MOF-based solid electrolyte and preparation method and application thereof

Abstract

The invention discloses an MOF (Metal Organic Framework)-based solid electrolyte as well as a preparation method and application thereof, and relates to the technical field of batteries, the solid electrolyte comprises two types, namely MIL-53-4F and MIL-53-4Cl; a preparation method of the MIL-53-4F / MIL-53-4Cl comprises the following steps: mixing aluminum nitrate nonahydrate and tetrafluoroterephthalic acid / tetrachloroterephthalic acid, and fully grinding and uniformly mixing; transferring the mixed powder into a high-pressure reaction kettle, and reacting in a drying oven at 120 DEG C for 24 hours; and after fully cooling, washing the obtained product with N, N-dimethylformamide, ethanol and methanol respectively for three times, and drying in a vacuum drying oven at 80 DEG C for 12 hours to obtain the product. The structure of the MIL-53 material is designed through a functional modification strategy, specific functional groups-F and-Cl are introduced into a framework of the MIL-53 material, the ion transmission environment is effectively regulated and controlled, and then the ionic conductivity of the MIL-53 material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a MOF-based solid electrolyte and a preparation method and application thereof. Background Art

[0002] With the growing demand for high energy density batteries in electric vehicles and large-scale energy storage, it is urgent to develop high energy density and long cycle life lithium-ion batteries to carry out forward-looking research on new system batteries.

[0003] Solid-state lithium metal batteries have energy density and safety far exceeding traditional liquid lithium batteries, and are ideal next-generation batteries. Solid electrolytes, as the most critical component of all-solid-state lithium batteries, are the focus and difficulty of research. At present, all-solid-state lithium metal batteries have the problem of low room temperature ion conductivity, which not only causes Li + The transmission impedance is large, the battery charges and discharges slowly, and it also leads to problems such as the growth of lithium dendrites and battery degradation. Metal organic frameworks (MOFs) have gradually become a research hotspot for solid electrolytes due to their uniform porous structure, large specific surface area, and strong designability. MOF solid electrolytes are expected to solve the problem of inefficient ion transport: first, the ordered porous structure of MOF provides an efficient transmission pathway for ions; second, the MOF is structurally designed, and the organic ligands are functionally modified to meet the needs of ion transport regulation. Therefore, the present invention intends to prepare a series of MOF-based solid electrolytes for use in lithium metal batteries to improve ion transmission efficiency. Summary of the invention

[0004] In view of the above problems, the present invention provides a MOF-based solid electrolyte and a preparation method and application thereof.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a method for preparing a MOF-based solid electrolyte, wherein the solid electrolyte includes two types, specifically: MIL-53-4F and MIL-53-4Cl; The preparation method of MIL-53-4F is as follows: aluminum nitrate nonahydrate and tetrafluoroterephthalic acid are mixed, and the mixture is fully ground and mixed; the mixed powder is transferred to a high-pressure reactor, and reacted in an oven at 120° C. for 24 hours; after being fully cooled, the obtained product is washed with N,N-dimethylformamide, ethanol, and methanol for 3 times, respectively, and dried in a vacuum drying oven at 80° C. for 12 hours to obtain the obtained product; The preparation method of the MIL-53-4Cl is as follows: Mix aluminum nitrate nonahydrate and tetrachloroterephthalic acid, and grind and mix them thoroughly; transfer the mixed powder into a high-pressure reaction kettle and react in an oven at 120 °C for 24 hours; after sufficient cooling, wash the obtained product three times with N,N-dimethylformamide, ethanol, and methanol respectively, and dry it in a vacuum drying oven at 80 °C for 12 hours to obtain the product.

[0006] Furthermore, in the preparation of the MIL-53-4F, the molar ratio of aluminum nitrate nonahydrate to tetrafluoroterephthalic acid is 1:1.

