Functional composite fiber diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a functional composite fiber diaphragm and a preparation method and application thereof.The preparation method of the functional composite fiber diaphragm comprises the steps that the two faces of a fiber membrane are coated with the same composite solution respectively, composite coatings are obtained on the two faces of the fiber membrane respectively, and the functional composite fiber diaphragm is obtained, the fiber membrane is a polyimide fiber membrane containing a perovskite type oxide filler, the composite solution comprises a lithium salt, a metal organic framework material, polyvinylidene fluoride and a first solvent, the metal organic framework material is one of a zinc-based metal organic framework and a bismuth-based metal organic framework, and the perovskite type oxide filler is lanthanum cobaltate. A fiber membrane is prepared by using an electrostatic spinning technology and a high-temperature calcination method, and the functional composite fiber diaphragm is obtained by coating two surfaces of the fiber membrane with a composite solution. The functional composite fiber diaphragm has excellent thermal stability, and the battery assembled by the functional composite fiber diaphragm has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to a functional composite fiber separator, its preparation method, and its application. Background Technology

[0002] Lithium metal batteries, with their outstanding advantages such as ultra-high theoretical energy density, ultra-long cycle life, and extremely low self-discharge rate, have been widely used in new energy vehicles, power batteries, high-end portable electronic devices, and smart grid energy storage systems. As end-use applications continue to demand higher energy density and safety from batteries, solid-state lithium metal batteries, due to their inherent safety characteristics, ultra-high theoretical energy density, and potential for ultra-thin and flexible design, are widely recognized as the breakthrough direction for next-generation energy storage technology. This places higher demands on the core component of solid-state lithium metal batteries—the solid electrolyte membrane.

[0003] However, traditional solid-state electrolyte membranes suffer from poor resistance to lithium dendrite growth, low mechanical strength, and poor high-temperature stability. These issues increase the probability of short circuits during long-cycle operation, thereby reducing battery safety. Therefore, there is an urgent need to develop a functional composite fiber separator to address the shortcomings of solid-state electrolyte membranes. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing a functional composite fiber membrane.

[0005] Another object of the present invention is to provide a functional composite fiber membrane obtained by the above preparation method.

[0006] Another object of the present invention is to provide the application of the above-mentioned functional composite fiber separator in lithium batteries, wherein the functional composite fiber separator is an electrolyte membrane.

[0007] The objective of this invention is achieved through the following technical solution.

[0008] A method for preparing a functional composite fiber membrane includes: coating both sides of a fiber membrane with the same composite solution to obtain composite coatings on both sides of the fiber membrane, thereby obtaining a functional composite fiber membrane. The fiber membrane is a polyimide fiber membrane containing a perovskite oxide filler. The composite solution includes: a lithium salt, a metal-organic framework (MOF), polyvinylidene fluoride (PVDF), and a first solvent. The MOF is either a zinc-based MOF or a bismuth-based MOF. The perovskite oxide filler is lanthanum cobalt oxide (LaCoO3, LCO). The ratio of lithium salt, MOF, PVDF, and the first solvent by mass is (0.48~0.52):(0.2~0.25):(0.8~1.2):(9.8~10.2).

[0009] In the above technical solution, the metal-organic framework material (MOF) is preferably a zinc-based metal-organic framework (Zn-MOF).

[0010] In the above technical solution, the method for preparing the fiber membrane includes:

[0011] Step 1: Mix pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and the second solvent until homogeneous to obtain a first system (polyimide precursor solution). Mix the perovskite oxide filler and the first system until homogeneous to obtain a first electrospinning solution. The ratio of pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and the second solvent by mass is (0.4~0.45):(0.4~0.45):(1.5~1.8). The ratio of perovskite oxide filler to pyromellitic dianhydride (PMDA) by mass is 0.0255:(0.4~0.45).

[0012] Step 2: Electrospinning is performed using the first electrospinning solution to obtain a fiber membrane precursor;

[0013] Step 3: The fiber membrane precursor is calcined in a stepwise manner and cooled to room temperature to obtain the fiber membrane.

[0014] In the above technical solution, a composite solution is coated on a glass plate, a fiber membrane is placed on the surface of the composite solution on the glass plate so that the bottom surface of the fiber membrane is in contact with the composite solution, and then the composite solution is coated on the top surface of the fiber membrane. After standing and drying, a composite coating is obtained on both sides of the fiber membrane, resulting in a functional composite fiber membrane.

[0015] In the above technical solution, the composite coating obtained on both sides of the fiber membrane has the same thickness, which is 20~30μm.

[0016] In the above technical solution, the thickness of the fiber membrane is 30~40μm.

[0017] In the above technical solution, the standing is carried out at room temperature for 20-30 minutes.

[0018] In the above technical solution, the drying temperature is 60~80 ℃ and the drying time is 20~24 h.

[0019] In the above technical solution, the first solvent is N-methyl-2-pyrrolidone (NMP).

[0020] In the above technical solution, the second solvent is N,N-dimethylacetamide (DMAC).

