A functional diaphragm and its preparation method and application

Abstract

The application belongs to the technical field of batteries, and particularly relates to a functional diaphragm and a preparation method and application thereof. The functional diaphragm comprises a polymer base diaphragm 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 -2, the thickness of the porous coordination polymer functional coating is 20-60 mu m. The liquid retention per unit area of the modified diaphragm is 20-45 mg·cm ‑2 -2. The functional diaphragm provided by the application can effectively improve the cycle stability, cycle life and rate charge-discharge performance of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a functional separator and a preparation method and application thereof. BACKGROUND

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

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

[0004] Therefore, it is necessary to improve the separator so as to better meet market demand. SUMMARY

[0005] In view of the problems existing in the prior art, the purpose of the application is to provide a functional separator and a preparation method and application thereof. The separator in the application has excellent chemical stability and structural stability, which 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 sodium metal ion deposition overpotential is reduced by 2 times, and the cycle life is increased by 8 times.

[0006] In order to achieve the above application purpose, the application realizes the technical scheme as follows:

[0007] A functional separator comprises a polymer base film 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 metal-silver alloy layer solid-state electrolyte interface film 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 pm, preferably 0.35-0.45 pm.

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

[0010] Further, in the functional separator, the functional separator of the polymer base film and the porous coordination polymer functional coating is in a flexible solid state during application; preferably, the functional separator is composed of 50-70 wt% of the porous coordination polymer functional coating and 30-50 wt% of the polymer base film.

[0011] Further, in the functional separator, the functional separator can form a metal-silver alloy layer solid-state electrolyte interface on the surface of the metal negative electrode in the battery operating voltage range, and the solid-state electrolyte interface is mainly composed of inorganic matter; preferably, the solid-state electrolyte interface is composed of 40-50 wt% of the metal-silver alloy, 10-30 wt% of the metal fluoride, 0-10 wt% of the metal oxide, 0-10 wt% of the metal organic compound, and the rest of the unavoidable impurities (such as metal sulfide and metal nitride), and the total content of the above components is 100 wt%.

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

[0013] Preferably, the preparation method of the functional separator of the polymer base film and the porous coordination polymer functional coating of the present application comprises the following steps:

[0014] (1) Post-treatment of the porous coordination polymer: the porous coordination polymer is dispersed in deionized water, then a certain amount of silver nitrate is added and stirred in the dark environment for a period of time, then a certain amount of sodium borohydride is added and stirred, and finally washed with ethanol.

[0015] The porous coordination polymer can be prepared by existing technology; preferably, the following steps are used for synthesis, and the synthesis steps of the porous coordination polymer are as follows: the organic ligand (2-amino terephthalic acid) is dissolved in the solvent (N, N-dimethylformamide:methanol = 75:8, mass ratio), then tetrabutyl titanate is added, and solvothermal reaction is carried out at 150℃ to generate a porous coordination polymer with metal nodes and organic ligand connecting units.

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

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

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

[0019] (3) Preparation of functional separator: The activated porous coordination polymer is dispersed in an emulsion containing ethanol and polyvinylidene fluoride, and the emulsion containing the porous coordination polymer is uniformly coated on at least one surface of the polymer base film using a doctor blade, and is placed in a vacuum oven for vacuum drying to obtain a functional separator.

[0020] Preferably, in the emulsion of ethanol and polyvinylidene fluoride, 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; the weight percentage of the functional coating is 50-70%, and the weight percentage of the polymer base film is 30-50%; the temperature of the vacuum oven is 60-80℃.

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

[0022] The 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 a secondary battery, its sodium ion conductivity is as high as 1.5 mS cm -1 .

[0023] The above-mentioned secondary battery, including button cell, cylindrical cell, soft pack cell and aluminum shell cell, is used in the field of high energy density energy storage.

