MOF (Metal Organic Framework)-based solid electrolyte composite membrane as well as preparation method and application thereof

Abstract

The invention discloses an MOF-based solid electrolyte composite membrane as well as a preparation method and application thereof, and an efficient and stable flexible composite solid electrolyte membrane based on MOF is constructed through the synergistic effect of PVDF-HFP, UIO-66 and ionic liquid ([EMIM] [TFSI]). The prepared optimal composite solid electrolyte membrane shows high ionic conductivity, high Li < + > transference number, moderate electrochemical window, excellent mechanical stability and good interface stability at room temperature. The Li / / Li symmetric battery equipped with the PHM21-IL solid electrolyte shows a stable lithium deposition / stripping behavior within a time period of more than 1000 hours. Meanwhile, the assembled solid-state LiFePO4 / / Li battery shows excellent rate capability and long cycle stability at room temperature, and can operate safely and stably even in a soft package battery.

Description

Technical Field

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

[0002] Efficient energy storage systems and devices are essential to meet the growing global energy demand. Over the past few decades, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and grid-scale energy storage. With the booming global automotive electrification, the demand for high-performance batteries with high energy density, long cycle life and absolute safety is increasing. However, the current market-dominant lithium-ion batteries based on intercalation reactions cannot meet the demand for higher energy density; at the same time, the traditional organic electrolytes they use are flammable, toxic and prone to leakage, which may lead to safety accidents such as fire or explosion.

[0003] Solid-state lithium metal batteries (with lithium metal as anode) have attracted much attention due to their intrinsic safety and high energy density. Compared with liquid electrolytes, solid electrolytes usually do not burn, and their high mechanical strength can inhibit the formation of lithium dendrites, which is of great benefit to improving the performance of lithium metal batteries. The most widely studied solid electrolytes can be divided into three categories: polymer solid electrolytes, inorganic solid electrolytes, and organic-inorganic composite solid electrolytes. Polymer solid electrolytes are usually composed of a polymer matrix (such as polyethylene oxide) and a lithium salt, and have the advantages of high flexibility, low cost, good interface compatibility, and easy manufacturing. However, polymer solid electrolytes have low room temperature ionic conductivity and poor mechanical strength. Inorganic solid electrolytes are mainly oxides and sulfides, showing high ionic conductivity, wide electrochemical window, and high mechanical strength. However, their inherent brittleness and high interfacial contact resistance hinder their practical application in solid-state batteries. In contrast, composite solid electrolytes are expected to combine the advantages of polymer solid electrolytes and inorganic solid electrolytes, showing great potential for practical applications. However, current research on composite solid electrolytes still faces problems such as undesirable side reactions or phase separation.

[0004] Metal-organic frameworks (MOFs) are a new type of porous materials composed of metal ions / clusters and organic ligands. Due to their unique properties, such as adjustable porous structure, ultra-high specific surface area, abundant Lewis acid functional groups and continuous transmission channels, they provide an effective means for the design of composite solid electrolytes. Specifically: adjustable pores with unsaturated metal sites can limit anion transport and promote the dissociation of lithium salts, thereby increasing the lithium ion migration number; the ordered pore structure of MOF helps to regulate the uniform deposition of lithium ions, thereby stabilizing the interface and inhibiting the formation of dendrites; the ultra-high surface area of ​​MOF enables it to fully contact with the polymer matrix and lithium salt, thereby reducing the ion transport resistance.

[0005] Based on these advantages, many kinds of MOFs have been used as modifiers for composite solid electrolytes and have shown excellent electrochemical properties. For example, the patent application with publication number CN114709470A discloses a solid electrolyte based on MOF-based ion conductors and its preparation method and application. The preparation method includes: dissolving metal salts and organic ligands in an organic solvent to form a mixed solution, placing an organic polymer substrate in the mixed solution, stirring the reaction so that the MOF material self-assembles on the organic polymer substrate to form a self-assembled MOF structure; mixing a lithium ion-containing liquid with the self-assembled MOF structure, heating the reaction, and obtaining a self-assembled MOF-based ion conductor; dispersing the polymer matrix and lithium salt in an organic solvent, heating and stirring to obtain a polymer electrolyte, casting the polymer electrolyte on the self-assembled MOF-based ion conductor, and vacuum drying to obtain a solid electrolyte based on MOF-based ion conductors. The invention provides a long-range continuous lithium ion transmission path by introducing a self-assembled MOF-based ion conductor, enhancing the ionic conductivity and mechanical properties of the solid electrolyte, thereby effectively improving the safety of solid-state batteries. However, the room temperature ionic conductivity of the solid electrolyte provided by the patent is still low, there is no clear data description for its mechanical properties (flexibility, strength, etc.), and no evaluation is made for safety indicators such as flame retardancy of the solid electrolyte, which is crucial for the safe operation of high energy density solid-state batteries. In addition, the patent with publication number CN112670543A also proposes a composite solid electrolyte membrane based on a hollow structure MOF and its preparation method and application, but it also faces safety issues such as mechanical properties and flame retardancy. At the same time, there is the question of whether large soft-pack batteries can be constructed, which is equally important for the commercial application of solid electrolytes.