[0021] In the above technical solution, the method for preparing the composite solution includes: mixing lithium salt, metal-organic framework material (MOF), polyvinylidene fluoride (PVDF) and a first solvent, and stirring at room temperature for 20-24 h until homogeneous to obtain the composite solution.

[0022] In the above technical solution, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0023] In the above technical solution, in the method of preparing the fiber membrane, pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA) and a second solvent are mixed and stirred at room temperature for 12-24 h until homogeneous to obtain the first system.

[0024] In the above technical solution, in the method of preparing fiber membrane, perovskite oxide filler and the first system are mixed and stirred at room temperature for 12-24 h until homogeneous to obtain the first electrospinning solution.

[0025] In the above technical solution, in the method of preparing the fiber membrane, the first electrospinning solution is drawn into the syringe and then electrospinning is performed. The distance between the receiver and the metal needle of the syringe is 15~18 cm, the DC voltage of electrospinning is 15~18 kV, and the ambient temperature of electrospinning is 20~30 ℃.

[0026] In the above technical solution, the step calcination method for preparing the fiber membrane includes: raising the temperature from room temperature to 80~120℃ and holding it at 80~120℃ for 30 min, raising the temperature from 80~120℃ to 180~220℃ and holding it at 180~220℃ for 30 min, and raising the temperature from 180~220℃ to 280~320℃ and holding it at 280~320℃ for 60 min.

[0027] In the above technical solution, the method for preparing lanthanum cobalt oxide (LCO) includes: mixing a cobalt source, a lanthanum source, polyvinylpyrrolidone (PVP), and a third solvent until homogeneous at room temperature to obtain a second electrospinning solution; performing electrospinning using the second electrospinning solution to obtain a lanthanum cobalt oxide precursor (existing in the form of a nanofiber membrane); and calcining the lanthanum cobalt oxide precursor at 650~700℃ for 2~3 h to obtain lanthanum cobalt oxide (LCO). The ratio of cobalt in the cobalt source to lanthanum in the lanthanum source is 1:1 by molar percentage, and the ratio of the molar percentage of cobalt in the cobalt source, the mass percentage of polyvinylpyrrolidone, and the mass percentage of the third solvent is (0.7~0.8):(0.5~0.6):(4.5~5.5). The unit of molar percentage is mmol, and the unit of mass percentage is g.

[0028] In the above technical solution, in the method for preparing lanthanum cobalt oxide (LCO), the second electrospinning solution is drawn into a syringe before electrospinning is performed. The distance between the receiver and the metal needle of the syringe is 15~18 cm, the DC voltage of electrospinning is 15~18 kV, and the ambient temperature of electrospinning is 20~30 ℃.

[0029] In the above technical solution, the third solvent is N,N-dimethylformamide (DMF).

[0030] The functional composite fiber membrane obtained by the above preparation method includes: a fiber membrane and a composite coating on both sides of the fiber membrane. The composite coating includes: lithium salt, metal-organic framework (MOF) material and polyvinylidene fluoride (PVDF). The fiber membrane is a polyimide fiber membrane containing perovskite oxide filler.

[0031] The above-mentioned functional composite fiber separators are used in lithium batteries.

[0032] The beneficial effects of this invention are as follows:

[0033] This invention utilizes electrospinning and high-temperature calcination to prepare a fiber membrane. A composite solution is then coated onto both sides of the fiber membrane to obtain a functional composite fiber separator. The functional composite fiber separator of this invention exhibits excellent thermal stability, and the battery assembled from it demonstrates superior electrochemical performance. This is due to two main reasons: First, the interconnected fiber network in the composite solution and fiber membrane forms a continuous lithium-ion transport path, effectively promoting lithium-ion migration. Second, the fiber network is rich in lanthanum cobalt oxide (LaCoO3), a perovskite-type oxide filler. Lanthanum cobalt oxide, as an ABO3-type perovskite composite ceramic oxide, has numerous acidic sites and oxygen vacancies on its surface, which can react with anions (bis(trifluoromethanesulfonyl)imide ions, TFSI...). -The addition of Zn-MOF can complex and dissociate lithium ions, releasing a large number of free lithium ions, which can significantly reduce the dissociation energy of lithium salts and increase the lithium ion concentration; finally, the added Zn-MOF can also be used to generate lithium ions (Li... + This invention provides a transport channel, increases Lewis acid sites, and reduces crystallinity, thereby enhancing lithium-ion dissociation and transport. It improves ionic conductivity and lithium-ion transference number by optimizing the lithium-ion migration path and enhances overall battery safety by optimizing the electrolyte membrane structure. Attached Figure Description

[0034] Figure 1 SEM image of the fiber membrane prepared in Example 1;

[0035] Figure 2 SEM image of the cross-section of the functional composite fiber membrane prepared in Example 1;

[0036] Figure 3 XRD pattern of Zn-MOF;

[0037] Figure 4 SEM image of Zn-MOF;

[0038] Figure 5 The XRD pattern of lanthanum cobaltate is shown.

