Composite separator, method for preparing the same, and lithium sulfur battery containing the composite separator

Abstract

The present invention relates to a composite separator, a method for preparing the same, and a lithium-sulfur battery including the composite separator. The composite separator includes a polymer base film and a composite layer disposed on the surface of the polymer base film. The composite layer includes a molecular sieve and a conductive carbon material, and the molecular sieve contains cobalt and optionally lithium. Compared with the separators of the prior art, the surface of the composite separator according to the present invention has a composite layer including a molecular sieve containing cobalt and optionally lithium. Thereby, the rate performance and cycle stability of the battery can be significantly improved.

Description

Detailed Description of the Invention

[0001] [Technical Field] The present disclosure relates to the technical field of battery separators, and in particular to a composite separator, a preparation method thereof, and a lithium-sulfur battery comprising the composite separator.

[0002] [Background] With the rapid development of science and technology, lithium-ion batteries can no longer meet the demand for batteries with higher energy density in new energy electric vehicles and large-capacity energy storage systems due to the low theoretical specific capacity of their cathode materials. Lithium-sulfur batteries have relatively high theoretical specific capacity (1675mAh / g) and theoretical energy density (2600Wh / kg), and are promising alternatives to lithium-ion batteries. Lithium-sulfur batteries have become a research focus of next-generation high specific capacity energy secondary batteries. In addition, sulfur, which is a cathode active material, has advantages such as abundant natural reserves, low cost, and environmental friendliness.

[0003] However, at present, the practical application of lithium-sulfur batteries still faces many challenges. Among them, the "shuttle effect", which is a side reaction inside the battery, can be the biggest obstacle limiting their application. Specifically, the shuttle effect refers to the effect that a lithium-sulfur battery can generate a series of sulfur-containing intermediates during the charging and discharging process, and long-chain polysulfide (Li2S x , 2<x≤8) is easily soluble in the electrolyte, and passes through the separator under the action of concentration gradient and electric field to cause chemical side reactions with the lithium anode. This causes loss of active materials and increase in the internal resistance of the battery, thereby leading to a decrease in battery capacity and a deterioration in cycle performance. Furthermore, the electrochemical reaction process of a lithium-sulfur battery may involve multi-step solid-liquid conversion, and sulfur and lithium sulfide, which is the final discharge product, may have low electronic conductivity. Therefore, the conversion rate of polysulfides is slow, and the rate performance of the battery is poor.

[0004] Currently, in this field, it has been proposed to use molecular sieves when improving conventional separators to suppress the shuttle effect in lithium-sulfur batteries; see, for example, CN107546356A and CN103490027A. These utilize the physical barrier effect of molecular sieves such as ZSM-5, SAPO-34, 3A, and 13X to suppress the Li2S effect in the electrolyte. x This improves battery performance by limiting the movement and diffusion of particles to some extent.

[0005] In order for (lithium-sulfur) batteries to meet the demand for batteries with higher energy density in new energy electric vehicles and large-capacity energy storage systems, it is necessary to develop battery separators with further improved performance.

[0006] [Summary of the Invention] This disclosure aims to address the problems of poor battery rate characteristics, low battery capacity, and poor cycle performance in the prior art. The inventors have found that the performance of a lithium-sulfur battery can be further improved by using a molecular sieve containing cobalt and optionally lithium in the lithium-sulfur battery separator, thereby meeting the aforementioned needs in the prior art. Therefore, we provide a composite separator comprising a composite layer of a molecular sieve containing cobalt and optionally lithium. The composite separator according to this disclosure can improve the rate characteristics and cycle stability of the battery. In this disclosure, a method for preparing a composite separator and a lithium-sulfur battery comprising the composite separator are further provided.

[0007] In Embodiment 1, the present disclosure provides a polymer substrate film and a composite layer disposed on the surface of the polymer substrate film, wherein the composite layer comprises a molecular sieve and a conductive carbon material, and the molecular sieve is a composite separator containing cobalt. In aspect 2, the information provided in this disclosure is: (1) A step of mixing a molecular sieve containing cobalt with a conductive carbon material to obtain a mixture, (2) A step of dispersing the mixture and the binder in a solvent to obtain a coating slurry, (3) A method for preparing the above-described composite separator, comprising the step of applying the coating slurry to the surface of the polymer substrate film, and then removing the solvent to obtain the composite separator. In Embodiment 3, the present disclosure provides the use of the above-described composite separator in a lithium-sulfur battery. In Embodiment 4, the present disclosure provides a lithium-sulfur battery comprising a positive electrode, a negative electrode, and the composite separator between the positive electrode and the negative electrode.

[0008] This disclosure may include the following items: 1. A molecular sieve-modified separator comprising a polymer substrate film and a composite layer of a cobalt-doped molecular sieve / conductive carbon material disposed on the surface of the polymer substrate film.