[0007] Furthermore, in the preparation of the MIL-53-4Cl, the molar ratio of aluminum nitrate nonahydrate to tetrachloroterephthalic acid is 1:1.

[0008] The present invention also provides a MOF-based solid electrolyte prepared by the preparation method of the MOF-based solid electrolyte.

[0009] The present invention also provides an application of the MOF-based solid electrolyte in the preparation of lithium-ion batteries.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: In the present invention, the structure of the aluminum-based metal-organic framework - MIL-53 material is designed by a functionalization modification strategy, and specific functional groups -F and -Cl are introduced into its framework to effectively regulate the ion transport environment and further improve its ionic conductivity. Specifically, strong electronegative groups such as -F and -Cl can inhibit the migration of anions in the pores through electrostatic interaction and promote the dissociation of lithium salts; at the same time, the orderly arranged active sites in the fluorinated and chlorinated MOF frameworks provide a low-energy barrier hopping path for lithium ions to achieve rapid conduction. By modifying functional groups on the organic ligands of MOF, a series of fluorinated and chlorinated MOF-based solid electrolytes are prepared and synthesized, aiming to design and prepare MOF-based solid electrolytes with high ionic conductivity, improve the ion transport effect, and ultimately achieve high-efficiency metal batteries with long cycle life. Description of the Drawings

[0011] Figure 1 are the electron micrographs of (a) MIL-53, (b) MIL-53-4F, and (c) MIL-53-4Cl of the present invention; (d) XRD patterns of the three materials; (e) infrared spectra; (f) X-ray photoelectron spectroscopy survey spectra; (g) F 1s fine spectra of the MIL-53-4F material; (h) Cl 2p fine spectra of the MIL-53-4Cl material; (i) nitrogen adsorption and desorption isotherms of the three materials; Figure 2These are the EIS spectra of (a) MIL-53, MIL-53-4F, MIL-53-4Cl and PVDF electrolytes at room temperature; (b) MIL-53-4F electrolyte at different temperatures; (c) MIL-53-4Cl electrolyte at different temperatures; (d) Arrhenius fitting plots of MIL-53, MIL-53-4F, MIL-53-4Cl and PVDF electrolytes; (e) comparison of activation energies of MIL-53, MIL-53-4F, MIL-53-4Cl and PVDF electrolytes; (f) EIS tests of MIL-53-4F electrolyte before and after polarization, with the inset showing the I-t curve; (g) EIS tests of MIL-53-4Cl electrolyte before and after polarization, with the inset showing the I-t curve; (h) long cycle comparison of MIL-53 series materials at 0.2C. Detailed implementation manners

[0012] In order to make the objectives and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0013] The instruments, reagents, materials, etc. involved in the following embodiments, unless otherwise specified, are all conventional instruments, reagents, materials, etc. existing in the prior art and can be obtained through regular commercial channels. The experimental methods, detection methods, etc. involved in the following embodiments, unless otherwise specified, are all conventional experimental methods, detection methods, etc. existing in the prior art.

[0014] Example 1 This example provides a preparation method for MOF-based solid electrolytes, including two types, specifically: MIL-53-4F and MIL-53-4Cl; The preparation method of MIL-53-4F is as follows: Mix 10 millimoles (3.75 grams) of aluminum nitrate nonahydrate and 10 millimoles (2.38 grams) of tetrafluoroterephthalic acid, and grind and mix them thoroughly; Transfer the mixed powder to a high-pressure reaction kettle and react in an oven at 120°C for 24 hours; After sufficient cooling, the obtained product is washed 3 times with N,N-dimethylformamide, ethanol, and methanol respectively, and dried in a vacuum drying oven at 80°C for 12 hours to obtain the product. The structural formula is as follows: ; The preparation method of MIL-53-4Cl is as follows: Mix 10 mmol (3.75 g) of aluminum nitrate nonahydrate and 10 mmol (3.039 g) of tetrachloroterephthalic acid, and grind and mix them thoroughly; transfer the mixed powder to a high-pressure reaction kettle and react in an oven at 120 °C for 24 hours; after cooling sufficiently, wash the obtained product 3 times with N,N-dimethylformamide, ethanol, and methanol respectively, and dry it in a vacuum drying oven at 80 °C for 12 hours to obtain the product. The structural formula is as follows: 。

