Composite separator, method for preparing the same, and lithium-sulfur battery including 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 particularly to composite separators, methods for preparing the same, and lithium-sulfur batteries including the composite separators.

[0002] 〔Background〕 With the rapid development of science and technology, due to the low theoretical specific capacity of the cathode material, 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. Lithium-sulfur batteries have relatively high theoretical specific capacity (1675 mAh / g) and theoretical energy density (2600 Wh / kg), and are promising batteries to replace lithium-ion batteries. Lithium-sulfur batteries have become the research focus of next-generation high specific-capacity energy secondary batteries. In addition, sulfur, which is the cathode active material, has advantages such as rich natural resources, low cost, and environmental friendliness.

[0003] However, at present, the practical application of lithium-sulfur batteries still seems to face many problems. Among them, the "shuttle effect", which is a side reaction inside the battery, can be the biggest obstacle restricting its application. Specifically, the shuttle effect is an effect in which a lithium-sulfur battery can generate a series of sulfur-containing intermediates during the charge and discharge process, and long-chain polysulfides (Li2S x , 2 < x ≦ 8) are easily soluble in the electrolyte and pass through the separator under the action of the concentration gradient and electric field to cause a chemical side reaction with the lithium negative electrode. This causes loss of the active material and an increase in the internal resistance of the battery, leading to a decrease in battery capacity and cycle performance. Furthermore, the electrochemical reaction process of lithium-sulfur batteries may involve multi-stage 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 low.

[0004] Currently, in this technical field, in order to suppress the shuttle effect in lithium-sulfur batteries, it has been proposed to use molecular sieves when improving conventional separators. For example, refer to CN107546356A and CN103490027A. These use the physical barrier effect of molecular sieves such as ZSM-5, SAPO-34, 3A, 13X, etc. to limit the movement and diffusion of Li2S in the electrolyte to a certain extent, thereby improving battery performance. x By restricting the movement and diffusion of

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

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

[0007] In aspect 1, what is provided in the present disclosure is a composite separator comprising 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, what is provided in the present disclosure is (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 a binder in a solvent to obtain a coating slurry; (3) A method for preparing the above-mentioned composite separator, which includes a step of applying the coating slurry on the surface of the polymer base film and then removing the solvent to obtain the composite separator. In Embodiment 3, what is provided in the present disclosure is the use of the above-mentioned composite separator in a lithium-sulfur battery. In Embodiment 4, what is provided in the present disclosure is a lithium-sulfur battery including a positive electrode, a negative electrode, and the above-mentioned composite separator between the above-mentioned positive electrode and the above-mentioned negative electrode.

[0008] The present disclosure may include the following items. 1. A molecular sieve modified separator, characterized by comprising a polymer base film and a composite layer of a cobalt-doped molecular sieve / conductive carbon material disposed on the surface of the polymer base 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 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). The molecular sieve modified separator according to Item 1.

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

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

[0012] 5. (1) A step of pulverizing 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 the molecular sieve modified separator according to any one of items 1-4, comprising a step of applying the coating slurry on the surface of the polymer base 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 including the steps of adding a cobalt ion solution to a Na-type molecular sieve, drying and reducing to obtain the cobalt-doped molecular sieve. Preferably, the cobalt-doped molecular sieve includes the step (S1) of exchanging a Na-type molecular sieve with a lithium ion solution, washing and drying to obtain a precursor I. The cobalt-doped lithium molecular sieve is prepared by a method including the step (S2) of adding a cobalt ion solution to the precursor I, drying and reducing to obtain the cobalt-doped lithium molecular sieve. Preferably, the lithium ion solution in S1 is at least one of a lithium chloride solution, a lithium sulfate solution, and a lithium nitrate solution. The exchange in S1 is performed 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, where 0.01 ≦ b / y ≦ 0.2 and 10 ≦ y / z ≦ 50. 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 a cobalt chloride solution, a cobalt nitrate solution, a cobalt sulfate solution, and a cobalt acetate solution. The reduction in the method according to item 5 is performed at a reduction temperature of 600 - 750 °C for 1 - 4 hours in a hydrogen atmosphere.

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

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

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

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

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

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

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

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

[0022] 6. The conductive carbon material is at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotube, carbon nanofiber, acetylene black, Super P, and ketjen black, preferably at least one of graphene, graphene oxide, and reduced graphene oxide. The lithiated molecular sieve modified separator according to any one of items 1 - 5.

