Functional diaphragm as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a functional diaphragm as well as a preparation method and application thereof. The functional diaphragm comprises a polymer base membrane and a porous coordination polymer functional coating, wherein the weight per unit area of the porous coordination polymer functional coating is 0.2-1 mg.cm <-2 >; and the thickness of the porous coordination polymer functional coating is 20-60 [mu] m. And the liquid retention capacity of the modified diaphragm in unit area is 20-45mg. Cm <-2 >. When the functional diaphragm provided by the invention is used in the battery, the cycle stability, cycle life and rate charge-discharge performance of the battery can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and specifically relates to a functional separator and its preparation method and application. Background Art

[0002] Sodium-ion batteries have always been regarded as the best choice for large-scale energy storage applications due to their rich resources and low prices.

[0003] However, sodium-ion batteries still face many challenges. For example, the reaction between the liquid electrolyte and the metal negative electrode will form an unstable solid electrolyte interface, resulting in the continuous consumption of the metal negative electrode and the electrolyte. In addition, the lithium dendrites generated by the uneven deposition of sodium ions will cause the separator in the sodium metal battery to be pierced, resulting in poor safety and short cycle life.

[0004] Therefore, it is necessary to improve the separator to better meet the market demand. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a functional separator and its preparation method and application. The separator in this application has excellent chemical stability and structural stability. It not only significantly enhances the wettability on the surface of the metal negative electrode, but also is conducive to the uniform deposition of metal cations and inhibits the growth of dendrites. The overpotential of sodium metal ion deposition is reduced by 2 times, and the cycle life is increased by 8 times.

[0006] In order to achieve the above invention purpose, the present invention is realized through the following technical solutions:

[0007] A functional separator, which comprises two parts: a polymer-based membrane and a porous coordination polymer functional coating; the porous coordination polymer functional coating prepared by the doctor blade method not only provides a path for the migration of metal cations, but also forms a solid electrolyte interface film of a metal-silver alloy layer on the surface of the metal negative electrode, which can guide the uniform deposition of metal cations and effectively inhibit the growth of dendrites.

[0008] Further, in the functional separator, the weight per unit area of the porous coordination polymer functional coating is 0.2 - 1 mg·cm -2 , preferably 0.45 - 6 mg·cm -2 ; the thickness of the porous coordination polymer functional coating is 20 - 60 μm, preferably 0.35 - 0.45 μm.

[0009] Further, in the functional separator, the liquid retention per unit area is 20 - 45 mg·cm -2 , preferably 30 - 40 mg·cm -2 .

[0010] Further, in the functional separator described above, the functional separator composed of a polymer-based membrane and a porous coordination polymer functional coating presents as a flexible solid state during the application process; preferably, the composition of the functional separator is: 50-70% by weight of the porous coordination polymer functional coating and 30-50% by weight of the polymer-based membrane.

[0011] Further, in the functional separator described above, within the battery operating voltage range, the functional separator can form a solid electrolyte interface of a metal-silver alloy layer on the surface of the metal negative electrode, and the solid electrolyte interface is mainly composed of inorganic substances; preferably, the composition of the solid electrolyte interface by mass percentage is: the metal-silver alloy accounts for 40-50%, the metal fluoride accounts for 10-30%, the metal oxide accounts for 0-10%, the metal organic compound accounts for 0-10%, and the balance is inevitable impurities such as (metal sulfide, metal nitride), and the sum of the total content percentages is 100%.

[0012] Further, the functional separator described above is used as a separator for secondary batteries, and its sodium ion conductivity is as high as 1.5 mS·cm -1 。

[0013] Preferably, the preparation method of the functional separator of the present invention with a polymer separator as the base film and a porous coordination polymer as the functional coating includes the following steps:

[0014] (1) Post-treatment of the porous coordination polymer: Disperse the porous coordination polymer in deionized water, then add a certain amount of silver nitrate and stir for a period of time in a dark environment, then add a certain amount of sodium borohydride and continue stirring, and finally wash with ethanol.

[0015] The porous coordination polymer can be prepared by using existing technologies; it can also be preferably synthesized by the following steps. The synthesis steps of the porous coordination polymer are: Dissolve the organic ligand (2-aminoterephthalic acid) in a solvent (N,N-dimethylformamide:methanol = 75:8, mass ratio), then add tetrabutyl titanate, and carry out a solvothermal reaction at 150 °C to generate a porous coordination polymer with a metal as the node and an organic ligand as the connecting unit.