[0006] Therefore, constructing advanced MOF-based composite solid-state electrolytes remains a huge challenge, which requires not only providing continuous ion transport channels for rapid lithium ion migration, reducing the interfacial impedance between the electrolyte and the electrode, and achieving high room-temperature ionic conductivity, but also ensuring a certain mechanical strength and absolute safety. Summary of the invention

[0007] Based on the deficiencies in the prior art, the present invention provides a MOF-based solid electrolyte composite membrane and a preparation method and application thereof, specifically: through the synergistic effect of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), UIO-66 and ionic liquid (IL, 1-ethyl-3-methylimidazole-bis(trifluoromethylsulfonyl)imide salt ([EMIM][TFSI])), an efficient and stable MOF-based flexible composite membrane is constructed, so that the composite solid electrolyte has excellent comprehensive properties, including strong ion conductivity, strong interface compatibility, high mechanical strength, good physical flexibility, high thermal stability, good flame retardancy, etc. The process of the present invention is simple, the conditions are mild, and it is compatible with industrial production processes. It can be used as a feasible strategy to prepare a MOF-based composite solid electrolyte film to achieve a quasi-solid-state lithium metal battery with high safety and high energy density.

[0008] The specific technical solutions of the present invention are as follows:

[0009] The invention provides a method for preparing a MOF-based solid electrolyte composite film. The solid electrolyte composite film comprises a polymer, a metal organic framework (MOF) material and an ionic liquid containing a lithium salt uniformly dispersed therein.

[0010] Further, the polymer includes one of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), etc., or any composite structure thereof, and the polymer has certain ion conductivity, good mechanical properties and electrochemical stability;

[0011] Furthermore, the MOF material is a porous structure material formed by coordination of at least one metal ion or metal ion cluster with an organic ligand;

[0012] The metal ions include Mg 2+ 、Al 3+ , Ca 2+ 、Ti 4+ 、V 4+ 、V 3+ 、V 2+ Cr 3+ , Mn 3+ , Mn 2+ , Fe 3+ , Fe 2+ 、Co 3+ 、Co 2+ 、Ni 2+ 、Ni + , Cu 2+ , Cu + 、Zn 2+ , Ga 3+ ,Ge4+ ,Ge 2+ 、As 5+ 、As 3+ 、As + , Y 3+ 、Zr 4+ 、Mo 3+ , Pd 2+ , Pd + ,pt 2+ , Pt + 、Ag + 、Cd 2+ 、In 3+ ,La 3+ 、Ce 4+ 、Ce 3+ , Hf 4+ One or more of;

[0013] The organic ligands include terephthalic acid, 2-methylimidazole, benzene-1,2,4,5-tetracarboxylic acid, 5-nitroisophthalic acid, isophthalic acid, nicotinic acid, 3-nitrophthalic acid, imidazole, 5-aminoisophthalic acid, isonicotinic acid, 1,3,5-tricarboxylic acid benzene, 2,3-pyridinedicarboxylic acid, 2,2'-bipyridine, 1,4-cyclohexanedicarboxylic acid, thiophene-2,5-dicarboxylic acid, pyrazine, butynedioic acid, [1,1'-biphenyl]-4-carboxylic acid, trans-1,4-cyclohexanedicarboxylic acid, cis-1,2 -cyclohexanedicarboxylic acid, 2,3,5,6-tetrafluoroterephthalic acid, 2-nitroterephthalic acid, pyrazine-2,3-dicarboxylic acid, 4,4'-biphenyldicarboxylic acid, fumaric acid, 3,4-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 4-aminobiphenyldicarboxylic acid, salicylic acid azine, 1H-imidazole-4,5-dicarboxylic acid, 1H-pyrazole-3,5-dicarboxylic acid hydrate, 4,4'-bipyridine, 3,6-di-2-pyridyl-1,2,4,5-tetrazine, 2,5-dibromoterephthalic acid, 2,5- dichlorobenzoic acid, trans-1,2-cyclohexanedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, (1R,2R)-1,2-cyclohexanedicarboxylic acid, 2,2'-biphenyldicarboxylic acid, 3,5-pyridinedicarboxylic acid, trimellitic acid, naphthalene-1,4-dicarboxylic acid, 4-hydroxyphthalic acid, 2,5-dihydroxyterephthalic acid, 5-hydroxyisophthalic acid, 1,4-phenylenedicarboxylic acid, 4-carboxyphenylacetic acid, 2-aminoterephthalic acid, cyclohexane-1,3-dicarboxylic acid, cis-1,4-cyclohexanedicarboxylic acid, 2 , 6-naphthalene dicarboxylic acid, cyclohexane-1,2,4,5-tetracarboxylic acid, 2-bromoterephthalic acid, 9-anthracenecarboxylic acid, 1,4-dibromo-2,5-diiodobenzene, 4,4′-dimethoxy-1,1′-biphenyl, 1-ethyl-2-methylquinolin-1-ium iodide, 1-ethyl-3-vinylimidazolium bromide, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, iron phthalocyanine, 1,3-dibromo-5-(tert-butyl)benzene, tetrafluorophthalic acid, tetrachlorophthalic acid hemihydrate;

[0014] The MOF material can be synthesized by all feasible methods, and the particle size of the MOF material is 2-500nm; the pore size of the MOFs material is 0.1-50nm, and the particle size of the MOF material can be selected from UIO-66, ZIF-8, HKUST-1, MIL-53, MIL-100, MOF-801, etc.

