Lithium ion battery composite diaphragm material as well as preparation method and application thereof

Abstract

The invention discloses a lithium ion battery composite diaphragm material as well as a preparation method and application thereof. The lithium ion battery composite diaphragm material is a polymer-coated and MOF-modified composite glass fiber diaphragm material, and comprises a glass fiber (GF) diaphragm substrate, a UiO crystal nano modification layer and a PVDF / PVDF-HFP coating layer. A glass fiber membrane with high ionic conductivity and high-temperature thermal stability is used as a lithium ion battery diaphragm substrate, UiO crystals are grown on the surface of the glass fiber membrane through an in-situ growth method, and then the functional composite diaphragm is prepared through polymer coating. The composite diaphragm has excellent ion transmission performance, high-temperature thermal stability, high mechanical stability and comprehensive electrochemical performance, and shows relatively high specific discharge capacity, good cycle stability, long cycle life and good compatibility to electrode materials in electrochemical rate and cycle tests.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage materials, and particularly relates to a composite separator material for lithium-ion batteries, its preparation method and application, and also relates to a GF-UiO@PVDF / PVDF-HFP composite separator material, its preparation method and application in lithium-ion batteries. Background Art

[0002] Lithium-ion batteries (LIBs) have the advantages of relatively light weight, high energy density, long cycle life, strong adaptability to high and low temperatures, no memory effect, environmental friendliness, etc., and are widely used in high-performance energy storage devices in electric vehicles, electronic devices and aerospace fields. While developing and applying high-energy-density LIBs, the safety issues of LIBs have also attracted people's attention and research. Among the components of LIBs, the safety performance is mainly determined by the properties of the electrolyte and the separator material. The properties of the LIBs separator determine the interfacial resistance during the operation of LIBs. Its compatibility with the positive and negative electrode materials of LIBs and the microscopic interfacial structure determine the cycle stability of LIBs, and also have a substantial impact on the capacity and safety performance of LIBs. Currently, commercial LIBs separators are mostly single-layer polyolefin separators, such as single-layer PP and single-layer PE separators, or multi-layer composite polyolefin separators, such as three-layer PP / PE / PP separators. The preparation process of polyolefin separators is mostly unidirectional or bidirectional stretching method, resulting in uneven pore distribution inside and low ionic conductivity (0.66 mS cm -1 ), which leads to reduced ion transport efficiency. In addition, the melting point of polyolefin separators is relatively low (the melting point of PP is about 165 °C, and the melting point of PE is about 135 °C), and the thermal stability is poor. When the temperature approaches the melting point, it will melt, resulting in the closing of the pores of the separator and preventing Li + ions from passing through the separator, causing LIBs to stop working. Although polyolefin separators have thermal blocking properties, the battery will continue to heat up after the pores of the separator are closed, and the separator may shrink or even melt, ultimately leading to battery short circuit and posing a safety hazard. The poor ion transport performance and thermal stability greatly limit the application and development of polyolefin separators in high-energy-density LIBs. Therefore, it is of great significance to develop functional composite separators with high ionic conductivity and thermal stability.

[0003] Glass fiber (GF) separators have become a type of battery separator widely studied in recent years due to their high ionic conductivity (9 mS cm -1 ) and high thermal stability (melting point / about 680 °C). However, its relatively high interfacial impedance and less-than-ideal electrochemical performance have hindered its widespread application in the field of lithium-ion batteries.

[0004] To ensure further improvement of the electrochemical performance of glass fiber separators on the basis of high ionic conductivity and thermal stability, it is necessary to modify the separator substrate. Metal-organic frameworks (MOFs) are a class of porous crystalline compounds formed by the self-assembly of metal clusters and organic ligands through coordination bonds. Their three-dimensional porous network structure usually uses metal ions as connection points and organic ligands as supporting structures to form a three-dimensional extended system in space. MOF materials have high crystallinity, rich pore structures, large porosity, high specific surface area, high thermal stability, excellent designability and functionalization properties. Modifying glass fiber separators with MOF materials can further improve their ion transport performance and electrochemical performance. Therefore, the preparation of functional composite separator materials with high ionic conductivity, high thermal stability and excellent electrochemical performance has broad application prospects. The UiO (University of Oslo) series of MOF materials were first synthesized and named by the Lillerud research group. They have outstanding high-temperature thermal stability and chemical stability. The crystal structure can remain stable at 500 °C, and the crystal framework structure can withstand a mechanical pressure of 1.0 MPa. They can maintain structural stability in common solution systems such as water, DMF (N,N-dimethylformamide), benzene or acetone, and have excellent chemical stability, making them ideal materials for modifying lithium-ion battery separators.

[0005] In addition, to further improve the mechanical stability of the composite separator and ensure that it can effectively overcome the stress changes generated on the electrode surface under long-term cycling conditions, a polymer coating is introduced to coat the glass fiber separator. Polyvinylidene fluoride (PVDF) has excellent mechanical properties, thermal stability and chemical stability, as well as characteristics such as easy film formation, and has received extensive attention in the field of lithium-ion battery separators. It often exists as an organic separator matrix or a modified coating material.