[0016] Preferably, the concentration of silver nitrate is 0.1 mol / L; the stirring time in the dark environment is 2-4 h; the proportional relationship between silver nitrate and sodium borohydride is 0.8-2 mL:3-7 mg; the stirring time after adding sodium borohydride is 1-2 h.

[0017] (2) Activation of the porous coordination polymer: Vacuum activate the post-treated porous coordination polymer to obtain the activated porous coordination polymer.

[0018] Preferably, the vacuum activation conditions of the porous coordination polymer are: temperature 50-80 °C, time 12-24 h.

[0019] (3) Preparation of the functional separator: Take the activated porous coordination polymer and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. Use a scraper to evenly scrape the emulsion containing the porous coordination polymer onto at least one surface of the polymer-based membrane, and place it in a vacuum oven for vacuum drying to obtain the functional separator.

[0020] Preferably, in the ethanol and polyvinylidene fluoride emulsion, the density of the PVDF emulsion is 1.032 ± 0.3 g / cm -3 ; the mass ratio of the porous coordination polymer to polyvinylidene fluoride is 9:1; based on a weight percentage of 100, the weight ratio of the functional coating is 50 - 70%, and the weight ratio of the polymer-based membrane is 30 - 50%; the temperature of the vacuum oven is 60 - 80 °C.

[0021] This application also protects the use of the above-mentioned functional separator or the functional separator prepared by the above method in secondary batteries.

[0022] This application also protects a secondary battery containing the above-mentioned functional separator or the functional separator prepared by the above method. When used as a separator for secondary batteries, its sodium ion conductivity is as high as 1.5 mS cm -1 .

[0023] The above-mentioned secondary batteries include button cells, cylindrical batteries, soft-pack batteries, and aluminum-shell batteries, and are used in the field of high-energy density energy storage.

[0024] The steps for assembling the secondary battery are as follows: In an environment filled with argon (H2O, O2 < 0.1 ppm), the battery consists of a positive electrode material, a negative electrode material, a modified separator, and a liquid electrolyte of sodium / lithium batteries.

[0025] The liquid electrolyte consists of a lithium salt / sodium salt and an organic solvent. The lithium salt / sodium salt is selected from one of lithium / sodium bis(trifluoromethanesulfonyl)imide, lithium / sodium bis(fluorosulfonyl)imide, lithium / sodium hexafluorophosphate, lithium / sodium perchlorate, and lithium / sodium bis(oxalato)borate, etc.; the organic solvent for dissolving the lithium / sodium salt is selected from at least one of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, ethyl acrylate, propylene glycol methyl ether acetate, 1,3-dioxolane, and ethylene glycol dimethyl ether; the polymer-based membrane is selected from at least one of polyethylene (PE) separators, polypropylene (PP) separators, and polyethylene-polypropylene composite separators

[0026] In the porous coordination polymer functional coating of the present invention, negatively charged amino groups are carried in the pore structure, and these groups produce an electrostatic repulsion effect on anions in the electrolyte, thereby effectively promoting the transport of metal cations. On the other hand, during the cycling of the battery, the nano-silver particles distributed on the surface of the porous coordination polymer can in-situ form a highly stable solid electrolyte interface film of metal-silver alloy with the metal negative electrode. This interface film significantly enhances the wettability of the interface, effectively prevents further reaction between the electrolyte and the metal negative electrode, and at the same time guides the uniform deposition of metal cations, thereby effectively inhibiting the growth of dendrites.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The functional separator provided by the present invention consists of two parts: a polymer-based membrane and a porous coordination polymer functional coating. The porous coordination polymer in the functional separator, as a functional coating, has a rich porosity and a periodically arranged pore structure, which can provide a path for the migration of metal cations. The porous coordination polymer has excellent pore volume and can effectively improve the liquid retention performance of the separator.

[0029] (2) By forming a solid electrolyte interface of metal-silver alloy on the surface of the metal negative electrode, the present invention enhances the interface wettability of the metal negative electrode. Secondly, the porous coordination polymer functional coating in the functional separator carries negatively charged amino groups, which have an electrostatic repulsion effect on anions in the electrolyte, can promote the transport of metal cations, and improve the ion diffusion rate of metal cations. Through the synergistic effect of the above two advantages, the uniform deposition of metal cations is effectively guided, the growth of dendrites is inhibited, and the overall performance of the battery is improved.

