Lithium ion battery diaphragm containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs), preparation method of lithium ion battery diaphragm and lithium ion battery

Abstract

The invention 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), a preparation method of the lithium ion battery diaphragm and a lithium ion battery, and the preparation method comprises four steps which are shown in Figure 1 in attached drawings in the specification. -COOH of the MOFs not only has electrostatic attraction with imidazole on the OPBI, but also has hydrogen bond interaction with-OH of the HNTs. According to the invention, the MOFs-HNTs mixture is introduced into the diaphragm, so that the problem of poor compatibility between the inorganic filler and the diaphragm matrix OPBI is solved, and uniform dispersion is realized. And the MOFs-HNTs mixture changes the diffusion force in the non-solvent phase inversion method to obtain the high-temperature-resistant lithium ion battery diaphragm of which the microscopic pore structure consists of regular finger-shaped pores and spongy pores. The porous structure is cooperated with the larger specific surface area of the MOFs-HNTs and polar groups, so that more sites and microscopic channels are provided for lithium ion transmission, and disordered growth of lithium dendrites is inhibited. And the assembled lithium battery is excellent in electrochemical performance and low in electrode polarization degree.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery diaphragm containing a MOFs-HNTs mixture, a preparation method thereof, and a lithium ion battery. Background Art

[0002] The separator is one of the core components of lithium-ion batteries (LIBs). Its function is to separate the positive electrode from the negative electrode to prevent the battery from short-circuiting and causing safety accidents. At the same time, it ensures that lithium ions can pass through the microporous channels normally during charging and discharging to ensure the normal operation of the battery. The performance of the separator directly affects the safety, capacity, rate, life and other performance of the battery during service.

[0003] Polyolefin diaphragms, such as polyethylene (PE) diaphragms, polypropylene (PP) diaphragms, and PE / PP composite films, are diaphragm products commonly used in the production process of commercial lithium-ion batteries. Their production processes mainly include dry and wet processes. Due to the limitations of material properties and production processes, polyolefin separators still face more difficult problems in the application process: First, the melting point of polyolefin materials is low, which is its inherent property. Therefore, polyolefin separators have poor heat resistance and are prone to thermal shrinkage at high temperatures, which can cause battery short circuits and lead to dangerous events such as lithium battery fires and explosions; second, the electrical conductivity, electrolyte wettability, flame retardancy, and electrochemical stability window of polyolefin separators are not ideal; third, batteries assembled with polyolefin separators have severe lithium dendrite growth during service, and lithium dendrites can easily pierce the separator, causing micro-short circuits inside the lithium battery, posing a safety hazard to the lithium battery; fourth, batteries assembled with polyolefin separators have poor cycle stability at high temperatures (such as 50°C, 90°C); fifth, the polarization of battery electrodes assembled with polyolefin separators is relatively large.

[0004] In order to improve the safety of use and electrochemical performance of lithium batteries, some materials are coated on the surface of polyolefin diaphragms through different coating processes to form coated polyolefin diaphragms; the coated diaphragms on the market mainly include inorganic coated diaphragms, organic coated diaphragms, and organic + inorganic coated diaphragms. This coating of heat-resistant materials (inorganic, organic, inorganic / organic mixed) on the surface of polyolefin diaphragms improves the heat resistance of the diaphragm to a certain extent. However, the substrate material under the coating - polyolefin still has the risk of thermal shrinkage causing the collapse of the overall structure of the diaphragm at a sufficiently high temperature and a sufficiently long time. Therefore, this modification scheme based on polyolefin diaphragms cannot fundamentally solve the problem of heat resistance of the diaphragm, and cannot completely solve the safety of lithium batteries. In addition, the growth of anode lithium dendrites in lithium batteries assembled with such coated polyolefin diaphragms is still relatively serious during the charge and discharge cycle. As we all know, coating will also produce a series of negative effects, such as increased diaphragm thickness, increased body resistance (R b ) increases, the charge / discharge efficiency decreases, etc.

[0005] Therefore, the existing diaphragm technology still needs to be improved and developed. Summary of the invention

[0006] In view of the above-mentioned deficiencies of the existing diaphragm technology, the purpose of the present invention is to provide a lithium-ion battery diaphragm containing a MOFs-HNTs mixture and a preparation method thereof, and a lithium-ion battery, aiming to solve the following problems: a. The existing polyolefin diaphragms are prone to thermal shrinkage at high temperatures; b. The lithium dendrites on the anode surface of the lithium-ion battery assembled with the existing polyolefin diaphragms have serious disordered growth; c. The high-temperature cycle stability of the lithium-ion battery assembled with the existing polyolefin diaphragms is poor; d. The electrode polarization of the lithium-ion battery assembled with the existing polyolefin diaphragms is relatively large; e. The electrical conductivity, electrolyte wettability, flame retardancy, electrochemical stability window, etc. of the polyolefin diaphragms are not ideal.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture comprises the following steps:

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

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

[0011] The OPBI@MOFs-HNTs mixed solution is coated on a substrate, and the solvent in the OPBI@MOFs-HNTs mixed solution is removed to obtain a lithium ion battery separator containing a MOFs-HNTs mixture.

