Preparation method and application of PVDF-based composite electrolyte membrane

Abstract

The invention relates to a preparation method and application of a PVDF-based composite electrolyte membrane, and belongs to the technical field of lithium battery electrolyte. The preparation method of the PVDF-based composite electrolyte membrane comprises the following steps: mixing dehydrated zeolite and lithium chloride, and replacing a sodium element in the dehydrated zeolite with a lithium element to prepare lithium zeolite; and preparing the lithium zeolite, polyvinylidene fluoride and lithium salt into an electrolyte membrane. The PVDF-based composite electrolyte membrane prepared by adopting the method has good ionic conductivity, relatively low activation energy and relatively high exchange current density and critical current density, can promote uniform deposition of lithium when being used for a lithium battery, has relatively high lithium ion transfer number and relatively wide electrochemical window, and can be applied to the lithium battery. And the lithium ion battery has relatively good cycle performance under different current densities, and shows excellent electrochemical performance.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a PVDF-based composite electrolyte membrane, belonging to the technical field of lithium battery electrolytes. Background Art

[0002] High-energy-density, high-safety lithium-ion batteries are crucial for the rapid development of the electric vehicle industry. Using a metallic lithium anode and a high-voltage cathode can significantly increase the battery's energy density. However, the electrochemical window of traditional organic liquid electrolytes is too narrow to accommodate high-voltage cathode materials. Furthermore, organic liquid electrolytes themselves present safety issues such as flammability and leakage.

[0003] Solid-state lithium batteries have high energy density and safety, and are expected to become the development direction of the next generation of lithium batteries. Among them, polymer solid electrolytes have excellent flexibility and the advantages of easy large-scale preparation, showing great application prospects. Among polymer solid electrolyte materials, polyvinylidene fluoride (PVDF) has good thermal stability and high dielectric constant and has been widely studied. However, PVDF has a high degree of crystallinity, which makes the room temperature ionic conductivity of PVDF-based polymer solid electrolytes low and difficult to form a stable electrolyte-electrode interface, limiting its application in the field of high-voltage lithium metal batteries.

[0004] To address the problems with PVDF-based polymer solid electrolytes, researchers have proposed a variety of strategies, such as physical improvements through inorganic filler filling and blending modification, or chemical improvements through grafting and cross-linking to improve the polymer backbone. The inorganic filler filling strategy can not only reduce polymer crystallinity but also improve the electrolyte's electrochemical window and mechanical properties. However, current PVDF-based polymer solid electrolytes modified with inorganic fillers still suffer from electrochemical performance deviations. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a PVDF-based composite electrolyte membrane, which can solve the problem of electrochemical performance deviation of PVDF-based polymer solid electrolytes currently modified with inorganic fillers.

[0006] Another object of the present invention is to provide an application of a PVDF-based composite electrolyte membrane, which can solve the problem of electrochemical performance deviation of the current PVDF-based polymer solid electrolyte modified with inorganic fillers.

[0007] In order to achieve the above objectives, the technical solution adopted by the preparation method of the PVDF-based composite electrolyte membrane of the present invention is:

[0008] (1) mixing a dehydrated zeolite and a lithium salt solution, and performing solid-liquid separation to obtain a lithium zeolite; wherein the dehydrated zeolite is selected from dehydrated clinoptilolite, dehydrated mordenite, or dehydrated 3A zeolite;

[0009] (2) A polyvinylidene fluoride electrolyte, a lithium salt, a lithium zeolite and an organic solvent are mixed and coated on a substrate, and dried to obtain a PVDF-based composite electrolyte membrane; the polyvinylidene fluoride electrolyte is selected from polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer; the mass ratio of the polyvinylidene fluoride electrolyte, the lithium salt and the lithium zeolite is 40:(27-30):(2-6).

[0010] The present invention's method for preparing a PVDF-based composite electrolyte membrane involves mixing dehydrated zeolite with lithium chloride, replacing the sodium element in the dehydrated zeolite with lithium to produce the lithium zeolite. The lithium zeolite is then combined with a polyvinylidene fluoride electrolyte, a lithium salt such as bis(fluorosulfonyl)imide, and the like to form an electrolyte membrane. The PVDF-based composite electrolyte membrane prepared using this method exhibits good ionic conductivity, low activation energy, high exchange current density, and critical current density. When used in lithium batteries, it promotes uniform lithium deposition, exhibits a high lithium ion transfer number, and a wide electrochemical window. Furthermore, it exhibits good cycling performance at various current densities, demonstrating excellent electrochemical performance.

