Sulfonyl ZIF-8 metal organic framework material, lithium-sulfur battery diaphragm and preparation method of lithium-sulfur battery diaphragm

Abstract

The invention relates to the technical field of lithium-sulfur batteries, and discloses a sulfonyl ZIF-8 metal organic framework material, a lithium-sulfur battery diaphragm and a preparation method of the lithium-sulfur battery diaphragm. The preparation method of the sulfonyl ZIF-8 metal organic framework material comprises the following steps: dissolving a metal precursor and a mixed ligand in an organic solvent, and carrying out a coordination reaction under the action of organic alkali; solid is collected, washed and dried, and the sulfonic group ZIF-8 metal organic framework material is obtained. The metal precursor is soluble zinc salt; the mixed ligand comprises 2-methylimidazole and an imidazole derivative containing a sulfonic acid group. The sulfo group ZIF-8 metal organic framework material is prepared through a ligand doping strategy and is used for functional modification of the lithium-sulfur battery diaphragm; the shuttle behavior of lithium polysulfide (LiPS) can be effectively inhibited through the electrostatic repulsion effect of sulfonic acid groups and the synergistic effect of high-polarity adsorption sites; and the migration of Li < + > and the conversion efficiency of LiPS are remarkably promoted by an efficient ion transmission network, so that the cycle performance of the lithium-sulfur battery is improved.

Description

Technical Field

[0001] This application relates to the technical field of lithium-sulfur batteries, and specifically relates to a sulfonic acid-based ZIF-8 metal-organic framework material, a lithium-sulfur battery separator, and a preparation method thereof. Background Art

[0002] With the rapid development of portable electronic devices and electric vehicles, the demand for high-energy-density, long-cycle-life, and low-cost energy storage systems is becoming increasingly urgent. Lithium-sulfur (Li-S) batteries, with a theoretical energy density of up to 2600 Wh / kg, abundant and environmentally friendly sulfur-based cathode materials, etc., are regarded as strong competitors for the next-generation energy storage systems. However, the practical application of Li-S batteries still faces many challenges, among which the "shuttle effect" of polysulfides (LiPS) is the key bottleneck restricting the performance improvement. Polysulfides dissolve in the electrolyte during charge and discharge and migrate between the positive and negative electrodes, resulting in the loss of active materials, capacity decay, and reduced Coulomb efficiency.

[0003] To suppress the polysulfide shuttle, researchers have proposed various strategies, including cathode material modification, electrolyte additives, and separator functionalization, etc. Among them, separator functionalization has attracted much attention due to its simplicity and effectiveness. Traditional commercial polyolefin separators (such as polyethylene and polypropylene) usually have poor thermal stability, poor electrolyte wettability, and their micron-sized pore diameters (>100 nm) cannot effectively block the migration of polysulfides. Metal-organic framework materials (MOFs) show great potential in the modification of Li-S battery separators due to their high specific surface area, adjustable pore size, and rich surface chemical properties. As an important member of the MOF family, zeolitic imidazolate framework materials (ZIFs) have both excellent chemical stability and thermal stability, making them ideal candidate materials for separator modification.

[0004] In recent years, there have been studies attempting to apply ZIFs materials to Li-S battery separators to utilize their porous structure and surface chemical properties to suppress the polysulfide shuttle. However, traditional ZIFs materials have limited adsorption capacity for polysulfides and are difficult to meet the requirements of high-performance Li-S batteries.

[0005] Based on this, there is an urgent need to develop new ZIFs materials to enhance the adsorption and catalytic conversion ability of Li-S battery separators for polysulfides. Summary of the Invention

[0006] This application provides a sulfonic acid-based ZIF-8 metal-organic framework material, a lithium-sulfur battery separator, and a preparation method thereof, aiming to solve the technical problem that the existing Li-S battery separator has low adsorption and catalytic conversion ability for polysulfides and is difficult to solve the "shuttle effect" of LiPS during the operation of lithium-sulfur batteries.

[0007] To achieve the above object, the present application adopts the following technical solutions for implementation.