[0030] (3) A functional separator provided by the present invention consists of two parts: a polymer-based membrane and a porous coordination polymer functional coating. The porous coordination polymer functional coating is uniformly coated on the surface of the polymer-based membrane by a doctor blade method to prepare the functional separator. The porous coordination polymer functional coating can effectively improve the problem of low ion diffusion rate of metal cations at the separator.

[0031] (4) For the functional separator of the present invention, it is prepared by a doctor blade method. The separator preparation method is simple and the operation is convenient. The functional separator containing the porous coordination polymer functional coating presents as a flexible solid during application.

[0032] (5) In order to achieve high performance of the battery, the solid electrolyte interface formed by the functional separator on the surface of the metal negative electrode is mainly composed of metal-silver alloy. The preferred composition of the solid electrolyte interface is: the proportion of metal-silver alloy is 30-50%, the proportion of metal fluoride is 20-30%, the proportion of metal oxide is 0-10%, and the proportion of metal organic compound is 0-10%.

[0033] (6) The nano silver particles contained in the functional separator provided by the present invention can form a solid electrolyte interface film of a metal-silver alloy layer on the surface of the metal negative electrode. This solid electrolyte interface film has excellent chemical stability and structural stability. It not only significantly enhances the wettability of the metal negative electrode surface, but also facilitates the uniform deposition of metal cations and inhibits the growth of dendrites. The overpotential of sodium metal ion deposition is reduced by 2 times, and the cycle life is increased by 8 times. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of the modified separator in Example 1 of the present invention.

[0035] Figure 2 It is the room temperature ionic conductivity and ionic migration activation energy of the functional separator in Experimental Example 1 of the present invention.

[0036] Figure 3 It is the voltage-time curve of the deposition / stripping cycle test of the sodium symmetric battery with the functional separator in Experimental Example 2 of the present invention.

[0037] Figure 4 It is a scanning electron microscope image of the surface of the sodium metal negative electrode after the deposition / stripping cycle test of the sodium symmetric battery with the functional separator in Experimental Example 2 of the present invention.

[0038] Figure 5 It is the long-term cycling performance at 1C of the full battery prepared with the functional separator in Experimental Example 3 of the present invention.

[0039] Figure 6 It is the voltage-time curve of the deposition / stripping cycle test of the sodium symmetric battery with the functional separator in Comparative Experimental Example 1 of the present invention.

[0040] Figure 7 It is a scanning electron microscope image of the surface of the sodium metal negative electrode after the deposition / stripping cycle test of the sodium symmetric battery with the functional separator in Comparative Experimental Example 1 of the present invention.

[0041] Figure 8 It is the long-term cycling performance at 1C of the full battery prepared with the functional separator in Comparative Example 2 of the present invention. Detailed Embodiments

[0042] The present invention will be further described below in conjunction with the embodiments. The described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0043] In this application, unless otherwise specified, % represents its mass percentage, i.e., wt%; reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained by purchasing in the market.

[0044] Example 1:

[0045] This example provides a modified separator and its preparation method and application. The preparation method of the modified separator is as follows:

[0046] Dissolve 1.81 g of 2-aminoterephthalic acid in a mixed solvent containing 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner and heat at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it in a blast oven at 60 °C for 6 h.

[0047] Take 0.1 g of the porous coordination polymer and disperse it in 50 mL of deionized water. Add 1.03 mL of AgNO3 solution (concentration: 0.1 mol / L) and stir in the dark for 2 h. Then add 3.9 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer with a silver content of 10 mass%. Finally, vacuum dry it at 100 °C for 12 h to obtain the activated porous coordination polymer.

[0048] Take the activated porous coordination polymer with a silver content of 10 mass% and disperse it in an emulsion containing ethanol and polyvinylidene fluoride (the density of the PVDF emulsion is 1.032 ± 0.3 g / cm -3 )), where the mass ratio of the porous coordination polymer with a silver content of 10 mass% to polyvinylidene fluoride is 9:1. Use a scraper to evenly coat the porous coordination polymer emulsion on both sides of the surface of the polymer base film. The coating thickness is 40 μm, and place it in a vacuum oven and vacuum dry it at 60 °C for 12 h to obtain a functional separator.