[0012] The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture is characterized in that the MOFs-HNTs mixture is a mixture obtained by physical mixing, and the metal organic framework (MOFs) is UiO-66MOFs.

[0013] The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture, wherein the solvent of the MOFs-HNTs mixed dispersion solution and the solvent of the OPBI solution are jointly selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0014] The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture, wherein, in the mixed solution of the MOFs-HNTs mixture, the total mass of the MOFs-HNTs mixture is 5%-30% of the mass of OPBI.

[0015] The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture, wherein the MOFs-HNTs mixture preparation process is: 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.

[0016] The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture, wherein the preparation process of the OPBI solution is: adding 0.3g of OPBI powder to a solvent, and vigorously stirring at 60-100°C for 18-24 hours; the preparation process of the MOFs-HNTs mixed dispersion solution is: adding the MOFs-HNTs mixture to a solvent, ultrasonically treating for 1-3 hours, and stirring for 0.5-1.5 hours; the preparation process of the OPBI@MOFs-HNTs mixed solution is: slowly pouring the MOFs-HNTs mixed dispersion solution into the OPBI solution, stirring for 0.5-1.5 hours, ultrasonically treating for 0.5-1.5 hours, and stirring at a low speed for 18-24 hours.

[0017] The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture, wherein the method for removing the solvent in the OPBI@MOFs-HNTs mixed solution is: placing a substrate coated with the OPBI@MOFs-HNTs mixed solution in anhydrous methanol for immersion treatment, and the immersion treatment is standing at room temperature for 8-15 minutes.

[0018] A lithium ion battery separator containing a MOFs-HNTs mixture is prepared by a non-solvent phase transfer method (NIPS), and the microscopic pores of the separator are composed of regular, uniform, dense finger-like pores and sponge-like pores.

[0019] The lithium-ion battery separator containing the MOFs-HNTs mixture has a thickness of 20-40 microns.

[0020] A lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet and a lithium-ion battery separator containing a MOFs-HNTs mixture; the lithium-ion battery separator containing the MOFs-HNTs mixture is located between the positive electrode sheet and the negative electrode sheet.

[0021] Beneficial effects: The present invention provides a lithium ion battery diaphragm containing a MOFs-HNTs mixture, a preparation method thereof, and a lithium ion battery. The preparation method comprises 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 a lithium ion battery diaphragm containing a MOFs-HNTs mixture; and assembling a lithium ion battery using the lithium ion battery diaphragm containing a MOFs-HNTs mixture. The present invention introduces a MOFs-HNTs mixture into a battery separator, and has the following advantages: (1) the -COOH group on the MOFs not only has an electrostatic attraction with the imidazole structure on the OPBI, but also has a hydrogen bond interaction with the -OH group on the HNTs, thereby solving the problem of poor compatibility between the inorganic material HNTs and the polymer separator matrix material OPBI. Therefore, the HNTs can be well dispersed and fixed in the OPBI matrix; (2) the introduction of HNTs into the OPBI matrix is ​​conducive to the preparation of a separator with multi-morphological channels having finger-like channels, and the use of MOFs to evenly disperse the HNTs in the OPBI matrix can obtain richer and more uniform ion channels; (3) the porosity and designability of MOFs, coupled with the stability and special structure of HNTs, make the material have a higher specific surface area, which is more conducive to the transmission of lithium ions. The affinity between the diaphragm prepared by the present invention and the electrolyte is increased, and more sites and microscopic channels are provided for the transmission of lithium ions; the MOFs-HNTs mixture is used to change the diffusion force in the non-solvent phase conversion process to obtain a high-temperature resistant lithium-ion battery diaphragm with a microscopic pore structure composed of regular finger-like pores and sponge-like pores. The diaphragm has good wettability to the electrolyte, high conductivity, and good electrochemical stability. It also induces lithium ions to pass through the diaphragm more quickly and deposit evenly on the surface of the lithium metal anode through a unique pore structure and ion coordination structure, effectively inhibiting the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium-ion batteries. The battery assembled using the diaphragm exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially excellent charge and discharge stability at high temperatures; in addition, the polarization degree of the battery electrode is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 and Figure 2 The present invention is a process diagram of a method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture and assembling a button-type half-cell.