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

[0025] The liquid electrolyte is composed of lithium salt / sodium salt and 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; the organic solvent for dissolving 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 base film is selected from at least one of polyethylene (PE) separator, polypropylene (PP) separator and polyethylene-polypropylene composite separator

[0026] The functional coating of the porous coordination polymer in the application carries negative-charged amino groups in the pore structure, which has electrostatic repulsion effect on anions in the electrolyte, thereby effectively promoting the transmission of metal cations. On the other hand, during the cycle of the battery, the nano-silver particles distributed on the surface of the porous coordination polymer can form a highly stable metal-silver alloy solid-state electrolyte interface film in situ 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 guides the uniform deposition of metal cations, thereby effectively inhibiting the growth of dendrites.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] (1) The functional separator provided by the application comprises a polymer base film and a porous coordination polymer functional coating. The porous coordination polymer in the functional separator serves as a functional coating and has high porosity and periodic pore structure, which can provide a path for the migration of metal cations. The porous coordination polymer has excellent pore volume, which can effectively improve the liquid retention performance of the separator.

[0029] (2) The application forms a metal-silver alloy solid-state electrolyte interface on the surface of the metal negative electrode, thereby enhancing the wettability of the metal negative electrode. In addition, the porous coordination polymer functional coating in the functional separator carries negative-charged amino groups, which have electrostatic repulsion effect on anions in the electrolyte, thereby promoting the transmission of metal cations and improving 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) The functional separator provided by the application comprises a polymer base film and a porous coordination polymer functional coating, and the porous coordination polymer is uniformly coated on the surface of the polymer base film by using a scraping coating method to prepare the functional separator. The porous coordination polymer functional coating can effectively improve the low ion diffusion rate of metal cations in the separator.

[0031] (4) The functional separator described in the application is prepared by using a scraping coating method, and the preparation method of the separator is simple and convenient to operate. The functional separator containing the porous coordination polymer functional coating is flexible and solid in the application process.

[0032] (5) In order to realize high performance of the battery, the solid-state electrolyte interface formed on the surface of the metal negative electrode of the functional separator mainly comprises metal-silver alloy, and the preferred composition of the solid-state electrolyte interface is as follows: 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] (VI) The functional separator provided by the present application contains nano-silver particles that can form a metal-silver alloy layer solid-state electrolyte interface film on the surface of the metal negative electrode. This solid-state electrolyte interface film has excellent chemical stability and structural stability, which not only significantly enhances the wettability of the surface of the metal negative electrode, but also facilitates the uniform deposition of metal cations and inhibits the growth of dendrites. The sodium metal ion deposition overpotential is reduced by 2 times, and the cycle life is increased by 8 times. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The structure of the modified separator in Example 1 of the present application is shown.

[0035] Figure 2 The room temperature ionic conductivity and ion migration activation energy of the functional separator in Experimental Example 1 of the present application.

[0036] Figure 3 The voltage-time curve of the sodium symmetric battery deposition / detachment cycle test of the functional separator in Experimental Example 2 of the present application.

[0037] Figure 4 The scanning electron microscope image of the surface of the sodium metal negative electrode after the deposition / detachment cycle test of the sodium symmetric battery of the functional separator in Experimental Example 2 of the present application.

[0038] Figure 5 The long cycle performance of the full battery prepared by the functional separator in Experimental Example 3 of the present application at 1C.

[0039] Figure 6 The voltage-time curve of the sodium symmetric battery deposition / detachment cycle test of the functional separator in Experimental Comparative Example 1 of the present application.

[0040] Figure 7 The scanning electron microscope image of the surface of the sodium metal negative electrode after the deposition / detachment cycle test of the sodium symmetric battery of the functional separator in Experimental Comparative Example 1 of the present application.

[0041] Figure 8 The long cycle performance of the full battery prepared by the functional separator in Comparative Example 2 of the present application at 1C. DETAILED DESCRIPTION

[0042] The present application will be further described below in conjunction with the examples, which are only a part of the examples of the present application, and not all the examples. Based on the examples in the present application, other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0043] In the present application, the % not specifically marked represents its mass percentage, i.e. wt%; the reagents or instruments not marked with the manufacturer are all conventional products that can be purchased on the market.