[0006] However, here, its copolymer polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is introduced for blending to form a PVDF / PVDF-HFP polymer modification layer, reducing the crystallinity and interfacial resistance and improving the electrolyte affinity of the polymer modification layer. Summary of the Invention

[0007] Aiming at the problem that the high crystallinity and interfacial resistance of polyvinylidene fluoride in the prior art will cause adverse capacity attenuation, the present invention provides a lithium-ion battery composite separator material, its preparation method and application, and also a novel lithium-ion battery functionalized composite separator and its preparation method and application. Specifically, it is a polymer-coated and MOF-modified composite glass fiber separator material (GF-UiO@PVDF / PVDF-HFP composite separator material) and its preparation method and use in lithium batteries. The present invention comprehensively utilizes the advantageous characteristics of glass fiber (GF) separators, MOFs materials and PVDF / PVDF-HFP polymer modification layers, and adopts a variety of synthesis methods to prepare a GF-UiO@PVDF / PVDF-HFP composite separator material with excellent ion transport performance, high-temperature thermal stability, high mechanical stability and comprehensive electrochemical performance.

[0008] The object of the present invention is achieved by the following technical solutions: A preparation method of a lithium-ion battery composite separator material, which is also a preparation method of a GF-UiO@PVDF / PVDF-HFP composite separator material, includes the following steps: S1. Preparation of UiO precursor solution: Mix inorganic metal salt compounds, organic ligands, crystallization regulators and solvents, and mix them evenly by ultrasonic to obtain UiO precursor solution; The molar ratio of the inorganic metal salt compounds, organic ligands and crystallization regulators is 1:1:3000, and the solvent dosage is adjusted according to the reactant dosage to control the concentration of inorganic metal salts and organic ligand reactants at 0.01 mol L -1 ; The inorganic metal salt compounds are selected from one of Ti salts, Zr salts, Hf salts and Ce salts; The organic ligands are selected from one of carboxylic acid ligands such as 1,4-benzenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-terphenyl dicarboxylic acid and their derivatives; The crystallization regulators are selected from one of substances such as formic acid, acetic acid, hydrochloric acid, phenylacetic acid, etc. that can promote the formation of MOFs material crystal nuclei and regulate the crystal growth rate; The solvents are selected from one of methanol, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide; The ultrasonic mixing time is 30-60 min, the temperature is 20-30 °C, and the power is 100-300 W; S2. Preparation of various GF@UiO composite separator materials, including the following steps: S2-1. Preparation by diffusion synthesis method: Transfer the UiO precursor solution prepared in S1 to a conical flask, cover the conical flask with a glass dish, heat it to 90 - 110 °C, and keep the temperature for 14 days to obtain the GF@UiO composite separator material; S2-2. Preparation by solvothermal synthesis method: Transfer the UiO precursor solution prepared in S1 to a polytetrafluoroethylene autoclave, and place a commercial glass fiber separator into it. Conduct a solvothermal reaction in an electric heating blast drying oven at a reaction temperature of 120 - 150 °C for 24 h to obtain the GF@UiO composite separator material; S2-3. Preparation by microwave-assisted heating method: Transfer the UiO precursor solution prepared in S1 to a polytetrafluoroethylene autoclave, and place a commercial glass fiber separator into it. Conduct a microwave-assisted heating reaction in a microwave synthesizer at a reaction temperature of 125 - 175 °C for 30 min with a microwave power of 800 W to obtain the GF@UiO composite separator material; S2-4. Preparation by continuous flow method: Independently pump the UiO reactant solution prepared in S1 into a coil reactor through two independent pumps for heating and mixing, and finally flow through a back pressure regulator into a sealed container soaked with a glass fiber separator at a heating temperature of 120 - 140 °C and a synthesis reaction flow rate of 90 mL min -1 , and react for 24 h to obtain the GF@UiO composite separator material; Ultrasonically clean, dry, and cut the GF@UiO composite separator materials prepared in S2-1 to S2-4; The pore size of the GF@UiO composite separator is 2.80 - 3.00 nm, the BJH adsorption cumulative pore volume is 0.20 - 0.30 cm 3 g -1 , and the Langmuir specific surface area is 1000 - 1100 m 2 g -1 ; S3. Preparation of various GF-UiO@PVDF / PVDF-HFP composite separator materials, including the following steps: S3-1. Preparation by polymer immersion method: Transfer the GF@UiO composite separator prepared in S2 to a beaker containing a PVDF / PVDF-HFP blend solution, fully immerse it, then transfer it to a beaker containing an ethanol solution for pore formation for 2 - 5 min, and then conduct vacuum drying to obtain the GF-UiO@PVDF / PVDF-HFP composite separator material; S3-2. Preparation by polymer doctor blade coating method: Transfer the GF@UiO composite separator prepared in S2 onto a glass plate, and use a four-sided doctor blade to scrape the PVDF / PVDF-HFP blend solution onto the GF@UiO composite separator. The specifications of the four-sided doctor blade are 100 μm, 150 μm, 200 μm, and 250 μm, and then vacuum drying is carried out to obtain the GF-UiO@PVDF / PVDF-HFP composite separator material; S3-3. Preparation by electrospinning method: Fix the GF@UiO composite separator prepared in S2 onto the receiver of the electrospinning machine, load the PVDF / PVDF-HFP blend solution into a syringe and fix it on the feeding and conveying system. Set the corresponding parameters to spin the polymer liquid onto the GF@UiO composite separator. The working DC voltage range of the electrospinning method is 15 - 25 kV, and then vacuum drying is carried out to obtain the GF-UiO@PVDF / PVDF-HFP composite separator material; For the PVDF / PVDF-HFP blend solution, PVDF and PVDF-HFP are in a mass ratio of 1:1; The prepared GF-UiO@PVDF / PVDF-HFP composite separator material has an ionic conductivity of 9.0 - 10.0 mScm -1 , and the lithium ion transference number t Li+ is 0.80 - 0.90; Assemble a lithium metal half-cell with the GF-UiO@PVDF / PVDF-HFP composite separator material, match it with the NCM811 cathode material and the lithium metal anode material for testing. The discharge specific capacity data for the first five cycles at 0.2C and 2.8 - 4.3V is 202.60 - 206.80 mAh g -1 , and the discharge specific capacity in the first cycle can reach 204.70 mAh g -1 . After 100 charge-discharge cycles, the capacity retention rate is 89.25%, and the cycle life reaches 480 cycles.