[0039] Figure 6 The constant current charge-discharge cycle curves are shown below, where a is the constant current charge-discharge cycle curve corresponding to Example 1, b is the constant current charge-discharge cycle curve corresponding to Comparative Example 5, c is the constant current charge-discharge cycle curve corresponding to Comparative Example 6, and d is the constant current charge-discharge cycle curve corresponding to Comparative Example 7.

[0040] Figure 7 The constant current charge-discharge cycle curves are shown below, where a is the constant current charge-discharge cycle curve corresponding to Comparative Example 1, b is the constant current charge-discharge cycle curve corresponding to Comparative Example 2, c is the constant current charge-discharge cycle curve corresponding to Comparative Example 3, and d is the constant current charge-discharge cycle curve corresponding to Comparative Example 4.

[0041] Figure 8 The constant current charge-discharge cycle curves are for Example 2. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0043] Pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and polyvinylidene fluoride (PVDF, M w =400000) were purchased from Beijing Innocare Technology Co., Ltd.

[0044] N,N-Dimethylacetamide (DMAC) and N,N-Dimethylformamide (DMF) were purchased from Fuchen Chemical Reagent Co., Ltd.

[0045] N-Methyl-2-pyrrolidone (NMP) was purchased from Tianjin Guangfu Technology Development Co., Ltd.

[0046] Zinc nitrate hexahydrate and bismuth nitrate pentahydrate were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0047] 2-Methylimidazole was purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0048] 2-Aminobenzimidazole was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0049] The stainless steel sheet is made of 304 stainless steel.

[0050] Ion conductivity testing: Using 0.5mm thick stainless steel sheets as both positive and negative electrodes, a stainless steel symmetrical battery (CR2032 coin cell) was assembled in a glove box. Specifically, the negative electrode shell, spring contact, negative electrode sheet, separator, positive electrode sheet, and positive electrode shell were placed sequentially from bottom to top, and then packaged using a coin cell packaging machine to obtain the stainless steel symmetrical battery. The ion conductivity of the stainless steel symmetrical battery was tested using electrochemical impedance spectroscopy (EIS) on a Chenhua electrochemical workstation, obtaining the Nyquist curve. The test conditions were: frequency 10... -1 -10 5 The Hz frequency was measured at a temperature of 60℃. Ionic conductivity (σ) is calculated using the following formula: σ = L / (R*A) Where L is the thickness of the diaphragm, and A is the area of ​​the stainless steel sheet (a circular sheet with a diameter of 15.5 mm), A = 1.886 cm². 2 R is the bulk resistance (the value at the intersection of the Nyquist curve and the X-axis (the real part of the impedance)).

[0051] Lithium-ion transport number test: Using 0.5mm thick lithium sheets as both positive and negative electrodes, lithium-ion symmetrical batteries (CR2032 coin cells) were assembled in a glove box. Specifically, the following steps were performed: placing the negative electrode shell, spring contact, stainless steel gasket, negative electrode sheet, separator, positive electrode sheet, stainless steel gasket, and positive electrode shell in the following order from bottom to top. The batteries were then packaged using a coin cell packaging machine to obtain the lithium-ion symmetrical battery. The lithium-ion transport number test employed a combination of electrochemical impedance spectroscopy (EIS) and chronoamperometry, both performed using a Chenhua electrochemical workstation. The initial-state interfacial impedance was obtained by testing the lithium-ion symmetric cell using electrochemical impedance spectroscopy (EIS). Then, the polarization current was obtained by testing the lithium-ion symmetric cell using chronoamperometry (applying a polarization voltage of 10 mV for 4000 seconds). The polarization current includes the initial-state current and the steady-state current. Finally, the steady-state interfacial impedance (i.e., the interfacial impedance after polarization) was obtained by testing the lithium-ion symmetric cell using EIS, and thus the lithium-ion transference number (t) was obtained. Li + The electrochemical impedance spectroscopy (EIS) and chronoamperometry methods were both tested at a temperature of 60 °C and a frequency of 10 Hz. -1 -10 5 Hz. t Li + The calculation formula is as follows:

[0052] , among which, I SS I is the steady-state current, I0 is the initial state current, and R is the steady-state current. SS R0 is the steady-state interface impedance, ΔV is the initial state interface impedance, and ΔV is the polarization voltage.

[0053] Electrochemical window testing: Linear sweep voltammetry (LSV) was used in the Chenhua electrochemical workstation. An asymmetric battery (CR2032 coin cell) was assembled in a glove box using a 0.5mm thick stainless steel sheet as the positive electrode and a 0.5mm thick lithium sheet as the negative electrode. Specifically, the negative electrode shell, spring, stainless steel gasket, negative electrode, separator, positive electrode, and positive electrode shell were placed sequentially from bottom to top. The battery was then packaged using a coin cell packaging machine to obtain the asymmetric battery. The asymmetric battery was placed in a 60℃ environment, with a scan range of 2~6V and a scan rate of 10mV / s to obtain the LSV curve. The oxidation decomposition potential was obtained from the LSV curve, and the reduction stability potential was assumed to be 0V. The interval between the reduction stability potential and the oxidation decomposition potential is the electrochemical window.

