Modified diatomite diaphragm material, preparation method and application thereof

Abstract

This invention provides a modified diatomaceous earth membrane material, its preparation method, and its applications. By flotation of diatomaceous earth followed by molten salt exfoliation to uniformly disperse metallic cobalt within the pores of the diatomaceous earth, cobalt agglomeration is reduced, and its catalytic activity is improved, resulting in a modified diatomaceous earth membrane material. Coating this modified diatomaceous earth membrane material onto the surface of commonly used lithium-sulfur battery membranes enhances the adsorption and catalytic conversion capabilities of polysulfides, thereby improving the cycle stability of lithium-sulfur batteries. The method provided by this invention uses cobalt dispersed in diatomaceous earth, resulting in cobalt with more active sites, achieving a cobalt loading exceeding 10% and higher catalytic activity. This accelerates the polysulfide conversion process, effectively suppresses the "shuttle effect" in lithium-sulfur batteries, and improves the long-cycle performance of lithium-sulfur batteries. The lithium-sulfur battery can cycle 2000 times at 1.0C with a decay of only 0.036% per cycle, demonstrating excellent application prospects.

Description

Technical Field

[0001] This invention belongs to the field of metal battery technology, specifically relating to a modified diatomaceous earth membrane material, its preparation method, and its application. Background Technology

[0002] Novel energy storage devices have become an effective solution for addressing the fossil fuel crisis and environmental pollution. Among them, lithium-sulfur batteries, involving an electrochemical reaction with 16 electrons, have a theoretical specific capacity of 1675 mAh g⁻¹. -1 It is far superior to lithium-ion batteries using lithium iron phosphate (approximately 170mAh g). -1 The theoretical energy density of lithium-sulfur batteries is as high as 2600 Wh / kg. -1 The sulfur content is several times that of currently commercial lithium-ion batteries. Furthermore, compared to ordinary lithium-ion battery cathode materials, sulfur has advantages such as abundant natural reserves, environmental friendliness, and low cost. However, lithium-sulfur batteries face problems such as the polysulfide shuttle effect, lithium anode dendrite formation, and slow kinetic processes, which need to be addressed. The shuttle effect arises because the reduction rate of polysulfides is slow during discharge, leading to their dissolution in the electrolyte, or because the large pores of the lithium-sulfur battery separator allow polysulfides to pass through the separator to reach the anode. Therefore, modifying the separator to address these shortcomings is a typical strategy for structural modification of lithium-sulfur batteries.

[0003] Currently used membrane modification materials mainly improve lithium-sulfur battery performance in two aspects: suppressing the shuttle effect and accelerating the kinetic reaction rate. On the one hand, using adsorbents with high porosity can utilize physical confinement to control polysulfides on the positive electrode side, thereby suppressing the shuttle effect and reducing capacity loss. On the other hand, addressing the slow kinetic process, using catalysts that accelerate polysulfide conversion can effectively improve the reaction kinetics of lithium-sulfur batteries. Among these, metal catalysts have attracted widespread attention because they can accelerate the reaction kinetics of lithium-sulfur through Lewis acid-base interactions. Although metal catalysts play a significant role in accelerating the catalytic conversion of lithium-sulfur batteries and can effectively chemically immobilize polysulfides, the metal catalyst loading in lithium-sulfur battery membrane modification materials is very low. Membrane modification materials require an easily dispersible support in the early stages of metal catalyst growth to promote the separation of highly active metal catalysts and prevent them from hindering ion conduction by covering or filling the pores on the membrane.

[0004] Chinese patent CN202011537447.4 discloses the application of nitrogen-doped carbon-coated Co and / or Co3ZnC composite materials in the preparation of lithium-sulfur battery separators. A separator modification material with catalytic properties is obtained by calcining a carbon source precursor with a cobalt-zinc salt. However, in application, the battery cycle life of this material is only 100 cycles, with a decay of 0.25% per cycle. This indicates that the catalytic performance of this separator modification material is insufficient, its suppression of the polysulfide shuttle effect is limited, and its short cycle life makes it difficult to meet commercial requirements. Therefore, this separator has certain limitations in improving lithium-sulfur batteries. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned shortcomings of the prior art by providing a modified diatomaceous earth membrane material, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first objective of this invention is to provide a method for preparing a modified diatomaceous earth membrane material, comprising the following specific steps:

[0008] Step S1, diatomaceous earth flotation

[0009] Diatomaceous earth is mixed with ultrapure water to form a slurry, a dispersant is added and ultrasonically stirred, and then flotation is performed to obtain refined diatomaceous earth.