[0023] Figure 3Schematic diagram of the principle of using a MOFs-HNTs mixture to evenly disperse in the OPBI membrane matrix to eliminate the poor compatibility between inorganic materials and the organic matrix.

[0024] Figure 4 TEM image and particle size distribution diagram of MOFs.

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

[0026] Figure 6 Composition and structure characterization diagrams of MOFs, HNTs, and MOFs-HNTs hybrids, where (ac) are TEM images of MOFs, HNTs, and MOFs-HNTs, (d) is the EDS spectrum of MOFs-HNTs, and (e) and (f) are FT-IR spectra and XRD spectra of MOFs, HNTs, and MOFs-HNTs, respectively.

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

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

[0029] Fig. 9 Photos of the folded and bent morphologies of the OPBI@M-H10 diaphragm.

[0030] Fig.10 The heat resistance and flame retardancy test results of PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators.

[0031] Fig.11 The electrochemical performance of the battery. Among them, (a) is the AC impedance curve of the double steel plate symmetrical battery assembled with PP, OPBI, OPBI@M-H5 and OPBI@M-H10 membranes, (bc) are the Nyquist plots and LSV curves of the symmetrical battery with double lithium electrodes sandwiched with PP, OPBI and OPBI@M-H10 membranes respectively; (d) is the plating / stripping cycle curve of the double lithium electrode symmetrical battery equipped with PP and OPBI@M-H10 membranes; (ef) is the 200 charge and discharge cycle stability results and rate performance of the battery equipped with PP, OPBI, OPBI@M-H5 and OPBI@M-H10 membranes; (gh) is the charge and discharge voltage curve of the battery assembled with PP and OPBI@M-H10 membranes.

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

[0033] Fig.13 The cycling stability of button cells assembled with PP and OPBI@M-H10 separator at 50°C and 90°C at 0.5C charge and discharge. DETAILED DESCRIPTION

[0034] The present invention provides a lithium ion battery separator containing a MOFs-HNTs mixture and a preparation method thereof, and a lithium ion battery. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] It will be understood by those skilled in the art 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 in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as herein.

[0036] like Figure 1 As shown, the present invention provides a method for preparing a lithium ion battery separator containing a MOFs-HNTs mixture and a lithium ion battery, comprising the steps of:

[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 a MOFs-HNTs mixture;

[0040] Step S40: assembling a lithium-ion battery using the lithium-ion battery separator containing the MOFs-HNTs mixture.

[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 with the electrolyte. Therefore, it is prepared into a polymer membrane and applied to lithium-ion batteries to improve the safety and electrochemical performance of the battery. Metal organic frameworks (MOFs) are a class of porous materials with a 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 use of MOFs-HNTs hybrids to modify OPBI membranes has the following advantages: (1) The -COOH group on MOFs not only has an electrostatic attraction with the imidazole structure on OPBI, but also has a hydrogen bond interaction with the -OH group on HNTs, which solves the problem of poor compatibility between the inorganic material HNTs and the polymer membrane matrix material OPBI. Therefore, HNTs can be well dispersed and fixed in the OPBI matrix; (2) The introduction of HNTs into the OPBI matrix is ​​conducive to the preparation of separators with multi-morphological channels such as finger-like channels and sponge-like channels. Using MOFs to evenly disperse HNTs in the OPBI matrix can obtain richer and more uniform ion channels; (3) The porosity and designability of MOFs, coupled with the stability and special structure of HNTs, make the material have a higher specific surface area, which is more conducive to the transmission of lithium ions.

[0043] The affinity between the prepared diaphragm and the electrolyte is increased, and more sites and microscopic channels are provided for the transmission of lithium ions. The MOFs-HNTs mixture is used to change the diffusion force in the non-solvent phase conversion process to obtain a high-temperature resistant lithium-ion battery diaphragm with a microscopic pore structure composed of regular finger-like pores and sponge-like pores. The diaphragm has good electrolyte wettability (electrolyte absorption rate 377%) and high conductivity (1.59mS cm -1 ), good heat resistance and electrochemical stability, and through the unique pore structure and ion coordination structure, it induces lithium ions to pass through the diaphragm more quickly and deposit evenly on the surface of the lithium metal anode, effectively inhibiting the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium ion batteries. The battery assembled using the diaphragm exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially excellent charge and discharge stability at high temperatures; in addition, the polarization degree of the battery electrode is low. LiFePO assembled using the lithium ion battery diaphragm 4 The peak discharge capacity of the Li battery at 0.5C is 161 mAh g-1 After 200 cycles, the battery capacity retention rate is 90.28%. 4 / Li batteries can also operate at temperatures of 50°C and 90°C with considerable capacity retention.