[0008] In the first aspect of the present application, a preparation method of a sulfonic acid group ZIF-8 metal-organic framework material is provided, including:

[0009] Dissolve a metal precursor and a mixed ligand in an organic solvent, and carry out a coordination reaction under the action of an organic base; collect the solid, wash and dry it to obtain the sulfonic acid group ZIF-8 metal-organic framework material;

[0010] The metal precursor is a soluble zinc salt;

[0011] The mixed ligand includes 2-methylimidazole and an imidazole derivative containing a sulfonic acid group.

[0012] Preferably, the imidazole derivative containing a sulfonic acid group includes an imidazole or substituted imidazole containing a sulfonic acid group, and a benzimidazole or its derivative containing a sulfonic acid group.

[0013] More preferably, the imidazole derivative containing a sulfonic acid group includes any one of the following compounds:

[0014]

[0015] Preferably, the soluble zinc salt is zinc nitrate hexahydrate or zinc acetate;

[0016] And / or,

[0017] The organic base includes triethylamine or pyridine;

[0018] And / or,

[0019] The organic solvent is at least one of methanol or N,N-dimethylformamide.

[0020] Preferably, the molar ratio of the metal precursor to the mixed ligand is 1:(5-7);

[0021] And / or,

[0022] In the mixed ligand, the molar ratio of the imidazole derivative containing a sulfonic acid group to 2-methylimidazole is 1:(1.5-19);

[0023] And / or,

[0024] The molar ratio of the organic base to the imidazole derivative containing a sulfonic acid group is 1:(3-6).

[0025] In the second aspect of the present application, a sulfonic acid group ZIF-8 metal-organic framework material prepared by the above preparation method is provided.

[0026] In the third aspect of the present application, a lithium-sulfur battery separator is provided, which is prepared by the following method:

[0027] Disperse the above-mentioned sulfonic acid group ZIF-8 metal-organic framework material, conductive agent and binder in N-methylpyrrolidone, and mix them evenly by ball milling and stirring to obtain a modified slurry;

[0028] Uniformly coat the modified slurry on the surface of the PP separator, and form a modified coating on the surface of the PP separator by drying to obtain a lithium-sulfur battery separator.

[0029] Preferably, the mass ratio of the ZIF-8 metal-organic framework material to the conductive agent is 1:(1-9); the mass of the binder accounts for 10% of the mass of the modified slurry;

[0030] The conductive agent includes any one of SuperP, acetylene black or carbon nanotubes;

[0031] The binder includes polyvinylidene fluoride or sodium carboxymethyl cellulose.

[0032] Preferably, the thickness of the PP separator is 20-30 μm;

[0033] The thickness of the modified coating is 3.5-4.5 μm.

[0034] In the fourth aspect of the present application, a lithium-sulfur battery is provided, and its separator is the above-mentioned lithium-sulfur battery separator.

[0035] Compared with the prior art, the beneficial effects of the present application are as follows:

[0036] In the present application, the sulfonic acid group ZIF-8 metal-organic framework material is prepared by a ligand doping strategy and is used for the functional modification of the lithium-sulfur battery separator. On the one hand, the electrostatic repulsion of the sulfonic acid group and the synergistic effect of the high-polarity adsorption sites can effectively inhibit the shuttle behavior of LiPS; on the other hand, the efficient ion transport network formed by the sulfonic acid group ZIF-8 metal-organic framework material significantly promotes the migration of Li + and the conversion efficiency of LiPS, thereby improving the performance of the lithium-sulfur battery.

[0037] The lithium-sulfur battery using the lithium-sulfur battery separator of the present application has high cycle stability; its initial discharge specific capacity reaches 972.6 mAh g-1 at a rate of 1C, and still maintains a reversible capacity of 699.5 mAh g-1 after 300 complete charge and discharge cycles. Description of the Drawings

[0038] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments described in the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0039] Figure 1 SEM image of ZIF-8-SO3H(1) prepared in Example 1;

[0040] Figure 2 XRD patterns of ZIF-8-SO3H(1) prepared in Example 1 and ZIF-8 prepared in Comparative Example 2;

[0041] Figure 3 FT-IR spectra of ZIF-8-SO3H(1) prepared in Example 1 and ZIF-8 prepared in Comparative Example 2;