[0010] Step S2, Preparation of modified diatomaceous earth membrane material

[0011] Using the refined diatomaceous earth and cobalt-zinc based metal-organic framework material obtained in step S1 as raw materials, and LiCl and KCl as molten salt media, a crude product is obtained by calcination. After the crude product is cooled to room temperature, it is washed and dried multiple times with deionized water to obtain the product modified diatomaceous earth membrane material.

[0012] Furthermore, in step S1, the mass ratio of diatomaceous earth to distilled water is 1:(20-35), and the amount of dispersant added is 1-5% of the total mass of diatomaceous earth and distilled water.

[0013] Furthermore, the dispersant includes any one of sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate.

[0014] Furthermore, in step S2, the refined diatomaceous earth comprises: 85-90% SiO2, <4% Na2O, <4% Al2O3, <2% Fe2O3, and <1% other compounds.

[0015] Furthermore, the diatomaceous earth has a disc-shaped structure with a diameter of approximately 30–100 μm and a pore size of 200–500 nm.

[0016] Furthermore, the mass ratio of the refined diatomaceous earth to the cobalt-zinc based metal-organic framework material is 1:(3-7), the mass ratio of LiCl to KCl is 1:(3-6), and the mass ratio of LiCl to refined diatomaceous earth is (10-40):1.

[0017] Furthermore, the cobalt-zinc based metal-organic framework materials include ZIF-L, ZIF-67, ZIF-8, MOF-74, and MOF-700.

[0018] Furthermore, the calcination process involves raising the temperature to 300–600°C at a rate of 1–3°C / min and holding it for 2–4 hours, followed by raising the temperature to 800–900°C at a rate of 1–3°C / min and holding it for 2–4 hours.

[0019] A second objective of this invention is to provide a modified diatomaceous earth membrane material prepared by the above method.

[0020] A third object of the present invention is to provide a modified diatomaceous earth membrane comprising a membrane and the aforementioned modified diatomaceous earth membrane material coated thereon.

[0021] Furthermore, the diaphragm includes any one of polypropylene membrane, polyethylene membrane, polyester membrane, cellulose membrane, polyimide membrane, spandex membrane, and aramid membrane.

[0022] The fourth objective of this invention is to provide a method for preparing the modified diatomaceous earth membrane described above, comprising grinding and mixing the modified diatomaceous earth membrane material, conductive carbon black, and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of (6-7):(2-3):(1-2) to prepare a slurry; coating the slurry onto a membrane and vacuum drying it at 20-30°C for 6-12 hours to obtain the modified diatomaceous earth membrane.

[0023] A fifth objective of the present invention is to provide a lithium-sulfur battery comprising the above-described modified diatomaceous earth separator.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) This invention provides a modified diatomaceous earth membrane material, its preparation method, and its application. Diatomaceous earth is used as a raw material and refined through flotation to obtain refined diatomaceous earth with larger pore sizes and stronger adsorption capacity. Subsequently, through a molten salt stripping evaporation method, the defects caused by zinc evaporation are utilized to give the material higher conductivity and catalytic activity, uniformly dispersing metallic cobalt in the pores of the diatomaceous earth, reducing cobalt agglomeration, and further increasing the active sites of cobalt, resulting in a modified diatomaceous earth membrane material. This material is further coated onto the surface of commonly used lithium-sulfur battery membranes to obtain a modified diatomaceous earth membrane, which can improve the adsorption capacity and catalytic conversion capacity of polysulfides, and improve the cycle stability of lithium-sulfur batteries.

[0026] (2) The method provided by the present invention uses cobalt dispersed in diatomite, which can obtain cobalt with more active sites, so that cobalt has a loading of more than 10% and has higher catalytic activity, thereby accelerating the conversion process of polysulfides, effectively suppressing the "shuttle effect" of lithium-sulfur batteries, improving the long cycle performance of lithium-sulfur batteries, and enabling lithium-sulfur batteries to cycle 2000 times at 1.0C with a decay of only 0.036% per cycle.

[0027] (3) The preparation method provided by the present invention is simple and low in cost. The modified diatomaceous earth membrane prepared can be used in lithium-sulfur batteries to enable the batteries to undergo 2000 charge-discharge cycles, and has good market value and application prospects. Attached Figure Description

[0028] Figure 1 Scanning electron microscope image of the modified diatomaceous earth membrane material prepared in Example 1;

[0029] Figure 2 The elemental distribution diagram of the modified diatomaceous earth membrane material prepared in Example 1 is shown under a scanning electron microscope.