[0049] Among them, Figure 1 is a schematic structural diagram of the modified separator prepared in Example 1.

[0050] Example 2:

[0051] Dissolve 1.81 g of 2-aminoterephthalic acid in a mixed solvent containing 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner and heat at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it in a blast oven at 60 °C for 6.5 h.

[0052] Disperse 0.1 g of the porous coordination polymer in 50 mL of deionized water, add 0.85 mL of AgNO3 solution (concentration: 0.1 mol / L), and stir for 2 h in a dark environment. Then add 3.2 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash with ethanol to obtain a porous coordination polymer with a silver content of 8.3 mass%. Finally, heat it under vacuum at 100 °C for 12.5 h to obtain the activated porous coordination polymer.

[0053] Disperse the activated porous coordination polymer with a silver content of 8.3 mass% in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 8.3 mass% to polyvinylidene fluoride is 9:1. Use a spatula to evenly spread the porous coordination polymer emulsion on both sides of the surface of the polymer substrate film. The coating thickness is 40 μm, and place it in a vacuum oven and dry under vacuum at 60 °C for 12 h to obtain the functional separator.

[0054] Example 3:

[0055] Dissolve 1.81 g of 2-aminoterephthalic acid in a mixed solvent containing 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless steel autoclave with a PTFE liner and heat at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash with ethanol to obtain the porous coordination polymer. Finally, heat it in a forced-air oven at 60 °C for 7 h.

[0056] Disperse 0.1 g of the porous coordination polymer in 50 mL of deionized water, add 1.8 mL of AgNO3 solution, and stir for 2 h in a dark environment. Then add 6.8 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash with ethanol to obtain a porous coordination polymer with a silver content of 17.5 mass%. Finally, activate it by heating under vacuum at 1000 °C for 13 h.

[0057] Disperse the activated porous coordination polymer with a silver content of 17.5 mass% in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 17.5 mass% to polyvinylidene fluoride is 9:1. Use a spatula to evenly spread the porous coordination polymer emulsion on both sides of the surface of the polymer substrate film. The coating thickness is 40 μm, and place it in a vacuum oven and dry under vacuum at 60 °C for 12 h to obtain the functional separator.

[0058] Example 4:

[0059] Dissolve 1.81 g of 2-aminoterephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner and heat it at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it in a blast oven at 60 °C for 8 h.

[0060] Take 0.1 g of the porous coordination polymer and disperse it in 50 mL of deionized water. Add 1.03 mL of AgNO3 solution and stir for 2 h in a dark environment. Then, add 3.9 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer with a silver content of 10% by mass. Finally, heat it under vacuum at 100 °C for 13.5 h for activation.

[0061] Take the activated porous coordination polymer with a silver content of 10% by mass and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 10% by mass to polyvinylidene fluoride is 9:1. Use a spatula to evenly coat the porous coordination polymer emulsion on both sides of the surface of the polymer substrate membrane. The coating thickness is 30 μm, and place it in a vacuum oven and dry it under vacuum at 60 °C for 12 h to obtain a functional separator.

[0062] Example 5:

[0063] Dissolve 1.81 g of 2-aminoterephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner and heat it at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it in a blast oven at 60 °C for 6 h.

[0064] Take 0.1 g of the porous coordination polymer and disperse it in 50 mL of deionized water. Add 1.03 mL of AgNO3 solution and stir for 2 h in a dark environment. Then, add 3.9 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer with a silver content of 10% by mass. Finally, heat it under vacuum at 100 °C for 12 h for activation.

[0065] Take the activated porous coordination polymer with a silver content of 10% by mass and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 10% by mass to polyvinylidene fluoride is 9:1. Use a scraper to evenly apply the porous coordination polymer emulsion on both sides of the surface of the polymer substrate film. The coating thickness is 50 μm, and then place it in a vacuum oven and dry it under vacuum at 60 °C for 12 h to obtain a functional separator.

[0066] Comparative Example 1:

[0067] Dissolve 1.81 g of 2-aminoterephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless steel autoclave lined with polytetrafluoroethylene and heat it at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it in a blast oven at 60 °C for 6 h.

[0068] Take 0.1 g of the porous coordination polymer and disperse it in 50 mL of deionized water. Add 0.7 mL of AgNO3 solution and stir it in the dark for 2 h, then add 2.65 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer with a silver content of 6.8% by mass. Finally, heat it under vacuum at 100 °C for 12 h for activation.