[0009] 2. The composite layer of the cobalt-doped molecular sieve / conductive carbon material has a thickness of 5-50 μm, preferably 10-40 μm, and / or The molecular sieve-modified separator according to item 1, wherein the conductive carbon material and the cobalt-doped molecular sieve in the composite layer of the cobalt-doped molecular sieve / conductive carbon material are in a mass ratio of 1:(1-9), preferably 1:(2-9).

[0010] 3. The cobalt-doped molecular sieve has a chemical composition of aCo·bM2O·ySiO2·zAl2O3, preferably at least one selected from the group consisting of MFI, MWW, GIS, BEC, FAU, and MOR, and more preferably at least one of MFI, MWW, and GIS. 0.02 ≤ a / y ≤ 0.2, 0.01 ≤ b / y ≤ 0.2, 10 ≤ y / z ≤ 50, and M is an alkali metal element of group IA, preferably one or more selected from the group consisting of Na, K, and Li. Preferably, the cobalt-doped molecular sieve is a cobalt-doped lithium molecular sieve having the chemical composition aCo·bLi2O·ySiO2·zAl2O3, and the molecular sieve modification separator according to item 1 or 2, where 0.02 ≤ a / y ≤ 0.2, 0.01 ≤ b / y ≤ 0.2, and 10 ≤ y / z ≤ 50.

[0011] 4. The material of the polymer substrate film is at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene, and polyvinylidene fluoride, preferably polyethylene and / or polypropylene, and / or The molecular sieve-modified separator according to any one of items 1-3, wherein the conductive carbon material is at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjenblack, preferably at least one of graphene, graphene oxide, and reduced graphene oxide.

[0012] 5. (1) A step of grinding and mixing a cobalt-doped molecular sieve and a conductive carbon material to obtain a mixture of the cobalt-doped molecular sieve and the conductive carbon material, (2) A step of dispersing the mixture of the cobalt-doped molecular sieve and the conductive carbon material and a binder in a solvent to obtain a coating slurry, (3) A method for preparing a molecular sieve-modified separator according to any one of items 1-4, comprising the step of applying the coating slurry to the surface of a polymer substrate film, and then removing the solvent to obtain the molecular sieve-modified separator.

[0013] 6. The cobalt-doped molecular sieve is prepared by a method that includes the steps of adding a cobalt ion solution to a Na-type molecular sieve, drying and reducing it to obtain the cobalt-doped molecular sieve. Preferably, the cobalt-doped molecular sieve is obtained by replacing a Na-type molecular sieve with a lithium ion solution, washing and drying it to obtain precursor I (S1); A cobalt-doped lithium molecular sieve is prepared by a method comprising the step (S2) of adding a cobalt ion solution to the precursor I, drying and reducing it to obtain the cobalt-doped lithium molecular sieve. Preferably, the lithium ion solution in S1 is at least one of lithium chloride solution, lithium sulfate solution, and lithium nitrate solution. The exchange in S1 is carried out under conditions including a temperature of 40-100°C and a liquid-to-solid ratio of 10-50. The Na-type molecular sieve has a chemical composition of bNa2O·ySiO2·zAl2O3, with 0.01≦b / y≦0.2 and 10≦y / z≦50, and preferably the Na-type molecular sieve has at least one topological structure selected from the group consisting of MFI, MWW, GIS, BEC, FAU and MOR. The cobalt ion solution is at least one of the following: cobalt chloride solution, cobalt nitrate solution, cobalt sulfate solution, and cobalt acetate solution. The reduction is carried out in a hydrogen atmosphere at a reduction temperature of 600-750°C for 1-4 hours, as described in item 5.

[0014] 7. The method according to item 5 or 6, wherein the solvent in step (2) is at least one selected from the group consisting of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N-methylpyrrolidone.

[0015] 8. The method according to any one of items 5-7, wherein the binder in step (2) is at least one of polyvinyl alcohol, carboxymethylcellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber, and polyacrylate, preferably polyvinylidene fluoride.

[0016] 9. The method according to any one of items 5-8, wherein the coating in step (3) is at least one of casting, blade coating, spray coating, and spin coating, preferably blade coating.

[0017] 10. Use of molecular sieve-modified separators described in any one of items 1-4 in lithium-sulfur batteries. This disclosure may further include the following items: 1. A modified lithium molecular sieve separator comprising a composite layer of lithium molecular sieve / conductive carbon material and a polymer substrate film, wherein the composite layer of lithium molecular sieve / conductive carbon material is disposed on the surface of the polymer substrate film.

[0018] 2. The lithified molecular sieve modified separator according to item 1, wherein the lithified molecular sieve comprises at least one of lithified MFI molecular sieve, lithified MWW molecular sieve, lithified GIS molecular sieve, lithified BEC molecular sieve, lithified FAU molecular sieve, and lithified MOR molecular sieve, preferably at least one of lithified MFI molecular sieve, lithified MWW molecular sieve, and lithified GIS molecular sieve.

