A lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) and a preparation method thereof, and a lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) and a preparation method thereof and a lithium ion battery, the preparation method comprises four steps, and details are shown in figure 1 in the accompanying drawings. The -COOH of the MOFs not only has electrostatic attraction with the imidazole on the OPBI, but also has hydrogen bond interaction with the -OH of the HNTs. The application solves the problem of poor compatibility of inorganic fillers with the diaphragm matrix OPBI by introducing the MOFs-HNTs mixture into the diaphragm, and realizes uniform dispersion. The MOFs-HNTs mixture changes the diffusion force in the non-solvent phase inversion method, and a high-temperature-resistant lithium ion battery diaphragm with a micro-pore structure composed of regular finger-shaped pores and sponge-shaped pores is obtained. The pore structure, the large specific surface area of the MOFs-HNTs and the polar groups are synergistic, more sites and micro-channels are provided for lithium ion transmission, and the disorderly growth of lithium dendrites is inhibited. The assembled lithium battery has excellent electrochemical performance and low electrode polarization degree.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) and a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] The diaphragm is one of the core components of a lithium ion battery (LIB), which functions to separate the positive electrode from the negative electrode to prevent short circuit and ensure the normal passage of lithium ions through the microporous channel during charging and discharging to ensure the normal operation of the battery, and the performance thereof directly affects the safety, capacity, rate, service life and other performances of the battery during service.

[0003] Polyolefin diaphragms, such as polyethylene (PE) diaphragms, polypropylene (PP) diaphragms and PE / PP composite diaphragms, are currently widely used in the production process of commercial lithium ion batteries, and the production processes thereof mainly include dry and wet methods. Due to the limitations of material properties and production processes, the polyolefin diaphragms still face some problems in the application process: first, the melting point of polyolefin materials is low, which is an inherent attribute, and therefore the polyolefin diaphragm has poor heat resistance and is prone to thermal shrinkage at high temperatures, thereby causing short circuit of the battery and further causing fire, explosion and other dangerous events of the lithium battery; second, the electrical conductivity, electrolyte wettability, flame retardancy and electrochemical stability window of the polyolefin diaphragm are not ideal; third, the lithium battery assembled by using the polyolefin diaphragm has serious lithium dendrite growth during service, and the lithium dendrite is easy to pierce the diaphragm, causing micro-short circuit in the lithium battery and posing a safety hazard to the lithium battery; fourth, the lithium battery assembled by using the polyolefin diaphragm has poor cycle stability at high temperatures (such as 50℃ and 90℃); and fifth, the lithium battery assembled by using the polyolefin diaphragm has large electrode polarization.

[0004] In order to improve the use safety and electrochemical performance of the lithium battery, some materials are coated on the surface of the polyolefin diaphragm by different coating processes to form a coated polyolefin diaphragm; the coated diaphragm on the market mainly includes inorganic coated diaphragm, organic coated diaphragm and organic+inorganic coated diaphragm. Coating heat-resistant materials (inorganic, organic and inorganic / organic mixture) on the surface of the polyolefin diaphragm improves the heat resistance of the diaphragm to a certain extent, however, the substrate material-polyolefin under the coating still has the risk of thermal shrinkage leading to the collapse of the overall structure of the diaphragm at a high enough temperature for a long enough time. Therefore, this modification scheme based on the polyolefin diaphragm cannot fundamentally solve the heat resistance problem of the diaphragm and cannot completely solve the use safety of the lithium battery. In addition, the lithium battery assembled by using the coated polyolefin diaphragm still has serious growth of anode lithium dendrites during the charging and discharging cycle. As known, coating also produces a series of negative effects, such as increased diaphragm thickness, bulk resistance (R b) increase, charge / discharge efficiency reduction, etc.

[0005] Therefore, the existing diaphragm technology needs to be improved and developed. SUMMARY

[0006] In view of the above-mentioned deficiencies of the existing diaphragm technology, the purpose of the present application is to provide a lithium ion battery diaphragm containing metal organic framework (MOFs) and halloysite nanotubes (HNTs) and a preparation method thereof, and a lithium ion battery, aiming to solve the following problems: a. the existing polyolefin diaphragm is prone to thermal contraction at high temperature; b. the lithium ion battery assembled by the existing polyolefin diaphragm has serious disorderly growth of anode surface lithium dendrites; c. the lithium ion battery assembled by the existing polyolefin diaphragm has poor high-temperature cycle stability; d. the lithium ion battery assembled by the existing polyolefin diaphragm has large electrode polarization; e. the electrical conductivity, electrolyte wettability, flame retardancy, and electrochemical stability window of the polyolefin diaphragm are not ideal.

[0007] The technical scheme of the present application is as follows:

[0008] A preparation method of a lithium ion battery diaphragm containing metal organic framework (MOFs) and halloysite nanotubes (HNTs), comprising the steps of:

[0009] providing an OPBI solution and a MOFs-HNTs mixed dispersion solution;

[0010] mixing the OPBI solution and the MOFs-HNTs mixed dispersion solution to obtain an OPBI@MOFs-HNTs mixed solution;

[0011] coating the OPBI@MOFs-HNTs mixed solution on a substrate and removing the solvent in the OPBI@MOFs-HNTs mixed solution to obtain a lithium ion battery diaphragm containing metal organic framework (MOFs) and halloysite nanotubes (HNTs).

[0012] The preparation method of the lithium ion battery diaphragm containing metal organic framework (MOFs) and halloysite nanotubes (HNTs), characterized in that the MOFs-HNTs mixture is a mixture after physical mixing, and the metal organic framework (MOFs) is UiO-66 MOFs.