[0044] In some embodiments, the solvent of the MOFs-HNTs mixed dispersion solution and the solvent of the OPBI solution are jointly selected from but not limited to one or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide; the solvents of the MOFs-HNTs mixed dispersion solution and the OPBI solution are ensured to be consistent, so as to facilitate the subsequent non-solvent induced 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 can contain an appropriate amount of MOFs-HNTs, so that MOFs-HNTs are used to improve the diffusion force during the non-solvent phase conversion method to obtain a high-temperature resistant lithium-ion battery separator (OPBI@MOFs-HNTs) whose microscopic pores are composed of regular finger-like pores and sponge-like pores. The separator has good wettability, high conductivity, and good electrochemical stability. It also induces lithium ions to pass through the separator more quickly and deposit uniformly on the surface of the lithium metal anode through a unique pore structure and ion coordination structure, effectively inhibiting the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium-ion batteries. The battery assembled using the separator exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially excellent charge and discharge stability at high temperatures; in addition, the battery electrode polarization is low.

[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-methylpyrrolidone as a solvent; the solvent of the OPBI solution is N-methylpyrrolidone; 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 a 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 diaphragm can increase the affinity between the diaphragm and the electrolyte, while providing more coordination sites and microscopic channels for the transmission of lithium ions. MOFs-HNTs are used to change the diffusion force during the non-solvent phase conversion method to obtain a high-temperature resistant lithium-ion battery separator with a microscopic pore structure composed of regular finger-like pores and sponge-like pores. Therefore, in view of the material characteristics of polybenzimidazole, sHNT-Li, and MOFs, the MOFs-HNTs mixture is evenly dispersed in the OPBI matrix to prepare a separator for use in lithium-ion batteries, which helps to solve the safety issues of lithium-ion batteries caused by the heat resistance, flammability and disordered growth of lithium dendrites of the separator, improve the electrochemical properties of lithium-ion batteries such as rate, cycle stability (including room temperature and high temperature) from the perspective of the separator, and reduce the polarization of battery electrodes.

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

[0048] In some embodiments, in step S30, the method for removing the solvent in the mixed solution is: placing the substrate coated with the mixed solution in anhydrous methanol for immersion treatment, the immersion treatment is standing at room temperature for 8-15 minutes, and preparing the lithium ion battery separator using a non-solvent induced phase separation process. Since OPBI is insoluble in methanol, MOFs-HNTs are 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 allowed to stand at room temperature for 8-15 minutes, and methanol is used to make the mixed solution quickly form a film, and replace NMP or DMSO or DMAC to form pores, so that the prepared lithium ion battery separator has a microscopic pore structure composed of regular finger-like pores and sponge-like pores, which is conducive to the uniform deposition of lithium ions on the anode surface, thereby inhibiting the disordered growth of lithium dendrites and improving the safety of the battery during service.

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

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

[0051] In addition, the present invention also provides a lithium-ion battery separator, which is prepared by using the preparation method of the lithium-ion battery separator containing MOFs-HNTs.

[0052] In this embodiment, a MOFs-HNTs mixture is introduced into the lithium-ion battery separator, and the MOFs-HNTs mixture is used to improve the diffusion force during the non-solvent phase conversion method to obtain a high-temperature resistant lithium-ion battery separator (OPBI@MOFs-HNTs) whose microscopic pores are composed of regular finger-like pores and sponge-like pores. The lithium-ion battery separator has excellent thermal stability and flame retardancy, does not shrink at 200°C, and does not show obvious combustion when placed on a flame; the lithium-ion battery separator has good electrolyte wettability, high electrolyte absorption rate (377%), and high conductivity (1.59mS cm -1 ), good electrochemical stability; the lithium-ion battery separator has a variety of 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 microscopic pore structure composed of regular finger-like pores and sponge-like pores, which can induce lithium ions to pass through the separator more quickly and deposit evenly on the surface of the lithium metal anode, effectively inhibiting the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium-ion batteries. The battery assembled using the separator exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially excellent charge and discharge stability at high temperatures; in addition, the polarization degree of the battery electrode is low.

[0053] In some embodiments, the thickness of the lithium-ion battery separator containing MOFs-HNTs is 20-40 microns; the lithium-ion battery separator at this thickness has excellent thermal stability and can inhibit the disordered growth of lithium dendrites.

[0054] In addition, the present invention also provides a lithium-ion battery, including a positive electrode sheet, a negative electrode sheet and a lithium-ion battery separator containing MOFs-HNTs; the lithium-ion battery separator containing MOFs-HNTs is located between the positive electrode sheet and the negative electrode sheet.