[0030] Figure 3 Scanning electron microscope image of the diatomaceous earth material prepared in Example 2;

[0031] Figure 4 The graph shows the cycle performance of the modified diatomaceous earth membrane prepared in Example 12 under charge-discharge testing at a rate of 1.0C.

[0032] Figure 5 Rate performance diagram of the modified diatomaceous earth membrane prepared in Example 12;

[0033] Figure 6 A comparison of charge-discharge curves of the membranes prepared in Comparative Example 1, Comparative Example 2 and Example 12;

[0034] Figure 7 The graph shows a performance comparison of symmetrical cells assembled using the separators prepared in Comparative Example 1, Comparative Example 2 and Example 12, respectively.

[0035] Figure 8 The graph shows the discharge cycle test results at 1.0C for the modified diatomaceous earth membrane prepared in Example 13.

[0036] Figure 9 X-ray diffraction patterns of Comparative Example 1, Comparative Example 2, and Example 12;

[0037] Figure 10 Scanning electron microscope image of the diatomite lithium-sulfur battery separator prepared for Comparative Example 1;

[0038] Figure 11The pore size distribution diagram is shown for the diatomite lithium-sulfur battery separator prepared in Comparative Example 1.

[0039] Figure 12 Cyclic performance of the diatomite lithium-sulfur battery separator prepared for Comparative Example 1;

[0040] Figure 13 Scanning electron microscope image of the diatomite lithium-sulfur battery separator prepared for Comparative Example 2;

[0041] Figure 14 The cycling performance of the diatomaceous earth lithium-sulfur battery separator prepared for Comparative Example 2 is shown in the figure. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments and accompanying drawings are described in further detail below. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0043] In a first aspect, the present invention provides a method for preparing a modified diatomaceous earth membrane material, specifically, the method comprising:

[0044] S1, Diatomaceous Earth Flotation

[0045] According to an embodiment of the present invention, in this step, diatomaceous earth is first mixed with ultrapure water to form a slurry, a dispersant is added and ultrasonically stirred, and then flotation is performed to obtain refined diatomaceous earth.

[0046] Specifically, diatomaceous earth powder can be mixed with ultrapure water. More specifically, mixing can be achieved by vigorous vortex oscillator to ensure that the diatomaceous earth is evenly mixed in ultrapure water, and can be supplemented with ultrasonic treatment, for example, ultrasonic treatment for about 10 minutes after vortex oscillation.

[0047] As mentioned earlier, the mass ratio of diatomaceous earth to ultrapure water in the slurry is not particularly limited, as long as it can be mixed evenly and is suitable for conventional stirring and ultrasonication. For example, a mass ratio of diatomaceous earth to distilled water of 1:(20-35) can be selected, such as 1:20, 1:23, 1:25, 1:28, 1:30, 1:33, 1:35, etc.

[0048] To further improve the dispersibility of diatomaceous earth in ultrapure water and achieve more uniform mixing, a dispersant can be added to the slurry. Specifically, the dispersant can be selected from sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate. After flotation, the purified diatomaceous earth should have the following composition: SiO2 85-90%, Na2O <4%, Al2O3 <4%, Fe2O3 <2%, and other compounds <1%; the purified diatomaceous earth should have a disc-shaped structure with a diameter of approximately 30-100 μm and a pore size within 200-500 nm. For example, the amount of dispersant added is 1%-5% of the slurry mass. For example, it can be 1%, 2%, 3%, 4%, 5%, etc. This process can obtain larger-sized diatomaceous earth particles, resulting in stronger adsorption capacity.

[0049] S2. Preparation of modified diatomaceous earth membrane material

[0050] In this step, using the refined diatomaceous earth and cobalt-zinc based metal-organic framework material obtained in step S1 as raw materials, and LiCl and KCl as molten salt media, a crude product is obtained through calcination. After the crude product is cooled to room temperature, it is washed and dried multiple times with deionized water to obtain the modified diatomaceous earth membrane material. This method is simple to operate, easy to scale up production, and the obtained modified diatomaceous earth membrane material has at least one of the following advantages: more cobalt active sites, high cobalt loading, accelerated polysulfide conversion, and improved long-cycle performance of lithium-sulfur batteries.

[0051] According to an embodiment of the present invention, cobalt is loaded onto diatomaceous earth using a molten salt exfoliation method, with the cobalt loading amount being not less than 10%. Specifically, using the refined diatomaceous earth and cobalt-zinc based metal-organic framework material obtained in step S1 as raw materials, and LiCl and KCl as molten salt media, calcination is performed: the temperature is raised to 300-600°C at a heating rate of 1-3°C / min and held for 2-4 hours, then raised to 800-900°C at a heating rate of 1-3°C / min and held for 2-4 hours to obtain a crude product. After the crude product is cooled to room temperature, it is washed multiple times with deionized water and dried to obtain the product modified diatomaceous earth membrane material.