[0019] 3. The lithiated molecular sieve modified separator according to item 1 or 2, wherein the material of the polymer base film is at least one selected from the group consisting of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene and polyvinylidene fluoride, preferably polyethylene and / or polypropylene.

[0020] 4. The lithiated molecular sieve modified separator according to any one of items 1 to 3, wherein the composite layer of the lithiated molecular sieve / the conductive carbon material has a thickness of 2-40 μm, preferably 5-25 μm.

[0021] 5. In the composite layer of the lithiated molecular sieve / the conductive carbon material, the mass ratio of the conductive carbon material to the lithiated molecular sieve is 1:(1-9), preferably 1:(2-9), and / or The lithiated molecular sieve modified separator according to any one of items 1 to 4, wherein the lithiated molecular sieve has a chemical composition of xLi₂O·ySiO₂·zAl₂O₃, 0.01≦x / y≦0.2, and 10≦y / z≦50.

[0022] 6. The lithiated molecular sieve modified separator according to any one of items 1 to 5, wherein the conductive carbon material is at least one selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjen black, preferably at least one selected from the group consisting of graphene, graphene oxide, and reduced graphene oxide.

[0023] 7. (1) a step of pulverizing and mixing a lithiated molecular sieve and a conductive carbon material to obtain a mixture of the lithiated molecular sieve and the conductive carbon material; (2) a step of dispersing the mixture of the lithiated molecular sieve and the conductive carbon material and a binder in a solvent to obtain a coating slurry; A method for preparing a lithium molecular sieve modified separator according to any one of items 1-6, comprising the step of (3) applying the coating slurry to the surface of a polymer substrate film, and then removing the solvent to obtain the lithium molecular sieve modified separator.

[0024] 8. In step (2), the solvent is at least one selected from the group consisting of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N-methylpyrrolidone, and / or The binder is at least one of polyvinyl alcohol, polytetrafluoroethylene, polyvinylpyrrolidone, carboxymethylcellulose, styrene-butadiene rubber, polyvinylidene fluoride, and polyacrylate, preferably polyvinylidene fluoride, and / or The coating in step (3) is at least one of casting, blade coating, spray coating, and spin coating, preferably blade coating, and / or The lithified molecular sieve is prepared by a method that includes the steps of replacing a Na-type molecular sieve with a lithium ion solution, washing and drying to obtain a Li-type molecular sieve. The Na-type molecular sieve has a chemical composition of xNa2O·ySiO2·zAl2O3, with 0.01≦x / y≦0.2 and 10≦y / z≦50. Preferably, the Na-type molecular sieve is at least one selected from the group consisting of MFI molecular sieve, MWW molecular sieve, GIS molecular sieve, BEC molecular sieve, FAU molecular sieve, and MOR molecular sieve. The lithium ion solution is at least one selected from the group consisting of lithium chloride solution, lithium sulfate solution, and lithium nitrate solution. The exchange is carried out under conditions including a temperature of 40-100°C and a liquid-to-solid ratio of 10-50, as described in item 7.

[0025] 9. Use of a lithium molecular sieve-modified separator as described in any one of items 1-8 in a lithium-sulfur battery.

[0026] 10. A lithium-sulfur battery comprising a positive electrode shell, a positive electrode sheet, a separator, a lithium sheet, a nickel foam, and a negative electrode shell, wherein the separator is a lithified molecular sieve modified separator as described in any one of items 1-6. This disclosure may have the following advantages. The method for preparing the composite separator according to this disclosure is simple and has little adverse effect on the energy density of the battery.

[0027] The composite separator according to this disclosure comprises a molecular sieve containing cobalt and optionally lithium in the composite layer. When used in a lithium-sulfur battery, the pore structure of the molecular sieve provides a physical barrier effect to Li2S x The movement and diffusion of ions can be effectively restricted. This reduces side reactions within the battery. The molecular sieve according to this disclosure contains cobalt. The introduced cobalt not only improves the conductivity of the positive electrode side of the separator but also functions as an active site that increases the rate of polysulfide conversion. If the molecular sieve further contains lithium, the introduced lithium can provide numerous sites for adsorbing and moving lithium ions during the battery cycle. This improves the lithium ion transport characteristics of the separator. More importantly, if the molecular sieve contains both lithium and cobalt, a synergistic effect is achieved in the resulting composite separator. This can significantly improve the rate characteristics and cycle stability of the lithium-sulfur battery. [Description of the drawing]

[0028] Figure 1 is a scanning electron microscope image of the composite separator obtained in Example 2-1. Figure 2 shows the charge-discharge curves of the lithium-sulfur battery sample obtained in Example 2-1 when the current density was changed. [Detailed explanation]

[0029] It should be understood that the endpoints of the ranges and any values ​​disclosed herein are not limited to exact ranges or values, but rather encompass values ​​close to those ranges or values. Regarding ranges of values, it is possible to combine the intervals between the endpoints of each range, the intervals between the endpoints of each range and individual points, and the intervals between individual points, to give one or more new ranges of values, as if these ranges of values ​​were specifically disclosed herein. Except in the examples, all numerical values ​​of parameters herein should be understood to be modified in all cases by the term "approximately," regardless of whether "approximately" actually appears before the numerical value.