[0015] Furthermore, the lithium salt is a common lithium salt used in lithium secondary battery electrolyte, including but not limited to lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonyl imide, lithium bis(oxalatoborate), etc.

[0016] Furthermore, the ionic liquids are applicable to any ionic liquids having high ionic conductivity, good chemical stability, low volatility and high thermal stability, mainly including imidazole or pyridine ionic liquids, such as 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide

[0017] ([EMIM][TFSI]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]), 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]), 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]), propylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([PMPyr][TFSI]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-methylimidazolium bis(trifluoromethylsulfonyl)imide ([MIm][NTf2]), 1-methylimidazolium chloride ([MIm][Cl]), etc.

[0018] The present invention provides a method for preparing the MOF-based solid electrolyte composite membrane, comprising the following steps:

[0019] (1) dissolving a polymer in a first organic solvent to obtain a mixed solution a;

[0020] (2) dissolving the MOF material in a second organic solvent to obtain a mixed solution b;

[0021] (3) mixing the lithium salt and the ionic liquid to obtain a mixed solution c;

[0022] (4) mixing the mixed solution a and the mixed solution b uniformly, and then adding the mixed solution c and continuing to mix uniformly to obtain a mixed solution d;

[0023] (5) pouring the mixed solution d obtained in step (4) on a substrate and drying it to obtain the MOF-based solid electrolyte composite membrane;

[0024] Among them, the mass ratio of MOF material to polymer is 1:2~4.

[0025] In some technical schemes of the present invention, the first organic solvent and the second organic solvent are N,N-dimethylformamide (DMF), dimethylacetamide, N-methylpyrrolidone (NMP) chloroform, dichloromethane, acetonitrile, dimethyl sulfoxide and acetone.

[0026] In some technical solutions of the present invention, the concentration of the polymer in the mixed solution a is 5wt% to 25wt%; the concentration of the MOF material in the mixed solution b is 5wt% to 15wt%.

[0027] In some technical solutions of the present invention, the concentration of lithium salt in the mixed solution c is 1-3 mol L -1 .

[0028] In some technical solutions of the present invention, in step (4), the amount of the mixed solution c added is 10%-30% of the mass of the lithium salt to the mass of the polymer.

[0029] Preferably, in step (5), the thickness of the mixed solution d cast on the substrate is 200-400 μm; the vacuum heating and drying temperature is 50-70° C., and the time is 20-40 hours;

[0030] After drying, the thickness of the MOF-based solid electrolyte composite membrane is less than 50 μm, preferably 18 μm-35 μm.

[0031] The present invention also provides a MOF-based solid electrolyte composite membrane prepared by the preparation method.

[0032] The present invention also provides the use of the MOF-based solid electrolyte composite film in the preparation of solid or semi-solid lithium metal batteries. For the battery, systems such as lithium iron phosphate, high nickel ternary, and lithium sulfur batteries can be selected.

[0033] The present invention has the following beneficial effects:

[0034] The present invention constructs an efficient and stable MOF-based flexible composite solid electrolyte membrane through the synergistic effect of PVDF-HFP, UIO-66 and ionic liquid (IL, [EMIM] [TFSI]), so that the composite solid electrolyte exhibits excellent comprehensive properties, including robust ion conductivity, excellent mechanical properties and good flame retardancy.

[0035] Among them: (1) The porous confinement effect and abundant open metal sites of UIO-66 can effectively restrict the movement of TFSI- anions and promote the Li + dissociation, which helps Li + Efficient transmission;

[0036] (2) The interconnected MOF network constructs continuous ion channels and improves mechanical strength, which can homogenize Li + flux and inhibit the growth of lithium dendrites;

[0037] (3) The rich pores of MOF can support IL, which not only reduces the interfacial impedance but also provides continuous Li + Conductive network, promoting Li + transport in the body and at the interface, but also ensure the flexibility of the composite electrolyte and balance the mechanical properties (tensile strength of 6.63MPa and elongation of 232%) and electrochemical characteristics.

[0038] Therefore, the best composite solid electrolyte membrane prepared showed high ionic conductivity (5.55×10 -4 Scm -1 ), Gao Li + The Li / / Li symmetric cell equipped with PHM21-IL solid electrolyte exhibits stable lithium deposition / stripping behavior for more than 1000 hours. At the same time, the assembled solid-state LiFePO4 / / Li cell exhibits excellent rate performance at room temperature (discharge capacity of 128 mAh g at 3C rate). -1 ) and long cycle stability (capacity retention rate is 96.8% after 500 cycles at 1C), which can operate safely and stably even in pouch cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A thickness test diagram (a), a flexibility test diagram (b), a scanning electron microscope top view (c) and a scanning electron microscope cross-sectional view (d) of a solid electrolyte composite membrane provided in Example 1 of the present invention;

[0040] Figure 2 The combustion test diagram of the solid electrolyte composite membrane of Example 1 and Example 2 of the present invention;

[0041] Figure 3 It is a stress-strain curve diagram of the solid electrolyte composite membrane of Examples 1-2 of the present invention and Comparative Example 1;