[0055] In this embodiment, the LiFePO400 assembled by the lithium-ion battery separator containing MOFs-HNTs is 4 The peak discharge capacity of the Li battery at 0.5C is 161 mAh g -1 After 200 cycles, the battery capacity retention rate was 90.28%. 4 / Li batteries can also operate at temperatures of 50°C and 90°C and have a considerable capacity retention rate; and batteries assembled using the lithium-ion battery separator containing MOFs-HNTs can operate smoothly and safely at high temperatures (such as 50°C, 90°C).

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

[0057] Example 1

[0058] This embodiment provides a method for preparing a lithium-ion battery separator (OPBI@MOFs-HNTs composite membrane) containing MOFs-HNTs and a lithium-ion battery, and its flow diagram is shown in FIG. Figure 1 As shown, the steps include:

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

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

[0061] Step S2: adding the MOFs-HNTs mixture solution to the OPBI solution and continuously stirring at 80° C. for 24 hours to obtain a mixed solution, wherein the total mass of the MOFs-HNTs mixture in the mixed solution is 5% or 10% of the mass of the OPBI.

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

[0063] Step S4: assembling a lithium-ion battery using the lithium-ion battery separator containing MOFs-HNTs.

[0064] The preparation process of MOFs: First, ZrCl 4 (466 mg, 2 mM) was pre-dissolved in 72 mL of a mixed solvent of DMF and HCl at a volume ratio of 5:1. 2 BDC (324 mg, 2.8 mM) was pre-dissolved in 2 ml of DMF. Subsequently, the metal solution and the ligand solution were mixed evenly and poured into a 100 ml Teflon container. The container was then treated with high-temperature steam at 80 °C for 24 h. After 24 h, the Teflon container was cooled to room temperature and the obtained UiO-66 MOFs were centrifuged three times. Finally, the MOFs were dried in an oven at 80 °C for 24 h for further use.

[0065] Preparation process of MOFs-HNTs mixture: MOFs and HNTs are added into a mortar in a ratio of 10:3 and ground and mixed for 1 hour.

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

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

[0068] Figure 2 Schematic diagram of the preparation process of OPBI@MOFs-HNTs composite membrane.

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

[0070] Figure 4 TEM image and particle size distribution diagram of MOFs, showing that the average particle size of MOFs is 42.59±4.09nm.

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

[0072] Figure 6 The composition and structural characterization diagrams of MOFs, HNTs, and MOFs-HNTs hybrids, where (ac) are TEM images of MOFs, HNTs, and MOFs-HNTs, (d) is the EDS spectrum of MOFs-HNTs, and (e) and (f) are the FT-IR spectra and XRD spectra of MOFs, HNTs, and MOFs-HNTs, respectively. Pure UiO-66 metal organic frameworks (MOFs) exhibit nanoparticle-like aggregate morphology with an average size of 42.59±4.09nm. Halloysite nanotubes (HNTs) exhibit a typical tubular morphology. When UiO-66MOFs and HNTs are combined at a mass ratio of 10:3, MOFs aggregates can be observed attached to HNTs, indicating that the physical mixing of MOFs and HNTs did not cause any damage to their structure and morphology. Energy dispersive spectrometer (EDS) analysis confirmed the presence of the constituent elements in the MOFs-HNTs composite material. Among them, Si and Al belong to HNTs, while Zr belongs to UiO-66MOFs. Fourier transform infrared spectroscopy (FT-IR) verifies the chemical bonding. -1 Up to 1500cm -1 The spectral absorption band between 1347cm and 1347cm is caused by the skeleton vibration of the benzene ring in MOFs. -1 The peak at 1031 cm is due to the stretching absorption of CN in MOFs. -1 The vibration at 534 cm is attributed to the Si-O bonds in HNTs. -1 The characteristic peak at 483 cm is attributed to the Al-O bond in HNTs, while the peak at 483 cm -1The peak at is attributed to the Zr-O vibration in UiO-66. Based on the above observations, the physical morphology and chemical structure of UiO-66MOFs and HNTs were successfully verified to be correct. The X-ray diffraction (XRD) pattern shows that MOFs-HNTs do not show any significant differences compared with MOFs. An obvious diffraction peak can be observed at 19.9°, which is attributed to the presence of HNTs in the MOFs-HNTs composite material. The BET results show that the specific surface area, pore volume and pore size of MOFs-HNTs are increased compared with pure HNTs. Among them, the specific surface area increased by about 17 times, providing more sites for the adsorption and desorption of ions. The reason is that MOFs have a nanoscale hollow three-dimensional structure, which increases the specific surface area. When MOFs are loaded on HNTs, HNTs can be better dispersed, thereby increasing the overall pore volume and pore size of the MOFs-HNTs composite material.