[0009] In the present invention: Furthermore, the inorganic metal salt compound described in S1 is selected from metal chloride salts.

[0010] Furthermore, the solvent described in S1 is selected from N,N-dimethylformamide.

[0011] Furthermore, for the ultrasonic mixing in S1, the washing solvent for ultrasonic cleaning is 99.5% anhydrous methanol.

[0012] Furthermore, the commercial glass fiber separator described in S2 is disc-shaped, with a diameter of 25 - 55 mm and a thickness of 260 - 675 μm, preferably a diameter of 25 mm and a thickness of 260 μm.

[0013] Further, in S2-1, the conical flask is heated to 100 °C and kept warm for 14 days.

[0014] Further, in S2-2, the solvothermal reaction temperature is 120 °C and the reaction time is 24 h.

[0015] Further, in S2-3, for the microwave-assisted heating, the reaction temperature is 150 °C, the reaction time is 30 min, and the microwave power is 800 W.

[0016] Further, in S2-4, for the continuous flow method, the heating temperature is 130 °C, the synthesis reaction flow rate is 90 mL min-1, and the reaction time is 24 h.

[0017] Further, in S2-2 to S2-4, the surface loading amount of UiO crystals on the glass fiber diaphragm is 0.001 mg mm -2 .

[0018] Further, in S2, in the electrothermal blast drying oven, it is dried at 80 °C for 5 h.

[0019] Further, the GF@UiO composite diaphragm prepared in S2 is assembled into a half-cell for electrochemical performance testing.

[0020] Further, the pore-forming time in S3-1 is 3 min.

[0021] Further, the specification distribution of the four-sided coater in S3-2 is 200 μm.

[0022] Further, the working DC voltage of the electrospinning method in S3-3 is 18 kV.

[0023] Further, in S3, for the vacuum drying, it is placed in a vacuum drying oven and vacuum dried at 90 °C for 10 h.

[0024] Further, the GF-UiO@PVDF / PVDF-HFP composite diaphragm prepared in S3 is assembled into a half-cell for electrochemical performance testing.

[0025] The present invention also relates to a GF-UiO@PVDF / PVDF-HFP composite diaphragm material prepared by the preparation method of the above-mentioned lithium-ion battery composite diaphragm material, and its ionic conductivity is 9.0 - 10.0 mS cm -1 , and the lithium ion transference number t Li+ is 0.80 - 0.90; The lithium metal half-cell assembled with the GF-UiO@PVDF / PVDF-HFP composite separator material, matching the NCM811 cathode material and the lithium metal anode material, was tested. The discharge specific capacity data for the first five cycles at 0.2C and 2.8 - 4.3V were 202.60 - 206.80 mAh g -1 , and the discharge specific capacity of the first cycle could reach 204.70 mAh g -1 . After 100 charge-discharge cycles, the capacity retention rate was 89.25%, and the cycle life reached 480 cycles; The modification of UiO crystals effectively improved the ionic conductivity and lithium ion transference number of the glass fiber (GF) separator substrate. The ultra-high specific surface area of UiO crystals themselves and the constructed adjustable porous ion channels improved the ionic transport performance of the composite separator, and the polymer coating improved the mechanical stability of the composite separator, contributing to long cycle stability.