[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; (3) After applying the coating slurry to the surface of the polymer base film, removing the solvent to obtain the lithiated molecular sieve modified separator, and a method for preparing the lithiated molecular sieve modified separator according to any one of items 1-6, characterized by including this step.

[0024] 8. In step (2), the solvent is at least one selected from the group consisting of deionized water, absolute 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, carboxymethyl cellulose, 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 lithiated molecular sieve is prepared by a method including the step of exchanging 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, where 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 method according to item 7, wherein the exchange is carried out under conditions including a temperature of 40-100 °C and a liquid-to-solid ratio of 10-50.

[0025] 9. Use of the lithiated molecular sieve modified separator according to 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 the lithiated molecular sieve modified separator according to any one of items 1-6. The present disclosure may have the following advantages. The method for preparing the composite separator according to the present disclosure is simple and has little adverse effect on the energy density of the battery.

[0027] The composite separator according to the present 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 can effectively limit the movement and diffusion of Li2S x through the physical barrier effect. Thereby, side reactions inside the battery can be reduced. The molecular sieve according to the present disclosure contains cobalt. The introduced cobalt not only improves the conductivity on the positive electrode side of the separator but also functions as an active site to increase the rate of polysulfide conversion. When the molecular sieve further contains lithium, the introduced lithium can provide a large number of sites for adsorbing and moving lithium ions during battery cycling. Thereby, the lithium ion migration characteristics of the separator are improved. More importantly, when the molecular sieve contains both lithium and cobalt, a synergistic effect is achieved in the resulting composite separator. Thereby, the rate performance and cycle stability of the lithium-sulfur battery can be significantly improved. 〔Description of Drawings〕

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

[0029] It should be understood that the endpoints and any values within the ranges disclosed in this specification are not limited to the exact ranges or values, but include values close to those ranges or values. For value ranges, combinations can be made between the endpoints of each range, between the endpoints of each range and individual points, and between individual points, so as to give one or more new value ranges as if these value ranges were specifically disclosed in this specification. Except for examples, all numerical values of parameters in this specification should be understood to be modified in all cases by the term "about", regardless of whether the term "about" actually appears before the numerical value.

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

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

[0032] In one embodiment, the molecular sieve can 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 is no limitation on the thickness of the composite layer in the present disclosure. In one embodiment, the composite layer can have a thickness of 5 - 50 μm, preferably 10 - 40 μm.

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

[0035] The material of the polymer substrate film may be those 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 those commonly used in the art. In one embodiment, the conductive carbon material is at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotube, carbon nanofiber, acetylene black, Super P, and ketjen black, preferably at least one of graphene, graphene oxide, and reduced graphene oxide.

[0037] In a second aspect, provided in the present disclosure is a method for preparing a composite separator, including the following steps: (1) Mix a molecular sieve containing cobalt and a conductive carbon material to obtain a mixture; (2) Disperse the mixture and a binder in a solvent to obtain a coating slurry; (3) Apply the coating slurry onto the surface of a polymer substrate film and remove the solvent to obtain the composite separator.

[0038] In one embodiment, cobalt is present in the molecular sieve in an amount of 1-30 wt%, preferably 1-15 wt%, more preferably 2-7 wt% based on elemental cobalt and based on the total weight of cobalt and the molecular sieve. In one embodiment, the method can further include a step of obtaining a molecular sieve by adding a cobalt ion solution to the raw molecular sieve, performing drying and reduction 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 wt%, preferably 0.2-3 wt%, more preferably 0.5-2.5 wt% based on lithium ions and based on the total weight of lithium and the molecular sieve. In one embodiment, the method further includes a step (S1) of exchanging the raw molecular sieve with a lithium ion solution, washing and drying to obtain a precursor I, and a step (S2) of adding a cobalt ion solution to the precursor I, drying and reducing to obtain the molecular sieve containing cobalt and lithium, and the step of obtaining the molecular sieve includes the step of obtaining the molecular sieve by these steps.

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

[0041] Preferably, the exchange is performed under conditions including a temperature of 40-100 °C and a ratio of liquid to solid 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 at a temperature of 600 - 750 °C for 1 - 4 hours under a hydrogen atmosphere.

[0044] Preferably, the raw molecular sieve can have a chemical composition of xM2O·ySiO2·zAl2O3. Here, 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) can have at least one topological structure selected from the group consisting of MFI, MWW, GIS, BEC, FAU, and MOR, and preferably can have at least one topological structure selected from the group consisting of MFI, MWW, and GIS.