[0013] The preparation method of the lithium ion battery diaphragm containing metal organic framework (MOFs) and halloysite nanotubes (HNTs), wherein the solvent of the MOFs-HNTs mixed dispersion solution and the solvent of the OPBI solution are selected from one or more of N-methyl pyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0014] The application discloses a preparation method of a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0015] The application discloses a preparation method of a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0016] The application discloses a preparation method of a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0017] The application discloses a preparation method of a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0018] The application discloses a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0019] The application discloses a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0020] A lithium-ion battery includes a positive electrode, a negative electrode, and a lithium-ion battery separator containing metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs); the lithium-ion battery separator containing metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs) is located between the positive electrode and the negative electrode.

[0021] Beneficial Effects: This invention provides a lithium-ion battery separator containing metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs), a method for preparing the same, and a lithium-ion battery. The preparation method includes the following steps: providing an OPBI solution and a MOFs-HNTs mixed dispersion solution; mixing the OPBI solution and the MOFs-HNTs mixed dispersion solution to obtain an OPBI@MOFs-HNTs mixed solution; coating the OPBI@MOFs-HNTs mixed solution onto a substrate and removing the solvent from the OPBI@MOFs-HNTs mixed solution to obtain a lithium-ion battery separator containing metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs); and assembling a lithium-ion battery using the lithium-ion battery separator containing metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs). This invention introduces a MOFs-HNTs mixture into the battery separator, which has the following advantages: (1) The -COOH groups on MOFs not only have electrostatic attraction with the imidazole structure on OPBI, but also have hydrogen bonding interaction with the -OH groups on HNTs, solving the problem of poor compatibility between inorganic material HNTs and polymer separator matrix material OPBI. Therefore, HNTs can be well uniformly dispersed and fixed in the OPBI matrix; (2) Introducing HNTs into the OPBI matrix is ​​beneficial for preparing separators with multi-morphological channels with finger-like channels. Using MOFs to uniformly disperse HNTs in the OPBI matrix can obtain richer and more uniform ion channels; (3) The porosity and designability of MOFs, combined with the stability and special structure of HNTs, make the material have a higher specific surface area, which is more conducive to the transport of lithium ions. The separator prepared in this invention exhibits increased affinity between the separator and the electrolyte, while providing more sites and microchannels for lithium-ion transport. By utilizing a MOFs-HNTs mixture to alter the diffusion forces during the solvent-free phase inversion process, a high-temperature resistant lithium-ion battery separator with a microporous structure composed of regular finger-like and sponge-like pores is obtained. This separator exhibits good electrolyte wettability, high conductivity, and good electrochemical stability. Furthermore, its unique pore structure and ion coordination structure induce lithium ions to pass through the separator more rapidly and deposit uniformly on the lithium metal anode surface, effectively suppressing the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium-ion batteries. Batteries assembled using this separator demonstrate excellent discharge specific capacity, cycle stability, and rate performance, especially outstanding charge-discharge stability at high temperatures; in addition, the battery electrode polarization is low. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 and Figure 2 A flowchart of a preparation method of a lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) and an assembly process of a button-type half cell.

[0023] Figure 3 A schematic diagram of the principle of using MOFs-HNTs mixture to uniformly disperse in OPBI separator matrix and eliminate poor compatibility between inorganic materials and organic matrix.

[0024] Figure 4 A TEM image and a particle size distribution graph of MOFs.

[0025] Figure 5 BET test results of MOFs and MOFs-HNTs.

[0026] Figure 6 Composition and structure characterization graphs of MOFs, HNTs and MOFs-HNTs mixture, wherein (a-c) are TEM images of MOFs, HNTs and MOFs-HNTs, (d) is an EDS spectrum of MOFs-HNTs, (e) and (f) are FT-IR spectra and XRD spectra of MOFs, HNTs and MOFs-HNTs, respectively.

[0027] Figure 7 SEM images of PP separator, OPBI separator, OPBI@M-H5 separator and OPBI@M-H10 separator.

[0028] Figure 8 Test results of electrolyte wettability, contact angle and electrolyte absorption rate of PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators.

[0029] Figure 9 Folded and bent shape photos of OPBI@M-H10 separator.

[0030] Figure 10 Test results of heat resistance and flame resistance of PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators.

[0031] Figure 11Fig. 6 shows the electrochemical performance of the battery. (a) is the AC impedance curve of the double-steel-plate symmetrical battery assembled with PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators, (b-c) are the Nyquist diagram and LSV curve of the symmetrical battery with double lithium electrodes clamping PP, OPBI and OPBI@M-H10 separators respectively, (d) is the plating / peeling cycle curve of the symmetrical battery with double lithium electrodes equipped with PP, OPBI@M-H10 separators, (e-f) are the 200th charge-discharge cycle stability results and rate performance of the battery equipped with PP, OPBI, OPBI@M-H5, OPBI@M-H10 separators, (g-h) are the charge-discharge voltage curves of the battery assembled with PP, OPBI@M-H10 separators.

[0032] Figure 12 Fig. 7 shows the SEM images of the anode lithium sheet after 200 cycles of the pure lithium sheet PP and the button cell assembled with PP, OPBI, OPBI@M-H10 separators, and the schematic diagram of lithium dendrite growth on the surface of the anode lithium sheet of the battery.

[0033] Figure 13 Fig. 8 shows the cycle stability of the button cell assembled with PP, OPBI@M-H10 separators at 50°C and 90°C at 0.5C charge-discharge. DETAILED DESCRIPTION

[0034] The present application provides a lithium ion battery separator containing metal organic framework (MOFs) and halloysite nanotubes (HNTs) and a preparation method thereof and a lithium ion battery. In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0035] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. It should also be understood that terms such as those defined in a general dictionary should be understood as having meanings consistent with those in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as such.