[0026] The present invention also relates to the application of the above GF-UiO@PVDF / PVDF-HFP composite separator material in a lithium ion battery, which is applied to a lithium battery.

[0027] Furthermore, the lithium battery is a liquid lithium metal battery.

[0028] Compared with the prior art, the present invention has the following advantages: 1. For the preparation method of the lithium ion battery composite separator material described in the present invention, UiO crystals are prepared by different synthesis methods and in-situ grown on the glass fiber separator to achieve the functionalization of modifying and improving the separator substrate. Then, the mechanical and electrochemical stability of the composite separator is further improved by polymer coating modification. The rich pore structure and large specific surface area of UiO crystals can effectively regulate the ion transport process, adsorb impurity small molecules generated during the electrochemical reaction process, and slow down the decomposition effect of the electrolyte.

[0029] 2. The lithium ion battery composite separator material described in the present invention is a GF-UiO@PVDF / PVDF-HFP composite separator material with high ionic conductivity, high thermal stability, high mechanical stability and excellent comprehensive electrochemical performance. The PVDF / PVDF-HFP polymer modification layer effectively improves the interfacial contact between the electrode and the composite separator, enhances the thermal stability and mechanical stability, and regulates the ion transport process. This functional composite separator effectively improves the comprehensive electrochemical performance and safety performance of the lithium ion battery. Description of the Drawings

[0030] Figure 1 is the scanning electron microscope image of the GF@UiO-66-NH2 composite separator prepared in Example 1, Example 2 and Example 3 of the present invention at different temperatures; Figure 2It is the scanning electron microscope image of the GF-UiO-66-NH2@PVDF / PVDF-HFP composite separator prepared in Example 4 of the present invention; Figure 3 It is the graph of the rate performance comparison of the GF@UiO-66-NH2 composite separators prepared in Example 1, Example 2, and Example 3 of the present invention at different temperatures; Figure 4 It is the graph of the comparison of electrochemical impedance spectra in the ion conductivity test of the GF@UiO-66-NH2 composite separator prepared in Example 3 of the present invention, the PP separator in Comparative Example 1, and the GF separator in Comparative Example 2; Figure 5 It is the graph of the cycle performance comparison of the GF@UiO-66-NH2 composite separator prepared in Example 3 of the present invention, the PP separator in Comparative Example 1, and the GF separator in Comparative Example 2 when assembling lithium metal half-cells with NCM811 cathode material and lithium metal anode material respectively; Figure 6 It is the graph of the cycle performance comparison of the GF-UiO-66-NH2@PVDF / PVDF-HFP composite separator prepared in Example 4 of the present invention and the GF@UiO-66-NH2 composite separator prepared in Example 3 when assembling lithium metal half-cells with NCM811 cathode material and lithium metal anode material respectively; Figure 7 It is the scanning electron microscope image of the GF@UiO-66-NH2 composite separator of Example 3 of the present invention; Figure 8 It is the scanning electron microscope image of the GF-UiO-66-NH2@PVDF / PVDF-HFP composite separator of Example 4 of the present invention. Detailed implementation manners

[0031] The preparation method of the present invention will be further described in detail below with reference to specific examples. It should be understood that the following examples are only for illustrative explanation of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection of the present invention.

[0032] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; unless otherwise specified, the reagents, materials, etc. used in the following examples can all be obtained from commercial channels.

[0033] Example 1: Weigh 141.75 mg of 99.9% ZrCl4, 109.5 mg of 99.32% 2-aminoterephthalic acid, 10.83 g of 99.5% acetic acid, and 63.8 mL of 99.9% N,N-dimethylformamide into a beaker and mix them ultrasonically for 30 min. After cooling, pour the mixture into a reaction kettle, then place the glass fiber diaphragm that has been cleaned and dried into the reaction kettle. Place the sealed reaction kettle in an electrothermal blast drying oven and react at 100 °C for 24 h. When the hydrothermal reaction kettle has finished reacting and cooled to room temperature, take out the GF@UiO-66-NH2 composite diaphragm, transfer it to a beaker, pour in 100 mL of 99.5% anhydrous methanol, and ultrasonically clean it for 30 min. Repeat the cleaning step 3 times. Then place the cleaned GF@UiO-66-NH2 composite diaphragm in an electrothermal blast drying oven and dry it at 80 °C for 5 h, and then transfer it to a vacuum drying oven and vacuum dry it at 90 °C for 10 h. After all the drying steps are completed, take out the dried composite diaphragm, cut the composite diaphragm into a button cell diaphragm with a diameter of 19 mm using a cutting machine, and collect it in a sealed bag for storage. The microscopic structure of the GF@UiO-66-NH2 composite diaphragm prepared at 100 °C is as shown in Figure 1 (a), (b), and (c).