[0054] Thermal stability test: The diaphragm was cut into 16mm*16mm (initial area) sizes as samples. The samples were placed in a forced-air drying oven and held at five temperature points (60℃, 90℃, 100℃, 120℃, and 150℃) for 30 minutes each (after holding at each temperature point for 30 minutes, the temperature was increased to the next temperature. After holding at each temperature point, the diaphragm was removed and placed back in after the temperature was increased to the next temperature point). After holding at each temperature point, the diaphragm was removed and its shape was observed. When the diaphragm showed obvious deformation visible to the naked eye (curling, edge curling, or melting), the test at higher temperatures was stopped. The temperature at which the diaphragm first showed obvious deformation visible to the naked eye was taken as the tolerance temperature.

[0055] Critical Current Density (CCD) Test: Using 0.5mm thick lithium sheets as both positive and negative electrodes, a lithium-ion symmetrical battery (CR2032 coin cell) was assembled in a glove box. Specifically, the following steps were performed: placing the negative electrode shell, spring contact, stainless steel gasket, negative electrode sheet, separator, positive electrode sheet, stainless steel gasket, and positive electrode shell in the following order from bottom to top. The battery was then packaged using a coin cell packaging machine to obtain the lithium-ion symmetrical battery. The lithium-ion symmetrical battery was then allowed to stand at 60℃ until its voltage stabilized before a constant current charge-discharge test was conducted: the initial current density was 0.1 mA / cm². 2 Each charge-discharge cycle was performed according to the pattern of "1 hour of charging, 1 hour of discharging". After each charge-discharge cycle, the current density increased by 0.1 mA / cm². 2 The critical current density is the current density at which the lithium symmetric battery malfunctions, until an anomaly occurs.

[0056] In the above-mentioned ionic conductivity test, lithium ion transference number test, electrochemical window test, thermal stability test and critical current density test, the separator (electrolyte membrane) is one of the functional composite fiber separators prepared in Examples 1-2, Comparative Examples 1, 5 and 7, and the composite polymer solid electrolyte membranes prepared in Comparative Examples 2, 3, 4 and 6.

[0057] The method for preparing zinc-based metal-organic frameworks (Zn-MOF) includes: mixing 2.975 g of zinc nitrate hexahydrate and 100 mL of methanol at room temperature and stirring at 300 r / min for 1 hour until homogeneous to obtain a first solution; mixing 6.24 g of 2-methylimidazole, 0.532 g of 2-aminobenzimidazole and 100 mL of methanol at room temperature and stirring at 300 r / min for 1 hour until homogeneous to obtain a second solution; slowly adding all of the second solution dropwise (at a rate of 5 mL / min) to all of the first solution under stirring conditions (500 r / min), stirring at 500 r / min for 2 hours until homogeneous to obtain a first mixed solution (milky white solution), allowing it to stand at room temperature for 24 h, discarding the supernatant, washing with methanol by centrifugation to obtain a solid powder, and drying it in a vacuum oven at 100 °C for 24 h to obtain Zn-MOF.

[0058] The method for preparing bismuth-based metal-organic frameworks (Bi-MOFs) includes: mixing 2 mmol of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and 20 mL of ethylene glycol, and sonicating at 60 Hz for 2 h at room temperature until homogeneous to obtain a bismuth nitrate solution; mixing 3 mmol of terephthalic acid and 30 mL of N,N-dimethylformamide (DMF), and sonicating at 60 Hz for 2 h at room temperature until homogeneous to obtain a terephthalic acid solution; slowly adding the entire terephthalic acid solution dropwise (at a rate of 5 mL / min) to the entire bismuth nitrate solution under stirring (500 r / min), and stirring continuously at 500 r / min for 2 h to obtain a second mixed solution; transferring the second mixed solution to a 100 mL polytetrafluoroethylene (PTFE)-lined reactor, and hydrothermally reacting at 150°C for 16 h; naturally cooling to room temperature; filtering to collect the precipitate; and then reacting with N,N-dimethylformamide. The precipitate was washed with dimethylformamide (DMF) to remove impurities and dried in an oven at 60°C for 12 hours to obtain Bi-MOF.

[0059] The method for preparing lanthanum cobalt oxide (LCO) includes: mixing a cobalt source, a lanthanum source, polyvinylpyrrolidone (PVP), and a third solvent at room temperature, stirring at 100 r / min for 24 hours until homogeneous, to obtain a second electrospinning solution; drawing the second electrospinning solution into a syringe and then performing electrospinning (the distance between the receiver and the metal needle of the syringe is 15 cm, the DC voltage for electrospinning is 15 kV, and the ambient temperature for electrospinning is 30℃), to obtain a lanthanum cobalt oxide precursor (existing in the form of a nanofiber membrane); and calcining the lanthanum cobalt oxide precursor at 700℃ for 3 hours in an air atmosphere. h, grind to powder to obtain lanthanum cobaltate (LCO), wherein the cobalt source is cobalt nitrate hexahydrate, the lanthanum source is lanthanum nitrate hexahydrate, and the third solvent is N,N-dimethylformamide (DMF). By molar amount, the ratio of cobalt in the cobalt source to lanthanum in the lanthanum source is 1:1, and the ratio of the molar amount of cobalt in the cobalt source, the mass amount of polyvinylpyrrolidone, and the mass amount of the third solvent is 0.756:0.556:5. The unit of molar amount is mmol, and the unit of mass amount is g.