[0011] Preferably, in step (1), the concentration of Li in the lithium salt solution is 3-5 mol / L, and the lithium salt is lithium chloride.

[0012] Preferably, in step (1), the mixing method is as follows: first, the dehydrated zeolite and lithium chloride solution are ultrasonically dispersed at room temperature, and finally, stirred at 60-80° C. for 3-8 hours.

[0013] Preferably, in step (1), the particle size of the lithium zeolite is not greater than 200 mesh.

[0014] Preferably, in step (1), the dehydrated zeolite is prepared by calcining zeolite at 390-410° C. for 2-4 hours.

[0015] Preferably, in step (2), the mass ratio of the polyvinylidene fluoride electrolyte, lithium salt and lithium zeolite is 40:(27-28):(2-4).

[0016] Preferably, in step (2), the organic solvent is N,N-dimethylformamide; and the solid-to-liquid ratio of the polyvinylidene fluoride electrolyte to the organic solvent is 400 mg:(15-20) mL.

[0017] Preferably, in step (2), the drying temperature is 55-60° C. and the drying time is 16-24 h.

[0018] Preferably, in step (2), the lithium salt is one or both of bis(fluorosulfonyl)imide lithium salt and bis(trifluoromethanesulfonyl)imide lithium salt.

[0019] The technical solution adopted in the application of the PVDF-based composite electrolyte membrane of the present invention is:

[0020] An application of a PVDF-based composite electrolyte membrane prepared by the method for preparing the PVDF-based composite electrolyte membrane in a solid-state lithium battery.

[0021] The PVDF-based composite electrolyte membrane of the present invention has good ionic conductivity, low activation energy, high exchange current density, and critical current density. When used in lithium batteries, it can promote uniform lithium deposition, has a high lithium ion transfer number and a wide electrochemical window, and has good cycle performance at different current densities, showing excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM image of the clinoptilolite in Example 1 of the present invention;

[0023] Figure 2 This is a SEM image of the lithium zeolite in Example 1 of the present invention;

[0024] Figure 3 The XRD spectra of clinoptilolite and lithiite in Example 1 of the present invention are shown in FIG.

[0025] Figure 4 This is the XPS spectrum of the lithium zeolite in Example 1 of the present invention;

[0026] Figure 5 This is the Li 1s spectrum of the lithium zeolite in Example 1 of the present invention;

[0027] Figure 6 This is a bar graph comparing the ionic conductivity of polyvinylidene fluoride (PVDF) and the composite electrolyte membrane at room temperature in the present invention;

[0028] Figure 7 The Tafel curve of the Li / Li symmetrical battery composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane in the present invention;

[0029] Figure 8 The critical current density curve of the Li / Li symmetrical battery composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane in the present invention;

[0030] Figure 9 The polarization curve of the Li / Li symmetrical battery composed of the composite electrolyte membrane of the present invention and the AC impedance spectrum before and after polarization;

[0031] Figure 10The Li / Li symmetrical battery composed of polyvinylidene fluoride PVDF and composite electrolyte membrane in the present invention is 0.1mAcm -2 , 0.1mAh cm -2 Time-voltage curve under the conditions;

[0032] Figure 11 The Li / Li symmetrical battery composed of polyvinylidene fluoride PVDF and composite electrolyte membrane in the present invention is 0.2mAcm -2 , 0.2mAh cm -2 Time-voltage curve under the conditions;

[0033] Figure 12 This is the Arrhenius curve of the SS / SS (stainless steel symmetrical cell) composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane in the present invention;

[0034] Figure 13 The linear sweep voltammetry (LSV) curve of the Li / SS battery composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane in the present invention;

[0035] Figure 14 This is a rate performance diagram of a Li / NCM811 full battery composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane in the present invention;

[0036] Figure 15 The charge and discharge curves of the Li / NCM811 full battery composed of the composite electrolyte membrane of the present invention at different rates;

[0037] Figure 16 The long cycle performance of the Li / NCM811 full battery composed of polyvinylidene fluoride PVDF and composite electrolyte membrane at a rate of 1C in the present invention;

[0038] Figure 17 The charge and discharge curves of the Li / NCM811 full battery composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane at a rate of 1C and different cycle numbers are shown in the figure.