[0034] Figure 1 In (a), (b), and (c) are the scanning electron microscope images of the GF@UiO-66-NH2 composite diaphragm prepared in Example 1 at 100 °C. It can be observed from the figure that partial agglomeration of UiO-66-NH2 crystals occurs, the interfaces of the crystals are not clear enough, the octahedral morphology of some crystals is not complete, the overall sizes of the crystals are different, and the crystallinity is small.

[0035] Figure 2 The electrochemical test results in show that for the GF@UiO-66-NH2 composite diaphragm prepared at 100 °C, using NCM811 material as the positive electrode and metallic lithium as the negative electrode to assemble a lithium half-cell, under the conditions of 0.2 C and 2.8 - 4.25 V, its discharge specific capacity is 180.64 mAh g -1 . The specific rate performance parameters are shown in Table 1.

[0036] Example 2: Similar to Example 1, the difference is that the hydrothermal reaction temperature is 110 °C and the reaction time is also 24 h. When the hydrothermal reaction kettle finishes the reaction and cools down to room temperature, take out the GF@UiO-66-NH2 composite diaphragm, clamp it into a beaker with tweezers, pour 100 mL of 99.5% anhydrous methanol, and ultrasonically clean it for 30 min. Repeat the cleaning step 3 times. Then place the cleaned GF@UiO-66-NH2 composite diaphragm in an electrothermal blast drying oven and dry it at 80 °C for 5 h, and then transfer it to a vacuum drying oven and vacuum dry it at 90 °C for 10 h. After all the drying steps are completed, take out the dried composite diaphragm, cut the composite diaphragm into a button cell diaphragm with a diameter of 19 mm with a cutting machine, and collect it in a sealed bag for storage. The microstructure of the GF@UiO-66-NH2 composite diaphragm prepared at 110 °C is as follows Figure 1 (d), (e), (f) shown.

[0037] Figure 1 In (d), (e), (f) are the scanning electron microscope images of the GF@UiO-66-NH2 composite diaphragm prepared in Example 2 at 110 °C. It can be observed from the figure that compared with the UiO-66-NH2 crystals obtained in Example 1, there is a slight agglomeration phenomenon in the crystals of Example 2, while the crystal size is more uniform, the crystallinity is significantly increased, the distribution on the glass fiber is denser, and the octahedral contour of the crystal is clearer.

[0038] Figure 2 The electrochemical test results in show that for the GF@UiO-66-NH2 composite diaphragm prepared at 110 °C, using NCM811 material as the positive electrode and metallic lithium as the negative electrode to assemble a lithium half-cell, under the conditions of 0.2 C and 2.8 - 4.25 V, its discharge specific capacity is 163.86 mAh g -1 . The specific rate performance parameters are shown in Table 1.

[0039] Example 3: Similar to Example 1, the difference is that the hydrothermal reaction temperature is 120 °C and the reaction time is also 24 h. When the hydrothermal reaction kettle finishes the reaction and cools down to room temperature, take out the GF@UiO-66-NH2 composite diaphragm, clamp it into a beaker with tweezers, pour 100 mL of 99.5% anhydrous methanol, and ultrasonically clean it for 30 min. Repeat the cleaning step 3 times. Then place the cleaned GF@UiO-66-NH2 composite diaphragm in an electrothermal blast drying oven and dry it at 80 °C for 5 h, and then transfer it to a vacuum drying oven and vacuum dry it at 90 °C for 10 h. After all the drying steps are completed, take out the dried composite diaphragm, cut the composite diaphragm into a button cell diaphragm with a diameter of 19 mm with a cutting machine, and collect it in a sealed bag for storage. The microstructure of the GF@UiO-66-NH2 composite diaphragm prepared at 120 °C is as follows Figure 1As shown in (g), (h), and (i).

[0040] Figure 1 (g), (h), and (i) are scanning electron microscope images of the GF@UiO-66-NH2 composite membrane prepared at 120°C in Example 3. It can be observed from the figure that compared with the UiO-66-NH2 crystals obtained in Examples 1 and 2, the crystal outline in Example 3 is the sharpest and clearest, the growth and coating on the glass fiber is better, the distribution is more uniform, and the agglomeration phenomenon is significantly weakened.

[0041] Figure 3 The electrochemical test results show that the GF@UiO-66-NH2 composite membrane prepared at 120 °C has a discharge capacity of 183.46 mAh g-1 at 0.2 C and 2.8-4.25 V. -1 Specific rate performance parameters are shown in Table 1.

