Preparation of a S-rich porous zinc-based MOF flexible film and regulation of lithium battery performance

Abstract

The present invention specifically relates to a method for preparing a S-rich porous zinc-based MOF flexible film. This method coordinates tetrazole with carboxyl groups and zinc ions via a hydrothermal method, using pyrazine as a template and tetramethylammonium hydroxide as a pH regulator. This yields a new S-rich porous zinc-based metal-organic framework material with special pores containing negative electrons. This material is further blended with a lithium salt and a polymer to produce a metal-organic framework composite polymer viscous liquid, which is then applied to a glass plate and allowed to stand to yield a S-rich porous zinc-based MOF flexible film. The present invention has the advantage of effectively enhancing the electrochemical and thermal stability of lithium batteries. The assembled lithium iron phosphate (LFP) battery exhibits low electrochemical impedance characteristics, with a specific capacity of 140 mAh g at a current of 0.1 C. ‑1 The capacity retention rate is close to 100%, showing excellent cycle stability and good rate performance at different current densities.

Description

Technical Field

[0001] The present invention belongs to the technical field related to lithium-ion solid-state batteries, and specifically relates to a method for preparing a S-rich porous zinc-based MOF flexible film, and also relates to performance regulation of lithium-ion batteries based on the S-rich porous zinc-based MOF flexible film. Background Art

[0002] Lithium-ion batteries are widely considered to be the most efficient, environmentally friendly, and clean energy storage devices and have achieved great success in commercialization. With the widespread application of lithium-ion batteries in electric vehicles, safety issues have become increasingly prominent, especially the fire risk posed by flammable organic liquid electrolytes. Compared with lithium-ion batteries using flammable liquid organic electrolytes, solid-state lithium metal batteries using solid electrolytes are considered a promising strategy. However, solid electrolytes currently face problems such as low ionic conductivity, large interfacial resistance, and poor contact with electrodes, which limit the battery's energy density, cycling stability, and safety.

[0003] Solid polymer electrolytes have low ionic conductivity and poor stability. Although inorganic electrolytes have high conductivity, they have high interfacial resistance with the electrodes and cannot withstand large strains or pose safety risks. The development of new composite electrolyte membrane materials is expected to solve the above problems. An effective way is to add functional materials to polymer-based membranes. MOF is a functional material with a periodic porous structure. It has the characteristics of high specific surface area, adjustable chemical properties and uniform morphology. Using MOF's low ion transport resistance and uniform pores as a membrane modification material for lithium batteries has become a very promising method as a polymer-based ion conductive material. However, from the current technology, there are still problems such as low conductivity and poor stability of polymer electrolytes.

[0004] For example, in the paper "Metalorganic framework modified poly (vinylidenefluoride-co-hexafluoropropylen e) separator membranes to improve lithium-ion battery capacity fading" published in Chemical Engineering Journal in April 2022, the authors selected three MOFs with similar surface area and topological structure to modify PVDF-HFP membranes, using the porosity of MOF to improve battery performance, and conducted a series of characterization and electrochemical performance tests to explore the effects of different MOFs on membrane performance. Due to the differences in MOF particle size and pore structure, there are still problems such as low battery specific capacity, poor stability and low rate performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a S-rich porous zinc-based MOF flexible film in order to solve the problems of low battery specific capacity, unsatisfactory rate performance and poor stability in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is a method for preparing a S-rich porous zinc-based MOF flexible film, comprising the following steps:

[0007] Step 1: Weigh 5-methyl-1H-tetrazole and dissolve it in N,N-dimethylacetamide to obtain solution A; weigh 2,5-thiophenedicarboxylic acid and dissolve it in methanol to obtain solution B; after sonicating solution A and solution B for 10-15 minutes, slowly pour solution A into solution B, and then stir to obtain solution C; the molar ratio of 5-methyl-1H-tetrazole to 2,5-thiophenedicarboxylic acid is 4:1;

[0008] Step 2: Weigh the template agent pyrazine and add it to solution C with stirring to obtain solution D, wherein the molar ratio of pyrazine to 2,5-thiophenedicarboxylic acid is 3:2;

[0009] Step 3: Add a few drops of tetramethylammonium hydroxide to solution D to adjust the pH, and stir to obtain a mixed solution E;

[0010] Step 4: Add zinc salt to the mixed solution E at a molar ratio of 2,5-thiophenedicarboxylic acid to zinc salt of 1:2, and sonicate for 10-15 minutes; react in an oven, cool to room temperature, wash several times with N,N-dimethylacetamide, and dry to obtain pale yellow crystals F, which are then ground to obtain precursor G;

[0011] Step 5: Precursor G is used as a filler and blended with lithium salt and polymer in N-methyl-2-pyrrolidone at a mass ratio of G:polymer:salt of 1:8:1. Stir at room temperature for 40-50 hours to obtain a milky white viscous liquid H.