[0042] Figure 4 Digital photo images of the ZIF-8-SO3H(1)@PP separator prepared in Example 1 and a commercial PP separator;

[0043] Figure 5 SEM image of the ZIF-8-SO3H(1)@PP separator prepared in Example 1;

[0044] Figure 6 Wettability test images of the ZIF-8-SO3H(1)@PP separator prepared in Example 1 and a commercial PP separator for the electrolyte;

[0045] Figure 7 Cycling performance graph of the lithium-sulfur battery assembled with the separators of the embodiments and comparative examples of the present application. Detailed implementation manners

[0046] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0047] In the following description of this embodiment, terms such as "including", "comprising", "having", and "containing" are all open-ended terms, that is, they are intended to include but not be limited to.

[0048] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: the case where A exists alone, the case where B exists alone, and the case where A and B exist simultaneously. Here, A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0049] In the following description of this embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or its similar expressions refer to any combination of these items, including any combination of single item(s) or plural item(s). For example, "at least one of a, b or c", or, "at least one of a, b and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or plural respectively.

[0050] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0051] Those skilled in the art should understand that in the following description of the embodiments of this application, the sequence numbers do not imply the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic and should not constitute any limitation to the implementation process of the embodiments of this application.

[0052] Those skilled in the art should understand that the numerical ranges in the embodiments of this application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in this application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0053] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0054] In a first aspect, the present application provides a method for preparing a sulfonic acid group ZIF-8 metal-organic framework material, comprising:

[0055] Dissolving a metal precursor and a mixed ligand in an organic solvent, and carrying out a coordination reaction under the action of an organic base; collecting the solid, washing and drying to obtain the sulfonic acid group ZIF-8 metal-organic framework material;

[0056] The metal precursor is a soluble zinc salt;

[0057] The mixed ligand includes 2-methylimidazole and an imidazole derivative containing a sulfonic acid group.

[0058] In the present application, through a ligand doping strategy, a zinc-based metal precursor is coordinated with 2-methylimidazole and an imidazole derivative containing a sulfonic acid group. The reaction solution is centrifuged to collect the solid, washed with anhydrous methanol, and then vacuum dried at 80-100 °C to obtain the metal-organic framework material ZIF-8-SO3H with a sulfonic acid group.

[0059] Among them, the imidazole derivative containing a sulfonic acid group is imidazole containing a sulfonic acid group; or a substituted imidazole containing a sulfonic acid group, such as a methyl-substituted imidazole containing a sulfonic acid group;

[0060] Alternatively, the imidazole derivative containing a sulfonic acid group is benzimidazole containing a sulfonic acid group, or a benzimidazole derivative containing a sulfonic acid group.

[0061] As a preferred embodiment of the present application, the imidazole derivative containing a sulfonic acid group includes any one of the following compounds:

[0062]

[0063]

[0064] In the present application, the soluble zinc salt is zinc nitrate hexahydrate or zinc acetate.

[0065] In the present application, the organic base is used to promote the coordination reaction between the zinc salt and the imidazole compound; the organic base is preferably triethylamine or pyridine.

[0066] In the present application, the organic solvent is methanol or N,N-dimethylformamide, or a mixed solvent of methanol and N,N-dimethylformamide.

[0067] In the present application, in order to achieve a better coordination effect, the molar ratio of the metal precursor to the mixed ligand is 1:(5-7); among them, the molar ratio of the imidazole derivative containing a sulfonic acid group to 2-methylimidazole in the mixed ligand is 1:(1.5-19). The molar ratio of the organic base to the imidazole derivative containing a sulfonic acid group is 1:(3-6).

[0068] The sulfonic acid group ZIF-8 metal-organic framework material prepared by the ligand doping strategy in this application, the electrostatic repulsion of its sulfonic acid groups and the synergistic effect of high-polarity adsorption sites can effectively inhibit the shuttle behavior of LiPS; on the other hand, the efficient ion transport network formed by the sulfonic acid group ZIF-8 metal-organic framework material significantly promotes the migration of Li + and the conversion efficiency of LiPS, thereby improving the performance of the lithium-sulfur battery.