[0036] As shown in Figure 1 The present application provides a preparation method of a lithium ion battery separator containing metal organic framework (MOFs) and halloysite nanotubes (HNTs) and a lithium ion battery, which comprises the following steps:

[0037] Step S10: providing an OPBI solution and a MOFs-HNTs mixed dispersion solution;

[0038] Step S20: mixing the OPBI solution and the MOFs-HNTs mixed dispersion solution to obtain an OPBI@MOFs-HNTs mixed solution;

[0039] Step S30: coating the OPBI@MOFs-HNTs mixed solution on a substrate and removing the solvent in the OPBI@MOFs-HNTs mixed solution to obtain a lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs);

[0040] Step S40: assembling a lithium ion battery using the lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0041] In this embodiment, polybenzimidazole (OPBI) is a polymer with excellent thermal stability and mechanical properties. Since the OPBI molecular chain contains polar ether bonds and pyridine structures, it can enhance the affinity between the electrolyte, and therefore, when it is prepared into a polymer separator and applied to a lithium ion battery, it can improve the safety and electrochemical performance of the battery. Metal organic frameworks (MOFs) are a class of porous materials with periodic network structure formed by self-assembly of metal ions or clusters and organic ligands through coordination bonds. MOFs have unique advantages, such as high specific surface area, adjustable pore size and functionalized pores. Halloysite nanotubes (HNTs) are an inorganic nanomaterial with good chemical stability, unique tubular structure and abundant surface hydroxyl groups.

[0042] Specifically, in view of the characteristics of OPBI, MOFs and HNTs, the application of MOFs-HNTs mixture to modify OPBI separator has the following advantages: (1) the -COOH groups on MOFs not only have electrostatic attraction with the imidazole structure on OPBI, but also have hydrogen bond interaction with the -OH groups on HNTs, solving the problem of poor compatibility between inorganic material HNTs and polymer separator matrix material OPBI, so that HNTs can be well dispersed and fixed in the OPBI matrix; (2) the introduction of HNTs in the OPBI matrix is beneficial to the preparation of separators with multi-morphology channels such as finger-like channels and sponge-like channels, and the uniform dispersion of HNTs in the OPBI matrix by MOFs can obtain more abundant and uniform ion channels; (3) the porosity and designability of MOFs, combined with the stability and special structure of HNTs, make the material have a high specific surface area, which is more conducive to the transmission of lithium ions.

[0043] The prepared separator has increased affinity with electrolyte, and provides more sites and micro-channels for lithium ion transmission; the MOFs-HNTs mixture is used to change the diffusion force in the non-solvent phase inversion process to obtain a high-temperature-resistant lithium ion battery separator with micro-pore structure composed of regular finger-shaped pores and sponge-shaped pores. The separator has good electrolyte wettability (electrolyte absorption rate 377%), high conductivity (1.59 mS cm -1 ), good heat resistance and electrochemical stability, and through the unique pore structure and ion coordination structure, lithium ions are induced to pass through the separator more quickly and uniformly deposit on the surface of the lithium metal anode, effectively inhibiting the disorderly growth of lithium dendrites, and improving the use safety and electrochemical performance of the lithium ion battery. The battery assembled using the separator exhibits excellent discharge specific capacity, cycle stability, rate performance, and especially excellent charge-discharge stability at high temperature; in addition, the battery electrode has low polarization degree. The LiFePO4 / Li battery assembled using the lithium ion battery separator has a peak discharge specific capacity of 161 mAh g -1 at 0.5C, and after 200 cycles, the capacity retention rate of the battery is 90.28%. In addition, the LiFePO4 / Li battery assembled using the lithium ion battery separator can also operate at temperatures of 50°C and 90°C and has an appreciable capacity retention rate.

[0044] In some embodiments, the solvent of the MOFs-HNTs mixed dispersion solution and the solvent of the OPBI solution are collectively selected from, but not limited to, one or more of N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide; the solvents of the MOFs-HNTs mixed dispersion solution and the OPBI solution are consistent, which facilitates subsequent separation of the two solutions by a non-solvent induced phase separation process.

[0045] In some embodiments, in the OPBI@MOFs-HNTs mixed solution, the total mass of the MOFs-HNTs mixture is 5%-30% of the mass of OPBI; the lithium ion battery separator contains an appropriate amount of MOFs-HNTs, so that the MOFs-HNTs are used to improve the diffusion force in the non-solvent phase inversion process to obtain a high-temperature-resistant lithium ion battery separator (OPBI@MOFs-HNTs) with micro-pore structure composed of regular finger-shaped pores and sponge-shaped pores. The separator has good electrolyte wettability, high conductivity, and good electrochemical stability, and through the unique pore structure and ion coordination structure, lithium ions are induced to pass through the separator more quickly and uniformly deposit on the surface of the lithium metal anode, effectively inhibiting the disorderly growth of lithium dendrites, and improving the use safety and electrochemical performance of the lithium ion battery. The battery assembled using the separator exhibits excellent discharge specific capacity, cycle stability, rate performance, and especially excellent charge-discharge stability at high temperature; in addition, the battery electrode has low polarization degree.