[0042] Figure 4 The AC impedance test diagram of the solid electrolyte composite membranes of Examples 1-2 and Comparative Examples 1-3 of the present invention at room temperature;

[0043] Figure 5 This is a comparison chart of the room temperature ionic conductivity of the solid electrolyte composite membranes of Examples 1-2 and Comparative Examples 1-3 of the present invention;

[0044] Figure 6 This is a test chart of ion migration number applied to lithium-lithium battery in Example 1 of the present invention;

[0045] Figure 7 This is a test chart of ion migration number applied to lithium-lithium batteries in Example 2 of the present invention;

[0046] Figure 8 This is a test chart of ion migration number applied to lithium-lithium battery in comparative example 1 of the present invention;

[0047] Fig. 9 This is a test chart of ion migration number applied to lithium-lithium battery in comparative example 2 of the present invention;

[0048] Fig.10 The electrochemical window test diagram of the solid electrolyte membranes of Examples 1-2 and Comparative Examples 1-2 of the present invention applied to steel-lithium batteries; wherein a represents a side view of the solid electrolyte membrane of Example 1, b represents a side view of the solid electrolyte membrane of Example 2, c represents a side view of the solid electrolyte membrane of Comparative Example 1, and d represents a side view of the solid electrolyte membrane of Comparative Example 2;

[0049] Fig.11 This is a critical current density test diagram of the solid electrolyte membranes of Example 1-2 of the present invention and Comparative Example 1-2 applied to lithium-lithium batteries;

[0050] Fig.12 A test diagram of the cycle performance of the solid electrolyte membranes of Example 1 and Comparative Example 1 of the present invention applied to lithium-lithium batteries under one condition;

[0051] Fig.13 The solid electrolyte membranes of Example 1 and Comparative Example 1 of the present invention are scanning electron microscope images of the lithium surface after being applied to lithium-lithium batteries for cycling; wherein a and c represent scanning electron microscope images of the lithium surface of Example 1 and Comparative Example 1 at 500×, respectively, with a scale of 100 μm; b and d represent scanning electron microscope images of the lithium surface of Example 1 and Comparative Example 1 at 2000×, respectively, with a scale of 20 μm;

[0052] Fig.14 This is a rate performance test diagram of the solid electrolyte membranes of Example 1-2 of the present invention and Comparative Example 1-2 applied to lithium iron phosphate-lithium batteries at room temperature;

[0053] Fig.15 This is a test diagram of the cycle performance at room temperature of the solid electrolyte membranes of Example 1-2 of the present invention and Comparative Example 1-2 applied to lithium iron phosphate-lithium batteries;

[0054] Fig.16 This is a long cycle performance test diagram of the solid electrolyte membrane of Example 1-2 of the present invention applied to a lithium iron phosphate-lithium battery;

[0055] Fig.17 These are cycle performance test diagrams of the solid electrolyte membrane of Example 1 of the present invention applied to a lithium iron phosphate-graphite soft-pack battery and actual diagrams of a light-emitting diode device lighting up in different states. DETAILED DESCRIPTION

[0056] Example 1

[0057] The preparation method of MOF-based solid composite electrolyte film comprises the following steps:

[0058] (1) 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, molecular weight 400000) was dissolved in 4.5 g of N,N-dimethylformamide (DMF) at a mass concentration of 18 wt %, and stirred for 12 hours.

[0059] (2) 0.5 g of UIO-66 was dissolved in 4.5 g of DMF at a mass concentration of 10 wt %, and stirred for 12 hours.

[0060] (3) In an argon glove box, a certain amount of 2.8 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in 1 mL of 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) and stirred for 12 hours.

[0061] (4) The solution obtained in step (2) was mixed with the solution obtained in step (1) according to a mass ratio of PVDF-HFP to UIO-66 of 2:1, and stirred for 12 hours to form a uniform solution.

[0062] (5) The ionic liquid obtained in step (3) was added to the solution in step (4) according to the lithium salt accounting for 20 wt% of the mass of PVDF-HFP, and stirred for 12 hours to form a uniform slurry.

[0063] (6) The slurry obtained in step (5) was cast on a glass substrate, scraped evenly with a 250 μm film-making scraper, and placed in a 60° C. high vacuum oven for drying for 48 hours to evaporate the solvent to obtain a MOF-based composite solid electrolyte film, referred to as PHM21-IL.

[0064] The actual image and scanning electron microscope image of the obtained solid electrolyte film are as follows: Figure 1 As shown, Figure 1 (a) is the thickness test using a film thickness meter, (b) is a photo of wrapping it around an iron rod and hanging a heavy object, (c) is a top view using a scanning electron microscope, and (d) is a cross-sectional view using a scanning electron microscope. Figure 1 It can be seen that the prepared film has a thickness of about 25 μm, has good flexibility, a flat surface, uniform thickness and compact stacking, and the UIO-66 nanoparticles are evenly distributed on the surface.

[0065] The flame retardancy test results of the obtained solid electrolyte film are as follows: Figure 2 It can be seen that the solid electrolyte film obtained by the present invention can be quickly self-extinguished after being ignited and has good flame retardancy.

[0066] The flexibility test results of the obtained solid electrolyte film are as follows: Figure 3 It can be seen that the solid electrolyte film obtained by the present invention has good flexibility and high mechanical strength (the maximum elongation can reach 232%, and the highest tensile strength is 6.63MPa).