[0060] Example 1

[0061] A method for preparing a functional composite fiber membrane includes: coating a composite solution onto both sides of a fiber membrane (the thickness of the fiber membrane is approximately 40 μm), specifically including: uniformly coating the composite solution onto a glass plate using a doctor blade; placing the fiber membrane on the surface of the composite solution on the glass plate so that the bottom surface of the fiber membrane is in contact with the composite solution; then uniformly coating the top surface of the fiber membrane with the composite solution using a doctor blade; allowing it to stand at room temperature for 30 min; and then drying (curing) it in a vacuum oven at 60 ℃ for 24 hours. h, composite coatings (each with a thickness of approximately 25 μm) are obtained on both sides of the fiber membrane, and then peeled off from the glass plate to obtain a functional composite fiber membrane (sandwich structure). The method for preparing the composite solution includes: mixing lithium salt, metal-organic framework material (MOF), polyvinylidene fluoride (PVDF) and a first solvent, and stirring at 100 r / min for 24 h at room temperature until homogeneous to obtain a composite solution. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the metal-organic framework material (MOF) is Zn-MOF, and the first solvent is N-methyl-2-pyrrolidone (NMP). By mass fraction, the ratio of lithium salt, metal-organic framework material (MOF), polyvinylidene fluoride (PVDF) and the first solvent is 0.5:0.225:1:10.

[0062] Methods for preparing fibrous membranes include:

[0063] Step 1: Mix pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and the second solvent, and stir at 100 r / min for 24 h at room temperature until homogeneous to obtain the first system (polyimide precursor solution). Mix the perovskite oxide filler with the first system and stir at 300 r / min for 24 h at room temperature until homogeneous to obtain the first electrospinning solution. The perovskite oxide filler is lanthanum cobalt oxide (LCO), and the second solvent is N,N-dimethylacetamide (DMAC). By mass fraction, the ratio of pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and the second solvent is 0.425:0.425:1.65, and the ratio of perovskite oxide filler to pyromellitic dianhydride (PMDA) is 0.0255:0.425.

[0064] Step 2: The first electrospinning solution is drawn into the syringe and then electrospinned to obtain the fiber membrane precursor. The distance between the receiver and the metal needle of the syringe is 18 cm, the DC voltage of electrospinning is 15 kV, and the ambient temperature of electrospinning is 30℃.

[0065] Step 3: Under an air atmosphere, the fiber membrane precursor is placed in a muffle furnace and calcined in stages, then cooled to room temperature to obtain a fiber membrane (a polyimide (PI) fiber membrane containing perovskite oxide filler). The staged calcination includes: heating from room temperature to 100 °C and holding at 100 °C for 30 min (the time from room temperature to 100 °C is 27 min), heating from 100 °C to 200 °C and holding at 200 °C for 30 min (the time from 100 °C to 200 °C is 27 min), and heating from 200 °C to 300 °C and holding at 300 °C for 60 min (the time from 200 °C to 300 °C is 30 min).

[0066] SEM image of the fiber membrane prepared in Example 1 is shown below. Figure 1 As shown, the diameter of a single fiber was measured to be 399 nm.

[0067] SEM image of the cross-section of the functional composite fiber membrane prepared in Example 1 is shown below. Figure 2 As shown, by Figure 2 It can be seen that in the functional composite fiber membrane prepared in Example 1, the fiber membrane ( Figure 2 The composite coating on both sides of the "PI-LCO fiber layer" and the fiber membrane ( Figure 2 The PVDF-MOF layer is tightly bonded to the material. Figure 2It is only used to characterize the adhesion between the fiber membrane and the composite coating, and does not characterize the thickness of the fiber membrane and the composite coating (the shear force during sample preparation will cause non-uniform plastic deformation and slippage of the fiber membrane and the composite coating, resulting in a deviation between the thickness of the fiber membrane and the composite coating in SEM and the actual thickness).

[0068] Example 2

[0069] A method for preparing a functional composite fiber membrane is basically the same as in Example 1, except that "Zn-MOF" is replaced with "Bi-MOF". The thickness of the composite coating formed in Example 2 is approximately 25 μm.