[0039] Figure 18 The long cycle performance of the Li / NCM811 full battery composed of polyvinylidene fluoride PVDF and composite electrolyte membrane in the present invention at a rate of 2C. DETAILED DESCRIPTION

[0040] Description of the preferred embodiment of the method for preparing PVDF-based composite electrolyte membrane:

[0041] To address the problem of electrochemical performance deviation in current PVDF-based polymer solid electrolytes modified with inorganic fillers, the present invention utilizes a mixture of dehydrated zeolite and a lithium salt solution to replace the sodium element in the dehydrated zeolite with lithium, producing a lithium zeolite. The lithium zeolite is then combined with a polyvinylidene fluoride electrolyte and a lithium salt to form an electrolyte membrane. The PVDF-based composite electrolyte membrane prepared using this method exhibits excellent ionic conductivity, low activation energy, high exchange current density, and critical current density. When used in lithium batteries, it promotes uniform lithium deposition, exhibits a high lithium ion transfer number, and a wide electrochemical window. Furthermore, it exhibits good cycling performance at various current densities, demonstrating superior electrochemical performance.

[0042] Lithium zeolite is obtained by lithium-exchanging dehydrated zeolite. Its average particle size can be 50-100 nm.

[0043] The polyvinylidene fluoride electrolyte may be polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer, both of which are conventional polymer electrolyte matrices in the art. For example, a polyvinylidene fluoride electrolyte having a weight average molecular weight of 300,000-600,000 may be selected.

[0044] The lithium salt can be a conventional additive in the field of solid electrolyte membranes, and can be one or both of bis(fluorosulfonyl)imide lithium salt and bis(trifluoromethanesulfonyl)imide lithium salt. When a combination of bis(fluorosulfonyl)imide lithium salt and bis(trifluoromethanesulfonyl)imide lithium salt is selected, the mass ratio of the two salts can be (1-2):(1-2).

[0045] The technical solution of the present invention is described in detail below with reference to specific examples. In the following examples, unless otherwise specified, all raw materials used are commercially available raw materials, and the commercially available product Kynar761 is selected as PVDF.

[0046] 1. Specific embodiments of the method for preparing the PVDF-based composite electrolyte membrane of the present invention

[0047] Example 1

[0048] The preparation method of the PVDF-based composite electrolyte membrane of this embodiment specifically includes the following steps:

[0049] (1) calcining the clinoptilolite in a muffle furnace at 400°C for 3 h to remove moisture and organic matter from the clinoptilolite to obtain dehydrated clinoptilolite with an average particle size of 50 nm and a silicon-aluminum ratio of 4.3;

[0050] (2) 1.2845 g of lithium chloride (chemical formula: LiCl, purity: 98.5%) was dissolved in 10 mL of deionized water to obtain a 3 mol / L lithium chloride solution.

[0051] (3) Add 1 g of the dehydrated clinoptilolite obtained in step (1) to the lithium chloride solution obtained in step (2), and ultrasonically disperse (to achieve the desired dispersion effect, which can remove the impurity iron element in the natural zeolite mining process) for 10 minutes, and then place in an 80°C water bath and stir for 4 hours to obtain a mixture.

[0052] (4) The mixture was centrifuged, and the solid obtained by centrifugation was washed three times with water, and then dried in an 80°C forced air drying oven for 12 hours. The dried solid was then ground and passed through a 200-mesh sieve to obtain lithium zeolite with a particle size of not more than 200 mesh (i.e., the material under the 200-mesh sieve was taken).