[0067] The solid electrolyte obtained above was assembled into a stainless steel symmetrical blocking battery and the AC impedance spectrum was tested. The test figure is as follows Figure 4 As shown, the conductivity of the solid electrolyte is calculated, as Figure 5 As shown, the room temperature ionic conductivity is 5.5×10 -4 Scm -1 .

[0068] Example 2

[0069] This embodiment provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 1, except that the mass ratio of PVDF-HFP to UIO-66 is controlled to 4:1, and the other operations are the same to obtain a PHM41-IL composite solid electrolyte film.

[0070] The flame retardancy test results of the obtained solid electrolyte film are as follows: Figure 2 It can be seen that the solid electrolyte film obtained by the present invention can be quickly self-extinguished after being ignited and has good flame retardancy.

[0071] The flexibility test results of the obtained solid electrolyte film are as follows: Figure 3 It can be seen that the solid electrolyte film obtained by the present invention has good flexibility and high mechanical strength (the maximum elongation can reach 330%, and the highest tensile strength is 9.25 MPa).

[0072] The solid electrolyte obtained above was assembled into a stainless steel symmetrical blocking battery and the AC impedance spectrum was tested. The test figure is as follows Figure 4 As shown, the conductivity of the solid electrolyte is calculated, as Figure 5 As shown, the room temperature ionic conductivity is 4.6×10 -4 Scm -1 .

[0073] Example 3

[0074] This embodiment provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 2, except that the MOF type used is MIL-100, and the rest of the operations are the same to obtain a composite solid electrolyte film.

[0075] The basic property parameters of the obtained solid electrolyte film are shown in Table 1, which also shows good physical and electrochemical properties.

[0076] Table 1

[0077] Sample thickness Room temperature ionic conductivity Ion migration number Maximum electrochemical stability voltage Example 3 23μm <![CDATA[2.9×10 -4 S / cm]]> 0.55 4.90V Example 4 22μm <![CDATA[3.6×10 -4 S / cm]]> 0.44 4.76V Example 5 26μm <![CDATA[3.8×10 -4 S / cm]]> 0.41 4.69V Example 6 22μm <![CDATA[4.7×10 -4 S / cm]]> 0.52 4.99V

[0078] Example 4

[0079] This embodiment provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 2, except that the MOF type used is MIL-53, and the remaining operations are the same to obtain a composite solid electrolyte film.

[0080] The basic property parameters of the obtained solid electrolyte film are shown in Table 1, which also shows good physical and electrochemical properties.

[0081] Example 5

[0082] This embodiment provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 2, except that the MOF type used is ZIF-8, and the other operations are the same to obtain a composite solid electrolyte film.

[0083] The basic property parameters of the obtained solid electrolyte film are shown in Table 1, which also shows good physical and electrochemical properties.

[0084] Example 6

[0085] This embodiment provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 2, except that the MOF type used is MOF-801, and the other operations are the same to obtain a composite solid electrolyte film.

[0086] The basic property parameters of the obtained solid electrolyte film are shown in Table 1, which also shows good physical and electrochemical properties.

[0087] Comparative Example 1

[0088] This comparative example provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 1, except that UIO-66 is not added, and the remaining operations are the same to obtain a PH-IL composite solid electrolyte film.

[0089] The flexibility test results of the obtained solid electrolyte film are as follows: Figure 3 As shown, it can be seen that the solid electrolyte film has good flexibility (the maximum elongation can reach 432%), but poor mechanical strength (the highest tensile strength is 4.45MPa).

[0090] The solid electrolyte obtained above was assembled into a stainless steel symmetrical blocking battery and the AC impedance spectrum was tested. The test figure is as follows Figure 4 As shown, the conductivity of the solid electrolyte is calculated, as Figure 5 As shown, the room temperature ionic conductivity is 1.9×10 -4 Scm -1 .

[0091] Comparative Example 2

[0092] This comparative example provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 1, except that the mass ratio of PVDF-HFP to UIO-66 is controlled to 9:1, and the other operations are the same to obtain a PHM91-IL composite solid electrolyte film.

[0093] The solid electrolyte obtained above was assembled into a stainless steel symmetrical blocking battery and the AC impedance spectrum was tested. The test figure is as follows Figure 4 As shown, the conductivity of the solid electrolyte is calculated, as Figure 5 As shown, the room temperature ionic conductivity is 3.8×10 -4 Scm -1 .

[0094] Comparative Example 3

[0095] This comparative example provides a solid electrolyte composite membrane, and its preparation method is basically the same as that of Example 1, except that the mass ratio of PVDF-HFP to UIO-66 is controlled to 1:1, and the other operations are the same to obtain a PHM11-IL composite solid electrolyte film.

[0096] The solid electrolyte obtained above was assembled into a stainless steel symmetrical blocking battery and the AC impedance spectrum was tested. The test figure is as follows Figure 4 As shown, the conductivity of the solid electrolyte is calculated, as Figure 5 As shown, the room temperature ionic conductivity is 4.5×10 -5 Scm -1 .