[0070] Comparative Example 1

[0071] A method for preparing a functional composite fiber membrane includes: coating a composite solution onto both sides of a fiber membrane (the thickness of the fiber membrane is approximately 40 μm), specifically including: uniformly coating the composite solution onto a glass plate using a scraper; placing the fiber membrane on the liquid surface of the composite solution on the glass plate so that the bottom surface of the fiber membrane is in contact with the composite solution; then uniformly coating the top surface of the fiber membrane with the composite solution using a scraper; allowing it to stand at room temperature for 30 min; and then drying (curing) it in a vacuum oven at 60 °C for 24 h, resulting in composite coatings (the thickness of the composite coatings is approximately 25 μm) on both sides of the fiber membrane; and peeling it off from the glass plate to obtain a functional composite fiber membrane (sandwich structure). The method for preparing the composite solution in Comparative Example 1 includes: mixing lithium salt, polyvinylidene fluoride (PVDF), and a first solvent, and stirring at 100 r / min at room temperature for 24 hours. h until homogeneous to obtain a composite solution, wherein the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the first solvent is N-methyl-2-pyrrolidone (NMP), and the ratio of lithium salt, polyvinylidene fluoride (PVDF) and the first solvent by mass is 0.5:1:10;

[0072] The method for preparing the fiber membrane in Comparative Example 1 includes:

[0073] Step 1: Pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and the second solvent are mixed and stirred at 100 rpm for 24 h at room temperature until homogeneous to obtain the first system (polyimide precursor solution). The second solvent is N,N-dimethylacetamide (DMAC), and the ratio of pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and the second solvent by mass is 0.425:0.425:1.65.

[0074] Step 2: Using the first system as the electrospinning solution, the first system is drawn into a syringe and electrospinned to obtain a fiber membrane precursor. The distance between the receiver and the metal needle of the syringe is 18 cm, the DC voltage of electrospinning is 15 kV, and the ambient temperature of electrospinning is 30℃.

[0075] Step 3: Under an air atmosphere, the fiber membrane precursor is placed in a muffle furnace and calcined in stages, then cooled to room temperature to obtain a fiber membrane (PI fiber membrane). The staged calcination includes: heating from room temperature to 100 ℃ and holding at 100 ℃ for 30 min (the time from room temperature to 100 ℃ is 27 min), heating from 100 ℃ to 200 ℃ and holding at 200 ℃ for 30 min (the time from 100 ℃ to 200 ℃ is 27 min), and heating from 200 ℃ to 300 ℃ and holding at 300 ℃ for 60 min (the time from 200 ℃ to 300 ℃ is 30 min).

[0076] Comparative Example 2

[0077] A method for preparing a composite polymer solid electrolyte membrane includes: uniformly coating the composite solution from Example 1 onto a glass plate using a scraper, allowing it to stand at room temperature for 30 min, then drying (curing) it in a vacuum oven at 60 °C for 24 h, and peeling it off from the glass plate to obtain a composite polymer solid electrolyte membrane with a thickness of approximately 40 μm.

[0078] Comparative Example 3

[0079] A method for preparing a composite polymer solid electrolyte membrane includes: uniformly coating a solution B onto a glass plate using a doctor blade, allowing it to stand at room temperature for 30 min, then drying (curing) it in a vacuum oven at 60 °C for 24 h, and peeling it off from the glass plate to obtain a composite polymer solid electrolyte membrane with a thickness of approximately 40 μm. The method for preparing solution B includes: mixing lanthanum cobalt oxide, lithium salt, polyvinylidene fluoride (PVDF), and a first solvent, stirring at 100 r / min at room temperature for 24 h until homogeneous, to obtain solution B. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the first solvent is N-methyl-2-pyrrolidone (NMP). The mass ratio of lanthanum cobalt oxide, lithium salt, polyvinylidene fluoride (PVDF), and the first solvent is 0.0255:0.5:1:10.

[0080] Comparative Example 4

[0081] A method for preparing a composite polymer solid electrolyte membrane includes: uniformly coating a C solution onto a glass plate using a doctor blade, allowing it to stand at room temperature for 30 min, then drying (curing) it in a vacuum oven at 60 °C for 24 h, and peeling it off from the glass plate to obtain a composite polymer solid electrolyte membrane with a thickness of approximately 40 μm. The method for preparing the C solution includes: mixing a lithium salt, polyvinylidene fluoride (PVDF), and a first solvent, stirring at 100 r / min at room temperature for 24 h until homogeneous, to obtain the C solution. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the first solvent is N-methyl-2-pyrrolidone (NMP). The mass ratio of lithium salt, PVDF, and the first solvent is 0.5:1:10.

[0082] Comparative Example 5

[0083] A method for preparing a functional composite fiber membrane is basically the same as that in Example 1, except that no metal-organic framework (MOF) material is added when preparing the composite solution. The thickness of the composite coating formed in Comparative Example 5 is approximately 25 μm.