[0044] Example 1:

[0045] The present embodiment provides a modified separator and its preparation method and application, the preparation method of the modified separator is as follows:

[0046] 1.81 g of 2-amino terephthalic acid was dissolved in a mixed solvent containing 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, 0.8 mL of tetrabutyl titanate was added, and stirred for 0.5 h. It was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner, heated at 150°C for 24 h. Then, the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain a porous coordination polymer. Finally, it was heated by blowing air at 60°C for 6 h.

[0047] 0.1 g of the porous coordination polymer was dispersed in 50 mL of deionized water, 1.03 mL of AgNO3 solution (concentration of 0.1 mol / L) was added and stirred in the dark for 2 h, then 3.9 mg of sodium borohydride was added and stirred for 1 h, then the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain a porous coordination polymer containing 10 mass% of silver. Finally, it was vacuum dried at 100°C for 12 h to obtain an activated porous coordination polymer containing 10 mass% of silver.

[0048] The activated porous coordination polymer containing 10 mass% of silver was dispersed in an emulsion containing ethanol and polyvinylidene fluoride (PVDF emulsion density 1.032±0.3 g / cm -3 ), and the mass ratio of the porous coordination polymer containing 10 mass% of silver to polyvinylidene fluoride was 9:1. The porous coordination polymer emulsion was uniformly coated on both sides of the polymer substrate film using a doctor blade, the coating thickness was 40 μm, and it was placed in a vacuum oven at 60°C for vacuum drying for 12 h to obtain a functional separator.

[0049] wherein, Figure 1 is a schematic structure of the modified separator prepared in Example 1.

[0050] Example 2:

[0051] 1.81 g of 2-amino terephthalic acid was dissolved in a mixed solvent containing 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, 0.8 mL of tetrabutyl titanate was added, and stirred for 0.5 h. It was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner, heated at 150°C for 24 h. Then, the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain a porous coordination polymer. Finally, it was heated by blowing air at 60°C for 6.5 h.

[0052] Take 0.1 g of porous coordination polymer and disperse it in 50 mL of deionized water, add 0.85 mL of AgNO3 solution (concentration of 0.1 mol / L) and stir in the dark environment for 2 h, then add 3.2 mg of sodium borohydride and stir for 1 h, then centrifugal collection of light yellow solid. Finally, use ethanol to wash, get the silver content of 8.3 mass% of porous coordination polymer. Finally, it is heated under vacuum at 100°C for 12.5h to get the activated porous coordination polymer.

[0053] Take the activated silver content of 8.3 mass% of porous coordination polymer and disperse it in the emulsion containing ethanol and polyvinylidene fluoride, the mass ratio of silver content of 8.3 mass% of porous coordination polymer to polyvinylidene fluoride is 9:1, use a scraper to evenly scrape the porous coordination polymer emulsion on both sides of the polymer base film surface, the coating thickness is 40μm, and put it into a vacuum oven at 60°C for 12h vacuum drying, get the functional separator.

[0054] Example 3:

[0055] Dissolve 1.81g 2-amino terephthalic 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, stir for 0.5h. Transfer it to a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene liner, heat at 150°C for 24h. Then, centrifugal collection of light yellow solid. Finally, use ethanol to wash, get the porous coordination polymer. Finally, it is heated under air at 60°C for 7h.

[0056] Take 0.1 g of porous coordination polymer and disperse it in 50 mL of deionized water, add 1.8 mL of AgNO3 solution and stir in the dark environment for 2 h, then add 6.8 mg of sodium borohydride and stir for 1 h, then centrifugal collection of light yellow solid. Finally, use ethanol to wash, get the silver content of 17.5 mass% of porous coordination polymer. Finally, it is heated under vacuum at 1000°C for 13h to activate.