[0052] Among them, cobalt-zinc based metal-organic framework materials can be ZIF-L, ZIF-67, ZIF-8, MOF-74, or MOF-700.

[0053] By using the molten salt stripping evaporation method, cobalt agglomeration was reduced, and it was more evenly dispersed in the pores of diatomaceous earth, thereby increasing the activity of the catalyst and improving the adsorption and catalytic conversion capacity of the membrane modification material for polysulfides, thus improving the cycle stability of lithium-sulfur batteries.

[0054] In a second aspect, the present invention provides a modified diatomaceous earth membrane material prepared by the preparation method described above. This material exhibits excellent polysulfide adsorption capacity and catalytic activity.

[0055] In a third aspect, the present invention provides a modified diatomaceous earth membrane comprising the modified diatomaceous earth membrane material as described above. Application scenarios for the modified diatomaceous earth membrane material are also provided.

[0056] In a fourth aspect of the present invention, a method for preparing a modified diatomaceous earth membrane is provided, wherein modified diatomaceous earth membrane material, conductive carbon black and polyvinylidene fluoride are ground and mixed in N-methylpyrrolidone at a mass ratio of (6-7):(2-3):(1-2) to prepare a slurry; the slurry is coated on a membrane and vacuum dried at 20-30°C for 6-12 hours to obtain a modified diatomaceous earth membrane.

[0057] According to embodiments of the present invention, the specific material of the separator is not limited, as long as it can be used in lithium-sulfur batteries. For example, it can be any one of polypropylene membrane, polyethylene membrane, polyester membrane, cellulose membrane, polyimide membrane, spandex membrane, and aramid membrane.

[0058] It should be noted that the thickness of the slurry coating on the separator is not limited and can be designed according to actual application requirements. In the embodiments of the present invention, in order to better suppress the "shuttle effect" of lithium-sulfur batteries, the thickness of the slurry coating on the separator is 10-25 μm.

[0059] In a fifth aspect, the present invention provides a lithium-sulfur battery comprising a modified diatomaceous earth separator as described above.

[0060] According to embodiments of the present invention, the lithium-sulfur battery is manufactured using a process known to those skilled in the art. The lithium-sulfur battery includes a positive electrode material, a negative electrode material, an electrolyte, and a separator. The separator is a key internal component; its performance determines the interface structure and internal resistance of the metal battery, directly affecting its capacity, cycle life, and safety performance. Using the modified diatomaceous earth separator provided by this invention, the "shuttle effect" of the lithium-sulfur battery can be effectively suppressed, enabling the lithium-sulfur battery to cycle 2000 times at 1.0C with a decay of only 0.036% per cycle.

[0061] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0062] The cobalt-zinc based metal-organic framework materials ZIF-L, ZIF-67, ZIF-8, MOF-74, and MOF-700 used in the embodiments of this invention are all commercially available.

[0063] In the embodiments and comparative examples of this invention, the mass ratio of sublimed sulfur, conductive agent, and binder is 7:2:1. The conductive agent is Super P or acetylene black, the binder is polyvinylidene fluoride, the solvent is N-methylpyrrolidone, and the current collector is a carbon-coated aluminum foil disc with a diameter of 12 mm. After coating, it is dried in a vacuum drying oven at 60°C for 12 hours. Then, in an argon-filled glove box, a lithium metal sheet is used as the counter electrode, and the diaphragm is Celgard 2500.

[0064] The electrolyte was 1 mol / L LiTFSI dissolved in DME:DOL = 1:1V, with 1% LiNO3 added. The button cell used was model CR2025.

[0065] Electrochemical test: at 1.0C (1.0C = 1675 mA g) -1 Constant current charge-discharge tests were performed at a current density of 1.7–2.8V, with a voltage range of 1.7–2.8V. Rate tests were conducted at rates of 0.2C, 0.5C, 1.0C, and 2.0C. AC impedance testing was performed at open-circuit voltage, with a frequency range of 0.001–1000000Hz and an amplitude of 0.05V.

[0066] The symmetric cell used 0.1 mol Li2S6 solution as the active material and different lithium-sulfur battery separators were used. The current-voltage curves were tested in the range of -1.5 to 1.5 V.