[0046] In a preferred embodiment, the MOFs-HNTs mixture is a product of grinding after mixing MOFs and HNTs; the MOFs-HNTs mixed dispersion solution is a solution with N-methyl pyrrolidone as a solvent; the solvent of the OPBI solution is N-methyl pyrrolidone; polybenzimidazole has excellent thermal stability, mechanical properties, flame retardancy, etc., and contains polar ether bonds and pyridine structures in the molecular chain. Metal-organic frameworks (MOFs) are a class of porous materials with periodic network structure formed by self-assembly of metal ions or clusters and organic ligands through coordination bonds. MOFs have unique advantages such as high specific surface area, adjustable pore size and functionalized pores, and abundant surface carboxyl groups. Halloysite nanotubes (HNTs) are an inorganic nanomaterial with good chemical stability, unique tubular structure and abundant surface hydroxyl groups. The introduction of MOFs-HNTs into the separator can increase the affinity between the separator and the electrolyte, and at the same time provide more coordination sites and microchannels for the transmission of lithium ions. By using MOFs-HNTs to change the diffusion force in the non-solvent phase inversion process, a high-temperature-resistant lithium ion battery separator with micro-pore structure composed of regular finger-like pores and sponge-like pores is obtained. Therefore, in view of the material characteristics of polybenzimidazole, sHNT-Li and MOFs, uniformly dispersing the MOFs-HNTs mixture in the OPBI matrix to prepare a separator for lithium ion batteries can help to solve the safety problems of lithium ion batteries caused by the heat resistance, flammability of the separator and the disordered growth of lithium dendrites, improve the electrochemical performance of lithium ion batteries such as rate, cycle stability (including room temperature and high temperature) from the perspective of the separator, and reduce the electrode polarization of the battery.

[0047] In some embodiments, the preparation process of the OPBI solution is: 0.3 g of OPBI powder is added to the solvent, and stirred at 60-100°C for 18-24 hours; the preparation process of the MOFs-HNTs mixed dispersion solution is: the MOFs-HNTs mixture is added to the solvent, and ultrasonic treatment is performed for 1-3 hours, and stirring is performed for 0.5-1.5 hours; the preparation process of the OPBI@MOFs-HNTs mixed solution is: the MOFs-HNTs mixed dispersion solution is slowly poured into the OPBI solution, and stirring is performed for 0.5-1.5 hours, ultrasonic treatment is performed for 0.5-1.5 hours, and low-speed stirring is performed for 18-24 hours.

[0048] In some embodiments, the method for removing the solvent in the mixed solution in step S30 is: placing the substrate coated with the mixed solution into anhydrous methanol for immersion treatment, the immersion treatment is standing at room temperature for 8-15 minutes, and the lithium ion battery separator is prepared by using a non-solvent induced phase separation process. Since OPBI is insoluble in methanol, MOFs-HNTs is also insoluble in methanol at room temperature, and NMP or DMSO or DMAC is soluble in methanol, the substrate coated with the mixed solution is placed at room temperature for 8-15 minutes, the mixed solution is quickly formed by using methanol, and NMP or DMSO or DMAC is replaced to form a pore size, so that the prepared lithium ion battery separator has a micro-pore structure composed of regular finger-shaped pores and sponge-shaped pores, which is beneficial to the uniform deposition of lithium ions on the anode surface, thereby inhibiting the disorderly growth of lithium dendrites and improving the safety during the service of the battery.

[0049] In some embodiments, after the immersion treatment in step S30, a drying treatment is further performed to remove the methanol in the pores.

[0050] In some embodiments, the substrate is, but is not limited to, a glass plate.

[0051] In addition, the application also provides a lithium ion battery separator prepared by the method for preparing the lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs).

[0052] In the present embodiment, the MOFs-HNTs mixture is introduced into the lithium ion battery separator, and the diffusion force in the non-solvent phase inversion process is improved by using the MOFs-HNTs mixture to obtain a high-temperature-resistant lithium ion battery separator (OPBI@MOFs-HNTs) with a micro-pore structure composed of regular finger-shaped pores and sponge-shaped pores. The lithium ion battery separator has excellent thermal stability and flame retardancy, does not undergo thermal shrinkage at 200°C, and does not show obvious combustion phenomenon when placed on a flame; the lithium ion battery separator has good electrolyte wetting property, high electrolyte absorption rate (377%), high conductivity (1.59 mS cm -1 ), and good electrochemical stability; the lithium ion battery separator has diversified lithium ion transmission modes, which can improve the transport efficiency of lithium ions between the positive and negative electrodes of the battery; the lithium ion battery separator has a unique micro-pore structure composed of regular finger-shaped pores and sponge-shaped pores, which can induce lithium ions to pass through the separator more quickly and deposit uniformly on the surface of the lithium metal anode, effectively inhibiting the disorderly growth of lithium dendrites and improving the use safety and electrochemical performance of the lithium ion battery. The battery assembled using the separator shows excellent discharge specific capacity, cycle stability, rate performance, especially excellent charge-discharge stability at high temperature; in addition, the battery electrode has low polarization degree.

[0053] In some embodiments, the lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) has a thickness of 20-40 microns; the lithium ion battery separator at this thickness has excellent thermal stability while inhibiting the disorderly growth of lithium dendrites.

[0054] In addition, the present application also provides a lithium ion battery comprising a positive electrode sheet, a negative electrode sheet and a lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs); the lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) is located between the positive electrode sheet and the negative electrode sheet.

[0055] In this embodiment, the LiFePO4 / Li battery assembled using the lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) has a peak discharge specific capacity of 161 mAh g -1 at 0.5C, and after 200 cycles, the capacity retention rate of the battery is 90.28%. In addition, the LiFePO4 / Li battery assembled using the lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) can also operate at temperatures of 50°C and 90°C and has an appreciable capacity retention rate; and the battery assembled using the lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) can operate smoothly and safely at high temperatures (such as 50°C and 90°C).

