A modified lithium-sulfur battery separator for regulating the pore structure of nitrogen-azole-type MOFs, and its preparation method and application

Abstract

The present invention belongs to the technical field of lithium-sulfur battery separator modification, specifically relating to a modified lithium-sulfur battery separator that regulates the pore structure of nitrogen-azole-type MOFs, as well as its preparation method and application. The preparation process includes: reacting raw materials such as 5-aminotetrazole and biphenyldicarboxylic acid to form pale yellow crystals; mixing the crystals with a binder and conductive carbon black, and then adding a specific solution to form a slurry; and finally, producing the separator by a coating method. This separator promotes lithium ion transport and inhibits polysulfide shuttling, effectively increasing the active utilization rate of elemental sulfur and the battery's energy storage density. It forms an interface that both blocks lithium polysulfide shuttling and promotes lithium ion migration, thereby improving battery performance and cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur battery diaphragm modification, and specifically relates to a modified lithium-sulfur battery diaphragm for regulating the pore structure of nitrogen-azole-type MOFs, and a preparation method and application thereof. Background Art

[0002] With the rapid development of renewable energy and the growth of the electric vehicle market, the demand for high-energy-density, low-cost, and environmentally friendly battery technologies is increasing. Lithium-sulfur batteries, due to their extremely high theoretical energy density (approximately 2600Wh·kg1), are considered an important candidate for next-generation energy storage technology.

[0003] Lithium-sulfur batteries (LiS batteries) are a new type of battery with the potential for high energy density and low cost. However, in practical applications, the battery's cycling durability and energy efficiency are severely impaired by the shuttling problem of lithium polysulfides (LiPS) and the slow reaction process. LiPS easily dissolve in the electrolyte and shuttle between the positive and negative electrodes during charge and discharge, causing capacity fading and short-circuit risks. Researchers have been exploring various strategies to address these challenges, such as using nanostructured sulfur composites, designing advanced electrolytes and separators, and improving cathode materials.

[0004] The separator plays a key role in lithium-sulfur batteries, isolating the positive and negative electrodes and transferring lithium ions. By optimizing the separator design and material selection, the shuttling of polysulfides can be effectively reduced. Metal-organic frameworks (MOFSs) have come into the spotlight due to their controllable structure and adjustable pore size. Using MOFS materials to improve the separators of lithium-sulfur batteries, the shuttling effect can be suppressed by physically confining or chemically adsorbing lithium polysulfides, catalyzing their conversion, and other methods, thereby improving battery stability and safety. This opens new possibilities for the research and application of lithium-sulfur batteries. MOFs can be used as sulfur host materials, additives to electrode materials, or to construct solid-state electrolytes to improve the cycling stability and energy density of lithium-sulfur batteries. The pore structure of MOFs can provide sufficient storage space for sulfur, while their surface functional groups can form strong interactions with sulfur or polysulfides, improving sulfur utilization.

[0005] Application number 202311403058.6 discloses a "method for preparing lithium-sulfur batteries based on iodine-based metal-organic framework-modified diaphragm coatings." The hydrothermal method synthesizes iodine-based metal-organic framework materials to prepare lithium-sulfur battery diaphragms, promoting lithium ion transport and inhibiting the growth of lithium dendrites. However, the remaining issues are: the charge transfer rate at the catalyst interface is not ideal, the chemical bonds formed by the selected material ligands with the sulfur atoms in the polysulfide are not stable enough, and the dissolution and migration of polysulfides in the electrolyte cannot be completely resolved. Summary of the Invention

[0006] The present invention provides a modified lithium-sulfur battery separator for regulating the pore structure of nitrogen-azole-type MOFs, and a preparation method and application thereof, so as to solve the problems in the prior art of the inability to improve the polysulfide shuttle, which is a fatal problem for lithium-sulfur batteries, and the unsatisfactory battery performance.