[0042] Figure 7 is a scanning electron microscope image of the GF@UiO-66-NH2 composite membrane of Example 3; Table 1 Electrochemical properties of the GF@UiO-66-NH2 composite membranes prepared at different temperatures in Examples 1-3

[0043] Embodiment 4: Weigh 6.125 g of 99.9% PVDF, 6.125 g of 99.9% PVDF-HFP, 25 mL of 99.9% NN dimethylformamide, and 75 mL of 99.9% acetone in a beaker, and heat and stir at 60°C for 24 h to obtain a polymer solution. The GF@UiO-66-NH2 composite membrane obtained in Example 3 was placed in a glass culture dish containing the above polymer solution, and after being fully soaked, it was transferred to an ethanol solution and soaked for 3 min. The GF-UiO-66-NH2@PVDF / PVDF-HFP composite membrane after soaking was placed in an electric heating blower and dried at 80°C for 5 h, and then transferred to a vacuum drying oven and vacuum dried at 90°C for 10 h. After all the drying steps were completed, the dried composite membrane was taken out, and the composite membrane was cut into a button battery membrane with a diameter of 19 mm using a cutting machine, and collected in a sealed bag for storage. The microstructure of the GF-UiO-66-NH2@PVDF / PVDF-HFP composite membrane obtained by this method is shown in Figure 2 shown.

[0044] Figure 6The results of the electrochemical tests show that for the above-mentioned GF-UiO-66-NH2@PVDF / PVDF-HFP composite separator and the GF@UiO-66-NH2 composite separator prepared at 120 °C, a lithium half-cell was assembled with the NCM811 material as the positive electrode and metallic lithium as the negative electrode. The former can achieve more than 480 cycles of cycle life, while the latter short-circuited around 50 cycles, that is, the polymer coating modification can significantly improve the mechanical stability and cycle life of the composite separator.

[0045] Figure 8 It is the scanning electron microscope image of the GF-UiO-66-NH2@PVDF / PVDF-HFP composite separator of Example 4.

[0046] Table 2:

[0047] Comparative Example 1: First, commercially available polyolefin (PP) separator was ultrasonically cleaned with 99.7% anhydrous ethanol for 30 min, then the cleaned polyolefin separator was placed in an electrothermal blast drying oven and dried at 80 °C for 5 h, and then transferred to a vacuum drying oven and vacuum dried at 90 °C for 8 h. After all the drying steps were completed, the dried composite separator was taken out, and the composite separator was cut into a button cell separator with a diameter of 19 mm by a cutting machine and collected and stored in a sealed bag.

[0048] Figure 3 It is the graph of the rate performance comparison of the GF@UiO-66-NH2 composite separators prepared in Example 1, Example 2, and Example 3 at different temperatures; The results show that the ionic conductivity of the commercially available polyolefin (PP) separator is 0.66 mS cm -1 , and the lithium ion transference number t Li+ is 0.67. For the commercially available polyolefin (PP) separator, a lithium half-cell was assembled with the NCM811 material as the positive electrode and metallic lithium as the negative electrode. Under the conditions of 0.2 C and 2.8 - 4.3 V, its discharge specific capacity is 213.2 mAh g -1 . The specific electrochemical performance parameters are shown in Table 2.

[0049] Comparative Example 2: The commercially available glass fiber (GF) separator was ultrasonically cleaned with 99.7% anhydrous ethanol for 30 min, then the cleaned glass fiber separator was placed in an electrothermal blast drying oven and dried at 80 °C for 5 h, and then transferred to a vacuum drying oven and vacuum dried at 90 °C for 8 h. After all the drying steps were completed, the dried composite separator was taken out, and the composite separator was cut into a button cell separator with a diameter of 19 mm by a cutting machine and collected and stored in a sealed bag.

[0050] Figure 4It is a graph comparing the electrochemical impedance spectra in the ionic conductivity tests of the GF@UiO-66-NH2 composite separator prepared in Example 3, the PP separator in Comparative Example 1, and the GF separator in Comparative Example 2; Figure 5 It is a graph comparing the cycling performance of the GF@UiO-66-NH2 composite separator prepared in Example 3, the PP separator in Comparative Example 1, and the GF separator in Comparative Example 2 when assembling lithium metal half-cells with the NCM811 cathode material and the lithium metal anode material respectively; The results show that the ionic conductivity of the commercial glass fiber (GF) separator is 9 mS cm -1 , and the lithium ion transference number t Li+ is 0.81. When assembling a lithium half-cell with the commercial glass fiber (GF) separator using the NCM811 material as the cathode and lithium metal as the anode, under the conditions of 0.2 C and 2.8 - 4.3 V, its discharge specific capacity is 199.1 mAh g -1 . The specific electrochemical performance parameters are shown in Table 2.

[0051] Table 3 Electrochemical performance of different separators prepared in Example 3 and Comparative Examples 1 - 2

