A battery separator, a method for preparing the same, and a lithium-sulfur battery comprising the same

Abstract

The application discloses a battery diaphragm, a preparation method thereof and a lithium-sulfur battery containing the diaphragm. The battery diaphragm comprises a polymer matrix film and a composite layer distributed on one side surface of the polymer matrix film, wherein the composite layer comprises a heteroatom doped molecular sieve and a conductive carbon material, and the heteroatom is located in a crystal framework of the molecular sieve. The battery diaphragm can effectively inhibit the shuttling of polysulfides in the lithium-sulfur battery through the dual effects of physical confinement and chemical adsorption, reduce the loss of active substances, and improve the cycle performance and capacity of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery separators, specifically to a separator for lithium-sulfur batteries, a method for preparing the separator, and a lithium-sulfur battery containing the separator. Background Technology

[0002] With increasing energy demand, exploring alternative energy storage systems with higher specific capacity is crucial to alleviating over-reliance on lithium-ion batteries. Lithium-sulfur batteries have attracted widespread attention in next-generation high-energy-density battery systems due to their high theoretical specific capacity (1675 mAh / g) and energy density (2600 Wh / kg). Furthermore, sulfur resources are inexpensive, abundant, and environmentally friendly, thus considered a promising lithium-ion battery. However, several challenges remain before the practical application of lithium-sulfur batteries. For example, the inherent insulating properties of elemental sulfur (S8) and its final discharge product (Li2S) hinder electron transfer in the electrode, limiting sulfur utilization. Additionally, the sulfur cathode experiences volume expansion of up to 80% during charge and discharge, inevitably leading to electrode structure damage and gradually reducing cycle stability. Most seriously, the "shuttle effect" caused by the dissolution and migration of long-chain polysulfides (LiPSs) in the electrolyte often accompanies the deposition and passivation of Li2S on the lithium anode, significantly reducing the utilization rate of active materials and thus severely degrading the cycle stability and capacity of lithium-sulfur batteries.

[0003] To date, several promising strategies have been explored and adopted to improve the electrochemical performance of lithium-sulfur batteries, including designing sulfur hosts, modifying separators, and optimizing electrolytes. Among these, coating the separator surface with a modification layer is considered the most effective and economical strategy for blocking LiPSs shuttle and accelerating LiPSs redox kinetics. Commonly used separator modification materials include porous carbon, inorganic compounds, and metal-organic frameworks, but they suffer from limitations such as limited effectiveness, complex synthesis processes, and high costs.

[0004] Currently, some existing technologies also utilize molecular sieves to modify membranes, such as CN107546356A and CN103490027A. These technologies utilize the physical barrier properties of molecular sieves such as ZSM-35, SAPO-34, 3A, and 13X to limit the flow of Li2S to a certain extent. x Migration and diffusion within the electrolyte improve battery performance. However, the performance improvement achievable through a single physical action (i.e., sieving) is relatively limited.

[0005] To enable lithium-sulfur batteries to meet the demands of the rapid development of new energy electric vehicles and large-capacity energy storage systems, it is still necessary to provide battery separators that can further improve performance. Summary of the Invention

[0006] Through extensive research, the inventors of this invention discovered that by selecting molecular sieves with different compositions and structures and using them to modify lithium-sulfur battery separators, the performance of the battery can be further improved, thereby meeting the aforementioned needs of the prior art. Specifically, certain heteroatom-doped molecular sieves, more preferably lithium-containing heteroatom-doped molecular sieves, can effectively suppress polysulfide shuttle in lithium-sulfur batteries through physical confinement and chemical adsorption, reducing internal side reactions and improving the ion transport performance of the separator, thereby enhancing the battery's cycle performance and capacity. Thus, the inventors completed this invention.

[0007] This invention provides a battery separator, its preparation method, and a lithium-sulfur battery containing the separator. The battery separator of this invention can effectively suppress polysulfide shuttle in lithium-sulfur batteries through physical confinement and chemical adsorption, reducing internal side reactions and improving the ion transport performance of the separator, thereby improving the cycle performance and capacity of the battery.

[0008] The first aspect of the present invention provides a battery separator, comprising a polymer matrix membrane and a composite layer distributed on one side surface of the polymer matrix membrane, the composite layer comprising a heteroatom-doped molecular sieve and a conductive carbon material, wherein the heteroatoms are located in the crystal framework of the molecular sieve.