[0015] Comparative Example 1 Preparation of aluminum-based MOF, MIL-53: Dissolve 3.5 mmol (1.3 g) of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and 1.75 mmol (0.29 g) of terephthalic acid in a mixed solution of water and DMF, and ultrasonically treat the mixed solution for 10 minutes; transfer the obtained mixture to a high-pressure kettle and react at 150 °C for 24 hours; after cooling, wash it 3 times with N,N-dimethylformamide, ethanol, and methanol respectively, centrifuge to obtain the product, and dry it in a vacuum drying oven at 90 °C for 12 h to obtain the product. The structural formula is as follows: 。

[0016] Experimental Example 1 Material Characterization To determine the microscopic morphology of MIL-53, MIL-53-4F, and MIL-53-4Cl materials, SEM analysis and comparison were carried out. Specifically, MIL-53 particles showed a stacked irregular blocky morphology ( Figure 1 a). After introducing halogen groups, MIL-53-4F presented a regular blocky morphology with a length of about 1.4 µm ( Figure 1 b), the crystal size was about 1.4 µm, and MIL-53-4Cl showed an elongated rod-like structure ( Figure 1 c), and the crystal length was 4 µm.

[0017] The crystal structure and crystallinity of the synthesized MOFs were determined by X-ray diffraction (XRD) measurement ( Figure 1 d). The diffraction peaks of MIL-53 were consistent with the standard pattern reported in the literature (standard MIL-53). At the same time, significant peaks were detected at 9.4, 15.7, 19.1, and 21.8 for MIL-53-4F and MIL-53-4Cl, and their diffraction signals were also consistent with the simulated standard pattern. This confirmed the successful synthesis of MIL-53 and its fluoride MIL-53-4F and chloride MIL-53-4Cl.

[0018] The structures and functional groups of MIL-53, MIL-53-4F, and MIL-53-4Cl materials were analyzed by Fourier transform infrared spectroscopy (FT-IR) (Figure 1 e). As Figure 1 shown in e), the obtained Fourier transform infrared (FT-IR) spectrum has characteristic peaks at 1601 cm −1 and 1479 cm −1 corresponding to the stretching vibrations of the benzene ring -COO and -C=O of the terephthalic acid ligand. The absorption peak at 1050 cm −1 corresponds to the stretching vibration of Al-O, which is consistent with the previously reported MIL-53 structure. Comparing the IR spectrum of MIL-53, a characteristic peak appears at 1258 cm −1 in the IR spectrum of MIL-53-4F, corresponding to the stretching vibration of the C-F bond, verifying the successful introduction of fluorine groups into the MIL-53 framework. In addition, an absorption peak at 625 cm −1 appears in the spectrum of MIL-53-4Cl, which can be attributed to the stretching vibration of the C-Cl bond, demonstrating the successful modification of the -Cl group on the MIL-53 framework. Similarly, according to X-ray photoelectron spectroscopy analysis, the presence of F and Cl elements is shown in the survey spectra of MIL-53-4F and MIL-53-4Cl respectively ( Figure 1 f). In addition, the F 1s spectrum of MIL-53-4F shows a single -C-F peak at 687.9 eV ( Figure 1 g). The two peaks in the Cl 2p spectrum of MIL-53-4Cl ( Figure 1 h) are located at 200.5 (2p 1 / 2 ) and 198.9 (2p 3 / 2 ) eV, respectively, which are related to the -C-Cl band, indicating the successful introduction of F and Cl functional groups, which is consistent with the FT-IR results.