[0047] The solvent in step (2) may be those 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, absolute ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N-methylpyrrolidone.

[0048] The binder in step (2) may be one commonly used in the relevant technical field. In one embodiment, the binder in step (2) may be at least one of polyvinyl alcohol, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene butadiene rubber, and polyacrylate, preferably polyvinylidene fluoride.

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

[0050] In a fourth aspect, provided in the present disclosure is 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 known to those skilled in the art.

[0051] The composite separator according to the present 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 can effectively limit the movement and diffusion of Li2S x through a physical barrier effect. Thereby, side reactions inside the battery can be reduced. The molecular sieve according to the present disclosure contains cobalt. The introduced cobalt not only improves the conductivity on the positive electrode side of the separator, but also functions as an active site to increase the rate of polysulfide conversion. When the molecular sieve further contains lithium, the introduced lithium can provide a large number of sites for adsorbing and moving lithium ions during the battery cycle. Thereby, the lithium ion migration characteristics of the separator are improved. More importantly, when the molecular sieve contains both lithium and cobalt, a synergistic effect is achieved in the resulting composite separator. Thereby, the rate characteristics and the cycle stability of the lithium-sulfur battery can be significantly improved.

[0052] Hereinafter, the present invention will be described in detail through examples. List of raw materials: MFI molecular sieve, GIS molecular sieve, MWW molecular sieve, BEC molecular sieve: 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: Commercially available from Sinopharm Chemical Reagent Co., Ltd. <Test method> Assembly of lithium-sulfur battery samples:

[0053] First, sublimable sulfur as the active material, Ketjen black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder were mixed at a mass ratio of 6:3:1. N-methylpyrrolidone (NMP) was added thereto to form a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil and dried to obtain a positive electrode, thereby preparing a positive electrode. Next, a 2025 button battery was assembled in a glove box under an argon atmosphere with the content of water and oxygen less than 0.1 ppm by assembling a positive electrode shell, a positive electrode, a separator, a lithium negative electrode, foamed nickel, and a negative electrode shell in this order and adding 100 μL of an electrolytic solution. The electrolytic solution 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 at a volume ratio of 1:1).

[0054] The lithium-sulfur battery sample prepared as described above was subjected to a constant current charge-discharge test to detect the rate characteristics and cycle characteristics.

[0055] <Rate Characteristic Test> The lithium-sulfur battery sample was subjected to charge and discharge for 5 cycles in a voltage range of 1.7 - 2.7 V and at 1 C (1 C = 1675 mA / g). The specific discharge capacity of each charge-discharge cycle was recorded and used to calculate the average specific discharge capacity of the 5 cycles.

[0056] Average specific discharge capacity at 1 C for 5 cycles = Sum of specific discharge capacities from the 1st cycle to the 5th cycle / 5. Similarly, charge and discharge were repeated 5 cycles each at 2 C and 3 C, and the average specific discharge capacity of the 5 cycles at 2 C and 3 C was calculated respectively.

[0057] <Cycle Characteristic Test> The lithium-sulfur battery sample was subjected to two cycles of charge and discharge in the voltage range of 1.7 - 2.7V and at 0.1C and 0.2C respectively, and then further subjected to 100 and 150 cycles of charge and discharge at 0.5C. The specific discharge capacity of the first cycle and the specific discharge capacities of the 100th and 150th cycles at different current densities (i.e., 0.1C, 0.2C, and 0.5C) were recorded and used to calculate the capacity retention rates after 100 and 150 cycles at 0.5C according to the following formula to evaluate the cycle characteristics.

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

[0059] <Example 2-1> Preparation of composite separator (1) 5 g of raw molecular sieve (i.e., MFI molecular sieve with a chemical composition of Na2O·20SiO2·Al2O3) was subjected to ion exchange with a 0.5 mol / L LiCl solution (ratio of liquid to solid 20) at 80°C for 2 hours, and then centrifuged and washed. The ion exchange was repeated twice. The obtained sample was dried at 100°C overnight to obtain precursor 1-I. 2 g of the obtained precursor 1-I 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 an MFI molecular sieve containing lithium and cobalt.