[0009] Furthermore, in the heteroatom-doped molecular sieve, the heteroatom is at least one of Fe and Sn heteroatoms, preferably Fe or Sn; the topology of the molecular sieve is selected from at least one of MFI, MWW, FAU and MOR, preferably MFI.

[0010] Furthermore, in the heteroatom-doped molecular sieve, the heteroatom content, based on the weight of the heteroatom-doped molecular sieve, is 0.5%-10.0%, preferably 1.0%-7.0%. The heteroatom content is, for example, but not limited to: 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, etc.

[0011] Furthermore, characteristic absorption peaks of Fe appear at 247±5nm, 278±5nm and 621±5nm in the UV-Vis diffuse reflectance spectrum of the heteroatom-doped molecular sieve; characteristic absorption peaks of Sn appear at 206±2nm in the UV-Vis diffuse reflectance spectrum of the heteroatom-doped molecular sieve.

[0012] Furthermore, the polymer matrix film is made of at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene, and polyvinylidene fluoride, preferably polyethylene, polypropylene, or a polyethylene / polypropylene composite material.

[0013] Furthermore, the conductive carbon material is at least one of graphene, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjen black, preferably graphene.

[0014] Furthermore, the thickness of the composite layer is 1-40 μm, preferably 3-20 μm.

[0015] Furthermore, in the composite layer, the mass ratio of conductive carbon material to heteroatom-doped molecular sieve is 1:(1-20), preferably 1:(3-9).

[0016] Furthermore, the heteroatom-doped molecular sieve contains lithium, and the lithium content, based on the weight of the heteroatom-doped molecular sieve, is 0.1%-5.0%, preferably 0.2%-1.8%.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned battery separator, comprising:

[0018] (1) Mixing heteroatom-doped molecular sieves with conductive carbon materials yields a mixture;

[0019] (2) Disperse the mixture and binder in a solvent to obtain a coating slurry;

[0020] (3) Coating the slurry onto one side of the polymer matrix membrane and drying it to obtain the battery separator.

[0021] Further, in step (1), the mass ratio of the heteroatom-doped molecular sieve to the conductive carbon material is (1-20):1, preferably (3-9):1.

[0022] Further, in step (1), the method for preparing the heteroatom-doped molecular sieve includes:

[0023] (S1) H-type molecular sieve reacts with acid solution to obtain precursor I;

[0024] (S2) The precursor I obtained is mixed with heteroatom salt and calcined to obtain heteroatom-doped molecular sieve.

[0025] Further, in step (S1), the topology of the H-type molecular sieve is selected from at least one of MFI, MWW, FAU, and MOR, preferably MFI. The silicon-to-aluminum atomic ratio of the H-type molecular sieve is 5-100.

[0026] Further, in step (S1), the acid is selected from at least one of oxalic acid, sulfuric acid, and phosphoric acid, preferably oxalic acid. The concentration of the acid solution is 0.5-5.0 mol / L. The concentration of the acid solution is, for example, but not limited to, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, etc.

[0027] Further, in step (S1), the liquid-to-solid weight ratio of the acid solution to the H-type molecular sieve is 20-70.

[0028] Further, in step (S1), the reaction conditions are: reaction temperature 50-70℃, and reaction time 0.5-3h.

[0029] Furthermore, in step (S1), after the reaction is complete, precursor I is obtained through conventional operations such as centrifugation, washing, and drying. For example, the drying conditions are as follows: drying at 50-180℃ for 8-12 hours.

[0030] Furthermore, in step (S2), the heteroatom salt used is selected from iron salts and tin salts. For example, the iron salt is selected from at least one of ferrocene, ferrous lactate, and ferric citrate; the tin salt is selected from at least one of dimethylstannous chloride and dibutyltin.

[0031] Further, in step (S2), the amount of heteroatom salt (calculated as metal) added accounts for 0.5%-10.0% of the mass of the H-type molecular sieve, preferably 1.0%-7.0%, for example, but not limited to 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, etc.

[0032] Furthermore, in step (S2), the mixing is physical mixing, and the mixing method includes grinding, ball milling, etc.

[0033] Furthermore, in step (S2), the calcination temperature is 300-600℃ and the calcination time is 2-8h.