[0056] The following examples are further provided to illustrate the present application in detail. It should also be understood that the following examples are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application all belong to the protection scope of the present application.

[0057] Example 1

[0058] The present embodiment provides a preparation method of a lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) (OPBI@MOFs-HNTs composite membrane) and a lithium ion battery, a flowchart thereof is shown in Figure 1 The preparation method comprises the following steps:

[0059] Step S1: dissolving OPBI in NMP to form a uniform OPBI solution;

[0060] MOFs-HNTs are dissolved in NMP to form a MOFs-HNTs mixture solution with NMP as the solvent.

[0061] Step S2: The MOFs-HNTs mixture solution is added to the OPBI solution, and stirring is continued at 80℃ for 24 hours to obtain a mixed solution, and the total mass of the MOFs-HNTs mixture in the mixed solution is 5% and 10% of the mass of OPBI.

[0062] Step S3: The obtained OPBI@MOFs-HNTs mixed solution is coated on a glass plate with a scraper, and is transferred to anhydrous methanol (MeOH) for 10 minutes to obtain a porous membrane, and then the porous membrane is dried at room temperature to obtain OPBI@M-H5, OPBI@M-H10 composite membranes.

[0063] Step S4: The lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) is used to assemble a lithium ion battery.

[0064] The preparation process of MOFs is as follows: first, ZrCl4(466mg, 2mM) is pre-dissolved in a mixed solvent of 72mL DMF and HCl with a volume ratio of 5:1. At the same time, H2BDC (324mg, 2.8mM) is pre-dissolved in 2ml DMF. Then, the metal solution and the ligand solution are mixed uniformly and poured into a 100ml Teflon container. Then the container is treated with high-temperature steam at 80℃ for 24 hours. After 24 hours, the Teflon container is cooled to room temperature, and the obtained UiO-66 MOFs is centrifuged for three times. Finally, the MOFs is dried in an oven at 80℃ for 24 hours for further use.

[0065] The preparation process of MOFs-HNTs mixture is as follows: MOFs and HNTs are added to a mortar in a ratio of 10:3 for grinding and mixing, and the grinding time is 1 hour.

[0066] As a comparison, the present embodiment also provides a PP (polypropylene) film and an OPBI film, wherein the preparation method of the OPBI film is the same as that of the OPBI@MOFs-HNTs composite film, and both use the non-solvent phase transfer method.

[0067] The transport mode of lithium ions between the positive and negative electrodes in the battery assembled by the OPBI@MOFs-HNTs composite film is schematically shown as follows:

[0068] Figure 2 A schematic diagram of the preparation process of the OPBI@MOFs-HNTs composite film is shown.

[0069] Figure 3 A schematic diagram and structural schematic diagram of the principle of using UiO-66 MOFs to improve the interfacial compatibility between HNTs and the OPBI polymer matrix to realize the uniform dispersion of MOFs-HNTs in the OPBI polymer matrix.

[0070] Figure 4 The TEM images and the particle size distribution of MOFs show that the average particle size of MOFs is 42.59±4.09nm.

[0071] Figure 5 The BET test results of MOFs, MOFs-HNTs show that the specific surface area of MOFs, MOFs-HNTs is 22.3811m 2 / g, 382.1938m 2 / g, respectively.

[0072] Figure 6 The composition and structure characterization of MOFs, HNTs, MOFs-HNTs mixture, wherein, (a-c) are TEM images of MOFs, HNTs, MOFs-HNTs, (d) is the EDS spectrum of MOFs-HNTs, (e), (f) are FT-IR spectrum and XRD spectrum of MOFs, HNTs and MOFs-HNTs, respectively. Pure UiO-66 metal organic framework (MOFs) presents a nano-particle-like agglomeration morphology, with an average size of 42.59±4.09nm. Halloysite nanotubes (HNTs) exhibit a typical tubular morphology. When UiO-66 MOFs are combined with HNTs at a mass ratio of 10:3, it can be observed that the MOFs agglomerates are attached to the HNTs, indicating that the physical mixing of MOFs and HNTs does not cause any damage to their structure and morphology. Energy dispersive spectrometer (EDS) analysis confirms the presence of constituent elements in MOFs-HNTs composites. Among them, Si and Al belong to HNTs, and Zr belongs to UiO-66 MOFs. Fourier transform infrared spectroscopy (FT-IR) verifies the chemical bonding. The spectral absorption band between 1600cm -1 and 1500cm -1 is caused by the skeleton vibration of the benzene ring in MOFs. The peak at 1347cm -1 is due to the stretching absorption of C-N in MOFs, the vibration at 1031cm -1 is attributed to the Si-O bond in HNTs, the characteristic peak at 534cm -1 is attributed to the Al-O bond in HNTs, and the peak at 483cm -1The peaks at 400-800 cm"1are attributed to the Zr-0 vibrations in UiO-66. Based on the above observations, the physical morphology and chemical structure of UiO-66 MOFs and HNTs were successfully verified to be correct. X-ray diffraction (XRD) patterns show that MOFs-HNTs do not show any significant difference compared to MOFs. A distinct diffraction peak can be observed at 19.9°, which is attributed to the presence of HNTs in the MOFs-HNTs composite. BET results show that the specific surface area, pore volume and pore size of MOFs-HNTs are increased compared to pure HNTs. Among them, the specific surface area is increased by about 17 times, which provides more sites for the adsorption and desorption of ions. The reason is that MOFs have a hollow three-dimensional structure at the nanoscale, thereby increasing the specific surface area. When MOFs are loaded on HNTs, it can make HNTs better dispersed, thereby improving the overall pore volume and pore size of the MOFs-HNTs composite.