[0019] The N2 adsorption / desorption experiments were carried out at 77 K to test the specific surface area of the MIL-53 materials. As Figure 1 shown in i, the Brunauer-Emmett-Teller (BET) specific surface area of MIL-53 is as high as 870 m 2 g -1 . After Cl group modification, the specific surface area of MIL-53-4Cl is 771 m 2 g -1 , and the specific surface area of MIL-53-4F is 752 m 2 g -1The regular and orderly porous structure of MOF is conducive to the precise construction and rapid transfer of lithium ion transfer channels. After modification with fluorine and chlorine groups, MIL-53-4F and MIL-53-4Cl have a higher specific surface area, retaining the advantages of the large pore structure of MOF, which is conducive to the accommodation of more lithium salts and can improve the overall electrochemical performance of solid electrolytes. The specific surface area of ​​MOFs after functional modification is slightly smaller than that of the original MIL-53, which is due to the F and Cl functional groups arranged in the MOF channels.

[0020] Experimental Example 2 Battery Performance Test The MOFs materials obtained in Example 1 and Comparative Example 1 were respectively mixed and stirred with bistrifluorosulfonyl imide lithium salt (LiTFSI) in N-methylpyrrolidone solution for 12 hours to load the lithium salt into the pores of MOF, and the binder PVDF (MOFs: LiTFSI: PVDF = 1:1:0.7, mass ratio) was added and stirred for 12 hours to form a homogenous slurry, which was poured into a mold and placed in a vacuum dryer at 90°C to remove the solvent for 12 hours to obtain a solid electrolyte, which was then cut for later use.

[0021] Preparation of positive electrode sheets for lithium-ion batteries: Active ingredient lithium iron phosphate (LiFePO4), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are weighed at a mass ratio of 8:1:1, and then an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent is added. The small ball mill is shaken for 15 minutes, and the evenly mixed positive electrode slurry is coated on an aluminum foil substrate and vacuum dried at 90°C for 12 hours. After cutting, the positive electrode sheet is compacted at a pressure of 8MPa for standby use.

[0022] Button battery assembly: The battery assembly process, except for blocking the battery, was completed in an argon glove box.

[0023] Table 1 Battery assembly methods and corresponding test performance

[0024] Symmetric blocking cells were used to perform electrochemical impedance spectroscopy (EIS) tests at different test temperatures to obtain the ionic conductivity of the materials at different test temperatures and calculate their activation energies. The ionic conductivities of MIL-53, MIL-53-4F, and MIL-53-4Cl were 1.43×10 -3 Scm -1 , 2.15×10 -3 Scm -1 , 2.03×10 -3 Scm -1 It can be seen that after halogen modification, the ionic conductivity of MIL-53 has been greatly improved, and is significantly higher than the 3.63×10 -4Scm -1 ( Figure 2 (a-c). In the temperature range of 30 - 80 °C, the ionic conductivity shows a good linear relationship with temperature, conforming to typical Arrhenius behavior ( Figure 2 (d). The activation energies of electrolytes MIL-53, MIL-53-4F, and MIL-53-4Cl are calculated to be 0.15 eV, 0.08 eV, and 0.11 eV respectively from the slopes of the linearly fitted curves, which are significantly lower than 0.23 eV of traditional polymer electrolyte PVDF ( Figure 2 (e). The lower activation energy indicates a lower energy barrier for ion transport during ion migration, enhancing the rapid migration of lithium ions.

[0025] The lithium ion transference number is an important indicator for evaluating the conduction ability of solid electrolytes for Li + . After alternating current impedance testing and chronoamperometry testing (see Figure 2 (f-g)), the ionic transference numbers of the electrolytes are calculated. The specific values for the three electrolytes MIL-53, MIL-53-4F, and MIL-53-4Cl are: 0.54, 0.76, and 0.71. A high transference number is beneficial for the efficient transport of lithium ions and also for suppressing lithium dendrites by reducing the concentration gradient. Due to the introduction of electron-withdrawing groups -F and -Cl groups on the ligand, specific electronegative ion transport channels are constructed for lithium ions. The -F and -Cl sites on the MOF interact with the anions of the lithium salt, which can accelerate the dissociation of the lithium salt, increasing the number of free lithium ions in the pores.