[0053] (5) In a glove box with a water and oxygen value of less than 0.1 ppm, 400 mg of polyvinylidene fluoride (PVDF) (brand name Kynar761), 270 mg of lithium bis(fluorosulfonyl)imide (LiFSI) (purity>98%), and 20 mg of lithium zeolite (the mass of lithium zeolite is 5% of the mass of PVDF) were weighed. Then, the weighed polyvinylidene fluoride (PVDF), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium zeolite were magnetically stirred with 15 mL of N,N-dimethylformamide (DMF) for 6 h to obtain a precursor solution.

[0054] (6) The precursor solution was poured into a clean glass dish (90 mm in diameter) and dried at 55 °C for 18 h to obtain a composite electrolyte membrane (PVLZ) with a thickness of about 80 μm.

[0055] Example 2

[0056] The method for preparing the PVDF-based composite electrolyte membrane of this embodiment comprises the following steps:

[0057] (1) calcining the mordenite in a muffle furnace at 390°C for 4 h to remove moisture and organic matter from the mordenite to obtain dehydrated mordenite with an average particle size of 100 nm and a silicon-aluminum ratio of 20;

[0058] (2) Prepare a lithium chloride solution with a concentration of 4 mol / L;

[0059] (3) adding 1 g of the dehydrated mordenite obtained in step (1) to the lithium chloride solution obtained in step (2), ultrasonically dispersing the mixture for 10 min, and then stirring the mixture in a water bath at 80° C. for 3 h to obtain a mixture;

[0060] (4) The mixture was centrifuged, and the solid obtained by centrifugation was washed three times with water, and then dried in an 80°C forced air drying oven for 12 hours. The dried solid was then ground and passed through a 200-mesh sieve to obtain mordenite with a particle size of no more than 200 mesh (i.e., the material under the 200-mesh sieve was taken).

[0061] (5) In a glove box where the water and oxygen values ​​are all less than 0.1 ppm, 400 mg of polyvinylidene fluoride (PVDF) (brand: Kynar761), 300 mg of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (purity>98%), and 60 mg of mordenite were weighed, and then the weighed polyvinylidene fluoride (PVDF), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and mordenite obtained in step (4) were magnetically stirred with 15 mL of N,N-dimethylformamide (DMF) for 6 h to obtain a precursor solution.

[0062] (6) The precursor solution was poured into a clean glass dish (90 mm in diameter) and dried at 55 °C for 24 h to obtain a composite electrolyte membrane with a thickness of about 80 μm.

[0063] Example 3

[0064] The method for preparing the PVDF-based composite electrolyte membrane of this embodiment comprises the following steps:

[0065] (1) calcining 3A zeolite at 410°C for 2 h in a muffle furnace to remove moisture and organic matter from the 3A zeolite to obtain dehydrated 3A zeolite with an average particle size of 80 nm and a silicon-aluminum ratio of 2;

[0066] (2) Prepare a lithium chloride solution with a concentration of 5 mol / L;

[0067] (3) adding 1 g of the dehydrated 3A zeolite obtained in step (1) to the lithium chloride solution obtained in step (2), ultrasonically dispersing the mixture for 10 min, and then stirring the mixture in a 60° C. water bath for 8 h to obtain a mixture;

[0068] (4) The mixture was centrifuged, and the solid obtained by centrifugation was washed three times with water, and then dried in an 80°C forced air drying oven for 12 hours. The dried solid was then ground and passed through a 200-mesh sieve to obtain 3A zeolite with a particle size of not more than 200 mesh (i.e., the material under the 200-mesh sieve was taken).

[0069] (5) In a glove box with a water and oxygen value of less than 0.1 ppm, 400 mg of polyvinylidene fluoride (PVDF) (brand name Kynar761), 140 mg of lithium bis(trifluoromethanesulfonyl)imide (LiFSI) and 140 mg of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (purity > 98%), and 40 mg of 3A zeolite were weighed. The weighed polyvinylidene fluoride (PVDF), LiFSI and LiTFSI, the 3A zeolite obtained in step (4) and 20 mL of N,N-dimethylformamide (DMF) were magnetically stirred for 6 h to obtain a precursor solution.

[0070] (6) The precursor solution was poured into a clean glass dish (90 mm in diameter) and dried at 60 °C for 16 h to obtain a composite electrolyte membrane with a thickness of about 80 μm.