[0067] Example 1

[0068] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0069] The diatomaceous earth used in this embodiment is sourced from Xilong Chemical, with a content (calculated as SiO2) ≥ 85.0%.

[0070] Step S1, diatomaceous earth flotation

[0071] Diatomaceous earth was purified by flotation using sodium hexametaphosphate as a dispersant. A mixture of diatomaceous earth and ultrapure water at a mass ratio of 1:30 was prepared, followed by the addition of 2% sodium hexametaphosphate. The mixture was stirred and sonicated for 5 hours each, and the stirring and sonication cycles were repeated three times. The lower precipitate was then collected and allowed to stand. Subsequently, it was centrifuged and deionized to remove residual sodium hexametaphosphate, yielding refined diatomaceous earth.

[0072] Step S2, Preparation of modified diatomaceous earth membrane material

[0073] Step S21, Preparation of metal-organic framework materials

[0074] First, 2-methylimidazole was dissolved in deionized water at a mass ratio of 3:100 to obtain a 2-methylimidazole solution. Simultaneously, Co(NO3)2·6H2O and Zn(NO3)2·6H2O were dissolved in deionized water at a mass ratio of 1:1:140 to obtain a nitrate solution. Then, the nitrate solution was added to the 2-methylimidazole solution. The mixture was centrifuged and washed three times with deionized water, and finally dried overnight at 80°C to obtain the zeolite imidazole ester framework material ZIF-L.

[0075] Step S22, calcination

[0076] Refined diatomaceous earth and zeolite imidazole ester framework material ZIF-L were used as raw materials, mixed with LiCl and KCl in a ratio of 1:5:20:8. The mixture was heated to 500℃ at a rate of 3℃ / min under an argon atmosphere and held for 2 hours, then heated to 850℃ at a rate of 3℃ / min and held for 2 hours. Subsequently, after the product cooled to room temperature, the sample was washed repeatedly with deionized water and dried in a forced-air dryer at 80℃ for 10 hours to obtain the modified diatomaceous earth membrane material.

[0077] Example 2

[0078] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0079] The remaining steps are the same as in Example 1, except that in step S1, the diatomaceous earth is sourced from Guoyao Reagent and has a content (calculated as SiO2) ≥ 85.0%.

[0080] Example 3

[0081] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0082] The remaining steps are the same as in Example 1, except that in step S1, after mixing diatomaceous earth and ultrapure water at a mass ratio of 1:20, 1% sodium hexametaphosphate is added and stirred.

[0083] Example 4

[0084] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0085] The remaining steps are the same as in Example 1, except that in step S1, after mixing diatomaceous earth and ultrapure water at a mass ratio of 1:35, 5% sodium hexametaphosphate is added and stirred.

[0086] Example 5

[0087] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0088] The remaining steps are the same as in Example 1, except that in step S2, refined diatomaceous earth and zeolite imidazole ester framework structural material ZIF-L are used as raw materials and mixed with LiCl and KCl in a ratio of 1:3:30:10.

[0089] Example 6

[0090] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0091] The remaining steps are the same as in Example 1, except that in step S2, refined diatomaceous earth and zeolite imidazole ester framework structural material ZIF-L are used as raw materials and mixed with LiCl and KCl in a ratio of 1:5:80:20.

[0092] Example 7

[0093] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0094] The remaining steps are the same as in Example 1, except that in step S2, refined diatomaceous earth and zeolite imidazole ester framework structural material ZIF-L are used as raw materials and mixed with LiCl and KCl in a ratio of 1:7:240:40.

[0095] Example 8

[0096] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0097] The remaining steps are the same as in Example 1, except that in step S2, the cobalt-zinc based metal-organic framework material is ZIF-8.

[0098] Example 9

[0099] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0100] The remaining steps are the same as in Example 1, except that in step S2, the cobalt-zinc based metal-organic framework material is ZIF-67.

[0101] Example 10

[0102] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0103] The remaining steps are the same as in Example 1, except that in step S2, the temperature is increased to 300°C at a rate of 2°C / min under an argon atmosphere and held for 2 hours, and then increased to 800°C at a rate of 3°C / min and held for 2 hours.

[0104] Example 11

[0105] This embodiment provides a method for preparing a modified diatomaceous earth membrane material:

[0106] The remaining steps are the same as in Example 1, except that in step S2, the temperature is increased to 600°C at a rate of 3°C / min under an argon atmosphere and held for 2 hours, and then increased to 900°C at a rate of 2°C / min and held for 2 hours.

[0107] Example 12

[0108] This embodiment provides a method for preparing a modified diatomaceous earth membrane:

[0109] The modified diatomaceous earth membrane material prepared in Example 1 was used.