[0069] This application also provides a separator for a lithium-sulfur battery, which is prepared by the following method:

[0070] Disperse the above-mentioned sulfonic acid group ZIF-8 metal-organic framework material, conductive agent and binder in N-methylpyrrolidone, and mix them evenly by ball milling and stirring to obtain a modified slurry;

[0071] Uniformly coat the modified slurry on the surface of the PP separator, and form a modified coating on the surface of the PP separator by drying to obtain the lithium-sulfur battery separator ZIF-8-SO3H@PP.

[0072] In this application, the mass ratio of the ZIF-8 metal-organic framework material to the conductive agent is 1:(1-9); the mass of the binder accounts for 10% of the mass of the modified slurry. Among them, the conductive agent includes any one of SuperP, acetylene black or carbon nanotubes; the binder includes polyvinylidene fluoride or sodium carboxymethyl cellulose.

[0073] In this application, in order to achieve better technical effects, it is preferred that the thickness of the PP separator is 20-30 μm;

[0074] The thickness of the modified coating is 3.5-4.5 μm.

[0075] This application also provides a lithium-sulfur battery, the separator of which is the above-mentioned lithium-sulfur battery separator; its positive electrode, negative electrode and electrolyte are not limited, and conventional positive electrodes, negative electrodes and electrolytes of lithium-sulfur batteries can be used.

[0076] For a lithium-sulfur battery using the lithium-sulfur battery separator of this application, it can effectively inhibit the shuttle behavior of LiPS, and its efficient ion transport network significantly promotes the migration of Li + and the conversion efficiency of LiPS, and further makes the lithium-sulfur battery of this application have high cycle stability. Its initial discharge specific capacity reaches 972.6 mAh g-1 at a rate of 1C, and still maintains a reversible capacity of 699.5 mAh g-1 after 300 complete charge and discharge cycles.

[0077] The following further illustrates this application through examples.

[0078] Example 1

[0079] This application provides a preparation method of a sulfonic acid group ZIF-8 metal-organic framework material and a lithium-sulfur battery separator, including:

[0080] Weigh 3.9 mmol of zinc nitrate hexahydrate and dissolve it in 40 ml of anhydrous methanol to obtain solution A; dissolve 24.85 mmol of 2-methylimidazole, 5.7 mmol of 2-phenylbenzimidazole-5-sulfonic acid, and 370 μL of triethylamine in 40 mL of N,N-dimethylformamide to obtain solution B;

[0081] Among them, the chemical structure of 2-phenylbenzimidazole-5-sulfonic acid is:

[0082]

[0083] Mix solution A and solution B, stir at room temperature for 2 h, centrifuge the obtained milky white solution, collect the solid phase, wash it 3 times with anhydrous methanol, and then vacuum dry it at 80 °C for 24 h to obtain the sulfonic acid group ZIF-8 metal-organic framework material, denoted as ZIF-8-SO3H(1);

[0084] Disperse 0.6 g of ZIF-8-SO3H(1), 0.3 g of SuperP, and 0.1 g of polyvinylidene fluoride in 10 mL of N-methylpyrrolidone, and ball mill and stir for 5 h to mix the solution evenly to obtain a modified slurry;

[0085] Select a dry and clean commercial polypropylene separator (with a thickness of 25 μm), take the above-mentioned modified slurry, and evenly coat it on the commercial polypropylene separator using a 20-μm blade on an automatic coater, and vacuum dry it at 80 °C overnight to obtain a lithium-sulfur battery separator, denoted as ZIF-8-SO3H(1)@PP.

[0086] Example 2

[0087] This application provides a preparation method of a sulfonic acid group ZIF-8 metal-organic framework material and a lithium-sulfur battery separator, including:

[0088] Weigh 3.9 mmol of zinc nitrate hexahydrate and dissolve it in 40 ml of anhydrous methanol to obtain solution A; dissolve 16.6 mmol of 2-methylimidazole, 11 mmol of 2-methylimidazole-4-sulfonic acid, and 300 μL of triethylamine in 40 mL of N,N-dimethylformamide to obtain solution B;

[0089] Among them, the chemical structure of 2-methylimidazole-4-sulfonic acid is:

[0090]

[0091] Mix solution A and solution B, stir for 2 h at room temperature, centrifuge the resulting milky solution, collect the solid phase, wash it 3 times with anhydrous methanol, and then vacuum dry it at 80 °C for 24 h to obtain a sulfonic acid group ZIF-8 metal-organic framework material, denoted as ZIF-8-SO3H(2).