[0073] Figure 7 The SEM images of PP separator, OPBI separator, OPBI@M-H5 separator, and OPBI@M-H10 separator are shown in Figure 2. After the non-solvent induced phase separation (NIPS) process, it was found that the introduction of MOFs-HNTs into OPBI had a significant effect on the formation of pores in the separator. Through careful observation and analysis, it can be seen that the pore sizes of the top and bottom surfaces of OPBI and OPBI@MH-based separators are significantly larger than those of PP separators. In addition, in the cross section, the proportion of finger-like macropores increases, which is very beneficial for the separator to absorb and store more electrolytes. By comparing the OPBI separator with the OPBI@MH composite separator with different MOFs-HNTs introduction ratios, it can be concluded that as the incorporation of MOFs-HNTs increases from 5wt.% to 10wt.%, the pores in the resulting separator not only increase in number, but also become more evenly distributed. When analyzing the cross section, the ratio of finger-like macropores to sponge-like pores also shows a clear increasing trend. Therefore, the OPBI@MH composite separator can absorb more electrolytes, which is beneficial for the efficient transmission of lithium ions. During the NIPS process, due to the mutual diffusion effect of the solvent and non-solvent, the diffusion force perpendicular to the membrane surface increases, causing the HNTs to tend to be arranged vertically. Afterwards, the diffusion force perpendicular to the outer wall of the HNTs is suppressed, 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 the HNTs plays an important role, allowing the nanotubes to be evenly distributed according to the network pattern, making the finger-like pores more uniform and dense. There is no doubt that the dense finger-like pore structure of the composite separator has laid a solid foundation for its subsequent excellent electrolyte wettability.

[0074] Figure 8The results of electrolyte wettability, contact angle, and electrolyte absorption rate tests for PP, OPBI, OPBI@M-H5, and OPBI@M-H10 membranes are shown in Figure 2. The electrolyte absorption rate of the OPBI@M-H10 membrane is as high as 377%, which is 2.9 times that of the PP membrane. The contact angle of the OPBI@M-H10 membrane is relatively small, only 14.6°. In the AC impedance test of the steel symmetrical battery assembled with the membrane, the conductivity of the OPBI@M-H10 membrane (1.59mS·cm -1 ) is a PP diaphragm (0.63mS·cm -1 ) by 2.5 times. It is speculated that the porous channels inside the composite membrane, the cavity structure of MOFs, and the hollow tubes of HNTs all provide storage space for electrolytes and provide Li + It provides a convenient channel for transmission.

[0075] Fig. 9 The folding and bending photos of the OPBI@M-H10 separator show that the composite separator has good mechanical properties and can support the battery assembly process.

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

[0077] Fig.11The electrochemical performance of the battery. Among them, (a) is the AC impedance curve of the double steel plate symmetrical battery assembled with PP, OPBI, OPBI@M-H5 and OPBI@M-H10 membranes, (bc) are the Nyquist plots and LSV curves of the symmetrical battery with double lithium electrodes sandwiched with PP, OPBI and OPBI@M-H10 membranes respectively; (d) is the plating / stripping cycle curve of the double lithium electrode symmetrical battery equipped with PP and OPBI@M-H10 membranes; (ef) is the 200 charge and discharge cycle stability results and rate performance of the battery equipped with PP, OPBI, OPBI@M-H5 and OPBI@M-H10 membranes; (gh) is the charge and discharge voltage curve of the battery assembled with PP and OPBI@M-H10 membranes.

[0078] Compared with PP and OPBI separators, the composite separator exhibits lower bulk resistance (R b ), especially when the MOFs-HNTs addition amount reaches 10wt%. It is speculated that due to the high electrolyte absorption rate (377%) of OPBI@M-H10 separator, the abundant electrolyte storage helps to reduce the internal resistance. In addition, the -COOH groups on MOFs and the -OH groups on HNTs interact with lithium salts (LiPF 6 The coordination between the two membranes helps to desolvate Li+, thereby increasing the concentration of free ions. Therefore, the OPBI@M-H10 membrane has the highest conductivity, reaching 1.59 mS·cm -1 The electrochemical impedance spectroscopy (EIS) test of Li / separator / Li symmetric battery was carried out, and the electrode-electrolyte interface resistance (R i ) is represented by the semicircle diameter. Compared with PP diaphragm, OPBI diaphragm, OPBI@M-H10 diaphragm has lower R i , which is attributed to the excellent consistency brought by the excellent electrolyte wettability, higher porosity, and good interfacial compatibility between MOFs-HNTs and OPBI matrix.