[0057] Take the activated silver content of 17.5 mass% of porous coordination polymer and disperse it in the emulsion containing ethanol and polyvinylidene fluoride, the mass ratio of silver content of 17.5 mass% of porous coordination polymer to polyvinylidene fluoride is 9:1, use a scraper to evenly scrape the porous coordination polymer emulsion on both sides of the polymer base film surface, the coating thickness is 40μm, and put it into a vacuum oven at 60°C for 12h vacuum drying, get the functional separator.

[0058] Example 4:

[0059] Take 0.1 g of porous coordination polymer and disperse it in 50 mL of deionized water, add 1.03 mL of AgNO3 solution and stir in the dark environment for 2 h, then add 3.9 mg of sodium borohydride and stir for 1 h, then centrifugally collect the light yellow solid. Finally, use ethanol to wash to obtain a porous coordination polymer containing 10 mass% of silver. Finally, it is placed in a vacuum oven at 100°C and heated for 13.5 h for activation.

[0060] Take 0.1 g of porous coordination polymer and disperse it in 50 mL of deionized water, add 1.03 mL of AgNO3 solution and stir in the dark environment for 2 h, then add 3.9 mg of sodium borohydride and stir for 1 h, then centrifugally collect the light yellow solid. Finally, use ethanol to wash to obtain a porous coordination polymer containing 10 mass% of silver. Finally, it is placed in a vacuum oven at 100°C and heated for 13.5 h for activation.

[0061] Take the activated porous coordination polymer containing 10 mass% of silver and disperse it in an emulsion containing ethanol and polyvinylidene fluoride, with the mass ratio of porous coordination polymer containing 10 mass% of silver to polyvinylidene fluoride being 9:1. Use a doctor blade to uniformly coat the porous coordination polymer emulsion on both sides of the polymer base film surface with a coating thickness of 30 μm, and place it in a vacuum oven at 60°C and vacuum dry for 12 h to obtain a functional separator.

[0062] Example 5:

[0063] Take 0.1 g of porous coordination polymer and disperse it in 50 mL of deionized water, add 1.03 mL of AgNO3 solution and stir in the dark environment for 2 h, then add 3.9 mg of sodium borohydride and stir for 1 h, then centrifugally collect the light yellow solid. Finally, use ethanol to wash to obtain a porous coordination polymer containing 10 mass% of silver. Finally, it is placed in a vacuum oven at 100°C and heated for 13.5 h for activation.

[0064] Take 0.1 g of porous coordination polymer and disperse it in 50 mL of deionized water, add 1.03 mL of AgNO3 solution and stir in the dark environment for 2 h, then add 3.9 mg of sodium borohydride and stir for 1 h, then centrifugally collect the light yellow solid. Finally, use ethanol to wash to obtain a porous coordination polymer containing 10 mass% of silver. Finally, it is placed in a vacuum oven at 100°C and heated for 13.5 h for activation.

[0065] The activated porous coordination polymer with silver content of 10 mass% was dispersed in an emulsion containing ethanol and polyvinylidene fluoride, wherein the mass ratio of the porous coordination polymer with silver content of 10 mass% to polyvinylidene fluoride was 9:1, the porous coordination polymer emulsion was uniformly coated on both sides of the surface of the polymer base film using a doctor blade, the coating thickness was 50 μm, and the sample was placed in a vacuum oven at 60°C for vacuum drying for 12 h to obtain a functional separator.

[0066] Comparative Example 1:

[0067] 1.81 g of 2-amino terephthalic acid was dissolved in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, 0.8 mL of tetrabutyl titanate was added, and stirred for 0.5 h. It was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner, heated at 150°C for 24 h. Then, the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain a porous coordination polymer. Finally, it was heated with a blast at 60°C for 6 h.

[0068] 0.1 g of the porous coordination polymer was dispersed in 50 mL of deionized water, 0.7 mL of AgNO3 solution was added and stirred in the dark for 2 h, then 2.65 mg of sodium borohydride was added and stirred for 1 h, then the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain a porous coordination polymer with silver content of 6.8 mass%. Finally, it was activated by heating at 100°C under vacuum for 12 h.