[0052] Summary and discussion: According to the data obtained from the experimental tests and the attached figures, it can be seen that: 1. When comparing the ionic conductivity and lithium ion transference number data of Example 3, Example 4, Comparative Example 1, and Comparative Example 2, the separator using the GF substrate has a more significant advantage in ionic transport performance compared to the PP separator; when comparing the ionic conductivity and lithium ion transference number data of Example 3, Example 4, and Comparative Example 2 using the same GF substrate, the in-situ functionalization of MOF and polymer coating can further improve the ionic transport performance of the composite separator; 2. Regarding the electrochemical cycling performance, when comparing the first-cycle discharge specific capacity and 50-cycle capacity retention rate data of Example 3, Example 4, Comparative Example 1, and Comparative Example 2 under the test conditions of 0.2 C and 2.8 - 4.3 V, the separator using the GF substrate has a higher discharge specific capacity and capacity retention rate compared to the PP separator, and has more excellent electrochemical performance; When comparing the first-cycle discharge specific capacity and 50-cycle capacity retention rate data of Example 3, Example 4, and Comparative Example 2 under the test conditions of 0.2 C and 2.8 - 4.3 V, the in-situ functionalization of MOF and polymer coating can further improve the electrochemical performance of the composite separator; According to Figure 6For the cyclic data, in Example 3 and Example 4 during the cycling process, the GF@UiO-66-NH2 composite separator in Example 3 was prone to lithium dendrite penetration and short circuit after cycling about 50 times under the test conditions of 0.2 C and 2.8 - 4.3 V. However, the GF-UiO-66-NH2@PVDF / PVDF-HFP composite separator in Example 4 did not show any short circuit phenomenon after cycling more than 480 times under the test conditions of 0.2 C and 2.8 - 4.3 V. This indicates that the in-situ functionalization of MOF can only improve the electrochemical performance of the composite separator, but cannot effectively improve its cycle life and cycle stability. After polymer coating, the electrochemical performance and cycle life of the composite separator can be further improved simultaneously.

[0053] Generally speaking, the polymer-coated in-situ functionalized MOF composite separator in Example 4 has the best ion transport performance and comprehensive electrochemical performance, and has application value.

[0054] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite diaphragm material for a lithium-ion battery, characterized in that: The invention discloses a method for preparing a GF-UiO@PVDF / PVDF-HFP composite diaphragm material, comprising the following steps: S1. Preparation of UiO precursor solution: An inorganic metal salt compound, an organic ligand, a crystal modulator, and a solvent are mixed and uniformly mixed by ultrasonication to obtain a UiO precursor solution; The molar ratio of the inorganic metal salt compound, the organic ligand, and the crystal modulator is 1:1:3000. The amount of solvent is adjusted according to the amount of reactants, and the concentration of the inorganic metal salt and the organic ligand reactants is controlled to be 0.01 mol L -1 ; The inorganic metal salt compound is selected from one of Ti salt, Zr salt, Hf salt and Ce salt; The organic ligand is selected from one of 1,4-terephthalic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-terphenyldicarboxylic acid and their derivatives; The crystal modulator is selected from formic acid, acetic acid, hydrochloric acid, and phenylacetic acid, which are substances that promote the formation of MOF material nuclei and regulate the crystal growth rate; The solvent is selected from one of methanol, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide and N,N-diethylformamide; The ultrasonic mixing time is 30-60 min, the temperature is 20-30 ° C, and the power is 100-300 W; S2. Preparation of various GF@UiO composite diaphragm materials, including the following steps: S2-1, prepared by diffusion synthesis method: the UiO precursor solution prepared in S1 was transferred to a conical flask, the conical flask was covered with a glass dish, and heated to 90-110 °C for 14 days to obtain a GF@UiO composite diaphragm material; S2-2, prepared by solvent thermal synthesis method: the UiO precursor solution prepared in S1 was transferred to a polytetrafluoroethylene reactor, and a commercial glass fiber diaphragm was placed in the reactor, and a solvent thermal reaction was carried out in an electric heating blast drying oven at a reaction temperature of 120-150 °C and a reaction time of 24 h to obtain a GF@UiO composite diaphragm material; S2-3, prepared by microwave-assisted heating method: the UiO precursor solution prepared in S1 was transferred to a polytetrafluoroethylene reactor, and a commercial glass fiber diaphragm was placed in it, and a microwave-assisted heating reaction was carried out in a microwave synthesizer. The reaction temperature was 125-175 °C, the reaction time was 30 min, and the microwave power was 800 W to obtain a GF@UiO composite diaphragm material; S2-4, preparation by continuous flow method: The independent solution of UiO reactant prepared in S1 was pumped into the coil reactor by two independent pumps for heating and mixing, and finally flowed into a closed container soaked with a glass fiber diaphragm through a back pressure regulator. The heating temperature was 120-140 °C, and the synthesis reaction flow rate was 90 mL min -1 , the reaction time is 24 h, and the GF@UiO composite membrane material is obtained; The GF@UiO composite diaphragm materials prepared from S2-1 to S2-4 are ultrasonically cleaned, dried, and cut into pieces; The pore size of the GF@UiO composite membrane is 2.80-3.00 nm, and the BJH adsorption cumulative pore volume is 0.20-0.30 cm 3 g -1 , Langmuir specific surface area is 1000-1100 m 2 g -1 ; S3. Preparation of various GF-UiO@PVDF / PVDF-HFP composite diaphragm materials, including the following steps: S3-1, prepared by polymer soaking method: the GF@UiO composite membrane prepared in S2 is transferred to a beaker containing PVDF / PVDF-HFP blend solution, and after being fully soaked, it is transferred to a beaker containing ethanol solution for pore formation for 2-5 minutes, and then vacuum dried to obtain GF-UiO@PVDF / PVDF-HFP composite membrane material; S3-2, prepared by polymer blade coating method: the GF@UiO composite membrane prepared in S2 is transferred to a glass plate, and the PVDF / PVDF-HFP blend solution is blade coated on the GF@UiO composite membrane with a four-sided coater, the specifications of the four-sided coater are 100μm, 150μm, 200μm, and 250μm, and then vacuum dried to obtain the GF-UiO@PVDF / PVDF-HFP composite membrane material; S3-3, prepared by electrospinning: fix the GF@UiO composite membrane prepared in S2 to the receiver of the electrospinning machine, put the PVDF / PVDF-HFP blend solution in a syringe and fix it on the loading and conveying system, set the corresponding parameters to spin the polymer liquid onto the GF@UiO composite membrane, the working DC voltage range of the electrospinning method is 15-25kV, and then vacuum dry to obtain the GF-UiO@PVDF / PVDF-HFP composite membrane material; The PVDF / PVDF-HFP blend solution, wherein PVDF and PVDF-HFP are in a mass ratio of 1:1; The prepared GF-UiO@PVDF / PVDF-HFP composite membrane material has an ionic conductivity of 9.0-10.0 mS cm -1 , lithium ion migration number t Li+ 0.80-0.90; The lithium metal half-cell test of GF-UiO@PVDF / PVDF-HFP composite diaphragm material matched with NCM811 positive electrode material and metal lithium negative electrode material shows that the discharge capacity data of the first five cycles at 0.2C and 2.8-4.3V is 202.60-206.80 mAh g -1 The first cycle discharge capacity can reach 204.70 mAh g -1 After 100 charge and discharge cycles, the capacity retention rate is 89.25% and the cycle life reaches 480 cycles.