[0034] Further, in step (2), the solvent is at least one of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N-methylpyrrolidone.

[0035] Further, in step (2), the adhesive is at least one of polyvinyl alcohol, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber and polyacrylate, preferably polyvinylidene fluoride.

[0036] Further, in step (2), the mass ratio of the mixture to the adhesive is (1-15):1, preferably (6-10):1.

[0037] Furthermore, in step (3), the coating is one of the following methods: casting, scraping, spraying, spin coating, etc., preferably scraping.

[0038] Furthermore, the heteroatom-doped molecular sieve contains lithium, and its preparation method includes: exchanging the heteroatom-doped molecular sieve with a lithium ion solution to obtain a lithium-containing heteroatom molecular sieve.

[0039] Further, the lithium-ion solution is at least one of lithium chloride solution, lithium acetate solution, and lithium nitrate solution, and the concentration of the lithium-ion solution is 0.1-1.0 mol / L. The exchange conditions are: temperature 40-100℃, time 1-6h, liquid-solid weight ratio 10-50, and number of exchanges 1-3 times.

[0040] Furthermore, after the exchange process, lithium-containing heteroatom molecular sieves are obtained through routine operations such as centrifugation, washing, and drying. For example, the drying conditions are as follows: drying at 80-150℃ for 10-30 hours.

[0041] A third aspect of the present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, and the aforementioned separator located between the positive and negative electrodes.

[0042] Furthermore, the lithium-sulfur battery also includes an electrolyte. The positive electrode, negative electrode, and electrolyte can be selected from various positive electrodes, negative electrodes, and electrolytes known to those skilled in the art for use in lithium-sulfur batteries.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] 1. This invention selects heteroatom-doped molecular sieves, preferably lithium-containing heteroatom-doped molecular sieves, which can effectively suppress polysulfide shuttle in lithium-sulfur batteries through physical confinement and chemical adsorption, reduce internal side reactions of the battery, and improve the ion transport performance of the separator, thereby improving the cycle performance and capacity of the battery.

[0045] 2. The molecular sieve-modified separator of this invention employs heteroatom-doped molecular sieves, which can more effectively suppress the polysulfide shuttle effect in lithium-sulfur batteries through a dual effect of physical confinement and chemisorption. On one hand, the molecular sieve has sub-nanometer regular channels, which can block the migration and diffusion of polysulfides inside the battery through the sieving effect (physical confinement). On the other hand, the crystal framework of the molecular sieve contains Fe or Sn heteroatoms, which can act as anchoring sites, further enhancing the connection with polysulfides and restricting polysulfide shuttle through chemisorption. Through the dual physical and chemical effects brought about by the above composition and structure, the molecular sieve can more effectively suppress polysulfide shuttle in lithium-sulfur batteries and reduce the loss of active materials. When the heteroatom-doped molecular sieve further contains lithium, the introduced lithium can provide a large number of sites for lithium-ion adsorption and transport during battery cycling, improving the lithium-ion transport performance of the separator. Therefore, compared with existing molecular sieve-modified separators, the molecular sieve used in this invention to modify the separator can significantly improve the cycle performance and capacity of the battery. Attached Figure Description

[0046] Figure 1 The UV-Vis diffuse reflectance spectrum of the molecular sieve prepared in Example 1;

[0047] Figure 2 The UV-Vis diffuse reflectance spectrum of the molecular sieve prepared in Example 2;

[0048] Figure 3 The UV-Vis diffuse reflectance spectrum of the molecular sieve prepared in Comparative Example 2 is shown. Detailed Implementation

[0049] To better understand the present invention, the technical solution of the present invention will be further described below with reference to the embodiments. The following embodiments are only for illustration and not for limiting the present invention.

[0050] In this invention, the assembly and performance testing processes of the lithium-sulfur battery are as follows:

[0051] 1. Assembly of lithium-sulfur battery samples:

[0052] First, the positive electrode is prepared: sublimed sulfur (active material), Ketjen black (conductive agent), and polyvinylidene fluoride (binder) are mixed in a mass ratio of 6:3:1, and N-methylpyrrolidone is added to form a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil and dried to obtain the positive electrode. Then, 2025 coin cells are assembled in an argon glove box with a water and oxygen content below 0.1 ppm: the positive electrode shell, positive electrode, separator, lithium negative electrode, nickel foam, and negative electrode shell are assembled sequentially, and 100 μL of electrolyte is added. The electrolyte used is a 1,3-dioxolane / ethylene glycol dimethyl ether (DOL / DME, volume ratio 1:1) mixed solution containing 1 mol / L lithium bis(trifluoromethanesulfonyl)imide and 0.2 mol / L lithium nitrate.