[0084] Comparative Example 6

[0085] A method for preparing a composite polymer solid electrolyte membrane includes: uniformly coating solution A onto a glass plate using a doctor blade, allowing it to stand at room temperature for 30 min, then drying (curing) it in a vacuum oven at 60 °C for 24 h, and peeling it off to obtain a composite polymer solid electrolyte membrane with a thickness of approximately 40 μm. The method for preparing solution A includes: mixing lanthanum cobalt oxide, lithium salt, metal-organic framework (MOF), polyvinylidene fluoride (PVDF), and a first solvent, stirring at 100 r / min for 24 h at room temperature until homogeneous, to obtain solution A. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the metal-organic framework (MOF) is Zn-MOF, and the first solvent is N-methyl-2-pyrrolidone (NMP). The ratio of lanthanum cobalt oxide, lithium salt, metal-organic framework (MOF), polyvinylidene fluoride (PVDF), and the first solvent by mass is 0.0255:0.5:0.225:1:10.

[0086] Comparative Example 7

[0087] A method for preparing a functional composite fiber membrane is basically the same as that in Example 1, except that lanthanum cobalt oxide is not added during the preparation of the fiber membrane. That is, the fiber membrane formed in Comparative Example 7 is a polyimide (PI) fiber membrane with a thickness of approximately 40 μm.

[0088] Figure 3 The XRD pattern of Zn-MOF is shown below. Figure 3It can be seen that Zn-MOF exhibits a pure crystalline phase, and its X-ray diffraction (XRD) pattern is completely matched with the standard card of ZIF-8 (PDF#JCPDS 00-062-1030). In the preparation of Zn-MOF in this invention, 2-aminobenzimidazole is used as an organic ligand. Therefore, the Zn-MOF prepared in this invention is an amino-modified ZIF-8, namely ZIF-8-NH2.

[0089] Figure 4 The SEM image of Zn-MOF is provided by [source missing]. Figure 4 It can be seen that Zn-MOF (particles) have a regular polyhedral structure.

[0090] Figure 5 The XRD pattern of lanthanum cobaltate is shown below. Figure 5 It can be seen that the lanthanum cobalt oxide prepared by this invention exhibits a pure crystalline phase, and its X-ray diffraction (XRD) pattern is a perfect match with the standard card (PDF#01-075-8568) of lanthanum cobalt oxide.

[0091] The electrolyte membrane was subjected to ionic conductivity, lithium-ion transference number, electrochemical window, thermal stability, and critical current density tests to obtain the ionic conductivity (σ) and lithium-ion transference number (t). Li + The electrolyte membrane was selected from the functional composite fiber membranes prepared in Examples 1-2, Comparative Examples 1, 5, and 7, and the composite polymer solid electrolyte membranes prepared in Comparative Examples 2, 3, 4, and 6. The critical current density of the lithium-ion symmetric battery prepared from the functional composite fiber membrane of Example 1 was tested, and the constant current charge-discharge cycle curves obtained are shown below. Figure 6 As shown in Figure a, the critical current density of the lithium symmetric battery prepared from the functional composite fiber separator of Comparative Example 5 was tested, and the constant current charge-discharge cycle curves obtained are as follows. Figure 6 As shown in b, the critical current density of the lithium symmetric battery prepared from the composite polymer solid electrolyte membrane of Comparative Example 6 was tested, and the constant current charge-discharge cycle curves obtained are as follows. Figure 6 As shown in c, the critical current density of the lithium symmetric battery prepared from the functional composite fiber separator of Comparative Example 7 was tested, and the constant current charge-discharge cycle curves obtained are as follows. Figure 6 As shown in d, the critical current density of the lithium symmetric battery prepared from the functional composite fiber separator of Comparative Example 1 was tested, and the constant current charge-discharge cycle curves obtained are as follows. Figure 7 As shown in Figure a, the critical current density of the lithium symmetric battery prepared from the composite polymer solid electrolyte membrane of Comparative Example 2 was tested, and the constant current charge-discharge cycle curves obtained are shown in Figure a. Figure 7As shown in b, the critical current density of the lithium symmetric battery prepared from the composite polymer solid electrolyte membrane of Comparative Example 3 was tested, and the constant current charge-discharge cycle curves obtained are as follows. Figure 7 As shown in c, the critical current density of the lithium symmetric battery prepared from the composite polymer solid electrolyte membrane of Comparative Example 4 was tested, and the constant current charge-discharge cycle curves obtained are as follows. Figure 7 As shown in d, the critical current density of the lithium symmetric battery prepared from the functional composite fiber separator of Example 2 was tested, and the constant current charge-discharge cycle curves obtained are as follows. Figure 8 As shown. Ionic conductivity (σ), lithium-ion transport number (t) Li + The data for electrochemical window, withstand temperature, and critical current density (CCD) are shown in Table 1.

[0092] Table 1

[0093]

[0094] Comparing Comparative Examples 5 and 7 with Example 1, it can be seen that, due to the absence of Zn-MOF, Comparative Example 5 exhibits lower ionic conductivity, lithium-ion transference number, electrochemical window, and critical current density compared to Example 1. Similarly, Comparative Example 7, due to the absence of lanthanum cobalt oxide, also shows lower ionic conductivity, lithium-ion transference number, electrochemical window, and critical current density compared to Example 1. This demonstrates that both Zn-MOF and lanthanum cobalt oxide have a significant impact on the performance of functional composite fiber membranes.