[0069] Take the activated porous coordination polymer with a silver content of 6.8% by mass and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 6.8% by mass to polyvinylidene fluoride is 9:1. Use a scraper to evenly apply the porous coordination polymer emulsion on both sides of the surface of the polymer substrate film. The coating thickness is 40 μm, and then place it in a vacuum oven and dry it under vacuum at 60 °C for 12 h to obtain a separator.

[0070] Comparative Example 2:

[0071] Dissolve 1.81 g of 2-aminoterephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless steel autoclave lined with polytetrafluoroethylene and heat it at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it in a blast oven at 60 °C for 6 h.

[0072] Take 0.1 g of the porous coordination polymer and disperse it in 50 mL of deionized water. Add 2.2 mL of AgNO3 solution and stir for 2 h in a dark environment. Then add 8.33 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer with a silver content of 21.4% by mass. Finally, vacuum heat it at 100 °C for 12 h for activation.

[0073] Take the activated porous coordination polymer with a silver content of 21.4% by mass and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 21.4% by mass to polyvinylidene fluoride is 9:1. Use a spatula to evenly scrape the porous coordination polymer emulsion on both sides of the surface of the polymer substrate film. The coating thickness is 40 μm, and place it in a vacuum oven and dry it under vacuum at 60 °C for 12 h to obtain a separator.

[0074] Comparative Example 3:

[0075] Dissolve 1.81 g of 2-aminoterephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol. Add 0.8 mL of tetrabutyl titanate and stir for 0.5 h. Transfer it to a stainless steel autoclave lined with polytetrafluoroethylene and heat it at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it with forced air at 60 °C for 6 h.

[0076] Take 0.1 g of the porous coordination polymer and disperse it in 50 mL of deionized water. Add 1.03 mL of AgNO3 solution and stir for 2 h in a dark environment. Then add 3.9 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer with a silver content of 10% by mass. Finally, vacuum heat it at 100 °C for 12 h for activation.

[0077] Take the activated porous coordination polymer with a silver content of 10% by mass and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 10% by mass to polyvinylidene fluoride is 9:1. Use a spatula to evenly scrape the porous coordination polymer emulsion on both sides of the surface of the polymer substrate film. The coating thickness is 10 μm, and place it in a vacuum oven and dry it under vacuum at 60 °C for 12 h to obtain a separator.

[0078] Comparative Example 4:

[0079] Dissolve 1.81 g of 2-aminoterephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, and stir for 0.5 h. Transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner and heat at 150 °C for 24 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer. Finally, heat it in a blast oven at 60 °C for 6 h.

[0080] Take 0.1 g of the porous coordination polymer and disperse it in 50 mL of deionized water. Add 1.03 mL of AgNO3 solution and stir for 2 h in a dark environment. Then, add 3.9 mg of sodium borohydride and stir for 1 h. Then, centrifuge to collect the pale yellow solid. Finally, wash it with ethanol to obtain a porous coordination polymer with a silver content of 10 wt%. Finally, activate it by vacuum heating at 100 °C for 12 h.

[0081] Take the activated porous coordination polymer with a silver content of 10 wt% and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. The mass ratio of the porous coordination polymer with a silver content of 10 wt% to polyvinylidene fluoride is 9:1. Use a spatula to evenly scrape the porous coordination polymer emulsion on both sides of the surface of the polymer substrate membrane. The coating thickness is 70 μm, and place it in a vacuum oven and dry it under vacuum at 60 °C for 12 h to obtain a separator.

[0082] Experimental Example 1:

[0083] The functional separator used in this experimental example was prepared according to the method in Example 1. Assemble the functional separator into a stainless-steel symmetric cell and conduct room-temperature ionic conductivity tests and ion migration activation energy tests. As Figure 1 shown, the test results show that the room-temperature ionic conductivity of the functional separator is 1.5 mS cm -1 , and the ion migration activation energy is 0.14 eV. The test results indicate that the porous coordination polymer functional separator has excellent ionic conductivity and ion diffusion performance.

[0084] Experimental Example 2:

[0085] The functional separator used in this experimental example was prepared according to the method in Example 1.