[0092] Disperse 0.5 g of ZIF-8-SO3H(2), 0.4 g of SuperP, and 0.1 g of polyvinylidene fluoride in 10 mL of N-methylpyrrolidone, and stir by ball milling for 5 h to uniformly mix the solution to obtain a modified slurry.

[0093] Select a dry and clean commercial polypropylene separator (with a thickness of 25 μm), take the above-mentioned modified slurry, and uniformly coat it on the commercial polypropylene separator using a 20-μm blade on an automatic coater, and vacuum dry it at 80 °C overnight to obtain a lithium-sulfur battery separator, denoted as ZIF-8-SO3H(2)@PP.

[0094] Example 3

[0095] This application provides a preparation method for a sulfonic acid group ZIF-8 metal-organic framework material and a lithium-sulfur battery separator, including:

[0096] Weigh 3.9 mmol of zinc nitrate hexahydrate and dissolve it in 40 ml of anhydrous methanol to obtain solution A; dissolve 19.3 mmol of 2-methylimidazole, 8.3 mmol of 1H-benzoimidazole-2-sulfonic acid, and 320 μL of triethylamine in 40 mL of N,N-dimethylformamide to obtain solution B;

[0097] Among them, the chemical structure of 1H-benzoimidazole-2-sulfonic acid is:

[0098]

[0099] Mix solution A and solution B, stir for 2 h at room temperature, centrifuge the resulting milky solution, collect the solid phase, wash it 3 times with anhydrous methanol, and then vacuum dry it at 80 °C for 24 h to obtain a sulfonic acid group ZIF-8 metal-organic framework material, denoted as ZIF-8-SO3H(3);

[0100] Disperse 0.2 g of ZIF-8-SO3H(3), 0.7 g of SuperP, and 0.1 g of polyvinylidene fluoride in 10 mL of N-methylpyrrolidone, and stir by ball milling for 5 h to uniformly mix the solution to obtain a modified slurry.

[0101] Select a dry and clean commercial polypropylene separator (with a thickness of 25 μm), take the above-mentioned modified slurry, and uniformly coat it on the commercial polypropylene separator using a 20-μm blade on an automatic coater, and vacuum dry it at 80 °C overnight to obtain a lithium-sulfur battery separator, denoted as ZIF-8-SO3H(3)@PP.

[0102] Comparative Example 1

[0103] Commercial polypropylene separator

[0104] Comparative Example 2

[0105] Weigh 3.9 mmol of zinc nitrate hexahydrate and dissolve it in 40 ml of anhydrous methanol to obtain solution A; dissolve 27.6 mmol of 2-methylimidazole in 40 mL of N,N-dimethylformamide to obtain solution B;

[0106] Mix solution A and solution B, stir at room temperature for 2 h, centrifuge the obtained milky white solution, collect the solid phase, wash it 3 times with anhydrous methanol, and then dry it in vacuum at 80 °C for 24 h to obtain ZIF-8;

[0107] Disperse 0.2 g of ZIF-8, 0.7 g of SuperP and 0.1 g of polyvinylidene fluoride in 10 mL of N-methylpyrrolidone, and stir by ball milling for 5 h to mix the solution evenly to obtain a modified slurry;

[0108] Select a dry and clean commercial polypropylene separator (thickness 25 μm), take the above-mentioned modified slurry, and evenly coat it on the commercial polypropylene separator with a 20-μm doctor blade on an automatic coater, and dry it in vacuum at 80 °C overnight to obtain a separator, denoted as ZIF-8@PP.

[0109] The sulfonic acid group ZIF-8 metal-organic framework material ZIF-8-SO3H(1) prepared in Example 1 was structurally characterized, and its SEM image is as Figure 1 shown. From Figure 1 it can be seen that ZIF-8-SO3H(1) presents a rhombic dodecahedron, and the average particle size is about 96 nm.