[0012] Step 6: The viscous liquid H is formed into a film on a glass plate, and a S-rich porous zinc-based MOF flexible film is obtained after vacuum drying.

[0013] Furthermore, in the above step 4, the temperature of the oven is set at 100-140° C., and the reaction time is 48-72 hours.

[0014] Furthermore, in the above step 4, the zinc salt is zinc nitrate hexahydrate, zinc acetate or zinc chloride.

[0015] Furthermore, in the above step 5, the polymer is any one of polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyacrylonitrile (PAN).

[0016] Furthermore, in the above step 6, the vacuum drying temperature is 40-70° C., and the drying time is 10-20 hours.

[0017] Furthermore, in the above step 6, the viscous liquid H is first vacuum filtered for 15-40 minutes to remove bubbles before film formation.

[0018] Furthermore, in the above step 6, the film is formed by scraping the viscous liquid H onto the glass plate using a 1000 micron scraper.

[0019] Furthermore, in the above step 6, the film is formed by pouring the viscous liquid H onto the glass plate and rotating it to make it naturally level.

[0020] Furthermore, the S-rich porous zinc-based MOF flexible film prepared by the above preparation method.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention successfully synthesized a new metal-organic framework material with a large pore structure centered on zinc metal by precisely controlling the addition of a template agent and a pH regulator. This crystal forms a pore structure with negative electrons through tetrazole and carboxylic acid ligands. Because the sulfur atoms in its pores are lithium-philic groups, the precursor, the S-rich porous zinc-based metal-organic framework material, is incorporated into the polymer base material as an electrolyte filler to form an ultra-thin polymer flexible film that can be used as an excellent ion conductor.

[0023] (2) The present invention introduces longer carboxylic acid ligands, which increases the porosity and window size of the crystalline material, and together constructs a uniform and fast ion transmission path. The sulfur in the pores will adsorb metal cations, promote the conduction of metal cations, allow more lithium ions to be solvated and have less restriction, and provide a fast channel for the transmission of lithium ions, thereby preventing the formation of lithium dendrites that pierce the diaphragm during the cycle of the lithium-ion battery, and can effectively enhance the electrochemical stability of the lithium battery, showing excellent cycle stability, and also showing good rate performance at different current densities.

[0024] (3) In the preparation process of the present invention, a S-rich porous zinc-based metal organic framework material is dispersed in a polymer substrate to prepare a flexible film. This effective combination method not only retains the porous crystalline structure, but also promotes the movement of the chain segments and the contact at the interface. Therefore, the stable interface provided by the MOF / polymer composite membrane helps to prevent adverse reactions between the electrolyte and the electrode, thereby improving the electrochemical stability of the battery. The assembled lithium iron phosphate (LFP) battery exhibits low electrochemical impedance characteristics. The specific capacity of the battery at a current of 0.1C is 140mAhg -1, the capacity retention rate is close to 100%, which reduces the risk of internal short circuit of the battery and also has higher safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the preparation process of a S-rich porous zinc-based MOF flexible film according to the present invention;

[0026] Figure 2 The electrochemical impedance spectroscopy (EIS) of a lithium-ion battery assembled from the S-rich porous zinc-based MOF flexible film prepared in Example 1 of the present invention is shown in FIG.

[0027] Figure 3 This is the Nyquist plot at different temperatures of a stainless steel symmetric battery test assembled with a S-rich porous zinc-based MOF flexible film prepared in Example 1 of the present invention;

[0028] Figure 4 This is an Arrhenius plot of the ionic conductivity of a stainless steel symmetrical battery assembled with a S-rich porous zinc-based MOF flexible film prepared in Example 1 of the present invention at different temperatures;

[0029] Figure 5 This is a graph showing the relationship between the efficiency and specific capacity of a lithium-ion battery assembled with a S-rich porous zinc-based MOF flexible film prepared in Example 1 of the present invention after 100 cycles at a rated capacitance of 0.1C;

[0030] Figure 6 This is a rate performance diagram of a lithium-ion battery assembled with a S-rich porous zinc-based MOF flexible film prepared in Example 1 of the present invention at different currents. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0032] The preparation idea of ​​the present invention is shown in Figure 1 Tetrazolyl, carboxyl and zinc ions were coordinated by a hydrothermal method, with pyrazine as a template and tetramethylammonium hydroxide as a pH regulator, to obtain a new S-rich porous zinc-based metal-organic framework material with special pores containing negative electrons. After further blending it with lithium salt and polymer, a metal-organic framework composite polymer viscous liquid was obtained, which was then scraped onto a glass plate and allowed to stand to obtain a S-rich porous zinc-based MOF flexible film.