[0007] To achieve the above-mentioned object, the technical solution adopted by the present invention is: a method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs, comprising the following steps:

[0008] Step 1: Weigh 5-aminotetrazole and biphenyldicarboxylic acid and place them in a polytetrafluoroethylene reactor, add a mixed solution of methanol and N,N-dimethylformamide, stir at room temperature until the solution is uniform and transparent, add zinc salt solid and continue stirring, add tetramethylammonium hydroxide after the solid is completely dissolved, place in the reactor to react, cool to room temperature, take out, wash with methanol, and then dry to obtain a light yellow crystalline material;

[0009] Step 2: Finely grind and uniformly mix the light yellow crystalline material obtained in step 1 with a binder and conductive carbon black, then gradually add N-methylpyrrolidone solution and continue stirring to form a viscous slurry;

[0010] Step 3: Use a coating method to evenly apply the slurry prepared in step 2 on the surface of the PP diaphragm, and then place the diaphragm in a vacuum drying oven to dry to obtain a diaphragm with a uniform surface.

[0011] Furthermore, in the above step 1, the molar ratio of 5-aminotetrazole to biphenyldicarboxylic acid is 1:1, and the volume ratio of methanol to N,N-dimethylformamide solution is 1:1.

[0012] Furthermore, the zinc salt in the above step 1 is zinc nitrate hexahydrate, zinc acetate or zinc chloride.

[0013] Furthermore, the conductive carbon black in the above step 2 is Ketjen black, Super P or acetylene black, and the binder is polyvinylidene fluoride, polyvinyl alcohol or polyacrylic acid.

[0014] Furthermore, the coating thickness in the above step 3 is 50 to 150 nm.

[0015] Furthermore, in the above step 3, the vacuum drying temperature is 50° C. to 70° C. and the time is not less than 6 hours.

[0016] Furthermore, the battery separator prepared by the above preparation method.

[0017] Furthermore, the above battery separator is used in lithium-sulfur batteries.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) The present invention prepares a hybrid zeolite material by a hydrothermal method, adds aminotetrazole and biphenyldicarboxylic acid ligands to form layered columnar crystals with a large pore size, and prepares a functional diaphragm for application in lithium-sulfur batteries. It can promote the transfer of lithium ions, inhibit the shuttling of polysulfides, stabilize the interaction between the positive electrode and the electrolyte interface, and improve the cycle stability of the battery.

[0020] 2) The present invention utilizes a hydrothermal method to synthesize a three-dimensional azole-type MOFs material. The prepared material contains long-chain carboxylic acid ligands, has large pores, and has bifunctional ion transport channels of tetrazole and carboxyl groups. The polyazole groups and carboxyl groups can form stable chemical bonds with the sulfur atoms in the polysulfides, such as hydrogen bonds, electrostatic interactions, or coordination effects. This enhanced chemical adsorption capacity helps to fix polysulfides and reduce their dissolution and migration in the electrolyte. Through a reasonable synthesis method, a hybrid zeolite material with a highly ordered pore structure and rich surface functional groups is prepared; the carboxylic acid group can form a good interaction with the lithium salt and the solvent, which helps to regulate the compatibility between the diaphragm and the electrolyte, promote the transmission of lithium ions, and at the same time reduce the interfacial impedance and improve the electrochemical performance of the battery.

[0021] 3) To enhance the separator's ability to suppress the lithium polysulfide shuttling effect, the metal-organic framework synthesized in this invention features a porous structure. The long chains of the biphenyl dicarboxylic acid ligands provide large molecular channels, increasing porosity and window size, facilitating lithium ion transport and inducing uniform deposition at the lithium metal interface. The addition of biphenyl dicarboxylic acid not only effectively increases the material's internal porosity and total surface area, but also significantly increases the active interface for electrochemical reactions, significantly contributing to improved sulfur utilization and the battery's energy storage density.

[0022] 4) In the present invention, the prepared azole-type MOFs material is coated to form one or more functional membranes, and the zeolite material is evenly distributed on the membrane, thereby forming an interface that can both block the shuttle of lithium polysulfide and promote the migration of lithium ions.