[0086] Assemble the functional separator into a sodium symmetric cell and conduct deposition / stripping cycle tests. As Figure 2 shown, this kind of battery can perform deposition / stripping cycle tests for 2000 h under the conditions of a current density of 0.2 mA cm -2 , a deposition amount of 0.1 mAh cm -2 , and the polarization voltage is only 29 mV. Subsequently, conduct scanning electron microscopy characterization on the surface of the sodium metal negative electrode after the deposition / stripping cycle. As Figure 3As shown, no dendrite growth was observed on the surface of the sodium metal anode, and the deposition morphology was uniform and dense, indicating that the present invention effectively inhibited the generation of dendrites during the cycling of the sodium metal anode and improved the electrochemical performance of the sodium metal anode.

[0087] Experimental Example 3:

[0088] The functional separator used in this experimental example was prepared according to the method in Example 1.

[0089] The sodium vanadium phosphate cathode material, the functional separator, and the sodium metal anode were assembled into a full cell, and long-term cycling performance tests were carried out at different charge-discharge rates. As Figure 4 shown, at a charge-discharge rate of 1C, the initial capacity of the full cell was as high as 101 mAh g -1 and it could stably cycle 836 times, and the capacity retention rate was as high as 90%.

[0090] Experimental Comparative Example 1:

[0091] As a comparison with Example 2, an untreated polymer-based membrane was made into a symmetric cell for deposition / stripping cycling tests. As Figure 5 shown, at a current density of 0.2 mA cm -2 and a deposition amount of 0.1 mAh cm -2 , after 200 h of deposition / stripping cycling tests, the cell short-circuited, and the polarization voltage was as high as 60 mV. The cycle life of the cell was only 1 / 8 of that in Experimental Example 1 of the present invention, and the polarization voltage was 2 times that in Experimental Example 1 of the present invention. As Figure 6 shown, the functional separator effectively inhibited the growth of dendrites, while a large number of dendrites were found in the comparative example. Through comparison, it is shown that the solid electrolyte interface film of the metal-silver alloy layer formed on the surface of the metal anode by the functional separator of the present invention can effectively inhibit the growth of dendrites, thereby improving the cycle life of the cell.

[0092] Experimental Comparative Example 2:

[0093] As a comparison with Example 3, an untreated polymer-based membrane, the sodium vanadium phosphate cathode material, and the sodium metal anode were assembled into a full cell for long-term cycling tests. As Figure 7 shown, at a charge-discharge rate of 1C, the initial capacity of the cell was 85 mAh g -1 , but after 280 cycles, the capacity of the cell decreased to 70 mAh g -1 , and the capacity loss rate per cycle was as high as 0.63‰, which was more than 5 times that in Example 3 of the present invention. Through comparison, it is shown that the functional separator of the present invention improved the overall performance of the full cell.

[0094] The separator obtained in the comparative example was used to prepare a separator battery in the same manner as in Experimental Example 1, but the electrochemical performance of the prepared separator battery was worse than that of Experimental Example 1.

[0095] The separator performances of Examples 1 to 3 and Comparative Examples 1 to 3 were studied according to the above experimental method, and the specific results are shown in Table 1.

[0096] Table 1 Performance Comparison between Examples and Comparative Examples

[0097]

[0098] As can be seen from Table 1, the functional separator prepared by this method has excellent ionic conductivity and ionic diffusion performance; and effectively inhibits the generation of dendrites during the cycling of the sodium metal anode, improving the electrochemical performance of the sodium metal anode; at a 1C charge-discharge rate, the full cell has a high initial capacity, can stably cycle up to 836 times at most, and the capacity retention rate is as high as 90%.

[0099] In summary, the functional separator provided by the present invention includes two parts: a polymer-based membrane and a porous coordination polymer functional coating. The porous coordination polymer functional coating is uniformly coated on the polymer-based membrane by a doctor blade method to prepare the functional separator. First, the orderly arranged pore structure in the porous coordination polymer provides a path for the migration of metal cations, guides the uniform deposition of metal cations, and effectively inhibits the growth of dendrites. Second, the negatively charged groups (amino groups) in the pores of the porous coordination polymer have an electrostatic repulsive effect on the anions in the electrolyte, which can promote the transport of metal cations. Finally, during the battery cycling process, the silver nanoparticles on the surface of the porous coordination polymer can in-situ form a solid electrolyte interface membrane of a metal-silver alloy layer with the metal anode, significantly enhancing the wettability of the metal anode surface and inhibiting the growth of dendrites. Using the functional separator provided by the present invention in a battery can effectively improve its cycle stability, cycle life and rate charge-discharge performance.