[0030] Provided in this disclosure is a composite separator comprising a polymer substrate film and a composite layer disposed on the surface of the polymer substrate film. The composite layer comprises a molecular sieve and a conductive carbon material, wherein the molecular sieve contains cobalt. In one embodiment, the cobalt is elemental cobalt-based and is present in the molecular sieve in an amount of 1-30% by weight, preferably 1-15% by weight, and more preferably 2-7% by weight, based on the total weight of the cobalt and the molecular sieve.

[0031] In one embodiment, the molecular sieve may further contain lithium. Preferably, lithium is present in the molecular sieve in an amount of 0.1–5% by weight, preferably 0.2–3% by weight, and more preferably 0.5–2.5% by weight, based on lithium ion basis and the total weight of lithium and the molecular sieve.

[0032] In one embodiment, the molecular sieve may have at least one topological structure selected from the group consisting of MFI, MWW, GIS, BEC, FAU, and MOR, preferably at least one topological structure selected from the group consisting of MFI, MWW, and GIS.

[0033] There are no limitations on the thickness of the composite layer in this disclosure. In one embodiment, the composite layer may have a thickness of 5-50 μm, preferably 10-40 μm.

[0034] In this disclosure, there are no limitations on the mass ratio of the conductive carbon material and the molecular sieve in the composite layer. In one embodiment, the mass ratio of the conductive carbon material and the molecular sieve in the composite layer is 1:(1-9), preferably 1:(2-9), for example, 1:1, 1:2, 1:4, 1:6, 1:8, or 1:9.

[0035] The material of the polymer substrate film may be one that is commonly used in the art. In one embodiment, the material of the polymer substrate film is at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene, and polyvinylidene fluoride, preferably polyethylene and / or polypropylene.

[0036] The conductive carbon material may be one that is commonly used in the art. In one embodiment, the conductive carbon material is at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjenblack, and preferably at least one of graphene, graphene oxide, and reduced graphene oxide.

[0037] In a second embodiment, the present disclosure provides a method for preparing a composite separator, comprising the following steps: (1) A step of mixing a molecular sieve containing cobalt and a conductive carbon material to obtain a mixture; (2) A step of dispersing the mixture and the binder in a solvent to obtain a coating slurry; (3) A step of applying the coating slurry onto the surface of a polymer substrate film and removing the solvent to obtain the composite separator.

[0038] In one embodiment, cobalt is present in the molecular sieve in an amount of 1-30% by weight, preferably 1-15% by weight, and more preferably 2-7% by weight, based on elemental cobalt and the total weight of cobalt and the molecular sieve. In one embodiment, the method may further include the step of obtaining a molecular sieve by adding a cobalt ion solution to the raw molecular sieve, drying and reducing it to obtain a cobalt-containing molecular sieve.

[0039] In one embodiment, the molecular sieve may further contain lithium. Preferably, lithium is present in the molecular sieve in an amount of 0.1–5% by weight, preferably 0.2–3% by weight, and more preferably 0.5–2.5% by weight, based on lithium ion basis and the total weight of lithium and the molecular sieve. In one embodiment, the method further includes the steps of obtaining the molecular sieve by exchanging a raw molecular sieve with a lithium ion solution, washing and drying to obtain a precursor I (S1), and adding a cobalt ion solution to the precursor I, drying and reducing to obtain the molecular sieve containing cobalt and lithium (S2).

[0040] Preferably, the lithium ion solution is at least one selected from the group consisting of lithium chloride solution, lithium sulfate solution, and lithium nitrate solution.

[0041] Preferably, the exchange is carried out under conditions including a temperature of 40-100°C and a liquid-to-solid ratio of 10-50. The exchange can be performed one or more times, for example, 1-3 times.

[0042] Preferably, the cobalt ion solution is at least one selected from the group consisting of cobalt chloride solution, cobalt nitrate solution, cobalt sulfate solution, and cobalt acetate solution.

[0043] Preferably, the reduction is carried out in a hydrogen atmosphere at a temperature of 600-750°C for 1-4 hours.

[0044] Preferably, the raw molecular sieve may have the chemical composition xM2O·ySiO2·zAl2O3, where 0.01 ≤ x / y ≤ 0.2 and 10 ≤ y / z ≤ 50. M is one or two selected from the group consisting of Na and K. Preferably, the raw molecular sieve is a Na-type molecular sieve where M is Na.