[0071] 2. Specific Examples of Applications of the PVDF-Based Composite Electrolyte Membrane of the Present Invention in Solid-State Lithium Batteries

[0072] When the PVDF-based composite electrolyte membrane of this embodiment is used in a solid-state lithium battery, it is used as a separator of the solid-state lithium battery and can be assembled into a solid-state lithium battery in an existing manner.

[0073] 3. Experimental Examples

[0074] Experimental Example 1

[0075] In this experimental example, the structure and elemental composition of the clinoptilolite in step (1) of Example 1 and the lithium zeolite prepared in step (4) were analyzed. The SEM image of the clinoptilolite in step (1) is shown in FIG. Figure 1 As shown, the SEM image of the lithium zeolite prepared in step (4) is as follows Figure 2 As shown, the XRD spectra of the clinoptilolite in step (1) and the lithium zeolite prepared in step (4) are as follows Figure 3 As shown, the XPS spectra of the clinoptilolite in step (1) and the lithium zeolite prepared in step (4) are as follows Figure 4 As shown, the Li1s spectrum of the lithium zeolite prepared in step (4) is as follows Figure 5 shown.

[0076] From the above experimental results, it can be seen that compared with the clinoptilolite in step (1), the structure of the lithium zeolite prepared in step (4) has not changed, and the lithium ions have successfully exchanged the sodium ions in the zeolite.

[0077] Experimental Example 2

[0078] This experimental example tests the electrochemical properties of the polyvinylidene fluoride PVDF (PVDF+LiFSI, the electrolyte membrane prepared by PVDF and LiFSI, except that lithium zeolite is not added, the proportions of other substances are the same as those in step (5) of Example 1) and the composite electrolyte membrane prepared in Example 1. The test method is as follows: First, the electrochemical performance of the composite electrolyte membrane is characterized and tested using an electrochemical workstation. Secondly, the performance of the battery assembled with the composite electrolyte membrane is characterized and tested using a blue battery test platform. The test results are as follows: Figure 6-13 shown.

[0079] 2.1 Comparison of room temperature ionic conductivity

[0080] Testing process: 1. Assemble a stainless steel symmetrical cell in a glove box in the order of anode shell - spring - stainless steel sheet - electrolyte membrane - stainless steel sheet - cathode shell. 2. Connect the cell to an electrochemical workstation and measure the AC impedance R of the stainless steel symmetrical cell at room temperature. Calculate the room temperature ionic conductivity σ using the formula σ = L / RS (L is the thickness of the electrolyte membrane and S is the area of ​​the stainless steel sheet).

[0081] Figure 6 The bar chart shows the comparison of ionic conductivity of polyvinylidene fluoride (PVDF) and composite electrolyte membrane PVLZ at room temperature. The results show that the composite electrolyte membrane has higher room temperature ionic conductivity.

[0082] 2.2Li / Li symmetrical battery performance test

[0083] The Li / Li symmetrical battery was assembled in the manner of negative electrode shell-spring-gasket-lithium sheet-electrolyte membrane-lithium sheet-gasket-positive electrode shell, and then the exchange current density, critical current density, and time-voltage characteristics were tested. The results are as follows Figure 7-10 shown.

[0084] in, Figure 7 The Tafel plot of a Li / Li symmetric cell composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane (PVLZ) shows that the Li / Li symmetric cell using the composite electrolyte membrane (PVLZ) has a higher exchange current density, indicating faster lithium ion transfer kinetics at the electrolyte-electrode interface.

[0085] Figure 8 The critical current density curve of a Li / Li symmetric cell composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane is shown. The results show that the Li / Li symmetric cell using the composite electrolyte membrane PVLZ has a higher critical current density, indicating that the composite electrolyte membrane can withstand higher currents and has a stronger ability to inhibit dendrite growth.

[0086] Figure 9 Polarization curves and AC impedance spectra before and after polarization of a Li / Li symmetric cell constructed with a composite electrolyte membrane PVLZ. The results show that the Li / Li symmetric cell using the composite electrolyte membrane has a larger lithium ion transfer number, which helps to alleviate concentration polarization on the lithium metal anode surface and inhibit dendrite growth.