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

[0080] The interfacial stability between the separator containing electrolyte and the lithium electrode was analyzed by stripping / adsorption experiments of lithium symmetric cells.-2 A 1600-hour charge-discharge test was carried out at a current density of . In the battery assembled with the PP separator, the potential during the stripping / adsorption process of the lithium electrode was always above 10 mV, more than twice that of the OPBI@M-H10 separator. In addition, during the long-term cycling process, the potential was unstable, and the potential rose sharply to a high potential of 20 mV at about 1340 hours. In contrast, during the 1600-hour cycle of the OPBI@M-H10 separator, the potential remained stable and at an extremely low level, demonstrating excellent cycle reversibility and the ability to effectively inhibit the disordered growth of lithium dendrites at the negative electrode.

[0081] The initial discharge specific capacities of the batteries using PP, OPBI, OPBI@M-H5, and OPBI@M-H10 separators were 128.32 mAh g -1 、132.45mAh·g -1 、135.60mAh·g -1 and 148.12 mAh g -1 . Overall, the battery using the OPBI@M-H10 separator exhibited the highest discharge specific capacity. It is speculated that this is attributed to the dense and uniform pores of the OPBI@M-H10 composite separator and the excellent wetting properties of the separator, which helps to store more electrolytes, thereby increasing conductivity and improving the discharge specific capacity. In addition, after 200 charge and discharge cycles, we found that the battery using the PP separator only retained 78.56% of the capacity, while the battery using the OPBI@M-H10 separator still retained 90.28% of the capacity, indicating that the battery based on the composite separator has a longer service life. In addition, the charge and discharge efficiency of the battery using the OPBI@M-H10 separator is as high as 97.96%, indicating that it has good reversibility and can better meet the requirements of long-term battery cycling. LiFePO assembled using PP, OPBI, OPBI@M-H5 and OPBI@M-H10 separators 4 The rate curves of the OPBI@M-H10 / Li half-cell at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 0.1C show that the battery using the OPBI@M-H10 separator has the highest discharge capacity at different charge and discharge rates. Even at a charge and discharge rate of 5C, its discharge capacity can still reach about 98mAh·g -1. It is speculated that the improvement in discharge specific capacity is due to the dense finger-like pore structure of the composite separator, which promotes ion transport, and the combined effect of the MOFs-HNTs structure on the capture and release of ions. The charge-discharge voltage curves of the battery using PP and OPBI@M-H10 separators from the 1st cycle to the 200th cycle show that the battery using OPBI@M-H10 separator has a smaller potential difference between the charge and discharge voltage platforms, indicating a lower degree of electrode polarization. This is attributed to the small interface resistance between the composite separator filled with electrolyte and the electrode, as well as good electrolyte wettability and ionic conductivity.

[0082] Fig.12 The following are SEM images of the anode lithium sheets of pure lithium sheet PP and button batteries assembled with PP, OPBI, and OPBI@M-H10 separators after 200 cycles, as well as a schematic diagram of the growth of lithium dendrites on the surface of the battery anode lithium sheet. By comparing the surface morphology of pure lithium sheets, it was found that a large number of dendrite-like lithium crystals appeared on the surface of the lithium electrode in the battery assembled with the PP separator. In contrast, in the battery assembled with the OPBI separator, the surface of the lithium electrode was relatively flat, with only a few uneven parts. However, in the battery assembled with the OPBI@M-H10 separator, the surface flatness of the lithium electrode was excellent, indicating a significant effect in suppressing 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, which helps Li + In addition, the finger-like pore structure inside the OPBI@M-H10 separator facilitates the uniform transport of Li + Orderly deposition 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] Fig.13 The cycle stability of button cells assembled with PP and OPBI@M-H10 separators at 50°C and 90°C at 0.5C charge and discharge. At a charge and discharge rate of 0.5C, the battery assembled with the composite separator was tested for 100 cycles of charge and discharge in a high temperature environment (50°C and 90°C). At 50°C, the initial discharge capacity of the battery assembled with OPBI@M-H10 separator was 154.89 mAh g -1 , which is higher than that of the battery assembled with PP separator (128.54 mAh g -1 After 100 cycles, the capacity retention rate of the OPBI@M-H10 battery was 78.58%, which is 2.2 times that of the PP battery (35.48%). At 90°C, the initial discharge specific capacity of the battery assembled with the OPBI@M-H10 separator was 148.06 mAh g-1 , which is also higher than the battery assembled with PP separator (134.17 mAh g -1 After cycling, the capacity retention rate of OPBI@M-H10 battery is 76.18%, which is much higher than that of PP battery (18.39%). Through comprehensive analysis of test data and results, it is assumed that the dense porous network structure of the composite membrane and the additional ion transport channels formed by the internal MOFs-HNTs components work synergistically to achieve Li + This promotes the improvement of the performance of the composite separator, proves its feasibility under high temperature conditions, and provides important promotion and reference value for achieving the development goal of high-safety lithium-ion batteries.