[0069] The activated porous coordination polymer with silver content of 6.8 mass% was dispersed in an emulsion containing ethanol and polyvinylidene fluoride, wherein the mass ratio of the porous coordination polymer with silver content of 6.8 mass% to polyvinylidene fluoride was 9:1, the porous coordination polymer emulsion was uniformly coated on both sides of the surface of the polymer base film using a doctor blade, the coating thickness was 40 μm, and the sample was placed in a vacuum oven at 60°C for vacuum drying for 12 h to obtain a separator.

[0070] Comparative Example 2:

[0071] 1.81 g of 2-amino terephthalic acid was dissolved in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, 0.8 mL of tetrabutyl titanate was added, and stirred for 0.5 h. It was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner, heated at 150°C for 24 h. Then, the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain a porous coordination polymer. Finally, it was heated with a blast at 60°C for 6 h.

[0072] Take 0.1 g of porous coordination polymer dispersed in 50 mL of deionized water, add 2.2 mL of AgNO3 solution and stir in the dark environment for 2 h, then add 8.33 mg of sodium borohydride and stir for 1 h, then centrifugal collection of light yellow solid. Finally, use ethanol to wash, get the silver content of 21.4 mass% of porous coordination polymer. Finally, it is and vacuum heating at 100°C for 12 h for activation.

[0073] Take the activated silver content of 21.4 mass% of porous coordination polymer dispersed in the emulsion containing ethanol and polyvinylidene fluoride, wherein the mass ratio of silver content of 21.4 mass% of porous coordination polymer to polyvinylidene fluoride is 9:1, use a scraper to evenly scrape the porous coordination polymer emulsion on both sides of the polymer base film surface, the coating thickness is 40 μm, and put into a vacuum oven 60°C vacuum drying 12 h, get the diaphragm.

[0074] Comparative Example 3:

[0075] Dissolve 1.81 g of 2-amino terephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol, add 0.8 mL of tetrabutyl titanate, stir for 0.5 h. Transfer it to a stainless steel high-pressure reaction kettle lined with polytetrafluoroethylene, heat at 150°C for 24 h. Then, centrifugal collection of light yellow solid. Finally, use ethanol to wash, get the porous coordination polymer. Finally, it is and air heating at 60°C for 6 h.

[0076] Take 0.1 g of porous coordination polymer dispersed in 50 mL of deionized water, add 1.03 mL of AgNO3 solution and stir in the dark environment for 2 h, then add 3.9 mg of sodium borohydride and stir for 1 h, then centrifugal collection of light yellow solid. Finally, use ethanol to wash, get the silver content of 10 mass% of porous coordination polymer. Finally, it is and vacuum heating at 100°C for 12 h for activation.

[0077] Take the activated silver content of 10 mass% of porous coordination polymer dispersed in the emulsion containing ethanol and polyvinylidene fluoride, wherein the mass ratio of silver content of 10 mass% of porous coordination polymer to polyvinylidene fluoride is 9:1, use a scraper to evenly scrape the porous coordination polymer emulsion on both sides of the polymer base film surface, the coating thickness is 10 μm, and put into a vacuum oven 60°C vacuum drying 12 h, get the diaphragm.

[0078] Comparative Example 4:

[0079] A solution of 1.81 g of 2-amino terephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol was prepared, and 0.8 mL of tetrabutyl titanate was added, and stirred for 0.5 h. It was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner and heated at 150°C for 24 h. Then, the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain the porous coordination polymer. Finally, it was dried in a vacuum oven at 60°C for 6 h.

[0080] A solution of 1.81 g of 2-amino terephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol was prepared, and 0.8 mL of tetrabutyl titanate was added, and stirred for 0.5 h. It was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner and heated at 150°C for 24 h. Then, the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain the porous coordination polymer. Finally, it was dried in a vacuum oven at 60°C for 6 h.