[0033] Example 1, see Figure 1 A method for preparing a S-rich porous zinc-based MOF flexible film comprises the following steps:

[0034] Step 1: Weigh 5-methyl-1H tetrazole (1.2 mmol, 0.1 g) and dissolve it in 3 mL of N,N-dimethylacetamide to obtain solution A; weigh 2,5-thiophenedicarboxylic acid (0.29 mmol, 0.0499 g) and dissolve it in 3 mL of methanol to obtain solution B; sonicate solution A and solution B for 15 minutes, then slowly pour solution A into solution B, and stir to obtain solution C;

[0035] Step 2: Weigh 0.035 g of pyrazine and add it to solution C with stirring to obtain solution D;

[0036] Step 3: Add 1 drop of tetramethylammonium hydroxide to solution D to adjust the pH, and stir to obtain a mixed solution E.

[0037] Step 4: Zinc nitrate hexahydrate (0.54 mmol, 0.16 g) was added to the mixed solution E, and the mixture was ultrasonicated for 15 minutes. The mixture was transferred to a vial and reacted in an oven at 120°C for 48 hours, followed by natural cooling. The mixture was then washed three times with N,N-dimethylacetamide and dried to obtain pale yellow crystals F, which were then ground for 30 minutes to obtain precursor G.

[0038] Step 5: Take 0.125 g of precursor G as a filler, mix it with 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and 0.125 g of lithium bis(trifluoromethylsulfonyl)imide in 7 mL of N-methyl-2-pyrrolidone, and stir at room temperature for 48 hours to obtain a milky white viscous liquid H.

[0039] Step 6: First, vacuum filter the milky white viscous liquid H for 30 minutes to remove bubbles, then use a 1000-micron scraper to scrape the viscous liquid H onto a glass plate to form a thin film, and then dry it under vacuum conditions to finally obtain a solidified S-rich porous zinc-based MOF flexible film.

[0040] Example 2, a method for preparing a S-rich porous zinc-based MOF flexible film, comprising the following steps:

[0041] Step 1: Weigh 5-methyl-1H tetrazole (1.2 mmol, 0.1 g) and dissolve it in 4 mL of N,N-dimethylacetamide to obtain solution A; weigh 2,5-thiophenedicarboxylic acid (0.29 mmol, 0.0499 g) and dissolve it in 4 mL of methanol to obtain solution B; sonicate solution A and solution B for 10 minutes, then slowly pour solution A into solution B, and stir to obtain solution C;

[0042] Step 2: Weigh 0.035 g of pyrazine and add it to solution C with stirring to obtain solution D;

[0043] Step 3: Add 2 drops of tetramethylammonium hydroxide to solution D to adjust the pH, and stir to obtain a mixed solution E.

[0044] Step 4: Zinc nitrate hexahydrate (0.54 mmol, 0.16 g) was added to the mixed solution E, and the mixture was ultrasonicated for 15 minutes. The mixture was transferred to a small vial and reacted in an oven at 120°C for 50 hours, followed by natural cooling. The mixture was then washed twice with N,N-dimethylacetamide and dried to obtain pale yellow crystals F, which were then ground for 30 minutes to obtain precursor G.

[0045] Step 5: 0.125 g of precursor G was used as a filler and mixed with 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and 0.125 g of lithium bis(trifluoromethylsulfonyl)imide in 7 mL of N-methyl-2-pyrrolidone. The mixture was stirred at room temperature for 40 hours to obtain a milky white viscous liquid H.

[0046] Step 6: Pour the milky white viscous liquid H onto a glass plate and rotate it to allow it to naturally level out to form a thin film. After drying under vacuum conditions, a solidified S-rich porous zinc-based MOF flexible film material is finally obtained.