[0053] 2. The rate performance and cycle stability of the lithium-sulfur battery samples prepared as described above were tested by constant current charge-discharge testing.

[0054] (1) Ratio performance test:

[0055] The lithium-sulfur battery sample was subjected to 5 charge-discharge cycles at 1C within a voltage range of 1.7-2.7V. The specific charge capacity of each charge-discharge cycle was recorded, and the average specific charge capacity of the 5 cycles was calculated.

[0056] The average charge capacity over 5 cycles at 1C = the sum of the charge capacity from the 1st cycle to the 5th cycle / 5;

[0057] Similarly, the charge-discharge cycles were repeated 5 times at 2C and 3C respectively, and the average charge specific capacity of the 5 cycles at 2C and 3C was measured.

[0058] (2) Cyclic stability test:

[0059] The lithium-sulfur battery samples were activated by charge-discharge cycling at 0.1C and 0.2C for two cycles within a voltage range of 1.7-2.7V. Then, the samples were cycled at 0.5C for 150 cycles. The capacity retention rate after the first 150 cycles at 0.5C was recorded to characterize the cycle stability.

[0060] Capacity retention rate = (Specific charge capacity in the 150th cycle / Specific charge capacity in the 1st cycle) × 100%.

[0061] 3. In this invention, the diffuse reflectance test instrument for ultraviolet-visible spectroscopy is an ultraviolet-visible-near-infrared spectrometer, purchased from Agilent Technologies, instrument model: Cary 5000, wavelength test range: 200~800nm.

[0062] (Example 1)

[0063] Preparation of Fe-doped lithium-containing MFI molecular sieves:

[0064] 5g of H-type MFI molecular sieve with a silicon-to-aluminum atomic ratio of 10 was mixed with 100mL of 2.0mol / L oxalic acid solution and reacted at 60℃ for 2h. The mixture was then centrifuged, washed, and dried to obtain precursor I. Precursor I was then mixed with 0.30g of ferrocene powder and calcined at 500℃ for 6h to obtain Fe-doped MFI molecular sieve. The Fe-doped MFI molecular sieve was then subjected to lithium-ion exchange with 0.5mol / L LiCl solution (liquid-to-solid weight ratio of 20) at 80℃ for 2h, followed by centrifugation and washing. This lithium-ion exchange process was repeated twice. The resulting sample was then dried at 100℃ for 24h to obtain Fe-doped lithium-containing MFI molecular sieve.

[0065] Preparation of molecular sieve-modified membranes:

[0066] (1) 0.35g of Fe-doped lithium-containing MFI molecular sieve and 0.1g of graphene were ground and mixed in a mortar to obtain 0.45g of mixture;

[0067] (2) Disperse the above mixture with 0.05g of polyvinylidene fluoride in N-methylpyrrolidone, stir and mix evenly to obtain a coating slurry;

[0068] (3) The coating slurry is uniformly coated on one side of the polyethylene / polypropylene matrix membrane by scraping, and then dried to remove the solvent, to obtain a molecular sieve modified membrane, wherein the thickness of the Fe-doped lithium-containing MFI molecular sieve / graphene composite layer is 10 μm.

[0069] The molecular sieve obtained in Example 1 contained 1.8% Fe and 1.0% Li.

[0070] The UV-Vis diffuse reflectance spectrum of the molecular sieve obtained in Example 1 is shown in Figure 1. Figure 1 .

[0071] Performance testing of molecular sieve-modified diaphragms:

[0072] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0073]

Example 2

[0074] Compared with Example 1, the only difference is that the ferrocene powder is replaced with an equal amount of dimethylstannous dichloroethylene to obtain Sn-doped lithium-containing MFI molecular sieves, and the corresponding molecular sieve modified membranes are prepared.

[0075] The molecular sieve obtained in Example 2 contained 3.2% Sn and 1.0% Li.