[0073] Figure 7 SEM images of PP separator, OPBI separator, OPBI@M-H5 separator, OPBI@M-H10 separator. After the non-solvent induced phase separation (NIPS) process, it was found that the introduction of MOFs-HNTs into OPBI had a significant impact on the formation of pores in the separator. By careful observation and analysis, it can be seen that the pore size of the top and bottom surfaces of OPBI and OPBI@M-H-based separators is significantly larger than that of PP separator. In addition, on the cross-section, the proportion of finger-like macropores increases, which is very beneficial for the separator to absorb and store more electrolyte. By comparing OPBI separator with OPBI@M-H composite separator with different MOFs-HNTs introduction ratios, it can be concluded that as the amount of MOFs-HNTs incorporated increases from 5wt.% to 10wt.%, not only the number of pores in the resulting separator increases, but also the distribution is more uniform. When analyzing the cross-section, the proportion of finger-like macropores and sponge-like pores also shows a clear increasing trend. Therefore, OPBI@M-H composite separator can absorb more electrolyte, which is beneficial for the efficient transmission of lithium ions. During the NIPS process, due to the mutual diffusion effect of the solvent and the non-solvent, the diffusion force perpendicular to the membrane surface increases, which leads to the tendency of HNTs to arrange vertically. After that, the diffusion force perpendicular to the outer wall of HNTs is inhibited, which ultimately promotes the formation of finger-like pores. At the same time, the interconnected network structure formed by MOFs on the outer wall of HNTs plays an important role, enabling the nanotubes to be uniformly distributed according to the network pattern, thereby making the finger-like pores more uniform and dense. There is no doubt that the dense finger-like pore structure of the composite separator lays a solid foundation for its subsequent excellent electrolyte wettability.

[0074] Figure 8The results of electrolyte wettability, contact angle, and electrolyte uptake tests for PP, OPBI, OPBI@M-H5, and OPBI@M-H10 separators. The electrolyte uptake of OPBI@M-H10 separator was as high as 377%, which was 2.9 times that of the PP separator. The contact angle of OPBI@M-H10 separator was smaller, only 14.6°. In the AC impedance test of the steel symmetric cell assembled by the separator, the conductivity of OPBI@M-H10 separator (1.59 mS·cm -1 ) was 2.5 times that of the PP separator (0.63 mS·cm -1 ). It was speculated that the porous channels inside the composite separator, the cavity structure of MOFs, and the hollow tubes of HNTs all provided storage space for the electrolyte and convenient channels for the transmission of Li + .

[0075] Figure 9 The folding and bending photos of OPBI@M-H10 separator. The folding experiment of the separator proved that the composite separator had good mechanical properties and could support the battery assembly process.

[0076] Figure 10 The results of heat resistance and flame retardancy tests for PP, OPBI, OPBI@M-H5, and OPBI@M-H10 separators. At 150℃, the size of the PP separator changed significantly, and at 200℃, it shrank into a narrow strip. In contrast, OPBI and OPBI@M-H composite separators remained almost unchanged at 200℃. In the burning experiment, the PP separator melted and burned near the flame, while the OPBI@M-H10 composite separator formed carbon black at the flame end, remained unchanged at the other end, and retained carbon black throughout the burning process, which proved its excellent flame retardancy. In the thermogravimetric analysis (TGA) experiment, the weight of the PP separator rapidly decreased as the temperature rose to 300℃, which was probably due to the decomposition and volatilization of polypropylene. OPBI and OPBI@M-H series separators showed slight weight loss from 550℃, showing excellent resistance to thermal decomposition. The slight decrease around 250℃ was probably due to the volatilization of NMP and the evaporation of water. These tests verified the excellent high-temperature resistance of OPBI@M-H10 composite separator, providing a viable solution for high-temperature applications of lithium-ion batteries.

[0077] Figure 11The electrochemical performance of the batteries is shown below. (a) shows the AC impedance curves of a dual-plate symmetrical battery assembled with PP, OPBI, OPBI@M-H5, and OPBI@M-H10 separators; (bc) shows the Nyquist plots and LSV curves of symmetrical batteries with dual lithium electrodes sandwiching PP, OPBI, and OPBI@M-H10 separators respectively; (d) shows the plating / stripping cycle curves of a dual-lithium electrode symmetrical battery equipped with PP and OPBI@M-H10 separators; (ef) shows the stability results and rate performance of the battery equipped with PP, OPBI, OPBI@M-H5, and OPBI@M-H10 separators after 200 charge-discharge cycles; and (gh) shows the charge-discharge voltage curves of the battery assembled using PP and OPBI@M-H10 separators.

[0078] Compared to PP and OPBI membranes, composite membranes exhibit lower bulk resistivity (R0). b This is especially true when the MOFs-HNTs addition reaches 10 wt%. It is speculated that the high electrolyte absorption rate (377%) of the OPBI@M-H10 membrane, with its abundant electrolyte storage, helps reduce internal resistance. Furthermore, the synergistic effect between the -COOH groups on the MOFs and the -OH groups on the HNTs and the lithium salt (LiPF6) facilitates the desolvation of Li+, thereby increasing the concentration of free ions. Therefore, the OPBI@M-H10 membrane exhibits the highest conductivity, reaching 1.59 mS·cm. -1 Electrochemical impedance spectroscopy (EIS) was performed on the Li / membrane / Li symmetric cell to measure the electrode-electrolyte interfacial resistance (Ro). i The diameter is represented by the semi-circle diameter. Compared with PP membranes and OPBI membranes, OPBI@M-H10 membrane has a lower R value. i This is attributed to its excellent electrolyte wettability, higher porosity, and superior consistency resulting from the good interfacial compatibility between MOFs-HNTs and the OPBI matrix.