[0087] Figure 10 The Li / Li symmetric battery composed of polyvinylidene fluoride (PVDF) and composite electrolyte membrane is -2 , 0.1mAhcm -2 Time-voltage curve under the conditions; Figure 11The Li / Li symmetric battery composed of polyvinylidene fluoride (PVDF) and composite electrolyte membrane is -2 , 0.2mAh cm -2 The specific process is as follows: 1. Assemble the Li / Li symmetrical battery. 2. Connect the Li / Li symmetrical battery to the battery test system (Newway / Blue Electric), set up the battery test program (main content: stand for 6h-at 0.1mA cm -2 / 0.2mA cm -2 At a current density of 1000 nm, constant current charge was performed for 1 h, and the charge was left for 1 min. At a current density of 0.1 mA cm -2 / 0.2mA cm -2 1h-cycle of constant current discharge at a current density of 1000 nm). Figure 10 and 11 It is shown that at different current densities, the Li / Li symmetric batteries using composite electrolytes have longer stable cycles and lower polarization voltages, indicating that composite electrolytes can improve the cycling stability of lithium metal.

[0088] 2.3SS / SS (stainless steel) symmetrical battery performance test

[0089] Assemble the SS / SS (stainless steel) symmetrical battery in the order of negative electrode shell-spring-stainless steel sheet-electrolyte membrane-stainless steel sheet-positive electrode shell. Figure 12 This is the Arrhenius plot for a symmetrical SS / SS (stainless steel) battery composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane (PVLZ). The results show that the composite electrolyte membrane has a lower activation energy, indicating that the lithium ion migration barrier in the composite electrolyte membrane is lower, making lithium ion migration easier.

[0090] 2.4Li / SS battery

[0091] Assemble the Li / SS battery in the order of negative electrode shell-spring-gasket-lithium sheet-electrolyte membrane-stainless steel sheet-positive electrode shell. Figure 13 This is the linear sweep voltammetry (LSV) curve of a Li / SS battery constructed with polyvinylidene fluoride (PVDF) and a composite electrolyte membrane (PVLZ). The wider electrochemical window indicates that the composite electrolyte membrane is compatible with high-voltage cathodes, enabling higher energy density in lithium metal batteries.

[0092] From the above test results, it can be seen that the composite electrolyte membrane has higher ionic conductivity, lower activation energy, higher exchange current density, critical current density, higher lithium ion transfer number and wider electrochemical window, and has longer symmetrical battery long cycle at different current densities, showing excellent electrochemical performance.

[0093] Experimental Example 3

[0094] In this experimental example, the polyvinylidene fluoride PVDF in step (5) of Example 1 and the composite electrolyte membrane prepared in Example 1 were assembled into a Li / NCM811 full battery, and then the rate and cycle performance tests were carried out. The test method is as follows: 1. Li / NCM811 CR2032 button batteries were assembled in a vacuum argon-filled glove box with water and oxygen values ​​lower than 0.1ppm. The assembly order is: negative electrode shell-spring-gasket-lithium sheet (diameter 15.5mm)-electrolyte membrane-NCM811 positive electrode sheet (diameter 12mm)-gasket-positive electrode shell. After all battery components are assembled, they are stamped and sealed on a battery sealing machine. 2. The battery charge and discharge test is carried out using the Blue Electric Battery Test Platform. The test results are as follows: Figure 14-18 shown.

[0095] in, Figure 14 This is the rate performance diagram of the Li / NCM811 full battery composed of polyvinylidene fluoride PVDF and composite electrolyte membrane. The data shows that at different rates (the charge and discharge rates are the same, which are 0.2C, 0.5C, 1C, 2C, 3C, and 0.2C respectively), the Li / NCM811 full battery using the composite electrolyte membrane has a higher capacity.

[0096] Figure 15 The charge and discharge curves of the Li / NCM811 full battery composed of a composite electrolyte membrane at different rates. The data show that the Li / NCM811 full battery has a high capacity at different rates.

[0097] Figure 16 The long cycle performance of the Li / NCM811 full battery composed of polyvinylidene fluoride PVDF and composite electrolyte membrane at a rate of 1C (the charge and discharge rate is 1C). The data shows that the Li / NCM811 full battery using the composite electrolyte membrane still has a capacity retention rate of 91.2% after 500 cycles at a rate of 1C.