[0023] 5) This invention modulates the pore structure of azole-type MOFs. The material contains long-chain carboxylic acid ligands and possesses bifunctional tetrazole and carboxyl ion transport channels. This enhances the chemical adsorption capacity of polysulfides and reduces their dissolution and migration in the electrolyte. This clearly indicates improved electrochemical performance, including improved cycling stability. This is attributed to the rational design of the MOFs pore structure and surface functional groups, which helps stabilize the interaction between the positive electrode and the electrolyte interface. Experimental data from this invention confirms that the material is more suitable for battery application. The electrochemical impedance spectroscopy shows a smaller arc curvature radius, which means faster charge transfer at the catalyst interface and better battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a crystal structure diagram of the three-dimensional nitrogen-azole type MOFs material of Example 1 of the present invention;

[0025] Figure 2 is a graph showing the relationship between current density and potential of the lithium-sulfur battery of Example 1 of the present invention;

[0026] Figure 3 The electrochemical impedance spectroscopy diagram of the lithium-sulfur battery prepared in Example 1 of the present invention;

[0027] Figure 4 This is a relationship diagram between efficiency and specific capacity of the lithium-sulfur battery prepared in Example 1 of the present invention at a capacitance of 0.1C. Specific implementation methods

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] Example 1: A method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs, comprising the following steps:

[0030] Step 1: Weigh 0.5 mmol of 5-aminotetrazole and 0.5 mmol of biphenyldicarboxylic acid and place them in a polytetrafluoroethylene reactor, add a mixed solution of 5 mL of methanol and 5 mL of N,N-dimethylformamide, and stir at room temperature. After the solution becomes uniform and transparent, add 0.5 mmol of zinc nitrate hexahydrate and continue stirring. After the solid is completely dissolved, add 2 drops of tetramethylammonium hydroxide and place in a reactor at 100°C for 48 hours. After cooling to room temperature, take out, wash three times with methanol, and dry to obtain a light yellow crystalline material;

[0031] Step 2: Weigh 0.16 g, 0.02 g, and 0.02 g of the crystalline material obtained in step 1, polyvinylidene fluoride, and Ketjen black in a ratio of 8:1:1, respectively. Place the raw materials in an agate mortar and finely grind them to achieve a uniform mixing effect. Then, gradually add 3 mL of N-methylpyrrolidone solution and continuously stir to synthesize a viscous slurry;

[0032] Step 3: The prepared slurry is evenly coated on the surface of the PP diaphragm by a coating method with a coating thickness of 50 nm. The coated diaphragm is placed in a vacuum drying oven at 60°C and dried for 12 hours to obtain a modified lithium-sulfur battery diaphragm with a uniform surface.

[0033] Example 2: A method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs, comprising the following steps:

[0034] Step 1: Weigh 0.6 mmol of 5-aminotetrazole and 0.6 mmol of biphenyldicarboxylic acid and place them in a polytetrafluoroethylene reactor, add a mixed solution of 6 mL of methanol and 6 mL of N,N-dimethylformamide, and stir at room temperature. After the solution becomes uniform and transparent, add 0.6 mmol of zinc acetate and continue stirring. After the solid is completely dissolved, add 2 drops of tetramethylammonium hydroxide and place in a reactor at 100°C for 72 hours. After cooling to room temperature, take out, wash three times with methanol, and dry to obtain a light yellow crystalline material;

[0035] Step 2: Weigh 0.07 g, 0.02 g, and 0.01 g of the crystalline material obtained in step 1, Super P, and polyvinyl alcohol in a ratio of 7:2:1, respectively. Place the raw materials in an agate mortar and grind them finely to achieve a uniform mixing effect. Then, gradually add the pre-measured N-methylpyrrolidone solution and continue stirring to synthesize a viscous slurry;

[0036] Step 3: The prepared slurry is evenly coated on the surface of the PP separator by a coating method with a coating thickness of 80 nm. The coated separator is placed in a vacuum drying oven at 60°C and dried for 8 hours to obtain a modified lithium-sulfur battery separator with a uniform surface.