[0081] A solution of 1.81 g of 2-amino terephthalic acid in 30 mL of N,N-dimethylformamide and 3.2 mL of methanol was prepared, and 0.8 mL of tetrabutyl titanate was added, and stirred for 0.5 h. It was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner and heated at 150°C for 24 h. Then, the light yellow solid was collected by centrifugation. Finally, it was washed with ethanol to obtain the porous coordination polymer. Finally, it was dried in a vacuum oven at 60°C for 6 h.

[0082] Experimental Example 1:

[0083] The functional separator used in this experimental example was prepared according to the method in Example 1. The functional separator was assembled into a stainless steel symmetric battery, and the room temperature ionic conductivity test and ion migration activation energy test were performed. As shown in Figure 1 , the test results showed that the functional room temperature ionic conductivity was 1.5 mS cm -1 , and the ion migration activation energy was 0.14 eV. The test results showed that the porous coordination polymer functional separator had 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] The functional separator was assembled into a sodium symmetric battery, and the deposition / stripping cycle test was performed. As shown in Figure 2 , this battery could undergo a deposition / stripping cycle test 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 a polarization voltage of only 29 mV. Subsequently, the surface of the sodium metal anode after deposition / stripping cycle was characterized by scanning electron microscopy. As shown in Figure 3As shown, no dendrite growth is observed on the surface of the sodium metal anode, and the deposition morphology is uniform and dense, which indicates that the present application effectively suppresses the generation of dendrites during the cycle of the sodium metal anode, and improves the electrochemical performance of the sodium metal anode.

[0087] Experimental Example 3:

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

[0089] The positive electrode material sodium vanadium phosphate, the functional separator and the sodium metal anode are assembled into a full cell, and long cycle performance test is carried out at different charge and discharge rates. As shown in Figure 4 , the initial capacity of the full cell is as high as 101 mAh g -1 at 1C charge and discharge rate, and can stably cycle for 836 cycles, and the capacity retention rate is as high as 90%.

[0090] Experimental Comparative Example 1:

[0091] As a comparison of Example 2, the polymer-based film without post-treatment is prepared into a symmetrical cell, and deposition / stripping cycle test is carried out. As shown in Figure 5 , under the condition of a current density of 0.2 mA cm -2 and a deposition amount of 0.1 mAh cm -2 , the cell short-circuits after 200 h of deposition / stripping cycle test, and the polarization voltage is as high as 60 mV. The cycle life of the cell is only 1 / 8 of that of Experimental Example 1 of the present application, and the polarization voltage is 2 times that of Experimental Example 1 of the present application. As shown in Figure 6 , the functional separator effectively suppresses the growth of dendrites, while a large number of dendrites are found in the comparative example. Through comparison, it is shown that the metal-silver alloy layer solid-state electrolyte interface film formed on the surface of the metal anode by the functional separator of the present application can effectively suppress the growth of dendrites, and thus improve the cycle life of the cell.

[0092] Experimental Comparative Example 2:

[0093] As a comparison of Example 3, the untreated polymer-based film is assembled into a full cell with the positive electrode material sodium vanadium phosphate and the sodium metal anode for long cycle test. As shown in Figure 7 , the initial capacity of the cell is 85 mAh g -1 at 1C charge and discharge rate, but the capacity of the cell decreases to 70 mAh g -1 after 280 cycles, and the capacity loss rate of each cycle is as high as 0.63‰, which is more than 5 times that of Example 3 of the present application. Through comparison, it is shown that the functional separator of the present application improves the overall performance of the full cell.

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

[0095] Experimental Examples 1 to 3 and Comparative Examples 1 to 3 are subjected to the above-mentioned experimental method to study the performance of the separator, and the specific results are shown in Table 1.

[0096] Table 1 Performance comparison of examples and comparative examples

[0097]

[0098] As can be seen from Table 1, the functional separator prepared according to the method has excellent ion conductivity and ion diffusion performance; and effectively suppresses the generation of dendrites during the cycle of the sodium metal negative electrode, and improves the electrochemical performance of the sodium metal negative electrode; at a 1C charge-discharge rate, the initial capacity of the full battery is high, the highest can be stably cycled for 836 cycles, and the capacity retention rate is as high as 90%.