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

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

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

[0063] <Performance Test of Composite Separator> Based on the above test method, in assembling a lithium-sulfur battery sample and testing the sample for its performance, the prepared composite separator was used. 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 is a charge-discharge curve of a 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, and a GIS molecular sieve containing lithium and cobalt with the same chemical composition was prepared. Specifically, 5 g of as-received molecular sieve (i.e., GIS molecular sieve having a chemical composition of Na2O·20SiO2·Al2O3) was ion-exchanged with a 0.5 mol / L LiCl solution (ratio of liquid to solid: 20) at 80 °C for 2 hours, followed by centrifugation and washing. The ion exchange was repeated twice. The obtained sample was dried at 100 °C overnight 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 at 700 °C for 2 hours under a hydrogen atmosphere 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] Example 2-1 was repeated to use the prepared composite separator for assembling a lithium-sulfur battery sample, and the performance of the sample was tested. 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, and an MWW molecular sieve containing lithium and cobalt with the same chemical composition was prepared. Specifically, 5 g of as-received molecular sieve (i.e., an MWW molecular sieve having a chemical composition of 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, followed by centrifugation and washing. The ion exchange was repeated twice. The obtained sample was dried at 100 °C overnight 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 and dried in air at 80 °C for 8 hours, followed by treatment 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 the MWW molecular sieve 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] Example 2-1 was repeated to use the prepared composite separator for the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested. 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. Example 2-1 was repeated to use the prepared composite separator for the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested. 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. Example 2-1 was repeated to use the prepared composite separator for the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested. The test results are shown in Table 2-1.

[0074] <Example 2-7> Example 2-1 was repeated except that the MFI molecular sieve having the chemical composition of Na2O·20SiO2·Al2O3 was replaced with an MFI molecular sieve having the chemical composition of 2Na2O·5SiO2·Al2O3 to prepare an MFI molecular sieve containing lithium and cobalt.

[0075] Example 2-1 was repeated to use the prepared composite separator for assembling a lithium-sulfur battery sample, and the performance of the sample was tested. 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 as-received MFI molecular sieve. Example 2-1 was repeated to use the prepared composite separator for assembling a lithium-sulfur battery sample, and the performance of the sample was tested. 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. Example 2-1 was repeated to use the prepared composite separator for assembling a lithium-sulfur battery sample, and the performance of the sample was tested. 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. Example 2-1 was repeated to use the prepared composite separator for assembling a lithium-sulfur battery sample, and the performance of the sample was tested. The test results are shown in Table 2-1.

[0079] <Comparative Example 2-4> Example 2-1 was repeated except that the MFI molecular sieve containing lithium and cobalt was replaced with the precursor 1-I to prepare a composite separator. Example 2-1 was repeated to use the prepared composite separator for the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested. 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 as-received molecular sieve (i.e., MFI molecular sieve having a chemical composition of 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 in a hydrogen atmosphere to obtain an MFI molecular sieve containing cobalt. (2) 0.35 g of the MFI molecular sieve containing cobalt and 0.1 g of graphene were ground and mixed in a mortar to obtain a mixture.

[0081] (3) The mixture and 0.05 g of polyvinylidene fluoride were dispersed in N-methylpyrrolidone, uniformly stirred and mixed to obtain a coating slurry. (4) This coating slurry was uniformly applied to one side of a polyethylene / polypropylene substrate film by blade coating, and then dried to remove the solvent to obtain 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 above test method, in assembling a lithium-sulfur battery sample and testing the sample for its performance, the prepared composite separator was used. 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, and a GIS molecular sieve containing cobalt with the same chemical composition was prepared. Specifically, 2 g of as-received molecular sieve (i.e., a GIS molecular sieve having a chemical composition of 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 in 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] Example 3-1 was repeated to use the prepared composite separator for the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested. 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, and an MWW molecular sieve containing cobalt with the same chemical composition was prepared. Specifically, 2 g of as-received molecular sieve (i.e., an MWW molecular sieve having a chemical composition of 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 in a hydrogen atmosphere to obtain an MWW molecular sieve containing cobalt.

[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. Example 3-1 was repeated to use the prepared composite separator for the assembly of a lithium-sulfur battery sample, and the performance of the sample was tested. 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. Example 3-1 was repeated to prepare a composite separator for use in assembling a lithium-sulfur battery sample, and the performance of the sample was tested. 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. Example 3-1 was repeated to prepare a composite separator for use in assembling a lithium-sulfur battery sample, and the performance of the sample was tested. The test results are shown in Table 3-1.

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

Table 2

[0091] The 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 the embodiments of the present invention, and the various simple modifications include combinations of various technical features by any other suitable method. These simple modifications and combinations are also the content disclosed in this specification and should be regarded as being within the protection scope of this disclosure.