[0100] Although the main inventive examples affecting the present experiment have been described and listed, those of ordinary skill in the art can understand that various changes, explorations, modifications and combinations can be made to the embodiments without departing from the principles and purposes of the present invention. The scope of the present invention is defined by the claims and their equivalents.

[0101] The foregoing basic examples of the present invention and their respective further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed by the present invention. In the solution of the present invention, each selected example can be arbitrarily combined with any basic example and selected example. Those skilled in the art know that there are numerous combinations.

[0102] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A functional separator, characterized in that: It includes two parts: a polymer-based membrane and a porous coordination polymer functional coating; wherein the weight per unit area of the porous coordination polymer functional coating is 0.2-1 mg / cm -2 ; and the thickness of the porous coordination polymer functional coating is 20-60 μm.

2. The functional diaphragm according to claim 1, wherein: The weight per unit area of the porous coordination polymer functional coating is 0.45 - 6 mg / cm -2 ; the thickness of the porous coordination polymer functional coating is 0.35 - 0.45 μm.

3. The functional diaphragm according to claim 1 or 2, characterized in that: The liquid retention per unit area of the functional separator is 20 - 45 mg·cm -2 .

4. The functional separator according to claim 3, characterized in that: The liquid retention amount per unit area of the functional separator is 30-40 mg·cm -2 .

5. The functional diaphragm according to claim 1, 2 or 4, characterized in that: 50 - 70 wt% of the porous coordination polymer functional coating, 30 - 50 wt% of the polymer-based film, and the sum of the total weight percentages is 100%.

6. The functional separator according to claim 5, wherein: In the battery operating voltage range, the functional separator can form a solid electrolyte interface of a metal-silver alloy layer on the surface of the metal negative electrode, and the solid electrolyte interface is mainly composed of inorganic substances; the components of the solid electrolyte interface are calculated by mass percentage as 100%: 40 - 50% of the metal-silver alloy, 20 - 40% of the metal fluoride, 5 - 10% of the metal oxide, and 0 - 10% of the metal organic compound.

7. The preparation method of the functional diaphragm according to claim 1 or 6, characterized in that It includes the following steps: (1) Post-treatment of the porous coordination polymer: First, synthesize the porous coordination polymer; then disperse the synthesized porous coordination polymer in deionized water, add a certain amount of silver nitrate and stir for a period of time in a dark environment, then add a certain amount of sodium borohydride and stir again, and finally wash with ethanol to obtain the porous coordination polymer; (2) Activation of the porous coordination polymer: Vacuum activate the porous coordination polymer after post-treatment in step (1) to obtain the activated porous coordination polymer; (3) Preparation of the functional separator: Take the activated porous coordination polymer in step (2) and disperse it in an emulsion containing ethanol and polyvinylidene fluoride. Use a spatula to evenly scrape the porous coordination polymer emulsion on at least one surface of the polymer-based film, and place it in a vacuum oven for vacuum drying to obtain the functional separator.

8. The method for preparing the functional separator according to claim 7, wherein: In step (1), the mass g of the porous coordination polymer, the volume ratio of deionized water to the AgNO3 solution is 0.1:50:0.8 - 2; the stirring time in the dark environment is 2 - 4 h; the mass ratio of sodium borohydride to the porous coordination polymer is 0.03 - 0.07:1; the stirring time after adding sodium borohydride is 1 - 2 h; the concentration of the AgNO3 solution is 0.1 m / L; In step (2), the vacuum activation conditions of the porous coordination polymer are: temperature 50 - 80 °C, time 12 - 24 h; In step (3), in the ethanol and polyvinylidene fluoride emulsion, the density of polyvinylidene fluoride is 1.032 ± 0.3 g / cm -3 ; the mass ratio of the activated porous coordination polymer to polyvinylidene fluoride is 9:

1.

9. Use of the functional separator according to any one of claims 1-6 or the functional separator obtained by the method according to claim 7, characterized in that: Used as a separator for secondary batteries, it has a high sodium ion conductivity of 1.5 mS·cm -1 .

10. A secondary battery, characterized in that: Containing the functional separator according to any one of claims 1 - 6 or the functional separator obtained by the method described in claim 7.

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