[0045] Preferably, the raw molecular sieve is at least one selected from the group consisting of MFI, MWW, GIS, BEC, FAU, and MOR, and preferably at least one selected from the group consisting of MFI, MWW, and GIS.

[0046] In one embodiment, the molecular sieve in step (1) may have at least one topological structure selected from the group consisting of MFI, MWW, GIS, BEC, FAU, and MOR, and preferably at least one topological structure selected from the group consisting of MFI, MWW, and GIS.

[0047] The solvent in step (2) may be one that is commonly used in the art. In one embodiment, the solvent in step (2) may be at least one selected from the group consisting of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N-methylpyrrolidone.

[0048] The binder in step (2) may be one that is commonly used in the art. In one embodiment, the binder in step (2) may be at least one of polyvinyl alcohol, carboxymethylcellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber, and polyacrylate, preferably polyvinylidene fluoride.

[0049] The coating in step (3) may be one that is commonly used in the art. In one embodiment, the coating in step (3) is at least one of casting, blade coating, spray coating and spin coating, and is preferably a blade coating. In a third aspect, the present disclosure provides the use of the composite separator in a lithium-sulfur battery.

[0050] In a fourth embodiment, the present disclosure provides a lithium-sulfur battery comprising a positive electrode, a negative electrode, and the composite separator between the positive electrode and the negative electrode. The lithium-sulfur battery may further comprise an electrolyte. The positive electrode, the negative electrode, and the electrolyte can be selected from various positive electrodes, negative electrodes, and electrolytes used in lithium-sulfur batteries, as are known to those skilled in the art.

[0051] The composite separator according to this disclosure comprises a molecular sieve containing cobalt and optionally lithium in the composite layer. When used in a lithium-sulfur battery, the pore structure of the molecular sieve provides a physical barrier effect to Li2S x The movement and diffusion of the substance can be effectively restricted. This reduces side reactions within the battery. The molecular sieve according to this disclosure contains cobalt. The introduced cobalt not only improves the conductivity of the positive electrode side of the separator but also functions as an active site that increases the rate of polysulfide conversion. If the molecular sieve further contains lithium, the introduced lithium can provide numerous sites for adsorbing and moving lithium ions during the battery cycle. This improves the lithium ion transport characteristics of the separator. More importantly, if the molecular sieve contains both lithium and cobalt, a synergistic effect is achieved in the resulting composite separator. This can significantly improve the rate characteristics and cycle stability of the lithium-sulfur battery.

[0052] The present invention will be described in detail below through the examples provided. List of ingredients: MFI molecular sieves, GIS molecular sieves, MWW molecular sieves, and BEC molecular sieves are commercially available from Sigma-Aldrich. Graphene and graphene oxide: Commercially available from Shanghai Aladdin Biochemical Technology Co., Ltd. PVDF, NMP, CMC, DMF, and cobalt chloride are commercially available from Sinopharm Chemical Reagent Co., Ltd. <Testing Method> Assembly of lithium-sulfur battery samples:

[0053] First, sublimable sulfur as the active material, Ketjenblack as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder were mixed in a mass ratio of 6:3:1. N-methylpyrrolidone (NMP) was added to this mixture to form a positive electrode slurry. This slurry was then applied to aluminum foil and dried to obtain the positive electrode. Next, the positive electrode shell, positive electrode, separator, lithium negative electrode, foamed nickel, and negative electrode shell were assembled in that order, and 100 μL of electrolyte was added to assemble the 2025 button cell in a glove box under an argon atmosphere with a water and oxygen content of less than 0.1 ppm. The electrolyte used was a mixed solution containing 1 mol / L of lithium bis(trifluoromethylsulfonyl)imide and 0.2 mol / L of lithium nitrate in 1,3-dioxolane / dimethoxyethane (DOL / DME in a 1:1 volume ratio).

[0054] The lithium-sulfur battery samples prepared as described above were subjected to constant current charge-discharge tests to detect rate characteristics and cycle characteristics.

[0055] <Rate Characteristics Test> Lithium sulfur battery samples were subjected to five charge-discharge cycles in the voltage range of 1.7–2.7V and 1C (1C = 1675mA / g). The specific discharge capacity for each charge-discharge cycle was recorded and used to calculate the average specific discharge capacity for the five cycles.

[0056] The average specific discharge capacity for 5 cycles in 1C = the sum of the specific discharge capacities from the 1st to the 5th cycle / 5. Similarly, the charge-discharge cycle was repeated five times at 2C and 3C, respectively, and the average specific discharge capacity for these five cycles at 2C and 3C was calculated.

[0057] <Cycle Characteristics Test> Lithium sulfur battery samples were subjected to two charge-discharge cycles in the voltage ranges of 1.7–2.7V and 0.1C and 0.2C, respectively, and then subjected to 100 and 150 further charge-discharge cycles at 0.5C. The specific discharge capacity of the first cycle at different current densities (i.e., 0.1C, 0.2C, and 0.5C), and the specific discharge capacities of the 100th and 150th cycles were recorded and used to evaluate the cycle characteristics by calculating the capacity retention rate after 100 and 150 cycles at 0.5C using the following formula.