[0110] The modified diatomaceous earth membrane material was mixed and ground with conductive carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1 in N-methylpyrrolidone, and then coated onto the surface of Celgard 2500 membrane. After vacuum drying at 25°C for 12 hours, the coating thickness was 10 μm, thus obtaining the modified diatomaceous earth membrane.

[0111] Example 13

[0112] This embodiment provides a method for preparing a modified diatomaceous earth membrane:

[0113] The modified diatomaceous earth membrane material prepared in Example 2.

[0114] The remaining steps are the same as in Example 12.

[0115] Example 14

[0116] The remaining steps are the same as in Example 12, except that the mass ratio of the modified diatomaceous earth membrane material to the conductive carbon black and polyvinylidene fluoride is 6:3:1.

[0117] Example 15

[0118] The remaining steps are the same as in Example 12, except that the mass ratio of the modified diatomaceous earth membrane material to the conductive carbon black and polyvinylidene fluoride is 6:2:2.

[0119] Example 16

[0120] The remaining steps are the same as in Example 12, except that the coating thickness is 15 μm.

[0121] Example 17

[0122] The remaining steps are the same as in Example 12, except that the coating thickness is 20 μm.

[0123] Example 18

[0124] The remaining steps are the same as in Example 12, except that the coating thickness is 25 μm.

[0125] Comparative Example 1

[0126] This comparative example provides a diatomaceous earth lithium-sulfur battery separator:

[0127] S1, Diatomaceous earth flotation:

[0128] Diatomaceous earth was purified by flotation using sodium hexametaphosphate as a dispersant. A mixture of diatomaceous earth and ultrapure water at a mass ratio of 1:30 was prepared, followed by the addition of 2% sodium hexametaphosphate. The mixture was stirred and sonicated for 5 hours each, and the stirring and sonication cycles were repeated three times. The lower precipitate was then collected and allowed to stand. Subsequently, it was centrifuged and deionized to remove residual sodium hexametaphosphate, yielding purified diatomaceous earth.

[0129] S2, diaphragm coating:

[0130] The purified diatomaceous earth was mixed and ground with conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 7:2:1, and then coated onto the surface of Celgard 2500 separator. After vacuum drying at 25°C for 12 hours, the diatomaceous earth lithium-sulfur battery separator was obtained.

[0131] Comparative Example 2

[0132] This comparative example provides a diatomaceous earth lithium-sulfur battery separator:

[0133] S1. Preparation of metal-organic framework materials:

[0134] First, 2-methylimidazole was dissolved in deionized water at a ratio of 3:100 to obtain a 2-methylimidazole solution. Simultaneously, Co(NO3)2·6H2O and Zn(NO3)2·6H2O were dissolved in deionized water at a ratio of 1:1:140 to obtain a nitrate solution. Then, the nitrate solution was added to the 2-methylimidazole solution. The mixture was centrifuged and washed three times with deionized water, and finally dried overnight at 80°C to obtain the zeolite imidazole ester framework material ZIF-L.

[0135] S2, calcination:

[0136] Zeolite imidazole ester framework material ZIF-L was mixed with LiCl and KCl in a ratio of 3:10:4. The mixture was heated to 500℃ at a rate of 3℃ / min under an argon atmosphere and held for 2 hours, then heated to 850℃ at a rate of 3℃ / min and held for 2 hours. After cooling the product to room temperature, the sample was washed repeatedly with deionized water and dried at 80℃ for 10 hours to obtain the cobalt membrane modification material.

[0137] S3, diaphragm coating:

[0138] The obtained cobalt separator modification material, conductive carbon black and polyvinylidene fluoride, were mixed and ground in N-methylpyrrolidone at a mass ratio of 7:2:1, and then coated onto the surface of Celgard 2500 separator. After vacuum drying at 25°C for 12 hours, diatomaceous earth lithium-sulfur battery separator was obtained.

[0139] To better illustrate the properties of the modified diatomaceous earth membrane material and the modified diatomaceous earth membrane prepared in this invention, the applicant conducted the following research:

[0140] Performance characterization:

[0141] The modified diatomaceous earth membrane materials were characterized by scanning electron microscopy (SEM), and Examples 1-11 all exhibited similar morphologies. Taking Examples 1 and 2 as examples, refer to... Figure 1 as well as Figure 2 The SEM images of the upper surface show that cobalt mainly covers the porous surface of the diatomaceous earth, with a higher concentration near the pores. This is because diatomaceous earth itself is negatively charged, while cobalt is primarily positively charged. According to the principle of electrostatic attraction, cobalt is more evenly dispersed on the diatomaceous earth surface, indicating that cobalt has better dispersibility and catalytic activity. (Reference) Figure 3 Diatomaceous earth from different sources can also maintain a disc-shaped porous structure.