[0037] Example 3: A method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs, comprising the following steps:

[0038] Step 1: Weigh 0.5 mmol of 5-aminotetrazole and 0.5 mmol of biphenyldicarboxylic acid and place them in a polytetrafluoroethylene reactor, add a mixed solution of 3 mL of methanol and 3 mL of N,N-dimethylformamide, and stir at room temperature. After the solution becomes uniform and transparent, add 0.5 mmol of zinc chloride and continue stirring. After the solid is completely dissolved, add tetramethylammonium hydroxide (2 drops) and place in a reactor at 120°C for 48 hours. After cooling to room temperature, take out, wash three times with methanol, and dry to obtain a light yellow crystalline material;

[0039] Step 2: Weigh 0.16 g, 0.02 g, and 0.02 g of the crystalline material obtained in step 1, polyacrylic acid, and acetylene black in a ratio of 8:1:1, respectively. Place the raw materials in an agate mortar and grind them finely to achieve a uniform mixing effect. Then, gradually add the pre-measured N-methylpyrrolidone solution and continue stirring to synthesize a viscous slurry;

[0040] Step 3: The prepared slurry is evenly coated on the surface of the PP diaphragm by a coating method with a coating thickness of 100 nm. The coated diaphragm is placed in a vacuum drying oven at 70°C and dried for 12 hours to obtain a modified lithium-sulfur battery diaphragm with a uniform surface.

[0041] Example 4: A method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs, comprising the following steps:

[0042] Step 1: Weigh 0.5 mmol of 5-aminotetrazole and 0.5 mmol of biphenyldicarboxylic acid and place them in a polytetrafluoroethylene reactor, add a mixed solution of 3 mL of methanol and 3 mL of N,N-dimethylformamide, and stir at room temperature. After the solution becomes uniform and transparent, add 0.5 mmol of zinc nitrate hexahydrate and continue stirring. After the solid is completely dissolved, add 2 drops of tetramethylammonium hydroxide and place in a reactor at 120°C for 72 hours. After cooling to room temperature, take out, wash three times with methanol, and dry to obtain a light yellow crystalline material;

[0043] Step 2: Weigh 0.07 g, 0.02 g, and 0.01 g of the crystalline material obtained in step 1, Ketjen black, and polyacrylic acid in a ratio of 7:2:1, respectively, place the raw materials in an agate mortar and finely grind them to achieve a uniform mixing effect, then gradually add the pre-measured N-methylpyrrolidone solution, and continuously stir to form a viscous slurry;

[0044] Step 3: The prepared slurry is evenly coated on the surface of the PP diaphragm by a coating method with a coating thickness of 120 nm. The coated diaphragm is placed in a vacuum drying oven at 70°C and dried for 9 hours to obtain a modified lithium-sulfur battery diaphragm with a uniform surface.

[0045] Example 5: A method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs, comprising the following steps:

[0046] Step 1: Weigh 0.5 mmol of 5-aminotetrazole and 0.5 mmol of biphenyldicarboxylic acid and place them in a polytetrafluoroethylene reactor, add a mixed solution of 3 mL of methanol and 3 mL of N,N-dimethylformamide, and stir at room temperature. After the solution becomes uniform and transparent, add 0.5 mmol of zinc chloride and continue stirring. After the solid is completely dissolved, add 2 drops of tetramethylammonium hydroxide and place in a reactor at 110°C for 60 hours. After cooling to room temperature, take out, wash three times with methanol, and dry to obtain a light yellow crystalline material;

[0047] Step 2: Weigh 0.07 g, 0.02 g, and 0.01 g of the crystalline material obtained in step 1, acetylene black, and polyvinylidene fluoride, respectively, in a ratio of 7:2:1. Place the raw materials in an agate mortar and finely grind them to achieve a uniform mixing effect. Then, gradually add the pre-measured N-methylpyrrolidone solution and continuously stir to synthesize a viscous slurry.

[0048] Step 3: The prepared slurry is evenly coated on the surface of the PP diaphragm by a coating method with a coating thickness of 150 nm. The coated diaphragm is placed in a vacuum drying oven at 70°C and dried for 8 hours to obtain a modified lithium-sulfur battery diaphragm with a uniform surface.

[0049] The modified lithium-sulfur battery separators obtained in Examples 1-5 above were cut into 19 mm diameter discs or 4 cm × 4 cm square separators using a punch. The obtained separators were assembled with sulfur-loaded carbon nanotube composite positive electrode materials and lithium negative electrode materials in an argon-filled glove box to form soft-pack batteries, and the battery data was tested.