[0076] The UV-Vis diffuse reflectance spectrum of the molecular sieve obtained in Example 2 is shown in Figure 2. Figure 2 .

[0077] Performance testing of molecular sieve-modified diaphragms:

[0078] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0079]

Example 3

[0080] The only difference compared to Example 1 is:

[0081] In the preparation of heteroatom-doped molecular sieves, the H-type MFI molecular sieve with a silicon-to-aluminum ratio of 10 is replaced with the H-type MWW molecular sieve with a silicon-to-aluminum ratio of 35.

[0082] In the preparation of the molecular sieve modified diaphragm, the amount of molecular sieve in step (1) is adjusted to 0.42g and the amount of graphene is adjusted to 0.03g; the thickness of the composite layer obtained in step (3) is 25μm.

[0083] The molecular sieve obtained in Example 3 contained 1.8% Fe and 0.3% Li.

[0084] The UV-Vis diffuse reflectance spectrum of the molecular sieve obtained in Example 3 is similar to that of the molecular sieve obtained in Example 3. Figure 1 .

[0085] Performance testing of molecular sieve-modified diaphragms:

[0086] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0087]

Example 4

[0088] The only difference compared to Example 1 is:

[0089] In the preparation of heteroatom-doped molecular sieves, the H-type MFI molecular sieve with a silicon-to-aluminum ratio of 10 is replaced with the H-type FAU molecular sieve with a silicon-to-aluminum ratio of 25.

[0090] In the preparation of the molecular sieve modified diaphragm, the amount of molecular sieve in step (1) is adjusted to 0.40g and the amount of graphene is adjusted to 0.05g; the thickness of the composite layer in step (3) is 15μm.

[0091] The molecular sieve obtained in Example 4 contained 1.8% Fe and 0.4% Li.

[0092] The UV-Vis diffuse reflectance spectrum of the molecular sieve obtained in Example 4 is similar to that of... Figure 1 .

[0093] Performance testing of molecular sieve-modified diaphragms:

[0094] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0095]

Example 5

[0096] The only difference compared to Example 1 is:

[0097] In the preparation of heteroatom-doped molecular sieves, the H-type MFI molecular sieve with a silicon-to-aluminum ratio of 10 is replaced with the H-type MOR molecular sieve with a silicon-to-aluminum ratio of 15.

[0098] In the preparation of the molecular sieve modified diaphragm, the amount of molecular sieve in step (1) is adjusted to 0.30g and the amount of graphene is adjusted to 0.15g; the thickness of the composite layer in step (3) is 5μm.

[0099] The molecular sieve obtained in Example 5 contained 1.8% Fe and 0.7% Li.

[0100] The UV-Vis diffuse reflectance spectrum of the molecular sieve obtained in Example 5 is similar to that of the molecular sieve obtained in Example 5. Figure 1 .

[0101] Performance testing of molecular sieve-modified diaphragms:

[0102] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0103]

Example 6

[0104] Compared with Example 1, the only difference is that the heteroatom molecular sieve does not undergo lithium-ion exchange, and the Fe-doped MFI molecular sieve is directly used to prepare the corresponding molecular sieve modified membrane.

[0105] Performance testing of molecular sieve-modified diaphragms:

[0106] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0107]

Example 7

[0108] The only difference compared to Example 1 is the preparation process of the Fe-doped lithium-containing MFI molecular sieve, specifically:

[0109] 5g of H-type MFI molecular sieve with a silicon-to-aluminum atomic ratio of 10 was mixed with 100mL of 1.0mol / L oxalic acid solution and reacted at 60℃ for 2h. The mixture was then centrifuged, washed, and dried to obtain precursor I. Precursor I was then mixed with 0.15g of ferrocene powder and calcined at 500℃ for 6h to obtain Fe-doped MFI molecular sieve. Subsequently, the Fe-doped MFI molecular sieve was subjected to lithium-ion exchange with 0.1mol / L LiCl solution (liquid-to-solid weight ratio of 10) at 80℃ for 2h, followed by centrifugation and washing. This lithium-ion exchange process was repeated twice. The resulting sample was then dried at 100℃ for 24h to obtain Fe-doped lithium-containing MFI molecular sieve.

[0110] The preparation process of the molecular sieve modified diaphragm is the same as in the example.

[0111] The molecular sieve obtained in Example 7 contained 0.9% Fe and 0.1% Li.