[0058] Capacity retention rate after 100 cycles = Specific discharge capacity of the 100th cycle / Specific discharge capacity of the 1st cycle * 100%. Capacity retention rate after 150 cycles = Specific discharge capacity at the 150th cycle / Specific discharge capacity at the 1st cycle * 100%. Regarding the case where the molecular sieve contains lithium and cobalt:

[0059] <Example 2-1> Preparation of composite separators (1) 5 g of raw molecular sieves (i.e., MFI molecular sieves having the chemical composition Na2O·20SiO2·Al2O3) were ion-exchanged with a 0.5 mol / L LiCl solution (liquid-to-solid ratio of 20) at 80°C for 2 hours, and then washed by centrifugation. The ion exchange was repeated twice. The obtained sample was dried overnight at 100°C to obtain precursor 1-I. Two g of the obtained precursor 1-I was immersed in 18 mL of a 0.1 mol / L cobalt chloride solution, dried in air at 80°C for 8 hours, and then treated at 700°C for 2 hours under a hydrogen atmosphere to obtain an MFI molecular sieve containing lithium and cobalt.

[0060] (2) 0.35 g of MFI molecular sieves containing lithium and cobalt and 0.1 g of graphene were ground in a mortar and mixed to obtain a mixture.

[0061] (3) The above mixture and 0.05 g of polyvinylidene fluoride were dispersed in N-methylpyrrolidone and mixed uniformly by stirring to obtain a coating slurry.

[0062] (4) The coating slurry was uniformly applied to one side of a polyethylene / polypropylene substrate film by blade coating, and then dried to remove the solvent, thereby obtaining a composite separator having a composite layer uniformly dispersed on one side of the polymer substrate film. Here, the composite layer had a thickness of 15 μm.

[0063] <Performance testing of composite separators> Based on the test method described above, lithium-sulfur battery samples were assembled, and the prepared composite separator was used to test the performance of these samples. The test results are shown in Table 2-1.

[0064] Figure 1 is a scanning electron microscope image of the composite separator of Example 2-1. As shown in the figure, the composite layer uniformly covers the surface of the PP / PE film, forming a good barrier layer.

[0065] Figure 2 shows the charge-discharge curves of the lithium-sulfur battery sample containing the composite separator of Example 2-1 at different current densities.

[0066] <Example 2-2> Example 2-1 was repeated, except that the MFI molecular sieve was replaced with a GIS molecular sieve, to prepare a GIS molecular sieve containing lithium and cobalt with the same chemical composition. Specifically, 5 g of raw molecular sieve (i.e., a GIS molecular sieve with the chemical composition Na2O·20SiO2·Al2O3) was ion-exchanged with a 0.5 mol / L LiCl solution (liquid-to-solid ratio of 20) at 80°C for 2 hours, and then washed by centrifugation. The ion exchange was repeated twice. The obtained sample was dried overnight at 100°C to obtain precursor 2-I. 2 g of the obtained precursor 2-I was immersed in 18 mL of a 0.1 mol / L cobalt chloride solution, dried in air at 80°C for 8 hours, and then treated under a hydrogen atmosphere at 700°C for 2 hours to obtain a GIS molecular sieve containing lithium and cobalt.

[0067] Furthermore, the amount of the GIS molecular sieve containing lithium and cobalt was adjusted to 0.6 g, and the thickness of the composite layer was adjusted to 30 μm to prepare a composite separator.

[0068] The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0069] <Example 2-3> Example 2-1 was repeated, except that the MFI molecular sieve was replaced with an MWW molecular sieve, to prepare an MWW molecular sieve containing lithium and cobalt with the same chemical composition. Specifically, 5 g of raw molecular sieve (i.e., an MWW molecular sieve having the chemical composition Na2O·20SiO2·Al2O3) was ion-exchanged with a 0.5 mol / L LiCl solution (liquid-to-solid ratio of 20) at 80°C for 2 hours, and then washed by centrifugation. The ion exchange was repeated twice. The obtained sample was dried overnight at 100°C to obtain precursor 3-I. 2 g of the obtained precursor 3-I was immersed in 18 mL of a 0.1 mol / L cobalt chloride solution, dried in air at 80°C for 8 hours, and then treated at 700°C for 2 hours under a hydrogen atmosphere to obtain an MWW molecular sieve containing lithium and cobalt.

[0070] Furthermore, the amount of MWW molecular sieves containing lithium and cobalt was adjusted to 0.9 g, and the thickness of the composite layer was adjusted to 40 μm to prepare a composite separator.