[0110] The XRD patterns of ZIF-8-SO3H(1) and ZIF-8 in Comparative Example 2 are as Figure 2 shown. From Figure 2 it can be seen that the spectrum of ZIF-8-SO3H(1) is similar to that of ZIF-8, indicating that the doping of 2-phenylbenzimidazole-5-sulfonic acid maintains the structural integrity of ZIF-8 and does not cause lattice distortion. However, the relative intensity of the diffraction peaks of ZIF-8-SO3H is significantly enhanced, especially in the small-angle region, indicating that the crystallinity of the material has been improved after doping with 2-phenylbenzimidazole-5-sulfonic acid.

[0111] The chemical structure of ZIF-8-SO3H(1) was characterized by Fourier transform infrared spectroscopy (FT-IR), and its spectrum is as Figure 3 shown. From Figure 3 it can be seen that at 1084 cm -1 and 1027 cm-1 The characteristic absorption bands observed at [specific position] can be attributed to the asymmetric and symmetric stretching vibration characteristics of the S=O bond in the sulfonic acid group, and the absorption peak at 635 cm -1 corresponds to the in-plane bending vibration of the sulfonic acid group. It should be noted that the strong and broad peak appearing at 3424 cm -1 clearly corresponds to the stretching vibration of the hydroxyl group (-OH) in the sulfonic acid group (-SO3H), which provides direct evidence for the successful anchoring of the imidazole derivative containing the sulfonic acid group to the ZIF-8 framework. In particular, the characteristic peak of the C=N stretching vibration maintained at 1585 cm-1 confirms that the modified material effectively retains the original coordination framework of ZIF-8.

[0112] The lithium-sulfur battery separator prepared in this application was characterized, and its physical picture is as Figure 4 shown. Figure 4 In Figure a and Figure b in [reference], they are digital photos of the lithium-sulfur battery separator ZIF-8-SO3H(1)@PP prepared in Example 1, and Figure c is a digital photo of the commercial PP film in Comparative Example 1. From Figure 4 it can be seen that the ZIF-8-SO3H(1) layer forms a continuous coverage on the surface of the PP substrate.

[0113] The lithium-sulfur battery separator ZIF-8-SO3H(1)@PP in Example 1 was subjected to SEM testing to characterize its morphology, and the results are as Figure 5 shown. Among them, Figure 5 Figure a in [reference] is the SEM image of the surface of the ZIF-8-SO3H(1)@PP separator; Figure 5 Figure b in [reference] is the SEM image of the cross-section of the ZIF-8-SO3H(1)@PP separator. From Figure 5 it can be seen that the ZIF-8-SO3H(1) particles are evenly dispersed on the PP substrate, and SEM cross-section analysis shows that the coating has a uniform thickness of 4 μm.

[0114] The wettability of the lithium-sulfur battery separator ZIF-8-SO3H(1)@PP in Example 1 and the commercial PP film in Comparative Example 1 with respect to the electrolyte (DOL / DME) was tested, and the results are as Figure 6 shown. Among them, Figure 6 Figure a in [reference] is the contact angle of the ZIF-8-SO3H(1)@PP separator with respect to the electrolyte, and Figure b is the contact angle of the commercial PP separator with respect to the electrolyte. The surface of ZIF-8-SO3H(1)@PP exhibits super-liquidophilic characteristics with respect to the electrolyte (DOL / DME), and the contact angle is 9.1°, which is significantly lower than the contact angle of 21.3° of the commercial PP film, indicating that the modified separator of this application has better electrolyte wetting ability.

[0115] The lithium-sulfur batteries were assembled using the separators prepared in Examples 1-3, the commercial PP membrane of Comparative Example 1, and the separator of Comparative Example 2, and the cycle performance of the lithium-sulfur batteries was evaluated. The specific method is as follows:

[0116] The above-mentioned separators were respectively cut into circular pieces with a mold, and CR2032 coin cells were assembled with the positive electrode, negative electrode, and electrolyte in a glove box filled with argon, and the moisture and oxygen contents were both controlled below 1 ppm. Among them, 15 μL of 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) (1 / 1, v / v) with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt% LiNO3 were used as the electrolyte; carbon nanotubes (CNT, 15 wt%) and sulfur powder (60 wt%) were uniformly mixed and placed in a polytetrafluoroethylene container, and heated at about 155 °C for 24 h to promote the molten penetration of sulfur to obtain S / CNT; a slurry containing 75 wt% S / CNT, 15 wt% SuperP, and 10 wt% PVDF was uniformly coated on the surface of the aluminum foil, and the sulfur loading of the obtained positive electrode was about 1.2 mg cm-2; the negative electrode used a lithium foil.