[0050] Example 1 is the best embodiment of the present invention, and the experimental results of Example 1 are as follows:

[0051] The crystal structure of the three-dimensional nitrogen azole type MOFs material (PTA-MOFS) of the present invention is shown in FIG. Figure 1 As shown, it can be seen that a three-dimensional columnar MOFs material was synthesized. The columnar crystals synthesized using metal zinc salt, aminotetrazole and biphenyldicarboxylic acid have larger pore sizes and can promote the transfer of lithium ions.

[0052] The relationship between the current density and potential of the lithium-sulfur battery test using the diaphragm assembled using the nitrogen-azole MOFs material of the present invention is shown in the figure below: Figure 2 As shown in Figure 2, the CV curve of the lithium-sulfur battery shows two reduction peaks, representing the reduction of elemental sulfur to soluble long-chain polysulfides (Li2Sn, 4≤n≤8), which are further reduced to solid polysulfides (Li2S2 / Li2S). In the anodic scan, the overlapping peak near 2.4V represents the process of oxidizing Li2S / Li2S2 to Li2S8 / S8 in the electrode reaction.

[0053] The electrochemical impedance spectroscopy of the lithium-sulfur battery test using the diaphragm assembled with the three-dimensional nitrogen-azole MOFs material of the present invention is shown in FIG. Figure 3 As shown, the impedance material itself is represented by the arc curvature radius in the Nyquist diagram, that is, the smaller the arc curvature radius, the faster the charge transfer on the catalyst interface and the lower the photogenerated carrier recombination rate. The impedance material itself is represented by the arc curvature radius in the Nyquist diagram, that is, the smaller the arc curvature radius, the faster the charge transfer on the catalyst interface.

[0054] The specific capacity and long cycle diagram of the lithium-sulfur battery test using the diaphragm assembled with the nitrogen-azole type MOFs material of the present invention are shown in FIG. Figure 4As shown in the figure, the coulombic efficiency is still close to 100% after 50 cycles at a capacitance of 0.1C.

[0055] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs, characterized by: The following steps are involved: Step 1: Weigh 5-aminotetrazole and biphenyldicarboxylic acid and place them in a polytetrafluoroethylene reactor, add a mixed solution of methanol and N,N-dimethylformamide, stir at room temperature until the solution is uniform and transparent, add zinc salt solid and continue stirring, add tetramethylammonium hydroxide after the solid is completely dissolved, place in the reactor to react, cool to room temperature, take out, wash with methanol, and then dry to obtain a light yellow crystalline material; Step 2: Finely grind and uniformly mix the light yellow crystalline material obtained in step 1 with a binder and conductive carbon black, then gradually add N-methylpyrrolidone solution and continue stirring to form a viscous slurry; Step 3: Use a coating method to evenly apply the slurry prepared in step 2 on the surface of the PP diaphragm, and then place the diaphragm in a vacuum drying oven to dry to obtain a diaphragm with a uniform surface.

2. The method for preparing a modified lithium-sulfur battery separator for regulating the pore structure of nitrogen-azole-type MOFs according to claim 1, characterized in that: In step 1, the molar ratio of 5-aminotetrazole to biphenyldicarboxylic acid is 1:1, and the volume ratio of methanol to N,N-dimethylformamide solution is 1:

1.

3. The method for preparing a modified lithium-sulfur battery separator for regulating the pore structure of nitrogen-azole-type MOFs according to claim 1, characterized in that: The zinc salt in step 1 is zinc nitrate hexahydrate, zinc acetate or zinc chloride.

4. The method for preparing a modified lithium-sulfur battery separator for regulating the pore structure of nitrogen-azole-type MOFs according to any one of claims 1 to 3, characterized in that: The conductive carbon black in step 2 is Ketjen black, Super P or acetylene black, and the binder is polyvinylidene fluoride, polyvinyl alcohol or polyacrylic acid.

5. The method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs according to claim 4, characterized in that: The coating thickness in step 3 is 50-150 nm.

6. The method for preparing a modified lithium-sulfur battery separator by regulating the pore structure of nitrogen-azole-type MOFs according to claim 5, characterized in that: Step 3: vacuum drying at a temperature of 50°C to 70°C for no less than 6 hours.

7. A battery separator prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of the battery separator according to claim 7 in a lithium-sulfur battery.

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