[0071] The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0072] <Example 2-5> Example 2-1 was repeated, except that the amount of the MFI molecular sieve containing lithium and cobalt was adjusted to 1 g. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0073] <Example 2-6> Example 2-1 was repeated, except that the thickness of the composite layer was adjusted to 50 μm. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0074] <Example 2-7> An MFI molecular sieve containing lithium and cobalt was prepared by repeating Example 2-1, except that the MFI molecular sieve having the chemical composition Na2O·20SiO2·Al2O3 was replaced with an MFI molecular sieve having the chemical composition 2Na2O·5SiO2·Al2O3.

[0075] The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0076] <Comparative Example 2-1> Example 2-1 was repeated, except that the MFI molecular sieve containing lithium and cobalt was replaced with the unprocessed MFI molecular sieve. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0077] <Comparative Example 2-2> Example 2-1 was repeated, except that the MFI molecular sieve was replaced with a 13X molecular sieve, to prepare a 13X molecular sieve containing lithium and cobalt with the same chemical composition. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0078] <Comparative Example 2-3> Example 2-1 was repeated, except that the MFI molecular sieve was replaced with a SAPO-34 molecular sieve, to prepare a SAPO-34 molecular sieve containing lithium and cobalt with the same chemical composition. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1.

[0079] <Comparative Example 2-4> A composite separator was prepared by repeating Example 2-1, except that the MFI molecular sieve containing lithium and cobalt was replaced with precursor 1-I. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 2-1. The test results are shown in Table 2-1. [Table 1]

[0080] Regarding the case where the molecular sieve contains cobalt: <Example 3-1> (1) 2 g of raw molecular sieve (i.e., MFI molecular sieve having the chemical composition Na2O·20SiO2·Al2O3) was immersed in 18 mL of 0.1 mol / L cobalt chloride solution, dried in air at 80°C for 8 hours, and then treated at 700°C for 2 hours under a hydrogen atmosphere to obtain a cobalt-containing MFI molecular sieve. (2) 0.35 g of the MFI molecular sieve containing cobalt and 0.1 g of graphene were ground in a mortar and mixed to obtain a mixture.

[0081] (3) The above mixture and 0.05 g of polyvinylidene fluoride were dispersed in N-methylpyrrolidone and mixed uniformly by stirring to obtain a coating slurry. (4) The coating slurry was uniformly applied to one side of a polyethylene / polypropylene substrate film by blade coating, and then dried to remove the solvent, thereby obtaining a composite separator having a composite layer uniformly dispersed on one side of the polymer substrate film. Here, the composite layer had a thickness of 15 μm.

[0082] Based on the test method described above, lithium-sulfur battery samples were assembled, and the prepared composite separator was used to test the performance of these samples. The test results are shown in Table 3-1.

[0083] <Example 3-2> Example 3-1 was repeated, except that the MFI molecular sieve was replaced with a GIS molecular sieve, to prepare a GIS molecular sieve containing cobalt with the same chemical composition. Specifically, 2 g of unprocessed molecular sieve (i.e., a GIS molecular sieve having the chemical composition Na2O·20SiO2·Al2O3) was immersed in 18 mL of a 0.1 mol / L cobalt chloride solution, dried in air at 80°C for 8 hours, and then treated at 700°C for 2 hours under a hydrogen atmosphere to obtain a GIS molecular sieve containing cobalt.

[0084] Furthermore, the amount of the GIS molecular sieve containing cobalt was adjusted to 0.6 g, and the thickness of the composite layer was adjusted to 30 μm to prepare a composite separator.

[0085] The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 3-1. The test results are shown in Table 3-1.

[0086] <Example 3-3> Example 3-1 was repeated, except that the MFI molecular sieve was replaced with an MWW molecular sieve, to prepare an MWW molecular sieve containing cobalt with the same chemical composition. Specifically, 2 g of unprocessed molecular sieve (i.e., an MWW molecular sieve having the chemical composition Na2O·20SiO2·Al2O3) was immersed in 18 mL of a 0.1 mol / L cobalt chloride solution, dried in air at 80°C for 8 hours, and then treated at 700°C for 2 hours under a hydrogen atmosphere to obtain a cobalt-containing MWW molecular sieve.

[0087] Furthermore, the amount of the MWW molecular sieve containing cobalt was adjusted to 0.9 g, and the thickness of the composite layer was adjusted to 40 μm to prepare a composite separator. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 3-1. The test results are shown in Table 3-1.

[0088] <Example 3-4> Example 3-1 was repeated, except that the amount of the MFI molecular sieve containing cobalt was adjusted to 1 g. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 3-1. The test results are shown in Table 3-1.

[0089] <Example 3-5> Example 3-1 was repeated, except that the thickness of the composite layer was adjusted to 50 μm. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 3-1. The test results are shown in Table 3-1.