[0097] Test Example 1

[0098] The composite solid electrolyte membranes of Examples 1-2 and Comparative Examples 1-3 were applied to stainless steel / stainless steel batteries, and the AC impedance spectrum was tested at room temperature using an electrochemical workstation. The test conditions were 10 mV amplitude and a frequency range of 1 MHz to 0.1 Hz. Figure 4 As shown. According to the formula:

[0099]

[0100] Calculation of ionic conductivity σ(S cm) of different electrolyte films -1 ), where L is the thickness of the solid electrolyte membrane (cm), R is the volume resistance value read in the AC impedance spectrum (R), and S is the contact area between the solid electrolyte membrane and the stainless steel electrode (cm -2 ).like Figure 5 As shown in the figure, it can be clearly seen that with the increase of UIO-66 content, the ionic conductivity of the composite solid electrolyte first increases and then decreases, and the highest room temperature ionic conductivity (5.5×10 -4 S cm-1 ), which is much higher than the ionic conductivity of PH-IL (1.9×10 -4 S cm -1 Under the same conditions, the ionic conductivities of PHM91-IL, PHM41-IL, and PHM11-IL were 3.8×10 -4 S cm -1 , 4.6×10 -4 Scm -1 and 4.5×10 -5 S cm -1 The improvement of ionic conductivity can be explained from the following aspects: First, the overall distribution of MOF particles forms a continuous Li + transport channel, promoting Li + migration; secondly, due to the confinement effect of MOF pores and the Lewis acid effect of unsaturated metal sites, the dissociation degree of LiTFSI increases, resulting in an increase in the concentration of charge carriers; finally, the presence of MOF reduces the crystallinity of PVDF-HFP and promotes the movement of chain segments. However, when the UIO-66 content is excessively increased to 50wt% (PHM11-IL), the excessive stacking of "nanocages" not only limits [EMIM] + and [TFSI]- ions, and seriously affects the movement of Li + The migration of ions results in low ionic conductivity.

[0101] Test Example 2

[0102] The solid electrolyte membranes of Example 1-2 and Comparative Example 1-2 were applied to lithium / lithium batteries, and the chronoamperometric curves and AC impedance spectra were tested. According to the formula:

[0103]

[0104] Calculate the ion migration number (t Li+ ), where I0 and I SS are the initial current and steady-state current, ΔV is the applied polarization voltage (10 mV), R0 and R SS Represent the initial resistance and steady-state resistance respectively. Figure 6-9 It can be seen that the ion migration numbers of PHM21-IL, PHM41-IL, PHM91-IL and PH-IL are 0.52, 0.41, 0.37 and 0.28, respectively, indicating that the introduction of MOF can improve the ion migration number, and PHM21-IL shows the highest ion migration number. Li+ The improvement can be attributed to the confinement effect of UIO-66 nanopores on [EMIM]+ and [TFSI] - The inherent porous structure (pore size is about ) limits [EMIM]+ and [TFSI] - The movement of ions, and Li + The transmission due to its small size And not affected.

[0105] Test Example 3

[0106] The composite solid electrolyte membranes of Example 1-2 and Comparative Example 1-2 were applied to stainless steel / lithium batteries for electrochemical window testing. Linear sweep voltammetry curves were recorded using an electrochemical workstation at a scan rate of 0.5 mV s -1 The voltage range is from open circuit voltage to 6V, and the electrochemical stability window of different solid electrolyte membranes is read according to the current rise. Fig.10 As shown, the oxidation peak on the voltammetric curve of the PHM21-IL electrolyte appears at 4.35V, PHM21-IL is 4.29V, and PHM91-IL is 4.26V, all higher than PH-IL's 3.9V, which is mainly due to the easy oxidation of IL and PVDF-HFP at high voltage. The electrochemical window of the PHM21-IL electrolyte is very suitable for the LFP (test voltage range of 2.5-4.0V) and NCM cathode (test voltage range of 3.0-4.3V) systems.

[0107] Test Example 4

[0108] The solid electrolyte membranes of Examples 1-2 and Comparative Examples 1-2 were applied to lithium-lithium batteries to perform critical current density tests. Fig.11 As shown in the figure, the lithium-lithium battery equipped with different solid electrolyte membranes is changed from 0.1 mA cm -2 The current density starts to increase by 0.1 mA cm per cycle. -2 , until the battery fails, each cycle of charge and discharge lasts 15 minutes. The maximum current density before the battery fails is the critical current density, which is used to describe the maximum current density that the solid electrolyte membrane can carry. The solid electrolyte composite membranes of Examples 1 and 2 of the present invention have a current density of up to 2.4 mA cm -2 and 2.3 mA cm -2 The critical current density is significantly better than that of comparative example 1 (2.0 mA cm -2 ) and Comparative Example 2 (1.8 mA cm -2 ) solid electrolyte membrane.

[0109] Test Example 5

[0110] The solid electrolyte membranes of Example 1 and Comparative Example 1 were applied to lithium-lithium batteries to perform cycle performance tests. Fig.12 As shown, at room temperature 0.2 mA cm -2The current density is 0.1 mAh cm -2 When the battery is operated under the condition of area capacity, Example 1 can be stably cycled for more than 1000 hours, while the polarization of Comparative Example 1 increases sharply after cycling for about 300 hours.