[0099] In summary, the functional separator provided by the present application contains a polymer base film and a porous coordination polymer functional coating, and the porous coordination polymer functional coating is uniformly coated on the polymer base film by using a doctor blade method to prepare the functional separator. First, the ordered pore structure in the porous coordination polymer provides a path for the migration of metal cations, guiding the uniform deposition of metal cations and effectively suppressing the growth of dendrites. Second, the negative charge groups (amino groups) carried in the pores of the porous coordination polymer have electrostatic repulsion effect on the anions in the electrolyte, which can promote the transmission of metal cations. Finally, during the cycle of the battery, the nano-silver particles on the surface of the porous coordination polymer can form a metal-silver alloy layer solid-state electrolyte interface film in situ with the metal negative electrode, significantly enhancing the wettability of the metal negative electrode surface and suppressing the growth of dendrites. The functional separator provided by the present application can effectively improve the cycle stability, cycle life and rate charge-discharge performance of the battery when used in the battery.

[0100] Although the main examples of the present application affecting the experimental factors have been described and listed, those skilled in the art can understand that various changes, explorations, modifications and combinations can be made to the examples without departing from the principles and purposes of the present application, and the scope of the present application is defined by the claims and their equivalents.

[0101] The foregoing basic examples and each further selected example of the present application can be freely combined to form a plurality of examples, all of which are examples that can be used and claimed by the present application. In the present application, each selected example can be arbitrarily combined with any basic example and selected example. Those skilled in the art can know that there are numerous combinations.

[0102] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A functional separator, characterized by: Comprise a polymer base film and a porous coordination polymer functional coating two parts; wherein the porous coordination polymer functional coating unit area weight is 0.2-1 mg cm -2 ; the porous coordination polymer functional coating thickness is 20-60 µm; In the battery operating voltage interval, the functional separator can form a metal-silver alloy layer solid-state electrolyte interface on the surface of the sodium metal negative electrode; The porous coordination polymer functional coating in the functional separator has negative charge amino groups; The preparation method of the functional separator comprises the following steps: (1) porous coordination polymer post-treatment: first, synthesize the porous coordination polymer; then, disperse the synthesized porous coordination polymer in deionized water, add a certain amount of silver nitrate, stir in the dark environment for a period of time, then add a certain amount of sodium borohydride and stir again, and finally wash with ethanol to obtain the post-treated porous coordination polymer; (2) activation of the porous coordination polymer: vacuum activate the post-treated porous coordination polymer in step (1) to obtain the activated porous coordination polymer; (3) preparation of the functional separator: disperse the activated porous coordination polymer in step (2) in an emulsion containing ethanol and polyvinylidene fluoride, use a doctor blade to uniformly coat the porous coordination polymer emulsion on at least one side of the polymer base film, and place it in a vacuum oven for vacuum drying to obtain the functional separator.

2. The functional separator of claim 1, wherein: The porous coordination polymer functional coating has a weight per unit area of 0.45-6 mg cm -2 ; the porous coordination polymer functional coating has a thickness of 0.35-0.45 µm.

3. The functional separator according to claim 1 or 2, characterized in that: The functional diaphragm has a liquid retention of 20-45 mg•cm -2 .

4. The functional separator according to claim 3, characterized in that: The functional diaphragm has a liquid retention of 30-40 mg•cm -2 .

5. The functional septum of claim 1, 2, or 4, wherein: The porous coordination polymer functional coating is 50-70% by weight, the polymer base film is 30-50% by weight, and the total weight percentage content sum is 100%.

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

1.

7. Use of a functional separator according to any one of claims 1, 2, 4 and 6, characterized in that: As a secondary battery separator, its sodium ion conductivity is as high as 1.5 mS•cm -1 .

8. A secondary battery characterized by: containing the functional separator according to any one of claims 1, 2, 4 and 6.

Images