1.0 g of polyacrylonitrile and 0.5 g of polyurethane were added to 10 g of dimethyl sulfoxide and stirred to dissolve; 0.5 g of porous organic cage CC16 was dissolved in 5 g of N,N-dimethylformamide; the above two solutions were mixed uniformly to obtain an electrospinning solution.

[0080] (2) Electrospinning of the separator: the above electrospinning solution was added to a syringe, and electrospinning was performed under the conditions of a voltage of 15 kV, a receiving distance of 15 cm, and an extrusion speed of 2 ml / h. The collected composite membrane was placed in a vacuum drying box for normal temperature and reduced pressure treatment until no solvent residue was left, to obtain an electrospinning separator.

[0081] (3) Surface coating of the separator: 1.2 g of inorganic ceramic material titanium dioxide and 0.1 g of polyvinylidene fluoride were added to 5 g of N,N-dimethylformamide solution, which was uniformly ball-milled and dispersed, and then coated on both sides of the electrospinning separator, which was vacuum dried at 80°C for 24 h, to obtain a ceramic-coated electrospinning separator.

[0082] (4) Post-processing forming: the ceramic coated electrospun membrane is respectively subjected to five times of hot roller pressing (80℃, 260μm roll gap; 80℃, 230μm roll gap; 100℃, 200μm roll gap; 120℃, 180μm roll gap; 80℃, 160μm roll gap) and 120℃, 5MPa hot pressing treatment for 3min to form an electrospun porous organic cage hybrid nanofiber membrane.

[0083] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the preferred embodiments are disclosed above, the present application is not limited thereto. Any person skilled in the art can make some changes or modifications to the disclosed technical content without departing from the scope of the technical solutions of the present application, and such changes or modifications are equivalent to equivalent embodiments, and are within the scope of the technical solutions.

Claims

1. A nanofiber separator, characterized in that, the nanofiber separator comprises a separator and a film coated on the surface of the separator; the separator contains a porous organic cage; the film coated on the surface of the separator contains an inorganic ceramic material; the preparation method of the nanofiber separator comprises the following steps: mixing a porous organic cage, a polymer and a polar solvent to obtain a spinning solution, electrospinning to obtain a separator, coating a coating containing an inorganic ceramic material, polytetrafluoroethylene and N,N-dimethylformamide on the surface of the separator, and forming treatment to obtain the nanofiber separator; the nanofiber separator is applied to a water-based zinc ion battery.

2. The nanofiber separator of claim 1, characterized in that, the thickness of the nanofiber separator is 80-200 μm.

3. The nanofiber separator of claim 1, characterized in that, the porous organic cage is selected from at least one of CC1, CC2, CC3, CC4, CC16 and CC18; the inorganic ceramic material is selected from at least one of silicon dioxide, titanium dioxide, layered composite hydroxide, boehmite and aluminum oxide.

4. The nanofiber separator of claim 1, characterized in that, the polymer is selected from at least one of polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, polyurethane and polycaprolactone; the polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and tetrahydrofuran; the concentration of the polymer in the spinning solution is 8-20 wt%; the mass of the porous organic cage in the spinning solution is 5-30 wt% of the mass of the polymer.

5. The nanofiber separator of claim 1, characterized in that, the voltage of the electrospinning is 15-30 kv; the extrusion speed is 1.5-3 ml / h; the receiving distance is 8-25 cm.

6. The nanofiber separator of claim 1, characterized in that, the addition amount of polytetrafluoroethylene in the film coated on the surface of the separator is 5-15 wt% of the inorganic ceramic material; the addition amount of the inorganic ceramic material in the film coated on the surface of the separator is 10-40 wt% of the N,N-dimethylformamide.

7. The nanofiber separator of claim 1, characterized in that, the forming treatment comprises hot rolling and hot pressing; the temperature of the hot rolling is 60-120℃; the temperature of the hot pressing is 80-120℃; the pressure of the hot pressing is 5-15 MPa; the time of the hot pressing is 3-10 min.

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