[0026] The long-term stability of lithium ion transport is evaluated through constant current charge-discharge tests. Using LiFePO4 (LFP) as the positive electrode, a coin-type full cell is assembled and cycled at a rate of 0.2C. As Figure 2 (h) shows, the charge-discharge specific capacity of the MIL-53 full cell shows a rapid decay after 72 cycles, and the capacity retention rate is only 16% after 150 cycles. After fluorination modification, the cycle stability is greatly improved. The LFP|MIL-53-4F|Li full cell is continuously charged and discharged at 0.2C for 300 cycles. The initial charge-discharge specific capacities are 131 mAhg -1 and 129 mAhg -1 respectively, and it shows a capacity retention rate of 94% after 200 cycles and still 86% after 300 cycles. In contrast, the initial charge-discharge specific capacities of the MIL-53-4Cl full cell are 141 mAhg -1 and 136 mAhg -1 respectively, and its capacity retention rate is 51% after 300 cycles, and its cycle stability is worse than that of the fluorinated electrolyte.

[0027] In summary, the present invention designs and prepares a series of MOF-based solid electrolytes for use in lithium metal batteries. By functionalizing fluorine groups and chlorine groups in the MOF pores, the modification and regulation of the material structure by functionalization are analyzed, and the effects of fluorination and chlorination modifications on the ion transport performance and battery cycle stability of MIL-53 materials are investigated. Verified by experimental results, the MIL-53-4F and MIL-53-4Cl electrolytes effectively solve the problem of inefficient ion transport. By strengthening the capture of lithium salt anions through fluorination and chlorination modifications, the lithium ion conductivity and transference number are effectively improved, ultimately enhancing the ion transport efficiency and improving the battery cycle stability.

[0028] The foregoing are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of an MOF-based solid electrolyte, characterized in that: The solid electrolytes include two types, specifically: MIL-53-4F and MIL-53-4Cl; The preparation method of the MIL-53-4F is as follows: Mix aluminum nitrate nonahydrate and tetrafluoroterephthalic acid, and grind and mix them thoroughly; Transfer the mixed powder to a high-pressure reaction kettle and react in an oven at 120 °C for 24 hours; After sufficient cooling, the obtained product is washed three times with N,N-dimethylformamide, ethanol, and methanol respectively, and dried in a vacuum drying oven at 80 °C for 12 hours to obtain it; The preparation method of the MIL-53-4Cl is as follows: Mix aluminum nitrate nonahydrate and tetrachloroterephthalic acid, and grind and mix them thoroughly; Transfer the mixed powder to a high-pressure reaction kettle and react in an oven at 120 °C for 24 hours; After sufficient cooling, the obtained product is washed three times with N,N-dimethylformamide, ethanol, and methanol respectively, and dried in a vacuum drying oven at 80 °C for 12 hours to obtain it.

2. The preparation method of a MOF-based solid electrolyte according to claim 1, characterized in that: In the preparation of the MIL-53-4F, the molar ratio of aluminum nitrate nonahydrate to tetrafluoroterephthalic acid is 1:

1.

3. The preparation method of a MOF-based solid electrolyte according to claim 1, characterized in that: In the preparation of the MIL-53-4Cl, the molar ratio of aluminum nitrate nonahydrate to tetrachloroterephthalic acid is 1:

1.

4. A MOF-based solid electrolyte prepared by the preparation method of a MOF-based solid electrolyte according to any one of claims 1-3.

5. Use of the MOF-based solid electrolyte according to claim 4 in the preparation of a lithium-ion battery.

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