[0111] Test Example 6

[0112] The solid electrolyte membranes of Example 1 and Comparative Example 1 were applied to lithium-lithium batteries, and the batteries were disassembled after 200 hours of cycle performance testing, and the morphological evolution of the lithium electrode after the cycle was observed using a scanning electron microscope. Fig.13 As shown, for the battery of Comparative Example 1, the lithium surface exhibits a considerable degree of uneven lithium deposition, with messy holes and porous "dead lithium" all over, while the lithium electrode surface of Example 1 maintains a relatively smooth and dense morphology without obvious damage, proving that the addition of MOF can effectively inhibit the growth of lithium dendrites and stabilize lithium ion transport in the battery.

[0113] Test Example 7

[0114] The obtained solid electrolyte composite membrane was applied to lithium iron phosphate (LFP) / Li battery. The preparation method of the battery was as follows: commercial lithium iron phosphate, Ketjen black and PVDF were mixed with an appropriate amount of NMP in a mass ratio of 8:1:1 and then coated on aluminum foil to prepare a positive electrode sheet. The active material loading was 2 mg cm -2 . In a glove box filled with argon, 5 μL of commercial electrolyte was dripped on the surface of the positive electrode to wet the interface. The solid electrolyte membrane obtained in Example 1-2 and Comparative Example 1-2 was used as the electrolyte, and the metal lithium sheet was used as the negative electrode to assemble into a 2025 type button battery. After standing for 12 hours, the rate performance and cycle performance tests were carried out at room temperature (25°C).

[0115] like Fig.14 As shown, the solid-state battery prepared by using the solid electrolyte film of Example 1 has a current density of 0.1, 0.2, 0.5, 1, 2 and 3C (1C = 170 mAh g -1 ) were 157, 152, 150, 144, 134 and 128 mAh g -1 When the current density returns to 0.1C, the capacity can be restored to 156 mAh g -1 The solid-state battery prepared using the solid electrolyte film of Example 2 also exhibited comparable performance. In contrast, the solid-state batteries using the solid electrolyte films of Comparative Examples 1 and 2 exhibited lower discharge capacities at each current density.

[0116] like Fig.15As shown in the figure, a cycle performance test was carried out at 0.5C. It can be seen that the solid-state battery using the solid electrolyte of Example 1 exhibits excellent cycle stability. After 300 constant current charge / discharge cycles, the capacity is still 147 mAh g -1 The cycle performance of Example 2 and Comparative Example 2 is poor, and the capacities after 200 cycles are 130 mAh g -1 and 75mAh g -1 The battery capacity of comparative example 1 decays rapidly to 45 mAh g after 200 cycles. -1 .

[0117] Test Example 8

[0118] The solid electrolyte films of Example 1 and Example 2 were applied to LFP / lithium batteries in the same manner as in Test Example 7, and a long cycle performance test was performed at 1.0C. Fig.16 As shown in the figure, the solid-state batteries using the solid electrolyte films of Example 1 and Example 2 both exhibit extremely stable cycle capacity and ultra-high Coulomb efficiency. The first discharge capacity of the battery of Example 1 at 1C reaches 128 mAh g -1 After 500 cycles, the specific capacity is still maintained at 124 mAh g -1 The average coulombic efficiency exceeds 99.8%, the capacity retention rate is as high as 96.8%, and the calculated decay rate per cycle is as low as 0.06%. The discharge capacity of the solid-state battery in Example 2 increases from the initial 119 mAh g to 100 mAh g after 500 cycles. -1 Reduced to 113 mAh g -1 , and the decay rate is 0.1‰. It is proved that the electrolyte of the present invention has excellent electrochemical stability and can support long-term operation.

[0119] Test Example 9

[0120] The solid electrolyte membrane of Example 1 is applied to LFP / graphite soft pack batteries, such as Fig.17 As shown in Figure 2, the obtained soft-pack battery can be stably cycled for 100 times at a current density of 0.2C, and the capacity is maintained at 114 mAh g -1 When the soft-pack battery is fully charged, it can light up a bright light-emitting diode (LED) device, and can stably power the LED lamp under several harsh transition states (including folding, partial cutting, and cutting off 1 / 4) without a significant decrease in brightness, indicating that the solid electrolyte provided by the present invention has high safety and good application prospects.

Claims

1. A method for preparing a MOF-based solid electrolyte composite membrane, characterized in that: The solid electrolyte composite membrane comprises a polymer, a MOF material and an ionic liquid containing a lithium salt uniformly dispersed therein; The preparation method comprises the following steps: (1) dissolving a polymer in a first organic solvent to obtain a mixed solution a; (2) dissolving the MOF material in a second organic solvent to obtain a mixed solution b; (3) mixing the lithium salt and the ionic liquid to obtain a mixed solution c; (4) mixing the mixed solution a and the mixed solution b uniformly, and then adding the mixed solution c and continuing to mix uniformly to obtain a mixed solution d; (5) casting the mixed solution d obtained in step (4) on a substrate and drying it to obtain the solid electrolyte composite film; Among them, the mass ratio of metal organic framework material to polymer is 1:2~4.

2. The method for preparing a MOF-based solid electrolyte composite membrane according to claim 1, characterized in that: The polymer is at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, and polyacrylonitrile.