[0047] Example 3, a method for preparing a S-rich porous zinc-based MOF flexible film, comprising the following steps:

[0048] Step 1: Weigh 5-methyl-1H tetrazole (1.2 mmol, 0.1 g) and dissolve it in 5 mL of N,N-dimethylacetamide to obtain solution A; weigh 2,5-thiophenedicarboxylic acid (0.29 mmol, 0.0499 g) and dissolve it in 5 mL of methanol to obtain solution B; after sonicating solution A and solution B for 15 minutes, slowly pour solution A into solution B and stir to obtain solution C;

[0049] Step 2: Weigh 0.035 g of pyrazine and add it to solution C with stirring to obtain solution D;

[0050] Step 3: Add 1 drop of tetramethylammonium hydroxide to solution D to adjust the pH, and stir to obtain a mixed solution E.

[0051] Step 4: Zinc nitrate hexahydrate (0.54 mmol, 0.16 g) was added to the mixed solution E, and the mixture was ultrasonicated for 10 minutes. The mixture was transferred to a small vial and reacted in an oven at 110°C for 55 hours, then naturally cooled. The mixture was then washed four times with N,N-dimethylacetamide and dried to obtain pale yellow crystals F, which were then ground for 40 minutes to obtain precursor G.

[0052] Step 5: 0.125 g of precursor G was used as a filler and mixed with 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and 0.125 g of lithium bis(trifluoromethylsulfonyl)imide in 7 mL of N-methyl-2-pyrrolidone. The mixture was stirred at room temperature for 50 hours to obtain a milky white viscous liquid H.

[0053] Step 6: Apply the viscous liquid H on a glass plate to form a thin film, which is then dried under vacuum conditions to obtain a solidified S-rich porous zinc-based MOF flexible film material.

[0054] Example 4, a method for preparing a S-rich porous zinc-based MOF flexible film, comprising the following steps:

[0055] Step 1: Weigh 5-methyl-1H tetrazole (1.2 mmol, 0.1 g) and dissolve it in 6 mL of N,N-dimethylacetamide to obtain solution A; weigh 2,5-thiophenedicarboxylic acid (0.29 mmol, 0.0499 g) and dissolve it in 6 mL of methanol to obtain solution B; after sonicating solution A and solution B for 13 minutes, slowly pour solution A into solution B, and then stir to obtain solution C;

[0056] Step 2: Weigh 0.035 g of pyrazine and add it to solution C with stirring to obtain solution D;

[0057] Step 3: Add 2 drops of tetramethylammonium hydroxide to solution D to adjust the pH, and stir to obtain a mixed solution E.

[0058] Step 4: Zinc nitrate hexahydrate (0.54 mmol, 0.16 g) was added to the mixed solution E, and the mixture was ultrasonicated for 10 minutes. The mixture was transferred to a small vial and reacted in an oven at 130°C for 48 hours, followed by natural cooling. The mixture was then washed three times with N,N-dimethylacetamide and dried to obtain pale yellow crystals F, which were then ground for 30 minutes to obtain precursor G.

[0059] Step 5: 0.125 g of precursor G was used as a filler and mixed with 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and 0.125 g of lithium bis(trifluoromethylsulfonyl)imide in 6 mL of N-methyl-2-pyrrolidone. The mixture was stirred at room temperature for 72 hours to obtain a milky white viscous liquid H.

[0060] Step 6: Apply the viscous liquid H on a glass plate to form a thin film, which is then dried under vacuum conditions to obtain a solidified S-rich porous zinc-based MOF flexible film material.

[0061] The S-rich porous zinc-based MOF flexible films obtained in Examples 1-4 were cut into circular sheets with a diameter of 19 mm. These circular sheets served as separators I. Separators I were assembled with lithium iron phosphate cathode materials and lithium metal anode materials, along with springs and gaskets, to form lithium-ion batteries in an argon-filled glove box with a water-oxygen value of less than 0.01 ppm. The batteries were then tested for rate performance (0.1C, 0.2C, 0.5C, 1C, and 2C), ionic conductivity, and cycling performance (operating voltage range: 2.5V-4V).

[0062] Take embodiment 1 as the best embodiment, as Figure 2 Figure 2 shows an electrochemical impedance spectroscopy (EIS) test performed on a lithium-ion battery containing a S-rich porous zinc-based MOF flexible film prepared according to the present invention, at a frequency of 0.01-100,000 Hz, before cycling. The smaller semicircle in the figure indicates a lower charge transfer resistance before cycling, indicating that the S-rich porous zinc-based MOF flexible film facilitates faster charge transfer.