[0090] <Example 3-6> An MFI molecular sieve containing cobalt was prepared by repeating Example 3-1, except that the MFI molecular sieve having the chemical composition Na2O·20SiO2·Al2O3 was replaced with an MFI molecular sieve having the chemical composition 2Na2O·5SiO2·Al2O3. The prepared composite separator was used in the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested by repeating Example 3-1. The test results are shown in Table 3-1. [Table 2]

[0091] Preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical scope of the present invention, various simple modifications can be made to embodiments of the present invention, and these simple modifications include combinations of various technical features by any other preferred method. These simple modifications and combinations are also disclosed herein and should be considered to be within the scope of protection of this disclosure. [Brief explanation of the drawing]

[0092] [Figure 1] This is a scanning electron microscope image of the composite separator obtained in Example 2-1. [Figure 2] These are the charge-discharge curves of the lithium-sulfur battery sample obtained in Example 2-1 when the current density is changed.

Claims

1. The system comprises a polymer substrate film and a composite layer disposed on the surface of the polymer substrate film. The composite layer comprises a molecular sieve and a conductive carbon material. The molecular sieve contains cobalt, A composite separator characterized in that the molecular sieve has at least one topological structure selected from the group consisting of MFI, MWW, and GIS.

2. The composite layer has a thickness of 5-50 μm and / or, The composite separator according to claim 1, wherein the mass ratio of the conductive carbon material and the molecular sieve in the composite layer is 1:(1-9).

3. The composite layer has a thickness of 10-40 μm and / or, The composite separator according to claim 1, wherein the mass ratio of the conductive carbon material and the molecular sieve in the composite layer is 1:(2-9).

4. The composite separator according to claim 1, wherein the molecular sieve further comprises lithium.

5. Lithium is present in the molecular sieve in an amount of 0.1–5% by weight on a lithium ion basis, The composite separator according to claim 4, wherein cobalt is present in the molecular sieve in an amount of 1-30% by weight on an elemental cobalt basis.

6. Lithium is present in the molecular sieve in an amount of 0.5–2.5% by weight on a lithium ion basis, The composite separator according to claim 5, wherein cobalt is present in the molecular sieve in an amount of 2-7% by weight on an elemental cobalt basis.

7. The material of the polymer substrate film is at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene and polyvinylidene fluoride, and / or The composite separator according to claim 1, wherein the conductive carbon material is at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjenblack.

8. (1) A step of mixing a molecular sieve containing cobalt with a conductive carbon material to obtain a mixture, (2) A step of dispersing the mixture and the binder in a solvent to obtain a coating slurry, (3) The process includes the step of applying the coating slurry to the surface of the polymer substrate film, and then removing the solvent to obtain the composite separator, A method for preparing the composite separator according to claim 1, characterized in that the molecular sieve has at least one topological structure selected from the group consisting of MFI, MWW, and GIS.

9. The method according to claim 8, further comprising the step of obtaining a molecular sieve by mixing a cobalt ion solution with an unprocessed molecular sieve, drying and reducing it to obtain a cobalt-containing molecular sieve.

10. The molecular sieve further comprises lithium, The aforementioned method, The process involves replacing the unprocessed molecular sieve with a lithium ion solution, washing and drying it to obtain precursor I (S1), and The method according to claim 8, further comprising the step of obtaining the molecular sieve by mixing a cobalt ion solution with the precursor I, drying and reducing the mixture to obtain the molecular sieve containing cobalt and lithium (S2).

11. The lithium ion solution is at least one selected from the group consisting of lithium chloride solution, lithium sulfate solution, and lithium nitrate solution, and / or The exchange is carried out under conditions including a temperature of 40–100°C and a liquid-to-solid ratio of 10–50, and / or The cobalt ion solution is at least one selected from the group consisting of cobalt chloride solution, cobalt nitrate solution, cobalt sulfate solution, and cobalt acetate solution, and / or The reduction is carried out in a hydrogen atmosphere at a temperature of 600-750°C for 1-4 hours, and / or, The aforementioned unprocessed molecular sieve has the chemical composition xM₂O・ySiO₂・zAl₂O₃, 0.01 ≤ x / y ≤ 0.2, 10 ≤ y / z ≤ 50, and, The method according to claim 10, wherein M is one or two selected from the group consisting of Na and K.

12. The molecular sieve is Lithium is present in the molecular sieve in an amount of 0.1–5% by weight on a lithium ion basis, and / or The method according to claim 10, wherein cobalt is present in the molecular sieve in an amount of 1-30% by weight on an elemental cobalt basis.

13. The solvent in step (2) is at least one selected from the group consisting of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, and / or The binder in step (2) is at least one of polyvinyl alcohol, carboxymethylcellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber, and / or polyacrylate, The method according to claim 8, wherein the coating in step (3) is at least one of casting, blade coating, spray coating, and spin coating.

14. A lithium sulfur battery comprising a positive electrode, a negative electrode, and the composite separator described in Claim 1 between the positive electrode and the negative electrode.

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