3. The method for preparing the MOF-based solid electrolyte composite membrane according to claim 1, characterized in that: The MOF material is a porous structure material formed by the coordination of at least one metal ion or metal ion cluster and an organic ligand; The metal ions include Mg 2+ 、Al 3+ , Ca 2+ 、Ti 4+ 、V 4+ 、V 3+ 、V 2+ Cr 3+ , Mn 3+ , Mn 2+ , Fe 3+ , Fe 2+ 、Co 3+ 、Co 2+ 、Ni 2+ 、Ni + , Cu 2+ , Cu + 、Zn 2+ , Ga 3+ ,Ge 4+ ,Ge 2+ 、As 5+ 、As 3+ 、As + , Y 3+ 、Zr 4+ 、Mo 3+ , Pd 2+ , Pd + , Pt 2+ , Pt + 、Ag + 、Cd 2+ 、In 3+ ,La 3+ 、Ce 4+ 、Ce 3+ , Hf 4+ One or more of; The organic ligands include terephthalic acid, 2-methylimidazole, benzene-1,2,4,5-tetracarboxylic acid, 5-nitroisophthalic acid, isophthalic acid, nicotinic acid, 3-nitrophthalic acid, imidazole, 5-aminoisophthalic acid, isonicotinic acid, 1,3,5-tricarboxylic acid benzene, 2,3-pyridinedicarboxylic acid, 2,2'-bipyridine, 1,4-cyclohexanedicarboxylic acid, thiophene-2,5-dicarboxylic acid, pyrazine, butynedioic acid, [1,1'-biphenyl]-4-carboxylic acid, trans-1,4-cyclohexanedicarboxylic acid, cis-1,2 Cyclohexanedicarboxylic acid, 2,3,5,6-tetrafluoroterephthalic acid, 2-nitroterephthalic acid, pyrazine-2,3-dicarboxylic acid, 4,4'-biphenyldicarboxylic acid, fumaric acid, 3,4-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 4-aminobiphenyldicarboxylic acid, salicylic acid azine, 1H-imidazole-4,5-dicarboxylic acid, 1H-pyrazole-3,5-dicarboxylic acid hydrate, 4,4'-bipyridine, 3,6-di-2-pyridyl-1,2,4,5-tetrazine, 2,5-dibromoterephthalic acid, 2,5- dichlorobenzoic acid, trans-1,2-cyclohexanedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, (1R,2R)-1,2-cyclohexanedicarboxylic acid, 2,2'-biphenyldicarboxylic acid, 3,5-pyridinedicarboxylic acid, trimellitic acid, naphthalene-1,4-dicarboxylic acid, 4-hydroxyphthalic acid, 2,5-dihydroxyterephthalic acid, 5-hydroxyisophthalic acid, 1,4-phenylenedicarboxylic acid, 4-carboxyphenylacetic acid, 2-aminoterephthalic acid, cyclohexane-1,3-dicarboxylic acid, cis-1,4-cyclohexanedicarboxylic acid, 2 , 6-naphthalene dicarboxylic acid, cyclohexane-1,2,4,5-tetracarboxylic acid, 2-bromoterephthalic acid, 9-anthracenecarboxylic acid, 1,4-dibromo-2,5-diiodobenzene, 4,4′-dimethoxy-1,1′-biphenyl, 1-ethyl-2-methylquinolin-1-ium iodide, 1-ethyl-3-vinylimidazolium bromide, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, iron phthalocyanine, 1,3-dibromo-5-(tert-butyl)benzene, tetrafluorophthalic acid, tetrachlorophthalic acid hemihydrate; The particle size of the MOF material is 2-500 nm; the pore size of the MOFs material is 0.1-50 nm.

4. The method for preparing a MOF-based solid electrolyte composite membrane according to claim 1, characterized in that: The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonyl imide, and lithium bis(oxalatoborate); The ionic liquid is an imidazole or pyridine ionic liquid, The ionic liquid is at least one of the following: 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium dicyanamide, propylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-methylimidazolium chloride.

5. The method for preparing the MOF-based solid electrolyte composite membrane according to claim 1, characterized in that: The first organic solvent and the second organic solvent are both N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone, chloroform, dichloromethane, acetonitrile, dimethyl sulfoxide or acetone.

6. The method for preparing a MOF-based solid electrolyte composite membrane according to claim 1, characterized in that: The concentration of the polymer in the mixed solution a is 3wt% to 25wt%; the concentration of the MOF material in the mixed solution b is 5wt% to 15wt%; The concentration of lithium salt in the mixed solution c is 1-3 mol L -1 .

7. The method for preparing a MOF-based solid electrolyte composite membrane according to claim 1, characterized in that: In step (4), the amount of the mixed solution c added is calculated based on the lithium salt, and the mass of the lithium salt accounts for 10%-30% of the mass of the polymer.

8. The method for preparing the MOF-based solid electrolyte composite membrane according to claim 1, characterized in that: In step (5), the thickness of the mixed solution d cast on the substrate is 200 to 400 μm; after drying, the thickness of the MOF-based solid electrolyte composite membrane is less than 50 μm.

9. A MOF-based solid electrolyte composite membrane prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the MOF-based solid electrolyte composite membrane according to claim 9 in the preparation of solid-state or semi-solid-state lithium metal batteries.

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