[0142] Electrochemical tests were conducted on the modified diatomaceous earth membranes. Examples 12-18 all exhibited similar electrochemical performance, specifically in terms of cycle performance, rate performance, and charge-discharge characteristic curves. The test results of Examples 12 and 13 are provided as examples for detailed explanation:

[0143] refer to Figure 4 The cycle performance graph shows that after 10 cycles of activation at 0.2C, the discharge rate shifts to 1.0C, and the first discharge specific capacity is 1048.2 mAh g. -1 After 2000 cycles, the discharge specific capacity is 296.3 mAh g. -1 The degradation per cycle is 0.036%. This modified diatomaceous earth membrane, because it combines porous diatomaceous earth with highly active dispersed cobalt, has good adsorption and catalytic performance for polysulfides, which can improve the long-cycle performance of lithium-sulfur batteries.

[0144] refer to Figure 5 The rate performance graph shows the specific capacity of Example 12 at 0.2C, 0.5C, 1.0C, 2.0C, 1.0C, 0.5C, and the rate recovery to 0.2C, with discharge specific capacities of 1387.5, 1135.2, 977.4, 843.3, 893.3, and 965.8 mAh g, respectively. -1 When the discharge rate returns to 0.2C, the specific capacity is 1024.9 mAh g. -1 It then stabilized and exhibited good responsiveness.

[0145] refer to Figure 6 The graph shows the charge-discharge curves for Comparative Example 1, Comparative Example 2, and Example 12. As can be seen from the graph, Example 12 exhibits a higher discharge specific capacity, reaching 1290.6 mAh g⁻¹. -1 This is higher than the 946.3 mAh g of Comparative Example 1. -1 Compared with Comparative Example 2, 1109.6 mAh g -1 Furthermore, the longer second discharge plateau in Example 1 indicates a higher conversion efficiency of lithium polysulfides to Li2S in the second step, with more active materials participating in the reaction. This demonstrates that the catalyst dispersed in diatomaceous earth has stronger catalytic activity and a more significant effect in suppressing the polysulfide shuttle effect.

[0146] refer to Figure 7 The figure shows a comparison of the symmetrical battery performance of Comparative Example 1, Comparative Example 2, and Example 12. As can be seen from the figure, within a voltage range of ±1.5V, the battery using Example 12 exhibits a more pronounced peak value of the catalytic activity curve and a higher relative intensity, while also achieving a larger response current of 0.16 mA mg. -1 Comparative Example 2 was relatively small, at 0.12 mA mg. -1 The comparative example 1 showed the lowest current response, at only 0.06 mA mg. -1 This indicates that after removing cobalt, diatomaceous earth itself has a relatively small catalytic effect on Li2S6, while the examples can improve the catalytic effect on polysulfides by increasing the catalytic activity of cobalt, thereby promoting the cycle stability of lithium-sulfur batteries.

[0147] refer to Figure 8 Similarly, the lithium-sulfur battery from Example 13 was assembled and subjected to a 1.0C discharge cycle test. As shown in the figure, this lithium-sulfur battery can also cycle 2000 times, with an initial capacity of 793.9 mAh g at 1.0C. -1 The results are higher than those of Comparative Example 1 and Comparative Example 2, and the attenuation rate per cycle is only 0.034%, indicating that the method has a certain degree of universality.

[0148] refer to Figure 9 The X-ray diffraction patterns of Comparative Example 1, Comparative Example 2 and Example 12 show that the main components of Comparative Example 1 are quartz SiO2 and cristobalite SiO2, the main component of Comparative Example 2 is cobalt metal, and Example 12 contains quartz, cristobalite and cobalt metal.

[0149] refer to Figure 10 The image shown is a scanning electron microscope image of Comparative Example 1, which mainly consists of a complete porous disc-shaped structure, thus exhibiting good adsorption performance.

[0150] refer to Figure 11 The diagram shows the pore size distribution of Comparative Example 1, which contains a large number of pores with a diameter of 5 nm, thus exhibiting good adsorption performance.