[0079] The electrochemical stability of the membranes was tested using linear sweep voltammetry (LSV). The polarization voltage of the PP membrane was approximately 4.2 V, that of the OPBI membrane was approximately 4.5 V–5 V, and that of the OPBI@M-H10 membrane was approximately 5.9 V. A wider polarization voltage window indicates better electrochemical stability of the membrane and electrolyte system. This result demonstrates that the introduction of MOFs-HNTs enhances the interfacial affinity between the membrane and the electrolyte, thus making the composite membrane a promising candidate for application in high-potential lithium-ion batteries.

[0080] The interfacial stability between the electrolyte-containing separator and the lithium electrode was analyzed through stripping / adsorption experiments of a lithium-ion symmetric battery. The lithium-ion symmetric battery assembled using PP and OPBI@M-H10 separators exhibited stable interfacial stability at 0.5 mA·cm⁻¹. -2The batteries using PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators were subjected to 1600 hours of charge-discharge test at a current density of 0.1C. In the batteries assembled using PP separator, the potential during the stripping / adsorption process of lithium electrode was always higher than 10 mV, which was more than twice of that of OPBI@M-H10 separator. In addition, the potential was unstable during the long-term cycling, and sharply rose to a high potential of 20 mV at about 1340 hours. In contrast, the potential remained stable and at a very low level during the 1600 hours cycling of OPBI@M-H10 separator, showing excellent cycling reversibility and the ability to effectively suppress the disorderly growth of lithium dendrites at the negative electrode.

[0081] The initial discharge specific capacity of the batteries using PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators were 128.32 mAh·g -1 , 132.45 mAh·g -1 , 135.60 mAh·g -1 and 148.12 mAh·g -1 , respectively. Overall, the battery using OPBI@M-H10 separator showed the highest discharge specific capacity. It was speculated that this was due to the compact and uniform pore structure of OPBI@M-H10 composite separator, as well as the excellent wetting performance of the separator, which helped to store more electrolyte, thereby improving the conductivity and improving the discharge specific capacity. In addition, after 200 charge-discharge cycles, we found that the battery using PP separator only retained 78.56% of the capacity, while the battery using OPBI@M-H10 separator still retained 90.28% of the capacity, indicating that the battery based on composite separator had a longer service life. In addition, the charge-discharge efficiency of the battery using OPBI@M-H10 separator was as high as 97.96%, indicating that it had good reversibility and could better meet the requirements of long-term cycling of the battery. The rate curves of LiFePO4 / Li half-batteries assembled using PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 0.1C showed that the battery using OPBI@M-H10 separator had the highest discharge specific capacity at different charge-discharge rates. Even at a charge-discharge rate of 5C, its discharge specific capacity could still reach about 98 mAh·g -1 . It was speculated that the improvement in discharge specific capacity was due to the compact finger-like pore structure of the composite separator promoting ion transport, as well as the combined effect of the MOFs-HNTs structure on the capture and release of ions. The charge-discharge voltage curves of the batteries using PP and OPBI@M-H10 separators from the 1st cycle to the 200th cycle showed that the battery using OPBI@M-H10 separator had a smaller potential difference between the charge-discharge voltage platforms, indicating a lower degree of electrode polarization. This was due to the smaller interfacial resistance between the composite separator filled with electrolyte and the electrode, as well as the good electrolyte wetting and ionic conductivity.

[0082] Figure 12 SEM images of the anode lithium sheet after 200 cycles for pure lithium sheet PP and button cells assembled with PP, OPBI, OPBI@M-H10 separator, and schematic diagram of lithium dendrite growth on the surface of the cell anode lithium sheet. By comparing the surface morphology of the pure lithium plate, it is found that in the battery assembled with PP separator, a large number of dendritic lithium crystals appear on the surface of the lithium electrode. In contrast, in the battery assembled with OPBI separator, the surface of the lithium electrode is relatively flat, with only a few uneven parts. However, in the battery assembled with OPBI@M-H10 separator, the surface flatness of the lithium electrode is very good, indicating that it has a significant effect on inhibiting the disordered growth of lithium dendrites. It is speculated that compared with the PP separator, the OPBI separator and the OPBI@M-H10 separator have more uniform pores and higher electrolyte absorption rate, which helps the uniform transmission of Li + + On the surface of the lithium electrode. Therefore, it can effectively inhibit the disordered growth of lithium dendrites. Through the above analysis, it can be concluded that the introduction of MOFs-HNTs into the OPBI separator can improve the safety performance of the battery to a certain extent.

[0083] Figure 13 Cycle stability of button cells assembled with PP, OPBI@M-H10 separator at 0.5C charge-discharge at 50℃ and 90℃. At a charge-discharge rate of 0.5C, the battery assembled with the composite separator was tested for 100 cycles at high temperature (50℃ and 90℃). At 50℃, the initial discharge specific capacity of the battery assembled with OPBI@M-H10 separator was 154.89mAh·g -1 , higher than that of the battery assembled with PP separator (128.54mAh·g -1 ). After 100 cycles, the capacity retention rate of OPBI@M-H10 battery was 78.58%, which was 2.2 times of that of PP battery (35.48%). At 90℃, the initial discharge specific capacity of the battery assembled with OPBI@M-H10 separator was 148.06mAh·g -1 , also higher than that of the battery assembled with PP separator (134.17mAh·g -1 ). After cycling, the capacity retention rate of OPBI@M-H10 battery was 76.18%, much higher than that of PP battery (18.39%). Through comprehensive analysis of the test data and results, it is assumed that the dense porous network structure of the composite separator and the additional ion transmission channels formed by the internal MOFs-HNTs component synergistically realize the uniform transmission of Li + ​The high efficient and orderly transmission of lithium ions is promoted, the performance of the composite diaphragm is improved, the feasibility under high temperature conditions is proved, and important popularization and reference values are provided for the development goal of realizing high safety lithium ion batteries.