[0112] Performance testing of molecular sieve modified diaphragms

[0113] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0114]

Example 8

[0115] The only difference compared to Example 1 is the preparation process of the Fe-doped lithium-containing MFI molecular sieve, specifically:

[0116] 5 g of H-type MFI molecular sieve with a silicon-to-aluminum atomic ratio of 5 was mixed with 200 mL of 4.0 mol / L oxalic acid solution and reacted at 60 °C for 2 h. The mixture was then centrifuged, washed, and dried to obtain precursor I. Precursor I was then mixed with 1.2 g of ferrocene powder and calcined at 500 °C for 6 h to obtain Fe-doped MFI molecular sieve. Subsequently, the Fe-doped MFI molecular sieve was subjected to lithium-ion exchange with 1.0 mol / L LiCl solution (liquid-to-solid weight ratio of 20) at 80 °C for 2 h. After centrifugation and washing, the lithium-ion exchange was repeated twice. The resulting sample was then dried overnight at 100 °C to obtain Fe-doped lithium-containing MFI molecular sieve.

[0117] The preparation process of the molecular sieve modified diaphragm is the same as in Example 1.

[0118] The molecular sieve obtained in Example 8 contained 7.2% Fe and 1.9% Li.

[0119] Performance testing of molecular sieve modified diaphragms

[0120] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0121] Comparative Example 1

[0122] Compared to Example 1, the only difference is that instead of preparing a molecular sieve-modified membrane, a polyethylene / polypropylene matrix membrane was directly used to replace the molecular sieve-modified membrane to assemble lithium-sulfur battery samples and conduct performance tests. The test results are shown in Table 1.

[0123] Comparative Example 2

[0124] Compared with Example 1, the only difference is that the molecular sieve prepared is different. 5g of a Na-type MFI molecular sieve with a silicon-to-aluminum atomic ratio of 10 was immersed in 16mL of a 0.1mol / L ferric chloride solution, dried in air at 80°C, and then further treated at 700°C in air for 2 hours to obtain an MFI molecular sieve loaded with iron oxide. The Fe content in the obtained molecular sieve is the same as in Example 1.

[0125] The UV-Vis diffuse reflectance spectrum of the molecular sieve obtained in Comparative Example 2 is shown in Figure 2. Figure 3 .

[0126] Performance testing of molecular sieve-modified diaphragms:

[0127] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0128] Comparative Example 3

[0129] The only difference from Example 1 is the preparation of the Fe-doped lithium-containing MFI molecular sieve. Specifically, 5g of an H-type MFI molecular sieve with a silicon-to-aluminum atomic ratio of 10 was mixed with 100mL of concentrated nitric acid (65%) and reacted at 100°C for 24h. After centrifugation, washing, and drying, precursor I was obtained. Precursor I was then mixed with 0.30g of ferrocene powder and calcined at 200°C for 6h to obtain precursor II. Precursor II was then subjected to lithium-ion exchange with a 0.5mol / L LiCl solution (liquid-to-solid volume ratio of 20) at 80°C for 2h, followed by centrifugation and washing. This lithium-ion exchange was repeated twice. The resulting sample was then dried overnight at 100°C to obtain the Fe-doped lithium-containing MFI molecular sieve.

[0130] The molecular sieve obtained in Comparative Example 3 contained 2.0% Fe and 1.5% Li.

[0131] The molecular sieve obtained in Comparative Example 3 showed an Fe-characteristic absorption peak at 260±5 nm in its UV-Vis diffuse reflectance spectrum.

[0132] Performance testing of molecular sieve-modified diaphragms:

[0133] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0134] Comparative Example 4

[0135] Compared with Example 1, the only difference is that: H-type MFI molecular sieve with a silicon-to-aluminum atomic ratio of 10 is directly subjected to lithium-ion exchange with 0.5 mol / L LiCl solution (liquid-to-solid weight ratio of 20) at 80°C for 2 h, then centrifuged and washed, and the lithium-ion exchange was repeated twice. The resulting sample was then dried overnight at 100°C to obtain lithium-containing MFI molecular sieve.

[0136] The Li content in the molecular sieve obtained in Comparative Example 4 was 1.0%.