[0151] refer to Figure 12 The figure shows the cycling performance of Comparative Example 1. After 10 cycles of activation at 0.2C, the discharge rate was changed to 1.0C, and the discharge specific capacity in the first cycle was 425.5 mAh g. -1 After 439 cycles, the discharge specific capacity is 285 mAh g. -1 The decay rate was 0.075% per cycle. Because no additional catalyst was added, the low conductivity of diatomaceous earth itself resulted in a slow electrochemical reaction rate, low initial battery capacity, and the battery short-circuited due to lithium dendrites after 439 cycles.

[0152] refer to Figure 13 The image shown is a scanning electron microscope image of Comparative Example 2, which mainly shows a wrinkled, sheet-like structure loaded with some cobalt, but also shows some aggregated cobalt on the surface.

[0153] refer to Figure 14 The figure shows the cycle performance of Comparative Example 2. Charge-discharge tests were conducted at a 1.0C rate. Initially, the system was activated at 0.2C for 10 cycles, followed by 1.0C discharge. The first-cycle discharge specific capacity was 514.5 mAh g. -1 After 1138 cycles, the discharge specific capacity is 248.3 mAh g. -1 The degradation rate is 0.045% per cycle. Because cobalt will agglomerate without a good dispersion carrier, resulting in limited catalytic activity, the lithium-sulfur battery will be affected by the shuttle effect, and the battery will degrade rapidly, short-circuiting after 1138 cycles.

[0154] In summary, the electrochemical performance comparisons of Comparative Example 1, Comparative Example 2, and Example 12 are shown in Table 1.

[0155] Table 1

[0156] Serial Number <![CDATA[Initial week discharge specific capacity (mAh g -1 )]]> Long loop count Weekly capacity decay rate (%) Example 12 1048.2 2000 0.036 Comparative Example 1 425.5 439 0.075 Comparative Example 2 514.5 1138 0.045

[0157] For any points not covered above, existing technologies shall apply.

[0158] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a modified diatomaceous earth membrane material, characterized in that, The specific steps include the following: S1, Diatomaceous Earth Flotation Diatomaceous earth is mixed with ultrapure water to form a slurry, a dispersant is added and ultrasonically stirred, and then flotation is performed to obtain refined diatomaceous earth. S2. Preparation of modified diatomaceous earth membrane material Using the refined diatomite and cobalt-zinc based metal-organic framework material obtained in step S1 as raw materials, and LiCl and KCl as molten salt media, a crude product is obtained by calcination. After the crude product is cooled to room temperature, it is washed and dried multiple times with deionized water to obtain the product modified diatomite membrane material. The mass ratio of the refined diatomite to the cobalt-zinc based metal-organic framework material is 1:(3~7). The calcination process involves heating the temperature to 300-600°C at a rate of 1-3°C / min and holding it for 2-4 hours, followed by heating the temperature to 800-900°C at a rate of 1-3°C / min and holding it for 2-4 hours.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of diatomaceous earth to ultrapure water is 1:(20~35), and the amount of dispersant added is 1~5% of the mass of the slurry. The dispersant includes any one of sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate.

3. The preparation method according to claim 1, characterized in that, In step S2, the refined diatomaceous earth has the following composition: SiO2 85~90%, Na2O<4%, Al2O3<4%, Fe2O3<2%, other compounds<1%, and the sum of all components is 100%; the diatomaceous earth has a disc-shaped structure with a diameter of 30~100 μm and a pore size of 200~500 nm.

4. The preparation method according to claim 3, characterized in that, The mass ratio of LiCl to KCl is 1:(3~6), and the mass ratio of LiCl to refined diatomaceous earth is (10~40):

1. The cobalt-zinc based metal-organic framework material includes any one of ZIF-L, ZIF-67, ZIF-8, MOF-74 and MOF-700.

5. A modified diatomaceous earth membrane material prepared by the preparation method according to any one of claims 1-4.

6. A modified diatomaceous earth membrane, characterized in that, It comprises a diatomaceous earth diatomaceous earth membrane material as described in claim 5, coated thereon.

7. The modified diatomaceous earth membrane as described in claim 6, characterized in that, The diaphragm includes any one of polypropylene membrane, polyethylene membrane, polyester membrane, cellulose membrane, polyimide membrane, spandex membrane, and aramid membrane.

8. A method for preparing the modified diatomaceous earth membrane as described in claim 6, characterized in that, The process involves grinding and mixing the modified diatomaceous earth membrane material, conductive carbon black, and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of (6~7):(2~3):(1~2) to prepare a slurry; coating the slurry onto a membrane; and vacuum drying at 20~30°C for 6~12 h to obtain the modified diatomaceous earth membrane.

9. A lithium-sulfur battery, characterized in that, It includes the modified diatomaceous earth membrane as described in claim 6.

Images