[0084] In summary, the application provides a lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs), a preparation method thereof, and a lithium ion battery, the preparation method comprising the steps of: providing an OPBI solution and a MOFs-HNTs mixed dispersion solution; mixing the OPBI solution and the MOFs-HNTs mixed dispersion solution to obtain an OPBI@MOFs-HNTs mixed solution; coating the OPBI@MOFs-HNTs mixed solution on a substrate, and removing the solvent in the OPBI@MOFs-HNTs mixed solution to obtain the lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs); and assembling a lithium ion battery using the lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs). The application introduces MOFs-HNTs into the battery diaphragm, increases the affinity between the diaphragm and the electrolyte, and provides more sites and micro channels for the transmission of lithium ions. The MOFs-HNTs change the diffusion force in the non-solvent phase inversion process to obtain a high-temperature-resistant lithium ion battery diaphragm with regular finger-shaped pores and sponge-shaped pores. The diaphragm has good electrolyte wettability, high conductivity, and good electrochemical stability, and can induce lithium ions to pass through the diaphragm more quickly and be uniformly deposited on the surface of the lithium metal anode, effectively inhibiting the disorderly growth of lithium dendrites, improving the use safety and electrochemical performance of the lithium ion battery. The battery assembled using the diaphragm has excellent discharge specific capacity, cycle stability, rate performance, and especially excellent high-temperature charge-discharge stability; in addition, the battery electrode has low polarization.

[0085] It should be understood that the application of the application is not limited to the above examples, and can be improved or changed according to the above description for those skilled in the art, and all these improvements and changes shall belong to the protection scope of the appended claims of the application.

Claims

1. A method for the preparation of a lithium-ion battery separator comprising metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs), characterized in that, The method comprises the steps of: providing a mixed dispersion solution of metal organic frameworks MOFs and halloysite nanotubes HNTs, and a solution of polybenzimidazole OPBI; mixing the MOFs-HNTs mixed dispersion solution and the OPBI solution to obtain an OPBI@MOFs-HNTs mixed solution; coating the OPBI@MOFs-HNTs mixed solution on a substrate and removing the solvent in the OPBI@MOFs-HNTs mixed solution to obtain a lithium ion battery separator in which MOFs-HNTs mixed bodies are uniformly dispersed in an OPBI matrix; the metal organic frameworks MOFs are UiO-66 MOFs; in the OPBI@MOFs-HNTs mixed solution, the total mass of the MOFs-HNTs mixed bodies is 5%-30% of the mass of OPBI.

2. The method of making a lithium-ion battery separator of metal-organic frameworks, MOFs, and halloysite nanotubes, HNTs, according to claim 1, wherein, The MOFs-HNTs mixed bodies are mixed bodies after physical mixing.

3. The method of making a lithium ion battery separator of metal organic frameworks, MOFs, and halloysite nanotubes, HNTs, according to claim 1, wherein, The solvent of the MOFs-HNTs mixed dispersion solution and the solvent of the OPBI solution are selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

4. The method of making a lithium-ion battery separator of metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs) of claim 2, wherein, The MOFs-HNTs mixed bodies are prepared by adding MOFs and HNTs in a ratio of 10:3 into a mortar for grinding and mixing, and the grinding time is more than 0.5 hours.

5. The method of making a lithium ion battery separator of metal organic frameworks, MOFs, and halloysite nanotubes, HNTs, according to claim 1, wherein, The OPBI solution is prepared by adding 0.3 g of OPBI powder into a solvent, and stirring at 60-100 ℃ for 18-24 hours; the MOFs-HNTs mixed dispersion solution is prepared by adding the MOFs-HNTs mixed bodies into a solvent, ultrasonic treatment for 1-3 hours, and stirring for 0.5-1.5 hours; and the OPBI@MOFs-HNTs mixed solution is prepared by slowly pouring the MOFs-HNTs mixed dispersion solution into the OPBI solution, stirring for 0.5-1.5 hours, ultrasonic treatment for 0.5-1.5 hours, and low-speed stirring for 18-24 hours.

6. The method of making a lithium ion battery separator of metal organic frameworks (MOFs) and halloysite nanotubes (HNTs) of claim 1, wherein, The method for removing the solvent in the OPBI@MOFs-HNTs mixed solution is to immerse the substrate coated with the OPBI@MOFs-HNTs mixed solution in anhydrous methanol for immersion treatment, and the immersion treatment is to stand still at room temperature for 8-15 minutes.

7. A lithium-ion battery separator comprising metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs), characterized in that, The lithium ion battery separator containing metal organic frameworks MOFs and halloysite nanotubes HNTs is prepared by the method of any one of claims 1-6, and the micro-pore channels of the separator are composed of regular, uniform and dense finger-shaped pores and sponge-shaped pores.

8. The lithium-ion battery separator of metal-organic frameworks (MOFs) and halloysite nanotubes (HNTs) of claim 7, wherein, The thickness of the lithium ion battery separator containing metal organic frameworks MOFs and halloysite nanotubes HNTs is 20-40 microns.

9. A lithium-ion battery, characterized by The lithium ion battery separator containing metal organic frameworks MOFs and halloysite nanotubes HNTs is located between the positive electrode sheet and the negative electrode sheet.

Images