[0098] Figure 17 The charge and discharge curves of the Li / NCM811 full battery composed of polyvinylidene fluoride PVDF and composite electrolyte membrane at different cycle numbers at a rate of 1C (the charge and discharge rate is 1C). The data show that the Li / NCM811 full battery has a small capacity attenuation at different cycle numbers.

[0099] Figure 18 The long-cycle performance of the Li / NCM811 full battery composed of polyvinylidene fluoride (PVDF) and a composite electrolyte membrane at a rate of 2C (both the charge and discharge rates are 2C). The data show that at a rate of 2C, the Li / NCM811 full battery using a composite electrolyte membrane still has a high capacity after 500 cycles, with a capacity retention rate of 92%.

[0100] Therefore, the composite electrolyte membrane of the present invention can effectively improve the cycle performance and rate performance of the full battery.

[0101] Experimental Example 4

[0102] In order to evaluate the comprehensive performance of the PVDF-based composite electrolyte membrane prepared in the example, the conductivity, activation energy, exchange current density, critical current density, electrochemical window, initial discharge specific capacity and capacity retention rate (500 cycles at 1C rate) of the PVDF-based composite electrolyte membrane were tested according to the methods in Experimental Examples 2-3. The results are shown in Table 1.

[0103] Table 1 Comprehensive properties of PVDF-based composite electrolyte membranes prepared in various embodiments and comparative examples

[0104]

[0105]

[0106] Note: “\” in Table 1 means not tested.

[0107] As shown in Table 2, the composite electrolyte membranes prepared in Examples 1-3 have higher ionic conductivity and lower activation energy; higher exchange current density and critical current density, and exhibit better electrochemical performance.

[0108] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a PVDF-based composite electrolyte membrane, characterized in that: The following steps are involved: (1) mixing a dehydrated zeolite and a lithium salt solution, and performing solid-liquid separation to obtain a lithium zeolite; wherein the dehydrated zeolite is selected from dehydrated clinoptilolite, dehydrated mordenite, or dehydrated 3A zeolite; (2) A polyvinylidene fluoride electrolyte, a lithium salt, a lithium zeolite and an organic solvent are mixed and coated on a substrate, and dried to obtain a PVDF-based composite electrolyte membrane; the polyvinylidene fluoride electrolyte is selected from polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer; the mass ratio of the polyvinylidene fluoride electrolyte, the lithium salt and the lithium zeolite is 40:(27-30):(2-6).

2. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1, wherein: In step (1), the concentration of Li in the lithium salt solution is 3-5 mol / L, and the lithium salt is lithium chloride.

3. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1 or 2, wherein: In step (1), the mixing method is as follows: first, the dehydrated zeolite and lithium chloride solution are ultrasonically dispersed at room temperature, and finally stirred at 60-80° C. for 3-8 hours.

4. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1, wherein: In step (1), the particle size of the lithium zeolite is not greater than 200 mesh.

5. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1, wherein: In step (1), the dehydrated zeolite is prepared by calcining zeolite at 390-410° C. for 2-4 hours.

6. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1, wherein: In step (2), the mass ratio of the polyvinylidene fluoride electrolyte, lithium salt and lithium zeolite is 40:(27-28):(2-4).

7. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1 or 6, wherein: In step (2), the organic solvent is N,N-dimethylformamide; the solid-liquid ratio of the polyvinylidene fluoride electrolyte to the organic solvent is 400 mg:(15-20) mL.

8. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1, wherein: In step (2), the drying temperature is 55-60° C. and the drying time is 16-24 hours.

9. The method for preparing a PVDF-based composite electrolyte membrane according to claim 1, wherein: In step (2), the lithium salt is one or both of bis(fluorosulfonyl)imide lithium salt and bis(trifluoromethanesulfonyl)imide lithium salt.

10. Use of a PVDF-based composite electrolyte membrane prepared by the method for preparing a PVDF-based composite electrolyte membrane according to any one of claims 1 to 9 in a solid-state lithium battery.

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