[0063] like Figure 3 As shown in the figure, in the ionic conductivity test, the electrochemical impedance was tested in the temperature range of 25 to 85 ° C by the AC impedance method. It can be seen from the figure that the conductivity of the S-rich porous zinc-based MOF flexible film gradually increases with the increase of temperature. The lithium ion conductivity is 4.88×10 -4 S cm -1 , 1.21×10 at 85℃ -3 S cm -1 , which illustrates that the S-rich porous zinc-based MOF flexible film has high ionic conductivity.

[0064] like Figure 4 As shown, it can be seen that the conductivity shows a good linear relationship with the change of temperature. The activation energy of ion transition conduction of the S-rich porous zinc-based MOF flexible film is calculated to be 0.136 eV by the Arrhenius formula, which shows that the S-rich porous zinc-based MOF flexible film is conducive to the desolvation and ion transport of lithium ions.

[0065] like Figure 5 As shown in the figure, after 100 cycles at a current density of 0.1C, the S-rich porous zinc-based MOF flexible film has a specific capacity of 140 mAh g –1 , the capacity retention rate is close to 100%.

[0066] like Figure 6 As shown, the rate diagram of the S-rich porous zinc-based MOF flexible film after 10 cycles at different current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C. The corresponding charge and discharge specific capacities at different current densities are 148, 145, 139, 130, and 112 mAh g –1 , and the efficiency is close to 100%. This shows that the composite flexible film can maintain a high energy output and absorption rate at high magnification without losing too much energy due to high magnification.

[0067] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a S-rich porous zinc-based MOF flexible film, characterized in that: The following steps are involved: Step 1: Weigh 5-methyl-1H-tetrazole and dissolve it in N,N-dimethylacetamide to obtain solution A; weigh 2,5-thiophenedicarboxylic acid and dissolve it in methanol to obtain solution B; after sonicating solution A and solution B for 10-15 minutes, slowly pour solution A into solution B, and then stir to obtain solution C; the molar ratio of 5-methyl-1H-tetrazole to 2,5-thiophenedicarboxylic acid is 4:1; Step 2: Weigh the template agent pyrazine and add it to solution C with stirring to obtain solution D, wherein the molar ratio of pyrazine to 2,5-thiophenedicarboxylic acid is 3:2; Step 3: Add a few drops of tetramethylammonium hydroxide to solution D to adjust the pH, and stir to obtain a mixed solution E; Step 4: Add zinc salt to the mixed solution E at a molar ratio of 2,5-thiophenedicarboxylic acid to zinc salt of 1:2, and sonicate for 10-15 minutes; react in an oven, cool to room temperature, wash several times with N,N-dimethylacetamide, and dry to obtain pale yellow crystals F, which are then ground to obtain precursor G; Step 5: Precursor G is used as a filler and is blended with lithium salt and polymer in N-methyl-2-pyrrolidone at a mass ratio of G:polymer:salt of 1:8:

1. Stir at room temperature for 40-50 hours to obtain a milky white viscous liquid H; Step 6: The viscous liquid H is formed into a film on a glass plate, and a S-rich porous zinc-based MOF flexible film is obtained after vacuum drying.

2. The method for preparing a S-rich porous zinc-based MOF flexible film according to claim 1, characterized in that: In step 4, the temperature of the oven is set at 100-140° C., and the reaction time is 48-72 hours.

3. The method for preparing a S-rich porous zinc-based MOF flexible film according to claim 2, characterized in that: In step 4, the zinc salt is zinc nitrate hexahydrate, zinc acetate or zinc chloride.

4. The method for preparing a S-rich porous zinc-based MOF flexible film according to claim 3, characterized in that: In the step 5, the polymer is any one of polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyacrylonitrile (PAN).

5. The method for preparing a S-rich porous zinc-based MOF flexible film according to claim 4, characterized in that: In step 6, the vacuum drying temperature is 40-70° C., and the drying time is 10-20 hours.

6. The method for preparing a S-rich porous zinc-based MOF flexible film according to claim 5, characterized in that: In step 6, the viscous liquid H is first vacuum filtered for 15-40 minutes to remove bubbles before film formation.

7. The method for preparing a S-rich porous zinc-based MOF flexible film according to claim 6, characterized in that: In step 6, the film is formed by coating the viscous liquid H on the glass plate using a 1000 micron scraper.

8. The method for preparing a S-rich porous zinc-based MOF flexible film according to claim 6, characterized in that: In step 6, the film is formed by pouring the viscous liquid H onto the glass plate and rotating it to make it naturally level.

9. The S-rich porous zinc-based MOF flexible film prepared by the preparation method according to claim 1.

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