[0117] The cycle performance of the above-mentioned lithium-sulfur batteries was respectively tested at a 1C rate, and the test results are as Figure 7 shown. It can be seen from Figure 7 the figure that the initial discharge specific capacities of the ZIF-8-SO3H@PP(1), ZIF-8-SO3H@PP(2), and ZIF-8-SO3H@PP(3) systems reached 972.6, 982.0, and 927.7 mAh g-1, and still maintained reversible capacities of 699.5, 698.0, and 638.7 mAh g-1 after 300 complete charge-discharge cycles. In the comparison group, the ZIF-8@PP and PP systems showed relatively fast capacity decay trends, with initial discharge capacities of 818.6 and 557.7 mAh g-1 respectively, and the capacities decreased to 365.9 and 259.3 mAh g-1 after cycling. The test results show that the lithium-sulfur battery separator prepared in this application can greatly improve the cycle stability of the lithium-sulfur battery.

[0118] Although this application has been described in detail with general descriptions and specific embodiments in this specification, based on this application, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of this application all fall within the scope of protection required by this application.

Claims

1. A preparation method of a sulfonic acid group ZIF-8 metal-organic framework material, characterized in that, Comprising: Dissolve a metal precursor and a mixed ligand in an organic solvent and carry out a coordination reaction under the action of an organic base; Collect the solid, wash and dry it to obtain the sulfonic acid group ZIF-8 metal-organic framework material; The metal precursor is a soluble zinc salt; The mixed ligand includes 2-methylimidazole and an imidazole derivative containing a sulfonic acid group.

2. The preparation method according to claim 1, wherein The imidazole derivative containing a sulfonic acid group includes an imidazole or substituted imidazole containing a sulfonic acid group, and a benzimidazole or its derivative containing a sulfonic acid group.

3. The preparation method according to claim 2, characterized in that, The imidazole derivative containing a sulfonic acid group includes any one of the following compounds:

4. The preparation method according to claim 1, characterized in that, The soluble zinc salt is zinc nitrate hexahydrate or zinc acetate; And / or, The organic base includes triethylamine or pyridine; And / or, The organic solvent is at least one of methanol or N,N-dimethylformamide.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the metal precursor to the mixed ligand is 1:(5-7); And / or, In the mixed ligand, the molar ratio of the imidazole derivative containing a sulfonic acid group to 2-methylimidazole is 1:(1.5-19); And / or, The molar ratio of the organic base to the imidazole derivative containing a sulfonic acid group is 1:(3-6).

6. The sulfonic acid group ZIF-8 metal-organic framework material prepared by the preparation method according to any one of claims 1-5.

7. A lithium-sulfur battery separator, characterized in that It is prepared by the following method: Disperse the sulfonic acid group ZIF-8 metal-organic framework material, a conductive agent and a binder according to claim 6 in N-methylpyrrolidone, and mix them evenly by ball milling and stirring to obtain a modified slurry; Uniformly coat the modified slurry on the surface of the PP separator, and dry it to form a modified coating on the surface of the PP separator to obtain a lithium-sulfur battery separator.

8. The lithium-sulfur battery separator according to claim 7, wherein The mass ratio of the ZIF-8 metal-organic framework material to the conductive agent is 1:(1-9); the mass of the binder accounts for 10% of the mass of the modified slurry; The conductive agent includes any one of SuperP, acetylene black or carbon nanotubes; The binder includes polyvinylidene fluoride or sodium carboxymethylcellulose.

9. The lithium-sulfur battery separator according to claim 7, characterized in that, The thickness of the PP separator is 20-30 μm; The thickness of the modified coating is 3.5-4.5 μm.

10. A lithium-sulfur battery, characterized in that, The separator is the lithium-sulfur battery separator according to claim 7.

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