[0084] In summary, the present invention provides a lithium ion battery separator containing MOFs-HNTs, a preparation method thereof, and a lithium ion battery. The preparation method comprises 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 a lithium ion battery separator containing a MOFs-HNTs mixture; and assembling a lithium ion battery using the lithium ion battery separator containing MOFs-HNTs. The present invention introduces MOFs-HNTs into the battery separator to increase the affinity between the separator and the electrolyte, and at the same time provides more sites and microscopic channels for the transmission of lithium ions; MOFs-HNTs are used to change the diffusion force in the non-solvent phase conversion process to obtain a high-temperature resistant lithium-ion battery separator with a microscopic pore structure composed of regular finger-like pores and sponge-like pores. The separator has good electrolyte wettability, high conductivity, and good electrochemical stability. The unique pore structure can induce lithium ions to pass through the separator more quickly and deposit evenly on the surface of the lithium metal anode, effectively inhibiting the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium-ion batteries. The battery assembled using the separator exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially excellent charge and discharge stability at high temperature; in addition, the battery electrode polarization degree is low. The present invention uses HNTs to improve the interface compatibility between MOFs and the polymer matrix OPBI, so that the composite separator has a uniform and consistent composition.

[0085] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A lithium ion battery separator containing metal organic frameworks (MOFs) and halloysite nanotubes (HNTs), a preparation method thereof, and a lithium ion battery, characterized in that: Includes steps: Providing a mixed dispersion solution of metal organic frameworks (MOFs) and halloysite nanotubes (HNTs), and a polybenzimidazole (OPBI) solution; The MOFs-HNTs mixed dispersion solution and the OPBI solution are mixed to obtain a mixed solution; The OPBI@MOFs-HNTs mixed solution is coated on a substrate, and the solvent in the OPBI@MOFs-HNTs mixed solution is removed to obtain a lithium ion battery separator in which the MOFs-HNTs mixture is uniformly dispersed in an OPBI matrix.

2. The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture according to claim 1, characterized in that: The MOFs-HNTs mixture is a mixture obtained by physical mixing, and the metal organic framework (MOFs) is UiO-66MOFs.

3. The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture according to claim 1, characterized in that: The solvent of the MOFs-HNTs mixed dispersion solution and the solvent of the OPBI solution are jointly selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

4. The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture according to claim 1, characterized in that: In the OPBI@MOFs-HNTs mixed solution, the total mass of the MOFs-HNTs mixture is 5%-30% of the mass of OPBI.

5. The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture according to claim 2, characterized in that: The MOFs-HNTs mixture preparation process is as follows: MOFs and HNTs are added into a mortar in a ratio of 10:3 for grinding and mixing, and the grinding time is more than 0.5 hours.

6. The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture according to claim 1, characterized in that: The preparation process of the OPBI solution is as follows: 0.3 g of OPBI powder is added to the solvent and vigorously stirred at 60-100° C. for 18-24 hours; the preparation process of the MOFs-HNTs mixed dispersion solution is as follows: the MOFs-HNTs mixture is added to the solvent, ultrasonically treated for 1-3 hours, and stirred for 0.5-1.5 hours; the preparation process of the OPBI@MOFs-HNTs mixed solution is as follows: the MOFs-HNTs mixed dispersion solution is slowly poured into the OPBI solution, stirred for 0.5-1.5 hours, ultrasonically treated for 0.5-1.5 hours, and stirred at a low speed for 18-24 hours.

7. The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture according to claim 1, characterized in that: The method for removing the solvent in the OPBI@MOFs-HNTs mixed solution is as follows: placing the substrate coated with the OPBI@MOFs-HNTs mixed solution in anhydrous methanol for immersion treatment, wherein the immersion treatment is standing at room temperature for 8-15 minutes.

8. A lithium ion battery separator containing a MOFs-HNTs mixture, characterized in that: The method for preparing a lithium-ion battery separator containing a MOFs-HNTs mixture as described in any one of claims 1 to 7 is used, and the microscopic pores of the separator are composed of regular, uniform, dense finger-like pores and sponge-like pores.

9. The lithium-ion battery separator containing a MOFs-HNTs mixture according to claim 8, characterized in that: The thickness of the lithium ion battery separator containing the MOFs-HNTs mixture is 20-40 microns.

10. A lithium ion battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and a lithium ion battery separator containing a MOFs-HNTs mixture as claimed in any one of claims 8 to 9; the lithium ion battery separator containing a MOFs-HNTs mixture is located between the positive electrode sheet and the negative electrode sheet.

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