Brief Description of the Drawings

[0092]

Figure 1

Figure 2

Claims

1. A composite separator comprising a polymer base film and a composite layer disposed on the surface of the polymer base film, wherein the composite layer comprises a molecular sieve and a conductive carbon material, and the molecular sieve contains cobalt.

2. The composite layer has a thickness of 5 - 50 μm, preferably 10 - 40 μm, and / or the mass ratio of the conductive carbon material to the molecular sieve in the composite layer is 1:(1 - 9), preferably 1:(2 - 9). The composite separator according to claim 1.

3. The molecular sieve further contains lithium, preferably, lithium is present in the molecular sieve in an amount of 0.1 - 5 wt%, preferably 0.2 - 3 wt%, more preferably 0.5 - 2.5 wt% based on lithium ions, preferably, cobalt is present in the molecular sieve in an amount of 1 - 30 wt%, preferably 1 - 15 wt%, more preferably 2 - 7 wt% based on elemental cobalt. The composite separator according to claim 1 or 2.

4. The molecular sieve has at least one topological structure selected from the group consisting of MFI, MWW, GIS, BEC, FAU, and MOR, preferably, having at least one topological structure selected from the group consisting of MFI, MWW, and GIS. The composite separator according to claim 3.

5. The material of the polymer base film is at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene, and polyvinylidene fluoride, preferably polyethylene and / or polypropylene, and / or the conductive carbon material is at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotube, carbon nanofiber, acetylene black, Super P, and ketjen black, preferably at least one of graphene, graphene oxide, and reduced graphene oxide. The composite separator according to any one of claims 1 - 4.

6. (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 a binder in a solvent to obtain a coating slurry. (3) A step of applying the coating slurry to the surface of the polymer base film and then removing the solvent to obtain the composite separator, characterized by comprising the method for preparing the composite separator according to any one of claims 1 to 5.

7. The method further includes a step of obtaining the molecular sieve by mixing a cobalt ion solution and a raw molecular sieve, drying and reducing to obtain a cobalt-containing molecular sieve, according to the method of claim 6.

8. The molecular sieve further contains lithium, The method is, A step (S1) of exchanging the raw molecular sieve with a lithium ion solution, washing and drying to obtain a precursor I, and The method further includes a step of obtaining the molecular sieve by mixing a cobalt ion solution and the precursor I, drying and reducing to obtain the molecular sieve containing cobalt and lithium (step S2), according to the method of claim 6.

9. The lithium ion solution is at least one selected from the group consisting of a lithium chloride solution, a lithium sulfate solution, and a 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. Preferably, the exchange is carried out 1 - 3 times, and / or The cobalt ion solution is at least one selected from the group consisting of a cobalt chloride solution, a cobalt nitrate solution, a cobalt sulfate solution, and a cobalt acetate solution, and / or The reduction is carried out at a temperature of 600 - 750 °C for 1 - 4 hours under a hydrogen atmosphere, and / or The raw molecular sieve is xM ２ O·ySiO ２ ·zAl ２ O ３ and has a chemical composition of 0.01 ≦ x / y ≦ 0.2, 10 ≦ y / z ≦ 50, and M is one or two selected from the group consisting of Na and K. M is preferably Na, and / or The raw molecular sieve is at least one selected from the group consisting of MFI, MWW, GIS, BEC, FAU, and MOR. Preferably, it is at least one of MFI, MWW, and GIS, according to the method of claim 7 or 8.

10. The molecular sieve is, having at least one topological structure selected from the group consisting of MFI, MWW, GIS, BEC, FAU and MOR, preferably having at least one topological structure selected from the group consisting of MFI, MWW and GIS, preferably, lithium is present in the molecular sieve in an amount of 0.1-5 wt%, preferably 0.2-3 wt%, more preferably 0.5-2.5 wt% based on lithium ions, preferably, cobalt is present in the molecular sieve in an amount of 1-30 wt%, preferably 1-15 wt%, more preferably 2-7 wt% based on elemental cobalt, according to the method of claim 7 or 8.

11. the solvent in step (2) is at least one selected from the group consisting of deionized water, absolute ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N-methylpyrrolidone, and / or, the binder in step (2) is at least one of polyvinyl alcohol, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber 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, according to the method of any one of claims 6-9.

12. a lithium-sulfur battery, comprising a positive electrode, a negative electrode, and the composite separator according to any one of claims 1-5 between the positive electrode and the negative electrode.

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