[0095] The electrolyte membranes prepared in Comparative Examples 2, 3, 4 and 6 were all composite polymer solid electrolyte membranes, none of which introduced polyimide (PI) fiber membranes containing perovskite oxide fillers. The properties of the composite polymer solid electrolyte membranes prepared in Comparative Examples 2, 3, 4 and 6 were inferior to those in Examples 1 and 2, especially the composite polymer solid electrolyte membrane prepared in Comparative Example 4 (which was essentially a pure PVDF membrane), which had very poor thermal stability and electrochemical performance of the battery prepared from it.

[0096] Comparing the functional composite fiber membranes prepared in Examples 1 and 2, the ionic conductivity and critical current density of the functional composite fiber membrane prepared in Example 2 are slightly lower than those in Example 1, but the ionic conductivity, lithium ion transference number and electrochemical window of Example 2 are still better than those of Comparative Examples 1 to 7.

[0097] In summary, this invention achieves excellent thermal stability of the functional composite fiber membrane through the synergistic effect of metal-organic framework (MOF), polyimide (PI) fiber membrane containing perovskite oxide filler, and lanthanum cobalt oxide, and the battery prepared from the functional composite fiber membrane exhibits excellent electrochemical performance.

[0098] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a functional composite fiber membrane, characterized in that, include: The same composite solution is coated on both sides of the fiber membrane to obtain a composite coating on both sides of the fiber membrane, thereby obtaining a functional composite fiber membrane. The fiber membrane is a polyimide fiber membrane containing perovskite oxide filler. The composite solution includes: lithium salt, metal-organic framework material, polyvinylidene fluoride and a first solvent. The metal-organic framework material is one of zinc-based metal-organic framework and bismuth-based metal-organic framework. The perovskite oxide filler is lanthanum cobalt oxide. By mass parts, the ratio of lithium salt, metal-organic framework material, polyvinylidene fluoride and the first solvent is (0.48~0.52):(0.2~0.25):(0.8~1.2):(9.8~10.2).

2. The preparation method according to claim 1, characterized in that, The method for preparing the fiber membrane includes: Step 1: Mix pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and the second solvent until homogeneous to obtain a first system. Mix the perovskite oxide filler and the first system until homogeneous to obtain a first electrospinning solution. The ratio of pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and the second solvent by mass is (0.4~0.45):(0.4~0.45):(1.5~1.8), and the ratio of perovskite oxide filler to pyromellitic dianhydride by mass is 0.0255:(0.4~0.45). Step 2: Electrospinning is performed using the first electrospinning solution to obtain a fiber membrane precursor; Step 3: The fiber membrane precursor is calcined in a stepwise manner and cooled to room temperature to obtain the fiber membrane.

3. The preparation method according to claim 1, characterized in that, The composite coating obtained on both sides of the fiber membrane has the same thickness, which is 20~30μm.

4. The preparation method according to claim 1, characterized in that, The thickness of the fiber membrane is 30~40μm.

5. The preparation method according to claim 1, characterized in that, The lithium salt is lithium bis(trifluoromethanesulfonyl)imide, and the first solvent is N-methyl-2-pyrrolidone.

6. The preparation method according to claim 2, characterized in that, The first electrospinning solution is drawn into the syringe before electrospinning. The distance between the receiver and the metal needle of the syringe is 15~18 cm. The DC voltage for electrospinning is 15~18 kV. The ambient temperature for electrospinning is 20~30 ℃.

7. The preparation method according to claim 1, characterized in that, The method for preparing lanthanum cobalt oxide includes: mixing a cobalt source, a lanthanum source, polyvinylpyrrolidone, and a third solvent until homogeneous at room temperature to obtain a second electrospinning solution; performing electrospinning using the second electrospinning solution to obtain a lanthanum cobalt oxide precursor; and calcining the lanthanum cobalt oxide precursor at 650-700℃ for 2-3 h to obtain lanthanum cobalt oxide. The ratio of cobalt in the cobalt source to lanthanum in the lanthanum source is 1:1 by molar amount, and the ratio of the molar amount of cobalt in the cobalt source, the mass amount of polyvinylpyrrolidone, and the mass amount of the third solvent is (0.7-0.8):(0.5-0.6):(4.5-5.5). The unit of molar amount is mmol, and the unit of mass amount is g.

8. The preparation method according to claim 7, characterized in that, The second electrospinning solution is drawn into the syringe before electrospinning. The distance between the receiver and the metal needle of the syringe is 15~18 cm. The DC voltage for electrospinning is 15~18 kV. The ambient temperature for electrospinning is 20~30 ℃.

9. The functional composite fiber membrane obtained by the preparation method according to any one of claims 1 to 8, wherein the functional composite fiber membrane comprises: The fiber membrane and the composite coating on both sides of the fiber membrane, the composite coating comprising: lithium salt, metal-organic framework material and polyvinylidene fluoride, wherein the fiber membrane is a polyimide fiber membrane containing perovskite oxide filler.

10. The application of the functional composite fiber separator as described in claim 9 in lithium batteries.

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