[0137] Performance testing of molecular sieve-modified diaphragms:

[0138] As described above, lithium-sulfur battery samples were assembled using the prepared molecular sieve-modified separator, and their rate performance and cycle stability were tested. Specific test results are shown in Table 1.

[0139] Table 1. Electrochemical performance test results of lithium-sulfur batteries obtained in each example.

[0140]

[0141] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery separator, comprising a polymer matrix membrane and a composite layer distributed on one side surface of the polymer matrix membrane, the composite layer comprising a heteroatom-doped molecular sieve and a conductive carbon material, wherein the heteroatoms are located in the crystal framework of the molecular sieve; in the heteroatom-doped molecular sieve, the heteroatoms are Fe or Sn; the topology of the molecular sieve is selected from at least one of MFI, MWW, FAU and MOR; when the heteroatom is Fe, characteristic absorption peaks of Fe appear at 247±5 nm, 278±5 nm and 621±5 nm in the ultraviolet-visible diffuse reflectance spectrum of the heteroatom-doped molecular sieve; when the heteroatom is Sn, characteristic absorption peaks of Sn appear at 206±2 nm in the ultraviolet-visible diffuse reflectance spectrum of the heteroatom-doped molecular sieve.

2. The battery separator according to claim 1, characterized in that, In heteroatom-doped molecular sieves, the topology of the molecular sieve is MFI.

3. The battery separator according to claim 1, characterized in that, The thickness of the composite layer is 1-40 μm.

4. The battery separator according to claim 3, characterized in that, The thickness of the composite layer is 3-20 μm.

5. The battery separator according to claim 1, characterized in that, In the composite layer, the mass ratio of conductive carbon material to heteroatom-doped molecular sieve is 1:(1-20).

6. The battery separator according to claim 5, characterized in that, In the composite layer, the mass ratio of conductive carbon material to heteroatom-doped molecular sieve is 1:(3-9).

7. The battery separator according to claim 1, characterized in that, In the heteroatom-doped molecular sieve, the heteroatom content is 1.0%-7.0% based on the weight of the heteroatom-doped molecular sieve; And / or, the heteroatom-doped molecular sieve contains lithium, and the lithium content, calculated as an element, is 0.1%-5.0% based on the weight of the heteroatom-doped molecular sieve.

8. The battery separator according to claim 7, characterized in that, In the heteroatom-doped molecular sieve, the heteroatom content is 1.0%-7.0% based on the weight of the heteroatom-doped molecular sieve; And / or, the heteroatom-doped molecular sieve contains lithium, and the lithium content, based on the weight of the heteroatom-doped molecular sieve, is 0.2%-1.8% by element.

9. The battery separator according to claim 1, characterized in that, The polymer matrix film is made of at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene, and polyvinylidene fluoride. And / or, the conductive carbon material is at least one of graphene, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjen black.

10. The battery separator according to claim 9, characterized in that, The polymer matrix film is made of polyethylene, polypropylene, or a polyethylene / polypropylene composite material; and / or, the conductive carbon material is graphene.

11. A method for preparing the battery separator according to any one of claims 1-10, comprising: (1) Mixing heteroatom-doped molecular sieves with conductive carbon materials yields a mixture; (2) Disperse the mixture and binder in a solvent to obtain a coating slurry; (3) Coating the slurry onto one side of the polymer matrix membrane and drying it to obtain the battery separator.

12. The preparation method according to claim 11, characterized in that, The solvent in step (2) is at least one of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; And / or, the adhesive in step (2) is at least one of polyvinyl alcohol, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber and polyacrylate; And / or, the coating in step (3) is at least one of the following methods: casting, scraping, spraying, and spin coating.

13. The preparation method according to claim 12, characterized in that, The solvent in step (2) is N-methylpyrrolidone; and / or the binder in step (2) is polyvinylidene fluoride; and / or the coating in step (3) is by blade coating.

14. The preparation method according to claim 11, characterized in that, Methods for preparing heteroatom-doped molecular sieves include: (S1) The H-type molecular sieve reacts with an acid solution to obtain precursor I; (S2) The precursor I obtained is mixed with heteroatom salt and calcined to obtain heteroatom-doped molecular sieve.

15. A lithium-sulfur battery, characterized in that, The battery separator includes a positive electrode, a negative electrode, and a battery membrane located between the positive and negative electrodes as described in any one of claims 1-10.

Images