2. The method for preparing a lithium-ion battery composite diaphragm material according to claim 1, characterized in that: The inorganic metal salt compound described in S1 is selected from metal chloride salts; the solvent described in S1 is selected from N,N-dimethylformamide; the ultrasonic mixing described in S1, wherein the washing solvent for ultrasonic cleaning is 99.5% anhydrous methanol.

3. The method for preparing a composite diaphragm material for a lithium-ion battery according to claim 1, characterized in that: The commercial glass fiber separator described in S2 is in the shape of a disk with a diameter of 25-55 mm and a thickness of 260-675 μm.

4. The method for preparing a composite diaphragm material for a lithium-ion battery according to claim 1, characterized in that: In S2-1, the conical flask is heated to 100°C and kept warm for 14 days; In S2-2, the solvent thermal reaction temperature is 120 °C and the reaction time is 24 h; In S2-3, the microwave-assisted heating has a reaction temperature of 150°C, a reaction time of 30 min, and a microwave power of 800 W; In S2-4, the continuous flow heating temperature is 130 °C, and the synthesis reaction flow rate is 90 mL min -1 , the reaction time is 24h; In S2-2 to S2-4, the surface loading of UiO crystals on the glass fiber separator was 0.001 mg mm -2 .

5. The method for preparing a composite diaphragm material for a lithium-ion battery according to claim 1, characterized in that: In S2, the drying is carried out at 80°C for 5 h in an electric heated air drying oven.

6. The method for preparing a composite diaphragm material for a lithium-ion battery according to claim 1, characterized in that: The hole-making time described in S3-1 is 3 minutes; The specification distribution of the four-sided film applicator described in S3-2 is 200 μm; The working DC voltage of the electrospinning method described in S3-3 is 18 kV.

7. The method for preparing a composite diaphragm material for a lithium-ion battery according to claim 1, characterized in that: In S3, the vacuum drying is performed by placing the sample in a vacuum drying oven at 90° C. for 10 h.

8. A lithium-ion battery composite diaphragm material, characterized in that: The composite membrane material for lithium-ion batteries is prepared by the method for preparing the composite membrane material for lithium-ion batteries according to any one of claims 1 to 7, wherein the ionic conductivity is 9.0-10.0 mS cm -1 , lithium ion migration number t Li+ 0.80-0.90; The lithium metal half-cell test was performed by matching the GF-UiO@PVDF / PVDF-HFP composite diaphragm material with the NCM811 cathode material and the metal lithium anode material. The data of the first five cycles at 0.2C and 2.8-4.3V were 202.60-206.80 mAh g -1 The first cycle discharge capacity can reach 204.70 mAh g -1 After 100 charge and discharge cycles, the capacity retention rate is 89.25% and the cycle life reaches 480 cycles.

9. The use of a lithium-ion battery composite diaphragm material according to claim 8, characterized in that: Used to prepare lithium batteries.

10. The use of a lithium-ion battery composite diaphragm material according to claim 9, characterized in that: The lithium battery is a liquid lithium metal battery.

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